Characterization of liquid products obtained from co-cracking of petroleum vacuum residue with coal and biomass

J. Anal. Appl. Pyrolysis 81 (2008) 37–44 www.elsevier.com/locate/jaap

Characterization of liquid products obtained from co-cracking of petroleum vacuum residue with coal and biomass M. Ahmaruzzaman *, D.K. Sharma Centre for Energy Studies, Indian Institute of Technology Delhi, New Delhi 110016, India Received 13 April 2007; accepted 3 August 2007 Available online 10 August 2007

Abstract Co-processing of the petroleum vacuum residue (XVR) with coal and biomass (a Calotropis procera) has been performed in batch reactor under isothermal conditions at atmospheric pressure. The liquids obtained by co-processing have been characterized by Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance (NMR), 13C NMR, gel permeation chromatography (GPC) and inductively coupled argon plasma (ICAP) analyses. FT-IR analysis showed that the liquid products derived from co-cracking of XVR + SC contained a few phenols, indicating that the higher hydrogen content of the XVR acted as a hydrogenation medium for the coal product in the co-cracking of the mixture. NMR analysis indicated that aromatic carbon contents decreased (about 10.8%) in the liquid products obtained from the co-cracking of XVR + SC compared to their theoretical average. GPC analysis showed that liquid products derived from co-cracking of XVR + SC are much more similar (having the almost same molecular weight distribution as XVR) to the liquid products from XVR than to the liquid products from coal, reflecting synergy in the co-cracking reaction. However, the liquid products derived from co-cracking of XVR + CL showed the liquids are comparatively more viscous than that of XVR indicating that there is a definite interaction when they are co-cracked together. It is also interesting that the liquid products obtained from co-cracking with coal and biomass contained less than 1 ppm of Ni and V, respectively. The detailed results obtained are being reported. # 2007 Elsevier B.V. All rights reserved. Keywords: Characterization; Co-cracking; Petroleum vacuum residue; Coal; Biomass

1. Introduction The co-processing of petroleum vacuum residue with coal and biomass was studied for exploring the possibility of its utilization to obtain liquid products, which may have an interesting product pattern. To understand the chemical reactions and chemical transformations, which could have taken place, during the co-processing of petroleum residue with coal and biomass, it was necessary to characterize the products obtained from co-processing. In addition, characterization of the products would help in deciding the end use of the product. For example, cokes may have several applications which come out in the end of cracking. These cokes as such or after activation can be used for the removal of toxic substances from wastewater. The removal of toxic substances from wastewater

* Corresponding author. Tel.: +91 3842 242915. E-mail address: [email protected] (M. Ahmaruzzaman). 0165-2370/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jaap.2007.08.001

using residue carbon (carbon slurry, activated carbon, bottom ash, etc.) has been reported in the literature [1–4]. The cracking of petroleum residue (heavy ends of petroleum) mainly yields liquid products of hydrocarbon, although coke and gas are also formed. Analyses of the average structural parameters of these hydrocarbon constitutes of liquid products obtained from the cracking of petroleum residue helps toward understanding their physicochemical characteristics. Of such parameters, the type and distribution of isoparaffins determine the low-temperature and rheological properties of liquid feedstocks. 1H and 13C nuclear magnetic resonance (NMR) techniques have been utilized for the estimation of structural parameters of low- and higher boiling petroleum cuts [5–8]. The liquid derived from the pyrolysis of coal is extremely complex mixture, containing hundreds or thousands of components [9]. The determination of C/H ratios for the aromatic and alkyl carbons of the coal-derived liquids has been reported by Dorn and Wooton [10]. Qualitative

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M. Ahmaruzzaman, D.K. Sharma / J. Anal. Appl. Pyrolysis 81 (2008) 37–44

description of coal liquid fractions has also been reported [11]. 1 H and 13C NMR spectrometric techniques for the determination of a series of parameters describing the average molecular structure of coal-derived liquids have been reported by Cantor [12]. Structural characteristics of branched plus cyclic saturate from petroleum and coal-derived diesel fuels was reported by Cookson et al. [7]. Calkins and Tyler [13] characterized the tars obtained from the flash pyrolysis of coal by using NMR, FT-IR and GC–MS techniques. Gupta et al. [14] estimated the average structural parameters of petroleum crude and coalderived liquid by 13C and 1H NMR spectroscopy. Zhang et al. [15] characterized the liquid products from the pyrolysis of Taiheiyo coal. The cracking/pyrolysis of hydrocarbon materials such as coal and petroleum residue has the advantage over other conversion technologies of promoting transfer of hydrogen from the parent materials to the gas and liquid products, concentrating carbon in the residual char. This is an important advantage in the present energetic scenario in which carbonfree or at least low-carbon fuels need to be promoted to reduce CO2 emissions. Liquids from the pyrolysis of coal contain BTX, PTX and other aromatic compounds that can be upgraded into desired hydroaromatic fuel compounds or used as chemical feedstocks. However, the yields of these products are limited because of the low hydrogen to carbon ratio in coal. For this reason, it is necessary to supply hydrogen from external sources to increase the liquid yields obtained from the coal pyrolysis. One of the most promising ways to provide hydrogen at a reasonable cost is to take it from hydrocarbon wastes that can be co-pyrolysed with coal. On the other hand refineries need new technologies to convert the heavy streams into lighter or more valuable products in order to improve its strategic position. Low-value petroleum feed stocks is usually converted in oil refineries into useful products using the delayed coke process which is a kind of mild pyrolysis. Coal and petroleum residue can be copyrolysed and two benefits could be expected: (1) petroleum residue containing hydrogen rich compounds will act as hydrogen-donors promoting the conversion of coal and improving the quality of the products obtained and (2) the presence of coal could improve some properties of the products obtained from petroleum residue. There are few references in the literature on this subject because most of the work on coutilization of coal and petroleum residues has been reported to be performed under high hydrogen pressure as catalytic coprocessing reactions. Audeh and Yan [16] reported that coal is partially converted to the liquid and gaseous products during co-processing of petroleum residue with coal. They found that high-metalcontaining and low-metal-containing residues are dematalated to the same extent by the coal. Moliner et al. [17] carried out the co-pyrolysis of coal and petroleum residue mixtures. They found that the production of both light olefins and BTX increased with increase in temperature and the synergistic effect was observed in the co-pyrolysis of the mixture. Lazaro et al. [18] reported that the tar obtained from the coal/oil mixture is more similar to the tar from oil than to the tar from

