Research Article pubs.acs.org/journal/ascecg
Production of Levoglucosenone and Dihydrolevoglucosenone by Catalytic Reforming of Volatiles from Cellulose Pyrolysis Using Supported Ionic Liquid Phase Shinji Kudo,*,† Nozomi Goto,† Jonathan Sperry,‡ Koyo Norinaga,† and Jun-ichiro Hayashi†,§ †
Institute for Materials Chemistry and Engineering, Kyushu University, 6-1 Kasuga Koen, Kasuga 816-8580, Japan Center for Green Chemical Science, School of Chemical Sciences, The University of Auckland, 23 Symonds Street, Auckland, New Zealand § Research and Education Center of Carbon Resources, Kyushu University, 6-1 Kasuga Koen, Kasuga 816-8580, Japan
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S Supporting Information *
ABSTRACT: This paper presents a novel method for continuous production of a biomass-derived platform chemical, levoglucosenone (LGO), from cellulose without its pretreatment or use of solvent. First, cellulose is pyrolyzed, and then the volatiles are reformed over a catalyst consisting of a type of ionic liquid supported over porous char. The ionic liquid, having a moderate hydrogen-bond basicity, performs well in the dehydrative conversion of levoglucosan (LGA) and anhydrosugar oligomers in the volatiles to LGO at 275 °C. The catalytic reforming to LGO is highly selective, and consequently, the yield of LGO is determined mainly by the pyrolysis conditions that produce the LGO precursors. The highest LGO yield we obtained was 31.6% on a cellulose carbon basis (24.6 wt %) with fast pyrolysis that produced more precursors than the slow one. Furthermore, the reaction system is applicable to the production of dihydrolevoglucosenone (DLGO), a promising biobased alternative to dipolar aprotic solvents. Addition of hydrogen in carrier gas and a hydrogenation catalyst in the catalytic bed enables the production of DLGO, although improvement in hydrogenation selectivity is required in the present reforming system. KEYWORDS: Biomass, Cellulose conversion, Platform chemicals, Pyrolytic conversion, Catalyst, Ionic liquids, SILP, Hydrogenation
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INTRODUCTION Levoglucosenone (LGO; 1,6-anhydro-3,4-dideoxy-β-D-glycerohex-3-enopyranos-2-ulose) is a highly functionalized molecule that is produced in small amounts during pyrolysis of cellulose. LGO is unique among biomass-derived small molecules as it contains six differentially functionalized carbon atoms and two distinct chiral centers (retained from cellulose), making it an ideal substrate from which to construct novel biobased products in enantiopure form.1−7 Furthermore, a recent report showed that dihydrolevoglucosenone (DLGO), prepared from LGO via hydrogenation, is an attractive biobased alternative to dipolar aprotic solvents such as N-methylpyrrolidinone (NMP), N,N-dimethylformamide (DMF), and sulpholane.8−10 Derivatives available from DLGO include 1,6-hexanediol, a commodity chemical with widespread industrial applications.11,12 LGO is thus considered to be a promising biorenewable platform for both fine and commodity chemical industries. LGO has an advantage over other biomass-derived platform chemicals because it can be directly produced by pyrolysis of cellulose-containing materials including wastes such as waste© 2016 American Chemical Society
paper. Pyrolysis is a very fast reaction that does not require solvents or catalysts, and, hence, is an ideal strategy for cellulose depolymerization in terms of the rate and cost. Pyrolysis has recently drawn attention as a fast saccharification method alternative to a conventional enzymatic hydrolysis,13,14 because levoglucosan (LGA), a primary pyrolysis product from cellulose, can be easily hydrolyzed to glucose. However, the yield of LGO from a simple cellulose pyrolysis is generally low (less than 3 wt %) regardless of the operating conditions and type of feedstock.15 As a result, the cost of LGO is currently high, which prohibits a detailed evaluation of its full potential as a biorenewable platform chemical. To increase the accessibility of LGO, we need to develop a method for its efficient production in high yield. Various methods exist for the production of LGO from cellulose, mostly based on pyrolysis.12,16−31 High yields of LGO are reported for cellulose pyrolysis in polar aprotic solvents, Received: October 11, 2016 Revised: November 21, 2016 Published: December 8, 2016 1132
