【作者】 郑仙荣；

【导师】 谢克昌； 常丽萍；

【作者基本信息】 太原理工大学 ， 化学工程与技术， 2012， 博士

【摘要】 气化煤气和热解煤气共制合成气的双气头多联产技术是目前认为最具前景的洁净煤技术之一,将富含CO和CO2的气化煤气和富含H2和CH4的热解煤气进行重整,可获得最佳组成的合成气；通过生产焦、醇醚燃料和产生电能,可实现原料组成和能量的合理匹配与梯级利用。该技术中,作为原料用合成气对H2S的含量要求比较苛刻(H2S浓度必须低于0.1ppmv),同时为了避免脱硫过程中引起的“冷热病”和热能的损失,中温煤气脱硫便成为该技术中净化工艺的首选,而精脱硫用吸附剂的制备及其硫化行为是其中必须关注的重点。基于此,本文提出了加压浸渍法进行中温脱硫用吸附剂的水热合成的研究。首先对吸附剂载体和活性组分前驱体进行了筛选,然后对前驱体溶液浓度、浸渍压力、浸渍时间、煅烧温度和煅烧时间等操作参数进行了优化。研究结果显示,加压浸渍法是一种有效的吸附剂制备方法,半焦和硝酸锌是可选的吸附剂载体和活性组分；加压浸渍过程能够将锌基活性组分均匀浸渍到半焦载体、并同时有效改善载体半焦的孔隙结构。吸附剂的最佳制备条件为：20%的硝酸锌溶液与35ml的半焦载体,在20atm下浸渍5h,分别在50和100℃下干燥5h,再在500℃纯氮气吹扫下,煅烧5h。原料半焦经加压浸渍后,比表面积和孔容分别从16.65m2/g和0.01cm3/g最大增加到265.49m2/g和0.07cm3/g.针对氧化锌脱硫精度高但在中温强还原性气氛下活性组分不太稳定、氧化锰在中温脱硫过程中具有较好的脱硫活性及优良的机械稳定性、氧化铜是耐高温吸附剂的主要活性组分等现状,进行了适量的氧化锰和氧化铜改性氧化锌吸附剂的构思,以期优势互补,得到脱硫活性和机械稳定性俱佳的中温锌锰铜基吸附剂。以锌、锰和铜的可溶性硝酸盐为吸附剂的前驱体,在优选的操作条件下进行加压浸渍,过滤、干燥和高温煅烧,制得吸附剂Z20M4C6SC。在300-550℃范围内的活性评价结果显示,该吸附剂可将煤气中的H2S从500ppmv脱除到0.1ppmv以下(H2S脱除率大于99.98%),其穿透时间在500℃时达到56h,此时最大穿透硫容为13.84%。三组分吸附剂Z20M4C6SC的脱硫性能明显好于各单组分吸附剂,最大穿透硫容比三个相应含量单组分吸附剂的简单加和(8.98%)增加了54.12%；双组分吸附剂Z20M4SC的硫容(7.98%)与相应两种单组分吸附剂穿透硫容的加和值(8.02%)几乎相当,显示了三组分吸附剂中铜的引入促进了组分之间的协同作用。结合催化剂表征结果进行分析,认为吸附剂Z20M4C6SC脱除煤基气体中H2S的活性组分主要包括ZnO、MnO2、CuO和ZnMnO3,其中ZnMnO3与H2S反应的热力学平衡常数最大(5.499×1018),在脱硫反应中起主导作用。将铜添加到锌锰基吸附剂Z20M4SC中,促进了锌锰复合物ZnMnO3的生成；同时铜的添加提高了活性组分在载体表面的分散度,有利于活性组分和H2S的接触,促进了脱硫反应的进行；另外,铜的添加明显增大了吸附剂的机械强度,有益于改善吸附剂的硫化/再生循环性能。采用等效粒子模型分别对吸附剂Z20SC、Z20M4SC和Z20M4C6SC的动力学参数进行了估算,发现三类吸附剂的整个脱硫过程可分为两个反应控制阶段,即反应初期的表面化学反应控制区,和反应中后期的扩散控制区。吸附剂在化学反应控制区的活化能Ea和扩散控制区的活化能Ep显示,三组分吸附剂Z20M4C6SC的数值(6.23和9.39kJ/mol)明显小于双组分Z20M4SC(22.89和33.87kJ/mol)以及单组分Z20SC(18.10和51.21kJ/mol),说明锌基吸附剂Z20SC中添加的锰和铜的共同作用有效降低了硫化反应的活化能,活性组分在载体表面分散度的提高和活性组分粒径的减小可以降低其扩散控制区的活化能。CO、H2和H2O是煤气中的主要组成成分,吸附剂Z20M4C6SC对环境气氛的适应性考察实验结果显示,CO或H2独立存在于硫化反应气氛中,对脱硫反应存在明显的抑制作用,这主要是由于它们对吸附剂中活性组分ZnO和CuO的还原和对ZnMnO3的分解引起。但H2和CO的同时存在可以相互减弱各自对吸附剂脱硫性能的抑制程度。H2O作为硫化反应的产物之一,对吸附剂的硫化反应存在着抑制作用,但在复杂气氛H2/CO/H2O/N2/H2S中,优化制得的吸附剂Z20M4C6SC仍具有较好的脱硫效果,在脱硫精度为0.1ppmv时的穿透时间长达42h,说明该吸附剂具有较强的气氛适应能力,是一种较理想的吸附剂。硫化动力学参数结果表明,在不同气氛下的硫化反应均存在前期的表面化学反应控制和中后期的扩散控制,吸附剂Z20M4C6SC在H2/CO/N2/H2S、H2/CO/H2O/N2/H2S、H2O/N2/H2S、H2/N2/H2S和CO/N2/H2S各气氛中的穿透硫容大小顺序(13.84%>9.46%>7.64%>6.57%>6.15%)与其在扩散控制区的活化能Ep(9.39<13.44<13.96<14.31<18.10kJ/mol)成对应关系,同时扩散控制区的活化能Ep均大于化学反应控制区的活化能Ea,显示了扩散控制在锌基吸附剂脱硫过程中的重要性。更多还原

【Abstract】 The dual gas coal-based poly-generation technology is now considered as one of the most promising clean coal techniques. By this technology, the syngas with optimum composition can be acquired by reforming the pyrolysis gas rich in CH4combining with gasification gas rich in CO2, and the step utilization of raw material and rational proportion of energy can be achieved by producing coke, alcohol ether fuel and power. The limitation for the content of H2S in syngas used to synthetize chemicals is very strict (below0.1ppmv) in this technology. To avoid the heat loss caused by heating and cooling gas, the removal of H2S from hot coal gas at mid-temperature has been selected as the