Catalytic cracking of jatropha-derived fast pyrolysis oils with VGO and their NMR characterization

Abstract

Lignocellulosic biomass-derived fast pyrolysis oils are potential second-generation bio-fuels towards the reduction of greenhouse gas (GHG) emissions and carbon foot prints. This study pertains to co-process the Jatropha-derived heavy or tar fraction of fast pyrolysis oil (FPO) with vacuum gas oil (VGO) and hydrodeoxygenated fast pyrolysis oil (HDO) with VGO in a standard refinery fluid catalytic cracking (FCC) unit. The crude fast pyrolysis oil from Jatropha curcas is produced at 530 °C and atmospheric pressure using a bubbling fluidized bed pyrolyzer. The heavy fraction of FPO is hydrodeoxygenated over Pd/Al₂O₃ catalyst into HDO in an autoclave reactor at 300 °C and pressure of 80 bar. Further, HDO is co-processed with petroleum-derived VGO in an advanced cracking evaluation (ACE-R) unit to convert it into refinery FCC product slate hydrocarbons at a blending ratio of 5 : 95. FPO and HDO are characterized using ³¹P NMR, whereas FCC distillates, which are obtained on the co-processing of VGO with fast pyrolysis oil and HDO, are characterized using ¹H and ¹³C NMR spectroscopy techniques. The ³¹P NMR analysis of crude FPO and HDO indicated that hydroxyl, carboxylic and methoxy groups are reduced during the hydrodeoxygenation of FPO. The experimental results at the iso-conversion level on the co-processing of HDO with VGO indicated a higher yield of liquefied petroleum gases (LPG), while lower yields of gasoline and LCO have been observed as compared to FPO co-processing with VGO and co-processing of pure VGO. Furthermore, the results of co-processing of FPO with VGO indicated that the yields of gasoline and LCO increased from 29 to 35 wt% and 14.8 to 20.4 wt%, respectively, whereas the yields of dry gas and LPG decreased from 2.1 to 1.4 wt% and 38.8 to 23.7 wt%, respectively, for an increase in the blending ratio from 5% to 20%. Therefore, it can be concluded that the co-processing of HDO with VGO in a FCC unit would be feasible in order to achieve a higher yield of LPG.

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1. Introduction

The worldwide consumption of liquid fuels is bound to increase from 87 to 97 million barrels per day from 2010 to 2020, respectively, and it is projected to increase to 115 million barrels per day in 2040.¹ The proved world oil reserves were estimated to be ∼1638 billion barrels as of January 1, 2013.² The world oil reserves could be depleted soon in the coming decades with the present rate of consumption. Hence, research is focused on second generation bio-fuels (besides other resources) for the production of liquid fuels from lignocellulosic biomass. Therefore, the conventional (thermal) fast pyrolysis route is an effective approach to convert biomass into higher yields (50 to 75 wt%) of liquid fraction (crude fast pyrolysis oil) at atmospheric pressure and moderate temperature of ∼500 °C. The crude fast pyrolysis oil as such cannot be used as a liquid fuel due to its lower heating value (15–20 MJ kg⁻¹) and the presence of oxygenated compounds that self-react during handling at ambient temperatures to form larger molecules.^3,4 The crude fast pyrolysis oil is a complex mixture of water, carboxylic acids, hydroxy-aldehydes, hydroxy-ketones, phenolics, guaiacols, catechols, syringols, vanillins, sugars, and levoglucosan.⁵ Therefore, crude fast pyrolysis oil requires further upgrading in order to convert it into usable liquid hydrocarbons.

Thus, a number of upgrading technologies have been proposed in the last few decades, such as thermal treatment,^6,7 high pressure thermal treatment,^8,9 thermal hydrotreating,¹⁰ catalytic hydrotreating,^11–15 catalytic emulsion,¹⁶ and catalytic cracking.^17–19 Among the aforementioned upgrading techniques, catalytic cracking seems to be a good option for the effective use of trillion dollars refinery infrastructure as well as the integration of the fast pyrolysis process with refinery.²⁰ A critical review has been published by Talmadge et al.²¹ on the outlook of how to modify the overall chemistry of biomass-derived pyrolysis liquids in order to integrate the pyrolysis process with standard petroleum refineries. Chen et al.²² reported that the effective hydrogen index (H/C_eff) should be above the inflection point of 1.2 for energy production in FCC process with VGO as a feedstock; the same is applicable for co-processing of fast pyrolysis oil with VGO or LCO. Therefore, it is necessary to partially deoxygenate the fast pyrolysis oil to reduce the oxygen level in order to improve the H/C_eff of the pyrolysis oil for better processing in FCC units. Huber et al.⁷ proposed that, during the cracking of oxygenated molecules over the FCC catalyst, smaller hydrocarbons and coke can be obtained by dehydration reaction. In addition to dehydration the conventional catalytic cracking reactions such as cracking, hydrogen consuming, hydrogen producing and Diels–Alder (C–C bond formation) reactions also takes place. Fogassy et al.²³ also proposed a simplified reaction mechanism for oxygen removal from biomass-derived molecules.

The conventional FCC technology is aimed to improve the gasoline yield; however, while co-processing the fast pyrolysis oil with VGO, it is extremely essential to look into the product characterization and the causes of coke formation. Samolada et al.¹⁰ co-processed the hydrotreated flash pyrolysis oil (a heavy fraction) with light cycle oil (LCO) for 15 : 85 blending ratio in a modified MAT fixed bed reactor system (MAT, ASTM D3907-80) over FCC (ReUSY2) catalyst. An increase in coke and gasoline production by 32% and 56%, respectively, was reported while co-processing hydrotreated flash pyrolysis oil (a heavy fraction) with LCO as compared to the pure LCO processing. Fogassy et al.²³ reported higher dry gas and coke yields, lower LPG yields, similar yields of gasoline and LCO while co-processing HDO with VGO in 20 : 80 blending ratio as compared to the processing of pure VGO. They carried out the catalytic cracking reaction in a validated micro-activity test reactor (fixed bed quartz reactor) for VGO cracking over equilibrium FCC catalyst. They further extended the co-processing of HDO with VGO over various types of FCC catalysts in terms of structural parameters of zeolites.²⁴ It was mentioned that most of the lignin-derived molecules on the co-processing of HDO are partially cracked into smaller methoxyphenols over FCC, HY and HZSM-5 catalysts, and it was reported that very few oxygenated molecules enter into the pores of the zeolite.

