【作者】 刘国柱；

【导师】 米镇涛；

【作者基本信息】 天津大学 ， 化学工艺， 2005， 博士

【摘要】 滴流床反应器(TBR)是一种典型的气液固三相反应器,广泛应用于石油炼制中的加氢精制(脱硫、脱氮和脱芳烃),石油化工中的氢化、氧化和水合等反应过程,以及废水处理和生物发酵等工业过程。TBR的非定态操作是一种新兴的过程强化技术,已经成为近10年来多相反应工程领域的重要研究课题之一。非定态操作是通过周期性改变部分操作变量,在非定态条件下操作反应器。与传统的稳态操作相比,非定态操作可以强化外部传质速率,从而显著改善反应器的时均性能。尽管TBR非定态操作的研究已经取得了一定进展,但研究尚处于起步阶段,大多数工作是探索性的,仍存在以下问题亟待解决:(1)在基础研究方面,目前的研究集中于周期性调节液相进料流量对反应器性能的影响,而其他非定态操作形式对反应器性能的影响鲜有报道;(2)研究者大多选用简单反应为探针,如:α-甲基苯乙烯加氢反应,研究对反应器性能的影响,而周期性操作对复杂反应选择性和温度分布的影响规律未见报道;(3)在周期性操作的模型化方面,由于缺乏对TBR的非定态行为的深入认识,已有的数学模型不能准确预测反应器性能。解决上述问题对TBR的非定态操作技术在工业生产中的应用具有重要的理论和实际意义,这也是本文所要解决的主要问题。针对上述问题,本文选用恒温2-乙基-9,10-蒽醌(EAQs)加氢反应和非恒温双环戊二烯(DCPD)加氢反应为探针,系统研究了自发性脉冲流操作、周期性调节催化剂的活性和液相进料性质(包括流量、浓度)等非定态操作形式对反应转化率、选择性、加氢反应速率和床层温升的影响,建立了各种非定态操作滴流床反应器的数学模型,分析了各种非定态操作的特性。获得以下主要研究结果。一、为确定TBR中脉冲流的操作域和脉冲频率等性质,首先研究了实验体系的流体力学。以时间序列的统计分析方法为基础,建立了采用压降法识别滴流床流型的方法。实验测定了滴流与脉冲流的转变边界,以及脉冲流的压降和持液量,提出了预测流型转变的理论方法和估算压降和持液量的经验关联式。基于构建的脉冲流性质数据库,提出了预测脉冲流性质的人工神经元网络方法。选用标准化无因次准数(ReL,ReG,WeL,FrG,StG,EoL)和床层性质参数(Sb)作为输入向量,建立了三层反向传播神经网络。经训练的神经网络预测脉冲频率的平均相对偏差为10%,其预测能力明显高于经验关联式。采用神经网络模拟操作参数、床层几何性质和流体物理性质对脉冲流性质的影响规律,与文献结果吻合较好。二、研究了脉冲流和滴流区操作TBR对EAQs加氢速率的影响。结果表明,脉冲流的加氢速率比滴流高40-100%。脉冲流和滴流区EAQs加氢反应表观动力学研究表明,脉冲流的表观活化能(Eap=27.86 kJ/mol)比滴流(Eap=16.67 kJ/mol)更接近本征反应活化能(E=35~37 kJ/mol),证实了脉冲流操作对外部传质速率的强化作用。建立了描述脉冲流操作TBR的数学模型,模型预测结果与实验结果能很好地吻合。进一步模拟了脉冲性质对反应器性能的影响,结果表明,增大脉冲频率能显著提高反应转化率达80%,而脉冲结构对反应器性能的影响不明显。三、提出了空间尺度上周期性调节催化剂活性,即惰性颗粒和催化剂交替填充,强化外部传质速率的新思路。系统研究了TBR传统填充、混合填充和周期性填充EAQs加氢反应的性能。结果表明,高性能吸收填料和催化剂颗粒周期性填充的表观反应速率分别比传统填充和混合填充提高90%和10%。建立了考虑部分润湿和轴向返混的周期性填充TBR数学模型,模型预测结果与实验结果基本吻合。对EAQs加氢反应的模拟,解释了惰性段对气液传质速率的强化作用,同时指出采用高性能的惰性填料和优化填充结构是提高反应器性能的重要途径。四、系统研究了周期性ON-OFF调节液相流量的操作参数对EAQs加氢反应的影响。结果表明,与稳态操作相比周期性操作能分别提高反应转化率和选择性3%-21%和4%。建立了TBR周期性操作EAQs加氢反应的数学模型,对反应器性能的预测令人满意。模拟研究了液体的进料和流出行为以及周期性操作对相间传质系数的影响,从理论上阐明了周期性操作强化反应器性能的机理。五、采用半间歇搅拌釜反应器,研究了358.15-438.15 K和0.5-3 MPa下Pd/Al2O3催化双环戊二烯(DCPD)加氢反应的本征动力学,给出了DCPD加氢反应的Langmuir-Rideal型本征动力学方程,两步加氢反应的活化能分别为7.8945和12.2068 kJ/mol。六、研究了稳态条件下操作变量(压力、进料温度、浓度和液相流量)对DCPD加氢反应转化率、THDCPD收率、加氢反应速率和床层温度分布的影响。结果表明,液相流量和浓度两个操作变量,适宜作为周期性调节变量。另外,确定了比较稳态和周期性操作TBR性能的操作条件和基准。在上述工作的基础上,系统研究了5种周期性操作策略,即ON-OFF调节液相流量、PEAK-BASE调节液相流量、ON-OFF调节液相浓度,PEAK-BASE调节液相浓度和同步PEAK-BASE调节液相流量和BASE-PEAK调节液相浓度(同步调节液相流量和浓度),对DCPD加氢反应器性能和床层温度分布的影响。结果表明,操作策略是影响滴流床反应器的性能和床层温度分布的重要因素。ON-OFF调节液相流量和同步调节液相流量和浓度能分别提高加氢反应速率20%和15%,降低床层最大温升13 K以上;PEAK-BASE调节液相流量和PEAK-BASE调节液相浓度能提高加氢反应速率约10%,能降低床层最大温升小于10 K;ON-OFF调节液相浓度能提高加氢反应速率5%以下,但能降低床层最大温升12 K。七、建立了考虑热量衡算和溶剂挥发影响的TBR稳态操作和周期性操作DCPD加氢反应模型,其中催化剂颗粒模型采用考虑静态持液量影响传质速率的部分润湿三区模型。与所有实验数据的对比表明,建立的数学模型能很好地预测反应器的性能和床层温度分布。八、在总结了本文与文献非定态操作TBR研究结果的基础上,提出了TBR非定态操作的适用范围,操作方式和操作变量的选择方法,以及优化操作参数的基本方法,即通量匹配和时间匹配原则总之,非定态操作既强化相间传质速率,对于放热反应又充分利用反应热,从而提高反应速率和抑制床层飞温。该技术具有强化表观反应速率、利用反应热控制热点等综合优势,极具工业化应用前景。更多还原

【Abstract】 Trickle bed reactor (TBR), which is a typical gas-liquid-solid three-phase reactor, is wildly used for hydrocreaking and hydrorefining processes including desulfurization, denitrogen and dearomatics in the refinery indurstry and for hydrogenation, oxidation and hydration process in the petroleum chemical industry. Recently, more attention has been gained on the application in the waste water treatment and biochemical engineering process. Unsteady-state operation of TBR (USTBR), a novel and developing process intensification technology, is becoming one of the most important topics in the multiphase reactor engineering. Compared with the traditional steady-operaiton, a significant enhancement of time-average performance can be obtained by the Unsteady-state operation, i.e., periodically changing some operating parameters of TBR.Regardless of the advantages of USTBR, there still exit some important issues to be solved due to its short history. (1) Most of previous research focused on the modulation of liquid flow rate on performance, but little attention has been paid on the other practicable modes for the unsteady-state operation. (2) Since most of model reactions used in the literaures were the simple reactions, such as the hydrogenation ofα-methylstyrene, up to now little information was reported about the influence of USTBR on selectivity and temperature rise, which were important issues for the indurstial process. (3) Now it is still impossible to predict the performance of a TBR under periodic operation using a mathematic model due to the lacking of deep