Willow Lignin Oxidation and Depolymerization Under Low Cost
Total Page：16
File Type：pdf, Size：1020Kb
Subscriber access provided by University of Sussex Library Article Willow lignin oxidation and depolymerization under low cost ionic liquid Raquel Prado, Xabier Erdocia, Gilbert Francesco De Gregorio, Jalel Labidi, and Tom Welton ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b00642 • Publication Date (Web): 10 May 2016 Downloaded from http://pubs.acs.org on May 13, 2016 Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts. ACS Sustainable Chemistry & Engineering is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties. Page 1 of 37 ACS Sustainable Chemistry & Engineering 1 2 3 Willow lignin oxidation and depolymerization under low cost ionic liquid 4 5 a b a b a 6 R. Prado , X. Erdocia , G. F. De Gregorio , J. Labidi , T. Welton 7 8 9 a. Department of Chemistry, Imperial College London, Exhibition Road, SW7 2AZ, London, 10 11 UK 12 13 14 b. Chemical and Environmental Engineering Department, University of the Basque Country, 15 16 Plaza Europa 1, 20018, Donostia-San Sebastián, Spain 17 18 19 Corresponding author: [email protected] 20 21 22 Key words: Catalyst, heterogeneous, lignin, ionic liquids, oxidation. 23 24 25 Abstract 26 27 28 Willow biomass was subjected to different pretreatment conditions with triethylammonium 29 30 hydrogen sulfate as solvent and the produced lignin solutions were treated by oxidation either 31 32 homogeneously using H 2O2 as oxidant, or by heterogeneous catalysis using TiO 2. Lignin, 33 34 residual lignin, oil and the recovered IL were characterized in order to determine the effects 35 36 of each treatment. Lignin was successfully extracted and depolymerized by oxidation and 37 38 39 characterized by ATR-IR, HPSEC and py-GCMS. The obtained oil was characterized by 40 41 GCMS, it was composed mainly of acids derived from the sugar and lignin fractions, the 42 43 TiO 2 catalyzed oils were richer in phenolic derived compounds than sugar fractions. The final 44 45 ionic liquid was characterized in order to determine its suitability to be reutilized. 46 47 48 Introduction 49 50 51 Recently, the quest for greener technologies that decrease our dependence on fossil fuels has 52 53 become the principal target for many research groups. Efficient utilization of biomass is 54 55 becoming increasingly important as it is the most abundant renewable material on earth, with 56 57 1 58 a yearly global supply of approximately 200 billion metric tons . Lignocellulose consists 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 2 of 37 1 2 3 mainly of plant cell wall material; it is a complex natural composite with three main 4 5 biopolymers: cellulose (ca. 50%), hemicelluloses (ca. 25%) and lignin (ca. 25%) 2. The 6 7 structure and composition of lignocellulose varies greatly, depending on plant species, part of 8 9 1 10 the plant and growth conditions . 11 12 13 Lignin is a phenolic polymer synthesized via the oxidative coupling of three major C6-C3 14 15 phenylpropanoid units, namely, syringyl alcohol, guaiacyl alcohol and p-coumaryl alcohol, 16 17 which form a complex and random three dimensional structure inside the cell wall which 18 19 varies depending on the specie 3. Lignin is the main by-product in chemical pulping processes, 20 21 amounting to around 100 million tons per year, most of which is burned to generate energy 22 23 24 which is reintegrated into the plant for its own energy supply. However, as lignin is the only 25 26 renewable source of aromatic compounds, it can potentially be an important source of 27 28 different products with a range of applications 4. The diversity of functional groups present in 29 30 lignin allows it to be used as a dispersant in cement and gypsum blends 5, as an emulsifier or 31 32 6 33 chelating agent for removing heavy metals from industrial effluent , as a food additive, in 34 7 35 batteries as a coating for graphite electrodes and it has been added to composites as 36 37 reinforcement 8. 