Raw Bio-oil Research Articles

Pyrolysis-catalytic upgrading of bio-oil and pyrolysis-catalytic steam reforming of biogas: a review

Fast-rising population and economic growth are inducing a rapid increase in the energy demand. To date, fossil fuels constitute the primary energy source, but their combustion emits greenhouse gases responsible of global warming. Therefore, developing environment-friendly energy sources is critical. For instance, pyrolysis converts biomass into valuable compounds such as syngas, biochar, and bio-oil, yet produced bio-oil and biogas require further upgrading processes before their use. Current processes include gasification, purification, separation, and catalytic pyrolysis. For syngas synthesis, applying one or a couple of these processes leads to low product yields since they favor the production of bio-oil or biogas. Moreover, tar formation during biomass pyrolysis remains a major technological issue in reactor design. Catalytic reforming is an attractive and efficient method for tar removal via tar oxidation into valuable gases. More importantly, catalytic reforming of pyrolysis volatile products constitutes a promising approach for both tar removal and biogas conversion into syngas. Here, we review the two major catalytic approaches of biomass valorization: catalytic pyrolysis and pyrolysis-catalytic reforming. We demonstrate that the catalytic pyrolysis mainly upgrades bio-oil, while pyrolysis-catalytic efficiently converts biomass into syngas. We analyze the effects of temperature and steam-to-carbon ratio on the products derived from coupling the pyrolysis of agricultural biomass waste to catalytic reforming. Increasing the temperature and steam-to-carbon ratio enhances hydrogen yield. A complete conversion of pyrolysis volatile products into syngas was obtained at 600 °C with steam-to-carbon ratio of 4 for pinewood biomass and nickel catalyst. The use of nickel catalyst supported on lanthana–alumina Ni/La2O3-αAl2O3 for the steam reforming of raw bio-oil produced from pine sawdust pyrolysis enhanced the yields of hydrogen and carbon monoxide, reaching 95% and 93%, respectively, at 700 °C and steam-to-carbon of 15.

Single stage catalytic hydrodeoxygenation of pretreated bio-oil

Raw bio-oil was pretreated and tested for hydrodeoxygenation (HDO) using three types of the commercial catalysts (HT-36, HT2300, and HT951T) to improve physio-chemical properties and enhance hydrocarbon yields. The three catalysts prompted different levels of hydrodeoxygenation, and the organic phase products (OLPs) yields were 25.30, 27.83, and 13.05 wt%, respectively. Moreover, OLPs had lower water content, total acid numbers (TAN), and O content as well as higher heating value (HHV), C, and H contents. For the three catalysts, HT-36 had the best HDO effects, resulting in 34.8% hydrocarbon production with improved HHV, water content value and TAN as well as element contents. The different level of HDO depended on the catalyst components, structure, and morphology. This research is beneficial for the selection and preparation of effective catalysts for bio-oil upgrading.

Feasibility of online pre-reforming step with dolomite for improving Ni spinel catalyst stability in the steam reforming of raw bio-oil

This work studies the effect that a pre-reforming step (PSR) with low-cost catalyst (dolomite) has on the stability of a Ni-spinel catalyst in the steam reforming (SR) of raw bio-oil. PSR temperature varied in the 400–700 °C range, while SR conditions were kept at 700 °C, space-time = 0.14 gcatalysth/goxygenates, and Steam/Carbon = 3. Deactivated catalysts (characterized by XRD, Raman, TPO, and TEM) showed two types of amorphous coke, whose relative amount depends on the feed composition to SR step, which in turn depends on the prior PSR conditions. Phenols and aromatics (main products of the PSR at 700 °C) favor the formation of coke deposited mainly on Ni sites, whereas non-aromatic oxygenates (major products of the PSR at low temperature) are precursors of coke deposited all over the catalyst surface. PSR at 400 °C leads to low amounts of both coke fractions, enhancing the stability of the Ni spinel catalyst.

In-Depth Analysis of Raw Bio-Oil and Its Hydrodeoxygenated Products for a Comprehensive Catalyst Performance Evaluation

Biomass pyrolysis liquids (bio-oils) unavoidably require catalytic hydrodeoxygenation (HDO) for their upgrading and stabilization for commercial usage. The complex composition of bio-oil constrains...

