Multipurpose batch equipment

Most chiral chemicals are relatively small-scale products (1 to 1000 tonnes per year for pharmaceuticals, 500 to 10000 tonnes per year for agrochemicals) that are usually produced in multipurpose batch equipment This is probably the case for most catalytic reactions described in this chapter however, as a rule very little information on process technology is provided by the manufacturers. Here, we will discuss only briefly the reactor choices for hydrogenation reaction typically carried out in the liquid phase. For a successful implementation the following demands must be met ... 

Small-scale batch equipment is typically over designed for multipurpose use. 

Relatively small-scale products (1-1000 t/a for pharmaceuticals, 500-10000 t/a for agrochemicals), usually produced in multipurpose batch equipment. 

Enantiomerically pure compounds will be used above all as pharmaceuticals and vitamins [4], as agrochemicals [5], and as flavors and fragrances [6]. Pharmaceuticals and agrochemicals usually are multifunctional molecules that are produced via multistep syntheses. Compared to basic chemicals, they are relatively small scale products with short product lives, produced in multipurpose batch equipment. The time for development of the production process is often very short since time to market affects the profitability of the product. 

Most aroma chemicals are relatively high boiling (80—160°C at 0.4 kPa = 3 mm Hg) Hquids and therefore are subject to purification by vacuum distillation. Because small amounts of decomposition may lead to unacceptable odor contamination, thermal stabiUty of products and by-products is an issue. Important advances have been made in distillation techniques and equipment to allow routine production of 5000 kg or larger batches of various products. In order to make optimal use of equipment and to standardize conditions for distillations and reactions, computer control has been instituted. This is particulady well suited to the multipurpose batch operations encountered in most aroma chemical plants. In some instances, on-line analytical capabihty is being developed to work in conjunction with computer controls. 

Batch plants will have fewer MPls due to multipurpose utihzation of equipment... 

Finally, in multipurpose plants compounds, which can be deposited in various places (e.g. corners, zones near sealings) in equipment, can contaminate products of the subsequent batch. Therefore, all equipment must be thoroughly cleaned before the next production campaign starts. Contaminants can be formed in the process, sometimes at ppm level, and be recycled with streams of solvents and/or reactants. Hence, the influence of recycling on process performance indices must be included in the program of laboratory studies, at least in their final stage. 

The death of old products, the birth of new ones, changing demands, and the need to compose the optimal hierarchical production plan with an optimal use of the equipment and the shortest possible total production time make the timing of production more important than plant design. The use of rigorous optimization techniques can be most profitable at production planning and scheduling of existing batch plants, especially multipurpose plants. 

So far plants have been considered involving a single product. However, batch processes often produce multiple products in the same equipment. Here two broad types of process can be distinguished. In flowshop or multiproduct plants, all products produced require all steps in the process and follow the same sequence of operations. In jobshop or multipurpose processes, not all products require all steps and/or might follow a different sequence of steps9. 

On the other hand, in comparison to traditional recipe-driven multipurpose batch plants, new technical requirements arise from the use of mobile units. An important pre-requisite for a safe and automatic production are reliable docking systems that provide failure-free connections between the mobile vessels and the stationary processing stations. In the docking process of the mobile vessels the connection of pipes, of electric power and of signal processing equipment is necessary. The vessels therefore must be placed accurately. If vessels of different size are used, the connections must be flexible enough to cope with these. 

Comparison ofthe Plant Concepts To be able to compare the pipeless plant concept with the existing multipurpose batch plant, a reference plant was modelled using PPSiM. In the existing plant three conventional batch mixers work in a shifted parallel fashion. The three batch mixers were modelled by three stations and equipped with all technical functions necessary for the production of all recipes. Therefore each batch could be processed at one of the stations and the vessel transfers were limited to the transportation of empty or loaded vessels. All the other parameters of the model, e.g., charging mass flows, the durations of vessel cleanings and the recipes remained unchanged. 

Quantitative failure frequency data are difficult to obtain for multipurpose batch plants in the way that they are often used in the fine chemicals and pharmaceutical industries. Moreover, a quantitative assessment requires detailed knowledge of the control instruments, which may not be available during process development Therefore, a semi-quantitative approach is proposed, providing the required reliability for future plant equipment. 

The interaction between the batch and the continuous parts of the plant is a major concern of plant design and operating procedures. When the production volume reaches certain levels, continuous operation may be more economical. More often, batch chemical plants are built to produce more than one product. The objective is the use of existing equipment, which becomes idle when market demands are fulfilled. These plants can be classed in one of two broad categories multiproduct and multipurpose. The difference between the two types is illustrated in Fig. 1. 

Since numerous temporary piping connections are made to accommodate multipurpose use of several tanks during a campaign, leaks and/or small spills can occur. Thus, the cell cubicle floors and external portions of the equipment are flushed thoroughly after each campaign. All of the rework materials obtained between campaigns are accumulated, processed by means of one or two cycles of the Cleanex batch extraction process to remove miscellaneous impurities, and recycled to the next campaign. 

A non-periodic plant operating mode defined over a given time horizon is considered. Mixed storage policies, shared intermediated states, material recycles and multipurpose batch plant equipment units with continuous sizes, are allowed. 

Bulk active pharmaceutical ingredients are most often produced at the pilot scale under batch-mode operations with multipurpose equipment. In contrast, continuous operations are typically reserved for high volume products that can be produced in dedicated facilities. For this reason, these discussions are restricted to issues associated with batch operations. From a procedural perspective, batch operations more closely resemble bench-scale operations. However, the successful transformation of bench-scale experiments... 

---