understanding on the USTBR behaviors. Therefore, it is indispensable for the further understanding on unsteady-state operation technology and its potential application in the industry to resolve the problems described above.In the present work, the influences of several unsteady-state operation modes such as TBR under pulsing regime, periodic modulation of catalyst activity, and periodic modulations of liquid flow rate or concentration, on the reactor performances and temperature rises were systemically studied using hydrogenation of 2-ethyl-9,10-anthraquinones (EAQs) and dicyclopendidene (DCPD) as the test reactions for isothermal and nonisothermal systems. In addition, attempts were also made to develop the mathematic models for the described operating modes, and thus to analyze the unsteable behaviors of TBR under unsteady-state operations. As a result, the following results have been obtained.(1) The TBR hydrodynamics of pulsing regime for experimental system was studied to determine operating regime and properties of pulsing flow. To obtain the transition boundaries of trickling and pulsing regimes, regimes identification method was established by the statistic analysis on pressure drop signals. Pressure drop and liquid holdup of the pulsing flow were also experimentally measured. Furthermore, a theoretic method and several empirical correlations were also provided to predict regimes transition boundary, pressure drop and liquid holdup, respectively.Based on an extensive experimental database (946 measurements) set up from the literature published over past 30 years, a new correlation relying on artificial neural network (ANN) was proposed to predict basic pulsation frequency of pulsing flow in the trickle-bed reactors. Seven dimensionless groups employed in the proposed correlation were liquid and gas Reynolds (ReL, ReG), liquid Weber (WeL), gas Froude (FrG), gas Stokes (StG) and liquid Eotvos (EoL) numbers and a bed correction factor (Sb). The performance comparisons of literature and present correlations showed that ANN correlation is a significant improvement in predicting pulsation frequency with an AARE of 10% and a standard deviation less than 18%. The effects of the variables including the properties of fluid and bed, and flow rate of liquid and gas on pulsing frequency were investigated by ANN parametric simulations and the trends were compared with exiting experimental results which confirmed the coherence of the proposed method with the previous experiments.(2) EAQs hydrogenation in the TBR under pulsing and trickling regimes was studied to examine the effect of natural unsteady-state operation on the reactor performance. It is found that the hydrogenation rate under pulsing regime is 40%-100% higher than that of trickling regime. The apparent kinetics indicated that the apparent activity energy of pulsing flow is 27.86 kJ/mol, which is closer to the intrinsic activity energy of 35~37 kJ/mol and higher than trickling regime of 16.67 kJ/mol. This further confirmed that the enhancement of performance was a result of improvement of external mass transfer rate under high interaction regimes.A mathematic model for TBR operated under pulsing flow was developed with an assumption of square-wave function between mass transfer coefficients and the time. The developed model predicted the experimental results with a satisfactory accuracy. The effect of pulsing flow properties on the reactor performance was simulated with the model described above. The results showed that increase of pulsation frequency can improve the conversion up to 80%, but the effect of pulse structure is neglectable.(3) A novel unsteady-state mode was proposed to enhance TBR performance by periodic modulation of the activity of catalyst pellets. The reactor performances with different packing modes including traditional, diluted and periodic packing modes were systematically studied using EAQs hydrogenation as test reaction. It was found that periodic packing mode with higher capability packing can improve space time yields 90% and 10% as compared with traditional and diluted packing modes.A mathematic model for periodicaly packed TBR incorporating partial wetting and axial dispertion was developed, which can predict the experimental results accurately. Simulations with the developed model indicated that the higher performance packing and packing structure were essential factors for the performance enhancement.