| 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-?)]3and a differential form of f(?)=1/3(1-?)[-ln(1-?)]-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. |
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