Quantitative recovery and regeneration of acidic ionic liquid 1-butyl-3-methylimidazolium hydrogen sulphate via industrial strategy for sustainable biomass processing

https://doi.org/10.1016/j.biortech.2021.124726Get rights and content

Highlights

  • Acidic ionic liquid quantitatively recovered and regenerated.

  • Bmim[HSO4] recovery ratio reached 96.0%.

  • Energy consumption of specific Bmim[HSO4] recovery approached 9.0 kwh/kg.

  • Recovery cost for Bmim[HSO4] less than 1% of its purchasing price.

Abstract

Quantitative recovery is necessary for scale-up application of acidic ionic liquids (AILs). Ultrafiltration and bipolar membrane electrodialysis (BMED) was employed for the recovery and regeneration of acidic ionic liquid 1-butyl-3-methylimidazolium hydrogen sulphate (Bmim[HSO4]) after biomass pretreatment. Ultrafiltration was designed for the purification of BMED feed solution. During BMED treatment, Bmim+ retention with OH generation occurred in mixing section and SO42− immigration with H+ generation occurred in aciding section. Resulting aqueous Bmim[OH] in mixing section and H2SO4 in aciding section could be utilized for quantitative synthesis of Bmim[HSO4]. Influence of BMED operating mode and major parameters including BMED feed concentration and current density of BMED module were studied in detail. The highest recovery ratio for Bmim+ and SO42− reached 96.2% and 96.0%. And the lowest energy consumption of specific Bmim[HSO4] recovery approached 9.0 kwh/kg. Insight gained from this study suggested a sustainable biomass processing methodology using AILs.

Introduction

Lignocellulosic biomass has been widely studied for its stable and renewable sources with diverse conversion approaches (Li et al., 2020, Tang et al., 2015a, Tang et al., 2015b, Wang et al., 2016). Pretreatment is necessary for following high-value conversion of carbohydrates in biomass (Liu et al., 2020, Liu et al., 2019). Studies have been targeted to improve the sustainability and to cut down pollution discharging of biomass pretreatment (Liheng et al., 2014, Liu et al., 2013). And processing using solvent ionic liquids has been considered green conversion route for biomass due to the highlighted features of ionic liquids, such as structurally designable, thermo-stable, non-volatile, recyclable and so on (Yu et al., 2011, Yu et al., 2012).

Acidic ionic liquids (AILs) have been studied for catalytic chemistry (Rajabi et al., 2020), biofinery (Cheng et al., 2018) and so on (Jiang et al., 2020). AILs could serve as catalyst and solvent due to the existence of acid site, which makes AILs fine mediums for biomass fractionation and conversion (Asim et al., 2019). Da Costa Lopes (Da et al., 2018) used aqueous solution of 1-ethyl-3-methylimidazolium hydrogen sulfate (Emim[HSO4]) to hydrolyze hemicellulose fraction of wheat straw into pentose. And 80.5% wt % yield of pentose could be obtained. Brandt (Brandt et al., 2011) reported up to 90% glucose of miscanthus could be released by enzymatic hydrolysis after pretreatment with aqueous 1-butyl-3-methylimidazolium hydrogen sulfate (Bmim[HSO4]). Besides, [Bmim][HSO4] could serve as effective solvent and catalyst for in-situ transesterification of wet algae with 95% yield of crude biodiesel in 30 min at 200 °C (Sun et al., 2017). [Bmim][HSO4] also showed fine electrochemical stability for nanocrystalline chromium electrodeposition (He et al., 2015). And [Bmim][HSO4] could also be a fine hydrolysis medium for cellulose nanocrystal production (Mao et al., 2015).

Although plenty of applications have been performed in biomass-related research using AILs, lack of efficient recovery strategy still restricts the scale-up utilization of AILs for biomass processing (Amarasekara, 2016). Complicated electrolyte composition of AILs such as Emim[HSO4] and Bmim[HSO4] with disparate loss of each ions in AILs make the quantitative recovery and regeneration of these AILs a tough task after the dissolution or catalysis process. Commercial utilization of AILs requires recovery and recycling techniques possessing mature technology, low processing cost and long service time, which could be provide by membrane-based techniques such as ultrafiltration (Zhang and Fu, 2018), nanofiltration(Van der Bruggen et al., 2008), pervaporation (León et al., 2020) and electrodialysis (De Jaegher et al., 2020).

