Reactor Options

A second development has been the move toward cell-free extracts by the deUberate lysis of cells to overcome simultaneously transport as well as compartmentaUzation hmitations [18]. However, the resultant catalyst soup is rich in other enzymes, necessitating the addition of inhibitors (or alternatively using genetic engineering to massively overexpress the desired enzymes over other proteins). Alternatively heat treatment can be used in cases where thermostable isoenzymes are available. Likewise, cell debris is present in the reaction medium, necessitating the combination of microfiltration as well as ultrafiltration for recovery (and potential reuse). 

A further compHcation remains in the control of enzyme activities which to a large extent is dependent upon expression during the fermentation. One potential solution is to add supplementary enzymes to the cell-free extract. Such a precedent has already been set by a few reported cases where whole cells were mixed with the isolated enzyme for ex vivo cofactor recycle. E espite these problems, there is no doubt that as genetic engineering for expression of the desired enzyme is improved, more systems wiU be tested in the cell-free environment [26]. At the very least it is clear that cell-free extracts, combined with network topology analysis can provide an excellent basis for effective analysis and targeting of the network so as to insulate the desired pathway from undesired enzymatic reactions [27]. 

Perhaps the first decision to be made in process development is the difficult decision of whether the enzymes to be used should be used in an integrated format. Such a question does not arise with conventional single biocatalytic steps but is highly important in multienzyme processes. One of the key criteria here is whether the enzymes can be operated together without compromise to any of the individual enzyme s activity or stability. An interaction matrix (see Section 10.6) can be used to assist such decision making. In cases where the cost of one or more of the enzyme(s) is not critical, it will be possible to combine in a one-pot operation. In other cases, where the cost of an individual enzyme becomes critical, then it may be necessary to separate the catalysts, such that each can operate under optimal conditions. Likewise, selection of the biocatalyst format (immobilized enzyme, whole cell, cell-free extract, soluble enzyme, or combinations thereof) in combination with the basic reactor type (packed bed, stirred tank, or combinations thereof) and biocatalyst recovery (mesh, microfiltration, ultrafiltration, or combinations thereof) will determine the structure of the process flowsheet and therefore is an early consideration in the development of any bioprocess. The criterion for selection of the final type of biocatalyst and reactor combination is primarily economic and may best be evaluated by the four metrics in common use to assess the economic feasibility of biocatalytic processes [29]  

The balance between the four metrics is dependent upon the relative costs in a process. For example, a process with a high cost of biocatalyst requires a high biocatalyst yield, whereas those with a high cost of process plant will require a high space-time-yield and those with a high downstream processing cost require a high product concentration to leave the reactor. 

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Economic analysis of designs at lower natural hypochlorite strengths equally show potential investment benefits. They are, however, much less significant than the batch and high concentration cases described above. While an economic case can be made for retrofitting an in-loop reactor to a system that already has an end-of-pipe treatment system based on payback, it is not always clear that this is a better option than an end-of-pipe hybrid system as described earlier in the chapter. For a particular system the optimum solution is often as much a function of the required expenditure on the heat exchangers as it is the relative cost of the reactor options. 

Reactor options are determined primarily by the physical properties of the waste and the chemical and biochemical properties of the contaminants. System characteristics can favor a particular reactor option. If the waste is found in groundwater, then a continuous supported reactor is desirable, while a suspended... 

The first question to consider is what form the substrate and enzyme should be. Options include whole broth, purified, or immobilized. By answering key questions at an early stage about the nature of the substrate, enzyme, and product, it is possible to eliminate reactor options quickly without expensive experimentation [41],... 

G-3 Nuclear Reactor Options and Their Power Cycle Efficiency, 210 G-4 An Overview of Nuclear Hydrogen Production Options, 211 G-5 Capital Costs of Current Electrolysis Fueler Producing 480 Kilograms of Hydrogen per Day, 221... 

TABLE G-3 Nuclear Reactor Options and Their Power Cycle Efficiency... 

Figure 1.19. Application of integer programming to reactor design, (a) Unit cell of reactor options, (b) Superstructure of unit cells and recycles.

All these reactor options allow not only the development of new processes, and the holding of proprietary technologies, but also an improvement in productivity (thus saving energy per ton of product) and often a reduction in the emissions of waste, greenhouse gases and improved safety of operations, for example, improved process... 

Demonstrate the "trap grease"-to-hydrogen process in long-duration tests using the attrition-resistant catalysts. An alternative reactor option that uses a circulating bed to prepare 80 pm catalyst particles will also be considered. 

Liquid phase reactors Types of polymerizations Reactor options... 

Included in installation Multilayer ammonia reactor optional... 

Fischer-Tropsch synthesis is another industrially important case where the quest for a catalyst with higher rate as well as selectivity continues. This synthesis is exothermic, and catalysts with higher activity (higher rates) will impose a burden on the heat exchanging capacity of the multiphase reactor used. Development of better catalysts must be accompanied by multiphase reactors that can cater to the higher exotherm associated with faster rates. Section 3.4.1.4 discusses the various available reactor options. 

GT-MHR fresh fuel and spent fuel have higher resistance to diversion and proliferation than the fuel for any other reactor option. The GT-MHR fresh fuel has high proliferation resistance because the fuel is very diluted by the fuel element graphite (low fuel volume fraction). GT-MHR spent fuel has the self-protecting, proliferation resistance characteristics of other spent fuel (high radiation fields and spent fuel mass and volume). However, GT-MHR spent fuel has higher proliferation resistance than any other power reactor fuel because of the reasons given below. 

The reactor option for land-based siting is shown in Fig. II-6. The integral reactor is placed inside the leak-tight containment, which in turn is located within the concrete shock-resistant structure together with the biological shielding and reactor unit components. This structure enhances physical protection of the reactor unit from external impacts such as airplane crash, hurricane, tsunami, unauthorized access, etc. 

Process benefits Flexibility for process control Reduced separation of intermediates Better reaction control Opportunities to exploit modeling and rapid development methods Novel reactor options Possible to run processes under more productive conditions (e.g., higher concentrations and organic solvents). Green processes running under mild conditions... 

Targeted deployment date 2005 Sodium-cooled fast reactor was chosen as one of the two future reactor options deployable by 2030 -... 

As the AHTR concept includes a very high temperature reactor option (with the core outlet temperature of 1000°C), the additional design features to prevent the consequences of severe accidents are provided. The reactor has a second guard vessel and is located in an underground silo. The effectiveness of heat conduction to earth through the walls of the silo (an ultimate heat rejection in BDBA) is being examined. 

The PBMR, the GT-MHR, the GTHTR300 (Annex XVI) and the AHTR (Annex XXVI) target a very high temperature reactor option, which could make them competitive in future markets of non-electric applications, such as hydrogen production. 

Liquid fluoride salts can be used for multiple nuclear applications. The AHTR is the simplest reactor application (excellent compatibility between salt and graphite based fuel, once through fuel cycle, etc.) and thus the likely first commercial use for liquid salts in reactor applications. The base technology, however, leads to three long term sustainable advanced reactor options ... 

Creates large high-temperature-reactor option... 

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