Optimization-based predictive control of a simulated moving bed process using an identified model

For optimization-based dynamic control of simulated moving bed (SMB) process, a novel control strategy based on process identification, which is an extension of the earlier work (Song et al., 2006a. Identification and predictive control of a simulated moving bed process: purity control. Chemical Engineering Science 61, 1973-1986), is proposed. A linear output prediction model is obtained by the method of subspace identification and used for the dynamic control. The controller is designed for optimizing the production cost while maintaining the specified product purities. For all of these, the average purities over one switching period of the target components in extract and raffinate streams, the reciprocal productivity and the solvent consumption are selected as output variables, while the flow rates in 1, 2, 3 and 4 are chosen as the manipulated variables. The realization of this concept is discussed and assessed on a virtual eight column SMB unit for a system following a bi-Langmuir isotherm. The identified prediction model is proven to be in good agreement with the first principles model considered as the actual SMB process. For typical control objectives encountered in actual operation, i.e., disturbance rejection and set-point tracking, it is shown that the proposed controller exhibits excellent performance, hence it is an effective tool for optimization-based control of SMB process.     

Substructure-based virtual screening for adenosine A2A receptor ligands

A virtual ligand-based screening approach was designed and evaluated for the discovery of new A(2A) adenosine receptor (AR) ligands. For comparison and evaluation, the procedures from a recently published virtual screening study that used the A(2A) AR X-ray crystal structure for the target-based discovery of new A(2A) ligands were largely followed. Several screening models were constructed by deriving the distinguishing structural features from selected sets of A(2A) AR antagonists, so-called frequent substructure mining. The best model in statistical terms was subsequently applied to large-scale virtual screens of a commercial vendor library. This resulted in the selection of 36 candidates for acquisition and testing. Of the selected candidates, eight compounds significantly inhibited radioligand binding at A(2A) AR (>30%) at 10 μM, corresponding to a "hit rate" of 22%. This hit rate is quite similar to that of the referenced target-based virtual screening study, while both approaches yield new, non-overlapping sets of ligands.     

萃取精馏复合溶剂的复配选择

提出按溶剂之间复配形成氢键的情况和修正的UNIFAC模型相结合的方法选择分离共沸体系的萃取精馏复合溶剂。准确测量了共沸体系与萃取精馏单溶剂和复合溶剂的汽液平衡数据,结果表明采用的萃取精馏单溶剂和复合溶剂的选择方法具有较好的准确度,模拟值与实验值比较,相对偏差均小于9%。通过综合比较得到分离乙酸乙酯-乙醇、乙醇-水和环己烷-苯3个共沸体系的最佳复合溶剂及配比。在最佳复合溶剂组成下,原共沸体系的相对挥发度达到最大值,该值优于组成复合溶剂的单溶剂所达到的分离效果。在最佳复合溶剂组成下,改变原料体系组成,复合溶剂组成对原料体系相对挥发度的影响趋势基本相同,这表明复合溶剂在萃取精馏塔内不同原料组成下均能较好地增加体系的相对挥发度,为工业上在萃取精馏过程中使用复合溶剂提供了理论依据。     

基于相图分析的润滑油糠醛精制工艺改进

针对原料油中饱和分与芳香分分离精度低导致糠醛精制工艺抽余油收率低、抽出油质量差的问题,提出基于热力学相图分析的糠醛精制工艺的改进策略。基于虚拟组分法简化润滑油组分为饱和分、芳香分和极性分,采用NRTL模型预测不同温度下的相平衡数据,分析抽提过程液液相平衡关系及操作条件对萃取过程的影响规律,发现温度是影响平衡组成和传质效率的关键因素。基于相图对萃取过程的分析,通过设计多级抽出液回收系统,多温度梯级分离抽出液,解决抽提塔在较低温度下难以操作的问题。结合实际糠醛精制装置进行模拟计算,结果表明设置多级抽出液回收系统,抽提过程溶剂比及冷热公用工程量适当增加,抽余油收率较原工艺提高10%以上,抽出油质量极大改善,显著提升糠醛精制工艺的分离效率。     

