摘要
烯烃/烷烃的分离一直是石油化工行业中最重要和最耗能的过程之一,其中以分离乙烯/乙烷最具代表性。工业上,一直以来使用低温精馏方法分离乙烯/乙烷。尽管低温精馏已工业应用60多年,但其能耗巨大,研究人员一直致力于寻求一种高效、节能、低成本的方法以取代低温精馏。因此需要开展新型的烯烃/烷烃分离技术的研究,其中基于π络合原理的化学吸附分离具有良好的应用前景,受到国内外广泛关注。
本文在综述了络合吸附分离研究进展及工业应用现状的基础上,探讨了络合吸附机理,制备了高选择性、高分离能力的3-甲基丁烯络合分子筛吸附剂,并研究了络合分离的吸附平衡及固定床动态吸附,为低能耗的烯烃/烷烃分离过程的工业化奠定了基础。本论文采用水溶液离子交换法制备了分子筛吸附剂,并在固定床中考察了不同分子筛吸附剂脱除异戊烷中的3-甲基丁烯的效果及各种操作条件对床层净化效果的影响,主要内容如下:
采用水溶液离子交换法制备AgA,AgY,AgMOR分子筛吸附剂,通过XRD、TG、水静态饱和吸附和固定床吸附等测试手段对制备的分子筛吸附剂进行了表征与测试。研究发现,离子交换后,AgA分子筛结晶度明显降低,不适合作为吸附剂。AgY,AgMOR分子筛仍保持原有的骨架结构,AgMOR分子筛吸附剂对3-甲基丁烯的吸附能力较弱。在20℃,1 atm,原料气流速为40 mL/min时,AgMOR分子筛吸附剂的吸附量为0.84mg/g。而AgY分子筛吸附剂对3-甲基丁烯的吸附能力较强,在20℃,1 atm,原料气流速为40 mL/min时,AgY分子筛吸附剂的吸附量为115 mg/g,异戊烷中的3-甲基丁烯含量由600 ppm降至30 ppm。所以选用AgY分子筛作为吸附3-甲基丁烯的吸附剂。
在固定床中考察了吸附温度、床层高度、原料气流量等条件对吸附量、未利用床层高度(LUB)和床层利用率(Q)的影响。实验结果表明,随着温度的升高,AgY分子筛吸附剂对3-甲基丁烯吸附量减少,从饱和吸附量和节省能源的综合角度考虑,采用在20℃进行吸附脱除3-甲基丁烯;吸附量与床层高度无关;增加原料气流速不利于3-甲基丁烯和异戊烷的分离。LUB与流速有关,与床层高度无关,但只有当装填高度L超过LUB时,才能起到净化效果。Q随着原料气流速和床层高度的增加而增大。循环实验表明AgY分子筛吸附剂可脱附再生18次。
Olefin/paraffin separations represent a class of the most important as well as most expensive separations in the chemical and petrochemical industry, especially for ethylene/ethane separation. Cryogenic distillation has been used for many years for these separations from olefin plants; even so it remains the most energy-intensive process because of the close relative volatilities of the components. The large energy and capital investment requirement provides the incentive for ongoing of olefin/paraffin separation technology research. So a number of alternatives have been investigated. The most promising one appears to be separation viaπcomplexation.
In this paper, current situation of adsorption separation via complexation in industry application and complexation adsorbent research were summarized. At the same time, adsorption mechanism and preparation of new adsorbents with high adsorption selectivety of 3-methyl-1-butene were studied respectively, so did both adsorption equilibrium of the prepared sorbent and behavior of adsorption on fixed bed. All of these studies established a solid foundation of application in industry scale that the new process of olefin and paraffin's separation had lower economizes on energy. In this paper, the zeolites have been prepared for adsorption by cation exchange method in solution. The removal effects of 3-methyl-1-butene from isopentane in a fixed-bed microreactor by deficient zeolite adsorbents were investigated. The purifying effects of technology parameters during the adsorption process have been studied extensively. The main contents are as follows:
AgA, AgY and AgMOR zeolite adsorbents have been prepared by cation exchange method in solution. A series of characterization methods, such as XRD, TG and water adsorption capacity, have been employed to evaluate the as-prepared adsorbents. After cation exchange, the crystallinity of AgA zeolite decreases, and it could not be promised adsorbents.
By using fixed-bed, the adsorption properties of AgMOR and AgY zeolites to 3-methyl-1-butene have been investigated.
AgMOR zeolite has a low adsorption capacity to the adsorbate. Under the conditions of 20℃, 1 atm, and material gas flow rate 40 mL/min, AgMOR zeolite could adsorb 0.84 mg 3-methyl-1-butene per gram. However, AgY zeolite could be a good adsorbent for 3-methyl-1-butene in isopentane. The adsorbed quantity is 115 mg/g under the condition of 20℃, 1 atm and material gas flow rate 40 mL/min. After adsorption, the mass percentage of 3-methyl-1-butene in isopentane drops from 600 ppm to 30 ppm.
In the fixed-bed experiments, The effects of the adsorption temperature, bed height and gas flow rate on the adsorption breakthrough curve, adsorption capacity, LUB (equivalent length of unused bed) and Q (utilization rate of bed) were also discussed. It is shown that as the temperature rising, the adsorption quantity of 3-methyl-1-butene lowers down. We set 20℃as the appropriate temperature for removing 3-methyl-1-butene from pentane. The adsorption capacity is unrelated to the bed height, and the raising of the material gas flow rate is not propitious to the separation of 3-methyl-1-butene/pentane. The length of unused bed (LUB) was concerned to the gas flow rate but not to the bed height. The zeolite adsorbents can produce purified gas when the bed height was larger than LUB. The AgY adsorbents can be regenerated and reused for eighteen times.
引文
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