- Email: [email protected]
Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
Available online at www.sciencedirect.com
ScienceDirect http://www.elsevier.com/locate/biombioe
Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals Dieni Mansur a,*, Teruoki Tago b, Takao Masuda b, Haznan Abimanyu a a
Research Center for Chemistry, Indonesian Institute of Sciences, Kawasan Puspiptek Serpong, Tangerang Selatan, Banten 15314, Indonesia b Division of Chemical Process Engineering, Hokkaido University, N-13 W-8 Kita-Ku, Sapporo 060-8628, Japan
article info
abstract
Article history:
Recently, much attention has been devoted the generation of useful chemicals from
Received 4 November 2013
biomass. Cacao pod husks, a waste biomass, are one of the agricultural crop residues that
Received in revised form
can be utilized for this purpose. The husks were treated by pyrolysis to produce pyrolysis
18 March 2014
oil that contained several chemical compounds such as ketones, carboxylic acids, alde-
Accepted 31 March 2014
hydes, furans, heterocyclic aromatics, alkyl benzenes, phenols and benzenediols. There-
Available online xxx
fore, this biomass-derived pyrolysis oil is potentially a rich source of useful chemicals. The pyrolysis oil was upgraded over iron oxide catalysts. During the catalytic upgrade, keto-
Keywords:
nization, selective oxidation and demethoxylation reactions occurred and selectively
Cacao pod husks
produced aliphatic ketones (acetone, 2-butanone), phenol and alkyl phenols (cresol, xyle-
Pyrolysis
nol, ethylphenol). ª 2014 Elsevier Ltd. All rights reserved.
Iron oxide catalysts Useful chemicals Ketonization
1.
Introduction
The depletion of crude oil reserves and the effect of greenhouse gases on global warming call for the substitution of petrochemical processes with biomass-based processes for chemical production. Biomass as a renewable resource is considered to be the only raw material for sustainable production of chemicals [1]. It is different from other energy sources such as solar, hydropower, wind, nuclear, and geothermal energy. Recently, biomass used for chemical production has been derived from waste biomass due to its lower cost than virgin biomass. In fact, it often has negative costs. Waste biomass includes municipal solid waste, livestock and poultry manure, agricultural crop residues, forestry residues and industrial waste [2]. In this study, we utilize an agricultural crop residue
generated from a cacao plantation in Indonesia, which ranks third highest in the world in the production of cacao [3]. Cacao is an industrially important crop since cocoa beans and its processed products are the main ingredients of chocolate, one of the world’s most popular foods. However, in the production of the beans, waste in the form of cacao pod husks is also generated. Every ton of dry cacao beans generates 10 tons of wet cacao husks. The cacao’s pod, bean and husk are shown in Fig. 1 and the husk has composition as shown in Table 1. The husks are typically left to rot and decompose into organic manure on the cacao plantation. However, besides producing foul odors, rotting can propagate diseases such as black pod rot [6]. Proper usage of the husks could provide economic advantages and decrease their environmental impact. For example, the husks have been treated to produce pectin [6,7], a viable dietary supplement for fish [8] and pigs [9].
* Corresponding author. Tel.: þ62 21 756 0929; fax: þ62 21 756 0549. E-mail addresses: [email protected], [email protected] (D. Mansur). http://dx.doi.org/10.1016/j.biombioe.2014.03.065 0961-9534/ª 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
2
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
Fig. 1 e The cacao’s pod (fruit), bean and husk.
The utilization of biomass to increase its added value and to develop clean and sustainable technologies involves physical, chemical and biological processing to convert agricultural and organic raw materials into chemical products [1]. Most processes begin with pyrolysis, followed by catalytic upgrading to produce low-cost and environmentally friendly compounds. Pyrolysis is the thermal decomposition of materials in the absence of oxygen or when significantly less oxygen is present than required for complete combustion, which results in char, gas, and liquid products [10]. The char is a high quality solid fuel and fuel gas is used as a source of power generation [11,12]. The liquid product from biomass pyrolysis is known as tar or pyrolysis oil. The pyrolysis oil is a mixture of different molecules (alcohols, aldehydes, ketones, esters and phenolic compounds) derived from fragmentation of lignin, cellulose, hemicelluloses and extractives [1]. The yield and composition of biomass pyrolysis oil are dependent on the chemical and structural composition, particle size and species of the biomass used, as well as temperature, heating rate, and residence time of the pyrolysis [10,13]. Pyrolysis oil is a promising material for replacement of fossil oil for production of different chemicals from sustainable and renewable sources. Pyrolysis oil exhibits two main problems as a source of useful chemicals: its high water content and its instabilities, such as viscosity increase and phase separation. The instabilities result from a breakdown in the stabilized microemulsion and chemical reactions, which continue to occur in the oil. Stabilization of pyrolysis oil can be achieved by upgrading over catalysts [10,14]. Adam et al. investigated catalytic upgrading of pyrolysis vapor using mesoporous molecular sieves (MCM-41), FCC, and SBA-15 catalysts. All of the catalysts reduced the undesirable product yield, while the desirable product yield remained the same or increased [14].
Table 1 e Composition of cacao pod husk. Composition
Amount (g. kg1 dry matter)
Cellulose Hemicellulose Lignin Pectin Crude fiber Crude protein Ash
350a 108b e 110a 146a 61a 226a e 325b 59a e 76.6b 91a e 101b
a b
The values were according to Ref. [4]. The values were according to Ref. [5].
Adjaye et al. studied the catalytic upgrading of pyrolysis oil into hydrocarbons using HZSM-5, silicalite, H-mordenite, HeY and silicaealumina [15]. Moreover, Jackson et al. reported that ketonization of carboxylic acid into ketone over a mixed oxide of Fe, Ce, and Al is another approach to stabilize and upgrade pyrolysis oil [16,17]. In catalytic upgrading of pyrolysis oil, the high water content should be considered because water will deactivate the catalysts [18]. In our previous studies, iron oxide based catalysts selectively produced ketones from sewage sludge, woodchips and ethanol fermentation stillage, and phenols from lignin. These catalysts have been successfully utilized to upgrade oxygen-containing tars derived from thermochemical conversion of biomass [19e22]. Activity iron oxide catalyst also investigated by Taimoor et al. for ketonization of acetic acid and its activity increased by introducing H2 in carrier gas [23]. In this study, the cacao pod husk waste from a cacao plantation, was subjected to pyrolysis to produce pyrolysis oil, and the pyrolysis oil was then upgraded over zirconiaeiron oxide catalysts for production of useful chemicals such as ketones and phenols.
2.
Material and methods
2.1.
Material
The cacao pod husks were obtained from a cacao plantation in West Sumatera province, located in western Indonesia. The husks were separated from the beans, and then sun-dried for a week. Before being fed into the pyrolyzer, the husks were reduced in size using a size reducer (MF10, IKA-Werke GmbH & Co. KG) operating at 3500 rpm min1. The cut husks were sieved to obtain chips between 0.84 and 4 mm in length. Moisture content (water content) of the cacao pod husk chips was analyzed using moisture analyzer (MB45, Ohaus) at 105 C for 10 min and found that the moisture content was 14.93%. The samples were stored at 2 C to discourage the growth of fungi. The cacao pod husks contained 42.78 wt% carbon based on elemental analysis. This value was used as the basis for calculation of the total carbon yield of products after the pyrolysis process.
2.2.
Pyrolysis process of the cacao pod husks
The pyrolysis experiments were carried out in a fixed-bed quartz reactor. The length and inner diameter of the pyrolyzer were 0.5969 m and 0.0254 m, respectively. About 20 g of cacao pod husk chips were placed in the pyrolyzer. Nitrogen as a sweeping gas was passed through the pyrolyzer to remove air/oxygen. The nitrogen flow rate was set to 20 cc. min1, the temperature of the pyrolyzer was increased from room temperature (approximately 25 C) to 500 C for 9 min, and then the temperature was maintained at 500 C until pyrolysis had occurred for 50 min. Process pyrolysis of cacao pod husk can be classified into slow pyrolysis due to low heating rate as well as pyrolysis of pistachio shell that conducted by ApaydinVarol [24]. The temperature was measured using a thermocouple located just below the bed. A condenser (0 C) and cold trap
Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
(70 C) were installed to capture the vapor/liquid product, and non-condensable gas was collected in a gas pack during the process and for 15 min after heating of the pyrolyzer had stopped. A schematic diagram of the pyrolysis apparatus is given in Fig. 2. Heating of the pyrolyzer was terminated when the desired reaction time was reached, and the system was allowed to cool to room temperature. The pyrolyzer, condenser and cold trap, including all of the connections and downstream tubes, were carefully removed from the system and weighed. Char remained on the bed after pyrolysis. Heavy tar was recovered and its amount was calculated as the difference in weight of the pyrolyzer prior to and after pyrolysis. The heavy tar was located on top of the char bed. Condensable liquid in the condenser and cold trap were mixed together and designated pyrolysis oil. The pyrolyzer and its connections and downstream tubes were washed with acetone. Heated air was used to clean heavy tar from the pyrolyzer by combustion because this tar was difficult to remove with solvents. The yield of products after pyrolysis was reported in wt% and C-mol%. Yield in wt% was calculated based on weight of products divided with weight of feed. Moreover, C-mol% (or mol % of carbon) was determined by dividing mol of carbon in product with mol of carbon in feed, and then multiplied it with 100% (Eq. (1)). C mol% yield ¼ ½C mol product=C mol feed 100%
(1)
C-mol of feed was determined by multiplying weight of feed (g) with its carbon content (wt%) based on elemental analysis and then divided by atomic weight of carbon (12 g/ mol) as shown in Eq. (2). C mol feed ¼ ½gram feed wt:% C=12
(2)
3
Char and heavy tar were recovered from inside of the pyrolyzer and analyzed for their carbon content using an elemental analyzer (ECS 4010, Costech Instruments). C-mol of char and heavy tar were calculated as the same way with Cmol of feed according to their each carbon content. The gas product was analyzed using gas chromatographs with thermal conductivity and flame ionization detectors (GC-8A and GS-20B; Shimadzu Co., Ltd.) with activated charcoal and Porapak Q columns, respectively. Gas product was calculated using gas standard. Moles of each gas were divided by their carbon atom to find their C-mol, and then were divided by Cmol of feed in order the unit becomes C-mol%. Pyrolysis oil consisted of two separable phase and hereafter were called as aqueous and organic phases. The aqueous phase was analyzed by a gas chromatograph with a flame ionization detector (GC-2014; Shimadzu Co., Ltd.) and a gas chromatograph-mass spectrometer (GC-17A GCMS-QP5050; Shimadzu Co., Ltd.) with DB-Wax capillary columns using nbutanol as an internal standard. The organic phase was analyzed by a gas chromatograph with flame ionization detector (GC-2010; Shimadzu Co., Ltd.) and a gas chromatograph-mass spectrometer (GC-2014 GCMS Parvum2; Shimadzu Co., Ltd.) with DB-5 and DB-5MS capillary columns, respectively, using the same internal standard with the aqueous phase. Moles of 1-butanol were calculated, and then the value was divided by 4 to find its C-mol. C-mol per 1% area of 1-butanol was compared with % area of chemical compounds to find their C-mol, and then were divided by C-mol of feed in order the unit becomes C-mol%. Pyrolysis oil contained heavy components that were undetectable by gas chromatography, therefore, the amount of carbon measured by the elemental analyzer (Costech, ECS 4010 CHNS-O) was considered to be the total amount of carbon in the oil. The pyrolysis oil was used as the feed for the catalytic reaction. Feeds and
Fig. 2 e A schematic diagram of the pyrolysis apparatus of cacao pod husks. Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
4
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
products of pyrolysis and catalytic reaction were analyzed twice and the data were shown in average.
