Coprocessing of Petroleum Vacuum Residue with Plastics, Coal, and

Energy & Fuels 2007, 21, 891-897

891

Coprocessing of Petroleum Vacuum Residue with Plastics, Coal, and Biomass and Its Synergistic Effects M. Ahmaruzzaman* and D. K. Sharma Center for Energy Studies, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016, India ReceiVed March 7, 2006. ReVised Manuscript ReceiVed NoVember 29, 2006

Thermal decomposition of petroleum vacuum residue (XVR), polypropylene (PP), Bakelite (BL), Samla coal (SC), bagasse (BG), Calotropis procera (CL, a petrocrop), and their mixtures with petroleum residue was studied in a batch reactor under isothermal conditions at atmospheric conditions. The product distribution patterns have been determined. Kinetics of their thermal decomposition were also studied in order to compare the kinetics of cracking of individual materials with that of the mixture. Activation energy as well as rate constants have been calculated for the materials as well as their mixtures. Cocracking of a mixture of XVR, PP, and CL was found to show synergism of activation energy. The detailed results obtained are reported.

Introduction The processing of petroleum vacuum residue has gained interest because of the increasing demand of light oil fractions and depleting reserves of sweet crude oils. It has been recognized that heavy crude oil will be available in much larger quantities as the supplies of light crude oil are gradually dwindling. The heavier crudes yield more high-boiling residues, such as vacuum residue, which may have to be refined to yield lighter and valueadded products. Processing of heavier feedstocks needs the development of down-processing technologies such as hydrocracking with attendant risk of catalytic poisoning and requirement for high hydrogen pressure. However, residue upgradation technologies are constantly being improved, with the objective of improving the process, lowering the capital costs, and addressing safety and environmental concerns. There is a need to develop the technologies for the coprocessing of vacuum residues with other organic polymers such as coal, plastics, and petrocrops, which may replace the role of hydrogen. Coprocessing of vacuum residue with coal may synergize the production of lighter and value-added products. Some of the H-transfer and alkyl radical transfer reactions may proceed, leading to the production of lighter and value-added products. Thermal cracking of petroleum residue has been reported to be a first-order reaction. However, Martinez et al.1 reported secondorder rate kinetics in their studies on thermal cracking of asphaltenes. Di Carlo and Janis2 carried out a detailed study on the effect of composition of feedstocks on cracking behavior and product selectivities. They also reported the kinetic parameters of the cracking reactions for the studied feedstocks. Omole et al.3 reported thermal visbreaking of heavy oil from Nigerian tar sand. Al-Soufi et al.4 reported the kinetics of thermal conversion (visbreaking) of heavy Iraqi residue. Suzuki et al.5 * To whom correspondence should be addressed. E-mail: md_a2002@ rediffmail.com. (1) Martinez, M. T.; Benito, A. M.; Callejas, M. A. Fuel 1997, 76, 871. (2) Di Carlo, S.; Janis, B. Chem. Eng. Sci. 1992, 47, 2695. (3) Omole, O.; Olieh, M. N.; Osinowo, T. Fuel 1999, 78, 1489. (4) Al-Soufi, H. H.; Savaya, Z. F.; Mohammed, H. K.; Al-Azawi, I. A. Fuel 1988, 67,1714. (5) Suzuki, T.; Itoh, M.; Mishima, M.; Takegami, Y.; Watanabe, Y. Ind. Eng. Chem. Process Des. DeV. 1982, 21, 149.