preferred procedure of this technology for cleaning syngas. The preparation of sorbent and its desulfurization performance are the main concerns.On the basis of above analyses, the high-pressure impregnation method is proposed for the hydrothermal synthesis of the sorbent and the performance of prepared sorbent removing H2S from hot coal gas at mid-temperature is researched in this paper. Firstly, the support and active component precursors were screened out. Then, the optimal concentration of precursor solution and operation parameters of impregnation pressure, impregnation time, calcination temperature and calcination time were determined. The experiment results show that the high-pressure impregnation is an effective sorbent preparation method, and semi-coke (SC) and zinc nitrate are the suitable support and precursor, respectively. The high-pressure impregnation method presents an outstanding advantage of perfectly improving the pore structure of SC support at the same time of effectively impregnating the active component precursor on semi-coke support. The optimal Zn-based sorbent preparation conditions are shown as follows:35ml semi-coke support and20%Zn(NO3)2precursors solution were placed in an autoclave through high-pressure impregnation at20atm for5h, then the sample was filtered and dried at50℃for5h, dried at100℃for5h. Finally, the sample was calcined at500℃in pure N2for5h. The BET results show that by high-pressure impregnation, the specific surface area and pore volume of the raw semi-coke are expanded from16.65m2/g and0.01cm3/g to265.49m2/g and0.07cm3/g, respectively.Zinc oxide is recognized as high accuracy sorbent, but it is unstable at high temperature in the strong reducing atmosphere. While manganese oxide shows good desulfurization activity and excellent mechanical stability, and copper oxide exhibits excellent mechanical stability and good dispersion in the high temperature desulfurization process. So, an idea is designed that the desulfurization performance of Zn-based sorbent is modified by the join of manganese oxide and copper oxide, and the Zn-Mn-Cu-based sorbent with good desulfurization activity and mechanical stability is expected to get. Zinc nitrate, manganese nitrate, and copper nitrate aqueous solutions were used as precursors and the Z20M4C6SC sorbent was prepared at the optimal operation conditions by high-pressure impregnation. This sorbent possesses a good desulfurization performance and it can effectively remove H2S from500to below0.1ppmv (H2S removal efficiency is above99.98%) in a temperature range of300-550℃. It can maintain this high desulfurization precision of0.1ppmv for56h, with the maximal sulfur capacity of13.84%at500℃.The desulfurization performance of three metal Zn-Mn-Cu-based sorbent is obviously better than that of single metal sorbent, and its sulfur capacity is54.12%greater than the simple summation (8.98%) of three single