Deoxygenation Reaction Research Articles

Methane-assisted selective bio-oil deoxygenation for high-quality renewable fuel production: A rational catalyst design and mechanistic study

Methane is the main component of naturally abundant natural gas resources and is under-utilized. Bio-oil is a promising energy source with lower economic and environmental costs compared to fossil fuels. However, pyrolysis-derived bio-oil obtained from lipid sources is hindered by high oxygen content and unsaturated species. In this work, an Ir-Ga-Ce/TiO2-A catalyst is theorized and subsequently tailored to optimize deoxygenation product oil quality. After synthesis, 2-hexyl-1-decanol is employed as a model compound to understand the mechanism of deoxygenation under different atmospheres and rationalize the assistance of methane compared to inerts. It is found that methane significantly facilitates the deoxygenation and chain growth reactions by direct incorporation into the paraffinic and naphthenic liquid-phase products. In the gas-phase products, isotopic labeling studies reveal that methane is directly involved with deoxygenation as a major contributor to CO2, and potentially CO. The role of each catalyst component (Ir, Ga, Ce, and TiO2-A) is elucidated, resulting in a sophisticated network tailored for deoxygenation of alcohols with the assistance of methane. The Ir-Ga-Ce/TiO2-A catalyst is then subject to testing on a real pyrolysis-derived bio-oil and shows 84.7% deoxygenation, 0.07% water content by weight, 0.2 (mg KOH g−1) TAN and greater than 1.5% methane conversion, while maintaining the product oil’s structural integrity as a renewable fuel. This work illustrates the potential of a methane-assisted deoxygenation process and explains multiple roles methane can play in achieving better reaction performance and product quality. The effective utilization of methane for bio-oil deoxygenation demonstrates unique benefits for the natural gas and fatty waste industries.

PPh3‐Mediated Nucleophilic Sulfonation of Sulfonyl Chlorides with Arynes: Access to Manifold Aryl Sulfones

AbstractSulfonyl chlorides are a class of cheap and readily available basic chemicals, which have routinely served as electrophilic reagents in their chemical transformations. Herein, we disclose a novel PPh3‐mediated nucleophilic sulfonation method of sulfonyl chlorides with arynes. Different from the classical P(III)‐mediated reductive deoxygenation reaction of sulfonyl chlorides, the valence state of the sulfur atom has not been changed. This protocol exhibits broad functional group tolerance and provides a direct approach to a variety of aryl and alkyl sulfones.

Preparation of Co–Co9S8–MoS2 catalyst for efficient deoxygenation of lignin-derived aromatic oxy-compounds into arenes

The formidable challenge for the deoxygenation of lignin-derived aromatic oxy-compounds into arenes under mild conditions is how to engineer a robust catalyst. In this study, Co–Co9S8–MoS2 catalyst was prepared via thermal decomposition, in–situ sulfidation and following by H2 reduction, where Co was highly dispersed and mainly existed in the species of metallic Co and Co9S8. This catalyst exhibited high activity, allowing the reaction temperature for cleaving Caromatic–O bond lowered to 120 °C, which was attributed to that metallic Co accelerated the H2 dissociation and then enhanced the deoxygenation activity. Co–Co9S8–MoS2 also presented a high stability: both the conversion and product selectivity were unchanged after 8 continuous cycles, and the characterization results evidenced almost no structure change and sulfur loss during the deoxygenation reaction. In addition, other 20 aromatic oxy-compounds including acid, ester, guaiacol and dimer lignin linkages were also successfully deoxygenated, and the arenes selectivity could maintain higher than 98 %. This work offered a new strategy for constructing metal–sulfide–MoS2 type catalysts and provided an efficient route towards the practical application in bio-oil upgrading.

