钾元素对生物质及其三组分热解的影响

36燃料化学学报第43卷at 1%，3% and 5%，respectively, was mixed withpyrolysis was monitored. The maximum rate ofthe tested cellulose， hemicellulose and ligninweight loss decreased with the increase of the amountmechanically. The effect of KCl on TG performanceof KCl, which decreased from 2. 36%/C for the rawof cellulose，hemicelluloses, and lignin are shown incellulose to 1. 45%/C. However, the correspondingFigure 1.temperature at the maximum weight loss rate increasedto the maximum (370 C) when the addition of KCl一- celluloseamount was 3%，and then declined to 367 C whenCellosetoo KCIKCl content reached to 5%. At low temperature ( 259会60F. cellulose+5% KCi40F~ 312 C )，the cellulose could be transformed toactive cellulose. With temperature increasing， theactive cellulose was converted to non-condensablegas, liquid tar and solid charl14. The added KCl inthe cellulose inhibited formation of the active1.5-1.0cellulose, and this is adverse for the pyrolysis of0.5-cellulose. At the meantime, the heat and mass transfer豆00 100200 300 400 s0060000during the cellulose pyrolysis were suppressed with theTemperature 1/Caddition of KCl.Figure 1 (b) indicates the performances of theE100b) ~- heilulose+l%KC1hemicellulose pyrolysis were similar to those of the: 80hemiclulose+3% KCIcellulose. However， the weight loss was almost喜60-hemielulose+5% KClE 40[complete up to 550 C, and reached to 82. 0%. The20maximum rate of weight loss for hemicellulose wasonly 0. 73%/C at 296 C，which were obviouslylower than that of the cellulose. These results could beattributed to the different structures between cellulose0.4-and hemicellulose. Richness in branched chain02Astructure in hemicellulose could be responsible for100 200 300 400 50600 700these results. The more branched chain structure was,the worse thermal stability was for the hemicellulosewhich is prone to decompose into small molecules atg100F三8Cc)the lower temperature.蓄60-Comparing the behavior of cellulose pyrolysisy 40.... igninbefore and after the addition of KCI，there were no.. Tignin+3%kCi一夏20F--lignin+5% KCievident differences during the hemicellulose pyrolysiswhen different content of KCl was added. Only a皇20.20slow decreasing trend of the maximum weight loss rate营0.15(from 0.74%/C for 1% -KCl sample to 0.66%/C0.10for 5%-KCl sample ) for the hemicellulose was0.05observed. The addition of KCl makes the branched影0.00100 200300400500600700800chain structure break easier during the pyrolysis ofTemperature t/ehemicellulose, but too much KCl might inhibit theFigure 1 Efft of KCl on TG/DTG curves of cllulose (a),mass and heat transferl5hemicellulose (b) and lignin (c)Figure 1(c) shows the TG curves of lignin. TheAs shown in Figure 1(a) , the removal of surfacetemperature of the lignin pyrolysis experienced a widerbound water resulted in the weight loss of celluloseweight loss range from 105 to 800 C. The DTGbefore 105 C. When the temperature increased fromresults of lignin showed that there were two pyrolysis200 to 400 C，the release of volatiles from thepeaks at about 335 and 671 C. The weight loss atcellulose almost completed with a weight loss ofabout 335 C is mainly due to the cleavage of aliphaticapproximately 89. 6% . The maximum weight loss ratehydroxyl group in the lignin side chains ，producingwater and low molecular weight gas.At aboutfor cellulose was 2. 36%/C at 362 C.The influence of KCI addition on cellulose671 C, the ether bond in the lignin structure is likelyfracture ,generatingvariousphenolic第1期HAO Qing-lan et al: Efect of potassium on pyrolysis of rice husk and is components39and added K, on the pyrolysis of the diferent biomass husk samples after mechanical mixing treatmentsamples was observed.(section 2.3.2), the maximum weight loss rate ofthe impregnated samples increased with the increase of量100-AW rice huskKCl content. During mechanical mixing, KCl was580KCE-HIadhered to the surface of the biomass particles.60-. KCE-31Nevertheless, it is possible that the KCl also enters40F20F...into the intermal pores of the biomass particles throughthe diffusion during the impregnation process. On theother hand，compared with the mechanical mixing0.6-method, the contact area between biomass and KCl0.4during impregnation was larger. Therefore, the added雪0.2|KCl in the AW rice husk via impregnation had morecatalytic effect on the pyrolysis of AW rice husk.10020300400 500 600 70差Temperature 1/CAlthough the K content in raw rice husk was thehighest (0. 