【作者】 陈振；

【导师】 应卫勇；

【作者基本信息】 华东理工大学 ， 化学工艺， 2011， 博士

【摘要】 二甲醚(DME)作为一种新型的清洁能源和化工原料,是替代柴油和液化石油气的理想燃料。合成气一步法制取二甲醚工艺打破了合成气制甲醇时的反应平衡限制,在热力学上十分有利,可以提高CO单程转化率。浆态床反应器具有良好的传热性能,将其应用在强放热的二甲醚合成过程中,克服了传统固定床反应器自身移热能力的局限性,可以避免出现床层热点,容易实现恒温操作,减少催化剂积碳。传统复合双功能催化剂需经粉碎研磨后再分散到惰性液相中,且由于水分的存在而容易出现失活现象,本文采用的新型Cu-Zn-Al-Zr浆态催化剂,是采用从溶液到浆液的完全液相法制备,其始终处于液体介质分散之中,分散度高,颗粒度小,分布均匀,不存在与反应介质润湿问题,在近500 h变温变负荷实验中催化剂没有出现失活现象。在新型浆态催化剂上对合成气-步法制二甲醚宏观反应动力学的研究、浆态床反应器的数学模拟研究对浆态床反应器工业设计放大和工艺优化操作具有重要的指导意义。在Cu-Zn-Al-Zr浆态催化剂上建立了浆态床合成气一步法制二甲醚的宏观反应动力学模型。采用双头电导探针测定了浆态床空气-水-空心玻璃微珠体系气泡特征参数,采用溶解氧测定仪测定了溶解氧气液界面液相体积传质系数。通过因次分析建立了气泡特征参数及气液界面液相体积传质系数的关联式,并进行人工神经网络模拟预测。基于浆态床二甲醚合成宏观反应动力学、气液传质和颗粒沉降模型,建立了合成气一步法合成年产10万吨二甲醚浆态床反应器一维数学模型。在500mL高压搅拌釜中,压力3～7MPa,温度220～260℃,质量空速0.4～1.5 L/(g-h),气体摩尔分率yH20.65～0.75,yCO 0.14～0.20, yCO2 0.04～0.08的反应条件范围内,在新型Cu-Zn-Al-Zr浆态催化剂上进行了合成气一步法制二甲醚的宏观动力学研究。结果表明：随着温度的升高,CO的转化率、DME选择性是升高趋势。随着压力的增加,CO的转化率和二甲醚选择性也升高,甲醇选择性降低。随着空速的增加,CO转化率下降,DME的选择性下降,而中间产物甲醇的选择性增加。以CO、CO2加氢合成甲醇及甲醇脱水反应为独立反应,CO、CO2及DME为关键组分,建立了一步法合成二甲醚的Langmuir-Hinshelwood型宏观动力学模型。统计检验和残差分析显示该模型是适宜的,模型计算值与实验值吻合良好。在常温常压下,在Φ100mm冷模浆态床反应器中对空气-水-空心玻璃微珠三相体系,采用双头电导探针法测定了气泡特征参数,并采用动态气体吸收法用溶解氧测定仪测定了溶解氧气液界面液相体积传质系数。通过因次分析,建立了气泡特征参数(d32、εG、aL)及气液界面液相传质系数(kLaL、kL)与操作条件、物性参数之间的经验关联式,并采用拓扑结构为[3,15-12,1]的三层Elman反馈神经网络模型对对各参数进行了统计预测。结果表明：反应器床层气含率和气泡相界面积沿浆态床轴向高度没有明显变化,但随着轴向高度增大,气泡直径略有增大。随着表观气速的增大,局部气含率、气液相界面积和气泡平均直径增大,在湍流鼓泡区气泡平均直径渐于稳定。固含率增加,气液相界面积减小,气泡平均直径增大,而气含率在湍流鼓泡区随着固含率的增加而相应减小,在安静鼓泡区而几乎不变。气液界面液相体积传质系数kLaL受轴向位置的影响很小,而气液界面液相传质分系数kL在轴向位置上受流动过程中气泡的循环流影响,产生引起上下波动。kLaL随表观气速的增大而增大,kL呈减小趋势。kLaL随着固含率的增大而减小,但固含率<5%时,会加强气液传质,kLaL有略微增大趋势,而kL表现出先增大再减小趋势。基于二甲醚合成宏观反应动力学和颗粒沉降模型,建立了合成气一步法合成年产10万吨二甲醚工艺浆态床反应器一维数学模型。模拟计算了反应器结构参数及操作条件对催化剂颗粒床层轴向浓度分布的影响。结果表明：增大催化剂颗粒粒径及减小反应器直径对催化剂颗粒床层轴向浓度分布均匀性有较大影响。对超细浆态催化剂而言,催化剂床层轴向分布已经基本均匀,催化剂质量分数对催化剂浓度轴向分布也基本没有影响,可以在较高催化剂质量分数下进行二甲醚合成反应。在标准反应器进口气体流量为120000Nm3/h,气体组成为yH2 0.70, yco 0.15,yco2 0.05, yNz 0.10,催化剂固含量0.30,反应器直径2.50m,操作温度240℃,压力5 MPa条件下,对10万吨/年二甲醚合成浆态床反应器进行了数学模拟计算。计算结果表明：静液高度18.23 m,床层操作高度22.83 m,平均气含率0.20,表观气速0.260 m-s-1,石蜡油质量52.40t,催化剂质量22.46 t,出口气体组成为yH2 0.6021, yco 0.0068, yco20.0819, yH2O 0.0703, yM 0.0181, yDME 0.0837, yN2 0.1371,总碳转化率0.6765,二甲醚选择性0.8419,甲醇年产量16254.65t/a,二甲醚年产量108351.84t/a。模拟计算分析了浆态床反应器中温度、压力、反应器直径等对总碳转化率、二甲醚选择性、产物产量及床层高度的影响。结果表明：随着压力的增大,总碳转化率及二甲醚的选择性均增加,甲醇及二甲醚的产量也有所增加,操作床层高度下降,而静液床层高度下降相对较为平缓。随着温度的升高,总碳转化率和二甲醚的选择性均略有降低,甲醇产量基本不变,而二甲醚的产量有所减小,静液床层高度和操作床层高度均降低。总碳转化率、二甲醚的选择性、甲醇和二甲醚产量几乎不随直径的变化而变化。随着反应器直径的减小,床层平均气含率及表观气速均较大幅度的增加,静液床层高度和操作床层高度均增加。较佳的操作条件为压力5.0MPa,温度240℃,反应器直径2.5m。更多还原

【Abstract】 Dimethyl ether (DME) is a new chemical intermediate and ideal clean fuel which can substitute diesel fuel and liquefied petroleum gas for for its high cetane number and environmentally benign properties. From thermodynamical point of view, it is favorable to the direct DME synthesis from syngas process which breaks through the thermodynamics equilibrium limitation of methanol synthesis. In the result, a higher CO single conversion and a higher DME selectivity can be obtained. For its higher heat transfer coefficient for the existing of liquid inert media, bubble column slurry reactor has received growing attention in direct DME synthesis from syngas and easy to achieve constant temperature operation in the case of a strongly exothermic reaction which can cause temperature runaway in traditional tubular fixed-bed reactor and alleviate greatly carbon deposition. Commercial bi-functional catalysts were dispersed in liquid medium after smashing and grinding, and lead easily to irreversible deactivation for the existence of wateradhering to the surface of catalysts. Cu-Zn-Al-Zr slurry catalysts used in this study were prepared by a novel complete liquid-phase technology from a