2.3. Preparation and characterization of the iron oxide catalysts The catalytic reaction of pyrolysis oil for chemical production was carried out over ZrO2eFeOx catalysts. The catalysts were prepared by a co-precipitation method with aqueous solutions of iron (III) nitrate anneahydrate [Fe(NO3)3.9H2O] and zirconyl nitrate dehydrate [ZrO(NO3)2.2H2O] using aqueous ammonia until a pH of 7 was reached [21]. All reagents were purchased from Wako Pure Chemical Industries, Ltd., Japan. The zirconia content in the catalysts varied from 0e100 wt%. Crystalline structures and the specific surface areas of the catalysts prior to and after reaction were evaluated using Xray diffraction (XRD, JEOL, JDX-8020) and by a N2 adsorption and desorption method (Belsorp mini; BEL Japan, Inc.), respectively.
2.4.
Catalytic reaction of pyrolysis oil
The catalytic reaction of pyrolysis oil over the ZrO2eFeOx catalyst was carried out in a fixed bed flow reactor for 2 h under atmospheric conditions at 350 C. Nitrogen gas (10 cm3 min1) was used as the carrier gas. One ml. h1 of aqueous phase and organic phase of the pyrolysis oil were fed into the reactor separately. An aqueous phase was mixed with water under ratio of 1 before being fed into the reactor. On the other hand, 12 wt% of organic phase diluted in toluene and water with ratio of 1 was also fed into the reactor. W/F [W: Amount of catalyst bed (g) and F: Flow rate of feed (g. h1)] was 1 h. A schematic diagram of the apparatus used for the catalytic reaction is shown in Fig. 3. After the catalytic reaction, gas and liquid products were collected in a gas pack and a condenser (0 C), respectively, and then analyzed directly by the same apparatus as the gas and liquid products from the pyrolysis process. The amount of coke-like residue deposited on the catalyst was measured by an elemental analyzer. Product yields of the catalytic reaction were calculated based on the carbon content of each phase of the pyrolysis oil.
3.
Results and discussion
3.1. Pyrolysis of cacao pod husks for pyrolysis oil production Cacao pod husk chips were pyrolyzed in a fixed-bed quartz reactor in several batches of pyrolysis experiments to prepare the appropriate amount of pyrolysis oil for useful chemical production. All pyrolysis products were recovered and analyzed. The products were pyrolysis oil, char, heavy tar and gas. The average composition of pyrolysis products in wt% and C-mol% is shown in Table 2. The pyrolysis oil as 40.11 Cmol% was obtained in the form of two easily separable phases: an aqueous phase (bottom phase of 28.19 C-mol%) and an organic phase (top phase of 11.92 C-mol%) with more in the aqueous phase than the organic phase. The larger aqueous
Fig. 3 e A schematic diagram of the apparatus for catalytic reaction of pyrolysis oil.
phase was due to the high moisture content in the cacao pod husks because the feed was only treated by sun-drying, not oven-drying, before pyrolysis. In Table 2, the value of aqueous phase of pyrolysis oil in wt % is much higher than the value based on C-mol%, indicating that the chemicals containing in aqueous phase of pyrolysis oil are “hydrocarbons” with “high oxygen content”. High oxygen content would be derived from eOH groups, possibly due to decomposition and/or depolymerization of cellulose during pyrolysis. The chemical compounds from the aqueous and organic phases of pyrolysis oil in C-mol% and wt% are listed in Table 3. The chemical compounds of the aqueous and organic phases in C-mol% were calculated based on 27.66 wt% and 71.96 wt% of their carbon content, respectively. The aqueous phase was mainly composed of carboxylic acids and ketones that easily dissolved in water because their carboxyl and carbonyl
Table 2 e Composition of pyrolysis products. Composition Aqueous layer of pyrolysis oil Organic denser layer of pyrolysis oil Char Heavy tar Gas
Yielda (C-mol%)
Yield (wt%)
28.19 11.92
50.62 9.01
50.05 0.61 9.23
39.99 0.39 0.01
a
Calculated based on carbon content of cacao pod husks (C ¼ 42.78 wt%).
Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
Table 3 e Composition of pyrolysis oil. Composition
Aqueous layer
Organic denser layer
(C-mol%)a (wt%) (C-mol%)b (wt%) Hydroxyketones Aliphatic ketones Cyclic ketones Aromatic ketones Carboxylic acids Aldehydes Furans Heterocyclic aromatics Alkyl benzenes Phenols Alkyl phenols Methoxyphenols Benzenediols Other chemicals Heavy components
5.23 12.49 3.17 0.09 16.19 0.98 1.88 0.11 e 0.87 0.97 0.79 0.56 16.95 39.73
0.50 1.19 0.30 0.01 1.54 0.09 0.18 0.03 e 0.08 0.09 0.19 0.05 1.59 94.14
e 0.00 0.44 0.74 2.22 e e e 0.27 0.88 3.31 5.32 e 24.22 62.58
e 0.00 0.49 0.83 2.47 e e e 0.30 0.98 3.68 5.92 e 26.92 58.42
a
Calculated based on carbon content of an aqueous layer (C ¼ 27.66 wt%). b Calculated based on carbon content of an organic denser layer (C ¼ 71.96 wt%).
functional groups are polar organic functional groups. On the other hand, the organic phase contained aromatics such as alkyl- and methoxy-phenols that separated in the organic phase. The composition of pyrolysis oil (both phases) in Table 3 was also separated into light components and heavy components. The light components consisted of chemicals grouped into ketones, carboxylic acids, aldehydes, furans, heterocyclic aromatics, phenols, benzenediols, and other chemicals. Others chemicals were organics detectable by GC and GCMS, but they could not be identified. The heavy components were essentially organics dissolved in pyrolysis oil,
5
but they were undetectable by gas chromatography due to their high molecular weight. In Table 3, the wt% of heavy components in aqueous phase is quite different from the C-mol% of heavy components. The reason for this difference is the “hydrocarbons” with “high oxygen content” mentioned in Table 2. Accordingly, the heavy components in aqueous phase in Table 3 are “hydrocarbons” with “high oxygen content” derived from cellulose. In addition, in Table 3, heavy components in organic phase show almost the same values between wt% and C-mol%. OH groups are disappeared by dehydration. Heavy components in organic phase are hydrocarbons with low oxygen content. Therefore, these values are almost same each other due to complete dehydration.
3.2. Reaction of the aqueous phase of pyrolysis oil over ZrO2eFeOx catalyst The catalytic reactions of pyrolysis oil to produce useful chemicals were carried out separately with the aqueous and organic phases. First, the catalytic reaction of the aqueous phase was investigated over 0e100 wt% of zirconia contents in ZrO2eFeOx catalysts. The optimum conditions of the catalytic reaction of the aqueous phase were then adopted for conversion of the organic phase. Product yields after catalytic reaction of the aqueous phase using several different zirconia contents in the catalyst are shown in Fig. 4. The yield of aliphatic ketones increased after catalytic reaction over FeOx from 12 C-mol% in the feed to 16 C-mol% and then significantly increased up to 38 C-mol% over ZrO2(8.9)eFeOx. On the other hand, hydroxyketones and carboxylic acids decreased. Water remained in aqueous phase of pyrolysis oil derived from cacao pod husks was predicted higher than 60.5 wt% of water content in pyroligneous acid derived from woodchip [20] because of moisture content of the husk as feed of
Fig. 4 e Product yields of catalytic reaction of aqueous phase over several different zirconia contents in the catalyst. Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
6
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
pyrolysis higher than 3 wt% of moisture in the woodchips. Moreover, carbon content in the aqueous phase of pyrolysis oil derived from the husks that contain carboxylic acids was 27.66 wt%. As shown in Fig. 4, major reaction is ketonization from carboxylic acid. Ketonization is discussed based on number of carbon in carboxylic acid. Therefore, feed and products yield after catalytic reaction are shown based on Cmol%. In contrast, if we concern about volume or weight, the present of carbon and “oxygen” is considered. Whereas, there is no relationship between “ketonization reaction” and “oxygen atoms”, in the feed and product yields after catalytic reaction of aqueous phase in Fig. 4. To investigate the reaction pathways of these conversions, catalytic reactions of carboxylic acids, aliphatic ketones, and hydroxyketones, which were major detectable chemicals in the aqueous phase listed in Table 3, were carried out under the same operating conditions as the aqueous phase.
3.2.1. Reaction of chemical model compounds in aliphatic ketones production Figs. 5 and 6 show catalytic reactions of acetic and propionic acids, acetone, and hydroxyacetone as model compounds of carboxylic acids, aliphatic ketones and hydroxyketones, respectively. The results show that two molecules of acetic acid were selectively converted by ketonization to produce one molecule each of acetone and CO2, as shown in Eq. (3). 2 CH3 COOH/CH3 COCH3 þ CO2 þ H2 O
(3)
The formation of H2O could not be detected since the reaction was conducted in a steam atmosphere. The same reaction also occurred with propionic acid, with two molecules of propionic acid producing one molecule of 3-pentanone, as shown in Eq. (4). 2 C2 H6 COOH/C2 H5 COC2 H5 þ CO2 þ H2 O
(4)
Eq. (3) and Eq. (4), respectively, show that two molecules of C2 and C3 carboxylic acids create C3 and C5 ketones. Moreover, during the reaction of propionic acid, 2-butanone and a negligible amount of acetone were also produced. We predicted the conversion to 2-butanone and acetone from acetic acid present in the feedstock, based on a concentration of pure
Fig. 5 e Catalytic reaction of 10 wt% of carboxylic acid and aliphatic ketone model compounds over ZrO2(8.9) eFeOx; T: 350 C; W/F: 1 h; N2: 10 cc. minL1.
Fig. 6 e Catalytic reaction of hydroxyketone model compounds over ZrO2(8.9)eFeOx; T: 350 C; W/F: 1 h; N2: 10 cc. minL1.
propionic acid of 98%. As discussed previously, acetic acid is converted into acetone. Here, 2-butanone is a C4 ketone derived from 1 mol each of acetic acid (C2) and propionic acid (C3). This reaction is expressed in Eq. (5). CH3 COOH þ C2 H6 COOH/CH3 COC2 H5 þ CO2 þ H2 O
(5)
Over ZrO2eFeOx catalyst, carboxylic acids were converted into ketones. However, the ketone was inactive over the catalyst. This result is shown in Fig. 5 where 90 C-mol% of acetone remained unconverted, and only small amounts of CO2 and other components were produced. It is predicted that the same result (inactivity towards the catalyst) will be obtained for the reaction of other ketones such as 2-butanone or 3-pentanone. Based on Fig. 6 at a W/F of 2.0 and 4.0 kg-cat. kg-feed1. h1, hydroxyacetone was converted into acetone, 2-butanone, 3pentanone and CO2. At a W/F of 0.5 and 1.0 kg-cat. kgfeed1. h1, acetic acid and propionic acid appeared as intermediate products and some of the hydroxyacetone remained unconverted. The amounts of acetic acid, propionic acid and other compounds formed decreased, but the formation of CO2 increased with increasing W/F value. As W/F increased, the yield of acetone increased, however, the yield of 3-pentanone decreased, indicating that the formation of acetic acid was higher than that of propionic acid. CO2 was a by-product of the ketonization reaction. A probable mechanism of reaction for the conversion of carboxylic acid into ketone by ZrO2eFeOx catalyst is as follows. Pestman et al. reported that the formation of acetone (ketone) from acetic acid (carboxylic acid) over metal oxide takes place on the surface of the catalyst. First, acetic acid is adsorbed on the surface of catalyst. In the adsorbed acetic acid, a-hydrogen is abstracted, CeC bond is dissociated and produce the intermediate. The formation of methylene as intermediate is immediately followed by a reaction with a neighboring acetate to give acetone. Then, the carboxyl group splits into CO2 [25].
Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
7
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
3.2.2. phase
Catalytic activity during decomposition of the aqueous
Referring to results of the catalytic reaction of carboxylic acids, aliphatic ketones, and hydroxyketones in Figs. 5 and 6, it was clarified that the increase in yield of aliphatic ketones in Fig. 4 was caused by the ketonization reaction of carboxylic acids and oxidation followed by ketonization of hydroxyketones to form aliphatic ketones. Complete conversion of hydroxyketones into carboxylic acids and aliphatic ketones occurred over FeOx catalyst. Under the same conditions, some carboxylic acids were also converted into aliphatic ketones. Reaction of the aqueous phase over FeOx catalyst produced more aldehydes and an increase in heavy components; however, other chemicals decreased in yield. It was predicted that aldehydes derived from other chemicals in the aqueous phase consisted of many chemicals that could not be identified by gas chromatography. The decrease in other chemicals also suggested that polymerization occurred to form heavy chemicals leading to a coke-like residue deposited on the catalyst. Catalytic reaction over ZrO2(8.9)eFeOx catalyst produced more than three times the amount of aliphatic ketones compared to aliphatic ketones in the feed. Almost all the carboxylic acids and hydroxyketones were converted into aliphatic ketones. Refer to the results of the catalytic reaction of carboxylic acids, aliphatic ketones, and hydroxyketones as chemical model compounds in Figs. 5 and 6, it was clarified that hydroxyketones are converted into carboxylic acids and then two molecules of carboxylic acid produce one molecule of ketone. Moreover, aliphatic ketones were inactive over ZrO2eFeOx catalyst. Stoichiometric reactions of ketonization from carboxylic acid are shown in Eqs. (3)e(5). The yield of aliphatic ketones after catalytic reaction was estimated based on chemical compositions of aqueous phase in Table 3. The amount of hydroxyketones, carboxylic acids, and aliphatic ketones was 5.23, 16.19 and 12.49 C-mol%, respectively. If the reactions were stoichiometric, 23.2 C-mol% of aliphatic ketones would be produced. However, in Fig. 4 over ZrO2(8.9)e FeOx, yield of aliphatic ketones was 38 C-mol%. There is about 14.8 C-mol% of aliphatic ketones produced from newly formed of carboxylic acids. The newly formed of carboxylic acids were produced from selective oxidation of other chemicals and
Table 4 e Chemical compositions of aliphatic ketones in the product after catalytic reaction of aqueous phase over ZrO2(8.9)eFeOx catalyst. Aliphatic ketones Acetone 2-Butanone 2-Butanone, 3-methyl 2-Pentanone Methyl isobutyl ketone 2-Pentanone, 3-methyl 3-Hexanone 2-Hexanone
Yield [C-mol%]
Molecular weight [g. mol1]
17.94 17.60 0.58
58 72 86
1.49 0.11
86 100
0.20
100
0.12 0.32
100 100
heavy components using the lattice oxygen in FeOx, leading to the ketonization which then produced additional aliphatic ketones over the ZrO2(8.9)eFeOx catalyst [20]. The aliphatic ketones consisted of 17.94 C-mol% of acetone, 17.60 C-mol% of 2-butanone and about 2.82 C-mol% of other low molecular weight of aliphatic ketones as shown in Table 4. The average molecular weight of the evolved aliphatic ketones are 25.61 g mol1 that calculated by addition of multiplication between percentage yield and molecular weight of each ketones. An increase in ZrO2 contents from 10e90 wt% shows that the yield of aliphatic ketones was stable in the range from 31 to 34 C-mol%, lower than the yield after reaction over 8.9 wt% of ZrO2 in the catalyst. This indicated that catalytic activity of the catalysts in decomposition of the aqueous phase in aliphatic ketones production was almost the same. However, the activity was different against other chemicals, heavy components and residue on the catalyst. Formation of a cokelike residue deposited on the catalyst increased as the ZrO2 content increased, implying that the acidity of the catalyst from ZrO2 increased as well as BET surface area (see Table 5). Organic compounds of heavy molecular weight contained in other chemicals and heavy components were trapped in the cages of acidic ZrO2eFeOx catalysts, which resulted in carbon deposition on the catalysts [26]. Catalytic reaction of the aqueous phase over ZrO2eFeOx catalysts also produced gas. The composition of the product gas is shown in Fig. 7. The main composition of the product gas was CO2 as one of by-product of ketonization from carboxylic acids. As shown in Fig. 4, ratio of aliphatic ketones to gas (mainly CO2) was about 3e4. This result indicated that ketonization of carboxylic acids as well as selective oxidation occurred. On the other hand, yield of other chemicals and heavy components decreased. These results shown that selective oxidation of other chemicals and heavy components occurred to produce carboxylic acids followed by additional amounts of the aliphatic ketones. The product gas also contained trace amounts of C1 e C4 hydrocarbons and H2. Formation of H2 was predicted to be derived from carbon deposition of some hydrocarbon on the catalyst. After reaction over ZrO2 catalyst, the product gas contained CO. The yield of aliphatic ketones decreased to 29 C-mol% after catalytic reaction over ZrO2 catalyst. The results of the catalytic reaction of the aqueous phase over ZrO2eFeOx catalysts
Table 5 e Surface area of ZrO2eFeOx catalysts prior to and after reaction. Catalyst
FeOx ZrO2(8.9)eFeOx ZrO2(10)eFeOx ZrO2(18)eFeOx ZrO2(30)eFeOx ZrO2(50)eFeOx ZrO2(70)eFeOx ZrO2(90)eFeOx ZrO2(100)
SBET prior to SBET after Percent decline of reaction reaction surface area [%] (m2.g1) (m2.g1) 10.69 58.74 71.38 87.11 123.58 139.80 149.00 135.68 99.96
9.34 35.89 38.32 41.88 50.79 98.43 116.71 99.40 77.04
13 39 46 52 59 30 22 27 23
Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
8
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
Fig. 7 e The composition of product gas after catalytic reaction of the aqueous phase of pyrolysis oil over ZrO2eFeOx catalysts.
suggest that reactions over a single oxide catalyst such as FeOx or ZrO2 catalyst produced a low yield of aliphatic ketones. Therefore, ZrO2-supported FeOx as a combined oxide catalyst was needed for carrying out selective oxidation and ketonization reactions for aliphatic ketone production. In oxides with high lattice energy (high metaleoxygen bond strength) such as ZrO2 and a-Fe2O3, ketone formation occurs as a surface reaction. In addition to ketonization, selective oxidation occurs in the surface that involves lattice oxygen. Since the catalytic reaction of the aqueous phase over ZrO2eFeOx catalysts involved lattice oxygen, analysis of their crystallinity was required. Fig. 8 shows the crystallinity of the catalyst investigated by XRD. The XRD patterns of the catalyst prior to the reaction with ZrO2 contents of 0.0e30 wt% showed peaks corresponding to hematite (a-Fe2O3). The pattern of the FeOx catalysts without ZrO2 after reaction, in contrast, showed clear peaks corresponding to magnetite (Fe3O4), while the catalysts with ZrO2 contents from 8.9 to 30 wt% showed small peaks corresponding to hematite. It was considered that the heavy components as well as other chemicals were oxidized using the lattice oxygen of iron oxide. Since heavy components as well as other chemicals were oxidized using the lattice oxygen of iron oxide, therefore, the involved lattice oxygen need to be reproduced. Decomposition of water over ZrO2 generates active oxygen species that will replace the lattice oxygen. If there is no replacement of lattice oxygen, lattice oxygen deficiency will occur which resulting in transformation of crystallinity of the catalyst. In the present study, crystallinity of the catalyst prior to reaction is hematite structure (a-Fe2O3). When lattice oxygen deficiency occurred, the crystallinity of hematite structure will transform into magnetite (Fe3O4) or Fe3þ into Fe2þ. The transformation of hematite into magnetite happened after catalyric reaction of aqueous phase over FeOx catalyst (without ZrO2 content) as shown in Fig. 8. XRD patterns of the catalyst prior to and after reaction with ZrO2 contents of 50e70 wt% in Fig. 8 show that almost no peaks of FeOx and ZrO2 appeared due to low content of FeOx in the catalyst. However, with an increase in ZrO2 content to 90 and 100 wt%, peaks of ZrO2 appeared in the XRD patterns. XRD patterns of the catalysts with ZrO2 contents of 50e100 wt% prior to and after the reactions were
almost the same. It was thus revealed that crystallinity of these catalysts was stable. Moreover, in the field of solid catalysts, the surface area of catalysts is an important factor in catalytic activity. According to Fig. 4, there were several ZrO2 contents in the catalyst that produced aliphatic ketones from the aqueous phase of pyrolysis oil. Therefore, the surface area of each catalyst prior to and after reaction was investigated and the results are shown in Table 5. It was observed that an increase in ZrO2 content of fresh catalysts up to 70 wt% resulted in an increase in surface area. Moreover, as shown in Fig. 8, as the concentration of ZrO2 increased up to 70 wt%, the intensity of peaks corresponding to hematite gradually decreased. These results indicated that ZrO2 particles were highly dispersed in iron oxide, which suppressed the crystal growth of iron oxide during calcination. Hence, the BET surface area of the catalyst was increased with increasing ZrO2 concentration and exhibited the maximum value of 140e150 m2 g1 at the ZrO2 concentration of 50e70 wt%. It is reasonable to propose that catalysts having larger surface areas supply larger amounts of surface active sites for adsorption of reactants and surface reactions. However, the catalytic reaction of the aqueous phase gave higher yields for aliphatic ketones over the ZrO2(8.9)eFeOx catalyst. It was predicted that a large content of FeOx was needed for selective oxidation of other chemicals and heavy components to produce carboxylic acids as the source of aliphatic ketones. According to Table 5, the surface area of the catalyst after the reaction decreased. FeOx catalyst without ZrO2 prior to and after reaction showed the smallest surface area due to sintering and crystal phase changes in FeOx during preparation and reaction, respectively. ZrO2eFeOx catalysts with ZrO2 content ranging from 8.9 to 30 wt% showed a decrease in their surface area to approximately 40e50 m2 g1 after reaction. In addition, the catalysts with ZrO2 contents of 50e100 wt% maintained their surface area of about 100 m2 g1 after reaction. Iron oxide in the ZrO2-FeOx catalyst played an important role in the selective oxidation reaction of heavy components to produce carboxylic acids followed by ketonization. Therefore, from the results shown in Figs. 4 and 8, ZrO2(8.9)e FeOx was selected as the appropriate catalyst and applied to the catalytic conversion of the organic phase of pyrolysis oil.