766 9%), its maximum weight loss rateFigure 6 Effect of KCl (impregnation)was the lowest. This is because the pore size of theon TG/DTG curves of AW rice huskimpregnated samples was augmented to a certain extentHowever, different from pyrolysis of the riceduring the impregnation process ( Figure 7), whichfacilitated the mass and heat transfer during pyrolysis.@x200kFigure 7 SEM micrographs of rice husk (a) and KCI-3I sample (b)Generally the main elemental constituents of rice2.5 Effect of KCl on char yieldshusk minerals are Ca, Fe, Mg, Na and K. Among2.5.1 Addition KCl by mechanical mixingthem K content is the highest in the rice husk, whichThe char yields of rice husk are relevant tois more than twice of that of the others. The influencepyrolysis temperature. Above 600 C the weight loss wasof the mineral matter on the rice husk pyrolysisvery slow，and its variation could be ignored. Thecharacteristics should be atributed to the role ofresidue amount above 600 C was regard as the charpotassium. The inherent and added K is beneficialyield, which have eliminated the influence of additivefor pyrolysis of the rice husk, which varied dependingKCI. The effect of KCl addition by mechanical mixingon the addition methods of KCl.on the pyrolysis char yields are shown in Table 3.Table3 Effect of addition KCl on char yields of biomass pyrolysisChar yields" w/%No.K addition w/%cellulosehemicelluloseligninmodel rice husk AW rice husk12.424.459.727.424.9210. 923.227. 124.038.23.059.025.622. 14512.721.954.423.4.eliminate the influence of addition KCl on char yieldThe char yields of cellulose，hemicellulose andlignin were 2.4% , 24. 4% and 59.7% , respectively.第1期HAO Qing-lan et al: Effect of potassium on pyrolysis of rice husk and its components4114] DIEBOLD JP. A unified, global model for the pyrolysis of cllulose[J]. Biomass Bioenergy, 1994, 7(1/6): 75-85.[15] YANGHP, YAN R, CHEN HP, LEE D H, ZHENG C G. Charactristics of hemiellulose, ellulse and lignin pyrolyis{J]. Fuel, 2007.86(12/13): 1781-1788.[16] CHENC A, PAKDEL H, ROY C. Producion of monomeric phenols by thermochemical conversion of biomass: A review[J]. BioresourTechnol, 2001 .79(3): 277-299.[17] NAKAMURA T, KAWAMOTO H, SAKA S. Pyrolysis behavior of Japanese cedar wood lignin studied with various model dimers[J].」Anal Appl Pyrolysis, 2008, 81(2): 173-182.[18] BRITT P F, BUCHANAN m A C, THOMAS K B, LEE s K. Pyrolysis mechanisms of lignin: Surface imobilized model nice bhuskinvestigation of acid-catalyzed and free-radical reaction pathways[ J]. J Anal Appl Pyrolysis, 1995, 33: 1-19.[19] WORASUWANNARAK N, SONOBEA T, TANTHAPANICHAKOON W. Pyrolysis bchaviors of rice straw, nice husk and cormcob by TG-MS technique[J]. J Anal Appl Pyrolysis, 2007, 78(2): 265-271.[20] SUNJX, SUN XF, SUN RC, sU Y Q. Fractional extraction and structural charcterization of sugarcane bagse hemicelluloses[J].Catbobyd Polym, 2004, 56(2): 195-204.21] CHEN H z, LIUL Y. Unpolluted fractionation of wheat straw by steam explosion and ecthanol extraction[J]. Bioresour Technol, 2007, 98(3): 66676.[22] SADDAWI A, JONES J M, WILLIAMS A. Infuence of alkai metals on the kinetis of the thermal decompsition of biomass[J]. FuelProcess Technol, 2012, 104(12): 189-197.[23] WANGJ, ZHANG M X, CHEN M Q. MINFF, ZHANGSP, RENZ w, YAN Y J. Catalytic efects of six inorganic compounds onpyrolysis of three kinds of biomass[J]. Themochim Acta, 2006, 444(1): 110-114.钾元素对生物质及其三组分热解的影响郝庆兰'，李博仑'，刘垒'， 张征标'，豆宝娟”，王昶2(1.天津科技大学材料科学与化学工程学院，天津300457; 2.天津科技大学海洋科学与工程学院，天津300457)摘要:采用机械混合法将KCl加人到纤维素半纤维素、木质素以及稻壳和稻壳模拟物等生物质中，得到了一系列不同K含量的生物质样品,通过热重(TG)实验考察了K元素对生物质热解特性的影响。结果表明, K元素对生物质三组分热解特性的影响比较复杂,纤维素的最大热解失重速率随着KCl添加量的增加而降低,但KCl对半纤维素和木质素热解特性的影响不显著。无论是否添加KCI,模拟生物质的热解特性均可以认为是三组分热解的简单叠加。但酸预处理稻壳三组分间的稳定结构,导致其DTG曲线在300C左右的热解峰由稻壳模拟物的尖峰变为肩峰，其热解焦炭收率也比稻壳模拟物的略低。此外,实验还采用浸渍法向酸预处理稻壳中添加了KC。TG实验结果表明,K元素的存在对生物质热解具有.--定的催化作用,但KCI的添加方式不同,生物质的热解特性有明显差别,生物质样品经机械混合添加KCI后,其热解焦炭收率呈下降趋势(纤维素除外) ,浸溃法添加的KCl导致酸预处理稻壳的最大热解失重速率和焦炭收率升高。关键词:热重;稻壳;机械混合;浸渍; KCl中图分类号: TK6文献标识码: A