Optimization for microwave-assisted direct liquefaction of bamboo residue in glycerol/methanol mixtu

J. For. Res. (2015) 26(1):261-265DOI 10.1007/s1 1676-015-0032-1SHORT COMMUNICATIONOptimization for microwave-assisted direct liquefactionof bamboo residue in glycerol/methanol mixturesJiulong Xie . Jinqiu Qi . Chungyun Hse .Todd F. Shupe .Received: 30 October 2013/ Accepted: 28 December 2013/Published online: 27 January 20150 Northeast Forestry University and Springer- Verlag Berlin Heidelberg 2015Abstract Bamboo residues were liquefied in a mixture of Keywords Bamboo residue . Microwave . Liquefactionglycerol and methanol in the presence of sulfuric acid using Glycerolmicrowave energy. We investigated the effects of lique-faction conditions, including glycero/methanol ratio, liq-uefaction temperature, and reaction time on the conversion Introductionyield. The optimal liquefaction conditions were under thetemperature of 120 °C, the reaction time of 7 min, the As an important thermochemical method, liquefaction ofglycerol-methanol-bamboo ratio of 8/0/2 (W/W), and the woody materials has been carried out with various solventsmicrowave power of 300 W. Maximum conversion yield for different end products (Mishra and Saka 2013; Xie andwas 96.7 %. The liquid products were separated into two Shi 2006; Lin and Hse 2005). However, the most com-contents (water soluble part and precipitate part) by addi- monly explored solvents for liquefaction are derived fromtion of a sufficient amount of water. By Fourier transformpetroleum. These solvents are effective, but require largeinfrared (FT-IR), the water soluble content mainly con- quantities and are costly. A by-product of the transesteri-tained glycerol and its derivate and carbohydrate degra- fication process to manufacture bio-diesel is the productiondation products, and the precipitate content was mainly of glycerol. For each kilogram of biodiesel produced, therelignin derivatives.is about 0.1 kg of accompanying crude glycerol (Thomp-son and He 2006). Therefore, successful replacement ofpetroleum-based solvents, such as phenol by glycerol in aliquefaction process should have potential to improve theProject funding: The project was supported by“Key Laboratory ofeconomics of the process.Wood Industry and Furniture0 ndusry and Fumtire Eneerin of Scuan PovinctalCompared to conventional heating, microwave energyCollepenetrates and produces a volumtrically distributed heatThe online version is available at http://www .springerlink.comsource, and heat is generated throughout the material andleads to faster heating rate and improved kinetics. Recently,Corresponding editor: Yu Leimicrowave energy has been successfully applied to the liq-J. Xie.J. Qi (8)uefaction of lignocellulosic biomass (Krzan and Zagar 2009;College of Forestry, Sichuan Agricultural University,Panet al.2012; Xu et al.2012). Therefore, the development ofYa' an 625014, Sichuan, Chinaa liquefaction process combining the greater microwavee-mail: qijinqiu2005@ aliyun.comheating efficiency and the by-product glycerol from the bio-C. Hsediesel production to replace petroleum-based solvents is aSouthern Research Station, USDA Forest Service, Pineville,promising method to enhance economic viability of theLA 71360, USAprocess and benefit agricultural producers, bio-based pro-cessing industrieT. F. ShupeSchool of Renewable Natural Resource, Louisiana StateAs one of the中国煤化工，:urces, bambooUniversity Agricultural Center, Baton Rouge, LA 70803, USAis widely cultivaMHCNMHGthandCentral空Springer262J. Xie et al.America and has been used as one of the main resources for through Whatman No. 4 filter paper. The solid bambooflooring and furniture manufacturing (Gao et al. 2010). residue retained on the filter paper was oven-dried atHowever, because of the limited processing technologies 105 °C and the conversion yield was calculated as Eq. 1:and the special characteristics of bamboo culms, processConversion yield (%residues, such as bamboo branches, nodes, epidermis, wax,Oven dried weight of residueand pulping by-products, are cast aside as waste. Thus, an=(1-Oven dried weight of raw materia)< 100economically viable bamboo waste conversion technologyis needed to address problems concerning both waste dis-(1)posal and resource wastage. In the present study, we usedmicrowave heating to investigate the liquefaction of bam-Separation of