coal, reflecting synergy in the co-pyrolysis reactions. They [19] also found that the contents of metals (Cd, Ni, Pb, Cu, Cr and V) in the liquid products were significantly lower than that in the parent waste oil when coal slurry and mineral waste oil were copyrolysed together. The co-pyrolysis of biomass with petroleum residues could potentially be a good solution to improve the bio-oil quality. The high sulfur content of petroleum residues, the undesirable ash content and low pH of pyrolytic bio-oils might all be mitigated if biomass and petroleum residues are mixed together before being subjected to pyrolysis. On the other hand the presence of petroleum residue in a biomass feedstock could improve the reactor feeding process, leading to an increased reactor throughput capacity. Several studies have been conducted in order to elucidate interactions between biomass components and other feedstocks during their co-pyrolysis reactions. Most of the studies have been carried out between biomass and coal, but very few studies reported on co-pyrolysis of biomass and petroleum residue. Co-pyrolysis can reduce the corrosivity of the bagasse oil in the feeding system which is attributed to the presence of phenolic and acid compounds [20] while the presence of petroleum residue in the bagasse feedstock could contribute to solve operational difficulties caused by the low density and the polydispersity of bagasse. Garcia-Perez et al. [21] also studied the co-pyrolysis of petroleum residue and biomass. They reported that there exist important synergistic effects during the co-pyrolysis in a fixed bed reactor leading to an increase in charcoal yield. Again, the oil obtained from 50% bagasse and 50% petroleum residue was found to be stable. Maximum charcoal and minimum oil yields were obtained with 15 wt% of petroleum residue mixed with bagasse. Thus, to understand the chemical reactions and chemical transformations, which could have taken place, during the cocracking of petroleum vacuum residue (XVR) with coal (SC) and biomass (CL), the characterization of the liquid products obtained has been carried out presently. The main aim of the characterization of the liquid products was to find out the molecular weight distributions as well as the determination of average structural parameters. The techniques used for characterization were mainly FT-IR, 1H NMR, 13C NMR, high-performance liquid chromatography (HPLC), gel permeation chromatography (GPC), and inductively coupled argon plasma (ICAP) analyses. 2. Experimental 2.1. Materials and method The cracking experiments were conducted in batch mode using the stainless steel micro reactor. The details of the experimental setup were reported in the previous paper [22]. A thermocouple was used for the temperature measurement during the experimental run in microreactor. In a typical experiment, the reactor was flushed with nitrogen and heated to the reactor temperature with the help of nichrome wire. The feedstock (XVR as well as their mixture, 1:1 by weight) was

M. Ahmaruzzaman, D.K. Sharma / J. Anal. Appl. Pyrolysis 81 (2008) 37–44

taken in a small crucible-type container. The amount of feedstock taken was 4 g in each experimental run. The feedstock was introduced into the reactor as soon as the reactor reached the desired temperature and kept at this temperature for different time intervals. After reaction, the microreactor was flushed with nitrogen and the crucible was taken out from the reactor and then quickly cooled to room temperature by immersing it in the cold water. The loss in weight of the sample was determined by weighing the crucible before and after each experimental run. The liquid product was collected in a small vessel maintained at room temperature. The volume of gas produced was measured through displacement of water. The reproducibility of the cracking experiments was 2–3%. 2.2. Liquid product analysis 2.2.1. FT-IR The IR spectra were recorded as thin film between KBr windows. A total of forty scans were provided to get better signal to noise ratio. The spectra were recorded at 4 cm 1 resolution on Nicolet Magna 750 FT-IR system equipped with deuterated triglycene sulphate. 2.2.2. NMR 1 H and 13C NMR spectra were recorded on 300 MHz Bruker spectrospin instruments. The liquid samples were diluted with CDCl3 containing 0.1 M chromium acetyl acetonate as the relaxation agent and tetra methyl silane (TMS) as the internal reference. 2.2.3. ICAP The liquid samples were diluted 10 times with aviation turbine fuel and were subjected to ICAP analyses. A multi element standard (S-21) was used for calibration. The ICAP operating parameters were as follows: RF (power) kW, 1.3 (organic); coolant gas, 18 LPM; nebulizing type, V-groove; nebulizing pressure, 36 PSI; auxiliary gas (PSI), 1.2 (organic); sample uptake, 1.0 ml/min and integration time, 5 s. 2.2.4. HPLC HPLC analyses were carried out using n-hexane as the solvent. The column used was amino propyl silica—dual column (25 cm  4.6 mm). The instrument used was Waters 515 with UV and RI detectors. 2.2.5. GPC GPC analyses were carried using tetra hydro furan as the solvent. The GPC parameters were as follows: UV detectors: model M-2487 dual wavelength; RI detectors, model M-2410; ˚ , 60 cm column, flow, 1 ml/min; column, PL GEL 100 A 5 mm; and the standard used was paraffins having a molecular weight of 618, 492, 310 and 170. Samples were introduced through a 2 mL loop injection valve. The use of two detectors, namely UV and IR, enables more information to be obtained from the system. The output from the detectors was recorded on a microcomputer which analyzed the data. The Mw distribution

