• Energy Research

Abstract In the present study, Loblolly pine biomass residue was converted to bio-oil in a two-step process, consisting of 1) fast pyrolysis in the presence of zeolite ZSM-5 as a catalyst to produce pyrolysis oil, 2) hydrogenation of pyrolysis oil using formic acid as the hydrogen source in presence of Ru/activated carbon catalyst. Pyrolysis oils were analyzed by 13C, 31P and HSQC-NMR and the results revealed that the zeolite-induced catalytic fast pyrolysis process led to effective demethoxylation, producing more catechol and p-hydroxy-phenyl hydroxyl groups in the bio-oils, resulting in a decrease in the methoxyl group content by about 85 % and rich aromatic structures in the pyrolysis oils. The properties of pyrolysis oil with and without zeolite were in the bio-oil range. Hydrogenated pyrolysis oil showed that 79 % of the aromatic protons are eliminated and 87 % of protons are aliphatic in nature, with no oxygen attached to the α-carbon.

Abstract Catalytic fast co-pyrolysis (co-CFP) of bamboo sawdust and waste tire over HZSM-5 and MgO was conducted using a tandem pyrolysis and upgrading system which consists of a bubbling fluidized bed and a fixed bed reactor. HZSM-5 mixed and sequential with MgO modes were studied to explore the additive effect for the promotion of aromatic hydrocarbons. Experimental results indicated that co-CFP of bamboo sawdust with waste tire over pure HZSM-5 increased the yields of pyrolysis oil and char, while the gas yield decreased with the increasing of waste tire percentage in the feedstock blends. The product distribution of pyrolysis oil obtained from co-CFP of bamboo sawdust and waste tire over pure HZSM-5 was dominated by aromatic hydrocarbons, and the relative concentration increased from 26.71 to 71.50% as the waste tire percentage elevated from 0 to 60 wt%. Co-CFP of bamboo sawdust and waste tire using HZSM-5 mixed with MgO mode produced a higher yield of pyrolysis oil than the sequential mode when HZSM-5/MgO mass ratio was raised from 1:4 to 1:1. However, the sequential mode was proved to be more effective in the promotion of aromatic hydrocarbons than the mixed mode at a higher HZSM-5 proportion. A positive additive effect for alkylbenzenes was found when the sequential mode was used at varying HZSM-5/MgO mass ratios. Regarding the olefins, C10 olefins were main products, and limonene selectivity increased at first and then decreased with the highest selectivity of 38.87% occurring at HZSM-5/MgO of 2:3 in the mixed mode case. The additive effect of HZSM-5 and MgO indicated that both the mixed and sequential modes inhibited the formation of polycyclic aromatic hydrocarbons with the most significant additive effect obtained at HZSM-5/MgO mass ratio of 1:1 using the mixed mode.

Pyrolysis of renewable biomass has been developed as a method to produce green fuels and chemicals in response to energy security concerns as well as to alleviate environmental issues incurred with fossil fuel usage. However, pyrolysis oils still have limited commercial application, mainly because unprocessed oils cannot be readily blended with current petroleum-based transportation fuels. To better understand these challenges, researchers have applied diverse characterization techniques in the development of bio-oil studies. In particular, nuclear magnetic resonance (NMR) is a key spectroscopic characterization method through analysis of bio-oil components. This review highlights the NMR strategies for pyrolysis oil characterization and critically discusses the applications of 1H, 13C, 31P, 19F, and two-dimensional (2-D NMR) analyses such as heteronuclear single quantum correlation (HSQC) in representative pyrolysis oil studies.

Here, the recalcitrant nature of lignocellulosic biomass is a combined effect of several factors such as high crystallinity and high degree of polymerization of cellulose, lignin content and structure, and the available surface area for enzymatic degradation (i.e., accessibility). Genetic improvement of feedstock cell wall properties is a path to reducing recalcitrance of lignocellulosic biomass and improving conversion to various biofuels. An advanced understanding of the cellulose biosynthesis pathway is essential to precisely modify cellulose properties of plant cell walls. Here we report on the impact of modified expression of candidate cellulose biosynthesis pathway genes on the ultra-structure of cellulose, a key carbohydrate polymer of Populus cell wall using advanced nuclear magnetic resonance approaches. Noteworthy changes were observed in the cell wall characteristics of downregulated KORRIGAN 1 (KOR) and KOR 2 transgenic plants in comparison to the wild-type control. It was observed that all of the transgenic lines showed variation in cellulose ultrastructure, increase in cellulose crystallinity and decrease in the cellulose degree of polymerization. Additionally, the properties of cellulose allomorph abundance and accessibility were found to be variable. Application of such cellulose characterization techniques beyond the traditional measurement of cellulose abundance to comprehensive studies of cellulose properties in largermore » transgenic and naturally variable populations is expected to provide deeper insights into the complex nature of lignocellulosic material, which can significantly contribute to the development of precisely tailored plants for enhanced biofuels production.« less

The ability to accurately and rapidly measure plant cell wall composition, relative monolignol content and lignin-hemicellulose inter-unit linkage distributions has become essential to efforts centered on reducing the recalcitrance of biomass by genetic engineering. Growing (13)C enriched transgenic plants is a viable route to achieve the high-throughput, detailed chemical analysis of whole plant cell wall before and after pretreatment and microbial or enzymatic utilization by (13)C nuclear magnetic resonance (NMR) in a perdeuterated ionic liquid solvent system not requiring component isolation. 1D (13)C whole cell wall ionic liquid NMR of natural abundant and (13)C enriched corn stover stem samples suggest that a high level of uniform labeling (>97%) can significantly reduce the total NMR experiment times up to ~220 times. Similarly, significant reduction in total NMR experiment time (~39 times) of the (13)C enriched corn stover stem samples for 2D (13)C-(1)H heteronuclear single quantum coherence NMR was found.

