反应—分离双功能复合结构催化膜的制备及其在活性渗透汽化膜反应器中的研究

发布时间：2018-06-04 13:08

本文选题：催化膜 + 渗透汽化　；参考：《北京化工大学》2015年博士论文

【摘要】：平衡反应是自然界中的常见现象,它限制了化学反应在给定温度、压力、浓度、配比等条件下的最大转化率,在有机液相化学反应如酯化、硝化、缩酮、酰化等化学工业中的重要反应中尤为常见。同时,这类反应还多存在产物或原料的热稳定性差、副反应多、连串反应等问题。如何有效地提高这类反应的产率并进而提高其原料利用率、减轻后续分离过程的能耗是困扰有机化工生产的一个重要难题。本文提出采用浸没沉淀相转化法制备一种具有反应-分离双功能的,类似于“三明治复合结构”的,具有疏松多孔催化层的复合活性催化膜,构筑了一种新型的多功能反应器——活性渗透汽化膜反应器,用于有机液相平衡反应的研究。“三明治”复合结构为：顶层为疏松多孔的聚乙烯醇(Polyvinyl alcohol, PVA)催化层,其中通过相转化法将催化剂(固体酸,生物酶等)固定；中间为致密的选择性分离层,膜材料同样为PVA；底层为多孔聚醚砜(Polyethersulfone, PES)支撑层,起到机械支持作用。通过对复合膜结构尤其是催化层多孔结构的制备和优化,系统考察了催化层的催化活性,并通过丁醇水的脱除实验,研究了复合活性催化膜的分离特性,最后用乙酸／正丁醇合成乙酸正丁酯的反应为探针,考察了不同操作条件下该反应在多孔催化层CAMR (Catalytically Active Membrane Reactor)中反应和分离的特性,并通过与传统IMR (Inert Membrane Reactor)和致密催化层CAMR对比,探讨了膜反应器内不同组分随时间变化规律,研究其传质行为的特点和规律,尝试分析了活性膜反应器耦合强化机理,证明本文所制备的复合催化膜能进一步强化对反应转化率的提升,进而进一步提高原料的时空转化率。最后将本文提出的浸没沉淀相转化法制备复合催化膜拓展到固体催化体系和生物催化体系,表面该方法具有一定的通用性。对于制备纯PVA多孔膜和多孔催化膜,PVA浓度对成膜结构有较大影响,在PVA浓度为5wt.%时,形成胶粒状结构,而当PVA浓度为10wt.%时,形成封闭的胞腔或蜂巢状结构。凝固浴温度升高,有利于缩短成膜时间。在制备多孔催化膜时,催化剂浓度在10wt.%较为合适,催化剂浓度进一步升高,趋向于形成致密皮层,不利于成膜的多孔性。不同催化剂对探针反应的催化活性顺序为：致密催化层≈胶粒状催化层(PVA浓度5wt.%)游离催化剂胞腔状催化层(PVA浓度10wt.%)无催化剂。利用取得到动力学数据建立了拟均相模型,模型预测结果与实验值吻合良好。通过丁醇水的渗透汽化脱水实验,致密催化层CAMR中由于催化层为致密结构且膜厚较大,所以通量最小,组分扩散阻力最大,而在多孔催化层CAMR中由于催化层为疏松多孔结构,其通量较大,说明多孔结构有利于降低组分的传质阻力,不仅能改善反应物向催化位点的扩散,同时能够提高产物向膜后侧的传递,从而提高水的原位脱除作用,有利于实现真正的“原位”脱除。在反应-分离耦合强化实验中,在IMR,致密催化层CAMR和多孔催化层CAMR中,乙酸和正丁醇随时间同步减小,乙酸正丁酯和水在刚开始阶段同步上升,但一段时间之后,水的浓度变化与乙酸正丁酯的浓度曲线发生偏离,由于水的脱除速率大于水的生成速率,在膜反应器内水的浓度曲线出现拐点,逐渐随时间下降。提高温度能进一步提高乙酸的转化率。总通量的变化同样有两个阶段：在反应前期,通量先逐渐升高,达到拐点后逐渐下降。在85℃时,在多孔催化层CAMR中,前侧水浓度在28h时将为0,此后在膜反应器内不能检测到水,但后侧通量表明此时反应不断进行,水不断的脱除。说明在此时间以后,产物实现了真正的原位脱除作用,即生成一分子水,立即向膜下游侧扩散从而脱除。这种效果随着催化剂负载量减小更明显,在催化剂负载量将为2.25g/L时,前侧水浓度在23.5h即为O。说明实现真正原位脱除的关键在于合理调节催化膜的催化性能和分离性能。通过IMR和多孔催化层CAMR的对比,证明本文制备的复合催化膜能够进一步实现过程强化,由于水在膜表面生成,水的推动力更大,使得水的通量更大,最终表现在乙酸的转化率要更高。在约35.5 h时,IMR中乙酸转化率仅约75%,而在多孔催化层CAMR中,乙酸转化率达到约85%。而在致密催化层CAMR和多孔催化层CAMR对比中,由于多孔催化层传质阻力更低的优点,水的生成速率和脱除速率均更快,反应转化率更高。本文提出的利用浸没沉淀相转化法制备具有多孔催化层的复合催化膜的方法具有一定通用性。IER/PVA/PES复合催化膜同样能实现对水的原位移除,实现转化率的强化,并且膜结构在使用前后并未发生明显变化。而Lipase/PVA/PES复合催化膜能保持酶的生物活性,同时也能实现转化率的进一步强化。
[Abstract]:Equilibrium reaction is a common phenomenon in nature, which restricts the maximum conversion of chemical reactions at a given temperature, pressure, concentration, ratio and other conditions. It is particularly common in chemical reactions such as esterification, nitrification, ketone, acylation, etc. in organic liquid chemical reactions. It is an important problem in organic chemical production that how to effectively improve the yield of this kind of reaction and improve the utilization of raw materials and reduce the energy consumption in the subsequent separation process. Sandwich composite structure, a composite active catalytic membrane with loose porous catalytic layer, constructed a new multi-functional reactor, active pervaporation membrane reactor, used in the study of organic liquid equilibrium reaction. The sandwich composite structure is that the top layer is loose porous polyvinyl alcohol (Polyvinyl alcohol, PVA) catalysis The layer, in which the catalyst (solid acid, biological enzyme, etc.) is fixed by phase transformation, the intermediate is dense and selective separation layer, the membrane material is PVA, the bottom is the porous polyethersulfone (Polyethersulfone, PES) support layer, and it is supported by the mechanical support. The catalytic activity of the catalytic layer was observed and the separation characteristics of the composite active catalytic membrane were studied by the removal of butanol water. Finally, the reaction of n-butyl acetate was synthesized by acetic acid / n-butanol as a probe. The reaction and separation of the reaction in the porous catalytic layer CAMR (Catalytically Active Membrane Reactor) under different operating conditions was investigated. By comparing with the traditional IMR (Inert Membrane Reactor) and the dense catalytic layer CAMR, the characteristics and laws of the mass transfer behavior in the membrane reactor are investigated and the characteristics and laws of the mass transfer behavior are studied. The coupling strengthening mechanism of the reactive membrane reactor is analyzed, which proves that the composite catalytic film prepared in this paper can further strengthen the opposite. At last, the transformation rate of the raw material was further improved. Finally, the composite catalytic membrane was developed to the solid catalytic system and the biocatalytic system by the immersion precipitation phase transformation method proposed in this paper. The surface of the porous membrane and the porous catalytic membrane for the preparation of the pure PVA membrane and the porous membrane, the concentration of PVA on the membrane structure When the concentration of PVA is 5wt.