39

was determined as number and weight average Mw, in addition the polydispersity index of the liquid products was calculated. The number average molecular weight (Mn) is defined as the average molecular weight according to the number of molecules present of each species [23]. The weight average molecular weight (Mw) is the sum of the product of the weight of each species present and its molecular weight divided by the sum of the weights of the species. 3. Results and discussion The analyses of the materials (XVR, PP, SC and CL) used for co-cracking are reported in the Tables 1–3. Table 1 showed that the metal contents are high in the petroleum vacuum residue. Table 2 showed that the ash content is high for Samla coal (SC) and Calotropis procera (CL). Table 3 showed that the sulfur content is high in petroleum vacuum residue. 3.1. GPC analyses Table 4 shows the molecular weight distribution of the liquid products obtained from co-processing of petroleum vacuum residue with coal and biomass at 460 8C. The liquids obtained from cracking of petroleum vacuum residue were analyzed using gel permeation chromatography method to determine the molecular weight distribution of the liquid products. The number average (Mn) and weight average molecular weight (Mw) of the liquid products obtained from cracking of petroleum residue at 460 8C were found to be 105 and 168, respectively. Table 4 also shows the polydispersity, which reflects the deviation of the molecular weight distribution from the Gaussian distribution of an ideal single compound. The liquid products obtained from coal cracking showed a range of molecular weight. A total of 22.6% of the liquid products possess a number average molecular weight of 1228 and a weight average molecular weight 1253. It was found that most of the liquid products (62%) showed a number average and weight average molecular weight of 365 and 450, respectively. The polydispersity index of the liquids was found to be 1.23. The peak average molecular weight (Mp) of the liquid products from co-cracking of XVR + SC was found to be 259. The liquid products obtained from the co-cracking of XVR and SC were found to have a Mn and Mw of 117 and 193, respectively. It was found that the liquid products obtained from co-cracking of XVR + SC were found to be much more similar Table 1 Characteristics of petroleum vacuum residue (XVR) 1 2 3 4 5 6 7 8 9

Density@20 8C (gm/cc) Conradson carbon residue (CCR) (wt%) Viscosity @135 8C (cSt) Pour point (8C) Saturates (wt%) Aromatics (wt%) Asphaltenes (wt%) Ni (ppm) V (ppm)

1.022 21.52 202.11 57 77 23 7.13 51 94

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Table 2 Proximate analysis of Samla coal and Calotropis procera

1 2

Substance

Moisture (%)

Volatile matter (%)

Fixed carbon (%)

Ash (%)

Samla coal Calotropis procera

4.5 12.8

32.2 65.7

46.8 6.1

16.5 15.4

Table 3 Ultimate Analysis of Samla coal and Calotropis procera

1 2 3 a b

Substance

Ca (%)

Ha (%)

Na (%)

Sa (%)

Petroleum vacuum residue Samla coal Calotropis procera

85.34

9.75

0.68

4.23

72.39 41.74

4.88 5.97

1.32 1.94

0.48 0.02

Ob (%) – 20.93 50.35

3.2. FT-IR analyses

Dry, ash-free basis. By difference.

(having almost same molecular weight distribution as XVR) to the liquid products from XVR than to the liquid products from coal, reflecting synergy in the co-cracking reaction. This can be due to the fact free radicals generated from XVR cracking react with the pyrolysis products of SC. Thus, the cocracking of XVR aids the cracking of SC and may be acted as a H-donor solvent during cracking. Lazaro et al. [19] also reported the similar results. They found that the tar obtained from the coal/oil mixture is more similar to the tar from oil than to the tar from coal, reflecting synergy in the co-pyrolysis reactions of coal/oil mixtures. The addition of phenol on the cracking of XVR showed that there is an increase in liquid yield. Phenol may stabilize the radicals produced thermally from the residue, and the primary products distil out of the reacting zone without any secondary decomposition or recombination reaction, so increasing the oil yield. In the absence of phenol, some radicals may be converted to residual products by their recombination reaction and some other radicals may be changed to lighter oil by secondary decomposition reactions, so decreasing the yield of the oil of higher boiling point. However, it should be noted that more than 90% of phenol was recovered from the distilled oil. Phenol which may stabilize the radical by hydrogen transfer should revive by abstracting hydrogen from the co-existing Table 4 Molecular weight distribution of the liquid products obtained by co-processing of petroleum vacuum residue with coal and biomass Sample

