棉稈結構及熱解規律的研究

Agricultural Science Technology, 2011, 12(2): 175-178, 182Copyright 2011, Information Institute of HAAS. All rights reservedgricultural Basic Science and MethodResearch upon the Structure and Pyrolysis ofCotton stalkFENG Xue, HUA Jian, MAO Wei-kun, WU Li-li, YIN Hua-qiangDesulfurization Engineering Technology Center of Sichuan University, Chengdu 610065Abstract Purpose] To research upon the structure and pyrolysis of cotton stalk. Method] In this paper thermogravimetric analysis is adoptedto study pyrolysis characteristics on the longitudinal direction of cotton stalk(the stick and the root )and on the traverse direction( the cuticlecortex and medulla ).[ Result Cotton stalk is a material of uneven and irregular texture, and there are great differences in the structure of allthese parts on the longitudinal and traverse directions, especially in the contents of different components in each layer. The reaction in the stickand root becomes violent along with the increase in the rising rate of temperature, and carbon yield rate decreases in turn. Besides with thesame rising rate of temperature, carbon yield rate of cotton stick is higher than the one of cotton root, Carbon yield rates of cuticle, cortex andmedulla decrease in turn while the violence of the reaction in cuticle is less severe than in cortex and medulla. Conclusion It has provided theo-retical basis for obtaining activated carbon technology of cotton stickKey words Cotton stalk; Cotton root; Structure; PyrolysisAs renewable resources, waste biomass materials are cotton stalks. Therefore, in this paper, through thermograotential resources of energy and industrial chemicals. Ac- metric analysis pyrolysis characteristics of different parts ofcording to the statistics, the annual output of agricultural bio- cotton stalks are studied in order to provide theoretical basismass around the world is 30 billion tons, whose consumption for obtaining activated carbon technology of cotton stalksis only behind those of fossil fuels such as petroleum, coaland natural gas among world energy consumption. However, Materials and Methodsthe utilization of biomass resources is far from large-scale Materialscommercialization as the content of global biomass utilized asThe samples of cotton stalks come from Kuitun, Xinjiangenergy is less than 4% of the total, which promises a great Before analysis, samples were first dried in an oven, whichtialwere then cut into small regular particles The diameters ofAs a great power contributing to the output of cotton in the particles are from 0.5 to 1.0 mm)the world, China has the acreage of 533 300 hm cotton. CotMethodston stalks are the waste that cotton planters discard after pickSelect 20 sample cotton stalks to be weighed, separateing the cotton, weighing 3 375 to 3 750 kg/hm and amounting cuticle, cortex, and medulla to be weighed respectively, andto 1.53 million tons in China every year 1. In generalaverage their weights to get the average weight percentagericultural waste, cotton stalks are directly burned as fuels in each layer. Ash contents of cuticle, cortex, and medulla arethe countryside in the way that produces very low thermal effi- measured with reference to GB/T12496 3-1999. The pictureciency. The rest is dumped in the field that causes great of the structure of cotton stalks is taken by Samsung Digitalwaste. The discarded cotton stalks are materials rich in lignin Camera SL420 from the vertical height of 50 cm. The comso that it can be made into activated carbon that has a wide nents of each part of cotton stalks are measured according torange of use and high additional value, one of the efficient the international standard GT9888-89 Method of Quantitativeways to develop discarded cotton stalk resourcesAt present, thelication ofAnalysis of Ramie chemscai Components. 