(4) In general, the periodic ON-OFF modulation of liquid flow rate was taken as a most promising technology due to its enhancement on the mass transfer rate of gaseous reactants from gas to catalyst surface, and the effective wetting of catalyst pellets. The influence of periodic operation on a consecutive reaction, the EAQs hydrogenation over Pd/Al2O3, was studied. The effects of operating parameters including cycle period, split, pressure, temperature and time-average flow rate on the reactor performance were experimentally examined in comparison with the steady state operation. The results showed that under the interested operating conditions the conversion and the selectivity were improved by 3%-21% and 4%, respectively.Based on a nonlinear relationship of local liquid holdup with superficial liquid velocity (εL, uL), a dynamic model consisting of a set of partial differential equations (PDEs) was developed for the periodic operation of TBR. The developed model was verified compared with the experimental results. The feed/drainage behavior and effect of the periodic operation on the external mass transfer rate were simulated to explain the course-reason relationship of reactor performance enhancement.(5) The intrinsic kinetics of dicyclopentadiene (DCPD) hydrogenation into endo-tetrahydrodicyclopentadiene (endo-THDCPD) over Pd/Al2O3 catalyst was investigated using stirred semibatch reactors in the absence of transport limitations over the ranges of temperature (358.15-438.15 K) and hydrogen pressure (0.5-3 MPa). A Langmuir-Hinshelwood type model was proposed to fit the experimental data and its kinetic parameters were also regressed by comparing the calculated and experimental concentrations profiles of reactants and products. The activation energy for the first and second step reaction is 7.8945 and 12.2068 kJ/mol, respectively. It was found that the developed model was accurate to predict the experimental results with the averagerelative error (ARE) less than 12.7 %, and was reliable for the reactor design and modeling.(6) Effects of the steady-state operation parameters, such as pressuer, inlet temperature, concentration and liquid flow rate, on the DCPD hydrogenation performance and temperature profiles were studied to determine the practical modulation variables for the USTBR. The results indicated that liquid flow rate and concentration were suitably used as regulation variables for the performance enhancement by the unsteady-state operations.On the basis of above results, the unsteady-state behaviors under different operating modes including ON-OFF modulations of the liquid flow rate (mode A), PEAK-BASE modulations of the liquid flow rate (mode B), ON-OFF modulations of the liquid concentrations (mode C), PEAK-BASE modulations of the liquid concentrations (mode D) and the synchronous modulations of liquid concentration and flow rate (mode E) were systemically studied. It is shown that mode A and E can improve hydrogenation rate up to 20% and 15%, and reduce MTR more than 13 K; performance enhancement were about 10% for both mode B and D, which can reduce MTR less than 10 K; mode C has an effect less than 5% on the performance, but reduces MTR up to 12 K.(7) A mathematic model incorporating enthalpy balance and phase equilibria was developed based on a three-zone pellet-scale model considering the influence of static liquid holdup on the mass transfer rate. The comparison of experimental and simulated results indicated that the developed model was reliable to predict the performance and axial temperature profiles accurately.(8) Several principles for the selections and optimizations of USTBR operation parameters for the conception design were proposed from the experimental results reported in this work and literatures.To sum up, USTBR, as a promising process intensification technology for the large-scale applications in the industries, has several significant advantages over the steady operation in enhancing mass transfer rate and utilizing reaction heat to improve the reaction rate and eliminate the local hot point and the“run away”of reactor.更多还原