Mercader et al.¹⁵ carried out the co-processing of HDO with long residue in a fluidized bed MAT-5000 reactor over equilibrium FCC catalyst and reported near normal FCC gasoline (44–46 wt%) and LCO (23–25 wt%) products without an excessive increase in undesired coke and dry gases, as compared to the base feed. They further reported that high levels of oxygen can be allowed in upgraded HDO (up to 28 wt%) for co-processing in the FCC unit without deterioration of the yield structure.²⁵ These studies were further extended for the co-processing of catalytic pyrolysis oil (CPO) with VGO and compared with the results of the co-processing of HDO with VGO.²⁶ An increase in alkyl phenols, in addition to an increase in coke, olefins, and aromatics were reported, while co-processing CPO with VGO as compared to the HDO with VGO. In addition, several researchers^{17–19,27,28} studied the effect of fast pyrolysis oil representative model compounds on product yields while co-processing them with VGO/LCO; however, all these studies are limited to product yields.

Furthermore, ³¹P NMR is a powerful analytical technique for the identification and quantification of organic oxy-functional groups using the derivatization method, and it has a unique advantage over ¹H and ¹³C NMR for the measurement of oxy components in biomass. It provides the quantitative information for various types of major hydroxyl groups in a relatively short experimental time with small amounts of sample. Compared to ¹H NMR, the large range of chemical shifts reported for the ³¹P nucleus generates a better separation and resolution of signals. In addition, the 100% natural abundance of ³¹P and its high sensitivity renders ³¹P NMR a rapid analytical tool in comparison with ¹³C NMR. Among trivalent and pentavalent derivatization agents, trivalent phosphorous reagents provide a large difference in chemical shifts, which helps to carry out identification and quantification. Wroblewski et al.²⁹ examined five trivalent reagents to derivatize organic model compounds, including phenols, aliphatic alcohols, and aromatic and aliphatic acids, with 2 chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane (TMDP). This method may have broad applicability in biomass conversion to second generation bio-fuels.³⁰

The present investigation discusses the product distribution patterns of FCC on the co-processing of VGO with FPO at different blending ratios. The product profile at the iso-conversion level catalytic cracking of VGO, VGO with FPO, and VGO with HDO have been compared. Furthermore, ³¹P NMR spectroscopic technique has been employed to characterize FPO and HDO during the pretreatment of feed, while ¹H and ¹³C has been used for the characterization of products.

2. Materials and methods

2.1 Materials

Expelled Jatropha curcas cake (average particle size of ∼1.4 mm) was used as a biomass feedstock for fast pyrolysis experiments. Palladium (99.9%, Sigma-Aldrich Chemicals) and γ-alumina Al₂O₃ (97%, Sigma-Aldrich Chemicals) were chosen as active and support materials for the preparation of the hydrodeoxygenating catalyst. The commercially available VGO was used for the co-processing studies, and its characteristics are given in our previous paper.³⁸ The catalyst used in the advanced cracking evaluation unit was also an industrially available equilibrium fluid catalytic cracking (FCC) catalyst, i.e. E-CAT. The physicochemical characteristics of E-CAT are listed in our previous paper.³⁸ E-CAT contains synthetic faujacite zeolite (USY or REUSY), silica-alumina matrix, clay (e.g. Kaolin clay) with binder and special additives. The H/C_eff of FPO and HDO were found to be greater than the inflection point of 1.2 and are shown in Table 2. Particularly, the feedstock having H/C_eff ≥ 1.2 can be easily processed in the fluid catalytic cracking unit for energy production.²²

2.2 HDO catalyst preparation

Mesoporous alumina was prepared using the method proposed by Ray et al.³¹ Pd was loaded over alumina by the incipient wetness impregnation method. In a typical preparation method, 1.0 g of palladium(II) nitrate dihydrate was dissolved in 30 ml of water and 20 ml of ethanol. Subsequently, 20 g of γ-alumina (Al₂O₃) (surface area = 243 m² g⁻¹) was added. The mixture was stirred constantly at 80 °C for 5 hours to dry the sample. The dried sample was further dried at 120 °C overnight in an oven. Finally, the Pd metal loaded on alumina was calcined at 500 °C in a furnace for 8 h to prepare the Pd/Al₂O₃ catalyst (2% Pd on alumina). The typical pore diameter, of the mesoporous alumina, which is measured using the BET apparatus, was around 5 nm.

2.3 Fast pyrolysis

The continuous electrically heated bubbling fluidized bed fast pyrolyzer with sand as the fluidizing media was used for the fast pyrolysis of biomass at ∼530 °C and atmospheric pressure. The fluidizing gas (nitrogen) was preheated to 400 °C using an electric furnace. The biomass was fed into the reactor by a screw feeder system in continuous mode at a feed rate of 300 g h⁻¹. The char was separated by a cyclone separator next to the reactor, vapors were condensed and separated as crude fast pyrolysis oil in a series of condensers, and the non-condensable gases were vented off to the atmosphere. The schematic diagram of the fast pyrolysis unit is shown in Fig. 1.

Fig. 1 Schematic diagram of bubbling fluidized bed fast pyrolyzer.

2.4 Hydrodeoxygenation

The experiment aimed to produce partially hydrodeoxygenated fast pyrolysis oil, which is suitable for co-processing in a petroleum refinery fluid catalytic cracking unit. A known amount (2 wt%) of palladium on alumina catalyst was used in a 100 ml batch high pressure stirred reactor (USA made autoclave) to hydrogenate the heavy fraction of FPO. Initially, the reactor was purged with hydrogen gas for a period of 5 min, and then it was pressurized up to 80 bar. A constant speed of stirrer was maintained at 700 rpm. The reactor temperature was raised to reaction temperature from ambient temperature with a heating rate of 5 °C min⁻¹. The reaction temperature was maintained for a period of 4 h. The reactor was then cooled down to ambient temperature. The liquid products were collected and analyzed separately using NMR spectroscopy and are listed in Table 5. The water content in the liquid product was measured with a Mitsubishi MCI moisture meter using the Karl Fischer technique.