Low-temperature catalytic conversion of alkaline sewage sludge bio-oil to biodiesel: Product characteristics and reaction mechanisms

Sewage sludge is a promising biomass alternative for the production of liquid biofuels. In this study, bio-oil derived from the fast pyrolysis of domestic sewage sludge was upgraded in a micro Robinson–Mahoneyreactor at 4 MPa and 260 °C, and in the presence of hybridized Ni/HZSM-5 catalyst and ethanol. Fourier transform infrared and gas chromatography-mass spectrometry analyses were used to identify the functional groups and chemical components of raw and upgraded sewage sludge bio-oil. Results showed that catalytic upgrading reduced the relative content of acids, aldehydes, phenols, ketones, and nitrogenated compounds in the pyrolytic bio-oil. Thus, the main components of the upgraded bio-oil product included esters (48.59%), alkanes (10.12%), aromatics (9.38%), and alkenes (5.08%). Water and nitriles in the raw pyrolytic bio-oil together with in-situ-produced carbon oxides helped in the esterification of raw bio-oil. Reaction mechanisms such as nitrile hydrolysis, hydrogenation, and esterification were proposed to elucidate the conversion of the non-acidic pyrolytic bio-oil into ester-dominating upgraded bio-oil. Overall, upgrading sewage sludge pyrolytic oil is crucial to produce high-quality diesel-range biofuel.

Combination of acid washing and torrefaction on Co-production of syngas and phenoli-riched bio-oil via low-temperature catalytic pyrolysis

This study was targeted on investigating the facilitations of the combined pretreatment of acid washing and torrefaction on the co-production of syngas and phenols-rich bio-oil. Comparison of raw and modified samples indicated that combined pretreatments not only effectively removed the bulk of alkali and alkaline earth metals but also improved the fuel properties by decomposing unstable hemicellulose. Then, via the catalytic reforming of activated carbon catalyst, CO-rich syngas and phenols-rich bio-oil were obtained simultaneously. The optimal products was acquired from the acid-washed sample which torrefied at 240 °C (labeled as AT240). This syngas contained the maximal CO concentration of 61.86%, and its yield reached 174.34 mL/g. In bio-oil, relative content of phenolic compounds was 91.44%, in which the phenol occupied 71.72%. Quantitative analysis revealed the quantity of phenol in AT240 was 1.74 times of raw bio-oil. Furthermore, mechanism of combined pretreatment on catalytic co-production of syngas and phenols was proposed and discussed in this paper

Implications of feeding or cofeeding bio-oil in the fluid catalytic cracker (FCC) in terms of regeneration kinetics and energy balance

Feeding or cofeeding bio-oil (biomass pyrolysis oil) into the fluid catalytic cracking (FCC) has a direct impact on product distribution, reaction kinetics and deactivation of this key catalytic valorization strategy. In this work, we have analysed the impact in terms of the catalyst regeneration kinetics and energy balance of the unit. These factors are linked to the holistic viability of revamped refineries turned into biorefineries. Deactivated catalysts were obtained in FCC experiments using vacuum gasoil and raw bio-oil. The regeneration kinetics of coke combustion were analysed in a thermobalance, whereas the heats dissipated throughout the combustion (high heating values) were analysed in a calorimeter. Overall, the regenerator does not require major design amendments to treat bio-oil. We found a linear correlation between the higher heating value of the reactants and the coke produced, which enables to predict possible scenarios in the FCC unit. When incorporating higher amounts of bio-oil, the heat balance of the unit changes significantly: the temperature in the regenerator rises up to +36 K, requiring significant energy input for heating the bio-oil but offering the chance to recover more (electrical) energy when the proportion of bio-oil is greater than ca. 50%.