carried out two-stage pyrolysis of Taching vacuum residue and Arabian light atmospheric residue for the production of olefins in a flow-type reactor. Del Bianco et al.6 studied the kinetics of thermal cracking of petroleum vacuum residues and reported them to be first order with respect to distillate production. Kinetic behavior for the nonisothermal coking of four vacuum residua was reported by Yang et al.7 Suelves et al.8 have studied the copyrolysis of coal and petroleum residue. They reported that there exists significant synergistic interaction on the yield of main pyrolysis products when coal and petroleum residue are copyrolyzed. Audeh and Yan9 have reported the coprocessing of petroleum residue with coal. Qingfang et al.10 studied the composition changes in the cocarbonization of FCC slurry and vacuum residue. Moliner et al.11 carried out the copyrolysis of coal and petroleum residue mixtures. Lazaro et al.12 reported the pyrolysis of mineral waste oil and coal slurry in a continuous fluidizedbed reactor. They found that copyrolysis increases the quantity and quality (organic products and metal contents) of gases and liquids obtained as compared to the products obtained in coal pyrolysis without the mineral waste oil addition. Coprocessing of vacuum residue with plastics may synergize the cracking process to produce stabilized lighter products as a result of several electrophilic reactions. H-transfer and alkyl transfer reactions may also be involved in the coprocessing under ambient pressure conditions. This would again avoid highpressure hydrocracking reactions being involved and may also reduce the sulfur proportionately. Kastner and Kaminsky13 studied the thermal cracking of polyethylene in a fixed-bed reactor over the temperature range 500-600 °C and found that (6) Del Bianco, A.; Panariti, N.; Prandini, B.; Beltrame, P. L.; Caruiti, P. Fuel 1993, 72, 75. (7) Yang, J.; Chen, J.; Sun, Z.; Fau, Y. Fuel Sci. Technol. Int. 1993, 11, 909. (8) Suelves, I.; Moliner, R.; Lazaro, M. J. J. Anal. Appl. Pyrolysis 2000, 55, 29. (9) Audeh, C. A.; Yan, T. Y. Ind. Eng. Chem. Res. 1987, 26, 2419. (10) Qingfang, Z.; Yansheng, G.; Zhigang, Y.; Mingbo, W.; Yuzhen, M. Prepr.sAm. Chem. Soc., DiV. Pet. Chem. 2003, 48, 66. (11) Moliner, R.; Suelves, I.; Lazaro, M. J. Energy Fuels 1998, 12, 963. (12) Lazaro, M. J.; Moliner, R.; Suelves, I.; Domeno, C.; Nerin, C. J. Anal. Appl. Pyrolysis 2002, 65, 239. (13) Kastner, H.; Kaminsky, W. Hydrocarbon Process. 1995, 74, 109.

10.1021/ef060102w CCC: $37.00 © 2007 American Chemical Society Published on Web 01/30/2007

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Ahmaruzzaman and Sharma

Figure 1. Experimental setup used for cracking. Table 1. Characteristics of Petroleum Vacuum Residue (XVR) density @ 20 °C (g/cm3) Conradson carbon residue (CCR) (wt %) viscosity @ 135 °C (cSt) pour point (°C) saturates (wt %) aromatics (wt %) asphaltenes (wt %) total sulfur (wt %) Ni (ppm) V (ppm)

1.022 21.52 202.11 57 77 23 7.13 4.23 51 94

thermal cracking of polyolefin-rich streams yielded valuable refinery and petrochemical feedstocks. Walendziewski14 recently carried out thermal and catalytic cracking of the most popular polyolefins (polyethylene, polystyrene, and polypropylene) in an autoclave and pressure-less reactor. The influence of cracking parameters, i.e., reaction temperature, presence and amounts of cracking catalyst, and composition of the polymer feed, on products yields and composition of liquid and gas fractions is discussed. Williams and Williams15 studied the pyrolysis of a mixed plastic mixture in a fluidized-bed reactor. The influence of temperature on product yield and composition was studied. The influence of temperature, residence time, concentration level of reactants and products, and composition of the polymer mixture on the product spectra obtained from pyrolysis of polyethylene (PE) and polypropylene (PP) was determined by Westerhout et al.16 Arandes et al.17 have reported that plastics wastes may be transformed into fuels by cracking. Horvat and Ng18 studied the polyethylene thermolysis as a first step to synthetic diesel fuel. Pyrolysis characteristics and kinetics of (14) Walendziewski, J. Fuel 2002, 81, 473. (15) Williams, E. A.; Williams, P. T. J. Anal. Appl. Pyrolysis 1997, 40, 347. (16) Westerhout, R. W. J.; Kuipers, J. A. M.; van Swaaij, W. P. M. Ind. Eng. Chem. Res. 1998, 37, 841. (17) Arandes, J. M.; Abajo, I.; Lopez-Valerio, D.; Fernandez, I.; Azkoiti, M. J.; Olazar, M.; Bilbao, J. Ind. Eng. Chem. Res. 1997, 36, 4523. (18) Horvat, N.; Ng, F. T. T. Fuel 1999, 78, 459.

