Effect of Acid Pretreatment on the Primary Products of Biomass Fast Pyrolysis

Abstract

A high load of inorganics in raw lignocellulosic biomass is known to inhibit the yield of bio-oil and alter the chemical reactions during fast pyrolysis of biomass. In this study, palm kernel shell (PKS), an agricultural residue from palm oil production, and two other woody biomass samples (mahogany (MAH) sawdust and iroko (IRO) sawdust) were pretreated with distilled water or an acidic solution (either acetic, formic, hydrochloric (HCl) or sulfuric acid (H2SO4)) before fast pyrolysis in order to investigate its effect on the primary products and pyrolysis reaction pathways. The raw and pretreated PKS, MAH and IRO were pyrolysed at 600 °C and 5 s with a micro-pyrolyser connected to a gas chromatograph–mass spectrometer/flame ionisation detector (GC-MS/FID). Of the leaching solutions, HCl was the most effective in removing inorganics from the biomass and enhancing the primary pyrolysis product formed compared to the organic acids (acetic and formic acid). The production of levoglucosan was greatly improved for all pretreated biomasses when compared to the original biomass but especially after HCl pretreatment. Additionally, the relative content of the saccharides was maximised after pretreatment with H2SO4, which was due to the increased production of levoglucosenone. The relative content of the saccharides increased by over 70%. This increase may have occurred due to a possible reaction catalysed by the remaining acid in the biomass. The production of furans, especially furfural, was increased for all pretreatments but most noticeable when H2SO4 was used. However, the relative content of acids and ketones was generally reduced for PKS, MAH and IRO across all leaching solutions. The relative content of the phenol-type compound decreased to a large extent during pyrolysis after acid pretreatment, which may be attributed to dehydration and demethoxylation reactions. This study shows that the production of valuable chemicals could be promoted by pretreatment with different acid solutions.

Recent Advances in the Technologies and Catalytic Processes of Ethanol Production

“…The research on the bioconversion of lignocellulosic byproduct corn stover into the value-added fermentative product L-lactic acid using the furfural tolerant Enterococcus mundtii WX1 and Lactobacillus rhamnosus SCJ9 showed that corn stover pretreated with 1% (v/v) sulfuric acid was selected for L-LA fermentation and shows the highest efficacy of fermentable sugar with the optimal conditions achieved for the release of glucose and xylose at 24.5 g/L and 11.2 g/L, respectively, from 100 g/L pretreated corn stover at 121 • C for 30 min [102]. A similar result was presented by other researchers reported in the study of tobacco stem waste [103], palm kernel shell [104], sugarcane bagasse [105], and oil palm frond bagasse [106] that the dilute acid for chemical pretreatment is effective to attain high reactivity and generates protons that have a quick diffusion which substantially enhances the hydrolysis of amorphous cellulose chains and the solubilization of hemicellulose.…”

Coproduction of 1,4:3,6-Dianhydro-α-d-glucopyranose, Furfural, and Formic Acid through Oxalic Acid-Assisted Staged Fast Pyrolysis of Cellulose

“…In addition to the above inorganic acid/salt catalysts, organic acids possess milder acidity and have also been employed to control the cellulose pyrolysis process. Commonly, organic acids are utilized as solutions for leaching and impregnation pretreatments to eliminate inorganic components and alter the properties of biomass, thus enhancing the quality of bio-oil. − Rodríguez-Machín et al utilized citric acid to leach sugar cane residues and observed that citric acid effectively removed the inorganic components, leading to notable changes in the physicochemical properties of the feedstock. This approach also modified the pyrolytic properties of biomass and promoted the formation of anhydrosugars at the expense of furans and ketones.…”

Primary Products from Fast Co-Pyrolysis of Palm Kernel Shell and Sawdust

“…However, these processes are complex and costly due to the equipment requirement and the catalysts needed for the successful upgrade [4,5]. The pretreatment of biomass with dilute acid solutions has also been used to improve the quality and minimise the negative effects of inorganic materials during the fast pyrolysis of biomass [6][7][8]. Recently, attention has been directed towards the co-pyrolysis of different biomasses [9][10][11][12].…”

“…Furthermore, biomasses differ in their compositions and physical structures, and this can influence the quality of the bio-oil [3]. Palm kernel shell (PKS), for example, has a high lignin content (≈58 wt%) [8,24] compared to woody biomass (15-40%) [26], while woody biomass, such as mahogany (MAH), has a higher carbohydrate content (65 wt%) [27]. During the pyrolysis of raw biomass, cellulose and hemicellulose undergo dehydration, depolymerisation, and rearrangement reactions to form anhydrous sugars, furans, and light oxygenate compounds [28], while lignin undergoes depolymerisation, demethylation, and fragmentation reactions to form mainly phenolic-type compounds [29].…”