Sustainable production of aromatic-rich biofuel via catalytic co-pyrolysis of lignin and waste polyoxymethylene over commercial Al2O3 catalyst

Co-valorization of biomass and multiple solid wastes is essential to environment protection and energy security. Herein, aromatic-rich biofuel was produced from lignin and waste polyoxymethylene (POM) via catalytic co-pyrolysis process. Commercial and cheap γ-Al2O3 catalyst exhibited good catalytic performance. Series characterizations and bench-top pyrolysis experiments were conducted to illustrate the synergism between raw materials and the mechanism of aromatics formation. The TG analysis and thermodynamics calculation revealed that a remarkably positive synergistic effect existed between lignin and POM, which reduce the activation energies and make the reaction more conducive in terms of thermodynamics. Meanwhile, the yields of biochar and bio-oil increased considerably. Additionally, the operating conditions affected the product distributions significantly. The suitable mixing ratio of lignin to POM was around equal (5:5) with the bio-oil yield increased to 28.3 % and aromatic hydrocarbons selectivity increased to > 95 %. Moreover, POM, the precursor for alkylating reagents and hydrogen donors, could promote the deoxygenation reactions of phenolic intermediates and result into aromatic hydrocarbons. The acid sites of γ-Al2O3 promoted series secondary cracking reactions (alkylation, deoxygenation), and thus improved bio-oil quality. Finally, the stability test showed that commercial γ-Al2O3 catalyst was slightly deactivated after 4 cycles because of coke deposits and acid sites loss.

Biomass pyrolysis in a circulating fluidized bed reactor: Evaluating two strategies for the reduction of oxygen content in bio-oil

The use of a circulating fluidised bed (CFB) reactor promotes higher heat transfer to the biomass pyrolysis process and has the advantage of being energy self-sufficient through the continuous burning of biochar. CFB’s similarity with the fluidised catalytic cracking (FCC) of fossil streams represents a promising scenario of integration of lignocellulosic biomass in a conventional refining scheme. In this paper, two approaches were studied to enhance the deoxygenation reactions of biomass components in a pilot pyrolysis CFB reactor. First, in a noncatalytic pyrolysis, a lignocellulosic biomass was cofed with hydrogen-rich compounds produced in the oil refinery (methane and propane). In the second part, using a ZSM-5 catalyst in the bed, the effect of different catalyst-to-biomass ratios (CTB) in the bio-oils’ properties was evaluated. Compared with conventional pyrolysis, the cofeeding of methane or propane produced bio-oils with less oxygen content. The use of propane achieved better performance in terms of hydrocarbon concentrations in bio-oils, hence increasing benzene, toluene and xylene (BTX) production and being comparable with the results of catalytic pyrolysis. It was also shown that the increase of CTB in catalytic pyrolysis led to the enhancement of deoxygenation reactions, producing more O-free compounds. Both strategies were promising for improving the quality of bio-oil. Issues such as the cost of the catalyst and gases must be evaluated for possible integration into a conventional refining process.

Biofuel upgrading via catalytic deoxygenation in trickle bed reactor: Crucial issue in selection of pressure regulator type

Trickle bed reactors (TBRs) are commonly used in various chemical and associated processes. The selection of a proper back pressure regulator (BPR) is crucial for maintaining the system's upstream pressure. In this study, we investigate the impact of BPR selection on deoxygenation reaction in a TBR with two typical types of BPR, including gas-phase type back pressure regulator (Gas-BPR) and multiphase type back pressure regulator (Multi-BPR). Notably, Gas-BPR introduces interruptions and pressure drops during the sampling step, impacting the hydrogen flow rate, while Multi-BPR ensures more consistent hydrogen flow. To examine the performance of BPR systems, hydrotreating experiments were conducted at 330 °C, 50 bar of hydrogen over Ni/γ-Al2O3 catalyst using crude Pongamia pinnata oil as a feedstock and refined palm olein as a benchmark. Insignificant difference in the reaction performance between Multi-BPR and Gas-BPR systems was observed when using refined palm olein. Interestingly, there was a significant difference between the two systems when feeding with crude Pongamia pinnata oil. The multi-BPR system demonstrated superior performance, achieving 100% conversion of the feedstock over a prolonged period compared to the interrupted hydrogen flow in the Gas-BPR system. Further characterization of fresh and spent catalysts using N2 sorption, XRD, SEM-EDS and TGA-DTG-DSC techniques revealed that a gum and coke formation was a reason for the rapid catalyst deactivation. Furthermore, the interrupted flow in the Gas-BPR system led to substantial gum production, ultimately causing a blockage in the reactor bed. Consequently, for feedstocks with high impurities, a robust continuous flow of hydrogen is essential. Thus, the study strongly recommends selecting Multi-BPR for continuous operation in TBRs to enhance efficiency and avoid catalyst deactivation.

