TL;DR: An extensive research is still required for the development of new and more efficient pretreatment processes for lignocellulosic feedstocks yielding promising results.
Abstract: Lignocellulosic feedstock materials are the most abundant renewable bioresource material available on earth. It is primarily composed of cellulose, hemicellulose, and lignin, which are strongly associated with each other. Pretreatment processes are mainly involved in effective separation of these complex interlinked fractions and increase the accessibility of each individual component, thereby becoming an essential step in a broad range of applications particularly for biomass valorization. However, a major hurdle is the removal of sturdy and rugged lignin component which is highly resistant to solubilization and is also a major inhibitor for hydrolysis of cellulose and hemicellulose. Moreover, other factors such as lignin content, crystalline, and rigid nature of cellulose, production of post-pretreatment inhibitory products and size of feed stock particle limit the digestibility of lignocellulosic biomass. This has led to extensive research in the development of various pretreatment processes. The major pretreatment methods include physical, chemical, and biological approaches. The selection of pretreatment process depends exclusively on the application. As compared to the conventional single pretreatment process, integrated processes combining two or more pretreatment techniques is beneficial in reducing the number of process operational steps besides minimizing the production of undesirable inhibitors. However, an extensive research is still required for the development of new and more efficient pretreatment processes for lignocellulosic feedstocks yielding promising results.
TL;DR: In this article, the authors discuss the various pretreatment strategies currently in use and provide an overview of their utilization for the isolation of high-value bio-polymeric components, including cellulose, hemicellulose and lignin.
Abstract: Lignocellulosic biomass (LCB) is the most abundantly available bioresource amounting to about a global yield of up to 1.3 billion tons per year. The hydrolysis of LCB results in the release of various reducing sugars which are highly valued in the production of biofuels such as bioethanol and biogas, various organic acids, phenols, and aldehydes. The majority of LCB is composed of biological polymers such as cellulose, hemicellulose and lignin, which are strongly associated with each other by covalent and hydrogen bonds thus forming a highly recalcitrant structure. The presence of lignin renders the bio-polymeric structure highly resistant to solubilization thereby inhibiting the hydrolysis of cellulose and hemicellulose which presents a significant challenge for the isolation of the respective bio-polymeric components. This has led to extensive research in the development of various pretreatment techniques utilizing various physical, chemical, physicochemical and biological approaches which are specifically tailored towards the source biomaterial and its application. The objective of this review is to discuss the various pretreatment strategies currently in use and provide an overview of their utilization for the isolation of high-value bio-polymeric components. The article further discusses the advantages and disadvantages of the various pretreatment methodologies as well as addresses the role of various key factors that are likely to have a significant impact on the pretreatment and digestibility of LCB.
TL;DR: In this article, the application of selected emerging technologies such as ionizing and non-ionizing radiation, pulsed electrical field, ultrasound and high pressure are reviewed as promising technologies in the valorization of lignocellulosic biomass.
TL;DR: The selection of an effective and efficient pretreatment method discussed in the review and its process optimization can significantly reduce the production of inhibitory compounds and may lead to enhanced production of fermentable sugars and biochemicals.
TL;DR: Combination of relevant factors and specific measurements gathering simultaneously structural and chemical information should help to develop robust and efficient LB conversion processes into bioproducts.
Abstract: Lignocellulosic biomass (LB) is an abundant and renewable resource from plants mainly composed of polysaccharides (cellulose and hemicelluloses) and an aromatic polymer (lignin). LB has a high potential as an alternative to fossil resources to produce second-generation biofuels and biosourced chemicals and materials without compromising global food security. One of the major limitations to LB valorisation is its recalcitrance to enzymatic hydrolysis caused by the heterogeneous multi-scale structure of plant cell walls. Factors affecting LB recalcitrance are strongly interconnected and difficult to dissociate. They can be divided into structural factors (cellulose specific surface area, cellulose crystallinity, degree of polymerization, pore size and volume) and chemical factors (composition and content in lignin, hemicelluloses, acetyl groups). Goal of this review is to propose an up-to-date survey of the relative impact of chemical and structural factors on biomass recalcitrance and of the most advanced techniques to evaluate these factors. Also, recent spectral and water-related measurements accurately predicting hydrolysis are presented. Overall, combination of relevant factors and specific measurements gathering simultaneously structural and chemical information should help to develop robust and efficient LB conversion processes into bioproducts.
342 citations
Cites background from "Recent updates on different methods..."
...That is why some pre-treatment steps are mandatory to make cellulose more accessible by changing the physical and/or the chemical structure of LB and facilitating the conversion of polysaccharides into fermentable sugars (Zhao et al., 2012a; Kumar and Sharma, 2017)....
TL;DR: In this article, the authors present an insight on currently available pre-treatment technologies for deconstruction and fractionation of lignocellulosic biomass for development of LCL feedstock based biorefinery.
TL;DR: This paper reviews process parameters and their fundamental modes of action for promising pretreatment methods and concludes that pretreatment processing conditions must be tailored to the specific chemical and structural composition of the various, and variable, sources of lignocellulosic biomass.
6,110 citations
"Recent updates on different methods..." refers methods in this paper
...During this pretreatment, the hydrolysis of hemicellulose into glucose and xylose monomers is carried out by the acetic acid produced from the acetyl groups of hemicellulose; hence this process is also termed as autohydrolysis (Mosier et al. 2005)....
TL;DR: Simultaneous saccharification and fermentation effectively removes glucose, which is an inhibitor to cellulase activity, thus increasing the yield and rate of cellulose hydrolysis, thereby increasing the cost of ethanol production from lignocellulosic materials.
5,860 citations
"Recent updates on different methods..." refers background in this paper
...Although the biological pretreatment is highly intriguing, the rate of hydrolysis of lignocellulosic fractions is too slow which severely hampers to be foreseen as a potential pretreatment method at an industrial scale (Sun and Cheng 2002)....
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...The temperature range is between 140 and 210 °C with a reaction time of 90 min and percolation rate is 5 mL/min after which the ammonia is recycled (Sun and Cheng 2002; Kim et al. 2008)....
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...The temperature range is between 140 and 210 °C with a reaction time of 90 min and percolation
rate is 5 mL/min after which the ammonia is recycled (Sun and Cheng 2002; Kim et al....
[...]
...Although the biological pretreatment is highly intriguing, the rate of hydrolysis of lignocellulosic fractions is too slow which severely hampers to be foreseen as a potential pretreatment method at an industrial
scale (Sun and Cheng 2002)....
"Recent updates on different methods..." refers background in this paper
...The complex anionic species are formed between X− and either a Lewis or Brønsted acid Y (z refers to the number of Y molecules that interact with the anion) (Smith et al. 2014)....
TL;DR: Steam pretreatment, lime pret treatment, liquid hot water pretreatments and ammonia based Pretreatments are concluded to be pretreatment with high potentials, providing an improved accessibility of the cellulose for hydrolytic enzymes.
3,618 citations
"Recent updates on different methods..." refers background in this paper
...The vessel is heated to the required temperature and kept for several minutes at high temperatures (Hendricks and Zeeman 2009)....
TL;DR: This paper reviews the most interesting technologies for ethanol production from lignocellulose and it points out several key properties that should be targeted for low-cost and advanced pretreatment processes.
3,580 citations
"Recent updates on different methods..." refers background in this paper
...ARP is capable of solubilizing hemicellulose but cellulose remains unaffected (Alvira et al. 2010)....