Predicting the Substrate Scope of the Flavin-Dependent Halogenase BrvH

The recently described flavin-dependent halogenase BrvH is able to catalyse both the bromination and chlorination of indole, but shows significantly higher bromination activity. BrvH was annotated as a tryptophan halogenase, but does not accept tryptophan as a substrate. Its native substrate remains unknown. A predictive model with the data available for BrvH was analysed. A training set of compounds tested in vitro was docked into the active site of a complete protein model based on the X-ray structure of BrvH. The atoms not resolved experimentally were modelled by using molecular mechanics force fields to obtain this protein model. Furthermore, docking poses for the substrates and known non-substrates have been calculated. Parameters like distance, partial charge and hybridization state were analysed to derive rules for predicting activity. With this model for activity of the BrvH, a virtual screening suggested several structures for potential substrates. Some of the compounds preselected in this way were tested in vitro, and several could be verified as convertible substrates. Based on information on halogenated natural products, a new dataset was created to specifically search for natural products as substrates/products, and virtual screening in this database yielded further hits.     

Visualization of Large Experimental Space Using Holographic Mapping and Artificial Neural Networks. Benchmark Analysis of Multicomponent Catalysts for the Water Gas Shift Reaction

This paper reports the combination of Holographic Mapping (HM) and Artificial Neural Networks (ANNs) in order to provide a benchmark visualization of a multi-dimensional space in two-dimensional forms. In this approach each matrix point in HM represents virtual catalytic data generated by means of ANNs in order to visualize the given multi-dimensional experimental space. A 12-dimensional experimental space related to the composition of catalysts designed for the water gas shift reaction (WGSR) from 12 possible components supported on ZrO₂ is visualized. Catalytic data obtained in an earlier combinatorial screening process at 300 °C were used for training of the ANNs. The results show that the visualization of large experimental spaces having more than half a million virtual experimental points can be accomplished. The analysis of synergistic effects between different components revealed that the key components of water gas shift catalysts at 300 °C were Pt, Fe, Eu and V, while Co, Ru, Sb, Ge and Mo had a pronounced negative effect on the activity.     

Identification and predictive control of a simulated moving bed process: Purity control

A model predictive control strategy for a simulated moving bed (SMB) chromatographic process is proposed. For this, the average purities over one switching period of target components in extract and raffinate ports are selected as output variables, while the flow rates in Sections 2 and 3 of the SMB unit are chosen as the input variables. With this arrangement a linear input-output prediction model is identified through subspace identification and used for dynamic control. The realization of this concept is discussed and the implementation on a virtual eight column SMB unit is assessed, in the case of the separation of enantiomers behaving according to the binary bi-Langmuir adsorption isotherm. The identified prediction model is proven to be in good agreement with the first principles model used to simulate the actual SMB process. For typical control objectives encountered in real operation, i.e., disturbance rejection or set-point tracking, it is shown that the proposed controller demonstrates satisfactory control performances in minimizing off-spec products.     

Preparation of defect-free asymmetric membranes for gas separations

A technique was developed to prepare defect-free, asymmetric, polymer membranes for gas separation. The preparation method eliminates the need for coatings, which are usually required to render asymmetric, polymer based, membranes gas selective. In this method, a casting solution containing a polymer, solvent, and salt additive is given a desired shape and immersed in a coagulation bath containing a nonsolvent. The nonsolvent is selected to have a low affinity for both the solvent and salt additive. After the complete coagulation of the membrane, the additive salt is leached out in a second bath. This leads to the formation of an asymmetric membrane that has a well-interconnected porous network. The fine membrane structure is preserved by solvent exchange before it is finally dried. Polyetherimide (PEI) (Ultem® 1000) membranes were prepared from casting solutions containing 23, 25, and 26.5% (wt) PEI, various amounts of lithium nitrate and N-methyl-2-pyrrolidinone (NMP). Membrane performance was determined for the separation of oxygen from air. The effects of polymer concentration, additive salt concentration and the drying process on oxygen permeance, and the actual separation factor of the membrane are discussed. The addition of a small amount of solvent to the coagulation bath improved the leaching of the salt additive and produced membranes with a more open structure. A polymer concentration of 23% produced membranes with the highest performance. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1471–1482, 1999     

