微波加热条件下棉杆热解的产物特性分析 微波加热条件下棉杆热解的产物特性分析

微波加热条件下棉杆热解的产物特性分析

  • 期刊名字:农业工程学报
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  • 论文作者:李攀,王贤华,龚维婷,杨海平,陈应泉,陈汉平
  • 作者单位:华中科技大学煤燃烧国家重点实验室
  • 更新时间:2020-03-24
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论文简介

.第29卷第15期农业工程学报Vol.29 No.152002013年8 月Transactions of the Chinese Society of Agricultural EngineeringAug.2013微波加热条件下棉杆热解的产物特性分析李攀,王贤华※,龚维婷,杨海平,陈应泉,陈汉平(华中科技大学煤燃烧国家重点实验室,武汉430074)摘要:为了揭示微波加热方式对棉杆热解过程的影响,该文采用气相色谱和质谱分析仪(GC-MS)、 等温吸附仪(BET)以及傅立叶红外分析仪(FT-IR) 分析了棉杆热解产物的理化特性。研究表明随着热解温度的上升,气体产率和液体产率变化趋势相反,且均在500"C附近出现极值,而焦炭产量逐渐降低。微波加热条加下棉杆热解液体产物组分复杂,以乙酸、左旋葡聚糖、苯酚类物质为主,其中乙酸和左旋葡聚糖含量随温度升高而逐渐降低,酚类物质在450"C 含量最高,而后总体含量变化缓慢:随着温度的上升,焦炭的孔隙度先增加后降低,所含官能团逐渐减少,焦炭比表面积最大可达到400m/g。该文可为微波热解生物质用于产物品质提升的研究提供参考。关键词:热解,温度,秸杆,热解油,焦炭doi: 10.3969j.issn. 1002 -6819.2013.15.024中图分类号: TK 16文献标志码: A文章编号: 1002- 6819(2013)-15 -0200 -07李攀,王贤华,龚维婷,等微波加热条件下棉杆热解的产物特性分析[J].农业工程学报,2013, 29(15): 200-206.Li Pan, Wang Xianhua, Gong Weiting, et al. Property analysis of pyrolysis product from cotton stalk heating bymicrowave[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2013, 29(15):200- 206. (in Chinese with English abstract)所得的焦炭微孔中的类碳附着物比常规热解焦炭0引言少很多,其比表面积远大于常规热解。目前研究多微波加热技术因快速、均匀的特点而得到迅速侧重于微波加热引起单态产物的变化,而微波条件发展,在生物质资源化利用方面得到了广泛利用",下生物质热解产物的综合分析还鲜见报道,鉴于相比传统加热方式下的生物质热解,微波热解获得此,本文在固定床式微波加热反应器上对棉杆进行的生物油和焦炭的品质均有一- 定程度的提高[23, J热解试验,分析了棉杆热解的产物分布以及液体和AMenendez等[4-5对污泥微波热解进行的研究表固体产物特性,以期微波加热方式下生物质炭油联明,与常规电炉加热相比,微波热解的油产率高,产研究提供参考。气体产率低,并且在相同的热解温度下,微波热解1试验设置油中多环芳烃含量远小于常规热解; Huang 等0]进行了稻壳微波热解的试验研究,发现热解得到的焦1.1试验原料和试验装置炭是很好的微波吸收剂,能够强烈吸收微波并成为试验用棉杆来自武汉市蔡甸区,选取颗粒粒径“热点”,促进热解反应的进行:罗爱香等17对竹废5~10mm用作反应样品。其元素分析和工业分析料的微波裂解进行了研究,发现温度对竹废料微波结果见表1。裂解的产物组成有着显著的影响,得到制取生物油表1棉杆的工业分析与元素分析的最佳反应温度范围为450~ 550"C; MasakatsuTable 1 Proximate and ultimate analysis result of cotton stalkMiura等[81使用自制的微波加热系统对木块和纤维工业分析Proximate analysis元素分析Ultimate analysis素材料进行了热解试验。结果表明,木块微波热解20.70 59.65 2.63 17.02 39.69 3.09 1.03 0.02 32.85收稿日期: 2013-01-07修订日期: 2013-07-01注: ad为空干基, 0含量由差减计算得到基金项目:国家高技术研究发展计划(863计划)课题( 2012AA051803);国家自然科学基金重点资助项目(50930006、 51021065、 51076058)图1所示为棉杆微波热解试验装置图。微波加作者简介:李攀(1987-),博士生,主要从事生物质热解方面的研热装置采用南京杰全微波设备有限公司生产的究。武汉华中科技大学煤燃烧国家重点实验室,430074。Email: lipan. hust@ qq.comNJL2-1型实验室微波炉,微波工作频率2 450 MHz,※通信作者:王贤华(1978-),博士,主要从事生物质能源高效利用为其配备的3个微波磁控管可提供最大2 kW的输方面的研究。武汉华中科技 大学煤燃烧国家重点实验室,430074。出功率,并可按需要进行手动和自动调节。热解反Email: wangxianhua@hust.edu.cn第15期李攀等: 微波加热条件下棉杆热解的产物特性分析201应器采用刚玉管,内径35 mm,长度700 mm,智气化室气相色谱的运行条件是:在50"C 保持底部装有布风板。用于收集液体产物的蛇形冷凝管10 min,后以80"C/min的升温速度升至250"C并保是专门定制的,通过延长热解气的停留时间使冷凝持10 min,流量为1 L/min,分流比均为200: 1,更充分。气体净化干燥装置采用500 mL锥形瓶,进样量为1 pμL。