Optimization of reactive SMB and Varicol systems

A comprehensive optimization study on a simulated moving bed reactor (SMBR) system is reported in this article for the direct synthesis of methyl tertiary butyl ether (MTBE) from tertiary butyl alcohol (TBA) and methanol. The applicability of the Varicol process, which is based on non-synchronous shift of the inlet and outlet ports, is explored for the first time for a reactive system. Multi-objective (two and three objective functions) optimization has been performed for both existing as well as design stage for SMBR and Varicol systems and their efficiencies are compared. The optimization problem involves relatively large number of decision variables; both continuous variables, such as flow rates in various sections and length of the columns and discrete variables, such as number of columns and column configuration. Pareto optimal solutions are obtained. It is observed that a five-column Varicol performs better than an equivalent five-column SMBR and its performance is nearly equal to that of a six-column SMBR in terms of purity and yield of MTBE and minimal eluent consumption. This is an important inference as it enables the reduction of fixed and operating costs while at the same time helps to achieve high purity and yield of the desired product and conversion of the limiting reactant. A state-of-the-art optimization technique, viz., non-dominated sorting genetic algorithm (NSGA), which allows handling of these complex optimization problems, is employed for this study. This is the first time that, not only the separating potential of Varicol has been extended to reaction systems, but also was optimized for multiple objectives.     

异步模拟移动床色谱的数值模拟

Asynchronous simulated moving bed chromatography (ASMBC), known also as the “VARICOL“ process, is more efficient and flexible than the well-known and traditional simulated moving bed chromatography (SMBC). A detailed model of ASMBC, taking account of non-linear competitive isotherms, mass transfer parameters, and complex port switching schedule parameters, was developed to simulate the complex dynamics of ASMBC.The simulated performance is in close agreement with the experimental data of chiral separation reported in the literature. The simulation results show that ASMBC can achieve the performance similar to SMBC with fewer columns and can achieve better performance than SMBC with the same total column number. All design and operation parameters can be chosen correctly by numerical simulation. This detailed ASMBC model and the numerical technique are useful for design, operation, optimization and scale-up of ASMBC.     

Multiobjective Optimization of Simulated Moving Bed Reactor and its Modification — Varicol Process

A comprehensive optimization study on a Simulated Moving Bed Reactor (SMBR) system is reported in this article for the direct synthesis of Methyl Tertiary Butyl Ether (MTBE). In addition, the SMB technology, which is based on synchronous switching of ports, was modified to a new more flexible Varicol process based on non‐synchronous switching. Multi‐objective optimization has been performed for both SMBR and Varicol and their efficiencies were compared. A state‐of‐the‐art optimization technique, viz., Non‐dominated Sorting Genetic Algorithm (NSGA) that allows handling of these complex optimization problems is employed in this study.     

异步控制Varicol工艺分离愈创木酚甘油醚对映体过程研究

模拟移动床技术已经成为手性化合物拆分的重要手段。以Chiralcel OD为固定相、乙醇/正己烷混合物为流动相, 采用一种先进的模拟移动床技术(Varicol工艺)分离愈创木酚甘油醚对映体。针对进出料口位置异步切换模式建立了Varicol工艺数学模型, 采用有限元正交配置法对模型进行求解。从初始循环内愈创木酚甘油醚对映体内部浓度的时间进程曲线分析了Varicol工艺的分离过程。并且设计了5柱 (1-1.5-1.5-1) 构态的Varicol工艺分离愈创木酚甘油醚操作区, 确定了获得单一对映体产品纯度99%的分离条件, 通过实验数据进行了验证。理论和实验研究可以为Varicol工艺的工业应用提供基础依据。     

Continuous chromatographic processes with a small number of columns: Comparison of simulated moving bed with Varicol,PowerFeed, and ModiCon

The Simulated Moving Bed process and its recent extensions called Varicol, PowerFeed and ModiCon are studied, in the case where a small number of columns are used, i.e. from three to five. A multiobjective optimization approach, using genetic algorithms and a detailed model of the multicolumn chromatographic process, is applied to optimize each process separately, and allow for comparison of the different operating modes. The non-standard SMB processes achieve better performance than SMB, due to the availability of more degrees of freedom in the operating conditions of the process, namely the way to carry out asynchronous switches for Varicol, and the different flow rates and feed concentration during the switching interval for PowerFeed and for ModiCon, respectively. We also consider the possibility of combining two non-standard operating modes in a new hybrid process, and evaluate also in this case the possible performance. Finally, a critical assessment of the results obtained and of the potential for practical implementation of the different techniques is reported. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University. The importance of the seminal papers of Professor Rhee on first order partial differential equations and the theory of multicomponent chromatography (H.-K. Rhee, R. Aris, N. R. Amundson,Philos. Trans. Roy. Soc. London,A267 (1970) 419–455;A269 (1971) 187–215) for the SMB design and optimization tools (Triangle Theory) that the authors have developed over the years cannot be overestimated.     

模拟移动床色谱分离吴茱萸碱和吴茱萸次碱

以C18为固定相、甲醇/水=70/30（体积比）为流动相,利用三区带模拟移动床分离了两种生物碱,吴茱萸碱和吴茱萸次碱。通过前沿分析法测定了两种生物碱的吸附等温线,在实验浓度范围内符合线性吸附等温线,吴茱萸碱和吴茱萸次碱的亨利系数分别为3.11和5.25。利用经验公式估算了轴向扩散系数和有效传质系数。分别利用三角形理论和基于模型的优化方法对三区带模拟移动床的操作条件进行设计,在优化的条件下,最大进料流量为0.55 ml?min^-1,两种产品纯度均大于99%。通过异步切换策略,在不增加设备投资及保证产品纯度大于99%的前提下,将进料流量提高至0.62 ml?min^-1。