Molecular weight (%)

XVR

100

Mn

Mw

Mp

Polydispersity

105

168

209

1.60

SC

22.6 62.0 15.4

1228 365 138

1253 450 144

1379 316 184

1.02 1.23 1.04

CL

63.2 36.8

<100 225

204

117 222

193 170

259

1.65 1.3

XVR + SC XVR + CL

100 100

substances (XVR). This explains the mechanism of XVR as a hydrogen-donor solvent. The liquid products derived from the pyrolysis of C. procera (CL) showed that 63.2% of the liquids possess molecular weight less than 100, indicated the oil to be a low-viscosity-oil. A total of 36.8% of the liquid products have a number average (Mn) and weight average (Mw) molecular weight of 225 and 204, respectively. The polydispersity index was found to be 1.1. However, the liquid products derived from co-cracking of XVR + CL were found to have a Mn and Mw of 222 and 170, respectively. The liquid products derived from co-cracking of XVR + CL showed the liquids were comparatively more viscous than that of XVR indicating that there is a definite interaction when they are co-cracked together.

1.1

FT-IR spectra of the liquid products obtained from cracking of petroleum vacuum residue have been discussed in the previous paper [22]. FT-IR spectra of liquid products derived from coal showed a broad band with maximum near 3300 cm 1 is generally attributed to hydroxyl (–OH) groups. The position of the band also indicates hydrogen bonded OH groups. The peak at 2950 cm 1 indicates the presence of CH3 groups. The peaks at 2925 and 2850 cm 1 indicates the presence of aliphatic CH3, CH2 and CH groups but the dominant contribution probably comes from CH2 groups. It is not possible to decide whether the CH2 groups are present in aliphatic chains, in hydroaromatic structures or in cycloparaffins. The band maximum at 2925 cm 1 was taken as a measurement of the aliphatic hydrogen by Brown [24]. The strong band at 1600 cm 1 is mainly caused by aromatic C C bonding with the intensity accentuated by oxygen containing functional groups, as suggested by Tschamler and Riuter [25]. The fact that absorption at 1500 cm 1 is typical of the C C bonds in benzene rings has been clearly established in lignites and subbituminous coal by Elofson [26]. In this spectrum of the liquids derived from coal, this band is not observed. Elofson also found that the band did not appear in bituminous coal. This may be explained by the facts: (1) increased substitution of the benzene ring is known generally to weaken the bond and (2) as the degree of condensation increases, the band is displaced to smaller wave numbers and finally disappears in the strong absorption at 1450 cm 1. The strong absorption between 1440 and 1450 cm 1 is in part due to CH2 groups, but the contribution may originate from CH3 groups, aromatic C C bonds and strongly hydrogen bonded OH groups. However, in this study the lower intensity of the band compared with the 1600 cm 1 band suggests this may be due to aromatic C C stretching and CH2 (methylene) bridges between aromatic rings. A band at 1264 cm 1 is present because of a weak band of C O stretching and predominantly because of ethers of the types C6H5–O–CH3 or –CH2O–CH3. Evans and Hooper [27] also suggested that this might be due to the presence of etheric oxygen in coal. In an investigation of the products of oxidation, Gaikwad [28] has clearly shown that this band is due to etheric oxygen. The peak at 799 cm 1 indicates the presence of

M. Ahmaruzzaman, D.K. Sharma / J. Anal. Appl. Pyrolysis 81 (2008) 37–44

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from each component. The broad peak at nearly 3437 cm 1 in the FT-IR spectrum of the liquid products derived from XVR + CL co-cracking is an indication of the presence of hydrogen bonded –OH groups. The presence of ketonic functional groups is made evident by the 1721 cm 1 C O stretching band. The paraffinic structures of the oil are confirmed by the presence of peaks between 3000 and 2800 cm 1 and between 1350 and 1500 cm 1. The peak at 1641 cm 1 indicates the presence of olefinic compounds.