3.3. Catalytic reaction of the organic phase of pyrolysis oil to produce phenols Reaction of the organic phase was carried out using 12 wt% of organic phase diluted with toluene, which was inactive under the above conditions. Based on results of the catalytic reaction of the aqueous phase, in which ZrO2(8.9)eFeOx catalyst exhibited better activity and gave higher yield of aliphatic ketones compared to other contents of ZrO2 in the catalyst, the ZrO2(8.9)eFeOx catalyst was used for catalytic reaction of the organic phase. Fig. 9 shows yields of the catalytic reaction of the organic phase. After reaction, the amount of heavy and light components decreased and a trace amount of gas and coke-like residue deposited on the catalyst were produced [Fig. 9 (A)]. Light and heavy components are detectable and undetectable components by gas chromatography, respectively. Compared
Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
9
Fig. 8 e X-ray diffraction patterns of ZrO2eFeOx catalysts at different ZrO2 contents prior to and after reactions.
to the aqueous phase, other chemicals (unknown compounds in light components), heavy components in organic phase, and aromatics are higher (Table 3). It was predicted that some heavy components and other chemicals were trapped on the catalyst since the organic phase was composed of aromatic compounds that easily form coke depositions on the catalyst. Fig. 9 (B) shows the composition of light components in the feed and products of the catalytic reaction. After reaction, the yield of phenol and alkyl phenols increased, while methoxyphenols decreased. It has been reported that guaiacol (2-
methoxyphenol) was selectively converted into phenol over iron oxide catalysts [27]. Therefore, it is considered that demethoxylation of the methoxyphenols occurred via a similar reaction pathway as that of guaiacol. The reaction produced 7 C-mol% phenol and alkyl phenols (cresol, xylenol, and ethylphenol). Moreover, during catalytic reaction of the organic phase, the yield of carboxylic acids decreased and aliphatic ketones were formed. It was mentioned previously that ketonization of carboxylic acids produced aliphatic ketones. On the other
Fig. 9 e Catalytic reaction of the organic phase of pyrolysis oil over ZrO2(8.9)eFeOx catalyst. Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
10
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
hand, yields of alkyl benzenes, aromatic ketones, and cyclic ketones increased after reaction. Here, aromatic ketones are group of chemicals that have benzene ring and carbonyl group, for example acetophenone and 4-hydroxy-2-methylacetophenone. The decrease in methoxyphenols and carboxylic acids occurred simultaneously with an increase in phenol and alkyl phenols and aliphatic ketones, respectively. Therefore, the increase in alkyl benzenes, aromatic ketones, and cyclic ketones was suspected from selective oxidation of other chemicals and heavy components over the catalyst.
3.4. Industrial value of aliphatic ketones, phenol and alkyl phenols After catalytic reaction over ZrO2eFeOx catalyst of pyrolysis oil derived from cacao pod husks, aliphatic ketones (mainly acetone and 2-butanone), phenol, and alkyl phenols (cresol, xylenol, and ethylphenol) were recovered as useful chemical for the development of environmentally benign production of platform chemicals from renewable and abundant biomass. Acetone can be used as raw material for printing inks, adhesives, pharmaceutical, cleaning fluids, solvent for extraction of oils from bones, fish and seeds, acetate rayon solvent, paint remover, absorbent for compressed acetylene, and chemical intermediate (methacrylate resins, Bisphenol A, pharmaceuticals). Moreover, 2-butanone (or methyl ethyl ketone) is used as solvents for coatings and paints, extraction solvents for antibiotics and other pharmaceuticals, carrier solvent for pesticides, and chemical intermediate [28]. In application, phenol is used as antioxidant and polymer based phenols such as phenol formaldehyde resins [29]. Alkyl phenol and its derivatives are used as raw materials for the production of resins, novolaks (alcohol-soluble resins of the phenolformaldehyde type), herbicides, insecticides, antioxidants, and other chemicals [30].
4.
Conclusions
Production of useful chemicals from cacao pod husks was carried out by slow pyrolysis followed by catalytic reactions over ZrO2eFeOx catalyst. After pyrolysis, aqueous and organic phases of pyrolysis oil were recovered. The aqueous phase was converted into 38 C-mol% of aliphatic ketones over ZrO2 (8.9)eFeOx catalyst. This yield of aliphatic ketones reaches 48% in total liquid product. Aliphatic ketones consisted of 17.9 Cmol% of acetone and 17.6 C-mol% of 2-butanone. Moreover, the organic phase produced 7 C-mol% of phenol and alkyl phenols (cresol, xylenol, ethylphenol) over the same combined oxide catalyst.
Acknowledgments This work was supported by PT. L’Oreal Indonesia in collaboration with Indonesian National Commission for UNESCO, The Ministry of Education and Culture of The Republic of Indonesia through a program Fellowship Nasional L’OrealUNESCO for Women in Science awarded in December 2012.
references
[1] Clark JH, Deswarte FEI. Introduction to chemicals from biomass. Great Britain: Wiley; 2008. pp. 78e9. 163. [2] Klass DL. Biomass for renewable energy, fuels, and chemicals. San Diego: Academic Press; 1998. pp. 137e56. [3] The World Cocoa Foundation. Cocoa market update. Download date: August 1st, 2013, http:// worldcocoafoundation.org/wp-content/uploads/CocoaMarket-Update-as-of-3.20.2012.pdf; Mar 2012. [4] Sobamiwa O, Longe OG. Utilization of cocoa-pod pericarp fractions in broiler chick diets. Anim Feed Sci Technol 1994;47:237e44. [5] Donkoh A, Atuathene CC, Wilson BN, Adomako D. Chemical composition of cacao pod husk and its effect on growth and food efficiency in broiler chicks. Anim Feed Sci Technol 1991;35:161e9. [6] Vriesmann LC, de RD, Amboni MC, de CL, Petkowicz O. Cacao pod husks (Theobroma cacao L.): composition and hotwater-soluble pectins. Ind Crops Prod 2011;34:1173e81. [7] Mollea C, Chiampo F, Conti R. Extraction and characterization of pectins from cocoa husk: a preliminary study. Food Chem 2008;107:1353e6. [8] Pouomogne V, Takam G, Pouemegne J-B. A preliminary evaluation of cacao husks diets for juvenile Nile tilapia (Oreochromis niloticus). Aquaculture 1997;156:211e9. [9] Oddoye EOK, Rhule SWA, Agyente-Badu K, Anchirinah V, Ansah FO. Fresh cocoa pod husk as an ingredient in the diets of growing pigs. Sci Res Essays 2010;5(10):1141e4. [10] Mohan D, Pittman Jr CU, Steele PH. Pyrolysis of wood/ biomass for bio-oil: a critical review. Energy Fuels 2006;20:848e89. [11] Encinar JM, Gonzalez JF, Rodriguez JJ, Ramiro MJ. Catalysed and uncatalysed steam gasification of eucalyptus char: influence of variables and kinetics study. Fuel 2001;80:2025e36. [12] Nair SA, Pemen AJM, Yan K, Heesch van EJM, Ptasinski KJ, Drinkenburg AAH. Chemical processes in tar removal from biomass derived fuel gas by pulsed corona discharges. Plasma Chem Plasma Process 2003;23(4):665. [13] Dermibas A. Gaseous products from biomass by pyrolysis and gasification: effects of catalyst on hydrogen yield. Energy Convers Manag 2002;43:897e909. [14] Adam J, Antonakou E, Lappas A, Stocker M, Nilsen MH, Bouza A, et al. In situ catalytic upgrading of biomass derived fast pyrolysis vapours in a fixed bed reactor using mesoporous materials. Microporous Mesoporous Mater 2006;96:93e101. [15] Adjaye JD, Bakhshi NN. Upgrading of a wood-derived oil over various catalysts. Biomass Bioenergy 1994;7(1e6):201e11. [16] Jackson MA, Cermak SC. Cross ketonization of cuphea sp. Oil with acetic acid over a composite oxide of Fe, Ce, and Al. Appl Catal A 2012;431e432:157e63. [17] Jackson MA. Ketonization of model pyrolysis bio-oil solutions in a plug-flow reactor over a mixed oxide of Fe, Ce, and Al. Energy Fuels 2013;27:3936e43. [18] Nokkosmaki MI, Kuoppala ET, Leppamaki EA, Krause AOI. Catalytic conversion of biomass pyrolysis vapours with zinc oxide. J Anal Appl Pyrolysis 2000;55:119e31. [19] Fumoto E, Mizutani Y, Tago T, Masuda T. Production of ketones from sewage sludge over zirconia-supporting iron oxide catalysts in a steam atmosphere. Appl Catal B Environ 2006;68:154e9. [20] Mansur D, Yoshikawa T, Norinaga K, Hayashi J-i, Tago T, Masuda T. Production of ketones from pyroligneous acid of woody biomass pyrolysis over an iron-oxide catalyst. Fuel 2011;103:130e4.
Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
[21] Mansur D, Shimokawa M, Oba K, Nakasaka Y, Tago T, Masuda T. Conversion of ethanol fermentation stillage into aliphatic ketones by two-step process of hydrothermal treatment and catalytic reaction. Fuel Process Technol 2013;108:139e45. [22] Yoshikawa T, Yagi T, Shinohara S, Fukunaga T, Nakasaka Y, Tago T, et al. Production of phenols from lignin via depolymerization and catalytic cracking. Fuel Process Technol 2013;108:69e75. [23] Taimoor AA, Favra-Re´guillon A, Vanoye L, Pitault I. Upgrading of biomass transformation residue: influence of gas flow composition on acetic acid ketonic condensation. Catal Sci Technol 2012;2:359e63. [24] Apaydin-Varol E, Pu¨tu¨n E, Pu¨tu¨n AE. Slow pyrolysis of pistachio shell. Fuel 2007;86:1892e9. [25] Pestman R, Koster RM, van Duijne A, Pieterse JAZ, Ponec V. Reactions of carboxylic acids on oxides, 2. Bimolecular reaction of aliphatic acids to ketones. J Catal 1997;168:265e72.
11
[26] Huang J, Jiang Y, Marthala VRR, Bressel A, Frey J, Hunger M. Effect of pore size and acidity on the coke formation during ethylbenzene conversion on zeolite catalyst. J Catal 2009;263:277e83. [27] Yoshikawa T, Na-Ranong D, Tago T, Masuda T. Oxidative cracking of aromatic compounds related to lignin constituents with steam using ZrO2-Al2O3-FeOx catalyst. J Jpn Petrol Inst 2010;53:178e83. [28] The Dow Chemical Company. DOW oxygenated solvents e acetone derivatives. Download March 14, 2014, http://www. dow.com/oxysolvents/prod/acetone.htm; 1995e2014. [29] Rappoport Z. The chemistry of phenols. John Wiley & Sons, Ltd; 2003. [30] Kruschwitz JI, Howe-Grant M. Encyclopedia of chemical technology. 4th ed., vol. 2. New York: A wileyInterscience Publication John Wiley & sons; 1992. p. 107, 133,135,140.
Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
Available online at www.sciencedirect.com
ScienceDirect http://www.elsevier.com/locate/biombioe
Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals Dieni Mansur a,*, Teruoki Tago b, Takao Masuda b, Haznan Abimanyu a a
Research Center for Chemistry, Indonesian Institute of Sciences, Kawasan Puspiptek Serpong, Tangerang Selatan, Banten 15314, Indonesia b Division of Chemical Process Engineering, Hokkaido University, N-13 W-8 Kita-Ku, Sapporo 060-8628, Japan
article info
abstract
Article history:
Recently, much attention has been devoted the generation of useful chemicals from
Received 4 November 2013
biomass. Cacao pod husks, a waste biomass, are one of the agricultural crop residues that
Received in revised form
can be utilized for this purpose. The husks were treated by pyrolysis to produce pyrolysis
18 March 2014
oil that contained several chemical compounds such as ketones, carboxylic acids, alde-
Accepted 31 March 2014
hydes, furans, heterocyclic aromatics, alkyl benzenes, phenols and benzenediols. There-
Available online xxx
fore, this biomass-derived pyrolysis oil is potentially a rich source of useful chemicals. The pyrolysis oil was upgraded over iron oxide catalysts. During the catalytic upgrade, keto-
Keywords:
nization, selective oxidation and demethoxylation reactions occurred and selectively
Cacao pod husks
produced aliphatic ketones (acetone, 2-butanone), phenol and alkyl phenols (cresol, xyle-
Pyrolysis
nol, ethylphenol). ª 2014 Elsevier Ltd. All rights reserved.
Iron oxide catalysts Useful chemicals Ketonization
1.
Introduction
The depletion of crude oil reserves and the effect of greenhouse gases on global warming call for the substitution of petrochemical processes with biomass-based processes for chemical production. Biomass as a renewable resource is considered to be the only raw material for sustainable production of chemicals [1]. It is different from other energy sources such as solar, hydropower, wind, nuclear, and geothermal energy. Recently, biomass used for chemical production has been derived from waste biomass due to its lower cost than virgin biomass. In fact, it often has negative costs. Waste biomass includes municipal solid waste, livestock and poultry manure, agricultural crop residues, forestry residues and industrial waste [2]. In this study, we utilize an agricultural crop residue
generated from a cacao plantation in Indonesia, which ranks third highest in the world in the production of cacao [3]. Cacao is an industrially important crop since cocoa beans and its processed products are the main ingredients of chocolate, one of the world’s most popular foods. However, in the production of the beans, waste in the form of cacao pod husks is also generated. Every ton of dry cacao beans generates 10 tons of wet cacao husks. The cacao’s pod, bean and husk are shown in Fig. 1 and the husk has composition as shown in Table 1. The husks are typically left to rot and decompose into organic manure on the cacao plantation. However, besides producing foul odors, rotting can propagate diseases such as black pod rot [6]. Proper usage of the husks could provide economic advantages and decrease their environmental impact. For example, the husks have been treated to produce pectin [6,7], a viable dietary supplement for fish [8] and pigs [9].
* Corresponding author. Tel.: þ62 21 756 0929; fax: þ62 21 756 0549. E-mail addresses: [email protected], [email protected] (D. Mansur). http://dx.doi.org/10.1016/j.biombioe.2014.03.065 0961-9534/ª 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
2
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
Fig. 1 e The cacao’s pod (fruit), bean and husk.
The utilization of biomass to increase its added value and to develop clean and sustainable technologies involves physical, chemical and biological processing to convert agricultural and organic raw materials into chemical products [1]. Most processes begin with pyrolysis, followed by catalytic upgrading to produce low-cost and environmentally friendly compounds. Pyrolysis is the thermal decomposition of materials in the absence of oxygen or when significantly less oxygen is present than required for complete combustion, which results in char, gas, and liquid products [10]. The char is a high quality solid fuel and fuel gas is used as a source of power generation [11,12]. The liquid product from biomass pyrolysis is known as tar or pyrolysis oil. The pyrolysis oil is a mixture of different molecules (alcohols, aldehydes, ketones, esters and phenolic compounds) derived from fragmentation of lignin, cellulose, hemicelluloses and extractives [1]. The yield and composition of biomass pyrolysis oil are dependent on the chemical and structural composition, particle size and species of the biomass used, as well as temperature, heating rate, and residence time of the pyrolysis [10,13]. Pyrolysis oil is a promising material for replacement of fossil oil for production of different chemicals from sustainable and renewable sources. Pyrolysis oil exhibits two main problems as a source of useful chemicals: its high water content and its instabilities, such as viscosity increase and phase separation. The instabilities result from a breakdown in the stabilized microemulsion and chemical reactions, which continue to occur in the oil. Stabilization of pyrolysis oil can be achieved by upgrading over catalysts [10,14]. Adam et al. investigated catalytic upgrading of pyrolysis vapor using mesoporous molecular sieves (MCM-41), FCC, and SBA-15 catalysts. All of the catalysts reduced the undesirable product yield, while the desirable product yield remained the same or increased [14].
Table 1 e Composition of cacao pod husk. Composition
Amount (g. kg1 dry matter)
Cellulose Hemicellulose Lignin Pectin Crude fiber Crude protein Ash
350a 108b e 110a 146a 61a 226a e 325b 59a e 76.6b 91a e 101b
a b
The values were according to Ref. [4]. The values were according to Ref. [5].
Adjaye et al. studied the catalytic upgrading of pyrolysis oil into hydrocarbons using HZSM-5, silicalite, H-mordenite, HeY and silicaealumina [15]. Moreover, Jackson et al. reported that ketonization of carboxylic acid into ketone over a mixed oxide of Fe, Ce, and Al is another approach to stabilize and upgrade pyrolysis oil [16,17]. In catalytic upgrading of pyrolysis oil, the high water content should be considered because water will deactivate the catalysts [18]. In our previous studies, iron oxide based catalysts selectively produced ketones from sewage sludge, woodchips and ethanol fermentation stillage, and phenols from lignin. These catalysts have been successfully utilized to upgrade oxygen-containing tars derived from thermochemical conversion of biomass [19e22]. Activity iron oxide catalyst also investigated by Taimoor et al. for ketonization of acetic acid and its activity increased by introducing H2 in carrier gas [23]. In this study, the cacao pod husk waste from a cacao plantation, was subjected to pyrolysis to produce pyrolysis oil, and the pyrolysis oil was then upgraded over zirconiaeiron oxide catalysts for production of useful chemicals such as ketones and phenols.
2.
Material and methods
2.1.
Material
The cacao pod husks were obtained from a cacao plantation in West Sumatera province, located in western Indonesia. The husks were separated from the beans, and then sun-dried for a week. Before being fed into the pyrolyzer, the husks were reduced in size using a size reducer (MF10, IKA-Werke GmbH & Co. KG) operating at 3500 rpm min1. The cut husks were sieved to obtain chips between 0.84 and 4 mm in length. Moisture content (water content) of the cacao pod husk chips was analyzed using moisture analyzer (MB45, Ohaus) at 105 C for 10 min and found that the moisture content was 14.93%. The samples were stored at 2 C to discourage the growth of fungi. The cacao pod husks contained 42.78 wt% carbon based on elemental analysis. This value was used as the basis for calculation of the total carbon yield of products after the pyrolysis process.
2.2.
Pyrolysis process of the cacao pod husks
The pyrolysis experiments were carried out in a fixed-bed quartz reactor. The length and inner diameter of the pyrolyzer were 0.5969 m and 0.0254 m, respectively. About 20 g of cacao pod husk chips were placed in the pyrolyzer. Nitrogen as a sweeping gas was passed through the pyrolyzer to remove air/oxygen. The nitrogen flow rate was set to 20 cc. min1, the temperature of the pyrolyzer was increased from room temperature (approximately 25 C) to 500 C for 9 min, and then the temperature was maintained at 500 C until pyrolysis had occurred for 50 min. Process pyrolysis of cacao pod husk can be classified into slow pyrolysis due to low heating rate as well as pyrolysis of pistachio shell that conducted by ApaydinVarol [24]. The temperature was measured using a thermocouple located just below the bed. A condenser (0 C) and cold trap
Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
(70 C) were installed to capture the vapor/liquid product, and non-condensable gas was collected in a gas pack during the process and for 15 min after heating of the pyrolyzer had stopped. A schematic diagram of the pyrolysis apparatus is given in Fig. 2. Heating of the pyrolyzer was terminated when the desired reaction time was reached, and the system was allowed to cool to room temperature. The pyrolyzer, condenser and cold trap, including all of the connections and downstream tubes, were carefully removed from the system and weighed. Char remained on the bed after pyrolysis. Heavy tar was recovered and its amount was calculated as the difference in weight of the pyrolyzer prior to and after pyrolysis. The heavy tar was located on top of the char bed. Condensable liquid in the condenser and cold trap were mixed together and designated pyrolysis oil. The pyrolyzer and its connections and downstream tubes were washed with acetone. Heated air was used to clean heavy tar from the pyrolyzer by combustion because this tar was difficult to remove with solvents. The yield of products after pyrolysis was reported in wt% and C-mol%. Yield in wt% was calculated based on weight of products divided with weight of feed. Moreover, C-mol% (or mol % of carbon) was determined by dividing mol of carbon in product with mol of carbon in feed, and then multiplied it with 100% (Eq. (1)). C mol% yield ¼ ½C mol product=C mol feed 100%
(1)
C-mol of feed was determined by multiplying weight of feed (g) with its carbon content (wt%) based on elemental analysis and then divided by atomic weight of carbon (12 g/ mol) as shown in Eq. (2). C mol feed ¼ ½gram feed wt:% C=12
(2)
3
Char and heavy tar were recovered from inside of the pyrolyzer and analyzed for their carbon content using an elemental analyzer (ECS 4010, Costech Instruments). C-mol of char and heavy tar were calculated as the same way with Cmol of feed according to their each carbon content. The gas product was analyzed using gas chromatographs with thermal conductivity and flame ionization detectors (GC-8A and GS-20B; Shimadzu Co., Ltd.) with activated charcoal and Porapak Q columns, respectively. Gas product was calculated using gas standard. Moles of each gas were divided by their carbon atom to find their C-mol, and then were divided by Cmol of feed in order the unit becomes C-mol%. Pyrolysis oil consisted of two separable phase and hereafter were called as aqueous and organic phases. The aqueous phase was analyzed by a gas chromatograph with a flame ionization detector (GC-2014; Shimadzu Co., Ltd.) and a gas chromatograph-mass spectrometer (GC-17A GCMS-QP5050; Shimadzu Co., Ltd.) with DB-Wax capillary columns using nbutanol as an internal standard. The organic phase was analyzed by a gas chromatograph with flame ionization detector (GC-2010; Shimadzu Co., Ltd.) and a gas chromatograph-mass spectrometer (GC-2014 GCMS Parvum2; Shimadzu Co., Ltd.) with DB-5 and DB-5MS capillary columns, respectively, using the same internal standard with the aqueous phase. Moles of 1-butanol were calculated, and then the value was divided by 4 to find its C-mol. C-mol per 1% area of 1-butanol was compared with % area of chemical compounds to find their C-mol, and then were divided by C-mol of feed in order the unit becomes C-mol%. Pyrolysis oil contained heavy components that were undetectable by gas chromatography, therefore, the amount of carbon measured by the elemental analyzer (Costech, ECS 4010 CHNS-O) was considered to be the total amount of carbon in the oil. The pyrolysis oil was used as the feed for the catalytic reaction. Feeds and
Fig. 2 e A schematic diagram of the pyrolysis apparatus of cacao pod husks. Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
4
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
products of pyrolysis and catalytic reaction were analyzed twice and the data were shown in average.
