Zur diskontinuierlichen Rektifikation azeotroper Gemische mit Hilfsstoffeinsatz

Discontinuous Rectification of Azeotropic Mixtures with Use of Auxiliary Substances . Batchwise rectification is one of the most commonly used thermal separation operation in the production of fine chemicals and pharmaceiticals, where small amounts of mixtures containing several product or auxiliary components are generally separated. Greater plant flexibility with regard to mixture composition, throughput, and separation specification often also favours batchwise over continuous processing. This publication discusses process engineering possibilities of batchwise rectification of azeotropic mixtures with the aid of various examples. It gives a detailed presentation of two industrial batch rectifications with additional feed of auxiliary substances, viz. azeotropic rectification with entrainment agent and extractive rectification. In both cases the set goal is to minimise charge times and to maximise the quantities processed in plant operation, with time-optimised control of auxiliary substance throughput being of critical importance in both cases.     

Batch‐Rektifikation mit Mittelbehälter

Batch Distillation in Middle Vessel Columns Batch distillation in a middle vessel column is a promising alternative to conventional batch distillation as disadvantages such as high temperatures in the feed vessel or a high energy and time demand of the process can be avoided. The article describes the basics of the synthesis of processes for the separation of zeotropic and azeotropic mixtures using this type of column. Furthermore, experimental results are presented and the advantages of batch distillation in a middle vessel column are explained.     

Teilkondensation und nichtadiabate Rektifikation binärer Gemische in Füllkörperrohren

Partial condensation and non-adiabatic rectification of binary mixtures in packed columns. Vertical tube assemblies are preferred for partial condensation of vapour mixtures. The mixture of vapours is fed through the tubes in countercurrent flow to the falling condensate, while coolant flows through the jacket. Only with very large ratios of length L to diameter d of the tubes, i.e. L/d 200, does the separatory effect of partial condensation, owing to rectification mass transfer between the phases, exceed the enrichment effect of partial condensation. Use of ring-shaped packings drastically reduces the characteristic diameter, so that the additional separatory effect occurs at relatively short tube lengths. In the present paper, experimental results concerning the separation efficiency of tubes packed with Raschig rings for non-adiabatic rectification and partial condensation of the “negative” binary mixture n-heptane/benzene are reported and evaluated with the aid of the extended two-film theory. It is found that the resistance to mass transfer averaged over the length of the tube lies entirely on the liquid side on non-adiabatic rectification. Correlation of the Sherwood number of the condensate taken over the length of the tube and the condensate loading clearly shows that the usual calculation of partial condensation with average total mass transfer coefficients does not give physically meaningful results in the case of liquid-side resistance to transport. Calculating procedures which account for the variation of the partial mass transfer coefficients along the tube should lead to improved evaluation or prediction of separation efficiency.     

Automatisierung und Optimierung von Anfahr‐, Lastwechsel‐ und Batch‐Prozessen

Continuous processes show dynamics during load changes, start‐up and shutdowns whereas batch processes exhibit inherent dynamics. In the past, the major concern of automating these dynamics states of process operation were safe and reproducible operation, however, today modern methods of process operation allow for the economic optimization at the same time. The automation and optimization of batch processes pose challenges in several areas: Mastering the high complexity, connecting heterogeneous components by automation, and combining extensive knowledge from both process engineering and automation during project execution. This contribution describes approaches from industrial practice and punctually academic research, which solutions for the challenges are readily available and how to implement these.     

Verstärkte Thermoplaste – Theorie und Praxis

Reinforced thermoplastics are composites consisting of a viscoelastic plastics matrix of low strength and a material (mostly inorganic) which has a high strength and a high modulus of elasticity, showing purely elastic strain. Globular and fibrous particles can be used for reinforcing. In the first case, the reinforcing action is largely due to an isotropic reduction of the strainability of the thermoplastic. In the second, more important case, the fibres can also accumulate stress from the matrix. In both cases, the elastic and viscous components of strain are pushed closer together. In practice, irregularities in the orientation of the fibres and continually changing patterns of stress cannot be avoided. These give rise to difficulties in checking the theoretical treatment of thermoplastics reinforced with short fibres. The basic element itself, i.e., the individual fibre embedded in the matrix has several variants, i.e., the length of the fibre, the ratio of the fibre length to the diameter, the critical fibre length determined from the interfacial shear strength and fibre strength, and the tensile strength in the transverse direction.