【作者】 张艳军；

【导师】 常丽萍；

【作者基本信息】 太原理工大学 ， 化学工艺， 2011， 硕士

【摘要】 苯是重要的化工原料,主要来源于石油和焦化行业。近年来,化工企业迅速发展,苯乙烯、苯酚等下游产品的生产规模不断扩大,导致我国对纯苯的需求量持续增长。我国的石油资源相对短缺,煤炭资源相对丰富,焦化行业迅速发展,伴随着大量焦化苯的生产。焦化苯中存在一定量的噻吩类硫化物,这不仅会腐蚀金属设备,在后续生产应用时导致催化剂中毒,而且可能会带来环境污染,严重限制了焦化苯进一步加工利用。为此,国家标准对焦化苯中硫化物的含量要求越来越高。吸附法脱除噻吩类硫化物是近年发展起来的一种脱硫方法,该方法具有反应条件温和,投资费用少,脱硫效果好,并且可回收噻吩,吸附剂可再生,环境污染少等优点。从节能环保和资源充分利用的角度看,吸附法是一种非常有应用前景的脱硫方法。但存在吸附剂的选择性差、硫容较小等缺点,高性能吸附剂的研发是实现工业应用的关键。基于此,论文对苯中噻吩脱除用吸附剂的制备及其金属离子改性的条件进行了优化,并对其脱硫性能进行了考察,得出的主要结果如下。1)γ-Al2O3负载金属离子改性吸附剂γ-Al2O3是一种多孔性物质,每克的内表面积高达数百平方米,具有良好的吸附性和热稳定性,廉价易得,且结构比较简单,有助于在实验中对吸附机理的研究。实验首先选用γ-Al2O3作为载体,采用等体积浸渍法,负载金属元素制取了系列改性吸附剂,并对其脱除噻吩的性能进行了考察,发现硝酸银溶液负载改性制得的吸附剂的吸附性能最好。等体积浸渍法虽然可以准确控制活性组分的负载量,但存在活性组分分散不均的问题。而超声波具有空化作用,可以提高相间质量传递速率,改变吸附相平衡关系,进而提高活性组分的分散性。鉴于此,实验采用超声辅助对常规等体积浸渍法进行了优化改进。实验结果发现,超声辅助不仅缩短了吸附剂的制备时间,而且能丰富吸附剂的孔隙结构,细化活性组分Ag颗粒,使其分布均匀,有利于吸附剂对噻吩的脱除。吸附剂中Ag含量的改变可以引起吸附剂孔结构分布和比表面积的变化,进而对吸附剂的脱硫效果产生影响,超声辅助等体积浸渍法制备的Ag含量为15%的吸附剂,吸附噻吩效果最佳。其在室温、常压、剂液比为1：4(g/mL)时,可将噻吩浓度从500 mg/L降为1.7 mg/L,脱硫效率高于99%。在噻吩-苯、噻吩-环己烷、四氢噻吩-苯、四氢噻吩-环己烷四种溶液中的吸附实验结果,表明Ag改性的y-A1203型吸附剂脱除噻吩主要存在Ag与噻吩环的兀络合和与硫原子成键两种作用机理。2)Y型分子筛金属离子交换改性吸附剂Y型分子筛是一种具有网状晶体结构的硅铝酸盐,具有均一的孔道和晶穴,且具有比表面积大、热稳定性好、选择性吸附能力强等特点,可用于分离不同种类的分子。对NaY分子筛进行金属离子交换改性,可以明显提高其对苯中噻吩的吸附脱硫性能。其中,铈离子改性制得的CeY分子筛的脱硫效果最好,最佳的改性制备条件为：在0.1 mol/L的硝酸铈溶液中,加热回流离子交换4 h,然后在马弗炉中700℃下焙烧2 h,重复进行两次离子交换。制得的最佳吸附剂在室温、常压、剂液比为1：4(g/mL)时,可将噻吩浓度为500 mg/L的噻吩-苯溶液中的噻吩完全脱除；剂液比为1：14时,其脱硫效率为51.7%,吸附量趋于饱和,平衡硫容为5.74 mg/g。以静态脱硫实验中筛选出的最佳改性CeY分子筛作为吸附剂,进行固定床吸附性能研究,得到以下实验结果。吸附剂的粒径越小,越有利于吸附,但是粒径太小会增大床层间的传质阻力,增大能耗。溶液流速在0.2mL/min时较好,流速太大或太小都会使穿透时间变短。吸附反应在室温下进行即可,高温可能会减弱吸附剂与噻吩之间的作用力,从而使吸附性能降低。吸附法更适用于低浓度噻吩的脱除,当噻吩浓度为200 mg/L时,吸附剂的硫容为4.18 mg/g,处理量为20.91 mL/g。更多还原