solution to the slurry, and always dispersed in the organic medium, which has the advantages of small and uniform granularity, high dispersive, higher activity stability, well rheological property, stable surface structure and a good stability during the reaction of 440 h without significant catalyst deactivated. Study on global kinetics for the direct DME synthesis from syngas and mathematical simulation in BCSR over the Cu-Zn-Al-Zr slurry catalysts has important guiding significance to the industrial design and scale up and optimal operation of DME synthesis process.A global kinetics for DME direct synthesis has been proposed based on Langmuir-Hinshelwood mechanism in continuous stirred tank reactor over Cu-Zn-Al-Zr slurry catalyst. Bubble characteristic parameters in air/water/hollow glass beans system are measured experimentally using dual-tip conductivity probes, and gas-liquid volumetric mass transfer coefficient was determined experimentally by the means of a dynamic oxygen absorption technique in bubble column slurry reactor at ambient temperature and normal pressure. Empirical correlations by dimensional analysis and feed-forward back propagation neural network models were obtained to predict bubble characteristic parameters and gas-liquid volumetric mass transfer coefficient. It has been further developed a steady state one- dimensional mathematical model for an industrial scale bubble column slurry reactor with annual output of 100,000 tons dimethyl ether based on the global kinetic model for direct DME synthesis and and sedimentation-dispersion model of catalyst grains.Directy Dimethyl ether synthesis process from syngas was studied in 500mL stirred autoclave over the novel Cu-Zn-Al-Zr slurry catalyst in wide range of experimental operation conditions:pressure with 3-7MPa, temperature with 220-260℃, WHSV with 0.6-1.2L/(gcat-h) and the composition of syngas with yH2 0.65-0.75, yCO 0.14-0.20,yCO2 0.04-0.08 in the experiments. The influences of pressure, temperature and WHSV on the once-through conversion of CO, selectivity of DME were studied in detail:The conversion of CO and selectivity of DME increase gradually, yet selectivity of methanol has different changes with increasing pressure and increasing temperature, but both conversion of CO and selectivity of DME decrease gradually with the increasing WHSV.A global kinetics model for liquid phase DME direct synthesis based on Langmuir-Hinshelwood mechanism has been proposed by choosing methanol synthesis from CO hydrogenation and CO2 hydrogenation and methanol dehydration as independent reactions. The global kinetics model is suitably fitting experimental data, and its reliability was verified by statistical test and residual error analysis. Bubble characteristic parameters(d32,εG, aL) in air/water/hollow glass beans systems are measured experimentally using dual-tip conductivity probes, and mass transfer coefficient (kLaL,,kL) was determined by the means of a dynamic oxygen physical absorption technique with a polargrafic dissolved oxygen probe in bubble column slurry reactor at ambient temperatures and normal pressures. Empirical correlations by dimensional analysis were obtained to predict bubble characteristic parameters and gas-liquid mass transfer coefficient for air/water/hollow glass beans system. Feed-forward back propagation neural network models with the same 3-layer [3,15-12,1] topology are employed to predict these parameters. The increasing of axial height in the column has little or no influence on local gas holdup and gas-liquid interfacial area and slightly enhanced the Sauter-mean bubble diameter; Local gas holdup, gas-liquid interfacial area