【作者】 谢清若；

【导师】 童张法；

【作者基本信息】 广西大学 ， 化学工艺， 2014， 博士

【摘要】 亚热带生物质是取之不尽的天然资源,而且其废弃物产量非常大。传统的生物质废弃物利用方式能量利用率低,热裂解转化是一种高效的生物质废弃物高值化利用新技术。如何有效地利用热裂解技术由生物质原料制备生物油和活性炭成为研究的热门课题,而热裂解过程机理、动力学、装置及工艺是技术产业化应用的关键因素,本文为此以薯秆、竹材和桑枝秆等典型亚热带生物质废弃物为研究对象对其热解过程进行系统的研究。本文采用元素分析、工业分析、组分分析等方法,研究薯秆、竹材和桑枝秆原料的理化性质；采用热裂解-气质联用(Py-GC-MS)技术进行热裂解过程的反应分析,探讨反应机理及其差异；采用利用热重分析技术研究热裂解过程动力学；基于传统和现代模拟设计手段,自行研制了一套生物质废弃物热裂解装置,并利用该装置进行热裂解制备生物油试验,采用相应面法优化其过程工艺,同时以热裂解残炭为原料,采用磷酸活化法制备了活性炭。主要研究内容和结果如下：(1)研究了木薯秆、竹材和桑枝秆等原料的理化性质,结果表明,3种原料的固定碳和挥发份含量相差不大；碳、氢、氧三种元素总含量都在96%以上；纤维素、半纤维素和木质素总含量超过70%。同时,3种原料的混合物的纤维素、半纤维素和木质素含量分别为36.54%、25.58%和19.35%。(2)采用热裂解-气质联用(Py-GC-MS)技术进行热裂解反应分析。结果表明,皮层和芯层的混合物热裂解都获得酚类、酸类、烷烯烃类和醛酮类化合物,而芯层混合物热裂解还获得酯类和醇类化合物,另外多了9种产物；芯层混合物热裂解的糠醛含量高达16.50%,而皮层混合物热裂解产物的乙酸含量高达30.22%；亚热带生物质热裂解反应属于两步竞争反应机理,热裂解过程形成了中间产物-活性纤维素；纤维素含量的高低、木质素结构的差异和灰分含量的高低,决定了芯层和皮层物质热裂解机理的差异；紫丁香基结构单元的物质热裂解产物远远多于愈疮木基结构单元的物质,糠醛、香草醛、苯酚以及其它重要的酚类衍生物等分别来源于不同原料的热裂解。(3)测定混合物热裂解的热失重曲线,分析热裂解过程,进行数据处理并计算反应活化能和指前因子,确定热裂解反应动力学参数,建立了动力学模型。研究表明,热裂解过程分为四个阶段,随着升温速率提高,主反应区向高温区移动；反应的活化能为E=279.89KJ·mol-1,频率因子为A=1.12×1024s-1,其为成核和生长机理,反应级数n=3,动力学方程表示为Avrami-Erofeev方程,积分形式G(α)=[-In(1-α)].,微分形式f(α)=1/3(1-α)[-In(1-α)]2,升温速率的大小对活化能的影响不大,但对炭的产量有影响,较高升温速率对炭的生成有抑制作用。(4)根据热裂解过程原理,设计了热裂解装置的送料、反应、产物收集等主要系统,模拟了工艺流程、流化床反应器床内的颗粒速度分布、速度矢量及压力分布,并对自制的装置进行运行验证。结果表明,采用螺旋送料机和流化送料的方式,能够在0.2～1.0mm颗粒大小范围顺利送料,在0.5～4.5m·s-1流速范围内可选定一个优化的操作送料速度；采用调控颗粒拦截、旋风分离与滤网强化过滤以及球形冷凝空间,使高温气固分离效果进一步提高；在温度为450～1000℃,生物油收率达到62.29%；通过控制热裂解程度,可实现生物质液-固产物联产。(5)分别以木薯秆、竹材和桑枝秆为原料,进行制备生物油实验研究,并优化了过程工艺。结果表明,原料的纤维素、挥发分、灰分含量及其高分子结构特性对生物油产率有影响,桑枝秆热裂解的生物油产率最高；C、H、N、O等元素主要集中于生物油中；原料灰分高,二次反应促进了水的生成,对制备生物油不利；生物油产率先随温度的升高而上升,然后随温度的升高而下降；粒径对生物油的产率的影响较小,响应面法优化结果为：温度519.0℃C、气相停留时间2.1s、物料粒径0.18mm,生物油收率为58.17%。(6)采用调控液-固-气三者的比例的方法,获得了炭化效果较好的、比表面积达113.38m2·g-1的生物质热裂解炭材料,考察了磷酸浓度、浸渍比、活化时间和活化温度等因素对活性炭碘吸附值及产率的影响,探讨了孔结构形成机理,并表征了活性炭的结构。结果表明,热裂解残炭制备活性炭的最佳条件为取用70%-85%的磷酸、1.0的浸渍比、120min的活化时间、450℃的活化温度；活化过程中有磷酸盐或多磷酸盐桥、多聚磷酸混合物与炭的结构体的形成,对热裂解残炭的活化起着一定的作用；活性炭碘吸附值高达1389mg·g-1,比表面积为1421.38m2·g-1,孔径分布主要集中在18～60nm之间,以中孔结构为主。采用热裂解制炭-磷酸活化的活性炭制备新方法,可制备具有较高比表面积和较大中孔体积的活性炭,缩短了活性炭制备时间,提高了热裂解残炭的附加值。更多还原

【Abstract】 Subtropical biomass is a kind of inexhaustible natural resource, and the amount of its waste production is very large, and the energy efficiency of the traditional method of utilizing biomass waste is very low. pyrolysis is a new technology on the highly efficient conversion and high-value utilization of biomass waste. The technology about how to effectively use pyrolysis to prepare bio-oil and activated carbon from biomass is a focus at present, and the mechanism, kinetics, devices and processes of involved in the pyrolysis process are the key factors in the application of the technology in industry. In the present thesis, the typical subtropical biomasses, such as the stalk of cassava, bamboo, and mulberry, were systematic research on its pyrolysis process.Elemental analysis, industry analysis, and component analysis methods were used to study the physical and chemical properties of the stalk of cassava, bamboo and mulberry; pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) technology was used to analyze the pyrolysis process, and to explore the reaction mechanism and the differences; the therma gravimetric analysis technique was used to study the kinetics of pyrolysis. Based on the traditional and modern simulation design tools, a