Ionic liquids (ILs): advances in biorefinery for the efficient conversion of lignocellulosic biomass (original) (raw)

Progress on the pre-treatment of lignocellulosic biomass employing ionic liquids

Renewable and Sustainable Energy Reviews, 2019

The effective pre-treatment methods are required for the destruction of the complex biomass structure to economically produce high grade fuels and valuable platform chemicals. Ionic liquids have high potential for energy efficient biomass pre-treatment due to their low vapour pressure, emission profile, recyclability and tuneable properties; some ionic liquids can even be prepared from renewable biomass feedstocks. However, a number of issues currently impede the large scale uptake of ionic liquids including their cost of production, detailed understanding the macro, micro and molecular level deconstruction mechanisms which inhibits process optimisation and modelling, and the need for techno-economic astable sessment on large scale trials. So far, laboratory to bench scale IL pre-treatments of various lignocellulosic biomasses were studied by changing various process parameters where the aims were to investigate the biomass dissolution mechanism and understand the pretreatment performance of ILs. This review outlines current research gaps and potential applications for ionic liquids in the destruction of biomass into its components followed by separation of lignin, hemicellulose and cellulose rich fractions.

Assessment of the effect of ionic liquid pretreatments on various lignocellulosic biomasses

In this study, the effect of various ionic liquid pretreatments on lignocellulosic biomasses of different natures, such as sago hampas, sugarcane bagasse and rice husk, was assessed. The ionic liquids applied were 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc), and 1-ethyl-3-methylimidazolium diethyl phosphate ([EMIM]DEP). The ionic liquid pretreatments caused varying extents of structural disruption to the lignocelluloses, as a result of the dissolution action of the ionic liquids followed by the regeneration of cellulosic-rich material. Among the ionic liquid pretreatments, [EMIM]OAc-pretreated biomasses had the highest percentage of conversion. The starchy sago hampas has consistently showed the highest digestibility (45 – 59% enzymatic conversion) among the biomasses for all the ionic liquid pretreatments. The sugarcane bagasse and rice husk that are more recalcitrant were better pretreated with [EMIM]OAc than the other two ionic liquids. To consolidate the findings of structural disruption that improves digestibility, structural characterisation via Fourier transform-infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) were conducted for sugarcane bagasse and rice husk. The findings demonstrated that higher degree of structural disruption enhanced biomass conversion in enzymatic saccharification. The study has shown that ionic liquid pretreatment is a mediating step for the production of added-value compounds with significant economical potential.

Ionic liquid based pretreatment of lignocellulosic biomass for enhanced bioconversion

Bioresource Technology, 2020

Lignocellulosic biomass is the most plentiful renewable biomolecule and an alternative bioresource for the production of biofuels and biochemicals in biorefineries. But biomass recalcitrance is a bottleneck in their usage, thus necessitating their pretreatment for hydrolysis. Most pretreatment technologies, result in toxic by-products or have lower yield. Ionic liquids (ILs) have successfully advanced as 'greener and recyclable' alternatives to volatile organic solvents for lignocellulosic biomass dissolution. This review covers recent developments made in usage of IL-based techniques with focus on biomass breakdown mechanism, process parameter design, impact of cation and anion groups, and the advantageous impact of ILs on the subsequent processing of the fractionated biomass. Progress and barriers for large-scale commercial usage of ILs in emerging biorefineries were critically evaluated using the principles of economies of scale and green chemistry in an environmentally sustainable way.

Design of low-cost ionic liquids for lignocellulosic biomass pretreatment

The cost of ionic liquids (ILs) is one of the main impediments to IL utilization in the cellulosic biorefinery, especially in the pretreatment step. In this study, a number of ionic liquids were synthesized with the goal of optimizing solvent cost and stability whilst demonstrating promising processing potential. To achieve this, inexpensive feedstocks such as sulfuric acid and simple amines were combined into a range of protic ionic liquids containing the hydrogen sulfate [HSO 4 ] − anion. The performance of these ionic liquids was compared to a benchmark system containing the IL 1-ethyl-3-methylimidazolium acetate [C 2 C 1 im][OAc].