2.5 Catalytic cracking

Advanced Cracking Evaluation (ACE-R™) unit, M/s. Kayser Technology Texas (USA), was used for the catalytic cracking of the heavy fraction of the fast pyrolysis oil and HDO, which was equipped with an automated fixed-fluidized bed reactor. The schematic diagram of the ACE-R unit is shown in Fig. 2. A constant amount of catalyst (9 g) was loaded for each experiment and a constant C/O ratio of 5 was maintained by keeping a constant time on-stream (t) of 90 s, feed rate of 1.2 g min⁻¹ and weight hourly space velocity (WHSV) of 8 h⁻¹. The reaction was performed at atmospheric pressure and 530 °C. The catalyst was stripped off by nitrogen for a period of multiple of 7 times of the injection time. During the catalytic cracking and stripping steps, the liquid products were collected and maintained at −10 °C in a glass receiver, which was located at the end of the reactor exit. Moreover, the gaseous products were collected in a gas receiver by the water displacement method. After the cracking and stripping steps, the reactor was operated in regeneration mode, in which the coke deposited on the catalyst surface during the cracking reaction was burnt off with air at a temperature of 700 °C. The flue gases generated during the regeneration process were sent to the catalytic converter/furnace packed with cuprous oxide, where carbon monoxide was converted into carbon dioxide at 540 °C. The step of regeneration process/mode was continued till the amount of carbon dioxide formation became nil in the flue gases. The reactor effluent gases were measured on-line, which were used to estimate the amount of carbon deposited on E-CAT during cracking (coke).

Fig. 2 Schematic diagram of advanced cracking evaluation (ACE-R) FCC unit.

2.6 Product analysis

The product gases were analyzed with a Varian CP-3800 gas chromatograph equipped with three detectors, a flame ionization detector (FID) and two thermal conductivity detectors. The coke deposited on the catalyst was burned with air in regeneration mode, and the resulting total carbon dioxide was analyzed using IR spectroscopy. The liquid products were analyzed by a chromatographic simulated procedure described by the ASTM D-2887 method with an Agilent 6890 gas chromatograph, using a HP-1 methyl silicon column and a flame ionization detector. As in petroleum refinery practice, the product distribution was quantified by their boiling point range: dry gas (H₂ and C₁–C₂ hydrocarbons), LPG (C₃–C₄ hydrocarbons), gasoline (IBP – 216 °C), light cycle oil [LCO (216–370 °C)], heavy cycle oil [HCO (>370 °C)] and coke. The conversion was estimated using the following equation:

Conversion, wt% = 100 − (LCO wt% + HCO wt%)

For ³¹P NMR analysis, the solvents used with the bio-oil sample were usually a mixture of anhydrous pyridine and deuterated chloroform (1.6 : 1.0, v/v) containing a relaxation agent (i.e., chromium(III) acetylacetonate) and an internal standard. 20 mg of FPO was dissolved in pyridine CDCl₃ solvent of 0.5 ml. TMDP reagent (0.05–0.10 ml) was added, stirred and transferred into a 5 mm NMR tube for ³¹P NMR recording. Quantitative ³¹P NMR spectra were recorded with a long pulse delay of 10 s using a 90° ³¹P pulse. The number of transients recorded in inverse gated decoupling mode on a Bruker Avance III 500 MHz spectrometer at room temperature was 128. Chemical shifts are usually calibrated relative to the phosphitylation product of TMDP with water (sample moisture), which gives a sharp and stable signal at 132.2 ppm in pyridine-CDCl₃ solvent.

¹H and ¹³C NMR spectra of FCC liquid distillates, produced from the co-processing of FPO or HDO with VGO, were recorded on a Bruker Avance III NMR spectrometer equipped with a 5 mm BBFO probe resonating at the frequency of 500.13 and 125.7 MHz, for ¹H and ¹³C, respectively. The conventional ¹H spectra were recorded using 5% w/v sample solutions in CDCl₃ containing 0.03% TMS (99.8% Merck) with a sweep width of 6 kHz, 16 scans, 13.4 μs π/2 proton pulse and 2 s relaxation delay. The ¹³C NMR spectra of the sample were recorded using 30% (w/v) in CDCl₃ solutions. Quantitative ¹³C spectra were acquired using the nuclear overhauser effect (NOE) suppressed, inverse gated proton decoupled technique (Waltz-16), with a sweep width of 19 kHz. The number of scans collected was 8k, using a 5 s relaxation delay. All the ¹³C spectra were processed with 1.0 Hz line broadening prior to Fourier transform (FT). All the ¹H and ¹³C NMR spectra were referenced to TMS at 0 ppm. Before starting the analysis, the spectra obtained were corrected for phase and baseline, and then each of them was separated into different regions, which correspond to different types of protons and carbons according to their position in the molecule. Later, each spectrum was integrated thrice and averaged within the indicated regions.

3. Results and discussion

This section has been divided into two parts. In the first part, the discussion is restricted to the process, which includes an approach of char removal from the heavy fraction of Jatropha-derived fast pyrolysis oil and hydrodeoxygenation of FPO in order to convert it into HDO over Pd/Al₂O₃ catalyst (i.e. Section 3.1.1). The discussion is further extended to reactions such as the co-processing of FPO with VGO in an ACE-R FCC unit with the blending ratios of 5%, 10%, 15%, 17% and 20%. Furthermore, the product distribution pattern at an iso-conversion level of around 66% is discussed in Section 3.1.2 for the direct processing of VGO, co-processing of VGO with FPO at 17% blending ratio and co-processing of VGO with HDO at a blending ratio of 5%. The second part is highlighted with the discussion on NMR characterization of feed and product (i.e., Section 3.2).

3.1 Process

3.1.1 Pretreatment of fast pyrolysis oil. One of the reasons for the formation of coke on the FCC catalyst while co-processing may be the presence of fine char particles, which are not completely separated from the fast pyrolysis oil. The cyclone separator next to the fluidized bed fast pyrolysis reactor is not extremely effective to separate the fine char particles below 2–3 microns.³³ In addition, an ash content of ∼1.5% of biomass is enough to maximize the catalytic effect³⁴ that leads to the formation of fine char particles, which are difficult to separate with a cyclone separator.³⁵

Therefore, in the first step of the pretreatment of fast pyrolysis oil, a chemical treatment method was applied to free the char particles from the fast pyrolysis oil. Here, the Jatropha-derived fast pyrolysis oil obtained from the bubbling fluidized bed pyrolysis reactor is found to have a large concentration of char particles (nano-to-micro scale). Therefore, the heavy fraction of fast pyrolysis oil (in semi-solid form) is diluted with ethanol, and then larger size particles (>200 nm) were separated by membrane filtration under vacuum. Subsequently, the filtrate containing small particles was centrifuged at 8000 rpm for 20 minutes. As a result, the filtrate component was separated into two phases: an upper liquid phase containing a blend of fast pyrolysis oil and ethanol, and the deposited char particles at the bottom of the centrifuge tubes. The ethanol present in the residual pyrolysis oil was then recovered by vacuum distillation. After the process, the residual pyrolysis oil is thinner as compared to the earlier semi-solid like phase, and is termed as fast pyrolysis oil (FPO). The FPO was used for further hydrodeoxygenation, followed by catalytic cracking.

