Pretreatment of South African sugarcane bagasse using a low-cost protic ionic liquid: a comparison of whole, depithed, fibrous and pith bagasse fractions

Abstract

BackgroundSugarcane bagasse is an abundant and geographically widespread agro-industrial residue with high carbohydrate content, making it a strong candidate feedstock for the bio-based economy. This study examines the use of the low-cost protic ionic liquid triethylammonium hydrogen sulfate ([TEA][HSO4]) to fractionate a range of South African sugarcane bagasse preparations into a cellulose-rich pulp and lignin. The study seeks to optimize pretreatment conditions and examine the necessity of applying a depithing step on bagasse prior to pretreatment.ResultsPretreatment of five bagasse preparations, namely whole, industrially depithed, laboratory depithed (short and long fiber) and pith bagasse with [TEA][HSO4]:[H2O] (4:1 w/w) solutions produced highly digestible cellulose-rich pulps, as assessed by residual lignin analysis and enzymatic hydrolysis. Pretreatment under the optimized condition of 120 °C for 4 h produced a pretreated cellulose pulp with up to 90% of the lignin removed and enabled the release of up to 69% glucose contained in the bagasse via enzymatic hydrolysis. Glucose yields from whole and depithed bagasse preparations were very similar. Significant differences in lignin recovery were obtained for laboratory depithed bagasse compared with whole and industrially depithed bagasse. The silica-rich ash components of bagasse were seen to partition mainly with the pulp, from where they could be easily recovered in the post-hydrolysis solids.ConclusionsThe five bagasse preparations were compared but did not show substantial differences in composition or cellulose digestibility after pretreatment. Evidence was presented that a depithing step appears to be unnecessary prior to ionoSolv fractionation, potentially affording significant cost and energy savings. Instead, lignin re-deposition onto the pulp surface (and, in turn, particle size and shape) appeared to be major factors affecting the conditioning of bagasse with the applied IL. We show that pith bagasse, a common by-product of paper making, can be successfully conditioned for high glucose release while allowing recovery of lignin and silica-rich ash. The glucose yields obtained for bagasse using [TEA][HSO4]-water mixtures were ~ 75% as high as for conventional aprotic ionic liquids such as [Emim][OAc]; this result is highly promising for commercialization of ionoSolv processing given [TEA][HSO4] is 40 times less expensive, thermally stable and recyclable.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1247-0) contains supplementary material, which is available to authorized users.

Combining Cost‐Efficient Cellulose and Short‐Chain Carboxylic Acid Production: The Polyoxometalate (POM)‐Ionosolv Concept

“…The higher residual lignin content is likely an obstacle to achieving higher saccharification yield from the pulps, expecially for pine. While it has been shown that pine delignification by ionosolv solutions can be enhanced by applying temperatures above 150 °C and using different cations, the change in conditions may negatively affect FA‐yield and selectivity as shown for beech and an increased reaction temperature (Table ). Although the cellulose content was increased compared to untreated biomass (41 %), it is low if the target is material applications (>80 %, with the lignin content being as low as possible), hence improved delignification is a target for further optimisation.…”

“…Initially, there was a focus on cellulose dissolving ionic liquids, most prominently 1‐ethyl‐3‐methylimidazolium acetate, [EMIM][OAc] . More recently, a subclass of ionic liquids was discovered that has a high activity for separating cellulose and lignin but do not dissolve cellulose . This class of ionic liquids comprises inexpensive (∼$1.24/kg) and chemically stable ionic liquids containing hydrogen sulfate anions .…”

Characterisation of cellulose pulps isolated from Miscanthus using a low-cost acidic ionic liquid

“…This IonoSolv ionic liquid is protic, acidic and effective in the presence of significant amounts of water. While the fractionation effect has been demonstrated in multiple conditions on a range of feedstocks (Chambon et al 2018(Chambon et al , 2019Gschwend et al 2019;Weigand et al 2017), and the lignin has been characterised in detail (Brandt et al 2015), the material properties of the resulting cellulose pulp remain to be determined. To fill this gap, we prepared a number of ionoSolv cellulose pulps from the energy crop Miscanthus 9 giganteus, a highyielding perennial grass that is a potential biorefinery feedstock, and analysed their polymer molar weight, material porosity, particle size and the cellulose crystallinity.…”

One-Pot Deconstruction and Conversion of Lignocellulose Into Reducing Sugars by Pyridinium-Based Ionic Liquid–Metal Salt System

“…The reports exhibiting deconstruction along with saccharification follow a two-step protocol; at first, IL is used to separate lignin from cellulose, and then acids, alkalis, or enzymes are applied on the extracted delignified cellulose to yield sugars (Kassaye et al, 2017;Rocha et al, 2017;da Costa Lopes et al, 2018;Semerci and Guler, 2018). Some recent reports revealed the simultaneous removal of lignin and sugars from biomass using Brønsted acidic ILs but at high temperatures: 120-170 • C (Gschwend et al, 2012;Chambon et al, 2018).…”