Design strategy and process optimization for reactors with continuous transport of an immobilized enzyme

In order to operate a process which uses immobilized enzymes at constant conversion and constant capacity, the refreshment of the enzyme must be continuous. In this paper, two reactor types with continuous refreshment of the biocatalyst are discussed: the stirred tank and the multistage fluidized bed. A method is presented for dimensioning a reactor in such a way that the costs for the conversion of substrate to product are minimized. These costs are calculated as the sum of the biocatalyst consumption and overall reactor costs.\ud \ud In contrast with the stirred-tank reactor, the multistage fluidized bed can be operated at a non-uniform temperature. For the glucose isomerase process, an optimal temperature gradient results in a small reduction in the biocatalyst consumption (±5%). It is concluded that, in general, a temperature gradient will only favour the economy of processes with relatively expensive biocatalysts.\ud \ud Compared with conventional reactor types, such as the continuous stirred-tank reactor and the fixed-bed reactor, the multistage fluidized-bed reactor can improve the economy of an enzyme-catalysed reaction significantly

Design and Control of a Fully Heated-Integrated Pressure-Swing Azeotropic Distillation System

If the composition of a binary homogeneous azeotrope changes significantly with pressure, the chemical components can be efficiently separated by using two distillation columns that operate at different pressures. This process is called pressure-swing azeotropic distillation. This work updates the study reported over two decades ago by Abu-Eishah and Luyben (“Design and control of a two-column azeotropic system” Ind. Eng. Chem. Process Des. Dev. 1985, 24, 132-140). These authors studied a partially heat-integrated two-column system in which an auxiliary reboiler permitted independent adjustment of vapor boilup in both columns. In the present paper, the two columns operate in the “neat” mode without any auxiliary reboiler. The details of achieving rigorous steady-state and dynamic simulations of the neat system in Aspen Plus and Aspen Dynamics are discussed. The condenser duty in the high-pressure column must equal the reboiler duty in the low-pressure column. The heat-transfer rate depends on the temperatures on the hot and cold sides in the condenser/reboiler, which change with varying process conditions, both dynamically and at steady state. The pressure of the high-pressure column floats with changing conditions. The dynamic controllability of the fully heat-integrated system is compared with that of the partially heat-integrated system, and a significant trade-off between energy consumption and controllability is demonstrated

Women, Midwives, and a Medical Model of Maternity Care in Switzerland

This paper presents a case study on the organisation of maternity healthcare in Switzerland, which has a costly healthcare system with high intervention rates within an obstetric-led maternity care model. Evidence has shown that midwifery care is associated with lower cost, higher satisfaction rates amongst women and less intervention. However, in the current model, midwives are both marginalised and underutilised. The paper focusses on the distribution of power and knowledge between midwives, women and the medical model. The varying power structures that shape the maternity care system in Switzerland are examined, using a case study approach that draws on Foucault’s concepts of the gaze, surveillance, disciplinary power, and the docile body. This paper will critically analyses the model of maternity care received by women in Switzerland and how it negatively impacts on both women’s personal and midwives’ professional autonomy whilst simultaneously driving up costs. A better understanding of the underlying power structures operating within the maternity care system may facilitate the implementation of more midwifery led care currently being endorsed by the Swiss Midwifery Association and some government agencies. This could result in reduced cost and lower intervention rates

A post-graduate study in Process Design: An Innovative Model in the Netherlands

Applied Science

Integrating process design and control: An application of optimal control to chemical processes

In this paper, the optimal design of process systems generically used in chemical industries is studied. The closely coupled nature of optimal design specification of the equipment, the determination of the optimal process parameters in steady-state, moreover, some issues of the application of optimal control is shown. The solution of the overall optimization problem including (i) optimal design of the equipment and (ii) specification of its optimal control strategy can be found relying on two different design concepts, namely, on the conventionally used sequential or, on the newly emerged simultaneous design approaches. This paper gives the theoretical background of the ideas and presents a comparative summary of the approaches. The two approaches are contrasted to each other in which the effects of the interaction of optimal process design and optimal control is highlighted. A new simultaneous optimization procedure providing economic and operability benefits over the traditional stand-alone approach is proposed. The applicability of the idea is demonstrated by means of a design study carried out for optimal design of a coaxial heat exchanger and a reactive distillation column for the synthesis of ethyl tert butyl ether (ETBE), relying on the benefits of the utilization of optimal control