2.3. Preparation and characterization of the iron oxide catalysts The catalytic reaction of pyrolysis oil for chemical production was carried out over ZrO2eFeOx catalysts. The catalysts were prepared by a co-precipitation method with aqueous solutions of iron (III) nitrate anneahydrate [Fe(NO3)3.9H2O] and zirconyl nitrate dehydrate [ZrO(NO3)2.2H2O] using aqueous ammonia until a pH of 7 was reached [21]. All reagents were purchased from Wako Pure Chemical Industries, Ltd., Japan. The zirconia content in the catalysts varied from 0e100 wt%. Crystalline structures and the specific surface areas of the catalysts prior to and after reaction were evaluated using Xray diffraction (XRD, JEOL, JDX-8020) and by a N2 adsorption and desorption method (Belsorp mini; BEL Japan, Inc.), respectively.
2.4.
Catalytic reaction of pyrolysis oil
The catalytic reaction of pyrolysis oil over the ZrO2eFeOx catalyst was carried out in a fixed bed flow reactor for 2 h under atmospheric conditions at 350 C. Nitrogen gas (10 cm3 min1) was used as the carrier gas. One ml. h1 of aqueous phase and organic phase of the pyrolysis oil were fed into the reactor separately. An aqueous phase was mixed with water under ratio of 1 before being fed into the reactor. On the other hand, 12 wt% of organic phase diluted in toluene and water with ratio of 1 was also fed into the reactor. W/F [W: Amount of catalyst bed (g) and F: Flow rate of feed (g. h1)] was 1 h. A schematic diagram of the apparatus used for the catalytic reaction is shown in Fig. 3. After the catalytic reaction, gas and liquid products were collected in a gas pack and a condenser (0 C), respectively, and then analyzed directly by the same apparatus as the gas and liquid products from the pyrolysis process. The amount of coke-like residue deposited on the catalyst was measured by an elemental analyzer. Product yields of the catalytic reaction were calculated based on the carbon content of each phase of the pyrolysis oil.
3.
Results and discussion
3.1. Pyrolysis of cacao pod husks for pyrolysis oil production Cacao pod husk chips were pyrolyzed in a fixed-bed quartz reactor in several batches of pyrolysis experiments to prepare the appropriate amount of pyrolysis oil for useful chemical production. All pyrolysis products were recovered and analyzed. The products were pyrolysis oil, char, heavy tar and gas. The average composition of pyrolysis products in wt% and C-mol% is shown in Table 2. The pyrolysis oil as 40.11 Cmol% was obtained in the form of two easily separable phases: an aqueous phase (bottom phase of 28.19 C-mol%) and an organic phase (top phase of 11.92 C-mol%) with more in the aqueous phase than the organic phase. The larger aqueous
Fig. 3 e A schematic diagram of the apparatus for catalytic reaction of pyrolysis oil.
phase was due to the high moisture content in the cacao pod husks because the feed was only treated by sun-drying, not oven-drying, before pyrolysis. In Table 2, the value of aqueous phase of pyrolysis oil in wt % is much higher than the value based on C-mol%, indicating that the chemicals containing in aqueous phase of pyrolysis oil are “hydrocarbons” with “high oxygen content”. High oxygen content would be derived from eOH groups, possibly due to decomposition and/or depolymerization of cellulose during pyrolysis. The chemical compounds from the aqueous and organic phases of pyrolysis oil in C-mol% and wt% are listed in Table 3. The chemical compounds of the aqueous and organic phases in C-mol% were calculated based on 27.66 wt% and 71.96 wt% of their carbon content, respectively. The aqueous phase was mainly composed of carboxylic acids and ketones that easily dissolved in water because their carboxyl and carbonyl
Table 2 e Composition of pyrolysis products. Composition Aqueous layer of pyrolysis oil Organic denser layer of pyrolysis oil Char Heavy tar Gas
Yielda (C-mol%)
Yield (wt%)
28.19 11.92
50.62 9.01
50.05 0.61 9.23
39.99 0.39 0.01
a
Calculated based on carbon content of cacao pod husks (C ¼ 42.78 wt%).
Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
Table 3 e Composition of pyrolysis oil. Composition
Aqueous layer
Organic denser layer
(C-mol%)a (wt%) (C-mol%)b (wt%) Hydroxyketones Aliphatic ketones Cyclic ketones Aromatic ketones Carboxylic acids Aldehydes Furans Heterocyclic aromatics Alkyl benzenes Phenols Alkyl phenols Methoxyphenols Benzenediols Other chemicals Heavy components
5.23 12.49 3.17 0.09 16.19 0.98 1.88 0.11 e 0.87 0.97 0.79 0.56 16.95 39.73
0.50 1.19 0.30 0.01 1.54 0.09 0.18 0.03 e 0.08 0.09 0.19 0.05 1.59 94.14
e 0.00 0.44 0.74 2.22 e e e 0.27 0.88 3.31 5.32 e 24.22 62.58
e 0.00 0.49 0.83 2.47 e e e 0.30 0.98 3.68 5.92 e 26.92 58.42
a
Calculated based on carbon content of an aqueous layer (C ¼ 27.66 wt%). b Calculated based on carbon content of an organic denser layer (C ¼ 71.96 wt%).
functional groups are polar organic functional groups. On the other hand, the organic phase contained aromatics such as alkyl- and methoxy-phenols that separated in the organic phase. The composition of pyrolysis oil (both phases) in Table 3 was also separated into light components and heavy components. The light components consisted of chemicals grouped into ketones, carboxylic acids, aldehydes, furans, heterocyclic aromatics, phenols, benzenediols, and other chemicals. Others chemicals were organics detectable by GC and GCMS, but they could not be identified. The heavy components were essentially organics dissolved in pyrolysis oil,
5
but they were undetectable by gas chromatography due to their high molecular weight. In Table 3, the wt% of heavy components in aqueous phase is quite different from the C-mol% of heavy components. The reason for this difference is the “hydrocarbons” with “high oxygen content” mentioned in Table 2. Accordingly, the heavy components in aqueous phase in Table 3 are “hydrocarbons” with “high oxygen content” derived from cellulose. In addition, in Table 3, heavy components in organic phase show almost the same values between wt% and C-mol%. OH groups are disappeared by dehydration. Heavy components in organic phase are hydrocarbons with low oxygen content. Therefore, these values are almost same each other due to complete dehydration.
3.2. Reaction of the aqueous phase of pyrolysis oil over ZrO2eFeOx catalyst The catalytic reactions of pyrolysis oil to produce useful chemicals were carried out separately with the aqueous and organic phases. First, the catalytic reaction of the aqueous phase was investigated over 0e100 wt% of zirconia contents in ZrO2eFeOx catalysts. The optimum conditions of the catalytic reaction of the aqueous phase were then adopted for conversion of the organic phase. Product yields after catalytic reaction of the aqueous phase using several different zirconia contents in the catalyst are shown in Fig. 4. The yield of aliphatic ketones increased after catalytic reaction over FeOx from 12 C-mol% in the feed to 16 C-mol% and then significantly increased up to 38 C-mol% over ZrO2(8.9)eFeOx. On the other hand, hydroxyketones and carboxylic acids decreased. Water remained in aqueous phase of pyrolysis oil derived from cacao pod husks was predicted higher than 60.5 wt% of water content in pyroligneous acid derived from woodchip [20] because of moisture content of the husk as feed of
Fig. 4 e Product yields of catalytic reaction of aqueous phase over several different zirconia contents in the catalyst. Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
6
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
pyrolysis higher than 3 wt% of moisture in the woodchips. Moreover, carbon content in the aqueous phase of pyrolysis oil derived from the husks that contain carboxylic acids was 27.66 wt%. As shown in Fig. 4, major reaction is ketonization from carboxylic acid. Ketonization is discussed based on number of carbon in carboxylic acid. Therefore, feed and products yield after catalytic reaction are shown based on Cmol%. In contrast, if we concern about volume or weight, the present of carbon and “oxygen” is considered. Whereas, there is no relationship between “ketonization reaction” and “oxygen atoms”, in the feed and product yields after catalytic reaction of aqueous phase in Fig. 4. To investigate the reaction pathways of these conversions, catalytic reactions of carboxylic acids, aliphatic ketones, and hydroxyketones, which were major detectable chemicals in the aqueous phase listed in Table 3, were carried out under the same operating conditions as the aqueous phase.
3.2.1. Reaction of chemical model compounds in aliphatic ketones production Figs. 5 and 6 show catalytic reactions of acetic and propionic acids, acetone, and hydroxyacetone as model compounds of carboxylic acids, aliphatic ketones and hydroxyketones, respectively. The results show that two molecules of acetic acid were selectively converted by ketonization to produce one molecule each of acetone and CO2, as shown in Eq. (3). 2 CH3 COOH/CH3 COCH3 þ CO2 þ H2 O
(3)
The formation of H2O could not be detected since the reaction was conducted in a steam atmosphere. The same reaction also occurred with propionic acid, with two molecules of propionic acid producing one molecule of 3-pentanone, as shown in Eq. (4). 2 C2 H6 COOH/C2 H5 COC2 H5 þ CO2 þ H2 O
(4)
Eq. (3) and Eq. (4), respectively, show that two molecules of C2 and C3 carboxylic acids create C3 and C5 ketones. Moreover, during the reaction of propionic acid, 2-butanone and a negligible amount of acetone were also produced. We predicted the conversion to 2-butanone and acetone from acetic acid present in the feedstock, based on a concentration of pure
Fig. 5 e Catalytic reaction of 10 wt% of carboxylic acid and aliphatic ketone model compounds over ZrO2(8.9) eFeOx; T: 350 C; W/F: 1 h; N2: 10 cc. minL1.
Fig. 6 e Catalytic reaction of hydroxyketone model compounds over ZrO2(8.9)eFeOx; T: 350 C; W/F: 1 h; N2: 10 cc. minL1.
propionic acid of 98%. As discussed previously, acetic acid is converted into acetone. Here, 2-butanone is a C4 ketone derived from 1 mol each of acetic acid (C2) and propionic acid (C3). This reaction is expressed in Eq. (5). CH3 COOH þ C2 H6 COOH/CH3 COC2 H5 þ CO2 þ H2 O
(5)
Over ZrO2eFeOx catalyst, carboxylic acids were converted into ketones. However, the ketone was inactive over the catalyst. This result is shown in Fig. 5 where 90 C-mol% of acetone remained unconverted, and only small amounts of CO2 and other components were produced. It is predicted that the same result (inactivity towards the catalyst) will be obtained for the reaction of other ketones such as 2-butanone or 3-pentanone. Based on Fig. 6 at a W/F of 2.0 and 4.0 kg-cat. kg-feed1. h1, hydroxyacetone was converted into acetone, 2-butanone, 3pentanone and CO2. At a W/F of 0.5 and 1.0 kg-cat. kgfeed1. h1, acetic acid and propionic acid appeared as intermediate products and some of the hydroxyacetone remained unconverted. The amounts of acetic acid, propionic acid and other compounds formed decreased, but the formation of CO2 increased with increasing W/F value. As W/F increased, the yield of acetone increased, however, the yield of 3-pentanone decreased, indicating that the formation of acetic acid was higher than that of propionic acid. CO2 was a by-product of the ketonization reaction. A probable mechanism of reaction for the conversion of carboxylic acid into ketone by ZrO2eFeOx catalyst is as follows. Pestman et al. reported that the formation of acetone (ketone) from acetic acid (carboxylic acid) over metal oxide takes place on the surface of the catalyst. First, acetic acid is adsorbed on the surface of catalyst. In the adsorbed acetic acid, a-hydrogen is abstracted, CeC bond is dissociated and produce the intermediate. The formation of methylene as intermediate is immediately followed by a reaction with a neighboring acetate to give acetone. Then, the carboxyl group splits into CO2 [25].
Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
7
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
3.2.2. phase
Catalytic activity during decomposition of the aqueous
Referring to results of the catalytic reaction of carboxylic acids, aliphatic ketones, and hydroxyketones in Figs. 5 and 6, it was clarified that the increase in yield of aliphatic ketones in Fig. 4 was caused by the ketonization reaction of carboxylic acids and oxidation followed by ketonization of hydroxyketones to form aliphatic ketones. Complete conversion of hydroxyketones into carboxylic acids and aliphatic ketones occurred over FeOx catalyst. Under the same conditions, some carboxylic acids were also converted into aliphatic ketones. Reaction of the aqueous phase over FeOx catalyst produced more aldehydes and an increase in heavy components; however, other chemicals decreased in yield. It was predicted that aldehydes derived from other chemicals in the aqueous phase consisted of many chemicals that could not be identified by gas chromatography. The decrease in other chemicals also suggested that polymerization occurred to form heavy chemicals leading to a coke-like residue deposited on the catalyst. Catalytic reaction over ZrO2(8.9)eFeOx catalyst produced more than three times the amount of aliphatic ketones compared to aliphatic ketones in the feed. Almost all the carboxylic acids and hydroxyketones were converted into aliphatic ketones. Refer to the results of the catalytic reaction of carboxylic acids, aliphatic ketones, and hydroxyketones as chemical model compounds in Figs. 5 and 6, it was clarified that hydroxyketones are converted into carboxylic acids and then two molecules of carboxylic acid produce one molecule of ketone. Moreover, aliphatic ketones were inactive over ZrO2eFeOx catalyst. Stoichiometric reactions of ketonization from carboxylic acid are shown in Eqs. (3)e(5). The yield of aliphatic ketones after catalytic reaction was estimated based on chemical compositions of aqueous phase in Table 3. The amount of hydroxyketones, carboxylic acids, and aliphatic ketones was 5.23, 16.19 and 12.49 C-mol%, respectively. If the reactions were stoichiometric, 23.2 C-mol% of aliphatic ketones would be produced. However, in Fig. 4 over ZrO2(8.9)e FeOx, yield of aliphatic ketones was 38 C-mol%. There is about 14.8 C-mol% of aliphatic ketones produced from newly formed of carboxylic acids. The newly formed of carboxylic acids were produced from selective oxidation of other chemicals and
Table 4 e Chemical compositions of aliphatic ketones in the product after catalytic reaction of aqueous phase over ZrO2(8.9)eFeOx catalyst. Aliphatic ketones Acetone 2-Butanone 2-Butanone, 3-methyl 2-Pentanone Methyl isobutyl ketone 2-Pentanone, 3-methyl 3-Hexanone 2-Hexanone
Yield [C-mol%]
Molecular weight [g. mol1]
17.94 17.60 0.58
58 72 86
1.49 0.11
86 100
0.20
100
0.12 0.32
100 100
heavy components using the lattice oxygen in FeOx, leading to the ketonization which then produced additional aliphatic ketones over the ZrO2(8.9)eFeOx catalyst [20]. The aliphatic ketones consisted of 17.94 C-mol% of acetone, 17.60 C-mol% of 2-butanone and about 2.82 C-mol% of other low molecular weight of aliphatic ketones as shown in Table 4. The average molecular weight of the evolved aliphatic ketones are 25.61 g mol1 that calculated by addition of multiplication between percentage yield and molecular weight of each ketones. An increase in ZrO2 contents from 10e90 wt% shows that the yield of aliphatic ketones was stable in the range from 31 to 34 C-mol%, lower than the yield after reaction over 8.9 wt% of ZrO2 in the catalyst. This indicated that catalytic activity of the catalysts in decomposition of the aqueous phase in aliphatic ketones production was almost the same. However, the activity was different against other chemicals, heavy components and residue on the catalyst. Formation of a cokelike residue deposited on the catalyst increased as the ZrO2 content increased, implying that the acidity of the catalyst from ZrO2 increased as well as BET surface area (see Table 5). Organic compounds of heavy molecular weight contained in other chemicals and heavy components were trapped in the cages of acidic ZrO2eFeOx catalysts, which resulted in carbon deposition on the catalysts [26]. Catalytic reaction of the aqueous phase over ZrO2eFeOx catalysts also produced gas. The composition of the product gas is shown in Fig. 7. The main composition of the product gas was CO2 as one of by-product of ketonization from carboxylic acids. As shown in Fig. 4, ratio of aliphatic ketones to gas (mainly CO2) was about 3e4. This result indicated that ketonization of carboxylic acids as well as selective oxidation occurred. On the other hand, yield of other chemicals and heavy components decreased. These results shown that selective oxidation of other chemicals and heavy components occurred to produce carboxylic acids followed by additional amounts of the aliphatic ketones. The product gas also contained trace amounts of C1 e C4 hydrocarbons and H2. Formation of H2 was predicted to be derived from carbon deposition of some hydrocarbon on the catalyst. After reaction over ZrO2 catalyst, the product gas contained CO. The yield of aliphatic ketones decreased to 29 C-mol% after catalytic reaction over ZrO2 catalyst. The results of the catalytic reaction of the aqueous phase over ZrO2eFeOx catalysts
Table 5 e Surface area of ZrO2eFeOx catalysts prior to and after reaction. Catalyst
FeOx ZrO2(8.9)eFeOx ZrO2(10)eFeOx ZrO2(18)eFeOx ZrO2(30)eFeOx ZrO2(50)eFeOx ZrO2(70)eFeOx ZrO2(90)eFeOx ZrO2(100)
SBET prior to SBET after Percent decline of reaction reaction surface area [%] (m2.g1) (m2.g1) 10.69 58.74 71.38 87.11 123.58 139.80 149.00 135.68 99.96
9.34 35.89 38.32 41.88 50.79 98.43 116.71 99.40 77.04
13 39 46 52 59 30 22 27 23
Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
8
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
Fig. 7 e The composition of product gas after catalytic reaction of the aqueous phase of pyrolysis oil over ZrO2eFeOx catalysts.
suggest that reactions over a single oxide catalyst such as FeOx or ZrO2 catalyst produced a low yield of aliphatic ketones. Therefore, ZrO2-supported FeOx as a combined oxide catalyst was needed for carrying out selective oxidation and ketonization reactions for aliphatic ketone production. In oxides with high lattice energy (high metaleoxygen bond strength) such as ZrO2 and a-Fe2O3, ketone formation occurs as a surface reaction. In addition to ketonization, selective oxidation occurs in the surface that involves lattice oxygen. Since the catalytic reaction of the aqueous phase over ZrO2eFeOx catalysts involved lattice oxygen, analysis of their crystallinity was required. Fig. 8 shows the crystallinity of the catalyst investigated by XRD. The XRD patterns of the catalyst prior to the reaction with ZrO2 contents of 0.0e30 wt% showed peaks corresponding to hematite (a-Fe2O3). The pattern of the FeOx catalysts without ZrO2 after reaction, in contrast, showed clear peaks corresponding to magnetite (Fe3O4), while the catalysts with ZrO2 contents from 8.9 to 30 wt% showed small peaks corresponding to hematite. It was considered that the heavy components as well as other chemicals were oxidized using the lattice oxygen of iron oxide. Since heavy components as well as other chemicals were oxidized using the lattice oxygen of iron oxide, therefore, the involved lattice oxygen need to be reproduced. Decomposition of water over ZrO2 generates active oxygen species that will replace the lattice oxygen. If there is no replacement of lattice oxygen, lattice oxygen deficiency will occur which resulting in transformation of crystallinity of the catalyst. In the present study, crystallinity of the catalyst prior to reaction is hematite structure (a-Fe2O3). When lattice oxygen deficiency occurred, the crystallinity of hematite structure will transform into magnetite (Fe3O4) or Fe3þ into Fe2þ. The transformation of hematite into magnetite happened after catalyric reaction of aqueous phase over FeOx catalyst (without ZrO2 content) as shown in Fig. 8. XRD patterns of the catalyst prior to and after reaction with ZrO2 contents of 50e70 wt% in Fig. 8 show that almost no peaks of FeOx and ZrO2 appeared due to low content of FeOx in the catalyst. However, with an increase in ZrO2 content to 90 and 100 wt%, peaks of ZrO2 appeared in the XRD patterns. XRD patterns of the catalysts with ZrO2 contents of 50e100 wt% prior to and after the reactions were
almost the same. It was thus revealed that crystallinity of these catalysts was stable. Moreover, in the field of solid catalysts, the surface area of catalysts is an important factor in catalytic activity. According to Fig. 4, there were several ZrO2 contents in the catalyst that produced aliphatic ketones from the aqueous phase of pyrolysis oil. Therefore, the surface area of each catalyst prior to and after reaction was investigated and the results are shown in Table 5. It was observed that an increase in ZrO2 content of fresh catalysts up to 70 wt% resulted in an increase in surface area. Moreover, as shown in Fig. 8, as the concentration of ZrO2 increased up to 70 wt%, the intensity of peaks corresponding to hematite gradually decreased. These results indicated that ZrO2 particles were highly dispersed in iron oxide, which suppressed the crystal growth of iron oxide during calcination. Hence, the BET surface area of the catalyst was increased with increasing ZrO2 concentration and exhibited the maximum value of 140e150 m2 g1 at the ZrO2 concentration of 50e70 wt%. It is reasonable to propose that catalysts having larger surface areas supply larger amounts of surface active sites for adsorption of reactants and surface reactions. However, the catalytic reaction of the aqueous phase gave higher yields for aliphatic ketones over the ZrO2(8.9)eFeOx catalyst. It was predicted that a large content of FeOx was needed for selective oxidation of other chemicals and heavy components to produce carboxylic acids as the source of aliphatic ketones. According to Table 5, the surface area of the catalyst after the reaction decreased. FeOx catalyst without ZrO2 prior to and after reaction showed the smallest surface area due to sintering and crystal phase changes in FeOx during preparation and reaction, respectively. ZrO2eFeOx catalysts with ZrO2 content ranging from 8.9 to 30 wt% showed a decrease in their surface area to approximately 40e50 m2 g1 after reaction. In addition, the catalysts with ZrO2 contents of 50e100 wt% maintained their surface area of about 100 m2 g1 after reaction. Iron oxide in the ZrO2-FeOx catalyst played an important role in the selective oxidation reaction of heavy components to produce carboxylic acids followed by ketonization. Therefore, from the results shown in Figs. 4 and 8, ZrO2(8.9)e FeOx was selected as the appropriate catalyst and applied to the catalytic conversion of the organic phase of pyrolysis oil.