38 39 40 Willow is a commercially cultivated crop that has potential to be a dedicated biomass crop. 41 42 Willow’s leaves and bark are rich in compounds widely used in the pharmaceutical industry, 43 44 well recognized throughout Europe for treating inflammatory conditions and pains of 45 46 47 different origin. There are presently 24 willow varieties available that have been certified by 48 49 the EU. There are 10 of commercial use today and approximately one-two varieties are 50 51 developed annually9. 52 53 54 Room-temperature ionic liquids (ILs) are receiving a significant amount of interest owing to 55 56 their characteristics as environmentally friendly solvents for a range of chemical processes 57 58 59 60 ACS Paragon Plus Environment Page 3 of 37 ACS Sustainable Chemistry & Engineering 1 2 3 both for catalyzed and uncatalyzed reactions, or as possible constituents in electrochemical 4 5 devices 10,11 . Thus the molecular design, synthesis and characterization of ILs have been the 6 7 focus of many recent scientific investigations. Their unique properties, such as being liquid 8 9 10 over a wide temperature range, having negligible vapor pressure and high thermal, chemical 11 12 and electrochemical stability, allow a wide range of applications and make ILs good 13 14 alternatives to environmentally harmful volatile organic solvents 12 . The properties of ILs vary 15 16 enormously as a function of their molecular structure and considerable effort has been 17 18 19 devoted to identifying and understanding those that have superior properties in any given 20 13,14 21 application . 22 23 24 It is well known that the structure of lignin is affected by the extraction processes, which 25 15 26 cause chemical changes and fragmentation due to the chemical agents and conditions used . 27 28 This fact makes the study of how lignin is affected by each IL of paramount importance. For 29 30 example, Tan et al. observed that after delignification of sugarcane waste using 1-ethyl-3- 31 32 33 methylimidazolium alkylbenzenesulphonate ([C2C1im][ABS]), the obtained lignin had a 34 35 lower average molecular weight (MW) than autocatalysis lignin. Both lignins were acetylated 36 37 in order to allow comparison. Acetylated lignin from [C2C1im][ABS] had a lower Mw (3690 38 39 g/mol) than acetylated autohydrolysis lignin (19300 g/mol), polydispersity was also lower for 40 41 the [C C im][ABS] treated lignin (1.66 and 11.4 respectively)16. George et al . studied the 42 2 1 43 44 effect of different ILs (1-ethyl-3-methylimidazolium n-hexylsulfate ([C 2C1im][HxSO 4]), 1- 45 46 ethyl-3-methylimidazolium diethylphosphate ([C2C1im][Et 2PO4]), 1-ethyl-3- 47 48 methylimidazolium n-butylsulfate ([C2C1im][BuSO 4]), 1-ethyl-3-methylimidazolium 49 50 dimethylphosphate ([C2C1im][Me 2PO4]), 1-ethyl-3-methylimidazolium lactate 51 52 53 ([C2C1im][lac]), 1-ethyl-3-methylimidazolium chloride [C2C1im]Cl, 1-ethyl-3- 54 55 methylimidazolium acetate ([C2C1im][Me 2CO 2]), 1-butyl-3-methylimidazolium chloride 56 57 ([C4C1im]Cl), Cyphos 101, Cyphos 165 and 1-methyl-2-pyrrolidonium chloride ([C1pyr]Cl)) 58 59 60 ACS Paragon Plus Environment ACS Sustainable Chemistry & Engineering Page 4 of 37 1 2 3 with lignin from different sources (organosolv, alkali (NaOH) and moderately sulfonated 4 5 alkali lignin). It was observed that the anion had more influence on the lignin structure than 6 7 the cation. The effect of the anion in modifying lignin’s molecular weight follows the order: 8 9 10 sulfate>lactate>acetate>chloride>phosphate. It must be highlighted that the rate of 11 12 modification of lignin by the action of IL also depends on its source, with organosolv lignin 13 14 being more susceptible to structural changes than moderately sulfonated lignin and alkali 15 16 lignin 17,18 . 17 18 19 20 Due to its complex structure, few investigations using lignin directly as a substrate have been 21 22 23 conducted to study its reactivity. However, many studies have been carried out using lignin 24 25 model compounds in order to elucidate the reaction mechanisms and the proper conditions to 26 27 extend the reaction to lignin 15 . The depolymerization of lignin model compounds and lignin 28 29 in ILs have been studied under both reductive and oxidative conditions.