substituted benzene ring with two neighboring hydrogen or angular condensed systems. The absorptions peaks at 1091 and 1021 cm 1 may be due to the presence of little amount of ash in the coal-derived liquid products. A perpendicular Si–O vibration causes absorption at 1021 cm 1. The Si–O–Si stretching vibrations also contribute to absorption at 537– 540 and 470 cm 1. Thus, the peak at 470 and 537–540 cm 1 confirms the presence of Si functional groups indicating Si–OH and Si–O–, etc. It was found interestingly that FT-IR spectra of the liquid products derived from the co-cracking of XVR + SC closely resembled to that obtained from the petroleum residue (XVR) alone rather than that from the coal (SC). Like the liquids from XVR, the presence of peaks between 3000 and 2800 cm 1 and the peak in the region from 1350 to 1500 cm 1 due to the C–H bonds indicates the presence of aliphatic groups. The peak at 1605 cm 1 indicates the presence of aromatic ring stretching. In addition, a new peak at 1727 cm 1 shows the presence of carbonyl group. The absorption band at 1076 cm 1 is due to the presence of C–O stretching vibration. The aromatic structures present in the liquid from the mixtures are indicated by the group of peaks between 675 and 900 cm 1. FT-IR spectra also indicated that liquid products from coal contained phenols (broad band at nearly 3300 cm 1) whereas the liquid products from XVR did not contain phenols. The liquid products from co-cracking of XVR + SC contained a few phenols (a very weak broad band between 3200 and 3400 cm 1), indicating that the higher hydrogen content of the XVR acted as a hydrogenation medium for the coal product in the cocracking/pyrolysis of the mixture. FT-IR spectra of the liquid products from cracking of C. procera showed the absence of absorption bands in the 3100–3000 cm 1 (aromatic stretching vibration) and 1600– 1450 cm 1 region (skeletal vibration). This indicates that the liquid products are mainly non-aromatic in nature. The small absorption band at 1100 cm 1, which is due to the presence of C–O stretching vibration, makes it possible to assign the O–H absorption to alcohols. The presence of oxygenated functional groups is made evident by the large intense band of the intermolecular hydrogen bonded O–H stretching vibration at 3437 cm 1. The presence of olefinic compounds is confirmed by the band at 1638 cm 1, arising from the C C stretching vibration mode. The overall spectrum of the liquid products from CL cracking is dominated by the presence of aliphatic compounds. The FT-IR spectrum of the liquid products obtained from cocracking of XVR and CL essentially consists of mixed spectra

3.3. Metal analyses Results from metal analyses of the original petroleum vacuum residue and the liquid products obtained from the co-cracking of XVR with coal and petrocrops are shown in Table 5. The liquid products obtained from cracking of XVR were found to contain less than 1 ppm of Ni and V. It is also interesting that the liquid products obtained from co-processing of XVR with coal and petrocrops contained less than 1 ppm of Ni and V, respectively. The sulfur content in the liquid products from co-cracking of XVR and SC was also found to be 1.0%. However, the liquids obtained from XVR and CL were found to contain 0.5% sulfur. These liquid products can, therefore be utilized in secondary conversion processes (such as fluid catalytic cracking, hydrocracking, etc.) in petroleum refinery operations. The above results also indicate that the metals under study are trapped in the char during cracking as well as co-cracking processes; however, the retention depends on each metal. In particular, Ni, V and Fe show the biggest retention, so that the contents of these metals in the liquid products are significantly lower than in the parent petroleum residue. Miller et al. [29] reported that removal of metallic impurities from the oil during co-processing of coal with heavy oil was probably due to their deposition on the coal residue or pitch. Sanjay et al. [30] showed that in the co-processing of coal with waste materials, the coal could act as a trap for the metals removed from the oil during co-processing. The analyses of the oils derived from co-processing coals of different rank with automobile crankcase oil indicated that these oils had lower concentration of metals than those of untreated automobile crankcase oil [31]. 3.4. 1H and

13

C NMR spectral analyses

Definitions of the 1H and 13C NMR chemical shifts for hydrocarbons are given in Table 6 and the hydrogen distribution of the liquids from cracking of XVR is given in the Table 7. The carbon types in the liquids derived from XVR cracking were distributed between aromatic (100–160 ppm) and aliphatic

Table 5 Metal analyses of the liquid products obtained from co-processing of petroleum vacuum residue with coal and biomass Liquid (from)

Zn (ppm)

Ca (ppm)

Fe (ppm)

Mg (ppm)

Na (ppm)

XVR (original) XVR XVR + SC XVR + CL

12 5 14 5

3 <1 <1 <1

5 <1 <1 <1

5 <1 1

4 <1 2

Al (ppm)

Ni (ppm)

V (ppm)

<1 <1 <1

51 <1 <1 <1

94 <1 <1 <1

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M. Ahmaruzzaman, D.K. Sharma / J. Anal. Appl. Pyrolysis 81 (2008) 37–44

Table 6 Definitions of 1H and

13

C NMR chemical shifts for hydrocarbons

Parameters

Chemical shift (d)

Definition

HA HS Ha Hb+g HCH3 CS CPa CPb CPn CPg CA CAH CAI CACH3

9.0–6.0 4.0–0.5 4.0–2.0 2.0–1.0 1.0–0.5 10.0–50.0 14.1 22.7 29.6–30.1 32 100–150 100–130 129.2–132.5 132.5–137

% % % % % % % % % % % % % %

Aromatic protons Aliphatic protons CH3, CH2 and CH protons a to aromatic ring CH2 and CH protons of alkyl chains b or further to ring and CH3 protons b to the ring CH3 protons of alkyl chains g or further from aromatic ring or CH3 of saturated compounds Saturated aliphatic carbons Carbon of terminal methyl group of alkyl chain a CH3–(CH2)n– (n  4) Carbon of CH2 group b to terminal methyl of alkyl of alkyl chain with n  4 Carbon of g or higher of alkyl chain CH3–CH2–CH2–(CH2)n–CH2–CH2 Carbon of g CH2 in CH3–(CH2)g–CH2–(CH2)n Aromatic carbon Protonated carbon Bridgedhead (internal) aromatic carbon Methyl substituted aromatic carbon

Formulae for NMR parameters of hydrocarbons, C/H: carbon to hydrogen ratio: [CS + CA]/ [2CS + CA], FS: C/H ratio of saturated part of sample, FA: C/H ratio of aromatic part of sample, ACL: average chain length: 2CP/CPa, RA: number of aromatic rings per average molecule = (1 + CAI/2).