Chemical and structural changes of resins during the catalytic and non-catalytic aquathermolysis of heavy crude oils

Resins are important molecules for colloidal system (maintaining asphaltenes dispersed) of heavy oils and are responsible of their high viscosity (together with asphaltenes). The results of characterization of resins before and after aquathermolysis by molecular weight, elemental analysis, Fourier transform infrared, nuclear magnetic resonance, and ultraviolet fluorescence were collected and analyzed to highlight the changes in chemical and structural properties. The discussion is based on the transformations that resin molecules undergo via hydrogenation, deoxygenation, desulfurization, cracking, ring opening, dealkylation and pyrolysis reactions at steam injection conditions. Some correlations were developed between properties of resins. It was found that the type of ligand plays an important role for catalytic aquathermolysis besides the type of active metal since a synergic effect of these factors produces diverse results in the properties of resins. The molecular weight of resins is greater improved using oil-soluble catalysts compared with water-soluble catalysts and non-catalytic aquathermolysis. Mo-based catalysts usually exhibit higher hydrogenation capability and sulfur removal than other active metals, while Fe-based catalysts commonly improves dealkylation and pyrolysis of side chain reactions of resins.

Ternary molten salt-assisted lignin pyrolysis for the co-production of monophenols and value-added carbon materials

In this paper, the ternary molten salt (Li2CO3-Na2CO3-K2CO3) was introduced into the lignin pyrolysis process for the co-production of monophenols and value-added carbon materials. The effect of lignin/molten salt ratios (i.e., 3:1, 1:1, and 1:3) on lignin pyrolysis behaviour was investigated herein. The pyrolytic products were characterized by gas chromatography–mass spectrometry, ultimate analyses, scanning electron microscopy, nitrogen adsorption analyses, and Raman analyses. Results showed that molten salt media can promote the conversion of bulky phenolic oligomers into mono-phenols by enhancing the cracking and deoxygenation reactions. P-type phenols (49.76 %) were produced when the lignin/molten salt mass ratio was 1:3. The porosity and aromaticity of biochar were regulated in-situ using molten salt. The possible catalytic effect of molten salt on lignin pyrolysis was proposed. This study provides a case reference for lignin waste resource utilization.

Enhancing deoxygenation of waste cooking palm oil over CaO-MgO catalyst modified by K2O for green bio-fuel

There are challenges to replacing traditional fossil fuels completely, so producing efficient green biofuels is crucial. In this work, waste cooking palm oil (WCPO) was used as raw material to produce biofuel through pyrolytic catalysis cracking (PCC) over alkaline catalysts as CaO-MgO with various dopants at 0, 3, 6 and 9 wt% K2O contents. The WCPO reacted under atmospheric pressure without purging gases at 500, 525 and 550 °C, respectively. Catalysts were characterized by various techniques in terms of physical and chemical properties. The pyrolytic oil (PO) was separated from the crude oil product. Then, PO was characterized by TGA/DTG, CHNO, FTIR and GC–MS. The PO was distilled following an ASTM D86 method. The properties of biofuels, such as density, kinematic viscosity and acidity, were measured. The basicity of the catalyst increased with increasing K2O contents. K2O not only enhanced the pyrolytic-liquid product yield but also significantly reduced the oxygenated compounds in biofuel through the deoxygenation process to improve biofuel quality. The different reaction temperatures were observed in which low-temperature reaction provided incompletely cracking heavy molecules, and more gas product occurred at the high reaction temperature. Surprisingly, the fatty acid compounds of WCPO were transferred to hydrocarbon compounds by deoxygenation reactions confirmed by GC–MS and FTIR results. The highest pyrolytic oil yield was approximately 92 vol% compared with crude oil product, obtained from 3 wt% K2O-MgO/CaO and 525 °C. The paraffinic and olefinic compounds were the main hydrocarbon products with K2O doping catalysts, while ketone compounds were found in all catalysts via the ketonic decarboxylation mechanism. In this condition, pyrolytic oil was completely distilled to get gasoline, kerosene and diesel. The kinematic viscosity and density were under ASTM standards except for acidity. Remarkably, the acidity of biofuel with K2O doping was reduced about 2–3 times compared to MgO/CaO alone.