生物催化制备光学活性4-氯-3-羟基丁酸酯研究进展

综述了生物催化制备光学活性4-氯-3-羟基丁酸酯(CHBE)的研究进展,介绍了生物催化外消旋体拆分和不对称还原方法制备光学活性CHBE的研究现状,重点阐述了反应介质选择、辅助底物和添加剂的选择、细胞热处理等一些控制不对称还原4-氯-3-氧代丁酸酯(COBE)立体选择性的方法。对生物催化制备光学活性CHBE的工业化前景进行了展望。     

Neuer stofflicher Nutzungspfad von Treberpresswasser aus Biertreber unter Einsatz von Membrantrenntechnik in Lebens‐ oder Nahrungsergänzungsmitteln

A new utilization concept for brewers' spent grains, the main byproduct of the brewing industry, is introduced. First results from an ongoing research project beyond the actual state of the art of brewers' spent grains usage are presented. It is focused on developing an adaptable selective separation procedure of valuable components from press water arising by mechanical dewatering of brewers' spent grains for the use as food additive. Experimental results on micro‐, ultra‐ and nanofiltration for specific separation of the ingredients focused on substance classes are presented. The membrane applicability is evaluated by the membrane permeability and by the retention of valuable components like proteins and polyphenols. Results showed that the microfiltration of press water with a rotating membrane is comparable to commercial beer microfiltration in terms of permeate flux.     

From theory to bench experiment by computer-assisted drug design

Tight integration of computer-assisted molecular design with practical realization by medicinal chemistry will be essential for finding next-generation drugs that are optimized for multiple pharmaceutically relevant properties. ETH Zürich has established an interdisciplinary research group devoted to exploring the potential of this scientific approach by combining expertise from pharmaceutical chemistry and computer sciences. In this article, some of the group's activities and projects are presented. A current focus is on machine-learning applications aiming at hit and lead structure identification by virtual screening and de novo design. The central concept of 'adaptive fitness landscapes' is highlighted along with practical examples from drug discovery projects.     

Mobility and distribution of silicone additives in coatings; a spectroscopic study

The concentration of four prepared silicone/poly(ether) additives at the film-air (F-A) and film-substrate (F-S) interfaces of films prepared on glass and poly(ethylene) substrates is characterized via quantitative attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectroscopy. Three different coating systems, an acrylic/melamine solvent based system, an acrylic/isocyanate solvent based system, and an aqueous poly(urethane) suspension, were examined. It is found that the nature of the substrate, the mechanism of film formation, and the inherent coating/additive compatibility are all factors which may significantly influence additive behavior. Also the acrylic/melamine system generally reveals a slight degree of enrichment of both additive components to the F-A interface, but the acrylic/isocyanate system exhibits a more pronounced concentration gradient due to a lesser degree of compatibility. In contrast, the water-based poly(urethane) exhibits a more complex behavior, with the poly(ether) component revealing significant enrichment to the F-A interface, and the siloxane component exhibiting a decreased concentration as the interface is approached. Here, the mechanism of film formation involves a water flux passing out of the film which may serve to transport the water soluble poly(ether) components to the F-A interface. At the F-S interface, it is demonstrated that the nature of the substrate may influence additive behavior, and it is found that the concentration of the more polar poly(ether) components generally exhibits a lesser degree of enrichment to a poly(ethylene) substrate, relative to glass.     

The equilibrium distribution of wool-grease components and contaminants between the solvents hexane and aqueous isopropanol

A strategy has been developed that enables the equilibrium distribution of wool-grease components and contaminants to be specified in a form suitable for the design of a solvent extraction process. Experimentally determined equilibrium phase compositions for carefully selected model components were fitted by multi-variable least-squares regression to an empirical model to provide a convenient mathematical specification. The specification accounts for the dependency of distribution coefficient on concentration and also for the effects of component interactions.     

