Research On The Pyrolysis Characteristics And Products Formation Mechanism Of Oil Sand

With advanced testing techniques and experimantal methods, this paper specially focuses on the relationship between the chemical structre features and pyrolysis reaction characteristic. Based on the microcosmic change of oil sand during pyrolysis process, pyrolysis characteristics of oil sands were studied systematically from theoretical and experimental aspects. Then the pyrolysis reaction characteristics of oil sand was considered, so as to reveal the pyrolysis products generation mechanism essentially. Specifc research content are listed in the following:Pyrolysis experiments of oil sand were conducted on thermo-gravimetric analyzer with different heating rate, particle size and reaction atmosphere, respectively. The characteristics of oil sand pyrolysis based on the technologies of TG-DTG^TG-DSC and TG-FTIR have been obtained. The results show that all oil sands pyrolysis process includes four stages:initial dehydration, low temperature pyrolysis of bitumen, the decomposition of hydrocarbons and high temperature pyrolysis of minerals. Theoretically, kinetic parameters of oil sand pyrolysis were calculated. A lot of methods, such as Coats-Redfern method, Flynn-Wall-Ozawa method, DAEM method, untraditional Arrhenius theory and multiple peaks fitting method, have been extensively used to determine the activation energy and frequency factor. The change laws of Activation energy with the conversion relations in the pyrolysis process are received. An asymmetric multi-peak fitting method, bi-Gauss, was creatively introduced to separate the overlapping peak, and the oil sand pyrolysis reaction mechanism functions are determined. The results show that the bi-Gauss method can produce more satisfactory fitting results than the classical Gauss method. Moreover, the subpeaks follow a single mechaniasm, the overall stage does not follow a single mechanism and the mechanisms of the front and back segments of the overall stage are in accordance with those of the subpeaks, which prove the applicability of the two-component parallel model.In this paper, the combustion characteristics of oil sand were further studied. Also some combustion parameters such as:ignition temperature, the combustion stability Discriminant index and combustion reaction performance parameters were obtained. On this basis, the complex peaks of experimental DSC curves were effectively separated into multiple Gaussian function peaks, and the contribution of different pseudo components'combustion heat to the total heat effect of oil sands were discussed. Finally, the kinetic mechanism functions of each oil sand components were determined according to Malek's method, and the result shows that different component has different mechanism function.The gas products release characteristics during pyrolysis process was studied using TG-FTIR spectrometry, which examined the influence of heating rate on the release law of CO2, CO, H2and CH4. That revealed the release mechanism of gas products during oil sand pyrolysis.Pyrolysis experiments of oil sand were conducted in a bench-scale fixed-bed reactor to investigate the effect of temperature, heating rate on liquid and gas yield, the key pyrolysis parameters of oil sands were optimized. With increase of temperature, liquid yield and gas yield of pyrolysis all increase, but the char yield decrease. The gas product components were determined by using gas chromatograph analysis. The results showed that the major gases produced during oil sand pyrolysis were CO, CO2, H2, CH4, C2H4and C2H6. Gas calorific value is about33MJ/m3, with the increase of pyrolysis temperature, pyrolysis gas calorific values were presented a trend of firstly increase then decrease little.In this paper, the pore structure of oil sand char at different pyrolysis temperature was investigated in detail, and the pyrolysis temperature had a greater influence on the adsorption quantity of oil sands char. the FTIR experiment was used to analyze various functional groups characteristics, from which the oil sands pyrolysis reaction mechanism from the microscopic view revealed, the aromatic hydrocarbon, aliphatic hydrocarbon, hydroxyl and the oxygen functional groups in the samples were determined.Each functional group curve was separated into multiple Gaussian function peaks, then the characteristic absorption peak of organic component was determined, so as to receive the degree of rich hydrogen, the structure of the aliphatic hydrocarbon, aromaticity and other parameters.The1H and13C NMR experiments of oil sands oil were conducted on nuclear magnetic resonance spectrometer. Each spectrum was analyzed according to the spectral peaks affiliation, the improved Brown-Ladner method was used to calculate the average structure parameters of oil. The results show that, with the increase of the pyrolysis temperature, the oil chemical structure have obvious change.