Sustainable design and optimization of co-processing of bio-oil and vacuum gas oil in an existing refinery

In order to lower the production cost of bio-fuels and add renewable carbon into the fossil fuels, the co-cracking of bio-oil and vacuum gas oil (VGO) has been proposed by utilizing the existing infrastructures in a refinery. The co-processing technique demonstrates an excellent economic viability for its further commercialization. However, the environmental impacts of the co-processing system consisting of the co-processing process and the bio-oil production process remain unclear. In this work, a multi-objective model was built to achieve the optimum biomass raw material and bio-oil production technology by simultaneously minimizing the total cost and the environmental impacts of the co-process system. An investigation was also conducted into the effects of the FCC capability and the bio-oil/VGO feed ratio on the economic and environmental objectives. Two cases were proposed to demonstrate the multi-objective model. The results shown that the optimum biomass raw material and bio-oil production technology were heavily dependent on the objectives. The most efficiency way to reduce total cost was to lower the biomass consumption while the most efficiency way to mitigate the environmental impacts was to decrease the VGO consumption, which is because the impact of the non-renewable raw material remains the most significantly contributory to all the environmental impacts.

Bio-oil co-processing can substantially contribute to renewable fuel production potential and meet air quality standards

Co-processing raw bio-oil derived from lignocellulosic biomass in existing petroleum refineries represents a near-term greenhouse gas mitigation strategy by producing partially renewable and infrastructure-compatible hydrocarbon fuel with minimal capital requirements. One deterrent for risk-averse refinery owners is that a modification to their air permit may be required prior to any changes to refinery operations due to potential air emission changes. However, a lack of information on potential air emission changes resulting from bio-oil co-processing yields uncertainty, which could cause delay in obtaining required permit. To address this concern, we perform a quantitative evaluation of air emission changes across a range of bio-oil co-processing fractions in refineries’ fluid catalytic cracking units. We find that 92% of U.S. petroleum refineries could co-process 5% or more (up to 20%, by weight) raw bio-oil without triggering major permitting requirements. We then develop an upper bound estimate of the potential for co-processing bio-oil considering permitting and technical limits; our results suggest that U.S. refineries could co-process 573,000 barrels per day (0.79 cubic meter per second) of raw bio-oil, implying ~1.92 billion gallons gasoline equivalent of renewable fuel per year (0.23 cubic meter per second), equivalent to 1.4% of U.S. gasoline consumption or 18% of ethanol production in 2018. This first-of-its-kind analysis integrates process and environmental engineering with air permitting analysis and demonstrates the importance of coupling regulatory considerations with engineering analysis to guide informed decision-making to minimize investment risks while fully leveraging refinery infrastructure. This novel approach is also applicable to refineries in other jurisdictions.

Deactivation of Ni spinel derived catalyst during the oxidative steam reforming of raw bio-oil

Deactivation of a bulk catalyst derived from NiAl2O4 spinel during the oxidative steam reforming (OSR) of raw bio-oil has been studied. The experiments were performed in a continuous system with two units in series: a thermal treatment unit at 500 °C for the controlled deposition of pyrolytic lignin, and a fluidized bed reactor (700 °C; S/C, 6; O/C, 0.34; space time, 0.15 gcatalysth·gbio-oil−1; time on stream, 1, 2, 4 and 6 h) for the OSR of the remaining oxygenates. The deactivation affects the reforming of bio-oil oxygenates according to their reactivity (from lower to higher), with the reforming of phenols being rapidly affected. The causes of deactivation are: i) coke deposition on the Ni0 sites and on the Al2O3 support (6 wt% of each coke type after 6 h on stream), and; ii) sintering of Ni0 crystals (with an increase in crystal size from 10.8 to 17.7 nm (measured by TEM)). The catalyst deactivation rate increases with time on stream, with the bio-oil oxygenates being the main coke precursors.

Deoxygenation of wheat straw fast pyrolysis vapors over Na-Al2O3 catalyst for production of bio-oil with low acidity