In the second step of the pretreatment of FPO, a hydrodeoxygenation method was applied to reduce the oxygen content of the FPO. The obtained FPO, containing 32 wt% of oxygen, was subjected to hydrodeoxygenation with the Pd/Al₂O₃ catalyst in a batch stirred reactor at 80 bar pressure. Increase in the reactor pressure from 80 to 105 and 120 bars was observed with increase in temperature from ambient to 250 and 300 °C, respectively. The gas analysis indicated that the bound oxygen was removed in the form of carbon dioxide by decarboxylation reaction, which is higher in yield, i.e. 45 and 51 wt% at 250 and 300 °C, respectively. The respective CHNO elemental analyses of feed Jatropha curcas cake, FPO and HDO are shown in Table 1. From the elemental analysis (Table 1), it was found that the amount of oxygen content is reduced from 32 wt% to 22 and 10 wt% for 250 and 300 °C, respectively. If the oxygen content could not be removed, the deep or high deoxygenation level of >95% is needed to match the specifications of the pyrolysis oil with standard crude oil in terms of carbon–hydrogen ratio, oxygen content and density.¹⁰ The van Krevelen diagram for the dry H/C and O/C ratios of the FPO and HDO is shown in Fig. 3. The O/C atomic ratio of HDO is drastically decreased to 0.257 and 0.099, respectively, as compared to FPO (0.424), whereas a relatively minor change and decline in the H/C ratio at 250 °C and 300 °C, respectively, was observed. A similar trend was observed by Mercader et al.³⁶ From CCR analysis (Table 2), the carbon residue was found to be higher (∼16 wt%) in FPO, whereas it decreased to about 8 wt% on hydrodeoxygenation at 300 °C.

Table 1 Elemental analysis of Jatropha cake, fast pyrolysis oil and HDO

Sample name	C, wt%	H, wt%	N, wt%	O, wt%	S, wt%	H/C	O/C
Jatropha curcas cake	45.50	6.70	2.43	45.33	0.04	1.767	0.747
Fast pyrolysis oil	56.50	7.10	4.308	32.0	0.092	1.507	0.424
HDO at 250 °C	64.98	8.0	4.91	22.0	0.11	1.500	0.257
HDO at 300 °C	76.18	8.8	4.91	10.0	0.11	1.404	0.099

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Fig. 3 Van Krevelen diagram for dry H/C and O/C ratios of the FPO and HDO.

Table 2 Physico-chemical characterization and SIMDIST analysis of feedstock

Feedstock	Blending ratio	Density at 15 °C, g cm^−3	CCR, wt%	H/Ceff		Boiling point range, °C
						Mass recovery, wt%
						IBP	10%	30%	50%	70%	90%	FBP
VGO	100	0.919	3.64	1.725		350	369	400	441	489	550	550
FPO	100	1.18	16.26	—		36	162	259	328	357	445	592
VGO : FPO	95 : 5	0.932	4.27	1.65		36	359	393	435	482	545	592
	90 : 10	0.945	4.90	1.59		36	348	386	430	476	539	592
	85 : 15	0.958	5.53	1.53		36	337	379	424	469	534	592
	80 : 20	0.971	6.16	1.47		36	327	372	418	462	529	592
HDO	100	1.04	8.6	—		36	159	270	344	405	499	597
VGO : HDO	95 : 5	0.925	3.88	1.68		36	358	394	436	485	548	597

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3.1.2 Co-processing of FPO/HDO with VGO. The catalytic cracking studies on the co-processing of FPO with VGO were carried out in an advanced cracking evaluation (ACE-R) FCC unit at the optimum operating conditions. The operating parameters were determined on the basis of results obtained from the catalytic cracking of pure VGO in the FCC unit at different temperatures and C/O ratios, which are mentioned in our previous publication.³² The maximum yield of gasoline was found to be 44 wt% at a C/O ratio of 5 and 530 °C with the FCC conversion of ∼66%. A similar kind of optimized process parameters were used for further co-processing reactions of VGO with FPO/HDO.

Initially, the blending ratio of FPO with VGO was varied at 5%, 10%, 15%, 17%, and 20% in order to see its effect and optimize the same for obtaining a similar FCC conversion. The FCC conversion of different feeds and their product yields of dry gas, LPG, gasoline, LCO, HCO, and coke are shown in Table 3. The mass balance obtained was more than 98%. From Table 3, it can be seen that the conversion decreases from 75% to 64% with an increase in the blending ratio of FPO from 5% to 20%. The decrease in conversion is due to the decrease in the yield of dry gases and LPG from 2.1 to 1.4 and 38 to 23 wt%, respectively, whereas the yields of gasoline, LCO and HCO were increased from 29 to 35 wt%, 14 to 20 wt%, and 8 to 14 wt%, respectively, with an increase in the blending ratio of the FPO with VGO from 5 : 95 to 20 : 80. However, the results of co-processing at a lower blending ratio (5 : 95) indicated a higher conversion (around 9 wt%) as compared to the direct catalytic cracking of pure VGO at a constant C/O ratio and temperature. This was due to a higher yield (38 wt%) of the LPG fraction as compared to 15 wt% in the case of catalytic cracking of pure VGO. The increase in LPG yield was observed at the cost of gasoline yield, which was 29 wt%; however, the gasoline yield obtained from the catalytic cracking of pure VGO was 44 wt%. Further, there was also a decrease in the LCO and HCO yields by 5 and 4 wt%, respectively.

