Semi-continuous processes

An improvement of the productivity of the NF-based process to 7.1gl h is obtained by running the process semi-continuously [64]. Final lactic acid concentrations in the permeate can reach values between 10 and 60 g 1 . The higher values are at the lower limit of concentrations found in UF- and MF-based processes [60]. Based on these data, a three-step repetitive process has been proposed [64]. The first step is the cell multiplication step during which pH can be controlled, the second step is an acid production step, followed by NF. In this approach a constant pH is assumed during each separate process step. However, other strategies in the acidification stage, which make use of natural acidification by the lactic acid bacteria are also possible. 

Repeated fed-batch process (semi-continuous process or cyclic... 

Polymerisations may be categorised by both the polymerisation mechanism (e.g. radical polymerisation, anionic polymerisation etc.) and by the polymerisation technique (e.g. solution polymerisation, emulsion polymerisation etc.). A third factor is how the reactor is operated in batch mode, or by adding monomers during the process (semi-continuous) or by continuous operation. Mechanism, technique and process strategies (mode of operation) all have an influence on rates of polymerisation and characteristics of the formed polymer. In this chapter, we will focus on the special characteristics that can be distinguished in an emulsion polymerisation related to rate, development of molar mass and chemical composition. In Chapter 4 the effects of the process strategy will be discussed. 

Delayed Coking", is a semi-continuous process, developed at the end of the 1930 s. The reaction is conducted at 450-500°C under relatively low pressure, four atmospheres, maximum. 

There are three important processes for preparing PVAc latexes in the presence of PVA as a protective colloid batch, semi-continuous, and delayed addition of monomer [10]. In this Chapter, the effects of the addition of VAc and initiators on the properties of PVAc latexes are discussed using the three methods under the same charge of ingredients for polymerization as shown in Fig. 1 [1,11]. 

Additionally, the influence of the life time of the micro-structured devices as well as the expenditure of the peripheral equipment was estimated in order to obtain insight into the ecological hot-spots of the system. A conventional macro-scaled semi-continuously operated batch process was chosen as a reference process. The comparison of both technological systems was performed by means of the two-step synthesis of m-anisaldehyde serving as model reaction. 

The batch plant shown in Fig. 7.4-6 is to be optimized. The required production capacity is 11070 m per year. The cost coefficients (see Eqn. 7.3-4) are given in Table 7.4-7. The fixed processing times in the batch units, /i. r, are given in Table 7.4-8 together with initial values of processing times in the semi-continuous units, 04-( and those found by optimization. The total batch times, volumes, and costs are also given in this table. 

Rk - processing rate of semi-continuous equipment unit k kg/h... 

Qik - processing time in semi-continuous unit k for product i h... 

In this chapter the simulation examples are described. As seen from the Table of Contents, the examples are organised according to twelve application areas Batch Reactors, Continuous Tank Reactors, Tubular Reactors, Semi-Continuous Reactors, Mixing Models, Tank Flow Examples, Process Control, Mass Transfer Processes, Distillation Processes, Heat Transfer, and Dynamic Numerical Examples. There are aspects of some examples which relate them to more than one application area, which is usually apparent from the titles of the examples. Within each section, the examples are listed in order of their degree of difficulty. 

Semi-continuous and continuous reductive processes are best carried out with activated hydroxymethanesulphinates, since dithionites (even when stabilised) are unsuitable due to being oxidised too quickly by air [273]. 

The patent described a method for the removal of thiophenic compounds from fossil fuels, in which the reacting media might contain organic solvents. Additionally, the biocatalyst may be contacted with the fuel directly either as free enzyme or in its immobilized form. The process could, therefore, be performed either in a batch reactor or in a semi-continuous or continuous manner. Further, it may be performed either as a stand... 

Talbot A semi-continuous steelmaking process which combines the Bessemer and Open Hearth processes. Molten pig iron from a Bessemer converter is poured into an Open Hearth furnace containing fresh ore and lime. Impurities in the pig iron oxidize and enter the slag. The process improves the yield of steel and the throughput of the plant. Introduced by B. Talbot at Pencoed, PA, in 1900 and subsequently adopted in Europe. 

In this chapter, we first consider uses of batch reactors, and their advantages and disadvantages compared with continuous-flow reactors. After considering what the essential features of process design are, we then develop design or performance equations for both isothermal and nonisothermal operation. The latter requires the energy balance, in addition to the material balance. We continue with an example of optimal performance of a batch reactor, and conclude with a discussion of semibatch and semi-continuous operation. We restrict attention to simple systems, deferring treatment of complex systems to Chapter 18. 

Keller (1998) describes the semi-continuous reaction process of a vinyl ketone K with lithium acetylide LA to yield lithium ethinolate LE an intermediate in the vitamin production. In an undesired side reaction an oligomer byproduct BP is produced. During the process, reactant K is fed to the semi-batch reactor at a rate to maximize the selectivity for LE. 

In this case history, the control of the TMRaa (adiabatic Time-to-Maximum-Rate) is to be achieved in a semi-continuous reactor process by the dynamic optimization of the feed rate. Here it is desired to have the highest possible space-time-yield STY and it is necessary to achieve a thermally safe process (Keller, 1998). The reaction involves the addition of a sulfur trioxide on a nitro-aromatic compound... 

The reaction takes place in the liquid phase of a semi-continuous process, which allows the feed rate manipulation to control the rate of heat release, as shown below. 

Simulation Tools and Examples of Chemical Engineering Processes Intensities of Segregation in a Semi-Continuous Reactor... 

---