Catalytic upgrading of pyrolysis vapors from wheat straw over Na2CO3 impregnated γ-Al2O3 was studied as a promising route to biofuels. The Na species were homogenously distributed on the support and created a basicity of ~0.02 mmol CO2/g catalyst, at 80% lower catalyst acidity. Analytical pyrolysis using a micro-pyrolyzer showed that Na-Al2O3 particularly decreased the yield of acids via ketonization, which was confirmed by feeding carboxylic acid model compounds. The presence of Na decreased the coke yield and catalyzed the coke combustion, decreasing the combustion temperature by ~100 °C.Subsequently, 100 g Na-Al2O3 catalyst was tested in an ablative bench scale fast pyrolysis unit where ~5 kg of wheat straw was pyrolyzed and the vapors passed the catalytic reactor during six reaction/regeneration cycles. In agreement with the micro-pyrolyzer results, Na-Al2O3 was highly effective in reducing the acidity of the bio-oils. Total acid numbers (TAN) as low as ~1–4 mgKOH/g could be maintained up to high B:C ratios of ~13. For a given TAN, this allowed operating to higher B:C ratios and provided higher oil yields compared to using acidic catalysts such as γ-Al2O3 and HZSM-5 zeolite for vapor treatment. At bio-oil energy recoveries of ~60–70% relative to raw bio-oil, the deoxygenation was comparable to the acidic catalysts. Operation to higher B:C ratios allowed increasing the energy recovery to ~85% relative to the non-treated bio-oil while still obtaining a good deoxygenation performance of ~60%. Despite the hydrothermal conditions during reaction and oxidative regeneration, the activity of Na-Al2O3 was regained by coke combustion, the Na remained well dispersed on the support, and the catalyst maintained its capacity for CO2 adsorption at 500 °C after six reaction/regeneration cycles.

Roles of furfural during the thermal treatment of bio-oil at low temperatures

The reactive O-containing species in bio-oil could induce the polymerization of bio-oil during its thermal treatment, which affects the relevant utilization of bio-oil significantly. Furans, as the highly reactive O-containing species in bio-oil, play important roles during the thermal treatment of bio-oil. In this study, furfural was chosen as the representative of the furans in bio-oil to investigate its roles during the thermal treatment of bio-oil. The raw bio-oil with and without the addition of extra furfural (10 wt% of bio-oil) and pure furfural were pyrolyzed in a fixed-bed reactor at 200–500°C. The results show that the interactions among furfural and bio-oil components can take place prior to the evaporation of furfural (< 140°C) to form the intermediates, then these intermediates could be further polymerized to form large molecular compounds, and coke can be formed via the interactions at temperatures ≥ 300°C. At temperatures ≤ 300°C, furfural mainly interacts with anhydrosugars. As the temperature further increases, the aromatics are involved in the interactions to form coke. The increased percentage of the coke formed via the interactions is in a linear relation with the conversion of furfural during the pyrolysis at 300–500°C (no coke formed at 200°C). Meanwhile, more non-aromatic light components (≤ C6) and less aromatics in the tars could be formed due to the interactions.

Adaptable kinetic model for the transient and pseudo-steady states in the hydrodeoxygenation of raw bio-oil

The hydrodeoxygenation (HDO) of raw bio-oil is an attractive route for the production of fuels and chemicals from biomass. For the sake of advancing towards the implantation of HDO at larger scale, an adaptable kinetic model is presented for this process. A CoMo bifunctional catalyst supported on an activated carbon has been used. The P-functionalities of the activated carbon support provide the catalyst with enhanced acidic features. The HDO runs have been carried out in a continuous packed bed reactor at 425–475 °C. Two subsequent reaction stages have been observed during the experimental runs: a transient and a pseudo-steady state. In the former stage, the catalyst is partially deactivated whereas in the latter, an apparent constant activity is reached. The model decodes the complex reaction network of HDO with seven lumps and eleven reaction steps. The proposed model accounts for the evolution with time of the reaction medium composition in the transient state, considering the reactions involved in the gas phase and the ones of solid product deposition and catalyst deactivation. Important contributions of decarboxylation/decarbonylation/decomposition and repolymerization pathways towards CO/CO2/CH4 and thermal lignin are observed. The model also estimates the product distribution in the pseudo-steady state, in which the net deposition of solid products and the catalyst deactivation are negligible. In this state, the catalyst shows a partially inhibited conversion of phenolic compounds and the maximum yield of aromatics, which are the most interesting value-added chemicals. The proposed kinetic model could play a key role in the design of reactors for the HDO process at higher scale.