Table 3 Selectivity data for VGO : FPO, VGO : HDO and pure VGO at different blending ratios

Feedstocks	VGO : FPO				VGO : HDO	VGO	VGO : FPO
Blending ratio	95 : 5	90 : 10	85 : 15	80 : 20	95 : 5	100	83 : 17
FCC conversion	75.68	74.69	69.35	64.39	66.96	66.89	66.08
Yield, wt%
Dry gas	2.182	2.05	1.43	1.41	1.507	1.798	1.42
LPG	38.876	35.70	28.69	23.77	28.78	15.5	25.44
Gasoline	29.038	31.14	35.11	35.04	32.50	44.02	35.08
LCO	14.885	15.43	17.99	20.49	18.98	19.84	19.11
HCO	8.054	8.48	10.67	14.08	13.27	12.4	12.31
Coke	5.48	5.21	4.23	4.16	4.17	5.58	4.14

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However, with an increase in the blending ratio from 5 : 95 to 10 : 90, there was a decrease in the LPG yield by ∼3 wt%; increase in the gasoline yield by ∼2 wt%; increase in the LCO yield by ∼1 wt%; and a slight increase in the HCO yield by ∼0.5%. Clearly, these results indicate that the FPO could be co-processed with VGO at lower blending ratios of 5 : 95 and 10 : 90 for LPG production at the cost of gasoline, followed by LCO and HCO range hydrocarbons.

Furthermore, with an increase in the blending ratio from 10 : 90 to 15 : 85, a similar (as 10 : 90 blending studies) trend of LPG (decreased by 7 wt%), gasoline (increased by 4 wt%), LCO (increased by 2.5 wt%), HCO (increased by 2 wt%) yields were observed. Moreover, with an increase in the blending ratio FPO : VGO to 17%, the FCC conversion of ∼66% was observed. At this particular blending ratio, the dry gas, gasoline, and coke yields were lowered by 0.4, 9, and 1.4 wt%, respectively, whereas the yield of LPG was increased by ∼10 wt%, and the yields of LCO and HCO were found to be almost constant.

A similar trend in product yields was observed with an increase in the blending ratio from 17 : 83 to 20 : 80. From a general perspective, C5+ liquid hydrocarbons increase with an increase in H/C_eff, and a similar observation could be made in the present study: there was a decrease in C5+ hydrocarbons with an increase in H/C_eff. From the abovementioned results, it is also believed that in addition to H/C_eff, the type of oxygenated molecules present in FPO also plays a major role in the distribution of the FCC product profile. However, the increase in the yield of gasoline with the increase in the blending ratio of FPO with VGO is observed even with the decrease in H/C_eff. This was due to the presence of lignin monomers in FPO, and the same is discussed with the help of NMR analysis in the following section.

The coke yield for all blending ratios is within limits and is lower as compared to pure VGO processing. The previous studies on the co-processing of aliphatic oxygenates like acetic acid, hydroxyacetone and glycolaldehyde with VGO for similar conditions also indicated the coke yield to be within the limits, except on the co-processing of lignin-derived monomer (guaiacol) with VGO.^32,38 Water formation was also observed on the co-processing of FPO with VGO; however, the yield is not shown.

Furthermore, an attempt has been made to co-process HDO, obtained on the hydrodeoxygenation of FPO at 300 °C and 80 bar pressure with VGO in a blending ratio of 5 : 95 in an ACE-R unit. The conversion was found to be 66.96%, which is approximately equivalent to the conversion obtained on catalytic cracking pure VGO or co-processing of FPO with VGO for similar operating parameters. This shows that the highest conversion is possible with the co-processing of HDO with VGO as compared to pure VGO catalytic cracking and co-processing of FPO with VGO. The increase in conversion is due to increase in the yields of LPG and gasoline. However, the yields of LCO and HCO were observed in similar for all cases. The increase in the effective hydrogen index from 1.65 to 1.68 on the addition of HDO instead of FPO resulted in an increase in the yield of C5+ liquid hydrocarbons.

3.2 NMR characterization

3.2.1 Hydrodeoxygenation of FPO. ³¹P NMR has been employed for characterizing hydroxyls by phosphitylation with a phosphorous reagent, followed by quantitative ³¹P analysis.³⁷ The presence of oxygenates in the fast pyrolysis oil cause problems in analysis due to complex overlapping of signals; moreover, they induced complexity in ¹H NMR analysis, and it took a long time for ¹³C NMR measurement because of the long relaxation time of C–O groups. ³¹P derivatization is a preferred method for the fast analysis of the oxy-component in the pyrolysis oil. Thus, oxygenates like aliphatic and aromatic alcohols, as well as acids were derivatized using TMDP and quantified from ³¹P spectra. The reaction scheme for phosphorous derivatization is shown in Fig. 4. TMDP reacts with hydroxyl groups in the presence of a base such as pyridine to form the phoshitylated product, as well as with the base to capture the liberated HCl and drive the exothermic reaction to complete conversion. All the oxy-components were derivatized and the typical chemical shift assignment with integration regions are tabulated for different hydroxyl groups in Table 4. ³¹P NMR spectra of derivatized FPO and HDO (at 250 and 300 °C) are shown in Fig. 5. The chemical shifts are referenced with respect to the internal standard NHND (152 ppm). Carboxylic acids corresponding to the chemical shift region of 133–136 ppm are found to be absent in FPO, as shown in Fig. 5a. The abovementioned result is also evidenced from ¹³C NMR results, showing the absence of carboxylic carbon peaks. It is clearly observed from the spectra that the aliphatic alcohols, corresponding to the chemical shift regions from 145.07 to 150.02 ppm are present in FPO, whereas they are absent in HDO (300 °C). This indicated the reduction in hydroxyl groups due to process conditions, and the process is efficient for hydrodeoxygenation. FPO contains a major guaiacyl phenolic and p-hydroxy phenyl phenolics. Although from Fig. 5b it can be seen that the signals due to the phenols and syringyl alcohols, corresponding to the region 142–144 ppm, are present in HDO (obtained at 250 °C), Fig. 5c shows that the components are completely removed in HDO (obtained at 300 °C). Moreover, strong signals due to guaiacol, catechol and p-hydroxy phenyl groups are completely removed in HDO (obtained at 300 °C). On the basis of ³¹P NMR analysis, it was found that the hydroxyl and mono lignol groups were eliminated during hydrodeoxygenation. Thus, the HDO obtained at 300 °C can be used along with VGO as a co-processing feedstock for processing in a refinery FCC unit. The HDO obtained at 300 °C was used for further co-processing studies.

Fig. 4 A reaction scheme for the phosphitylation of hydroxyl groups of the lignin structural units with TMDP.

Table 4 Hydroxyl group contents of FPO and HDO determined by quantitative ³¹P NMR after derivatization with 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane (TMDP)

Sr. no.	Functional group	Integration region, ppm		FPO	HDO, 250 °C	HDO, 300 °C
		Ben et al.^39	Present study
1	Aliphatic OH	150.0 to 145.5	150.02 to 145.07	2.37	0.27	ab
2	C5 substituted β-5	144.7 to 142.8	145.07 to 140.42	1.23	0.6	ab
3	Guaiacyl phenolic OH	140.0 to 139.0	140.42 to 138.2	6.2	1.51	ab
4	p-Hydroxy-phenyl OH	138.2 to 137.3	138.2 to 136.96	5.75	1.89	ab

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Fig. 5 Quantitative ³¹P NMR of Jatropha-derived (a) FPO; (b) HDO at 250 °C; and (c) HDO at 300 °C.

