Reductive liquefaction of lignin to monocyclic hydrocarbons: ReS2/Al2O3 as efficient char inhibitor and hydrodeoxygenation catalyst

Thermochemical processing of lignin ends up with a major problem which is the high yield of char remained from lignin conversion, causing low yields of desired products. The ReS2/Al2O3 catalyst, used in this work, exhibited a high char-suppressing potential and high hydrodeoxygenation efficiency in the reductive liquefaction of kraft lignin. Compared to NiMo/Al2O3, as a conventional sulfide catalyst, ReS2/Al2O3 showed significantly better catalytic performance with 72.4 % lower char yield, due to its high efficiency in stabilizing the lignin-depolymerized fragments. The remarkable catalytic performance of ReS2/Al2O3 is attributed to its high oxophilicity, the metal-like behavior of rhenium sulfide and sufficient acidity. The effects of reaction temperature and different catalyst supports (Al2O3, ZrO2 and desilicated HY zeolite) were also studied. In an alkali (NaOH)-assisted depolymerization of lignin, it was revealed that ReS2/Al2O3-to-NaOH (stabilization-to-depolymerization) ratio plays a crucial role in determining the reaction pathway toward either solid char residues or liquid monomeric products

Stabilization of bio-oil from simulated pyrolysis oil using sulfided NiMo/Al2O3 catalyst

Pyrolysis oil comprises compounds with a broad range of functional groups making its thermal/catalytic upgrading challenging due to the formation of undesired char. In this context, the current contribution addresses the thermal and catalytic hydrotreatment of a simulated pyrolysis oil containing all the representative groups of compounds under bio-oil stabilization conditions (180–300 \ub0C, 60 bar, 4 h) using sulfided NiMo/Al2O3. The effect of reaction conditions and different oxygenated organic compounds on the yields and properties of products was compared thoroughly. Interestingly, a correlation between the presence/absence of oxygenated furan and sugar compounds was found to significantly affect the yield of liquid product containing stabilized compounds. The presence of such compound groups significantly enhances the solid formation via oligomerization and polymerization reactions. To gain further insight, the solid products were analyzed/characterized in detail to elucidate their characteristics by extracting them into a dimethyl sulfoxide (DMSO) soluble and insoluble solid fraction. It was found that in the presence of NiMo/Al2O3, increasing temperature from 180 to 300 \ub0C enhances the formation of liquid product due to transformation of some of the soluble solids, while for experiments without the catalyst, the formation of solids was significantly higher. Oppositely, during heating up to 180 \ub0C, no solids were found in the case without the catalyst, however the presence of the catalyst during heating resulted in solid formation due to various catalytic reactions that promoted char formation. Analysis of solids revealed that the structure of soluble solids at lower temperatures (180 \ub0C) using the catalyst was closely related to sugar derivatives, whereas the corresponding insoluble solids with higher molecular weight were not fully char-like developed. However, at higher temperatures, the soluble and insoluble solid compositions were found to contain aliphatic compounds and fully developed char, respectively. Therefore, the stabilization of furan particularly with attached carbonyl groups and sugars derivatives in pyrolysis oil is of great importance to improve upgrading efficiency

Enhancement of aromatic hydrocarbon production and suppression of coke formation in catalytic pyrolysis of biomass / Pouya Sirous Rezaei

The concern for depletion of fossil fuels and their growing environmental threats necessitates to develop efficient techniques for utilization of lignocellulosic biomass as an alternative fuel source which is renewable and environmentally safe. Pyrolysis is an economically feasible process for large-scale exploitation of biomass. However, bio-oil which is the liquid product of biomass pyrolysis has high oxygen content, and needs to be deoxygenated to hydrocarbons in order to be used as fuel additive. Catalytic pyrolysis using zeolites as catalyst is considered as an efficient technology since it includes both steps of pyrolysis and catalytic upgrading in one unit. Among the three major lignocellulosic components (cellulose, hemicellulose and lignin), lignin is the most difficult fraction of biomass to be deoxygenated. In catalytic conversion of methanol co-fed with m-cresol or phenol as lignin model compounds over HBeta catalyst in a fixed-bed reactor, it was revealed that co-feeding phenol or m-cresol with methanol causes significant deactivation of HBeta and remarkable reduction in aromatic hydrocarbons yield due to strong adsorption of phenolics on zeolite acid sites. Hence, pure zeolites are not appropriate catalysts for upgrading of the lignocellulosic biomass with high content of lignin. In this research, bifunctional Fe/HBeta catalyst showed to be efficient for production of aromatic hydrocarbons in catalytic pyrolysis of palm kernel shell waste with high lignin content of about 50 wt%. Lignin derived phenolics were deoxygenated through hydrogenolysis reaction promoted by Fe active sites. The adsorption of phenol on zeolite was shown to be highly affected by reaction temperature and catalyst properties such as pore size, crystallite size and strength distribution of zeolite acid sites. One main challenge in atmospheric upgrading of biomass derived feedstocks over zeolites is high formation and deposition of coke which results in rapid catalyst deactivation. Meanwhile, coke formation is a competing reaction with production of valuable compounds like aromatic hydrocarbons. Coke is one major undesired product of this process which its iv high yield is due to low hydrogen to carbon effective ratio of biomass and in turn low hydrogen content in hydrocarbon pool inside catalyst. In this study, catalytic pyrolysis of cellulose as biomass model compound was conducted using HZSM-5 (Si/Al: 30), HY (Si/Al: 30) and physically mixed catalysts of HZSM-5 (Si/Al: 30) and dealuminated HY (Si/Al: 327) in order to investigate the dependency of formation of both types of thermal and catalytic coke on zeolite characteristics. Coke formation over physically mixed catalysts of HZSM-5 and dealuminated HY was remarkably lower than that over HZSM-5 and HY. The aromatic hydrocarbons yield was also considerably enhanced over the physically mixed catalysts compared to HZSM-5 and HY. It was shown that there is a significant interaction between zeolite pore structure and density of acid sites which could be taken into account for designing more efficient catalysts to achieve lower coke formation and higher production of desired products. The catalysts used in this study were characterized by XRF, XRD, N2 adsorption, NH3-TPD, H2-TPR, FTIR and TGA, and liquid products were analyzed by GC/MS

Aromatic hydrocarbon production by catalytic pyrolysis of palm kernel shell waste using a bifunctional Fe/HBeta catalyst:Effect of lignin-derived phenolics on zeolite deactivation

Lignin-derived phenolics are tightly bound with zeolite acid sites, and act as coke precursors. A bifunctional Fe/HBeta catalyst is efficient for upgrading of biomass materials with high lignin content.</p