1106 Elementalted carbon has beenAnalyzer manufactured by CARLO ERBA, Italy, is adopted toincreasingly wide in environmental protection, national de-measure the content of carbon, hydrogen, and nitrogen. Setfense, chemistry, food and medicine and so on, and its quan- the weighttity demanded is also increasing. As the raw material of acti- the weight percentage when cotton stalks are carbonized tovated carbon is mainly of the consumption of coal and wood600C as effective carbon yield rate. Thermogravimetric analysis is done by TG209 F1 thermogravimetric analyzer manuresources, the research and exploration of the sources of its factured by NETZSCH Company, whose sensitivity reachesraw material have great realistic significance. There are fairy 0.001 mg. The shielding gas and the carrier gas in the experi-many researches upon the production of activated carbon from ment are both highly pure N2 of 99. 99% with a flowing rate ofbiomass( such as wood, bamboo, fruit shell or stalks )2, 20 ml/ min. The temperature rising rate is 10 K/min, and thewhich provide technical references to the research and exploration of activated carbon from discarded cotton stalks. Re-lrV凵中國煤化工8113Ksearch upon pyrolysis law of cotton stalks is the basis in theCNMHGization technology of discardedRescottonstalks, yet at present there are no reports upon pyrolysis of Analysis of the structure and components of cottonstalksMorphology and elemental composition of cotton stalksReceived: June 6, 2010 Accepted March 4, 2011According to the longitudinal and transverse direction of the而數棉r,E- mail: clouding68163.c0mstructures of cotton stalk parts, it can be divided into: bran-Agricultural Science Technology Vol 12, No 2, 2011ches and roots of cotton stalks( Fig. 1) in the longitudinaldifference in their functions including pyrolysis and it will defi-rection(upside down). At the growing stage parts below the nitely have great influences upon the weight of activated carground are the roots of cotton stalks while those above are all bon of cotton stalksas sticks. In the transverse direction( transverse section ofcotton stalks ), it is composed of cuticle, core cortex and coremedulla. The proportion of the weight of each part of cottonstalks in the whole can be set as the factor in analyzing anddetermining how it influences the weight of carbonized cottonstalkss the measurements show, cotton stick is the main partof the body materials, whose weight counts 75%of the totalcotton root counts 25%; and the weights of cuticle, core andmedulla of cotton stalk take up 24%, 73% and 3% of the totalrespectively. Therefore, it can be noticed that different fromother wood materials, discarded cotton stalks are not integralCot ton rootsCotton sticksmaterials weighed evenly. Different parts of cotton stalks haveFig 1 Longitudinal map of cotton stalksgreat differences instructure. which will result in theticleCortexMedullaCot ton sticksCuticleContexre medullaFig 2 Traverse map of cotton stalksFrom Fig. 2 it can be noticed that cuticle is the newly tween the contents of each element is below 10% while thegrown reddish-brown skin layer, which is attached to the sur- content of oxygen in the stick is 0. 98 times of the one in theface of the core. The core of cotton stalk is the circular hollow root. In the traverse structure, the differences among differentcore in the middle of the profile of cotton stalk, and core me- elements in cuticle, cortex and medulla of cotton stalk aredulla resembles a cylinder in general with a loose structure, quite evident. The contents of carbon in cuticle, cortex of cot-distinct space and holes in between. From below one third of ton stalk are 1. 02 and 1. 03 times of the one in the medulla ofthe main stem of cotton stick, all of medulla has been ligni- cotton stalk respectively and the content of nitrogen is 1.07fied, and above one third it increases with height and number times of the one in the medulla. However, the content of oxyof branches 3.gen is slightly below the one in the medulla. And the contentAfter measuring the elemental composition of cotton of hydrogen in cuticle is the lowest( Table 1). Compared withstalks, the results indicate that just like other plant materials other stalk materials such as corn and rice stalk, the contentthe chemical elements of cotton stalk are mainly hemicellu- of carbon in cotton stalk is 1.20 and 1.04 times of the one inlose, cellulose, and lignin and its main elements are carbon, corn stalk and rice stalk respectively the content of hydrogenhydrogen, oxygen and nitrogenis 1. 