(5–60 ppm) structures, but distinct regions can be identified within these bands for specific structures. The classification and results of carbon distributions of carbon types are given in Table 6. The liquids obtained from cracking of XVR showed the presence of olefins, which do not occur in the original petroleum vacuum residue. The liquid products were found to contain 95.4% aliphatic and 4.0% aromatic hydrogens. However, aliphatic hydrogen distributions were mainly Ha (10.1%), HCH3 (22.5%) and Hb+g (62.8%). Because of the possible overlap of the resonance signals of cyclic and acyclic methylene hydrogens, the amount of quantitative information about these protons types, which can be extracted from these spectra, is limited. The detailed analyses of the liquid products derived from XVR cracking have been reported in the previous paper [22]. Table 7 Average structural parameters (derived from 1H and 13C NMR data) of liquid products obtained from co-cracking of vacuum residue with coal and biomass Liquid from

XVR

CL

XVR + CL

SC

XVR + SC

CA CS CPa CPb CPn CPg CP HA Ha Hb+g HCH3 HS H/C CAL CN + CI CAI CAH CAP RA ACL

14.3 85.7 7.4 7.1 29.4 5.7 49.5 4.0 10.1 62.8 22.5 95.4 1.9 2.7 36.2 2.0 7.4 11.6 2.0 13.5

17.2 79.6 1.5 3.2 11.9 2.2 18.8 2.9 10.6 53.3 23.0 86.8 1.8 21.7 60.8 – 11.9 – – 24.3

25.0 75.0 5.1 5.6 5.0 21.6 37.3 3.9 9.0 56.4 26.7 96.1 1.8 6.0 37.7 – 31.2 – – 14.6

45.1 52.9 3.9 3.8 23.2 3.5 34.3 13.8 18.4 52.0 15.1 85.5 1.5 – 18.6 – – – – 17.6

18.9 80.8 6.6 8.0 31.4 7.3 53.3 2.8 11.6 63.6 21.8 97.0 1.8 – 27.5 – – – – 16.1

1

H NMR spectrum of the liquid products derived from cracking/pyrolysis of coal showed the presence of phenolic OH signal at 5.54 ppm. The integral intensity of the OH resonance represents 0.3% of the total protons of the liquid products. However, the liquids contained 85.5% aliphatic hydrogens. Aliphatic hydrogen distributions were Ha (18.4%) and Hb+g (52.0%) and HCH3 (15.1%). The presence of signals in the region between 6 and 8 ppm indicated the presence of aromatic hydrogens and was found to be 13.8% of total hydrogens. 13C NMR spectra of the coal cracking/pyrolysis liquids showed a small signal at 167.2 ppm indicated the presence of carbonyl type compounds. In addition, the signals (peaks) between 150 and 160 ppm showed the presence of phenolic type species. Approximately, 45.1% of the total carbon present in the liquid products arises from the aromatic species. However, protonated aromatic carbons were found to be 31.2%. The aliphatic region showed a number of relatively sharp lines. Prominent among these resolved spectral features are the absorption lines of a (14.1), b (22.7), g (32) and d (29.5) carbons of paraffinic alkyl groups. From an analysis of the integrals of the aliphatic region, it was estimated that approximately 34.3% of the aliphatic carbons are straight-chain alkanes with an average of about 18 carbons in the alkyl group. Naphthenic and iso-paraffinic compounds were found to be 18.6% of the total carbons. The 1H NMR spectrum of the liquids products from the cocracking of XVR and SC clearly demonstrates that the aliphatic hydrogens constituted the principal molecular species present (97.0%). It was interestingly found that the aliphatic hydrogen contents increased (6.6%) when XVR and SC were co-cracked together compared to their theoretical values. Aliphatic hydrogen distributions were mainly Ha (11.6%) and Hb+g (63.6%) and HCH3 (21.8%). The 13C NMR spectrum showed that 18.9% of the total carbons present in the liquids arise from aromatic species. The integrated data showed that 18.9% of the total carbons arise from aromatic species. The aromatic carbon contents had decreased (about 10.8%) in the liquid products obtained from the co-cracking of XVR + SC. From an analysis of the integrals of the aliphatic region, it was estimated that