municipal solid wastes were studied by Sorum et al.19 Yoon et al.20 studied the optimization of pyrolytic coprocessing of waste plastics and waste motor oil into fuel oil. Ultrapyrolytic upgrading of plastics and plastics/heavy oil mixtures to valuable light products was reported by Lovett et al.21 Uhmann et al.22 reported on the fundamental investigation of cocracking of crude oil residue and plastics in a modified visbreaking process. It was shown that synergistic effects offered the possibility of reaching a more intensive cracking of residues, without coke formation. They explained that the so-called depolymerization initiation in the mixture was the main reason for the observed synergistic effects. It was also reported23 that coprocessing was marked by reactions between asphaltenes and free radicals, resulting from the depolymerization of plastics. Gersten et al.24 reported the kinetic study of the thermal decomposition of polypropylene, oil shale, and their mixture. Collot et al.25 have studied the tar and total volatile yields from copyrolysis of coal and biomass in bench-scale fixed-bed and fluidized-bed reactors. GarciaPerez et al.26 reported the kinetics of copyrolysis of sugar cane bagasse with petroleum residue. Calotropis procera (CL) is a laticiferous plant that has been recommended as a potential petrocrop. Coprocessing of vacuum residue with petrocrops would also help in the production of lighter and value-added products under ambient pressure condi(19) Sorum, L.; Gronli, M. G.; Hustad, J. E. Fuel 2001, 80, 1217. (20) Yoon, W. L.; Park, J. S.; Jung, H.; Lee, H. T.; Lee, D. K. Fuel 1999, 78, 809. (21) Lovett, S.; Berruti, F.; Behie, L. A. Ind. Eng. Chem. Res. 1997, 36, 4436. (22) Uhmann, R.; Ko¨psel, R.; Simanjenkov, V.; Kuchling, T. Erdoel, Erdgas, Kohle 2000, 116, 611. (23) Ko¨psel, R.; Simanjenkov, V.; Kuchling, T.; Gartner, P.; Claussen, M. DGMK Tagungsber. 2000, 1, 99. (24) Gersten, J.; Fainberg, V.; Hetsconi, G.; Shidler, Y. Fuel 2000, 79, 1679. (25) Collot, A. G.; Zhuo, Y.; Dingwell, D. R.; Kandiyot, R. Fuel 1999, 78, 667. (26) Garcia-Perez, M.; Chaala, A.; Yang, J.; Roy, C. Fuel 2001, 80, 1245.

Coprocessing of Petroleum Vacuum Residue

Energy & Fuels, Vol. 21, No. 2, 2007 893

Table 2. Analysis of Polypropylene, Bakelite, Samla Coal, Bagasse, And Calotropis Procera substance

moisture (%)

volatile matter (%)

fixed carbon (%)

ash (%)

Ca (%)

Ha (%)

Na (%)

Ob (%)

polypropylene (MFI ) (2 g)/(10 min)) Bakelite Samla coal bagasse Calotropis procera

0 6.2 4. 5 13.1 12.8

100 53.4 32.2 66.9 65.7

0 25.5 46.8 18.7 6.1

0 14.8 16.5 1.4 15.4

86.28 47.51 72.39 47.54 41.74

13.24 5.15 4.88 6.19 5.97

0.48 2.74 2.4 1.39 2.24

44.6 19.77 44.88 50.05

a

Dry, ash-free basis. b By difference.

tions, i.e., without resorting to high-pressure hydrocracking reactions, and these may also proportionately reduce the sulfur contents. However, there is a need to study the coprocessing of vacuum residue with coal, plastics, bagasse, and petrocrops. Kinetic studies of the coprocessing of these materials may help in understanding the phenomenon. Presently, it was aimed to study the coprocessing of mixed vacuum residue with plastics, coal, or petrocrop. Isothermal kinetic studies were performed to understand the cracking reactions during coprocessing using a reactor in inert (nitrogen) atmosphere under ambient-pressure conditions. To the best of our knowledge, this kind of detailed study on the coprocessing of four materials together is not available in the literature. Experimental Section Petroleum vacuum residue, polypropylene, Bakelite (BL), coal, sugar cane bagasse (BG), and Calotropis procera (a petrocrop) were used for cracking as well as cocracking studies. Petroleum vacuum residue was used as a semisolid, whereas polypropylene was used in granulated form. Bakelite was used as a fine powder. Samla coal (SC) was ground and sieved to -60 to +120 BSS (British standard sieve) (120-250 micron) mesh size and dried in an oven at 105 °C for 24 h. After drying, the coal was stored in a desiccator. Calotropis procera was crushed and sieved to -60 to +120 BSS mesh size and dried in an oven at 105 °C for 24 h and stored in a desiccator. Fabrication of Small Batch Reactor. The experimental setup is shown in Figure 1. A stainless steel reactor was fabricated. The material of the construction of the steel reactor was selected as SS304. The length and diameter of the reactor were 10 and 2.5 cm, respectively. The lower part (A) of the reactor was cylindrical in nature. A valve (B) was fitted on the upper side of the reactor for inserting the crucible-type container inside the reactor. Both the upper and lower parts were attached through a flange (C). One inlet pipe (D) for nitrogen gas and an outlet pipe (E) were provided through which cracked vapor was passed and collected in a small container (F). The container was attached with small pipe (G) through which gas was collected in a cylindrical apparatus (H) by the displacement with water. A thermocouple was inserted inside the reactor for the measurement of temperature. The reactor was heated by nichrome wire attached with a mica sheet so that no heat is lost outside the reactor Procedure. Petroleum vacuum residue was obtained from R&D Centre Indian Oil Corporation Ltd, Faridabad. The crude from which it was obtained was a mixed crude. The petroleum vacuum residue that was used in the isothermal cracking experiments was designated as XVR. The cracking experiments were conducted in the batch mode using the stainless steel microreactor under ambient-pressure conditions. A thermocouple was used for the temperature measurement during the experimental run in the microreactor. In a typical experiment, the reactor was flushed with nitrogen and heated to the desired temperature electrically with the help