16 and 0. 81 times respectively; the content of oxygen isTable 1 Analysis of elemental weight of cotton stalks1. 30 and 1.01 times respectivelyStalksCarbon Hydrogen Nitrogen Oxygen Table 2 Analysis of the content of cotton stalk componeCotton stalks Cott44.475.600.5349.47Wax Hydrotrope Pectin Hemicellulose Lignin0.4450.Cuticle5,1627.079,7630,3627,6523.655.8517.1552.4220.492.65Cortex 40. 885.371.2652.50Medulla707.7637.04Medu|a39.685.480.7254.10YHa中國煤化工Corn stalks 4364.821.2837.98Rice stalks 5JCNMHGtton stalk It can be ob-0.8148.8ervedcontent of components in each part of cotton stalk. The conIn the longitudinal structure, there are some differences tent of ash in cotton stalk is comparatively higher than the onein the contents of each element in cotton stick and root. The of other biomasses. Effective carbon is mainly from lignin. Incontents ot caslightly high圖nn, and nitrogen in the stick arethe study, the content of lignin in cortex is the highesthose in the root and the difference be- amounting to 52. 42% of the total, which is 1. 9 times and 5. 4FENG Xue et al. Research upon the Structure and Pyrolysis of Cotton Stalk177times of the one in cuticle and medulla respectively. The con- weight loss of cotton stick(16%)is less than the one of thetents of hemicellulose and lignin are higher than the one of root(10%), that is, volatile components in the decompositionother components, and the main components in medulla are of the latter are more than the former, and cellulose andhemicellulose, cellulose, wax, and lignin. The content of ash hemicellulose as volatile components in the root are more thanin different layers also varies greatly as the one in cotton stick in the stickis 1.2 times of the one in the root in the longitudinal directionThe forth stage is from 310 to 900 C, also called as con-The content of ash in cuticle in the traverse direction is the tinuous carbonization. At this stage, weight loss becomesghest, 2.2 times and 1. 98 times of the one in cortex and slow and the remaining lignin gradually decomposes alongmedulla respectively. Therefore, the weight of effectivewith the increase of temperature, which is mainly about thebon after carbonization of cuticle and medulla is lower than the breakage of C-C and C-H bonds. The remaining volatileone of cortexmatter continues to precipitate, and weight loss becomes lessThermogravimetric analysis of cotton stalkand less. During this stage, the rate of weight loss in cotton/hole cotton stalk as well as in the characteristics of pyrol- the whole pyrolysis process. When the temperature reachesysis, analysis of pyrolysis curves of each part is made from the final one, the weight of remains becomes constant, andlongitudinal and traverse directionthe final residual of pyrolysis is solid coke羅=一獎羅2468Temperature℃Terperature℃Fig 3 TG/DTG curves of cotton stalk and rootFig 4 TG/DTG curves of cuticle, cortex, and medulla of cot-Thermogravimetric characteristics of cotton stick androot The first stage is dehydration and dryness of the mate- Characteristics of pyrolysis of cuticle, cortex, and medullarials from room temperature to 90 C. Along with the increase of cotton stalk The pyrolysis curves of cuticle, cortex, andin the temperature, water evaporates before pyrolysis, and medulla of cotton stalk are the same as the ones of the stick andsamples of cotton stick and root will have slight weight loss, the root, which can be divided into four stageswhich is shown as the decline of TG curve. In this stage, theThe first stage, with reaction temperature from room temveight loss of samples is water within the materials, as water perature to 110 C, is mainly of dehydrogenation and drynessloss in the stick is about 6% to 8 and the one in the root is of the materials. Weight loss at the skin layer is greater thanabout 4% to 5%in the core, while the weight loss in the core layer is higherln. The second stage is pre-carbonization from 90 to 210 C. than in the medulla. It is because that pectin and ash in cuti-this stage, tG-DTG curve is even and smooth that samples cle have strong ability of water absorption and medulla withof cotton stick have depolymerization, reorganization, and