3.2.2 Co-processing of FPO/HDO with VGO. The average structural parameters of FCC product liquid distillates were studied using NMR spectroscopy. The chemical shift region of ¹H spectrum was subdivided into aromatic hydrogen (9–6 ppm), aliphatic hydrogen (0–5 ppm), olefinic (5–6 ppm) and oxygenated hydrogen (3.5–5 ppm), as shown in Fig. 6a–c. The aliphatic proton region has been further subdivided into Hα (2–3 ppm), Hβ (1–2 ppm), and Hγ regions (0.5–1 ppm).^2,3 Furthermore, the aromatic region has been divided into mono aromatics (m-a; 6–7.2 ppm), diaromatic (d-a; 7.2–8.00 ppm) and polyaromatic proton regions (p-a; 8–10 ppm). The ¹³C NMR spectrum has been divided into different integration domains as aliphatic (0–50 ppm), oxygenated alcoholic (50–110 ppm), aromatic (110–150 ppm) and carboxylic (150–200 ppm) carbons (Fig. 6d–e). Fig. 7a–e and 8a–e represent the ¹H NMR and ¹³C NMR spectra of the blended VGO. From the normalized integrals of the signals, a series of average structural parameters such as average chain length (n), fraction of carbon aromaticity (f_a), percentage of proton aromatic carbon (Ch), bridgehead aromatic carbon (Cb), substituted aromatic carbon (ARq), branchiness index (BI), fraction of substituted aromatics (f^s_a), percentage of mono-aromatics (m-a), di-aromatics (d-a), and poly-aromatics (p-a) protons have been derived and are listed in Table 5. The results can only be considered approximate, since they present an over-simplified picture of very complex mixtures containing a wide range of components; however, the described method has the advantage that a few spectra can be obtained on the crude material without preliminary treatment. Table 5 shows the average structural parameters of VGO, and blended VGO and their products. The average alkyl chain length of VGO is 18, whereas in the products, the average chain length varies from 3 to 6. The fraction of carbon aromaticity varies from 0.13 in VGO to the range of 0.13–0.14 in FPO blended VGO and to 0.15 in HDO. In products, the aromaticity varies from 0.47 to 0.55. From Table 5, it can be seen that the addition of FPO with VGO results into an increase in f_a. This indicates the incomplete cracking of lignin-derived monomers, which are present in FPO, whereas the co-processing of HDO (obtained at 300 °C) with VGO resulted into a product with a similar f_a of ∼0.47, which indicates that the lignin-derived monomers are cracked with hydrodeoxygenation of FPO. This is also confirmed from the yield of gasoline on the co-processing of HDO with VGO, which is higher while co-processing FPO with VGO. Again, the total CH₃ carbon content remains same, and the amount of long end chain CH₃ is lower in the case of co-processing of FPO (at 5 : 95 ratio) as compared to the co-processing of HDO (at 5 : 95 ratio). The finding is also reflected from the higher value of branchiness index (BI) in oil (at 5 : 95). This indicates that the product of FPO, co-processing with VGO, contains more iso-paraffinic CH₃ substructure, and the product of HDO, co-processing with VGO, contains more paraffinic CH₃ substructure. Furthermore, the fraction of substituted aromatics f^s_a shows the fraction of aromatics substituted per molecule. In the feeds, H/C_eff is found to vary from 1.47 to 1.725. The aromatic protons vary from 15.5 to 21.69, with higher di-aromatic and poly aromatic protons in products for the blending ratios of 5 : 95 and 10 : 90. This indicates that the product of HDO, co-processing with VGO, contains more paraffinic CH₃ substructure, and the product of FPO, co-processing with VGO, contains more iso-paraffinic CH₃ substructure. Furthermore, the normalized average percentage of protonated aromatic carbons varies from 37.2 to 44.2, that of bridgehead aromatic carbons varies from 2.9 to 3.3, and that of substituted aromatics varies from 6.3 to 7.8. The branchiness index shows the percentage of branching within the alkyl side chains. Higher the Branchiness Index, more is the branched side chains to aromatics. Table 5 also shows that the side chains are more branched in the blending ratio of 20 : 80.

Fig. 6 (a) ¹H NMR of HDO at 300 °C; (b) ¹H NMR of HDO at 250 °C; (c) ¹H NMR of FPO; (d) ¹³C NMR of HDO at 300 °C; (e) ¹³C NMR of HDO at 250 °C; (f) ¹³C NMR of FPO.

Fig. 7 ¹H NMR of FCC liquid distillates on the co-processing of FPO with VGO in a blending ratio of (a) 5 : 95; (b) 10 : 90; (c) 15 : 85; (d) 20 : 80 and (e) co-processing of HDO with VGO in a blending ratio of 5 : 95.

Fig. 8 ¹³C NMR of FCC liquid distillates on the co-processing of FPO with VGO in a blending ratio of (a) 5 : 95; (b) 10 : 90; (c) 15 : 85; (d) 20 : 80 and (e) co-processing of HDO with VGO in a blending ratio of 5 : 95.

Table 5 NMR derived average structural parameters of feedstocks and their liquid distillates (denoted with*) at a constant C/O ratio of 5

Feedstock	Blending Ratio	n	fa	Ch	Cb	ARq	BI	f^sa	m-a	d-a	p-a
VGO	100	18	0.13	4.90	1.36	5.70	0.35	0.44	2.33	1.6	0.55
VGO*		6	0.48	37.27	3.19	7.32	—	0.15	9.2	7.63	2.15
FPO : VGO	5 : 95		0.13
FPO : VGO*		3	0.55	43.5	3.3	7.8	0.47	0.14	10.56	8.66	2.47
FPO : VGO	10 : 90		0.13
FPO : VGO*		3	0.54	44.2	3.1	6.4	0.53	0.12	10.00	8.51	2.58
FPO : VGO	15 : 85		0.14
FPO : VGO*		3	0.52	41.7	3.0	6.8	0.47	0.13	10.46	6.84	1.05
FPO : VGO	20 : 80		0.14
FPO : VGO*		3	0.49	39.5	2.9	6.7	0.6	0.14	10.05	5.26	0.19
HDO : VGO	5 : 95		0.15
HDO : VGO*		3	0.47	37.2	3.0	6.3	0.53	0.13	9.67	5.51	0.79

