A review on the production and recovery of sugars from lignocellulosics for use in the synthesis of bioproducts

In this study, concepts of systematic mapping (SM) were used to conduct a literature review covering the research on the production and recovery of sugars from lignocellulosics to synthesize bioproducts, mostly xylose-derived products. The SM approach constitutes a rigorous evidence review methodology used to catalog evidence, identifying knowledge gaps, unknown trends, and research clusters (Cook et al., 1997, James et al., 2016). Our results showed that some classical pretreatment methods (H2SO4 acidolysis and alkaline) are still among the most used methodologies for the initial processing of lignocellulosics. Some other technologies, such as liquid hot water and steam explosion, were used to minimize the production of inhibitors and waste generations related to the use of those classical pretreatments. Other eco-friendly strategies (ultrasonic, gamma irradiation, and ultra-high-pressure pretreatments) were rarely reported in our dataset and have been confined to small-scale operations thus far. The enzymatic hydrolysis stage was mainly conducted using commercial enzyme cocktails, which are more feasible and commonly used in large-scale processes than crude preparations. Physical separation systems (washing, drying, centrifugation, and macro filtration) were used to separate extracts and/or hydrolysates from unconverted biomass and then, in a few cases, purification methods (evaporation, chromatographic separation, crystallization, distillation, and precipitation) were used to separate the sugars from other components. Detoxification strategies were used in both cases. Ethanol was the main sugar-derived product addressed by the papers we assessed, followed by xylooligosaccharides, xylitol, lactic acid, and lipids. On the other hand, some products such as biogas, fatty acid methyl esters, diols, methane, and succinic acid, still constitute a minor fraction of the products targeted. The analysis of keywords revealed that many co-occurrences were found among most enzymatic activities and sugar-recovery methods, but a weak co-occurrence network was identified among pretreatment methods and sugar-derived products.

Automated summary

This study conducted a literature review using the systematic mapping approach to examine the production and recovery of sugars from lignocellulosics for bioproduct synthesis. The results showed that classical pretreatment methods are still widely used, but there are also emerging eco-friendly strategies. Enzymatic hydrolysis stage mainly utilizes commercial enzyme cocktails, and physical separation systems and purification methods are employed for sugar separation. Ethanol is the most discussed sugar-derived product.