set of biomass waste pyrolysis equipment was developed, and was used to prepare bio-oil by pyrolysis, and the conditions of the process were optimized by using the response surface method. Simultaneously, using the residue carbon of pyrolysis as raw material, activated carbon was prepared phosphoric acid activation. The main results are shown as follows:(1) The physicochemical properties of stalks of cassava, bamboo and mulberry stalk were studied. The results showed that the fixed carbon and volatile component in the three kinds of raw materials were almost the same:the total content of C, H, and O is more than96%, and the total content of cellulose, hemicellulose and lignin is more than70%. Meanwhile, the content of cellulose, hemicellulose and lignin in the mixture of the above three materials were36.54%,25.58%and19.35%, respectively.(2) Pyrolysis-gas chromatography-mass spectra (Py-GC-MS) technique was used to analyze the pyrolysis reaction. The results show that the main products of the mixture of the cortex and the core materials of the mulberry stalk were phenols, acids, alkyl hydrocarbon, aldehydes and ketones compounds, in which, the pyrolysis of the cortex mixture obtained alcohols and esters and9more products. And the content of furfuraldehyde was16.50%in the pyrolysis product of cortex mixture, and the content of acetic acid was30.22%in the pyrolysis product of cortex mixture. South subtropical biomass pyrolysis reaction attribute to a two-step reaction mechanism of competition, and the intermediate product-active cellulose was formatted in the pyrolysis process. The content of fiber, the difference of the lignin structure and ash content are related to the formation of pyrolysis products, which determines the difference of the pyrolysis mechanism of the core and the cortex materials. Innovatively, the content of the material with a syringyl structural units lysates far more than that of the guaiacyl structural units and furfural, vanillin, phenol and other phenolic derivatives are come from the pyrolysis of biomass of different materials.(3) By recording the TGA curve of the mixture, the pyrolysis process was analyzed, and to determine the kinetic parameters and model of the pyrolysis, the data was treated and the activation energy and pre-exponential factor were calculated. Kinetic studies of pyrolysis found that the pyrolysis process of the mixture of south subtropical biomass included4stages of dry, preheated-cracking, pyrolysis and calcination charring. With the increase of heating rate, the main reaction zone moves to the high temperature zone, the activation energy of the pyrolysis reaction is E=279.89kJ·mol-1, and the frequency factor is A=1.12×1024s-1, which is a mechanism of nucleation and growth, and the reaction order n=3, the kinetic equation is a Avrami-Erofeev equation with a integral form of G(a)=[-ln(1-α)]3and a differential form of f(α)=1/3(1-α)[-ln(1-α)]-2. The heating rate has little effect on the activation energy, but affected on the yield of carbon, and particularly high heating rate will inhibit the generation of carbon.