Batch Optimization

The optimum operation of this fed-batch reactor involves finding the trajectory of feed versus time that maximizes (or minimizes) some economic performance criterion. Of course, the batch time is also an operating optimization variable. 

For example, suppose that the conversion of component A is specified to be 75% and the selectivity is specified to be 76%. These are determined from the overall economics of the process, which include the cost of raw materials, the value of products, and the cost of separation. Fixing conversion determines the batch time that is, we run until 75% of the reactant A initially charged to the reactor has been consumed. Selectivity will depend on the feed flowrate trajectory. 

For simplicity, we restrict ourselves to having a feed flowrate that starts at some value F0 and ramps down with a constant slope S. This practical approach to trajectory optimization is recommended by Smith and Choong6 for batch processes. We want to find the values of F0 and S that achieve the desired conversion and selectivity. There will be many pairs of values that will satisfy the two criteria. Each will have a different batch time and a different amount of C produced. 

Our objective function is the rate of production of C, which is the amount of C produced divided by the batch time  

Smith and L. Choong, Optimizing batch operations, Chem. Eng. Prog., 102, 31-36 (Jan. 2006). 

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Struempel M, Ondruschka B, Stark A (2009) Continuous production of the diazomethane precursor N-methyl-N-nitroso-p-toluenesulfonamide batch optimization and transfer into a microreactor setup. Org Process Res Dev 13(5) 1014—1021... 

C. Loeblein, J.D. Perkins, B. Srinivasan, D. Bonvin, Performance analysis of on-line batch optimization systems, Comp. Chem. Eng. 21 (Suppl) (1997) s867-s872. 

Donnet, M., Bowen, P., Jongen, N., Lemaitre, J., Hofmann, H., Schreiner, A., Jones, A. G., Schenk, R., Hofmann, C., Successful scale-up from millilitre batch optimization to a small scale continuous production using the segmented flow tubular reactor example of calcium carbonate precipitation, Chem. Eng. Trans. 2002, 1,1353-1358. 

Batch Optimal Charging Policy Optimal Batch... 

Is the cleaning operation in between batches optimized Is there a possibility of wash-solvent recycle here without affecting the overall product quality ... 

A lab-scale procedure for refolding the recombinant protein, secretory leukocyte protease inhibitor, was scaled to 1000 liter production batches. Optimization of reaction conditions by a statistical experimental design approach resulted in consistent activity recoveries of 80-85%, and lowered cost. The statistical design method allows simultaneous optimization of interacting process variables. Changes in the refold reaction conditions greatly influence the level of specific contaminants, thus purity becomes an important parameter in addition to yield. Our experience in the development, scale-up, and cost analysis of a protein refolding operation is presented. 

In this manuscript we describe our experience in the development and scale-up of the refolding procedure from initial lab preparations to a production scale of 175 g rSLPI in a 1000 liter refold batch. Optimization studies to... 

SCHEME 7.15 The process flowchart for manufacture of robalzotan (NAD-299) the structures representing the different compound codes are specified in Scheme 7.4. Boxes in bold indicate isolated stages. Batch sizes for each step are given inside the boxes together with the number of discrete batches optimized to achieve a good materials throughput in the process. Yields are as depicted and represent the status at closure of the project. 

Patnaik reported fed-batch optimization of PHB synthesis through mechanistic, cybernetic, and neural approaches. Enhancement of PHB productivity was investigated by applying two artificial neural networks to a bioreactor with finite dispersion and noise in feed streams. One network filtered the noise and other controlled the filtered feed rates of carbon and nitrogen sources. The study revealed that neural optimization doubled the maximum PHB concentration in fed-batch fermentation with R. eutropha by optimizing the time dependent feed rates. 

Patnaik PR. Fed-batch optimization of PHB synthesis through mechanistic, cybernetic and neural approaches. Bioautomation 2006 5 23-38. 

Dong, D., McAvoy, J. and Zafiriou, E. 1996, Batch-to-batch optimization using neural network models, Ind. Eng. Chem. Res. 7,2269. 

Mass transfer coefficients may be obtained by fitting to process data. Including DPC loss, production capacity (reaction time), and unwanted side products in a cost function, the optimization leads to a balancing of mass transfer and reaction rate. This means that an optimal process is neither entirely mass-transfer nor ki-netically controlled. To avoid side reactions that impair product quality, the lowest temperature that kinetics and mass transfer allow is chosen. The results of the semi-batch optimization can be transferred to the design of a staged, continuous process [154]. 

In batch process optimization, one of the principal objectives is to improve equipment utilization through reduction in dead time. This requires both structural and parameter optimization, with many options available. 

Consider changing from batch to continuous operation. Batch processes, by their very nature, are always at unsteady state and thus are difficult to maintain at optimal conditions. 

Optimization of Cycle Times. In batch filters, one of the important decisions is how much time is allocated to the different operations such as filtration, displacement dewatering, cake washing, and cake discharge, which may involve opening of the pressure vessel. Ah. of this has to happen within a cycle time /. which itself is not fixed, though some of the times involved may be defined, such as the cake discharge time. 

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. 

Spreadsheet Applications. The types of appHcations handled with spreadsheets are a microcosm of the types of problems and situations handled with fuU-blown appHcation programs that are mn on microcomputers, minis, and mainframes and include engineering computations, process simulation, equipment design and rating, process optimization, reactor kinetics—design, cost estimation, feedback control, data analysis, and unsteady-state simulation (eg, batch distillation optimization). 

Westerberg, A. W. Optimization in A. K. Sunol, D. W. T. Rippin, G. V. Reklaitis, O. Hortacsu (eds.). Batch Pr ocessing Systems Engineering Current Status and Future Dir ections. vol. 143, NATO ASI Series F, Springer, Berlin (1995). 

Batch readers—optimum residence time for series and complex reactions, minimum cost, optimal operating temperature, and maximum rate of reaction... 

Production Controls The nature of the produc tion control logic differs greatly between continuous and batch plants. A good example of produc tion control in a continuous process is refineiy optimization. From the assay of the incoming crude oil, the values of the various possible refined products, the contractual commitments to dehver certain products, the performance measures of the various units within a refinery, and the hke, it is possible to determine the mix of produc ts that optimizes the economic return from processing this crude. The solution of this problem involves many relationships and constraints and is solved with techniques such as linear programming. 

Because of the differences in primary and secondaiy metabolism, a reactor may have a dual-stage fed-batch system. In other words, fed-batch operation optimizes growth with little or no product formation. When sufficient biomass has accumulated, a different fed-batch protocol comes into play. 

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