Case process intensification

Figure 4 shows the impact of process intensification for this hypothetical case. With a temperature increase of only 41°C, the number of reactors for such comparatively big units is reduced from 20, hardly feasible in view of costs and process control, to four, feasible for the same reasons. Thus, the costs decrease by almost a factor of five (not exactly, since fixed costs have a small share). Another 21°C temperature increase halves the number of reactors again, and at 249°C, which is 149°C higher than the base temperature, an equivalent of 0.2 micro-structured reactors is needed. This means that practically one micro-structured reactor is taken and either reduced in plate number or in the overall dimensions. The costs of all microstructured reactors scales largely with their number only at very low numbers do fixed costs for microfabrication lead to a leveling off of the cost reduction. 

Microreactor and microprocess technology has, in some fine-chemical cases, approached commercial applications and become competitive with existing technology. Two main developments are awaited. Firstly, optimizing the process protocol conditions such that the chemistry is set to the limit of the reactor s capabilities in terms of mass and heat transfer. This so-called novel chemistry approach achieves the highest process intensification and can improve the costing of microprocess... 

Arthur de Little, SenterNovem (2006) Full study presented to platform for chain efficiency (PKE). Building a business case on process intensification Belloni A (2006) Process 13 64-65... 

Process intensification also offers substantial improvements to those sectors of the chemical industry in which time to market plays a crucial role, e.g., the fine chemical and pharmaceutical sectors. Ramshaw (35) discussed how process intensification could shorten the time to market in case of a low-tonnage pharmaceutical process. The idea consists in developing a continuous lab-scale process and using it directly as the commercial-scale process. One must not forget that liquid flow of only 1 milliliter per second means, in continuous operation, circa 30 tons per year, which is quite a reasonable capacity for many pharmaceuticals. 

The toolbox for process intensification is schematically shown in Figure 7. It includes process-intensifying equipment (PI hardware) and process-intensifying methods (PI software). Obviously, in many cases overlap between these two domains can be observed as new methods may require novel types of equipment to be developed and, vice versa, novel apparatuses already developed sometimes make use of new, unconventional processing methods. In Figure 7, examples of both PI hardware and PI software are shown. Many of them will be discussed in detail in other chapters of this book. Here, we give only a brief overview of the more important PI items. 

Elaborate descriptions of process intensification will be found elsewhere in this book. Here a short description suffices, followed by an assessment on its potential to contribute to sustainable development, based on present industrial cases and general features. 

Present Status of Process Intensification from Industrial Cases... 

Social Acceptance. Social acceptance of chemical plants is still an issue. This is due to the fact that big disasters have occasionally occurred (Bhopal, Seveso) and also because chemical plants smell, due to diffusive emissions of volatile components. Via process intensification the amount of chemically hazardous, reactive material can be reduced considerably, by which the size of an emission in the case of an explosion will be far less and the chance of an explosion itself reduced by the lowered hazardous, reactive content. 

For benzene hydroxylation an analytical system [37] was successfully used at the interface. This system contains Fe3+ hydrophobic complexes, which promote the process intensification. It is shown [38, 39] that compared with hydrophobic complexes, Fe3+ complexes with the phase transfer—tertiary ammonium salts and crown ethers—display more effective action. At 20-50 °C, owing to the use of trimethylacetylammonium bromide as the phase transferring agent, benzene is successfully hydroxylated in the two-phase water-benzene system in the presence of Fe3+ ions [40], Hence, it is Shilov s opinion [41] that in the case of cytochrome P-450 a radical reaction is probable. It produces radicals, which then transform in the cell, as follows ... 

To this purpose, in a study on the photocatalytic degradation of 4-chlorophenol, Camera-Roda and Santarelli [89] proposed an integrated system in which photocatalysis is coupled with pervaporation as process intensification for water detoxification. Pervaporation represents a useful separation process in the case of the removal of VOCs and in this study it is used to remove continuously and at higher rate the organic intermediates that are formed in the first steps of the photocatalytic degradation of the weakly permeable 4-CP. 

A wide range of dilferent reactor types e.g. continuous, membrane, bubble) have been used to perform large scale processes using alternative solvents. Conventional batch reactors and extraction vessels have been used in many cases. However, process intensification is moving forward hand in hand with alternative solvents and therefore engineering solutions often have an important role to play in this field. Nevertheless, these are not discussed at length in this chapter and will probably be the subject of another book within the green chemistry series. 

Case study of peracetic acid process intensification... 

In many publications, an effect of the ionic liquid solvent on the rate or selectivity of organic and catalytic reactions has been reported [129], For industrial applications, it has been recognised that process intensification using ionic liquids is in most cases not a question of retrofitting by simply substituting a solvent by an ionic liquid, but further tuning strategies, such as the immobilisation of catalysts... 

Process Intensification provides a new incentive in the assessment of chemical processes. In this report a gas-liquid reaction forms the basis of a comparison between conventional and novel reactor concepts. The considered reaction can be applied in all of the described reactor concepts, in some cases however a process modification is needed. For the application of Process Intensification a good insight is required for both the reaction as well as the tools (reactor systems) in which the reaction is being applied. Regarding the novel reactor concepts however design data are scarce, which induces uncertainties to come to a correct validation of the potentials. 

In micro-process technology, micro-structured process components such as heat exchangers, mixers or reactors are being developed in which very intensive heat and mass transfer can be realized. In many cases, under defined conditions, this allows process intensification with drastically reduced residence times for the reacting components and simultaneously a considerable increase in selectivity and yield. Due to the low degree of hold-up, hazardous components can be handled safely, even under extreme pressure and temperature conditions. 

In the example of the dehydrogenation reaction above, the mass flows are assumed invariant, their composition is not disturbed. Pressure and temperature are dictated by the thermodynamics of the system to attain a certain conversion of the feed. An alternative form of PI (process intensification) can be seen when one selectively removes one of the reaction products to shift the equilibrium and intensify the process. The combination of reaction and separation is a key example of PI. The literature aboimds with schemes to accomplish this. Its commercial use, however, is limited to a small number of cases. Following are examples, successful and not so successful, of this mode of operation ... 

Where appropriate, an actual measure of possible process intensification will be given. In some cases, a reaction system will be used to show the potential of the improved process. 

Two case studies are presented below to illustrate the impact of process intensification. They show how distributed production of hydrogen-age fuels can compete with a larger scale centralized production followed by transportation, provided one can invoke logistical circumstances as well as very intense capital utilization. 

This chapter has introduced the concept of process intensification (PI) as a collection of methodologies aimed at reducing the capital cost of chemical processing. Examples have been given of successful and less successful strategies. The area of microreaction technology has also been situated for some cases, an attempt has been made to quantify the degree of PI achievable. 

Two case studies have been presented, looking somewhat ahead to a scenario of multiple energy sources. In the first, the distributed co-production of power and methanol has been found to compete with local US centralized methanol production. In the second case, the intensification of distributed hydrogen production has been discussed, through better process integration and judicious choice of equipment. 

In many cases where mass transfer occurs between a liquid and a vapor, micro technology offers the advantage of process intensification through control of the liquid phase thickness. This intensification often occurs because the diffusivity is typically orders of magnitude lower in the liquid phase than in the gas phase hence, control of the liquid thickness decreases the primary impedance to mass transfer. This control benefits operations such as absorption and desorption, and processes based on these phenomena. 

Distillation represents an ideal case for process intensification, since it accoimts for 95% of the total separation energy used in the refining and chemical process... 

---