of nichrome wire. The feedstocks (XVR as well as PP, SC, and CL, along with their binary, ternary, and quarternary mixtures) were taken in a small crucible-type container and introduced into the reactor as soon as the reactor reached the desired temperature; it was 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 residue, left inside the reactor, was treated with tetrahydrofuran (THF) and then filtered through a Whatman 42 filter paper to separate THF-soluble material from coke/char. The liquid product was collected in a small vessel maintained at room temperature. The volume of gas produced was measured through displacement of water, as shown in Figure 1. In order to define a kinetic scheme and to calculate the kinetic parameters of the thermal cracking, the feedstocks were thermally cracked at 380, 400, 420, 440, and 460 °C for reaction times up to 2-3 h under ambient-pressure conditions. The loss in weight of the sample was recorded at different time intervals. Some of the cracking experiments have been repeated, and the reproducibility was found to be (3%. Results and Discussion Effect of Severity on Conversion and Product Yields. Tables 1 and 2 show the analysis of XVR, PP, BL, SC, BG, and CL. The results of the cracking experiments of petroleum vacuum residue (XVR) carried out at various reaction severities by changing residence time and temperature are shown in Table 3. The yields of three pseudocomponents, coke, distillate, and gas, were determined during the cocracking reaction. The distillate yield of cracking of XVR was found to increase with an increase in temperature as well as with an increase in residence time. The maximum distillate yield was found to be at 460 °C at a residence time of 30 min, and after that, it remains fairly constant. Figure 2 shows the distillate yield after different times at various temperatures during the thermal cracking of XVR. Figure 3 shows the coke/char yield versus residence time at different temperatures. At 380 °C, the amount of coke formed from XVR increased with an increase in residence time (Table 3). At a residence time of 180 min, the amount of coke/char formed was a maximum (6.40 wt %). It has been found that XVR yielded coke at residence times from 90 to 180 min. It has been found that the coke/char yield was a maximum at a residence time of 180 min at a temperature of 420 °C and that the yield of coke from petroleum residue increased with an increase in residence time from 15 to 180 min. At 440 °C, the amount of coke formed was found to be a maximum at a residence time of 60 min. At 460 °C, coke formation rapidly proceeds to completion (Table 3). The amount of coke formed after 30 min was essentially the same as the amount of coke formed after 15 min, and this represents the completion of coke



Table 3. Products Yields of Petroleum Vacuum Residue Thermal Crackinga time (min)

loss in weight (%)

15 30 45 60 90 120 150 180

13.09 23.32 36.37 41.74 47.14 54.99 62.15 63.55

temperature 380 °C n.d. n.d. n.d. n.d. 0.41 1.49 4.99 6.40

9.16 16.80 27.60 31.28 34.65 42.16 46.24 47.56

25 35 45 60 75 95 100 105

5 10 15 20 30 45 60 120 180

25.63 31.51 35.60 49.92 56.03 67.00 71.38 77.04 77.75

temperature 420 °C n.d. n.d. 0.15 2.46 5.96 10.13 15.12 19.23 19.45

19.30 23.69 26.72 39.85 46.41 58.29 57.60 57.91 n.d.

32 37 41 55 80 120 132 150 n.d.

2 5 7 10 15 30 60 120

42.15 64.14 67.89 69.78 74.78 78.77 79.33 79.65

temperature 460 °C 2.20 6.06 10.10 19.54 20.12 20.30 20.38 n.d.