Efficient biomass pretreatment using ionic liquids derived from lignin and hemicellulose

Ionic liquids (ILs), solvents composed entirely of paired ions, have been used in a variety of process chemistry and renewable energy applications. Imidazolium-based ILs effectively dissolve biomass and represent a remarkable platform for biomass pretreatment. Although efficient, imidazolium cations are expensive and thus limited in their large-scale industrial deployment. To replace imidazolium-based ILs with those derived from renewable sources, we synthesized a series of tertiary amine-based ILs from aromatic aldehydes derived from lignin and hemicellulose, the major by- products of lignocellulosic biofuel production. Compositional analysis of switchgrass pretreated with ILs derived from vanillin, p-anisaldehyde, and furfural confirmed their efficacy. Enzymatic hydrolysis of pretreated switchgrass allowed for direct compari- son of sugar yields and lignin removal between biomass-derived ILs and 1-ethyl-3-methylimidazolium acetate. Although the rate of cellulose hydrolysis for switchgrass pretreated with biomass- derived ILs was slightly slower than that of 1-ethyl-3-methylimida- zolium acetate, 90–95% glucose and 70–75% xylose yields were obtained for these samples after 72-h incubation. Molecular mod- eling was used to compare IL solvent parameters with experimen- tally obtained compositional analysis data. Effective pretreatment of lignocellulose was further investigated by powder X-ray diffrac- tion and glycome profiling of switchgrass cell walls. These studies showed different cellulose structural changes and differences in hemicellulose epitopes between switchgrass pretreatments with the aforementioned ILs. Our concept of deriving ILs from lignocel- lulosic biomass shows significant potential for the realization of a “closed-loop” process for future lignocellulosic biorefineries and has far-reaching economic impacts for other IL-based process tech- nology currently using ILs synthesized from petroleum sources.

Room temperature ionic liquids as emerging solvents for the pretreatment of lignocellulosic biomass

Biotechnology and Bioengineering, 2011

Room temperature ionic liquids (RTILs) are emerging as attractive and green solvents for lignocellulosic biomass pretreatment. The unique solvating properties of RTILs foster the disruption of the 3D network structure of lignin, cellulose, and hemicellulose, which allows high yields of fermentable sugars to be produced in subsequent enzymatic hydrolysis. In the current review, we summarize the physicochemical properties of RTILs that make them effective solvents for lignocellulose pretreatment including mechanisms of interaction between lignocellulosic biomass subcomponents and RTILs. We also highlight several recent strategies that exploit RTILs and generate high yields of fermentable sugars suitable for downstream biofuel production, and address new opportunities for use of lignocellulosic components, including lignin. Finally, we address some of the challenges that remain before large-scale use of RTILs may be achieved.

Ionic liquid solvent properties as predictors of lignocellulose pretreatment efficacy

Green Chemistry, 2010

Effective pretreatment of lignocellulosic biomass is vital to its bioconversion to a usable liquid fuel. A growing body of work has focused on using room temperature ionic liquids (RTILs) to pretreat lignocellulose for subsequent fermentation. However, little is known about the physicochemical parameters of RTILs that promote effective pretreatment. In this work we examine the relationship between the Kamlet- a, b, and p* solvent polarity parameters of different RTILs ([Emim][OAc], [Bmim][OAc], and [Bmim][MeSO 4 ]) and effective pretreatment of lignocellulosic biomass. We find the b parameter is an excellent predictor of pretreatment efficacy. Acetate containing RTILs (b > 1.0) remove >32% of lignin from maple wood flour and significantly reduce cellulose crystallinity, resulting in >65% glucose yields after 12 h cellulase hydrolysis. Pretreatment in [Bmim][MeSO 4 ] (b = 0.60) results in the removal of only 19% of the wood flour's lignin with no decrease in crystallinity, and no improvement in sugar yield over untreated wood flour. The addition of water and the dilution of the acetate anion with the methyl sulfate anion decrease the b value and subsequently have a negative impact on lignin extraction, cellulose crystallinity, and sugar yields.

Role of Ionic Liquids in the Processing of Lignocellulosic Biomass

Multifaceted Protocols in Biotechnology, Volume 2, 2021

This chapter discusses the treatment of palm oil empty fruit bunch using ionic liquids (ILs) pretreatment. By mixing IL and cellulase enzyme (IL-E) in a single pot, the empty fruit bunch (EFB) was pretreated with simultaneous fermentation. Choline acetate [Ch][Ac], which has excellent biological compatibility and renewability, has been used for pretreatment. Chemical analysis, electron scanning microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) were used to characterize the EFB and its hydrolysate. After 24 and 48 h of enzymatic hydrolysis, sugar yield improved from 0.058 g/g EFB in the crude (untreated) sample to 0.283 and 0.62 06 g/g in the IL-E phase. EFB hydrolysate demonstrates suitability for the production of ethanol (EtOH) with a yield of 0.275 g EtOH/g EFB in the presence of [Ch][Ac] without additional nutrients, compared to the low yield without IL pretreatment.