Highly selective production of light aromatics from lignin through integrated approach of the torrefaction deoxygenation pretreatment and the dual-catalyst catalytic fast pyrolysis using Nb modified γ-Al2O3 and HZSM-5

Light aromatics are extremely important building blocks for manufacturing of numerous industrial products. The integrated approach of the torrefaction deoxygenation pretreatment (TDP) and the dual-catalyst catalytic fast pyrolysis (DC-CFP) using the HZSM-5 and metal (Nb, Zn, Ga, Ni, Ce) modified γ-Al2O3 as catalyst was employed to enhance the production of light armatics from the hardwood lignin. The torrefaction deoxygenation mechanism was established based on the evolution of chemical structure of lignin. The maximum removal rate of oxygen element was 22.82%, achieved at the TDP temperature of 300 °C. The oxygen element was removed through the cleavage of β–O–4 bond, the aliphatic–OH and aliphatic–HC═O on the side-chain, and the aromatic–OH and aromatic–OCH3 on the aromatic nucleus, releasing as the oxygenated gaseous compounds (CO2, H2O, and CO). The synergistic effect between HZSM-5 and metal modified γ-Al2O3 in DC-CFP was observed, remarkably improving the yield of light aromatics. Metal modified γ-Al2O3 aimed to first convert lignin into macromolecular phenols, and HZSM-5 was complementary used to convert the macromolecular phenols into light aromatics by the deoxygenation reactions. The maximum selective yield of bio-BTX were 74.39%, obtained at TDP temperature of 250 °C, lignin-to-catalyst ratio of 1:3, and HZSM-5-to-15%Nb/Al2O3 of 2:2.

Promotion of bio-oil production from the microwave pyrolysis of cow dung using pretreated red mud as a bifunctional additive: Parameter optimization, energy efficiency evaluation, and mechanism analysis

To address the issues of high oxygen content and energy consumption in the microwave-assisted pyrolysis of biomass for biofuel production, this study used high-temperature pretreated red mud (RM) as an additive. The pretreated RM exhibited dual functionalities, namely microwave absorption and catalytic properties, during the microwave-assisted pyrolysis of cow dung (CD). This study also evaluated the optimization potential of energy recovery efficiency. The results showed that the addition of pretreated RM significantly increased the oil yield during the microwave-assisted pyrolysis of CD. The highest oil yield (59.63%) was obtained via the microwave-assisted pyrolysis of CD over catalysis with RM pretreated at 750 °C (RM750). Through the optimization of the RM750-to-CD mixing ratio, optimal oil quality and energy recovery efficiency were achieved. At a mixing ratio of 1:1, the pyrolysis oil featured the highest aromatic hydrocarbon content and lowest acid content. The high-temperature pretreatment of RM increased the Fe2O3 content, which enhanced the dielectric properties and magnetic loss ability of the reactants. This resulted in localized high temperatures and the formation of “hot spots,” which can promote the deoxygenation and hydrogenation reactions of oil. Consequently, the lower heating rate of oil increased from 35.12 to 40.11 MJ kg−1. The released oxygen escaped in the form of CO. In addition, pyrolytic char was used as an in situ microwave absorbing material owing to its increased Fe2O3 content and graphitization degree, leading to an increase in energy recovery efficiency from 4.71% to 9.98%. This study provides valuable guidance for the efficient utilization of diversified solid wastes and demonstrates the potential application of microwave-assisted pyrolysis technology in the resource utilization of solid wastes.