35.8 53.9 56.7 57.6 59.8 61.5 61.3 n.d.

50 90 110 122 149 171 178 n.d.

a

coke yield (%)

liquid yield (%)

volume of gas (cm3)

n.d. ) no data.

formation. Coke yields were somewhat less at shorter residence times. The amount of coke formed at completion is related to the atomic H/C ratio of the residue. The trend of coke formation shows an induction period, which decreases as temperature increases, and this suggests that coke is probably generated via a reaction intermediate. It has also been found that the coke yield increased with an increase in temperature. It is generally accepted that coke formation is mainly associated with asphaltene cracking. However, at high severity, the coke yields exceed the initial amount of asphaltenes, and therefore, the retropolymerization reaction also involves oil components. The cross-condensation reactions between polyaromatic ring moieties result in the formation of coke/char, where dehydrogenation, dealkylation, and deoxygenation reactions also take place. Figure 4 shows the gas yield at different residence times at different temperatures. The gas production from the cracking of petroleum residue has been found to increase with an increase in temperature as well as with an increase in residence time. The maximum gas production was found at 460 °C with a residence time of 60 min. Formation of gas is due to thermal cracking reactions of liquid or volatile products formed. The liquid yield from the cracking of PP was found to be 86% at 380 °C with a residence time up to 120 min. The maximum liquid yield of 91.5% was obtained at 420 °C with a residence time of 30 min. PP decomposed into liquid and gaseous products without the formation of residue. The same was also reported by Ballice.27 Thermal cracking of PP to liquid products is a known phenomenon. Cocracking of PP and XVR showed that the maximum loss in weight was 88.75% at 380 °C and 91.25% at 460 °C. Loss in weight of the mixture of XVR and PP was found to be higher (27) Ballice, L. Fuel 2002, 81, 1233.

Figure 2. Liquid yield versus time at various temperatures during the thermal cracking of XVR.

Figure 3. Coke yield versus time at various temperatures during the thermal cracking of XVR.

than theoretical average values. However, as the temperature increased, there was a slight increase in loss in weight of the mixture compared to their theoretical values. This suggests that, at lower temperature (380 °C), the cocracking of the mixture of XVR and PP showed synergistic effects. Cracking of PP may generate -CH2• free radicals, which may be involved in transalkylation types of reactions with the cracked products of XVR. The effects of temperature and residence time on the product yields of Calotropis procera (CL) have shown that the maximum loss in weight was 63.7% at 380 °C. However, the liquid yield was 25.7% at this temperature. As the temperature increases, the loss in weight was increased slightly and was found to be 65.7% at 460 °C. However, the volume of gas production was higher at 460 °C. Concerning the variation of experimental yields with temperature, it can be shown that, as the temperature increased, char yield decreased and, simultaneously, the gas yields increased. Thus, gas-forming reactions seem to have replaced the cross-condensation reactions which led to the formation of char/coke. Cocracking of XVR + CL (1:1, wt/wt) showed that the maximum loss in weight was 69.7% at 380 °C. Comparing the theoretical loss in weight of XVR and CL, it was observed that loss in weight increased during the cocracking of XVR + CL at 380 °C. As the temperature increased, the loss in weight was also increased and was found to be 75.3% at 460 °C. The loss in weight of the mixture of XVR + CL at high temperature was found to be almost similar compared to their theoretical average values. This suggests that, at lower temperature (380 °C), the cocracking of XVR + CL showed a synergistic effect. This showed that the thermally degraded products from the cracking of XVR and CL have good reactivity toward the formation of liquid products. However, at higher temperatures, individual condensation reactions seem to be predominating. The loss in weight during the pyrolysis of BG was found to be 72.9% at 380 °C with a residence time of 120 min. It was also found that loss in weight increased when XVR and BG were cocracked together at a temperature of 380 °C. Thus, there


Figure 4. Gas yield versus time at various temperatures during the thermal cracking of XVR.