(4) According to the mechanism of the pyrolysis process, the main system of feed, reaction, and product collection of the pyrolysis equipment was designed, and the process, distribution of the velocity of particle in the fluidized bed reactor, and the distribution of velocity vectors and pressure were simulated, and the self-developed equipment was verify in the operation. The results show that, when the feeding system of screw feeder and the fluidizing feed was employed, and the particles with a size of0.2～1.0mm can be smoothly feed, and an optimized operation feeding speed can be selected in0.5-4.5m·s-1. Regulation of the particles intercept, cyclonic separation, enhanced filtration by a filter, and cryogenic condensation of a spherical condensation space were used to improve the gas-solid separation at high temperature. At450～1000℃, the yield of bio-oil reached62.29%, And through controlling the pyrolysis level, the products of liquid-solid-generation of biomass can be realized.(5) stalks of cassava and mulberry, bamboo was used as raw materials to prepared bio-oil, and the process conditions were optimized. The results showed that the content of the cellulose, volatile components, ash and the characteristics of the polymer structure affect the yield of the bio-oil, and the yield of bio-oil was maximum by using mulberry stalk as raw material. After pyrolysis of the biomass, the elements of C, H, N, and O were sum up in the bio-oil. For the material with higher ash content, the secondary pyrolysis reaction promotes the generation of water, which is unfavorable for the preparation of bio-oil. The yield of bio-oil raised with the increasing of the pyrolysis temperature in the first stage, and then decreased in higher temperature, and the effect of particle size on the yield of bio-oil is smaller. The optimization pyrolysis conditions are as follows:the pyrolysis temperature is519.0℃, the residence time of gas is2.1s, and the particle size of the raw material is0.18mm, and the yield of bio-oil is58.17%.(6) Regulated the proportion of liquids, solids, and gases, a biomass charcoal material with better carbonization and a surface area of113.38m2/g was obtained from the pyrolysis residues. The effects of the concentration of phosphoric acid, impregnation ratio, activation time and activation temperature on the adsorption of iodine on the activated carbon and yield of activated carbon were studied, and the formation mechanism of pore structure was discussed by characterization of the structure of activated carbon. The results show that the optimal condition of the preparation of the activated carbon are the phosphate concentration range was70%to85%, the impregnation ratio was1.0and impregnated at℃80and activated at4502℃for120min. In the process of the carbon residue phosphorylation, there are the formation process of the generation of the phosphate or the phosphate bridge, and the generation of the structure of poly-phosphate mixture and charcoal, which plays a certain role in the activated of the carbon residue. The absorption iodine value and surface area of the prepared active carbon are1389mg·g-1and1421.38m2·g-1, respectively. The pore size distribution concentrated in the18～60nm. The pore is mainly of mesopore and porous. Using the new method of pyrolysis to prepare charcoal-phosphoric acid activation, activated carbon with a high specific surface area and pore volume can be prepared, and which reduced the preparation time and increased the addition-value of the pyrolysis carbon residue.更多还原