Synthesis and Reactivity of Trifluoromethylthiophosphonium Salts†

Comprehensive SummaryThis article described an unprecedented synthesis of trifluoromethylthiophosphonium salts from allyl trifluoromethyl sulfoxide and phosphines in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf) through Mislow‐Evans‐type rearrangement. The resulting trifluoromethylthiophosphonium salts were firstly isolated and fully characterized. These fluoroalkylphosphonium salts, as exemplified by trifluoromethylthio triphenylphosphonium salt (6a), exhibited unique and versatile reaction with nucleophiles and deoxygenative trifluoromethylthiolation reaction of carboxylic acids. Furthermore, the photoredox catalytic tunable radical hydrotrifluoromethylation and hydrotrifluoromethythiolation of unactivated alkenes with 6a was successfully developed.

Passivation coating on titanium powder surface via SnCl4-Ti gas–solid fluidization reaction

Titanium powder is easily oxidized in the forming and sintering process due to its active chemistry. In this study, a passivation coating is formed on Ti powder surface via SnCl4-Ti gas–solid fluidization reaction using fluidized bed. It is found that at 200–350 ℃, Ti-Sn-Cl-O passivation layer is formed on Ti powder surface on account of the reaction among SnCl4, oxide film on powder surface, and Ti matrix. Upon further increasing the temperature to above 500℃, deoxygenation reaction occurs accompanied by the formation of gaseous TiClm and TiOxCly escaping from Ti powder matrix, resulting in the decreasing of surface oxygen content. Besides, elemental Sn and Ti-Sn compounds are formed on Ti powder surface, and part of Sn is diffused into titanium matrix. The passivation behavior is mainly consisted of oxygen film destruction and oxygen removal with the fluidization temperature increasing. Overall, the suitable temperature is about 350℃ to form a passivation coating on Ti powder surface, which can achieve oxidation isolation and deoxygenation in subsequent forming and sintering process.

The behavior of heteroatom compounds during the pyrolysis of waste composite plastics

Multilayer composite packaging plastic is commonly used in daily life. Due to the complex structures and the existence of heteroatoms, such as nitrogen and oxygen, the recycling of this kind of plastic is challenging. Recycling through the pyrolysis method may provide an efficient option with respect to the mechanical and solvent methods. An understanding of the behaviour of heteroatoms during pyrolysis is significant to optimize the operating conditions. In this work, two composite packaging plastics of PET/LDPE (Polyethylene Terephthalate/Low Density Polyethylene) and PA/LDPE (Polyamide//Low Density Polyethylene) were pyrolysed at various temperatures between 400 and 500 °C in a fixed bed reactor. Heteroatom balance and composition analysis were conducted. Especially, the composition of O- and N-containing compounds in oils was fully understood by using GC-MS (Gas Chromatograph - Mass Spectrometer) and APPI FT-ICR MS (Atmospheric Pressure Photoionization Fourier Transform-Ion Cyclotron Resonance Mass Spectrometer) instruments. At 400 °C, only 2.2 wt% oxygen was left in 53.9 wt% solid residues for PET/LDPE and 3.6 wt% nitrogen was retained in 61.0 wt% solid residues for PA6/LDPE, whereas nearly no oxygen was retained in solid residues for PA6/LDPE. So the PET/PA6 can be degraded in a much lower temperature range than LDPE indicating the possibility of separating heteroatoms by step-wise pyrolysis. A large amount of O-containing compounds were observed in oils from PET/LDPE pyrolysis, while O, N-containing compounds existed in oils from PA6/LDPE. The APPI FT-ICR MS analysis revealed that parts of O-containing compounds were generated through the interaction between O-containing functional groups and aliphatics during the PET/LDPE pyrolysis. For PA6/LDPE, the deoxygenation reaction was easier to occur than the denitrification reaction.