The pyrolysis of softwood (SW) kraft lignin in the presence of NiCl2 and ZSM-5 zeolite as an additive was examined at 700 °C. Gel permeation chromatography (GPC), quantitative 13C and 31P NMR were used to characterize the pyrolysis oil. Based on the results of 13C and 31P NMR for the pyrolysis oils, the use of zeolite during pyrolysis caused the near complete loss of aliphatic hydroxyl and carboxyl groups in the bio-oil and about 80% of methoxyl groups were also eliminated. The zeolite was shown to improve the decomposition of aliphatic hydroxyl groups, carboxyl, methoxyl groups, and ether bonds in the lignin during pyrolysis. In addition, as determined by 13C NMR, the oxygen content in the bio-oil decreased after the use of zeolite. The results of GPC analysis indicated that the addition of H-ZSM-5 zeolite with lignin provided a bio-oil that had ∼10% lower average molecular weight than the pyrolysis product acquired without the additive.

This study examined the chemical structural characteristics of cellulolytic enzyme lignin isolated from switchgrass focusing on comparisons between wild-type control and caffeic acid 3-O-methyltransferase (COMT) down-regulated transgenic line. Nuclear magnetic resonance (NMR) techniques including 13C, 31P, and two-dimensional 13C-1H heteronuclear single quantum coherence (HSQC) as well as gel permeation chromatography (GPC) were employed. Compared to the wild-type, the COMT down-regulated transgenic switchgrass lignin demonstrated a decrease in syringyl (S): guaiacyl (G) ratio and p-coumarate:ferulate ratio, an increase in relative abundance of phenylcoumaran unit, and a comparable content of total free phenolic OH groups along with formation of benzodioxane unit. In addition, COMT down-regulation had no significant effects on the lignin molecular weights during its biosynthesis process.

Abstract The main objective of the present study is to investigate the effect of a Lewis acid, Bronsted acid, and their combined use on the hydrothermal liquefaction of lignocellulosic biomass. Hydrothermal liquefaction of teak wood was conducted at 250, 300 and 350 °C for 15, 30 and 60 min. Hydrothermal liquefaction of teak wood was carried out at 300 °C for 30 min (the best optimum conditions) without and with the use of Mg(ClO4)2, HClO4, and HClO4/Mg(ClO4)2 at various loadings (2–10 mmol/15 g wood). The highest bio-oil yield was obtained with the non-catalytic run. All tested catalysts have negative effect on bio-oil yields. The bio-oil yields generally decreased with increasing the catalyst loadings. The deoxygenation degree in bio-oils changed depending on the type of catalyst and loading. A high degree of de-oxygenation took place with Mg(ClO4)2 catalysts. An increased catalyst loading led to decreased aromatic contents of bio-oils catalysed by either Mg(ClO4)2 or HClO4. The use of a catalyst increased total naphtha fractions in bio-oils. The highest heating value of the bio-oil was estimated to be approximately 30 MJ/kg. Gas chromatography–mass spectrometry analysis revealed that the bio-oils from the non-catalytic and catalytic runs contained aldehydes, ketones, phenols, acids, esters and alcohols. The relative yields of the oxygenated compounds were affected by catalyst type.

Abstract Catalytic conversion of rubber wastes to produce an alternative fuel resource is a promising approach to dispose of solid wastes and address environmental issues. In this study, catalytic fast pyrolysis (CFP) of rubber wastes over acidic zeolites was conducted, and the effect of SiO2/Al2O3 mole ratio of USY zeolites on the formation of aromatic hydrocarbons was explored. Experimental results indicated that alkenes and aromatic hydrocarbons were the main pyrolytic products obtained from fast pyrolysis of rubber wastes, and the pyrolysis temperature played a vital role in the formation of aromatics with the highest concentration achieved at 750 °C. Moreover, catalyst types also affected the catalytic degradation of rubber wastes since limonene was completely decomposed in the presence of zeolites. Compared to SAPO-34, zeolites with higher external surface area, stronger Bronsted acid sites, and larger pore size, including USY, HY, and Hβ, were more effective in the production of aromatic hydrocarbons with the highest content obtained from USY catalyzed run. Given the observed effect of SiO2/Al2O3 mole ratio of USY zeolites on the formation of aromatic hydrocarbons during the CFP of rubber wastes, USY with low SiO2/Al2O3 ratio of 5.3 was more beneficial to the generation of aromatic hydrocarbons, while that with higher SiO2/Al2O3 mole ratio (11.5) facilitated the formation of alkenes. Simultaneously, the product distribution of aromatic hydrocarbons obtained from CFP of rubber wastes over USY zeolites was dominated by xylenes, alkylbenzenes, and toluene, and USY with SiO2/Al2O3 mole ratio of 5.3 was more active in the production of toluene and xylenes.