Ultrafiltration (UF) works well in the purification for aqueous solution by the interception of macromolecule impurities (Gao et al., 2019), which could be effective for the removal of derivate generated by pretreatment. Besides, electrodialysis has been proven feasible for ions recovery and separation from aqueous solution (Gmar and Chagnes, 2019). And bipolar membrane electrodialysis (BMED) could be considerable for AILs recovery task due to the selective transfer of ions with generation of H+ and OH in different section by water dissociation at the interfacial hydrophil layer of bipolar membrane (Melnikov et al., 2020). It’s clear that HSO4 would get ionized into H+ and SO42− in aqueous solution. And it can be achieved in BMED module that H+ gets neutralized with OH generated by bipolar membrane and OH gets enriched with the cation existed in aqueous solution. While SO42− could be transferred from original section through anion exchange membrane to another section and got enriched in the subsequent section with the H+ generated by bipolar membrane. Thus cation and SO42− of AILs could get separated in different section after BMED treatment, which lays the foundation for AILs regeneration. However, very few studies have been focused on the recovery and regeneration of AILs after catalysis or dissolution tasks (Khalafi-Nezhad and Mohammadi, 2013), especially using membrane-based UF and BMED.

Therefore, this study was conducted to quantitatively recovery and regenerate acidic ionic liquid Bmim[HSO4] using UF and BMED after biomass pretreatment. Bmim[HSO4]-water mixture was employed as the solvent for miscanthus pretreatment and aqueous Bmim[HSO4] obtained by pretreatment was purified by UF treatment. A lab-scale three-compartment BMED module was set up for the recovery and regeneration of Bmim[HSO4] with UF filtrate as BMED feed solution. Influence of BMED current density and feed concentration on Bmim[HSO4] recovery performance was studied in detail. Comparison between intermittent BMED operation mode and semi-continuous BMED operation mode was also performed. Besides, recycling performance of regenerated Bmim[HSO4] samples was determined. The economic feasibility of UF-BMED based Bmim[HSO4] recovery strategy was assessed according to recovery cost calculated with variational UF-BMED operating conditions.

Section snippets

Materials and biomass pretreatment

Miscanthus powder with the size of 40–60 mesh was obtained after the air-drying, sieving and dewaxing for original miscanthus. Dewaxing of miscanthus powder was performed in soxhlet extractor using the mixture of ethanol and benzene (1:2 of volume ratio) with the extracting condition of 6 cycles per hour. Ionic liquid 1-butyl-3-methylimidazolium hydrogen sulphate (Bmim[HSO4]) was supplied by Lanzhou Yulu Fine Chemical Co. Ltd. Other chemicals employed in this research were reagent-grade and

Pretreatment and ultrafiltration treatment

Results for miscanthus pretreatment and following purification performance of UF treatment were listed in Fig. 2. It can be seen that 24.8% of cellulose, 63.4% of hemicellulose and 61.7% of lignin was removed from miscanthus powder after pretreatment with Bmim[HSO4]-water mixture. And 24.5% of lignin in miscanthus powder got precipitated after pretreatment. Bmim[HSO4]-water pretreatment showed its efficiency by the valid removal of hemicellulose and lignin, which would be helpful for following

Conclusion

Quantitative recovery and regeneration of acidic ionic liquid Bmim[HSO4] after biomass processing was achieved by industrial strategy of ultrafiltration with bipolar membrane electrodialysis. UF-BMED strategy showed its efficiency by efficient removal of lignin the potential pollutant for anion-exchange membrane and dipartite recovery of Bmim+ with SO42−. Semi-continuous mode was found to be more sufficient, efficient and economical than intermittent mode for BMED operation. Previous studies

CRediT authorship contribution statement

Xiaocong Liang: Investigation, Methodology, Data curation, Writing - original draft, Writing - review & editing. Junyu Wang: Investigation. Hantao Liu: Validation, Funding acquisition, Project administration.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by National Natural Science Foundation of China (Grant No. 51976203, Grant No. 51476150), Shanxi Province Science Foundation for Youths (Grant No. 201901D211218), Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi (Grant No. 2020L0278) and Science Foundation of North University of China (Grant No. XJJ201921).

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