DOI: 10.1021/acssuschemeng.6b02463 ACS Sustainable Chem. Eng. 2017, 5, 1132−1140
Research Article
ACS Sustainable Chemistry & Engineering
mL/min) to 350 °C, where the temperature was maintained for 20 min. In the heat treatment, cellulose was pyrolyzed, leaving porous char as a residue with IL. The residue was used as a catalyst. The SILP catalysts thus prepared are hereafter denoted by IL-X/C-(Y), where X is A = [BMMIM]OTf or B = [BMMIM]NTf2, and Y is the IL content. A portion of the prepared catalyst was used for the analysis of structural properties after separation into IL and char. The catalyst was suspended in ethanol to dissolve IL, and the suspension was stirred for 12 h under ambient conditions, followed by filtration with PTFE membrane filter (pore size: 0.45 μm). The IL content was obtained from the mass of liquid residue after evaporation of ethanol from the filtrate at 55 °C and 100 mbar for 3 h. Thermogravimetric analysis (TGA) of IL and catalysts was performed on a SII Nano Technology EXSTAR TG/DTA 7200. A sample of about 4 mg on a platinum crucible was heated in a flow of N2 at 200 mL/min. The pore structure of char was calculated from N2 isotherms at −196 °C and CO2 isotherms at ice temperature, which were measured on a Quantachrome, NOVA 3200e. The char samples were dried under vacuum at 200 °C for 3 h before the measurement. The Brunauer− Emmet−Teller surface area (SBET) and total pore volume (Vtotal) were obtained from the N2 isotherm. The CO2 isotherm was analyzed by the NLDFT (nonlocalized density functional theory) model, which was available in Quantachrome ASiQwin, to obtain micropore surface area (SCO2) and volume (VCO2). Activated carbon from palm shell (AC; SBET = 1250 m2/g) and HZSM-5 zeolite (SBET = 425 m2/g, SiO2/Al2O3 = 23 mol/mol) were used as reference catalysts. They were purchased from Wako Pure Chemical Industries and Zeolyst International, respectively. The 5 wt % Pd/Al2O3 and 5 wt % Pt/Al2O3 catalysts, used for DLGO production, were prepared by an impregnation method with γAl2O3 (Sigma-Aldrich, SBET = 130 m2/g) and aqueous solutions of PdCl2 (dissolved with double molar equivalent of HCl) and H2PtCl2, respectively. After the impregnation, they were dried at 120 °C, followed by calcination at 260 °C for 2 h under a flow of 10% O2/N2. Before reforming tests, the prepared catalysts were reduced at 350 °C for 3 h with 50% H2/N2. Procedure for Catalytic Reforming of Volatiles from Cellulose Pyrolysis. Two reactor configurations were employed for carrying out the reforming with two different volatiles from “slow” pyrolysis and “fast” pyrolysis. Schematics of the reactors are provided in the Supporting Information (Figure S1). The slow pyrolysis mode was typically used for evaluation of catalysts. Both reactors consisted of pyrolysis and reforming sections. In the slow pyrolysis mode, 0.5 g of microcrystalline cellulose on a quartz boat was heated to 380 °C at a rate of 2 °C/min, and the final temperature was maintained for 20 min. In the fast pyrolysis mode, cellulose was continuously fed to the pyrolysis zone (380 °C) with a particle feeder (Aishin Nano Technologies, TF-70-CT). The feeding was continued for 30 min at the rate of 40 mg/min. Cellulose was pyrolyzed in the course of the drop and after being trapped on quartz wool, and the volatiles were continuously fed to the reforming zone during the feeding time. The pyrolysis temperature of 380 °C was sufficiently high to complete the release of volatiles that contained precursors of LGO (Figure S2). In a comparative experiment, lignocellulosic biomass, Japanese cedar (powder,
