Abstract
The aim of the study was to assess the effectiveness of microwave pretreatment combined with acid catalysis in the decomposition of various types of biomass (pine and beech chips and hemp stems). It was clearly demonstrated that sulfuric acid was a catalyst enabling the most effective decomposition of the tested plant biomass, guaranteeing the highest concentrations of simple sugars released. Acid catalysis with 1% v/v sulfuric acid combined with microwave radiation provided high glucose concentrations of 89.8 ± 3.4, 170.4 ± 2.4 and 164.6 ± 4.6 mg/g for pine chips, beech chips and hemp stems, respectively. In turn, the use of nitric acid promoted the degradation of hemicellulose, which resulted in high concentrations of galactose and xylose, i.e., 147.6 ± 0.6, 163.6 ± 0.4 and 134.9 ± 0.8 mg/g of pine chips, beech chips and hemp stems, respectively, while glucose levels remained relatively low. It was also demonstrated that the undesirable dehydration of sugars such as glucose and xylose is more pronounced in sulfuric acid than nitric acid processes. The use of H2SO4 and increased pressure generated 5-hydroxymethylfurfural (5-HMF) and furfural at a concentration of ca. 12 and 6 mg/g, 10 and 45 mg/g and 14 and 30 mg/g, of pine chips, beech chips and hemp shoots, respectively. Our studies confirmed the usefulness of the combined use of microwaves and acid catalysis in the degradation of softwood, hardwood and non-wood plant biomass. It should be emphasized that obtaining high concentrations of released simple sugars (as potential substrates in biosynthesis), while maintaining low levels of toxic by-products (inhibitors), requires precise selection of process parameters such as pressure, exposition time and type of acid catalyst.
Highlights
Worldwide demand for energy increases with the development of the global economy.Currently, energy is mainly produced from fossil fuels, whose resources are limited
Microwave-assisted decomposition of cellulose from pine and beech chips was most effective when using sulfuric acid, which was reflected in the highest glucose concentration at 93 PSI
(54 PSI) promoted the decomposition of hemicellulose, which resulted in an increased concentration of galactose and xylose, while a higher pressure of 152 PSI increased sugar dehydration, which resulted in reduced carbohydrate concentration (Figure 1A,C)
Summary
Energy is mainly produced from fossil fuels, whose resources are limited. Their use generates huge amounts of carbon dioxide, nitrogen and sulfur oxides, and dust that contribute to air pollution. An alternative which would limit these negative effects is the production of energy from renewable sources such as plant-derived raw materials containing carbohydrates [1]. The first generation biofuel production technologies, such as the production of ethanol from raw materials containing starch or sucrose, are well known and widely used on an industrial scale. The growing use of these raw materials for biofuel production may lead to higher food and feed prices and, higher animal product prices. One of the solutions to this problem is the widespread production of second-generation biofuels by conversion of non-food plant biomass [2]
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