Figure 5. Plot of F(x) ) -ln{[(1 - x)(1 - n) - 1]/[n -1]} vs time for the cracking of XVR at (a) 380 °C, (b) 400 °C, (c) 420 °C, (d) 440 °C, and (e) 460 °C.

is a synergistic interaction (effect) at low temperature, when XVR and BG were cocracked together. The reason for this could be the predominance of self-condensation, polymerization, and cross-condensation reactions due to high-temperature (and highenergy) conditions. The effect of temperature and time on the products yield obtained from the cocracking of XVR + PP + CL (1:1:1, wt/ wt) showed a total loss in weight of 75.2% at 380 °C. The loss in weight increased from 75.2% to 83.9% as the temperature increased/changed from 380 °C to 460 °C. The liquid yield was also found to increase with an increase in temperature within the temperature range studied. The loss in weight of the mixture of XVR + PP + CL was found to be slightly higher as compared to their theoretical average values, when they were pyrolyzed separately. Cocracking of XVR + PP + SC + CL (1:1:1:1, wt/wt) at temperatures ranging from 380 °C to 460 °C showed that liquid yield increased from 39% to 45.5% as the temperature increased from 380 °C to 460 °C. The char yield showed a minimum at 380 °C. However, the gas yield shows a maximum at 460 °C. There is a slight increase in loss in weight from 61.9% to 66.1% within the temperature range studied. The studies on the characterization of liquid products obtained from the coprocessing of XVR with plastics, biomass, and coal were undertaken. These studies supported the present discussions of the results. Bakelite (BL) is a thermosetting plastic. The pyrolysis of this plastic is very difficult because of hardening when heated. Sato et al.28 reported the effect of solvents on the liquid-phase cracking of thermosetting resin in the presence of tetralin, decalin, etc. solvents. Therefore, attempts have been made to see the effect of XVR addition on the pyrolysis of BL because XVR may substitute H-donor like liquid properties in the (28) Sato, Y.; Kadora, Y.; Kamo, T. Energy Fuels 1999, 13, 364.


Figure 6. Arrhenius plot for the cracking of XVR.

reactions. Cracking of BL showed the conversion of 47% at a temperature of 460 °C. Experiments on cocracking/copyrolysis of XVR + BL (1:1, wt/wt) were carried out at temperatures from 380 to 460 °C with different residence times. It was observed that conversion (loss in weight) increased when XVR and BL were cocracked together at 380 °C. The maximum conversion was found to be 60.8% at 380 °C. As the temperature increased from 380 °C to 460 °C, conversion increased to 65.8% during the cocracking reactions. In order to increase the conversion of cocracking reactions, the ratio of XVR/BL was varied from 1:1 to 3:1. The cocracking reaction was conducted at 460 °C for a 2 h residence time. The conversion was found to be a maximum (80.2%) in the XVR/BL ratio of 3:1. Thus, the optimum ratio for the cocracking of XVR + BL was 3:1. Thus, it was quite evident that coprocessing of vacuum residue aids the cracking of Bakelite and may be acting as a H-donor solvent even during cracking. There may also be the possibilities of transalkylations, phenolation, and oxidative coupling reactions. The chemical affinity of cracking products from asphaltenes and asphaltols for these reactions with phenols or -CH2PhOH type reactive moieties is understably high. Isothermal Kinetic Studies. The intensive kinetics for the decomposition/cracking of a solid material follows the rate expression:

dx ) k(1 - x)n dt which on integration gives

F(x) ) -ln(1 - x) ) kt (n ) 1) (1 - x)1-n - 1 and F(x) ) ) kt (n * 1) n-1 where ln k ) ln A - E/RT (1) where x ) fractional conversion of the materials/fractional loss in weight; n ) order of the reaction; k ) rate constant; E ) activation energy of the reaction; R ) gas constant; T ) temperature; and A ) frequency factor. The loss in weight of individual sample versus time has been used to define a kinetic scheme and to calculate the kinetic parameters of the reactions. The values of rate constants, k, can be obtained by repeated least-square fit of eq 1 to experimental data. The method needs to make a first guess of n (order of reaction) on the left-hand side (LHS) of eq 1. Hence, the LHS can be plotted against time, t, as a linear function, and from the slope of the line, the rate constant, k, can be found. The rate constant, k, was determined at different temperatures as mentioned above. The values of E and A can be obtained by plotting ln k versus 1/T at different temperatures. Activation energy, E, can be found from the slope, and A can be found from the intercept. The maximum loss in weight was found to be 63.6% at 380 °C and 79.65% at 460 °C for the cracking of



Table 4. Activation Energy Obtained from Coprocessing of Petroleum Vacuum Residue with Plastics, Coal, and Biomass rate constants substance