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4. Conclusion

The petroleum-derived pure VGO and mixtures of the heavy fraction of Jatropha curcas cake-derived fast pyrolysis oil and its HDO with VGO were used as the feedstocks for the present co-processing studies. The FPO containing 32 wt% of oxygen seems to be unsuitable for co-processing with petroleum-derived VGO at optimized process conditions of the FCC unit for higher gasoline, as the FPO containing the lignin-derived monomers cannot be cracked with the FCC catalysts. However, the lower blending ratios of 5 : 95 and 10 : 90 of FPO with VGO is extremely suitable for the production of light olefins, mainly LPG, at the loss of gasoline range hydrocarbons, whereas the decrease in dry gas yield and increase in liquid hydrocarbons were observed with an increase in the FPO blending ratio with VGO. The hydrodeoxygenating Pd/Al₂O₃ catalyst seemed to be very effective in order to reduce the oxygen content of FPO from 32 to 10 wt% at the lower operating pressure of 80 bar and 300 °C. The co-processing of HDO with VGO resulted in an increase in the yields of gasoline and LCO as compared to the co-processing of FPO with VGO, at the similar blending ratio of 5 : 95. The FCC distillate on the co-processing of FPO with VGO contains more iso-paraffinic CH₃ substructure components, whereas the liquid on co-processing HDO with VGO contains more paraffinic CH₃ substructure. The coke yield was found to be within the limit, and in fact, lower than the pure VGO processing over the same equilibrium FCC catalyst. Based on the results of the present experimental investigations, HDO may be co-processed instead of FPO with VGO at a lower blending ratio of up to 5 : 95 in the FCC unit without many modifications in the process configuration and catalyst if the demand for LPG is more, as is the case in India.

Abbreviations

LPG	Liquefied petroleum gas
LCO	Light cycle oil
HCO	Heavy cycle oil
FPO	Heavy fraction of Jatropha-derived char free fast pyrolysis oil
H/Ceff	Effective hydrogen index based on elemental analysis
C/O	Catalyst-to-oil ratio
n	Average chain length
fa	Fraction of aromaticity
Ch	Protonated aromatic carbon
Cb	Bridgehead aromatic carbon
ARq	Substituted aromatic carbon
BI	Branchiness Index
f^sa	Fraction of substituted aromatics
m-a	Mono-aromatic protons
d-a	Di-aromatic protons
p-a	Poly-aromatic protons
ab	Absent
H/C	Hydrogen-to-carbon atomic ratio
O/C	Oxygen-to-carbon atomic ratio
E-CAT	Equilibrium FCC catalyst
IBP	Initial boiling point, °C
FBP	Final boiling point, °C
CCR	Conradson carbon residue, wt%

Acknowledgements

The authors would like to acknowledge Mr Shiv Prasad Nautiyal of CSIR-Indian Institute of Petroleum for his unconditional support/participation in the continuous operation of the biomass fast pyrolysis unit. Furthermore, the authors there are thankful to the FCC group of CSIR-IIP for allowing them to carry out the catalytic cracking studies in the ACE-R unit.