the liquefied productboo residues with glycerol-based solvents. The reactionparameters that affect the microwave liquefaction ofThe filtrated liquid was evaporated at 45 °C under vacumbamboo were optimized for the yield of liquid product. Theto remove methanol, then distilled water (10/1, W/W) wasliquid product obtained from this liquefaction system wasadded into the black crude bio-polyols. The mixer wasalso separated and evaluated.stirred thoroughly with a glass rod. Afterwards, the limousaqueous was centrifuged at 5,000 r min-' for 10 min. Thewater-soluble content was obtained by removal of theMaterials and methodswater from the supernatant fuid using a rotary evaporatorat 70 °C. The precipitate content was dried at 30 °C forMaterialsBamboo (Phyllostachys pubescens) residue used in theexperiments was collected from central Louisiana, USA. FT-IR analysisThe air-dried residues were reduced to particles. The par-ticles were screened to collect particles that passed through FT-IR analysis of the raw material and liquefied productsa 40-mesh sieve and then dried to a constant weight in anwas performed by a Nicolet Nexus 670 spectrometeroven at 80 °C. The dried particles were stored in poly- equipped with a Thermo Nicolet Golden Gate MKII Singleethylene bags and used without further treatment. All acids, Reflction ATR accessory. A small amount of sample wasglycerol, and methanol used were of reagent grade and applied directly on the diamond crystal. Data collectionobtained from commercial sources.was performed with a 4 cm-' spectral resolution and 32scans were taken per sample.Liquefaction processMicrowave liquefaction of bamboo was carried out in a Results and discussionMilestone (Shelton, CT, USA) MEGA laboratory micro-wave oven. A mixed glycerol and methanol ratio of 2/1 (w/ Effect of glycerol/methanol ratiow) was used as the solvent at a solvent to bamboo ratio of4/1 (w/w). Sulfuric acid content of 1.75 % of solvent The main solvents were glycerol and methanol. The effectweight was used as the catalyst. A typical reaction mixture of glycerol/methanol ratio on the conversion yield is pre-consisting of 2 g of bamboo particles, 8 g of solvent, and sented in Fig. 1. At 120。C, the conversion yield increased0.14 g of sulfuric acid was loaded in the Teflon vessels significantly with the increasing ratio of glycerol/methanolwith a magnetic stiring bar. The Teflon vessels were then (Fig. 1). Then the pure glycerol liquefaction of bambooplaced on the rotor tray inside the microwave cavity. The residues had maximum conversion yield (90.15 andtemperature was monitored using an ATC-400FO auto-94.04 % for 120 and 150 °C, respectively). It could bematic fiber optic temperature control system. Based on concluded that glycerol was very effective in enhancing themonitored temperature, the output power was auto-adjusted decomposition of bamboo residues at low temperature induring liquefaction. Temperature was increased from room this liquefaction system. Similar results showing that thetemperature to 150 。C at a heating rate of 37.5。C min-' addition of glycerol to PEG accelerated the liquefactionand then was kept constant for 3 min, unless otherwise rate were reported for other studies of lignocellulosicnoted. After a cooling period of 30 min, the material was liquefaction (Hassan and Shukry 2008). According to thedissolved in 150 mL of methanol under constant stirring results, glycerol中国煤化士”rduced thefor 4 h. The liquefied solutions were then vacuum-fitered expense of theMHCNMH G .包Springer .Optimization for microwave-assisted direct liquefaction263Effect of liquefaction temperaturestage but with remarkable enhancement of reaction kinet-ics. The conversion yield showed a slight decrease fromFigure 2 shows the temperature-dependence of the lique- 105 to 150 °C, which was attributed to the recondensationfaction curves for conversion yield at two levels of of the liquefaction intermediates (Lin et al. 2001; Chen andmicrowave power (300 and 500 W). At microwave power Lu 2009). Accordingly, taking reaction efficiency ancof 300 W, the conversion yield increased dramatically as energy consumption into consideration, the optimal reac-the liquefaction temperature increased from 75 to 120 °C tion temperature was 120 °C and optimal microwave(Fig. 2). The bamboo residues were nearly decomposed power was 300 W.within 7 min at 120 。