K380°C

K400°C

K420°C

K440°C

K460°C

activation energy (kJ/mol)

reaction order, n

XVR PP BL CL BG XVR + PP XVR + BL XVR + CL XVR + BG XVR + SC XVR + PP + CL XVR + PP + SC + CL

0.02 0.02 0.21 0.20

0.04 0.03

0.05 0.09 0.32 0.27

0.14 0.15

0.27 0.21 0.49 0.40

0.03 0.03 0.06 0.07 0.02 0.04 0.03

0.05

0.09 0.06 0.11 0.19 0.09 0.08 0.09

0.15

0.29 0.16 0.29 0.33 0.20 0.18 0.18

126 120 41 33 36 112 71 69 78 108 66 86

1.3 0.7 1.5 1 1 1 1.2 1.7 1.2 1 1 1

XVR. Figure 5 shows the plot of - ln{[(1 - x)(1-n) - 1]/(n 1)} vs time for different temperatures. It has been found that the loss in weight data was best described by 1.3 as an order for the cracking of XVR. Figure 6 shows the Arrhenius plot for the cracking of XVR, which was used to calculate the activation energy. Thus, by adopting this method of kinetic analysis, the overall cracking of XVR over the temperature range of 380-460 °C was found to follow n ) 1.3 and an activation energy of 126 kJ/mol. The cracking process was found to be mostly kinetically controlled as the activation energy was found to be high. The rate constants and pre-exponential factors have been shown in Table 4. The calculated apparent activation energies for the cracking of petroleum vacuum residue reported in the literature varied over a wide range. Del Bianco et al.6 determined activation energy of thermal cracking of petroleum residue as 198 kJ/mol as a function of distillate production with first-order kinetics. Al-Soufi4 reported an activation energy of 94.8 kJ/mol for the thermal conversion of heavy residue assuming first-order kinetics. Present studies showed the value of activation energy in between the reported values with a more precise order (1.3) of cracking reactions. The value seems to fall within the reported values of activation energy. The loss in weight of PP at different temperature showed that most of the PP cracked to form the lighter products. Cracking of PP has been found to follow an order of n ) 0.7 with an overall activation energy of 120 kJ/mol. Aguado et al.29 also reported the activation energy of pyrolysis of PP as 193 kJ/mol. It has been found that the activation energy is influenced by the method used to calculate the activation energy. It also depends on the experimental equipment and procedures. The cracking of PP is a kinetically controlled process. The overall order of the cracking of a mixture of XVR + PP was found to follow first-order kinetics with an activation energy of 112 kJ/mol, which was lower than the theoretical average of the activation energies of XVR and PP. This showed that free radicals generated from PP cracking are reactive enough, thereby facilitating the cocracking of XVR + PP within the temperature range studied. In the case of thermal decomposition/cracking of BL, the process was found to follow an order of 1.5 with an activation energy of 41 kJ/mol. However, the cracking of the mixture of XVR and BL showed an activation energy of 71 kJ/mol, which was lower than the theoretical average of the activation energies of XVR and BL. This implies that there exists a synergistic interaction, when XVR and BL are cocracked together. This may be due to the fact that BL generates reactive free radicals, which may stabilize the cracking products from XVR cracking. BL also possesses a three-dimensional structure; therefore, (29) Aguado, R.; Olazar, M.; Gaisaˇn, B.; Prieto, R. Bilbao, J. Ind. Eng. Chem. Res. 2002, 41, 4559.

cracking of BL alone is difficult. However, when BL was cocracked with XVR (having a higher H/C ratio than BL), XVR may act as a hydrogen donor solvent or medium, thereby facilitating the cocracking reaction. The values of the rate constants of the cracking of XVR + BL have been shown in Table 4. The reaction order of the mixture has also changed to 1.2 (n ) 1.3 for XVR and n ) 1.5 for BL). It was found that pyrolysis of CL and BG followed firstorder kinetics with activation energies of 33 and 36 kJ/mol, respectively. The cracking of the mixture of XVR + CL followed n ) 1.7 as the order with an activation energy of 69 kJ/mol. Thus, the activation energy of the mixture of XVR + CL was found to be less than their theoretical average values, implying synergistic interaction. It also suggests that the reaction mechanism as well as the rate-controlling step changes when XVR and CL are coprocessed together. It also reflects that a plethora of chemical reactions have taken place between the nascent decomposition products of XVR and CL during the cocracking reactions. The cracking of the mixture of XVR + BG showed an activation energy as 78 kJ/mol, which was different from that of XVR as well as BG. It implied that chemical interaction had taken place between their decomposition products. The order of the reaction changed to 1.2 (n ) 1.3 for XVR and n ) 1 for BG). It was also observed that the cracking of the mixture of XVR and BG was mainly kinetically controlled, because the activation energy was high. In the case of SC pyrolysis, loss in weight data for the first 10 min followed second-order kinetics with an activation energy of 25 kJ/mol. Then it followed n ) 2.5 as the order with an activation energy of 7 kJ/mol. This change in activation energies indicates a two-step process with distinct chemical processes for each step. Neufeld and Berkowitz30 reported the activation energy of coal pyrolysis as low as 12.6 to 20.9 kJ/mol. When XVR and SC were cocracked together, the mixture followed first-order kinetics with an activation energy of 108 kJ/mol. Thus, the cocracking of XVR + SC was found to be chemicalreaction controlled. This showed that the reactivity between cracking products of SC and XVR was low. Similarly, cracking of the ternary mixture of XVR + PP + CL was also carried out in order to compare the kinetic parameters with those obtained from individual cracking experiments. It was found that the cocracking of XVR + PP + CL followed first-order kinetics with an activation energy of 66 kJ/mol, which was less than their theoretical average values. The reduction in activation energy of the mixture showed that synergistic interaction occurred when XVR, PP, and CL were coprocessed together, reflecting that chemistry of reactions leads (30) Neufeld, L. F.; Berkowitz, N. Fuel 1964, 43, 1964.