MS (质谱)条件:电离方式EI,内部交替叠加脱脂棉和变色硅胶,起到脱除焦油和电子轰击能量70eV,光电倍增管电压500V,扫描水分的作用。质量范围50~ 500μ,扫描时间1 s,所得结果采用GC-MS自带的GG1034C软件参照标准库进行匹配1-田田h分析,由于每种物质的浓度与GC-MS得到的峰面积有一-定的线性关系,本文将以各组分的峰面积作_ 口0O为半定量数据进行后续分析10],选取了主要成分进行了半定量分析,包括乙酸、羟基丙酮、环戊烯、左旋葡聚糖和酚类物质等。.3.2 固体产物特性分析孔隙特性是热解焦炭物理结构的重要参数。焦1.温度显示仪2.微波控制器 3.微波发生器 4.转子流量计 5.微波炭孔隙是反应介质和反应产物的扩散通道,孔隙表反应器6.试验样品 7.试验床料 8.冷凝装置 9.蛇形冷凝管 10.过面是吸附相存在和发生化学反应的场所,其内表面滤装置1.Temperature display instrument 2.Microwave controling device积和孔容的大小直接决定了焦炭的吸附特性和反7, Bed materials 8.Condensation devices 9 Serpentine tubes i 10.Filters应速率",同时,焦炭孔结构对焦的气化、燃烧等图1生物质微波热解试验装置系统有显著的影响"2。因此,本文采用美国MicromeriticsFig.1 Schematic diagram of biomass microwave pyrolysis公司生产的ASAP2010型比表面积及孔径分析仪对reactor system微波热解固体产物的孔隙结构进行研究,有助于深入了解微波热解机理,并且对热解炭的应用具有-1.2试验过程每次试验称取10g样品置于刚玉管反应器中,定的指导作用。该仪器在液氮饱和温度(- 196'C )处于微波加热区域,用硅胶管将反应器出口与冷凝下对样品进行静态等温吸附测量,测量孔径范围为干燥吸收装置连接,刚玉管露出微波炉炉体部分与1.7~ 300 nm,相对压力p/po范围为0.01 ~0.995(p、冷凝管前的管路缠绕着电热带,以防止热解气中的po分别为氮低温吸附的平衡压力及饱和压力)。样品可凝成分提前凝结,用高纯氮气吹扫10 min后将流比表面积(SBEr) 通过Brunauer Emmett-Teller(BET)量稳定在1 L/min, 开启微波加热,设定相应微波方程进行线性回归得到;微孔面积(Smie) 和微孔容功率,加热20min后关闭微波炉并迅速将热电偶插积(Vmic)用t曲线法确定;结合Barett-Joyner-入反应器测量反应区温度( 考察终温为350、400、Halenda(BJH)模型计算总孔容积(V),计算所用数450、 500、550、 600、 650'C) ;将冷凝管和干燥据为氮吸附等温线的脱附分支131。样品在测量前在吸收装置称取质量,减去初始质量,得到热解液体105°C下抽真空以去除杂质气体。产量;并用同体积的丙酮将冷凝管内的热解油洗采用德国Bruker公司生产的VERTEX70型傅出,用采样瓶收集以备测试分析;关闭微波炉后继立叶红外分析仪对焦炭的有机官能团组成进行分续通入氮气,待反应器冷却至100C以下, 从刚玉析,光谱分析范围为400~4000 cm',分辨率为管中取出固体剩余物称取质量,因棉秆中灰分较4cm'。焦炭样品采用光谱级溴化钾进行稀释,取少,即可认为其为焦炭的产量;气体产量由差量计0.7 mg样品与70 mg溴化钾进行混合、研磨、压片。算得到。每个温度条件下在剔除异常点之外均进行2结果与分析至少2次平行试验,以保证试验数据的准确性。2.1棉杆热解产物分布特性1.3 分析方法不同热解终温下的产物分布规律如图2所示。1.3.1液体产物特性 分析从图2中可以看出:随着热解终温的升高,液生物油成分复杂,组成繁多,目前对生物油的体产物产率先逐渐增加,在450~ 500°C达到最大值,分析主要采用GC-MS分析I9。试验采用Agilent 公而后随热解终温的进一步升高而降低;气体产率变司生产的7890A/5975C型气质联用仪,GC色谱柱化与液体产率呈相反的趋势;热解炭产率总体呈下选用DB-WAX: 30 mx0.2 mm(.D.)x 25 μum石英毛降趋势,且在500"C之前下降较快,500~ *600°C下降细柱,载气为氦气,气化室工作温度最高为290C。趋势变缓。这主要是因为:在500C以前热解反应202农业工程学报.2013年+热解义Char半纤维素、纤维素和木质素的质量分数分别为_121 .98%、35 50%和19.87%,因此棉杆热解失重的第50 t1阶段主要是因为半纤维素和纤维素的受热分解;第2阶段为500~600°C,产率从15.36%缓慢降低10 t至13.49%,主要是因为木质素的分解,因此焦炭产率下降缓慢。在500°C之前,由于微波加热快速均匀的特性,随温度升高一次反应迅速加强,气体停留时间明显减少,二次反应程度降低,因此气体产s50 400 450 500 550 600 650率下降,液体产率上升;在550"C以后由于高温对温度Temperatre'C热解反应的促进作用更优,使得产物中大分子二次图2棉杆微波热解的产物分布图反应总体呈现加强趋势,从而导致热解油产率下Fig.2 Yields of pyrolysis products for cotton stalk microwave降,热解气产率上升15-16。pyrolysis2. 2液体产物 的特性分析在产物特性分析阶段,所有的温度点的产物均不充分,温度是影响挥发份析出的主要因素,而在作了后续分析,限于文章篇幅以及相应数据能够说500~ 550°C时热解反应已经较充分,继续提高温度明所述问题即可的思想,并未给出全部数据的罗对挥发份析出没有较大影响,因此热解炭产率变化列。不大。在Yang等4的研究表明生物质中半纤维素生物油是含氧量较高的有机成分的混合物7],首先在220~315"C分解,而315~400C则为纤维与传统加热方式下的热解试验类似,微波加热条件素分解区,高于400°C时木质素开始分解:棉杆中下的液体产物仍十分复杂,其组成特性见表2所示。