Revealing roles of CO2 and N2 in pressurized hydrothermal carbonization process for enhancing energy recovery and carbon sequestration

In this study, CO2– and N2-pressurized hydrothermal carbonization processes were investigated to understand the catalytic effects of CO2 on hydrochar production and its quality (e.g., surface properties, energy recovery, and combustion behaviour). Both CO2– and N2-pressurized HTC processes could enhance the energy recovery (from 61.5% to 63.0–67.8%) in hydrochar by enhancing the dehydration reactions. Nonetheless, the two systems exhibited contrasting trends in volatile release, oxygen removal, and combustion performance as a function of increasing pressure. High N2 pressure enhanced deoxygenation reaction, facilitating the release of volatiles and increasing the hydrochar aromaticity and combustion activation energy (172.7 kJ/mol for HC/5N). Without the contribution of CO2, excessively high pressure may cause an adverse impact on the fuel performance owing to higher oxidation resistance. This study presents an important and feasible strategy to utilise CO2-rich flue gas in the HTC process to produce high-quality hydrochar for renewable energy and carbon recovery.

Scale-Up Foreseeable Fabrication of CoS-MoS2 for Efficient Deoxygenation of Lignin-Derived Phenolics to Arenes

Catalysis plays a key role in oriented biomass valorization, and designing a robust catalyst and developing its correspondingly easy-to-scale-up preparation are particularly crucial in boosting biorefinery concept into reality. In this study, employing sulfur vacancies in MoS3 and their preferable adsorption to Co ions, CoS-MoS2 catalyst was fabricated via decomposition of MoS3 followed by in situ sulfidation of Co oxides. Co could be located at the edges of MoS2, constructing plenty of CoS–edge interfaces. This critical feature of the interface enhanced the adsorption of the reactant and decreased the energy barrier of the rate-limiting step in the deoxygenation of 4-methylphenol, leading to as high as 100% toluene yield at a low temperature of 120 °C. Moreover, this catalyst presented high stability in the deoxygenation reaction and could efficiently convert other lignin-derived aromatic oxy-compounds into arenes. Importantly, this facile method shows good versatility in fabricating different iron family element-promoted MoS2-based catalysts, and this preparation procedure is readily scaled up 200-fold without compromising catalytic activity, showcasing the potential for large-scale applications.

Pyrolysis of sawdust impregnated with xylose: Tailoring property of biochar with sugar-derived intermediates

Cellulose and hemicellulose are major components of woody biomass, pyrolysis of which would inevitably produce anhydrate sugars or sugar-like organics. These sugars might tailor property of biochar via interactions when they pass through inner and outer surface of biochar, which were investigated herein in pyrolysis of poplar sawdust impregnated with various loading of xylose, a model sugar from hemicellulose, at 600 °C. The results suggested that the addition of xylose enhanced the cracking reactions to form more gaseous products but less biochar and bio-oil. Nevertheless, the intermediates from xylose enhanced aromatization of volatiles to form more light phenolics while aided precipitation of heavy organics on surface of biochar. The accelerated carbonization, deoxygenation and dehydrogenation reactions with presence of xylose enhanced aromatization reactions, making the biochar carbon-rich with increased heating value, crystallinity and hydrophobicity. Additionally, xylose addition could substantially enhance thermal stability of the biochar, even with loading of only 5 wt%. The DRIFTS characterization showed that the degradation of xylose produced abundant carbonyls-containing species that react with organics on surface of biochar, forming large aromatics of fused ring structures.

Investigation on in-situ deoxygenation performance of bio-oil model compound guaiacol over Ce-Fe/Al2O3 catalyst