References

1. C. John, H. Paul, J. A. Beamon, S. Naolitano, A. M. Schaal, J. T. Turnure and L. Westfall, International Energy Outlook, 2013, Report number: DOE/EIA-0484 2013.
2. Worldwide look at reserves and production, Oil & Gas Journal, 2012, 110, 28–31, http://www.ogj.com, subscription site.
3. D. C. Elliott and E. G. Baker, Upgrading biomass liquefaction products through hydrodeoxygenation, Biotechnol. Bioeng. Symp., 1984, 14, 159–174.
4. D. C. Elliott and G. F. Schiefelbein, Liquid hydrocarbon fuels from biomass, Amer. Chem. Soc., Fuel Chem. Preprts., 1989, 34(4), 1160–1166.
5. A. Demirbas, Biorefineries: For biomass upgrading facilities, Green Energy and Technology, 2010, 75–92.
6. Approach to refining processes, http://petrofed.winwinhosting.net/upload/25-28May10/S_Bose.pdf, accessed on 23rd May 2014.
7. G. W. Huber and A. Corma, Synergies between Bio- and Oil Refineries for the Production of Fuels from Biomass, Angew. Chem., Int. Ed., 2007, 46, 7184–7201.
8. R. H. Venderbosch, A. R. Ardiyanti, J. Wildschut, A. Oasmaa and H. J. Heeres, Stabilization of biomass-derived pyrolysis oils, 2010, http://onlinelibrary.wiley.com/doi/10.1002/jctb.2354/pdf, accessed on 23rd May 2014.
9. F. M. Mercader, M. J. Groeneveld, S. R. A. Kersten, R. H. Venderbosch and J. A. Hogendoorn, Pyrolysis oil upgrading by high pressure thermal treatment, Fuel, 2010, 89, 2829–2837.
10. M. C. Samolada, W. Baldauf and I. A. Vasalos, Production of a bio-gasoline by upgrading biomass flash pyrolysis liquids via hydrogen processing and catalytic cracking, Fuel, 1998, 77, 1667–1675.
11. J. Wildschut, F. H. Mahfud, R. H. Venderbosch and H. J. Heeres, Hydrotreatment of Fast Pyrolysis Oil Using Heterogeneous Noble-Metal Catalysts, Ind. Eng. Chem. Res., 2009, 48, 10324–10334.
12. E. Churin, P. Grange and B. Delmon, Quality Improvement of Pyrolysis Oils, Report number: EUR 12441 EN, Commission of the European Communities, 1989.
13. R. J. French, J. Stunkel and R. M. Baldwin, Mild Hydrotreating of Bio-Oil: Effect of Reaction Severity and Fate of Oxygenated Species, Energy Fuels, 2011, 25, 3266–3274.
14. P. Grange, E. Laurent, R. Maggi, A. Centeno and B. Delmon, Hydrotreatment of pyrolysis oils from biomass: reactivity of the various categories of oxygenated compounds and preliminary techno-economical study, Catal. Today, 1996, 29, 297–301.
15. F. M. Mercader, M. J. Groeneveld, S. R. A. Kersten, N. W. J. Way, C. J. Schaverien and J. A. Hogendoorn, Production of advanced biofuels: Co -processing of upgraded pyrolysis oil in standard refinery units, Appl. Catal., B, 2010, 96, 57–66.
16. P. A. Zapata, J. Faria, M. P. Ruiz and D. E. Resasco, Condensation/Hydrogenation of Biomass-Derived Oxygenates in Water/Oil Emulsions Stabilized by Nanohybrid Catalysts, Top. Catal., 2012, 55, 38–52.
17. I. Graça, F. R. Ribeiro, H. S. Cerqueira, Y. L. Lam and M. B. B. de Almeida, Catalytic cracking of mixtures of model bio-oil compounds and gasoil, Appl. Catal., B, 2009, 90, 556–563.
18. A. Corma, G. W. Huber, L. Sauvanaud and P. O. Connor, Processing biomass-derived oxygenates in the oil refinery: Catalytic cracking (FCC) reaction pathways and role of catalyst, J. Catal., 2007, 247, 307–327.
19. G. Fogassy, N. Thegarid, G. Toussaint, A. C. Van veen, Y. Schuurman and C. Mirodatos, Biomass derived feedstock co-processing with vacuum gas oil for second-generation fuel production in FCC units, Appl. Catal., B, 2010, 96, 476–485.
20. S. B. Jones, J. E. Holladay, C. Valkenburg, D. J. Stevens, C. W. Walton, C. Kinchin, D. C. Elliott, and S. Czernik, Production of Gasoline and Diesel from Biomass via Fast Pyrolysis, Hydrotreating and Hydrocracking: A Design Case, US Department of Energy, February 2009, PNNL Report no. 18284.
21. M. S. Talmadge, R. M. Baldwin, M. J. Biddy, R. L. McCormick, G. T. Beckham, G. A. Ferguson, S. Czernik, K. A. Magrini-Bair, T. D. Foust, P. D. Metelski, C. Hetrick and M. R. Nimlos, A perspective on oxygenated species in the refinery integration of pyrolysis oil, Green Chem., 2014, 16, 407–453.
22. N. Y. Chen, J. T. F. Degnan and L. R. Koenig, Liquid Fuel from Carbohydrates, Chem. Tech., 1986, 16, 506–511.
23. G. Fogassy, N. Thegarid, G. Toussaint, A. C. van Veen, Y. Schuurman and C. Mirodatos, Biomass derived feedstock co-processing with vacuum gas oil for second-generation fuel production in FCC units, Appl. Catal., B, 2010, 96, 476–485.
24. G. Fogassy, N. Thegarid, Y. Schuurman and C. Mirodatos, From biomass to bio-gasoline by FCC co-processing: effect of feed composition and catalyst structure on product quality, Energy Environ. Sci., 2011, 4, 5068–5076.
25. F. M. Mercader, Pyrolysis oil upgrading for co-processing in standard refinery units, Ph.D. thesis, University of Twente, Netherlands, 2010.
26. N. Thegarid, G. Fogassy, Y. Schuurman, C. Mirodatos, S. Stefanidis, E. F. Iliopoulou, K. Kalogiannis and A. A. Lappas, Second-generation biofuels by co-processing catalytic pyrolysis oil in FCC units, Appl. Catal., B, 2013, 145, 161–166.
27. I. Graça, J. M. Lopes, M. F. Ribeiro, F. R. Ribeiro, H. S. Cerqueira and M. B. B. de Almeida, Catalytic cracking in the presence of guaiacol, Appl. Catal., B, 2011, 101, 613–621.
28. A. A. Lappas, S. Bezergianni and I. A. Vasalos, Production of biofuels via co-processing in conventional refining processes, Catal. Today, 2009, 145, 55–62.
29. A. E. Wroblewski, C. Lensink, R. Markuszewski and J. G. Verkade, Phosphorus-31 NMR spectroscopic analysis of coal pyrolysis condensates and extracts for heteroatom functionalities possessing labile hydrogen, Energy Fuels, 1988, 2, 765–774.
30. A. Majhi, Y. K. Sharma, R. Bal, B. Behera and J. Kumar, Upgrading of Bio-oils over PdO/Al₂O₃ Catalyst and Fractionation, Fuel, 2013, 107, 131–137.
31. J. C. Ray, K.-S. You, J.-W. Ahn and W.-S. Ahn, Mesoporous alumina(I): comparison of synthesis schemes using anionic, cationic, and non-ionic surfactants, Microporous Mesoporous Mater., 2007, 100, 183–190.
32. D. V. Naik, V. Kumar, B. Prasad, B. Behera, N. Atheya, K. K. Singh, D. K. Adhikari and M. O. Garg, Catalytic cracking of pyrolysis oil oxygenates (aliphatic and aromatic) with vacuum gas oil and their characterization, Chem. Eng. Res. Des., 2014, 92(8), 1579–1590.
33. M. Ringer, V. Putsche, and J. Scahill, Large-Scale Pyrolysis Oil Production: A Technology Assessment and Economic Analysis. National Renewable Energy Laboratory Technical Report, November 2006, NREL/TP-510–37779.
34. F. A. Agblevor, S. Besler and A. E. Wiselogel, Fast Pyrolysis of Stored Biomass Feedstocks, Energy Fuels, 1995, 4, 635–640.
35. K. Raveendran, A. Ganesh and C. K. Kartic, Influence of mineral matter on biomass pyrolysis characteristics, Fuel, 1995, 12, 1812–1822.
36. F. M. Mercader, M. J. Groeneveld, S. R. A. Kersten, C. Geantet, G. Toussaint, N. W. J. Way, C. J. Schaverien and K. J. A. Hogendoorn, Hydrodeoxygenation of pyrolysis oil fractions: process understanding and quality assessment through co-processing in refinery units, Energy Environ. Sci., 2011, 4, 985–997.
37. Y. Pu, S. Cao and A. J. Ragauskas, Application of quantitative ³¹P NMR in biomass lignin and biofuel precursors Characterization, Energy Environ. Sci., 2011, 4, 3154–3166.
38. D. V. Naik, V. Kumar, B. Prasad, B. Behera, N. Atheya, D. K. Adhikari, K. D. P. Nigam and M. O. Garg, Catalytic cracking of C2–C3 carbonyls with vacuum gas oil, Ind. Eng. Chem. Res., 2014 DOI:10.1021/ie501331b.
39. H. Ben and A.J. Ragauskas, One step thermal conversion of lignin to the gasoline range liquid products by using zeolites as additives, RSC Advances, 2012, 2, 12892–12898.

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