M. Ahmaruzzaman, D.K. Sharma / J. Anal. Appl. Pyrolysis 81 (2008) 37–44

approximately 53.3% of the aliphatic carbons are straight-chain alkanes with an average of about 16 carbons in the alkyl group. 1 H NMR spectra of the liquid products obtained from cracking/pyrolysis of C. procera showed the presence of resonance signals in the region 0.5–1.1 ppm. The resonance signals in the regions 4–6 ppm are indicative of the presence of hydrogens attached to carbon forming double bonds. Again, hydrogens attached to oxygen (may be phenolic or alcoholic) also showed peaks in the range 4–5.5 ppm. Therefore, the amount of quantitative information of these protons is limited due to the possible overlap of olefinic hydrogens and phenolic/ alcoholic hydrogen. However, integral intensity of the aliphatic region showed that aliphatic hydrogen distributions were mainly Ha (10.6%) and Hb+g (53.3%) and HCH3 (23.0%). The presences of peaks in the region between 6 and 8 ppm indicate the presence of aromatic hydrogens and were found to be 2.9% of total hydrogens. The overall 13C NMR spectrum of the liquids from cracking/ pyrolysis of C. procera was found to be quite complex probably due to the large number of components as well as the complex structure of each individual component present in the liquid products. The presence of peaks in the region 160–180 indicates the presence of carbonyl type compound and constitutes 2.2% of the total carbons. In addition, the peaks between 150 and 155 ppm showed the presence of phenolic type species and represents approximately 0.5% of the total carbons. Approximately, 17.2% of the total carbons present in the liquid products arise from aromatic species. The chemical shift between 65 and 95 ppm indicates the presence of terpenoid alcoholic and acetylinic carbons. The normal chemical shift region for aliphatic and cyclo aliphatic species falls between 10 and 60 ppm downfield from tetra methyl silane as mentioned above. The complexity of the aliphatic region is readily apparent by virtue of the broad envelope of unresolved lines. However, a number of relatively sharp lines are observed in this region. This result suggests the presence of a significant amount of repeating structures. Prominent among these resolved spectral features are the absorption lines of a (14.3 ppm), b (23 ppm), g (32 ppm), d (29 ppm) and e-carbons (29.7 ppm) of paraffinic alkyl groups. While the aliphatic spectral region is quite complex one can estimate a number average chain length of 24 carbons in the alkyl groups, but it is not possible to extract reliable data as to the fraction of saturated carbon lines that is associated with straight-chain alkyl groups. The remainder of the peaks in the 15–20 ppm range may be due to the presence of methyl carbons attached to aromatic rings or branched alkanes and/or naphthenes. The resonance signals in the 22–27 and the 32–40 ppm ranges are indicative of the presence of substantial amounts of branched or cyclic alkanes and alkyl aromatics. The presence of resonance signals in the region between 40 and 60 ppm may be associated with substituted cycloalkanes and bridge carbons of fused ring systems and represents 14.4% of the total carbons. 1 H NMR spectra of the liquid products obtained from the cocracking of XVR and CL indicates that aliphatic hydrogens constitute 96.1% of the total hydrogens. Aliphatic hydrogen distributions were mainly Ha (9.0%) and Hb+g (56.4%) and

43

HCH3 (26.7%). The spectrum also showed the presence of olefinic hydrogens. The 13C NMR spectrum of the liquid products from co-cracking of XVR and CL showed that the carbonyl carbons contents were very low (0.1%). The spectrum showed that aliphatic compounds constitute the principal molecular species present (75.0%). It was found that the aliphatic carbon contents decreased (about 7.7%) when XVR and CL were co-cracked together compared to their theoretical average values. From an analysis of the integrals of the aliphatic region, it was estimated that approximately 37.0% of the aliphatic/saturated carbons are straight-chain alkanes. The average chain length of the aliphatic carbons was found to be 14. The amount of substituted cycloalkane and/or bridgecarbons of fused ring in the liquid products from XVR and CL cracking were found to low (4.5%) compared to the CL-derived liquids. 3.5. HPLC analyses The determination of the aliphatics (mainly saturates) and aromatic groups (mono, di, polyaromatics) in liquid products obtained from cracking of petroleum vacuum residue along with its co-processing, is of great importance for their characterization. Such compositional data are required for the optimization of refining process, product performance evaluation, structure property-relations, combustion, cracking reactions, etc. Presently, no attempts were made to analyze the individual components present in the liquid products. There may, however, be more than thousands of compounds in each of the liquid or oil fractions. However, considering the fact that oil and other fractions are used as mixtures only, attempts were made to analyze the mixture of these compounds present in different fractions. However, in this situation mostly the group functional class analyses of the liquid products were carried out by HPLC. Petroleum vacuum residue (XVR) contained 72.1% saturates, 11.8% monoaroamtics and 14.4% polyaromatics. The liquid products derived from cracking of XVR were found to contain 71.7% saturates and 5.3% polyaromatics. Monoaroamtics content of the liquid products from cracking of XVR were found to be 15.8%. Thus, it was found that monoaromatics content in the liquid products obtained from XVR cracking increased as well as polyaromatics content decreased compared to that of original petroleum vacuum residue. HPLC chromatogram of the liquid products derived from XVR + SC co-cracking showed that saturates content in the liquid products decreased from 71.7 to 55.7% (Table 8), when Table 8 Analyses of the liquid products obtained from co-processing of petroleum vacuum residue by HPLC Sample