3.3. Catalytic reaction of the organic phase of pyrolysis oil to produce phenols Reaction of the organic phase was carried out using 12 wt% of organic phase diluted with toluene, which was inactive under the above conditions. Based on results of the catalytic reaction of the aqueous phase, in which ZrO2(8.9)eFeOx catalyst exhibited better activity and gave higher yield of aliphatic ketones compared to other contents of ZrO2 in the catalyst, the ZrO2(8.9)eFeOx catalyst was used for catalytic reaction of the organic phase. Fig. 9 shows yields of the catalytic reaction of the organic phase. After reaction, the amount of heavy and light components decreased and a trace amount of gas and coke-like residue deposited on the catalyst were produced [Fig. 9 (A)]. Light and heavy components are detectable and undetectable components by gas chromatography, respectively. Compared
Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
9
Fig. 8 e X-ray diffraction patterns of ZrO2eFeOx catalysts at different ZrO2 contents prior to and after reactions.
to the aqueous phase, other chemicals (unknown compounds in light components), heavy components in organic phase, and aromatics are higher (Table 3). It was predicted that some heavy components and other chemicals were trapped on the catalyst since the organic phase was composed of aromatic compounds that easily form coke depositions on the catalyst. Fig. 9 (B) shows the composition of light components in the feed and products of the catalytic reaction. After reaction, the yield of phenol and alkyl phenols increased, while methoxyphenols decreased. It has been reported that guaiacol (2-
methoxyphenol) was selectively converted into phenol over iron oxide catalysts [27]. Therefore, it is considered that demethoxylation of the methoxyphenols occurred via a similar reaction pathway as that of guaiacol. The reaction produced 7 C-mol% phenol and alkyl phenols (cresol, xylenol, and ethylphenol). Moreover, during catalytic reaction of the organic phase, the yield of carboxylic acids decreased and aliphatic ketones were formed. It was mentioned previously that ketonization of carboxylic acids produced aliphatic ketones. On the other
Fig. 9 e Catalytic reaction of the organic phase of pyrolysis oil over ZrO2(8.9)eFeOx catalyst. Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
10
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
hand, yields of alkyl benzenes, aromatic ketones, and cyclic ketones increased after reaction. Here, aromatic ketones are group of chemicals that have benzene ring and carbonyl group, for example acetophenone and 4-hydroxy-2-methylacetophenone. The decrease in methoxyphenols and carboxylic acids occurred simultaneously with an increase in phenol and alkyl phenols and aliphatic ketones, respectively. Therefore, the increase in alkyl benzenes, aromatic ketones, and cyclic ketones was suspected from selective oxidation of other chemicals and heavy components over the catalyst.
3.4. Industrial value of aliphatic ketones, phenol and alkyl phenols After catalytic reaction over ZrO2eFeOx catalyst of pyrolysis oil derived from cacao pod husks, aliphatic ketones (mainly acetone and 2-butanone), phenol, and alkyl phenols (cresol, xylenol, and ethylphenol) were recovered as useful chemical for the development of environmentally benign production of platform chemicals from renewable and abundant biomass. Acetone can be used as raw material for printing inks, adhesives, pharmaceutical, cleaning fluids, solvent for extraction of oils from bones, fish and seeds, acetate rayon solvent, paint remover, absorbent for compressed acetylene, and chemical intermediate (methacrylate resins, Bisphenol A, pharmaceuticals). Moreover, 2-butanone (or methyl ethyl ketone) is used as solvents for coatings and paints, extraction solvents for antibiotics and other pharmaceuticals, carrier solvent for pesticides, and chemical intermediate [28]. In application, phenol is used as antioxidant and polymer based phenols such as phenol formaldehyde resins [29]. Alkyl phenol and its derivatives are used as raw materials for the production of resins, novolaks (alcohol-soluble resins of the phenolformaldehyde type), herbicides, insecticides, antioxidants, and other chemicals [30].
4.
Conclusions
Production of useful chemicals from cacao pod husks was carried out by slow pyrolysis followed by catalytic reactions over ZrO2eFeOx catalyst. After pyrolysis, aqueous and organic phases of pyrolysis oil were recovered. The aqueous phase was converted into 38 C-mol% of aliphatic ketones over ZrO2 (8.9)eFeOx catalyst. This yield of aliphatic ketones reaches 48% in total liquid product. Aliphatic ketones consisted of 17.9 Cmol% of acetone and 17.6 C-mol% of 2-butanone. Moreover, the organic phase produced 7 C-mol% of phenol and alkyl phenols (cresol, xylenol, ethylphenol) over the same combined oxide catalyst.
Acknowledgments This work was supported by PT. L’Oreal Indonesia in collaboration with Indonesian National Commission for UNESCO, The Ministry of Education and Culture of The Republic of Indonesia through a program Fellowship Nasional L’OrealUNESCO for Women in Science awarded in December 2012.
references
[1] Clark JH, Deswarte FEI. Introduction to chemicals from biomass. Great Britain: Wiley; 2008. pp. 78e9. 163. [2] Klass DL. Biomass for renewable energy, fuels, and chemicals. San Diego: Academic Press; 1998. pp. 137e56. [3] The World Cocoa Foundation. Cocoa market update. Download date: August 1st, 2013, http:// worldcocoafoundation.org/wp-content/uploads/CocoaMarket-Update-as-of-3.20.2012.pdf; Mar 2012. [4] Sobamiwa O, Longe OG. Utilization of cocoa-pod pericarp fractions in broiler chick diets. Anim Feed Sci Technol 1994;47:237e44. [5] Donkoh A, Atuathene CC, Wilson BN, Adomako D. Chemical composition of cacao pod husk and its effect on growth and food efficiency in broiler chicks. Anim Feed Sci Technol 1991;35:161e9. [6] Vriesmann LC, de RD, Amboni MC, de CL, Petkowicz O. Cacao pod husks (Theobroma cacao L.): composition and hotwater-soluble pectins. Ind Crops Prod 2011;34:1173e81. [7] Mollea C, Chiampo F, Conti R. Extraction and characterization of pectins from cocoa husk: a preliminary study. Food Chem 2008;107:1353e6. [8] Pouomogne V, Takam G, Pouemegne J-B. A preliminary evaluation of cacao husks diets for juvenile Nile tilapia (Oreochromis niloticus). Aquaculture 1997;156:211e9. [9] Oddoye EOK, Rhule SWA, Agyente-Badu K, Anchirinah V, Ansah FO. Fresh cocoa pod husk as an ingredient in the diets of growing pigs. Sci Res Essays 2010;5(10):1141e4. [10] Mohan D, Pittman Jr CU, Steele PH. Pyrolysis of wood/ biomass for bio-oil: a critical review. Energy Fuels 2006;20:848e89. [11] Encinar JM, Gonzalez JF, Rodriguez JJ, Ramiro MJ. Catalysed and uncatalysed steam gasification of eucalyptus char: influence of variables and kinetics study. Fuel 2001;80:2025e36. [12] Nair SA, Pemen AJM, Yan K, Heesch van EJM, Ptasinski KJ, Drinkenburg AAH. Chemical processes in tar removal from biomass derived fuel gas by pulsed corona discharges. Plasma Chem Plasma Process 2003;23(4):665. [13] Dermibas A. Gaseous products from biomass by pyrolysis and gasification: effects of catalyst on hydrogen yield. Energy Convers Manag 2002;43:897e909. [14] Adam J, Antonakou E, Lappas A, Stocker M, Nilsen MH, Bouza A, et al. In situ catalytic upgrading of biomass derived fast pyrolysis vapours in a fixed bed reactor using mesoporous materials. Microporous Mesoporous Mater 2006;96:93e101. [15] Adjaye JD, Bakhshi NN. Upgrading of a wood-derived oil over various catalysts. Biomass Bioenergy 1994;7(1e6):201e11. [16] Jackson MA, Cermak SC. Cross ketonization of cuphea sp. Oil with acetic acid over a composite oxide of Fe, Ce, and Al. Appl Catal A 2012;431e432:157e63. [17] Jackson MA. Ketonization of model pyrolysis bio-oil solutions in a plug-flow reactor over a mixed oxide of Fe, Ce, and Al. Energy Fuels 2013;27:3936e43. [18] Nokkosmaki MI, Kuoppala ET, Leppamaki EA, Krause AOI. Catalytic conversion of biomass pyrolysis vapours with zinc oxide. J Anal Appl Pyrolysis 2000;55:119e31. [19] Fumoto E, Mizutani Y, Tago T, Masuda T. Production of ketones from sewage sludge over zirconia-supporting iron oxide catalysts in a steam atmosphere. Appl Catal B Environ 2006;68:154e9. [20] Mansur D, Yoshikawa T, Norinaga K, Hayashi J-i, Tago T, Masuda T. Production of ketones from pyroligneous acid of woody biomass pyrolysis over an iron-oxide catalyst. Fuel 2011;103:130e4.
Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065
b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 4 ) 1 e1 1
[21] Mansur D, Shimokawa M, Oba K, Nakasaka Y, Tago T, Masuda T. Conversion of ethanol fermentation stillage into aliphatic ketones by two-step process of hydrothermal treatment and catalytic reaction. Fuel Process Technol 2013;108:139e45. [22] Yoshikawa T, Yagi T, Shinohara S, Fukunaga T, Nakasaka Y, Tago T, et al. Production of phenols from lignin via depolymerization and catalytic cracking. Fuel Process Technol 2013;108:69e75. [23] Taimoor AA, Favra-Re´guillon A, Vanoye L, Pitault I. Upgrading of biomass transformation residue: influence of gas flow composition on acetic acid ketonic condensation. Catal Sci Technol 2012;2:359e63. [24] Apaydin-Varol E, Pu¨tu¨n E, Pu¨tu¨n AE. Slow pyrolysis of pistachio shell. Fuel 2007;86:1892e9. [25] Pestman R, Koster RM, van Duijne A, Pieterse JAZ, Ponec V. Reactions of carboxylic acids on oxides, 2. Bimolecular reaction of aliphatic acids to ketones. J Catal 1997;168:265e72.
11
[26] Huang J, Jiang Y, Marthala VRR, Bressel A, Frey J, Hunger M. Effect of pore size and acidity on the coke formation during ethylbenzene conversion on zeolite catalyst. J Catal 2009;263:277e83. [27] Yoshikawa T, Na-Ranong D, Tago T, Masuda T. Oxidative cracking of aromatic compounds related to lignin constituents with steam using ZrO2-Al2O3-FeOx catalyst. J Jpn Petrol Inst 2010;53:178e83. [28] The Dow Chemical Company. DOW oxygenated solvents e acetone derivatives. Download March 14, 2014, http://www. dow.com/oxysolvents/prod/acetone.htm; 1995e2014. [29] Rappoport Z. The chemistry of phenols. John Wiley & Sons, Ltd; 2003. [30] Kruschwitz JI, Howe-Grant M. Encyclopedia of chemical technology. 4th ed., vol. 2. New York: A wileyInterscience Publication John Wiley & sons; 1992. p. 107, 133,135,140.
Please cite this article in press as: Mansur D, et al., Conversion of cacao pod husks by pyrolysis and catalytic reaction to produce useful chemicals, Biomass and Bioenergy (2014), http://dx.doi.org/10.1016/j.biombioe.2014.03.065