loose structure is easier to regain moisture than cortex withmodification such as the destruction of crystalline regions, and tight structure. However, medulla lies in the core of cottonelease of compounds with small molecular weight. The stick and its water content is relatively low. In the secondweight of the samples of cotton stick and root has no distinct stage, the curves of all three layers are all comparativelychange with a weight loss rate less than 1%smooth and there is only a small gap between the beginningThe third stage is the main phase of pyrolysis, also called temperature of the curves and the terminating temperatureas carbonization, from 210 to 300 C, where most weight loss (110-200 C). The differences among pyrolysis of cuticleof cotton stalk occurs. TG curve slope is fairly large, and the cortex and medulla are mainly manifested in the third stageweight loss rate of cotton stick(45%)is less than the one of The reaction temperature in medulla ranges from 200-310the root (55%). The corresponding DTG curve also has the C, which is evidently below and narrower in comparison withmaximum peak, which of the cotton stick is -3 98 and of the the one in cuticle(200-375C)and the one in cortex(200root is.37, indicating that the reaction in the root is more 380C). Maximum peak value of DTG curves of cuticle andiolent than in the stick. In this stage, it is the pyrolysis com- cortex are both about 320C, but the peak of cortex is sharp-bination of the three main components in cotton stick and root er wit中國煤化工 the reaction in cortex issuch as hemicellulose, cellulose and lignin. At first, it is the morete of temperature. At 275decomposition of unstable hemicellulose. Along with the in- CCNMHcreasing of the temperature, after the reaction of hemicellu- action begins to slow down and the acuteness also lessenslose is basically done, parts of cellulose and lignin begin to However, the later appearance of shoulder-shaped peak isdecompose. After heating, pyrolysis will occur and release because that medulla materials made up of loosely arrangedyolatile gases including CO, H2, CH, and big thin walls have a small density while the sample takes up aetc. tar anIs coke[6-7. Under the same condition. large space. Therefore, during the test the contact betweenAgricultural Science Technology Vol 12, No 2, 2011samples and crucible is not even which results in the lag of ording to the differences in its morphological features. In theheat transmission and consequently influences the curve of traverse direction it can be divided into cuticle, cortex and me-heat analysis. At this stage, the rates of weight loss of the dulla. There are great differences in their elemental composi-three parts of cotton stalk profiles are respectively 39%, 57% tion as compared to ashes. Pyrolysis reaction of cotton stalkand 52%. During the fourth stage, the characteristics of the possesses similar laws with wood materials as it can be divid-curves of temperature change and weight loss are that pyroly- ed into four stages, that is, dehydrogenation( room tempera-sis of cuticle and cortex is close to the one of the stick while ture to 110 C), pre- carbonization(90-275 C),carboniza-the weight loss curve of medulla varies greatly. At this stage, tion(210-375 C), and continuous weight loss(310-900the rate of weight loss in medulla is higher than the one inC).As there are great differences in the structure of cottonicle and cortex, which are 13% and 8% respectively. And the stick and root, the differences in their pyrolysis law are shownrate of weight loss in medulla is 31%as there are great differences in their weight loss curve whenCarbon yield rate of each part of cotton stalkthe reaction temperature increases. The degree of pyrolysiss the compositions of each part in the stick, root, cuti- and the rate of weight loss in the root are higher than the onescle, cortex, and medulla are different from each other, the of the stick while the rate of carbonization in the stick is highdifferences in pyrolysis laws are also represented as differ- er than in the root. As the structure and composition of cuti-ences in carbon yield rates. From Fig. 5, it