SIMULATION OF CO-PROCESSING BIO-OIL AND VGO IN FLUID CATALYTIC CRACKING UNITS

Biofuel is a promising substitute for fossil fuels to reduce greenhouse gas emissions and to provide highly sustainable fuels. Several technical challenges are indeed present during upgrading bio-oil to transportation fuel on a large scale. Co-processing bio-oil with some petroleum fractions in existing refineries serves as an alternative method to minimise processing costs. This paper aims to evaluate the co-processing by exploring the effects of temperature, bio-oil ratios and types of bio-oil to the product yields and quality in a Fluid Catalytic Cracking (FCC) unit within a refinery complex. The considered bio-oil are produced from pyrolysis of Palm Kernel Shell (PKS) and Empty Fruit bunch (EFB). The results show that bio-oil from PKS is better suited to produce gasoline due to its aromatic nature and its carbon range similarities compared to that from EFB. A mixture of 20% of hydrodeoxygenated (HDO) PKS in vacuum gas oil (VGO) shows a 5% improvement of naphtha yield while 20% raw bio-oil from PKS produces 4% increase in light cycle oil (LCO) yield.&#x0D; Keywords: co-processing, fluid catalytic cracking, bio-oil, palm kernel shell, empty fruit bunch, simulation

Catalytic upgrading of tars generated in a 100 kWth low temperature circulating fluidized bed gasifier for production of liquid bio-fuels in a polygeneration scheme

Gasification of wheat straw, an agricultural residue with high ash content, was investigated in a low temperature circulating fluidized bed (LT-CFB) gasifier in combination with catalytic tar upgrading as a flexible process to co-produce high quality bio-oil, nutrient rich char, and utilize the producer gas for heat and power production. The change in product distribution and bio-oil quality was studied when conducting the catalytic treatment with HZSM-5/γ-Al2O3 and lower-cost γ-Al2O3. The fuel properties of the raw and upgraded bio-oils were analyzed by elemental composition, moisture, total acid number, size exclusion chromatography, basic nitrogen content, gas chromatography–mass spectrometry with flame ionization detection (GC–MS/FID), 1H nuclear magnetic resonance (NMR), 13C NMR, and two-dimensional heteronuclear single-quantum correlation (2D HSQC) NMR. The operating temperature of the LT-CFB pyrolysis chamber determined the tar yield and quality in the producer gas. With decrease in pyrolysis temperature from 690 to 570 °C, the tar concentration in the producer gas increased, while the higher heating value of the condensed oil phase decreased from ~35 to 30 MJ/kg and the oxygen content, moisture content, and acidity of the bio-oil increased. Both HZSM-5/γ-Al2O3 and γ-Al2O3 were effective catalysts as the tar treatment improved the bio-oil quality in terms of increased heating value and revaporization efficiency, and a reduction in oxygen content, moisture content, total acid number, and basic nitrogen content. Catalytic vapor treatment, e.g. using HZSM-5/γ-Al2O3 at 500 °C, decreased the energy content in the condensed bio-oil slightly from ~22% to ~20%. The oil quality improved significantly, as the oxygen content (water-free) and TAN of the bio-oil decreased from 13 wt% O and 34 mg KOH/g to 11 wt% O and 3 mg KOH/g, respectively. The catalytically treated bio-oils are thus better suited for further processing in existing oil refineries.

Dynamics of carbon formation during the catalytic hydrodeoxygenation of raw bio-oil

The formation, growth and transformation of carbon residue (coke) deposited on the catalyst during the raw bio-oil hydrodeoxygenation has been studied.

Dual catalyst-sorbent role of dolomite in the steam reforming of raw bio-oil for producing H2-rich syngas

The dual role that low-cost dolomite plays as a catalyst and CO2 sorbent in the steam reforming of raw bio-oil has been studied. The reactions were performed in a continuous regime at 700 °C and steam/carbon ratio of 3. The results show that calcined dolomite is a feasible catalyst for producing a H2-rich syngas from raw bio-oil, with efficient CO2 retention and positive impact on the CO2 global emissions balance. Reforming of oxygenates (mainly acids, alcohols and aldehydes) and cracking/hydrogenation of poly-substituted phenols are prevailing reactions during the effective CO2 capture, catalyzed by the CaO and MgO in the dolomite. Consequently, around 40% of bio-oil is converted into a CO2-free syngas with H2 and CO concentrations above 65 vol% and below 20 vol%, respectively, whereas the liquid product is primarily composed of phenol and alkyl-phenols. Products composition changes along reaction by two causes: i) saturation of dolomite by CaO carbonation, which drastically changes the liquid product composition leading to the formation of aromatics by alkyl-phenols hydrodeoxygenation (HDO), activated by the CaCO3 and Fe impurities; ii) coke deposition which involves a progressive decrease in H2/CO ratio (6–2.5 in 4 h) by deactivation of steam reforming and water-gas-shift reactions.