and Sauter-mean bubble diameter all increased with the superficial gas velocity increasing, and the Sauter-mean bubble diameter reached gradually stable value in coalesced bubble regime. Gas-liquid interfacial area decreased gradually and Sauter-mean bubble diameter increased gradually with the increasing solid holdup. Local gas holdup decreased with the increasing solid holdup in heterogeneous flow regime and then almost not changed in homogeneous flow regime; With axial height of the column increasing, volumetric mass transfer coefficient has remained approximately constant, while liquid-side mass transfer coefficient was fluctuated for bubble recirculation in bulk slurry phase; Volumetric mass transfer coefficient kLaL increased and liquid-side mass transfer coefficient kL decreased with the increase of superficial gas velocity. kLaL decreased generally with the increasing solid holdup, but have a slight increase in low solid holdup less than<5% which can enhance gas-liquid mass transfer characteristics, and kL has the corresponding changing tendency of the increasing firstly and and then decreasing with the increasing temperature.Based on the global kinetics of direct dimethyl ether synthesis and sedimentation-dispersion model of catalyst grains, a steady-state one-dimensional mathematical model for three-phase bubble column slurry reactor with annual output of 100,000 tons dimethyl ether has been established. The influence of operation conditions and reactor structure on catalyst axial concentration distribution with simulation results was discussed. It turns out that the particle diameter and reactor diameter are the main factors influencing concentration distribution uniformity. For ultrafine slurry catalyst, the influence of catalyst content on the catalyst axial concentration distribution has been not obvious. it can be carried out under the slurry catalyst with a higher mass content to achieve higher methanol/DME yield.The simulation calculation of bubble column slurry reactor design was carried out for 100,000 t/a dimethyl ether in the typical industrial operating conditions with the composition of coal-based syngas:yH20.70, yN20.10,yCO0.15, yCO20.05, Solid constent 30wt.%, reactor diameter 2.50m, temperature 240℃, pressure 5MPa. The simulation results were listed:static bed height 18.23 m, operating bed height 22.83 m, average gas holdup 0.20, superficial space velocity 0.260m·s-1, mass of paraffin 52.40t, mass of catalyst 22.46t, gas composition in the outlet:yH2 0.6021, yCO 0.0068, yCO2 0.0819, yH2O 0.0703, yM 0.0181, yDME 0.0837, yN2 0.1371, total carbon conversion 0.6765, DME seliectivity 0.8419, methanol yield 16254.65 t/a, DME yield 108351.84 t/a.The influence of temperature, pressure and reactor diameter on total carbon conversion, DME seliectivity, products output and bed height were simulated and analyzed.Total carbon conversion, selectivity of DME and yield of methanol/DME are all increased as pressure increases. Operating bed height is decreased greatly, while static bed height decreases slightly. Total carbon conversion, selectivity and yield of DME decrease slightly with increasing temperature. Static bed height and operating bed height drop suddenly as the temperature increases. Total carbon conversion, selectivity of DME, and yield of methanol/DME keep almost constant with reactor diameter. But both operating bed height and static bed height are increased obviously because average gas holdup and superficial space velocity are increased as reactor diameter decreases. The optimal operation conditions in BCSR were proposed: temperature at 240℃, pressure at 5MPa and reactor diameter of 2.5m.更多还原