metal oxide sorbents Z20SC, M4SC, and C6SC. The sulfur capacity (7.98%) of bi-metal Z20M4SC sorbent is nearly similar to the simple summation (8.02%) of Z20SC and M4SC. These results show that copper has a significant promoting function in the process of desulfurization of three metal Zn-Mn-Cu sorbent.XRD results show that CuO, ZnO, MnO2and ZnMnO3are the active components of Z20M4C6SC sorbent. The equilibrium constant of the reaction between ZnMnO3and H2S is the maximum (5.499×1018) and ZnMnO3in Z20M4C6SC sorbent plays an important role in the process of removing H2S from hot coal gas. The addition of copper in the Zn-Mn-sorbent promotes the formation of new phase ZnMnO3, and improves the dispersion of active components on support, thus enhances the reactivity of active components with H2S. Meanwhile, the addition of copper also enhances the mechanical strength of the sorbent and it is helpful for improving the sulfidation/regeneration performance.By the equivalent grain model, dynamic parameters of Z20SC, Z20M4SC and Z20M4C6SC were calculated respectively. It is suggested that the desulfurization reaction of the Zn-based sorbents is mainly controlled by the chemical reaction in the initial stage and later by the gas diffusion through the reacted layers. The chemical reaction activation energy Ea and diffusion activation energy Ep of three metal Z20M4C6SC sorbent (6.23and9.39kJ/mol) are lower than bi-metal Z20M4SC sorbent (22.89and33.87kJ/mol) and single metal Z20SC sorbent (18.10and51.21kJ/mol). These results show that the combined action of manganese and copper effectively reduces the desulfurization reaction active energy and improves the desulfurization activity of Zn-based sorbent.CO, H2and H2O are the main components of coal-based gas. The experiment results that the adaptability of Z20M4C6SC sorbent on ambient gas indicates that CO or H2independently existing in feeding gas clearly inhibites its desulfurization reaction. And this phenomenon is mainly caused by the reduction of active component ZnO and CuO, and decomposition of ZnMnO3in the reducing environment. But CO mixed in the gas containing H2, or H2mixed in the gas containing CO obviously weakens their inhibition degree for desulfurization performance. As one of the products of the desulfurization reaction, the effect of H2O on desulfurization reaction is negative, according to chemical reaction equilibrium principle. Obviously, the sulfur capacity of Z20M4C6SC (13.84%>9.46%>7.64%>6.57%>6.15%) in different ambient gas of H2/CO/N2/H2S, H2/CO/H2O/N2/H2S, H2O/N2/H2S, H2/N2/H2S and CO/N2/H2S is related to the diffusion activation energy Ep (9.39<13.44<13.96<14.31<18.10kJ/mol). And the diffusion activation energy Ep is higher than chemical reaction activation energy Ea. So, it is suggested that the diffusion through the reacted layers is very important for the desulfurization reaction of Zn-based sorbents and H2S.更多还原