%, a colloidal structure is formed and a closed cell cavity or honeycomb like structure is formed when the concentration of PVA is 10wt.%. The increase of the temperature of the coagulation bath is beneficial to the shortening of the film forming time. When preparing the porous catalytic film, the concentration of the catalyst is more suitable for 10wt.% and the concentration of the catalyst is further increased, which tends to form a compact skin. The catalytic activity of different catalysts for the reaction of the probe is: the dense catalytic layer of the granular catalytic layer (PVA concentration 5wt.%) free catalyst cell like catalytic layer (PVA concentration 10wt.%) without catalyst. The pseudo homogeneous phase model is established by the obtained kinetic data, the model prediction results are in good agreement with the experimental values. Well, through the pervaporation and dehydration test of butanol water, the dense catalytic layer CAMR, because the catalytic layer is dense and the thickness of the membrane is large, so the flux is the smallest and the diffusional resistance of the component is the largest. In the porous catalytic layer CAMR, because the catalytic layer is loose porous structure, the flux is larger, it is said that the porous structure is beneficial to reduce the mass transfer resistance of the component. It can only improve the diffusion of the reactant to the catalytic site, and increase the transfer of the product to the back of the membrane, thus improving the in situ removal of water, which is beneficial to the real "in situ" removal. In the reaction separation coupling strengthening experiment, the acetic acid and n-butyl alcohol decrease with time in the IMR, the compact catalytic layer CAMR and the porous catalytic layer CAMR. Small, n-butyl acetate and water rose synchronously at the initial stage, but after a period of time, the change of water concentration was deviated from the concentration curve of n-butyl acetate. As the removal rate of water was greater than that of water, the concentration curve of water in the membrane reactor decreased gradually with time. The increase of temperature could further improve the acetic acid. The change of the total flux also has two stages: at the early stage of the reaction, the flux rises first and reaches the inflection point. At 85, the water concentration in the porous catalytic layer CAMR will be 0 at 28h, and then the water can not be detected in the membrane reactor, but the back flux indicates that the reaction is constantly carried out and the water is constantly removed. It shows that after this time, the product realizes real in situ removal effect, that is, producing a molecular water, spreading to the downstream side of the membrane and removing it. This effect is more obvious with the decrease of the load of the catalyst. When the load of the catalyst is 2.25g/L, the water concentration in the front side in the 23.5h is O.. The catalytic performance and separation performance of the catalytic membrane are adjusted. Through the comparison of IMR and the porous catalytic layer CAMR, it is proved that the composite catalytic film prepared in this paper can further strengthen the process. As the water is generated on the surface of the membrane, the water has a greater driving force and the flux of water is greater, and the conversion rate of acetic acid is higher at the end of the table. At about 35.5 h, IMR The conversion rate of medium acetic acid is only about 75%, but in the porous catalytic layer CAMR, the conversion rate of acetic acid reaches about 85%., and in the contrast of the dense catalytic layer CAMR and the porous catalytic layer CAMR, the rate of water generation and removal is faster and the conversion rate is higher because of the lower mass transfer resistance in the porous catalytic layer. The method of preparation of composite catalytic membrane with porous catalytic layer has a certain versatility of.IER/PVA/PES composite catalytic membrane can also be used to remove the water in situ, achieve the enhancement of conversion rate, and the membrane structure has not changed obviously before and after use, and the Lipase/PVA/PES composite catalytic membrane can maintain the biological activity of the enzyme, and can also be real. Further intensification of the present conversion rate.
【学位授予单位】：北京化工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ032.4;TQ051.893

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