C (conversion yield = 96.7 %).Further increase in temperature to 150 °C did not signifi- Effect of reaction timecantly increase conversion yield.Similar decomposition was observed for liquefaction The effect of reaction time on liquefaction yield is shownwith microwave power of 500 W at the inital liquefaction in Fig. 3. With increasing reaction time, the liquefactionyield first increased and then decreased. Generally, theliquefaction of lignocellulosic biomass in an organic sol-100vent with an acid catalyst at high temperature is a complexsolvolysis process involving simultaneous reactions 0190●150Cchemical degradation/decomposition， de-polymerization,and re-condensation depending on the process parameters.80■Thus, at shorter times (3- -7 min), the increase in conversionyield is mainly due to the fact that degradation/decom-三70position outweighs repolymerization. Then, with the pro-longation of reaction time (9- -11 min)，degradation参60gradually decreased and repolymerization played the mainrole in liquefaction (Balat 2008; Zou et al. 2009; Xie et al.502014), which attributed to the decrease in conversion yield.To evaluate the effect of solvent pre-permeation treat-4Cment on conversion yield, 2 g bamboo samples measuring6(7090010 x 5 x 1 mm were first treated under 103.5 kPa, full-Glycerol content (%)cell pressure vacuum for 15 min. After the succesfulFig.1 Effect of glycerol content on conversion yield. Other condi-adsorption of the solvent (8 g) and catalyst (0.14 g), thetions: sulfuric acid of 1.75 %, solventbamboo of 4/1, reaction time of pressure was increased to 827.4 kPa for 30 min. Then, the3 minand microwave power of 500 Wmixture was subjected to the liquefaction system.■ControlPre-permeatione 70-量8060|406030一5(710535150Reaction time (min)Temperature('C)Fig. 3 Effect of time and pre- permeation on conversion yield. OtherFig. 2 Effect of temperature and microwave power on conversion conditions: solvent中国煤化工4/1, temperatureyield. Other conditions: solvent of glycerol, glycerol/bamboo of 4/1，of 150 °C, time (nd particle size ofthe reaction time of 7 min, and the sulfuric acid of 1.75 %10x5x1mmYHCNM HG包Springer264J. Xie et al.Liquefaction of the pre-permeation bamboo residues carbohydrate-degraded fragments and glycerol/methanolshowed higher conversion yield than the control samples blended solvents. The spectrum of the precipitate fractionuntil 7 min (Fig. 3). However, when liquefaction time was was significantly different from that of the water solubleprolonged to 9 min, the conversion yield for pre-treated content. Characteristic bands of lignin were observedbamboo was lower than that of the control samples. The (Fig. 4, Spectrum d), indicating that the precipitate contentpre- permeation treatment made distribution of the regents was comprised of lignin-degraded products.within the bamboo much more uniform. Hence, both theuniform distribution of regents and temperature contributedto the promotion of degradation/repolymerization.ConclusionFT-IR spectraBamboo residue was almost completely (maximum con-version yield of 96.7 %) converted to liquid phase innicrowave energy. Addition of methanolgroups presented in different contents. The spectra patterns into glycerol decreased the conversion yield. Glycerolfor different content samples were significantly different, alone can be recommended as a liquefaction solvent as theindicating that the main chemical groups were diverse maximum conversion yield reached maximum under mild(Fig.4).conditions (7 min/120 °C). Increasing liquefaction tem-From the spectrum of bamboo raw material (Fig. 4，perature (to 150 °C) or prolongation of reaction timeSpectrum b) peaks at 1,735, 1,420, 1,372, 1,320, 1,162，(9-11 min) led to the condensation reactions in this system.1,108, 899 cm-1 were related to carbohydrate (cellulose Higher microwave power and pre-permeation treatmentand hemicellulose) bands, and peaks at 1,596, 1 ,506, 1,456，could promote the reaction kinetics both in degradation andand 1,230 cm- were assigned to lignin. In the spectrum recondensation. The liquefied products could be success-for residue, the lignin/hemicellulose bands at 1,735, 1,596，fully separated into two contents by adding water.1,506, and 1,456 cm-1 were nonexistent, the cellulosebands weakened, and the residue content was mainly cel-lulose in construction. 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