Improving the quality of pyrolysis products through preliminary thermal treatment of woody raw materials

Rational processing of multi-ton wood and plant waste with the production of promising products is an important task. One of the approaches to solve this problem is the pyrolysis of solid organic waste with obtaining the secondary liquid useful products in the form of raw bio-oils or charcoal suspensions.In this regard, the work investigates the effect of pre-heat treatment of shredded wood on the mass yield of products processed by fast pyrolysis technology. As a result of the conducted research, it is revealed that the preliminary heat treatment has practically no effect on the mass yield of pyrolysis products. However, the output of the elemental composition of biomass changes: the content of carbon and hydrogen increases, the amount of oxygen decreases, the proportion of nitrogen remains unchanged, that improves the quality of the obtained pyrolysis products as raw materials for subsequent use in chemical technology.

Enhanced production of phenolics and aromatics from raw bio-oil using HZSM-5 zeolite additives for PtPd/C and NiW/C catalysts

This study delves into the performance of a Pt-Pd and a Ni-W catalyst supported on a phosphorus-containing activated carbon (ACP) in the hydrodeoxygenation (HDO) of raw bio-oil, as well as the enhancement of phenolic and aromatic product yields produced by incorporating physically mixed HZSM-5 zeolites (20 wt%) of different Si/Al ratio (15 and 140 in zeolites Z15 and Z140, respectively) in the catalytic bed. The HDO runs have been conducted in a fixed bed reactor at: 450 °C; 65 bar; space time, 0.15 gcat h g−1bio-oil; 90 ml min−1 H2; and time on stream up to 6 h. After a fast initial deactivation due to coke deposition the catalysts reached a pseudosteady state at which the carbon product yields are higher than in fresh catalyst conditions. The NiW catalyst provided yields of 42.3 wt% liquid carbon products (in a dry bio-oil basis), yielding 5.3 wt% phenolic and 12.3 wt% aromatic product yields. The NiW + Z140 combination was the most efficient catalyst (with a 47.3 wt% carbon production, including 6.8 wt% phenolics and 15.5 wt% aromatics) as a consequence of this low-acidity zeolite promoting the synergy with the dehydrogenation activity of metallic sites by favoring the acid-catalyzed cracking reactions of the bio-oil oxygenates, while simultaneously limiting gas product and coke formation. Two types of coke were detected, of thermal origin and catalytic coke, with the formation of the latter being dependent on the acidity of the zeolite.

Synergistic effect of highly dispersed Ru and moderate acid site on the hydrodeoxygenation of phenolic compounds and raw bio-oil

Hydrodeoxygenation (HDO) is an indispensable and important reaction in the fuel production process. Generally, the catalysts for HDO contain metal or acidic active sites, and the co-existence of them can significantly promote the HDO performance. While the subtle interaction between metal and acidic active sites is still not very clear. Herein, a series of Ru-based catalysts with different supports were prepared by photochemical method to obtain both of the high Ru dispersion and the moderate acidity. Among the catalysts with various supports, Ru/TiO2–Al2O3 showed the most efficient performance in the HDO process of phenolic compounds. Guaiacol was converted into cyclohexane with above 90% selectivity at 240 °C. Other typical phenolic compounds, including phenol, anisole, p-cresol, 1,2-dimethoxybenzene, benzofuran, eugenol and dibenzyl ether, were all transformed into the corresponding cycloalkanes with yield close to 100%. The synergistic effect between highly dispersed Ru and moderate acid site played the key role for the enhanced production of hydrocarbon fuels. Moreover, this catalytic system was also effective on the raw bio-oil upgradation for producing high yield of hydrocarbons and alkylphenols, which has the potential to be used as biofuels.