to liquid, gaseous, and solid products formation involving diverse reactions. Interplay of chemistry of reactions between a very large number of reactive moieties formed by decomposition of these macromolecules is very complex. Cocracking of the quaternary mixture of XVR + PP + SC + CL was found to follow first-order kinetics with an activation energy of 86 kJ/mol. The rate constants of the mixture are given in Table 4. The geometry (design), size of the reactor, mode of operation, sample size, and reaction dynamics, i.e., change of temperature conditions with time, all play a role in controlling and directing the kinetics and chemistry of the reactions. Again, liquid products derived from the quaternary mixture of XVR + PP + SC + CL showed that there was an overall reduction of molecular weight distributions when they were cocracked together.31 It was quite clear from the kinetic studies that the chemical moieties obtained from thermal degradation of vacuum residue, coal, plastics, and biomass react with each other to form stable liquid and gaseous products. The changing orders, activation energies, and rate constants of the reactions as a result of cocracking reveal the prevalence of complex series and parallel reactions between the products from reactive degrading moieties, which undergo reactions, and further reactions. Chemistry and chemical engineering of thermal degradation reactions in hot reactors leads to synergistic interactions to yield mainly liquid products. These findings were supported by the kinetic studies of such cocracking reactions under nonisothermal conditions in thermogravimetric analysis apparatus32 and by the studies of the characterization of products obtained from the coprocessing in the reactor.33 Coprocessing of petroleum vacuum residue with plastics helps in obtaining chemically modified diverse liquid products, which may be used to obtain valueadded specialty chemicals that are different from ones obtainable by cracking of individual polymers. Cracking of plastics may generate umpteen reactive moieties such as •CH3, •CH2, •H, Ar•, ArO•, ArCH2•, etc. The free radicals are electrically neutral. They possess addition properties and are extremely reactive. The high reactivity is due to the tendency of electrons to exist in pairs. Free radicals can abstract a hydrogen atom, dimerize, or react with other radicals to form stable products. Coprocessing of coal and lignocellulosic biomass along with vacuum residue affords a myriad of reactions in the reactor. The mineral matter present in the coal may also act as a catalyst in the cocracking reactions. Thus, the coprocessing may generate different prod(31) Ahmaruzzaman, M. Studies on co-processing of petroleum vacuum residue along with its non-fuel uses and utilization of petroleum coke obtained for the dephenolation of wastewater. Ph.D. Thesis, Indian Institute of Technology Delhi, New Delhi-110016, 2004. (32) Ahmaruzzaman, M.; Sharma, D. K. J. Anal. Appl. Pyrolysis 2005, 73, 263. (33) Ahmaruzzaman, M.; Sharma, D. K. Energy Fuels 2006, 20, 2498.


ucts (mainly liquid) under atmospheric conditions than those obtainable through high-pressure hydrocracking reactions using sophisticated catalysts. Coprocessing may also lead to demetalation, desulfurization, and denitrogenation of vacuum residue. The use of catalyst was also made in the cocracking reactions.31 The reaction chemistry and chemical reaction engineering of present coprocessing reactions cover a wide range of studies starting from the thermogravimetry of degradation of macromolecules to the complex reactions of chemical moieties obtained from the degradation reactions at moderately high temperature (

Coprocessing of Petroleum Vacuum Residue with Plastics, Coal, and

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