Saturates

Monoaromatics

Diaromatics

Polyaromatics

XVR (original) XVR XVR + SC XVR + CL

72.1 71.7 55.7 67.1

11.8 15.8 29.6 16.9

1.7 7.2 4.4 5.8

14.4 5.3 10.3 10.2

44

M. Ahmaruzzaman, D.K. Sharma / J. Anal. Appl. Pyrolysis 81 (2008) 37–44

XVR and SC were co-cracked together. Although, monoaroamtics as well as polyaromatics contents increased from 15.8 to 29.6% and 5.3 to 10.3%, respectively. The liquid products obtained from co-cracking of XVR + CL were found to contain 67.1% saturates 16.9% monoaromatics and 10.2% polyaromatics. However, polyaromatics yield increased from 5.3 to 10.2%. 4. Conclusions GPC analysis showed that the liquid products from cocracking of XVR + SC were found to be much more similar (having almost same molecular weight distribution as XVR) to the XVR-derived liquids. This reflects synergy in the cocracking reaction. Average structural parameters of the liquid products from co-cracking of XVR + SC and XVR + CL were obtained from NMR analyses. From ICAP analyses it was found that the liquid products obtained from co-cracking of XVR + SC and XVR + CL were found to contain less than 1 ppm of Ni and V, although XVR contained 51 and 94 ppm of Ni and V, respectively. HPLC analyses showed that the liquid products from XVR cracking were found to contain 71.7% saturates, whereas the liquid products obtained from XVR + SC cracking were found to contain 55.7% saturates. It was found that the FT-IR spectrum of the liquid products obtained from cracking of XVR + SC closely resembled to the XVR-derived liquids. References [1] V.K. Gupta, S. Sharma, Ind. Eng. Chem. Res. 42 (25) (2003) 6619. [2] V.K. Gupta, I. Ali, J. Colloid Interface Sci. 271 (2004) 321. [3] V.K. Gupta, A. Mittal, V.J. Gajbe, Colloid Interface Sci. 284 (1) (2005) 89.

[4] V.K. Gupta, I. Ali, V.K. Saini, T. Van Gerven, B. Van der Bruggen, C. Vandecasteele, Ind. Eng. Chem. Res. 44 (10) (2005) 3655. [5] M.U. Hasan, A. Bukhari, M.F. Ali, Fuel 64 (1985) 839. [6] S. Gillet, P. Rubini, J.J. Delpuech, J.C. Escalier, P. Valentin, Fuel 60 (1981) 221. [7] D.J. Cookson, C.L. Rolls, B.E. Smith, Fuel 68 (1989) 788. [8] C.E. Snape, Fuel 62 (1983) 621. [9] H.C. Anderson, W.R.K. Wu, Bull. US Bur. Mines (1963) 66. [10] H.C. Dorn, D.L. Wooton, Anal. Chem. 48 (1976) 2146. [11] R.J. Pugmire, D.M. Grant, K.W. Zilm, L.L. Anderson, A.G. Oblad, R.E. Wood, Fuel 56 (1977) 295. [12] D.M. Cantor, Anal. Chem. 50 (1978) 1185. [13] W.H. Calkins, R.J. Tyler, Fuel 63 (1984) 1119. [14] P.L. Gupta, P.V. Dogra, R.K. Kuchhal, P. Kumar, Fuel 65 (1986) 515. [15] A. Zhang, M. Kaiho, H. Yasuda, M. Zabat, O. Yamada, Fuel 81 (2002) 1189. [16] C.A. Audeh, T.Y. Yan, Ind. Eng. Chem. Res. 26 (1987) 2419. [17] R. Moliner, I. Suelves, M.J. Lazaro, Energy Fuels 12 (1998) 963. [18] M.J. Lazaro, R. Moliner, I. Suelves, A.A. Herod, R. Kandiyoti, Fuel 80 (2001) 179. [19] M.J. Lazaro, R. Moliner, I. Suelves, C. Domeno, C. Nerin, J. Anal. Appl. Pyrol. 65 (2002) 239. [20] F. Mobarak, Y. Fahmy, W. Schweers, Wood Sci. Technol. 16 (1982) 59. [21] M. Garcia-Perez, A. Chaala, C. Roy, Fuel 81 (2002) 893. [22] M. Ahmaruzzaman, D.K. Sharma, Energy Fuels 20 (2006) 2498. [23] L.F. Hatch, S. Matar, Hydrocarbon to Petrochemicals, Gulf Publishing Co., London, 1981. [24] J.K. Brown, J. Chem. Soc. (London) (1955) 744. [25] H. Tschamler, F. De Riuter, in: T.G.C. Dryden (Ed.), Chemistry of Coal Utilization, Supplementary Volume, J. Wiley, NY, 1963, Chapter 3. [26] R.M. Elofson, Can. J. Chem. 35 (1957) 926. [27] D.G. Evans, R.J. Hooper, in: M.L. Gorbaty, K. Ouchi (Eds.), Coal Structure, 191, ACS, Washington, DC, 1981. [28] R.P. Gaikwad, Ph.D. Thesis, McGill University Canada, 1985. [29] T.J. Miller, S.V. Panvelker, Y. Wender, Y.T. Shah, G.P. Huffman, Fuel Process Technol. 23 (1989) 23. [30] H.G. Sanjay, A.R. Tarrer, C. Marks, Energy Fuels 8 (1994) 99. [31] D.U. Skala, M.D. Saban, M. Orlovic, V.W. Meyn, D.K. Severin, I.G.H. Rahimian, M.V. Marjanovic, Ind. Eng. Chem. Res. 30 (1991) 2059.