A systematic method to create reaction constraints for stoichiometric matrices

Modeling rate-controlled chemically reactive systems in biocatalysis, fuel combustion, material science, and chemical process engineering involves the quantification and exploitation of interactions between many chemical species. These dynamic chemical systems, having relatively few limiting reactions, can be conceived as a series of snapshots where reactions have fixed extents but otherwise idle. Since the reactions affect the stoichiometric matrix of the internal constraints, such constrained equilibrium states cannot be defined in terms of conventional atomic mass balances.A systematic method for obtaining generalized equilibrium constraints for reaction mechanisms of arbitrary complexity is presented. Reaction matrices are converted into entity conservation matrices using row operations. The simultaneously introduced virtual components enable Gibbs energy calculations for complex reaction schemes including organic systems and enzyme-catalyzed biochemical transformations having multiple limiting reactions. Classical Gibbs energy minimization, which would otherwise readily model phase transformations and solvent interactions, is thereby made accessible to these emerging application fields.     

Bestimmung von Diffusionskoeffizienten nichtflüchtiger Additive in Polymerbeschichtungen mit Hilfe der inversen Mikro‐Raman‐Spektroskopie

In the scope of this work, the Fickian diffusion coefficient of a non‐volatile additive in the ternary system polymer/additive/solvent is determined by analysing the equalisation process of additive mass loading profiles in thin polymeric films by means of Inverse Micro Raman Spectroscopy (IMRS). The diffusion coefficients are obtained by fitting calculated to measured additive mass loading profiles. From the experiments presented in this work, for the first time the diffusion coefficient of the plasticizer triphenyl phosphate in polymeric solutions of methylene chloride and polyvinyl acetate could be determined over a wide range of additive and solvent mass loadings.     

基于高阶基团贡献法与COSMO-SAC模型的溶剂设计方法

提出了一种基于高阶基团贡献法与类导体屏蔽片段活度系数模型（conductor like screening model-segment activity coefficient, COSMO-SAC）的计算机辅助溶剂设计方法（computer-aided molecular design, CAMD）。首先,基于高阶基团贡献法（higher-order group contribution, GC⁺）与COSMO-SAC模型构建GC⁺-COSMO方法,关联分子基团组合与表面屏蔽电荷密度分布[σ-profiles, p(σ)]、分子空腔体积V_c,实现对二者的高通量预测;然后结合基于简化分子线性输入系统（simplified molecular input line entry system, SMILES）的异构体生成算法与GC⁺-COSMO方法实现CAMD技术对异构体的识别及性质区分;最后,通过目标函数与约束方程组成的混合整数非线性规划模型（mixed integer nonlinear programming, MINLP）来建立溶剂设计问题,进一步采用分解式算法优化求解,实现溶剂优化设计目标。基于以上模型和方法开展了狄尔斯-阿尔德（Diels-Alder, DA）竞争性反应溶剂设计,验证了提出的方法的可行性与有效性。     

MODELING AND SIMULATION OF BINARY APPROACH BY ENERGY CONSERVATION ANALYSIS

A new model for approach processes of two unequal or equal sized drops or bubbles is proposed based on a parallel film concept and energy conservation analysis. This model can estimate the interaction time and the maximum film area for an approach and the effects of Weber number, size ratio and curvature of film. It also gives a good explanation why the effective virtual mass coefficienl in the model of Chesters and Hofman (1982) changes with the size ratio of drops or bubbles.     

Membrane assisted crystallization using reverse osmosis: Influence of solubility characteristics on experimental application and energy saving potential

Membrane assisted crystallization is a promising concept to improve control over the generation of supersaturation and to reduce energy consumption of conventional solvent evaporation. In this work both the practical and theoretical feasibility of membrane assisted crystallization using reverse osmosis (MaC-RO) is investigated with an emphasis on the influence of solubility characteristics. An experimental setup is presented tailored towards reduction of the two main sources of risk for the concept, which are concentration polarization and scaling on the membrane surface. The performance is investigated for two model systems with different solubility behaviour, which are ammonium sulphate and adipic acid both crystallized from water. The latter system shows a much better operational performance. In addition, a model of a continuously operated MaC-RO process is developed and optimized, and the energy consumption as function of solubility characteristics is systematically compared to that of conventional evaporative crystallization. Both the experimental and theoretical study show that MaC-RO has potential for many applications and is economically and practically most suitable for components with a moderate solubility, high molecular weight, and a strong dependency of solubility on temperature.