【Abstract】 Benzene is an important chemical raw material and comes mainly from petroleum and coking industry. Along with the rapid development of chemical industry in recent years, styrene, phenol and other downstream products expand gradually, resulting in continued growth of the demand for pure benzene. Currently, the oil resources become more and more scarce, while the coal resources is relatively rich in China. The abundant coking benzene is generated with the rapid development of coking industry. But the existence of thiophenic sulfides in coking benzene, which can corrode metal equipment, poison catalysts during the following application, cause environmental pollution, and so on. This will seriously limit its utilization range. So the national standard of the sulfur content in coking benzene becomes more and more rigid.Adsorption removal of thiophenic sulfides has developed in recent years as a desulfurization method, which has the advantages of milder reaction conditions, smaller equipment corrosion, lower operating costs, recyclability of thiophene, less environmental pollution, and so on. From the point of energy saving and full utilization of resources, this method is very promising. However, and so on. So the research and development of highly efficient sorbents is the key to achieve industrial applications of this method.1) Sorbent ofγ-Al2O3 modified by supporting metallic ionγ-Al2O3 is a good sorbent carrier, with the features of high surface area, good thermal stability, simple structure, low expense, easy acquirement, and so on. It was selected as the sorbent carrier and was modified by incipient-wetness impregnation method in the different metallic nitrate solution. According the adsorption behavior in thiophene-benzene solution, it is found that the sorbent modified in silver nitrate solution has the best desulfurization ability.The amount of active component loaded onγ-Al2O3 can be accurately controlled by incipient-wetness impregnation method, but there is the problem of uneven dispersion of active component. The ultrasound can improve the rate of mass transfer between phases, change the equilibrium between adsorption phases. In view of this, the sorbent was prepared by the ultrasound-assisted impregnation method to improve impregnation performance. Experimental results show that the assistant ultrasound during sorbent preparation can not only shorten the preparing time, but also enrich the pore structure of sorbent and improve the size and distribution of the Ag particles, which is favorable to the removal of thiophene from benzene.The desulfurization capacity of sorbent changes with the content of Ag loaded inγ-Al2O3. The sorbent with 15% quality content of Ag prepared by ultrasound-assisted impregnation method has the highest desulfurization efficiency. It could reduce the thiophene concentration to 1.7 mg/L from 500 mg/L at room temperature and ambient pressure, with the desulfurization mg/L at room temperature and ambient pressure, with the desulfurization efficiency of more than 99%, when the ratio of sorbent to solution was 1:4 (g/mL).Comparing the desulfurization results in thiophene-cyclohexane, thiophene-benzene, tetrahydrothiophene-benzene, tetrahydrothiophene-cyclohexane solutions, it is found that there exist two kinds of connection between thiophene and sorbent modified in silver nitrate solution, theπ-complexation and the S-Ag bond.2) Sorbent of Y-type zeolite modified by metallic ion-exchangeY-type zeolite is a crystalline aluminosilicate with uniform pore structure and crystal cave, large surface area, good thermal stability, strong adsorption selectivity, which can be used to separate different types of molecules. So it was chosen as the sorbent carrier, and modified by liquid ion exchange method with different nitrate solutions. It is found that the desulfurization efficiency of the modified sorbents are all significantly improved, among which the sorbent modified in cerium nitrate solution has the best desulfurization ability. The optimum preparation conditions are that NaY zeolite is ion-exchanged in 0.1 mol/L Ce(NO3)3 solution at 100℃for 4 h, calcined at 700℃for 2 h, and repeated the above steps for two times. The sorbent prepared under the optimum conditions could remove entirely the thiophene in thiophene-benzene solution with 500 mg/L thiophene concentration, at room temperature and ambient pressure, when the ratio of sorbent to solution is 1:4 (g/mL). When the ratio of sorbent to solution was 1:14 (g/mL), its adsorptive capacity tends to saturation with the balance sulfur capacity of 5.74 mg/g.The fixed bed equipment was set up to study the adsorption ability of the optimal sorbent in the flow state. The results show that the smaller the sorbent the resistance of mass transfer and the energy consumption if the particle size was too small. The 0.2 mL/min flow rate of the solution presents the good desulfurization capacity. If it is too large or too small, the breakthrough time would be shortened. Room temperature is fine for the adsorption of thiophene because the interaction between sorbent and thiophene may be weakened and the adsorption ability is decreased at high temperature. Adsorption method is more suitable for the removal of thiophene with low concentration. When the thiophene concentration is 200 mg/L, the sulfur capacity of the sorbent is 4.18mg/g and the processing capability is 20.91 mL/g.更多还原