表2棉杆微波热解液体产 物的组成Table 2 Compound in liquid product by GC-MS峰面积百分比Peak Area Precent/%化合物名称Compounds350C450C650C乙酸Acetic acid11.49.569.275.27丁内酯Butyrolactone0.8121.311.241-羟基-2-丙酮I-hydroxy-2-propanone2.822.171.531-羟基2丁酮.1-hydroxy-2- butanone0.20.440.420.36糠醛Furfural0.961.211.37呋喃甲醇1.061.051.141.172-环戊烯2-cyclopentadiene1.131.280.980.712-羟基2-环戊烯2-hydroxy-2-cyclopentadiene0.680.720.790.753-甲基-2-环戊烯3-methyl-2-cyclopentadiene0.460.510.53吡啶Pyridine0.490.522-甲基吡啶2-methy-pyridine0.450.590.583-羟基吡啶3.683.77左旋葡聚糖Levoglucosan.8617.3316.9515.93吡喃葡萄糖D-Glucopyranose2.312.051.861.77四氟苯甲醚4-fluoroamisole6.134.25苯酚Phenol0.620.730.78苯二配Benzenediol2.512.632.752-甲氧基苯酚2-methoxyphenol2.041.0793对甲基苯酚p-methyiphenol0.890.942-甲氧基4甲基苯酚2-methoxy-4 -methy-phenol1.031.044-乙基-2-甲氧基苯酚4-thyl-2- methoxy -phenol320.95012-甲氧基4-乙烯基苯酚2-methoxy-4-vinylphenol phenol2.742.982.652.692.6-二甲氧基苯酚2.6-dimethoxy. phenol5.497.527.096.622-甲氧基4丙烯基苯酚2-methoxy-4-(l-propeny1)-phenol4.32.92.01生物油的组分主要包括酸类、酯类、酮类、呋乙酸含量在350~ 650C温度区间内逐渐减少,这是喃类、环戊烯、糖类、醚类。苯酚类及其衍生物等。因为二次反应加剧,乙酸发生了降解;糠醛含量随204农业工程学报2013年图7所示。当热解终温为350°C时,热解炭中的主Energy Resources, 2011, 29(3): 25- 29. (in Chinese with要有机官能团有: O-H (3 500~3 000cmh),C-HnEnglish abstract)(2 970~2860cm),C=O (1 730~1 700 cm*'),[2] Moen J, Yang C, Zhang B, et al. Catalytic microwaveC=C(1 632 cm+), C-O-C(1 260 cm'), C-H(900~assisted pyrolysis of aspen[J]. International Joumal of700cm') (28]。其中,O-H 及C=0具有较强的吸收Agricultural and Biological Engineering, 2010, 2(4): 70峰,且脂肪族结构特征峰很明显,表明此时木质素还未开始大量分解。在热解终温从350"C增大到[3]梅丽敏, 宗志敏,位艳宾,等.微波辅助下固体酸催550C的过程中,O-H峰值明显减弱,这主要是由化剂对稻壳热解油的催化加氢[].化工时刊,2011(7):于随温度的提高,生物质内半纤维素发生了分子内19-22.的脱水反应,C=O主要对应的是半纤维素内的醛酸Mei Limin, Zong Zhimin, Wei Yanbin, et al. Microwave-的羧基官能团,其吸光度也明显减弱,表明半纤维assisted catalytic hydroconversion of pyrolyzed oil from素发生了一系列的脱羧基、糖苷键断裂、环内C=Orice hull over solid acid catalyst[J]. Chemical Industry基团断裂、形成一一 系列的酸、醇、醛、醚类等物质,Times, 2011(7): 19 - 22. (in Chinese with English及CO、CO2等气体[29。在1600 cm-'附近出现了新abstract)的烯键峰,可能的原因是木质素分解时大量支链结4] Menendez J, Inguanzo M,Pis J. Microwave-inducedpyrolysis of sewage sludge[J]. Water Research, 2002,构消失而导致苯环类芳香族化合物的富集[30。当热36(13): 3261 - -3264.解终温增加到550°C时,各官能团的IR吸收峰均不明显,说明此温度下热解炭中的有机物质的含量已5] MenEndez J, DomiNguez A, Inguanzo M,et al.Microwave pyrolysis of sewage sludge: Analysis of the经很少。在终温650°C下的热解炭红外光谱图已接gas fraction[] Journal of Analytical and Applied近平滑曲线,只能够检测到微量的芳香族结构峰Pyrolysis, 2004, 71(2): 657- 667.(在1450~ 1600cmi'附近) ,表明此时焦炭已经接近6] Huang Y, Kuan W, Lo s, et al. Hydrogen-rich fuel gas完全热解,相比于电炉加热,焦炭在同等温度的微from rice straw via microwave-induced pyrolysis[J].