can be known that cle, cortex and medulla of cotton stalk are different, the varia-carbon yield rate from pyrolysis of cotton stick is higher than tion in their pyrolysis is shown as the rate of carbonization ofthe ones from all the other parts, which is about 8%higher cuticle, cortex and medulla decreases one by one, the peakthan the one from the root, 2% higher than the one from cuti- temperature of pyrolysis in the medulla is below the one incle, 21% higher than the one from cortex and 31% higher cortex, and the reaction in the cortex is most acutethan the one from medulla. According to the change in thegrowth and structure of cotton, the content of cellulose gradu- Referencesally increases from the top down in the whole stick, which be-[1]uL(李龍), SHENG GZ(盛冠忠),WL(吳磊). Development andcomes highest in the root. And in the stick the content ofutilization of cotton bast fibers resource(棉桿皮資源利用開(kāi)發(fā)研究)lignin is higher than the one in the root. Therefore, relating to[J]. Plant Fiber Sciences in China(中國麻業(yè)科學(xué)),2008,30(4)stick after pyrolysis is higher than the one of the root.Wnts[2YUJ(于娟), ZHANG MC(章明川), SHEN Y(沈鐵),eta!Thermore, carbon yield rate of cuticle, cortex and medulla of cotmogravimetric analysis of pyrolysis characteristics of biomass(=Ety質(zhì)熱解特性的熱重分析)[J]. Journal of Shanghai Jiaotong Univerton stalk decreases in turn, which is also determined by theircomposition. The main components in the medulla are cellu-[3]UXY(徐學(xué)耘). Preliminary analysis on the raw of cotton stalk(棉lose, hemicellulose, pectin, hydrotrope and a little gases and稈原料的初步分析)[J]. Building Artificial Boards(建筑人造板)1994(3):24-30carbohydrate in a loose arrangement with great spaces in be[4] SONG CC(宋春財),HUHQ(胡浩權),zUSW(朱盛維),etatween. Among these components, lignin mainly producesBiomass pyrolysis and its kinetic parameters with different methodsfixed carbon, while cellulose and hemicellulose mainly pro-生物質(zhì)秸稈熱重分析及幾種動(dòng)力學(xué)模型結果比較)[J]. Journal ofduces volatile matter. 6. There are certain amount of ligninFuel Chemistry and Technology(燃料化學(xué)學(xué)報),2003,31(4hemicellulose and cellulose in both cuticle and medulla layer311-315Carbon yield rate of cuticle is highest while its ash content i⑤F20(中水°團)paalso comparatively high(5. 85%), about twice of the one inprocess of grass biomass(草類(lèi)生物質(zhì)熱解特性及動(dòng)力學(xué)的對比研cuticle(2. 65%)and of the one in medulla(2. 95%).There-究鍋爐技術(shù))[J]. Boiler Technology(鍋爐技術(shù)),2009,40(3)fore, carbon yielded from the carbonization of cuticle is different from the one from cortex and medulla[6]DAWD(戴偉娣), TAO YB(陶淵博), ZHANG YP(張燕萍),etaStudies on pyrolysis of wooden material and structure of the ob-tained activated carbon(木質(zhì)原料熱解及活性炭結構的研究)J]Chemistry and Industry of Forest Products(林產(chǎn)化學(xué)與工業(yè))[7ANTAL MJ. Cellulose pyrolysis kinetics: the current states of knowdge[J]. Ind Eng Chem Res, 1995, 34(3): 703-717[8 JIANG H(SFF). Preparation of activated carbon from cotton stalkand analysis on its pore structure(農業(yè)廢棄物棉桿活性炭的制備及其孔隙結構分析)[J]. Journal of Anhui Agricultural Sciences(安徽農業(yè)科學(xué)),2010,38(35):20239-20240[9]oUJ(邱瑾), PANG JZ(龐金釗),LUz(劉忠),eta!. Effects ofStick Root Cuticle Cortex Medul labioconversion broth of cotton stalk pulping waste liquor on segermination and seedling growth of eggplant(棉桿制漿廢液生物轉化Fig 5 Carbon yield rate of every part of cotton stalk中國煤化工n0,(85):29-2024ConclusionCN MHGANBO嚴波), et al. 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Journal ofof micropore volume of activated carbons from adsorption dataHazardous Materials, 2008, 154(1/3): 337-346[J]. Carbon,1998,36(10):1469-1472Responsible editor: LI Ting-tingResponsible proofreader: WU Xiao-yan(上接第178頁(yè))棉稈結構及熱解規律的研究(摘要)馮雪,華堅,毛煒坤,吳莉麗,尹華強(四川大學(xué)脫硫工程技術(shù)中心,四川成都61006[目的]研究棉稈的結構及熱解規律。方法]采用熱重分析法研究了棉稈縱向(棉桿和棉根)及橫向(皮層、質(zhì)層和髓層)的熱解特性。結果]棉稈是一種質(zhì)地不均勻的材料,其橫、縱向各結枃存在較大差異,各層成分含量差異明顯。棉桿和棉根隨升溫速率增大反應程度越劇烈,炭得率依次減小,且相同升溫速率下,棉桿炭得率高于棉根;皮、芯、髓層炭得率依次減小,皮層反應劇烈程度小于芯和髓層。[結論]為獲得棉稈活性碳技術(shù)提供了理論依據。關(guān)鍵詞棉稈;棉根;結構;熱重作者簡(jiǎn)介馮雪(1984-),女,河北臨城人,碩士研究生,研究方向:棉稈活性炭炭化工藝、性能及應用,F-mil:cloudierκ66163.com。*通訊作者教授,博士,碩士生導師,內債煙氣脫硫工程材料、生態(tài)紡織材料和桑皮材料工程研究,E-muil:huajian@scu.edu.cn。收稿日期20100646修回日期2011403404中國煤化工CNMHG