Kalsilite based heterogeneous catalyst for biodiesel production

Kalsilite based heterogeneous catalyst for biodiesel production

Fuel 89 (2010) 2163–2165 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Short communication Kalsili...

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Fuel 89 (2010) 2163–2165

Contents lists available at ScienceDirect

Fuel journal homepage: www.elsevier.com/locate/fuel

Short communication

Kalsilite based heterogeneous catalyst for biodiesel production Guang Wen a,b,*, Zifeng Yan a, Marianne Smith b, Peng Zhang b, Ben Wen b a b

College of Chemistry and Chemical Engineering, China University of Petroleum, Qingdao 266555, PR China United Environment and Energy, LLC, Horseheads, NY 14845, USA

a r t i c l e

i n f o

Article history: Received 22 September 2009 Received in revised form 4 January 2010 Accepted 8 February 2010 Available online 18 February 2010 Keywords: Kalsilite Heterogeneous catalyst Transesterification Biodiesel

a b s t r a c t Kalsilite (KAlSiO4) was used as a heterogeneous catalyst for transesterification of soybean oil with methanol to biodiesel. Kalsilite showed relatively low catalytic activity for transesterification reaction. The catalytic activity of this catalyst was significantly enhanced by introducing a small amount of lithium nitrate by the impregnation method. A biodiesel yield of 100% and a kinematic viscosity of 3.84 cSt were achieved at a mild temperature of only 120 °C over this lithium modified kalsilite catalyst (2.3 wt.% Li). Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction Although interest in biodiesel is rapidly increasing, the process by which biodiesel is synthesized has not changed much in the last two decades. Currently, the majority of biodiesel in the US is made commercially by a homogeneous catalyst based transesterification process wherein soybean oil is reacted with methanol in the presence of sodium hydroxide and sodium methoxide. Purification of biodiesel and glycerol, by removing the homogeneous alkaline catalyst, is an energy and labor-intensive operation that produces a waste stream [1]. This process is far from being efficient, and the cost of biodiesel production is generally much higher than that of petroleum-based diesel. The development and use of effective heterogeneous catalysts can significantly simplify the downstream purification process by removing the neutralization and washing steps. Significant efforts have been made in academics and industry toward developing these heterogeneous catalysts. Hydrogenized guanidines on organic polymers [2], metal salts of amino acids [3], basic resins [4], alkali metal exchanged zeolites [5], zeolite Y [6], calcium acetate and barium acetate [7], titanium-based mixed oxide [8], Na/ NaOH/c-Al2O3 [9], immobilized lipases [10], tin oxide [11], Li/CaO [12,13], and zinc aluminate [14] were studied by different research groups. Generally, these catalysts have the difficulty in

* Corresponding author. Address: United Environment and Energy, LLC, Horseheads, NY 14845, USA. Tel.: +1 607 731 5922; fax: +1 607 796 0831. E-mail addresses: [email protected], [email protected] (G. Wen). 0016-2361/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2010.02.016

meeting the requirements for an effective heterogeneous catalyst for commercial biodiesel production due to one or more following problems: low catalytic activity causing unfavorable yields or reaction times, low thermal stability, low resistance to leaching of the active species out of the support, the requirement for very high reaction temperature or very high methanol usage. Kalsilite (KAlSiO4) is a type of basic silicate mineral. It has a framework of aluminosilicates containing a random network of tetrahedral Si and Al units with charge balancing alkali metal ions, conventionally produced at high pH by condensing a source of alumina and silica with an alkali silicate solution. The presence of the alkali metal ions in the crystal structure of the kalsilite prevents the leaching of the ions from the kalsilite even at relatively high temperatures. Kalsilite has macropores and strongly basic potassium active sites. These properties, along with its insolubility in vegetable oil and methanol, make kalsilite a promising candidate for transesterification of triglycerides to produce biodiesel. Kalsilite is currently used as a catalyst additive in ammonia synthesis and hydrogen production from steam reforming. However, the industrial grade kalsilite is produced by calcining FLINT CLAY (Al2O32SiO22H2O) with KOH at 1000 °C. This solid reaction method produces kalsilite with large particles, inhomogeneous composition, and irregular pore size and structure, which make it unsuitable for the transesterification reaction. In this study, a coprecipitation method was used to synthesize kalsilite and its catalytic activity for transesterification of soybean oil to biodiesel was explored. Property modification by lithium addition into the kalsilite was studied in order to improve its catalytic performance for the transesterification reaction.

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2000

Intensity /a.u.