波条件下热解更为充分。Bioresource Technology, 2010, 101(6): 1968- 1973.3.结论[7] 罗爱香.竹废料微波裂解及其产物性质的研究[D].南昌:南昌大学,2007.1)微波加热条件下,随着温度的上升,焦炭Luo Aixiang.Study on Microwave Pyrolysis of Bamboo产率下降,500"C以后趋于平缓;液体产率先增大Residues and Properties of Its Products[D]. Nanchang:后减小,在450~500C出现最大值;气体产率变化Nanchang University, 2007. (in Chinese with English则与之相反;2)棉杆微波热解的液体产物中有机成分主要8] Miura M, Kaga H, Tanaka S, et al. Rapid microwave由乙酸、苯酚、呋喃、糠醛、酯类、醛类、酮类等pyrolysis of wood[J]. Journal of Chemical Engineering of物质等组成,并且获得了较高产率的左旋葡聚糖Japan, 2000 33(2): 299- 302.(峰面积为19.86%)和乙酸(峰面积为11.47%),9]王贤华.生物质流化床热解液化实验研究及应用[D].其相对含量随温度升高逐渐降低;武汉:华中科技大学,2007.3)随着微波热解温度的上升,焦炭孔隙度先w ang Xianhua. Experimental Study and Application of增加,550°C时比表面积达到400.29 m2/g,之后逐BiomassFast Pyrolysis with Fluidized Bed[D]. Wuhan:渐下降,这主要与灰熔融及炭结构的缩合有关;焦Huazhong University of Science and Technology, 2007.炭的表面官能团随着温度的上升逐渐减少,650"C(in Chinese with English abstract)下几乎不存在表面官能团,说明此条件下热解较为[10] Yu F, Deng s, Chen P, et al. Physical and Chemical完全。综合生物油和焦炭的分析来看,550°C 条件Properties of Bio-oils From Microwave Pyrolysis of Corm下的微波热解可得到较好品质的炭、油产物。Stover[M] Applied Biochemistry and Biotecnology.Springer, 2007: 957-970.[参考文献][11] Williams P T, Taylor D T. Aromatization of tyre[]商辉,路冉冉,孙晓锋.微波热解生物质废弃物的研pyrolysis oil to yield polycyclic aromatic hydrocarbons[J].究[J].可再生能源,2011(3): 25 -29.Fuel, 1993, 72(11): 1469- 1474.Shang Hui, Lu Ranran, Sun Xiaofeng. Research on[12] Williams P, Bottrill R, Cunliffe A. Combustion of tyremicrowave pyrolysis of biomass waste[J]. Renewablepyrolysis oilJ]. Process Safety and Environmental Protection,206农业工程学报.2013年Property analysis of pyrolysis product from cotton stalk heating bymicrowaveLi Pan, Wang Xianhua , Gong Weiting, Yang Haiping, Chen Yingquan, Chen Hanping(State Key Laboratory of Coal Combustion Huazhong University of Science and Technology, Wuhan 430074, China)Abstract: The use of microwaves for heating is well established in society, and is being used in domestic andsome industrial processes. However, it has the potential to be introduced and applied to many other industrialheating processes, which offers unique advantages not attained from conventional heating. In this sense,microwave technology was being explored as one method to assist in pyrolysis process of cotton stalk. A studywas carried out on the effect of microwave on the liquid and solid products, then the physicochemical propertiesof pyrolysis products were analyzed by gas chromatography and mass spectrometry (GC-MS), isothermaladsorption analyzer (BET) and fourier transform infrared analyzer (FT-IR). The results showed that with the risingof the pyrolysis temperature, the yields of gas and liquid products had shown opposite trend, and the highest yieldof bio-oil was around 500"C (about 40%), however, the yield of char gradually decreased. Furthermore, within550-650C the changing rate became weaker. The bio-oil had a complex composition, and major compounds inthe liquid product were acetic acid, levoglucosan and phenolic substances. Besides the content of decreased aceticacid and levoglucosan with the increasing temperature, while acetic acid obtained by microwave heating wassignificantly lower comparing with conventional electric heating, which made the acidity of liquid productsdecrease, the high content of levoglucosan in the cotton stalk oil was discovered under microwave heating, whichcould go up to 19.86%. In addition, phenolic substances went up with the increasing temperature when below 450°Cthen multi-substituted phenolic substances had been declined but the content of phenol and hydroquinoneincreased when above 450"C, so it changed lttle in total phenolics. Conventionally pyrolysed char could not beused for further application since there persisted large and deep cracks due to the overheating of surfaces, whichmade them fragile and lost porous nature. Analysis of the product showed the adsorption loop type was L3.Moreover, microwave heating technique was conducive to the formation of the developed pore structure and thespecific surface area and micro-pore surface area were first increased and then decreased as the temperature rose,the maximum of SBET and Smic reached 400.29 m/g and 276.93 m/g at 550"C, which was known as microwaveheating and was highly effective in pyrolysing biomass, specifically the large size which otherwise if not possiblebut would had been difficult. The surface functional groups of char at 350*C mainly included O-H (3 500-3 000 cmC-Hn(2 970-2 860 cm '), C=O(1 730-1 700 cm "), C=C(1 632 cm ), C-O-C(1 260 cm') and C-H(900-700 cmi')then gradually decreased as temperature increased. Only small amount of aromatic structure peak (around1 450-1 600 cmi ) could be detected at 650C, which indicated the char had been close to completely pyrolysis.The comparative results showed that microwave pyrolysis had a very good prospect on the optimization of bio-oil,getting high value-added products such as levoglucosan, and also the preparation of activated char with highspecific surface area.Key words: pyrolysis, temperature, straw, pyrolysis oil, char(责任编辑:秦学敏)

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