The investigation of the low-cost deoxygenation of guaiacol (GUA, a model bio-oil compound) is of importance for upgrading bio-oil. At present, common sulfide catalysts for GUA deoxygenation reactions cause contamination of the liquid product, and noble metal catalysts are economically disadvantageous. In this study, four reduced Fe-based oxides with different Ce doping ratios were prepared and their effects on the in-situ deoxygenation performance of GUA in aqueous/methanol hydrogen donor solvents were explored. The results based on the deoxygenation degree, conversion degree, and higher heating value (HHV) of the products showed that the oxide catalyst with a Fe/Ce molar ratio of 2:1 in the methanol solvent performed very well. After selecting an excellent catalyst and a better hydrogen donor solvent, four factors (reaction temperature, reaction time, volume ratio of GUA dosage and methanol dosage, and the ratio of catalyst dosage at the bottom of the reactor to that at the top) in the deoxygenation degree of GUA were investigated using an orthogonal experimental method to further explore the performance of the catalyst. The results showed that the reaction temperature and time greatly influenced GUA deoxygenation. Under optimal experimental conditions, the deoxygenation degree and conversion degree of GUA could reach 34.36% and 92.56%, respectively, based on the relative peak area of gas chromatography–mass spectrometry, and the HHV of the liquid product was 32.27 MJ/kg. Although Fe/Ce catalysts mainly promote demethoxylation, demethylation, and methylation, the stability and quality of the liquid products were improved compared with GUA owing to the reduction in phenolic hydroxyl and ether content. The reduced catalyst in the process of GUA in-situ deoxygenation reactions in methanol maintained a steady performance, as revealed by X-ray diffraction and X-ray fluorescence.

Thermal pretreatment of poplar sawdust at 100 °C in water or with microwave heating impacts the pyrolysis behaviors

Drying at 100 °C is a common practice for processing many biomasses for their further thermochemical conversion via the routes such as pyrolysis. The drying temperature of 100 °C is low, but might not be too low to cause any impact on pyrolytic behaviors of a biomass feedstock. In this study, varied scenarios of thermal pretreatment of poplar sawdust (oven-drying, boiling in water and microwave heating) at 100 °C were screened for probing their potential influence on the pyrolytic behaviors at 500 and 750 °C. Comparing with oven-drying, boiling in water (cooking) and microwave heating at 100 °C could remove some oxygen-containing species, increasing carbon content of the pretreated sawdust and promoting carbonization in pyrolysis. This enhanced formation of biochar, heavy π-conjugated organics in bio-oil, but suppressed generation of gas. The cooking or microwave heating pretreatment also promoted aromatization to form the biochar of higher thermal stability, higher crystallinity, and higher aromatic degree, due to the enhanced deoxygenation reactions in the pyrolysis. The in-situ IR characterization suggested that microwave pretreatment promoted generation of unsaturated ketones and also the species with olefinic C = C, favoring their further aromatization. The cooking pretreatment impacted transformation routes of the oxygen-containing organics, thus modifying pyrolysis behaviors of the pretreated sawdust.

Valorisation of waste biomass and plastics toward light aromatics: Co-catalytic fast pyrolysis of torrefied bamboo and polyethylene over alkali and acid treated hierarchical HZSM-5

Light aromatics are extremely important building blocks which can be prepared from the co-catalytic fast pyrolysis (Co-CFP) of biomass and polyethylene. In this study, the bamboo was torrefied to remove part of oxygen element prior to pyrolysis, then being co-fed with polyethylene (HDPE, PE and LDPE) during CFP over alkali (NaOH and Na2CO3) and acid (H3PO4 and HCl) treated HZSM-5. 40.3% oxygen element in bamboo could be eliminated at torrefaction temperature of 300 °C. After the acid dealumination or alkali desilication treatments, the mesopore was creased in HZSM-5, transforming into hierarchical structure with larger pore size and lower acidity. The effect of torrefaction temperature, the species of alkali or acid solutions and their concentrations, the mass ratio of HDPE-to-torrefied bamboo, the CFP temperature on the yields of light aromatics was systematically discussed. The maximum yield of BTX was 4.39 × 108 a.u./mg which was obtained by Co-CFP of torrefied bamboo (250 °C) and HDPE at mass ratio of 1:2 with 800 °C over 0.2 M NaOH treated hierarchical HZSM-5. The aromatization reaction of olefins, the deoxygenation reaction of oxygenates, and the Diels-Alder reaction between furans and olefins were key reactions for the formation of BTX during Co-CFP of torrefied bamboo and polyethylene.