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KS-1200 500

0 0

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Fig. 1. XRD pattern of the kalsilite KS-1200 powder catalyst.

fitted with mechanical stirrer, temperature control, and sample outlet. The refined soybean oil sample had a free fatty acid content of 0.2 mg KOH/g and a viscosity of 33.3 cSt at 40 °C. Catalyst powder (15 g) and methanol (150 g) were added to the reactor and mixed while stirring. Then 300 g of soybean oil were added into the reactor. The mixture was stirred at 1100 rpm. The catalyst powder was suspended and in intimate contact with the mixture of oil and methanol. Liquid samples were drawn through the filter screen at the sample outlet at 1-min intervals. The catalyst was retained in the reactor and the liquid contained no solid catalyst. After removing the methanol and glycerol, the sample was analyzed using a HP 5890 Series II Gas Chromatograph (GC) installed with a flame ionization detector and DB-5 capillary column. The soybean oil conversion and biodiesel yield were determined by comparing the sample GC data with those of a standard sample containing 5% soybean oil and 95% biodiesel. The kinematic viscosity of the biodiesel was measured using Cannon Ubbelohde Shear Dilution (CUSD) Viscometers according to ASTM D445.

2. Experimental

3. Results and discussion

KAlSiO4 was prepared by mixing 1000 ml of 0.3 mol/l potassium silicate (K2O3.9SiO2, Alfa Aesar) aqueous solution with 3000 ml of 2.0 mol/l potassium hydroxide aqueous solution and then adding dropwise 1000 ml of 1.0 mol/l aluminum nitrate (Al(NO3)39H2O, Alfa Aesar) aqueous solution into the above mixture under continuous magnetic stirring. The addition rate of the aluminum nitrate solution was controlled to maintain the pH of the solution at 13. Deionized water was used throughout all the experiments. The resulting slurry was stirred for an additional 15 min and aged quiescently at 25 °C for 2 h. After washing thoroughly with water, the slurry was dried at 120 °C in air for 4 h and calcined in air at 1200 °C. The resulting material was designated KS-1200. Lithium nitrate was added to KS-1200 by impregnation with lithium nitrate aqueous solution. After the impregnation, the material was dried at 120 °C for 6 h and calcined in air at 545 °C for 3 h. The powder catalyst was called KSLI and had a lithium loading of 2.3 wt.%. The transesterification of refined soybean oil with methanol was performed in a Parr 1000 ml Bolted Closure Stirred Reactor,

The XRD pattern in Fig. 1 indicates that the calcination at 1200 °C produced very crystallized kalsilite (KSiAlO4). There were no other potassium phases observed, suggesting a state of complete charge compensation by K+ for the substitution of Al3+ for Si4+. The SEM images of the KL-1200 are shown in Fig. 2. The catalyst powder was in the form of agglomerates, consisting of very fine particles. The catalyst was very porous with surface pores ranging from 0.2 to 1.0 lm, which provided passages for the reactants to access the active sites. The KS-1200 kalsilite catalyst was tested for the transesterification of soybean oil to biodiesel over the range 120–180 °C. The weight ratio of soybean oil:methanol:catalyst powder was 100:50:5. The stirring rate was 1100 rpm. As shown in Fig. 3, the reaction temperature had a significant effect on the biodiesel yield. The biodiesel yield increased with an increase in reaction temperature. The biodiesel yield was 19.8% at 120 °C and increased to 51.6% at 160 °C. The kinematic viscosity of the biodiesel obtained

Fig. 2. SEM image of kalsilite KS-1200 powder catalyst.

G. Wen et al. / Fuel 89 (2010) 2163–2165

Biodiesel yield

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Reaction temperature / oC Fig. 3. Effects of reaction temperature and time on the transesterification reaction over kalsilite KS-1200.

biodiese yield o

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4. Conclusion

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Kalsilite synthesized by the method used in this study has suitable physical properties as a heterogeneous catalyst. With the addition of LiNO3, this catalyst exhibited high catalytic performance for the transesterification reaction of soybean oil with methanol to produce biodiesel, which makes this catalyst a candidate for commercial application, especially in a fixed-bed reactor. References

140 C, 2 min 20

Biodiesel yield /%

in Fig. 4. The biodiesel yield at 120 °C was only 19.8% over KS-1200. However, under the same reaction conditions, a biodiesel of 100% was achieved over KSLI. The high catalytic performance of KSLI at mild temperature of 120 °C makes the continuous flow fixed-bed application feasible. LiNO3 was not active in the transesterification reaction, and it cannot be responsible for the improved activity [12,13]. The significantly higher catalytic activity of the KSLI may result from a synergistic interaction between K and Li to produce more KAlO2 superbasic sites, which were considered to be the active species of this catalyst [15].

4

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KSLI

Catalyst Fig. 4. Catalytic activity of Li modified kalsilite.

at 120 °C was 19.39 and 7.44 cSt at 160 °C. However, the effect became less pronounced at high temperatures (between 160 and 180 °C). The effect of the reaction time was investigated at 140 °C. As shown in Fig. 3, increasing the reaction time from 2 to 5 min increased the biodiesel yield from 40% to 51% and reduced the biodiesel viscosity from 9.71 to 7.53 cSt. The catalytic activity of KS-1200 kalsilite in the temperature range of 120–180 °C suggests that this catalyst cannot be used directly for industrial application. To improve activity of kalsilite, lithium nitrate was introduced into the KS-1200 kalsilite by the impregnation method. The introduction of lithium nitrate into the kalsilite significantly increased the catalytic activity, as shown

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