New reactors

Developments in experimental and mathematical techniques in the 1970s have initiated an interest in the development of better laboratory reactors for catal5d ic studies. Besides the many publications on new reactors for general or special tasks, quite a few review articles have been published on the general subject of laboratory reactors for catalytic studies. 

New reactors should also be treated in air as mentioned above, before they are first used. After the treatment the light yellowish hue indicates the presence of the chromoxide layer on the surface. 

Tibbetts, G.G., Gorkiewicz, D.W., and Alig, R.A. A new reactor for growing carbon fibers from liquid- and vapor-phase hydrocarbons, Carbon, 993, 31(5), 809 814. Tibbetts, G.G., Bernardo, C.A., Gorkiewicz, D.W. and Alig R.L. Role of sulfur in the production of carbon fibers in the vapor phase. Carbon, 1994, 32(4), 569 576. 

Since the amount of fissile material in the fuel assemblies is only about 3 percent of the uranium present, it is obvious that there cannot be a large amount of radioactive material in the SNF after fission. The neutron flux produces some newly radioactive material in the form of uranium and plutonium isotopes. The amount of this other newly radioactive material is small compared to the volume of the fuel assembly. These facts prompt some to argue that SNF should be chemically processed and the various components separated into nonradioac-tive material, material that will be radioactive for a long time, and material that could be refabricated into new reactor fuel. Reprocessing the fuel to isolate the plutonium is seen as a reason not to proceed with this technology in the United States. 

The selectivity of the catalyst is of major importance in the case of chlorinated VOCs the oxidation products should not contain even more harmful compounds than the parent-molecule, for example, formation of dioxins should be avoided. In addition, the minimization of CI2 and maximization of HCl in a product gas should be achieved [61]. These are just a few examples of why researchers are continuing the search for VOC oxidation catalysts as well as new reactor concepts. The new possibilities include, for example, utilization of nanosized gold catalysts in the oxidation of sulfur-containing VOCs and microwave-assisted processes where combination of adsorption and oxidation is used in low-concentration VOC oxidation [62, 63]. 

The objective of the chemical industry is to have robust and flexible chemical reactors. It should also be possible to reach large-scale production of new chemicals in a very short time. The available reactors should be able to produce a large variety of chemicals with high selectivity. To obtain this, we must not only understand how existing reactors work in detail but also develop new reactors. 

Virtual prototyping will be the future method to develop new reactors and chemical processes. With a good description of the fluid dynamics, and mass and heat transfer in the reactor, the specific chemical reactions and physical properties of the fluid can be changed and a process optimization can be performed in virtual... 

One of the most interesting theorems of Worz et al. is that they see a serious potential for micro reactors to permit small-scale production of some different sort [110-112]. Micro channels serve as an ultra-precise measuring tool, whereas production is done in channels about 10 to 100 times larger, i.e. miUimeter-sized channels. The limit of tube diameter of industrial production reactors is reported to be 2 cm hence any new reactor of smaller characteristic dimensions bears some potential for improvement. Worz et al. conclude with the remark that the above strategy could be the most important result of their studies [110-112]. 

Groschel, L, Agar, D. W., Worz, O., Morgenschweis, K., The capillary-microreactor A new reactor concept for the intensification of heat and mass transfer in liquid-liquid reactions. Catalysis Today,... 

Caravieilhes, S., de Belleeon, C., Tanchoux, N., Dynamic methods and new reactors for liquid phase molecular catalysis, Catal. Today 66 (2001) 145-155. 

The cyclohexene hydrogenation is a well-studied process especially in conventional trickle-bed reactors (see original citations in [11,12]) and thus serves well as a model reaction. In particular, flow-pattern maps were derived and kinetics were determined. In addition, mass transfer can be analysed quantitatively for new reactor concepts and processing conditions, as overall mass transfer coefficients were determined and energy dissipations are known. In lieu of benchmarking micro-reactor performance to that of conventional equipment such as trickle-bed reactors, such a knowledge base facilitates proper, reliable and detailed comparison. 

The trickle-bed reactor (TBR) and slurry reactor (SR) are the most commonly used for multiphase reactions in the chemical industries. A new reactor type, the monolithic reactor (MR), offers many advantages. Therefore, these three types of reactors are discussed below in more detail. Their general characteristics are given in Table 5.4-44. With respect to slurry reactors, the focus will be on mechanically agitated slurry reactors (MASR) because these are more widely used in fine chemicals manufacture than column slurry reactors. 

FIG. 20-18 Physical properties of water versus temperature at 240 bar. [Reprinted from Kritzer and Dinjus, An Assessment of Supercritical Water Oxidation (SCWO) Existing Froblems, Tossibh Solutions and New Reactor Concepts Chem. Eng. ].,vol. 83(3), pp. 207-214, copyright 2001, withpermission form Elsevier ]... 

As the industry and the NRC gain experience with the new reactor oversight and assessment process, the approach will be modified and applied to other regulatory areas. 

One of the most important advantages of the bio-based processes is operation under mild conditions however, this also poses a problem for its integration into conventional refining processes. Another issue is raised by the water solubility of the biocatalysts and the biocatalyst miscibility in oil. The development of new reactor designs, product or by-product recovery schemes and oil-water separation systems is, therefore, quite important in enabling commercialization. Emulsification is thus a necessary step in the process however, it should be noted that highly emulsified oil can pose significant downstream separation problems. 

With apparatus and procedures of the type to be described, diboron tetrachloride production rates approaching 1.0 g./hour may be anticipated with a new reactor tube. Yields decrease with aging, but relatively long service with a production rate no lower than 0.20 to 0.50 g./hour can generally be relied upon. 

Quite new ideas for the reactor design of aqueous multiphase fluid/fluid reactions have been reported by researchers from Oxeno. In packed tubular reactors and under unconventional reaction conditions they observed very high space-time yields which increased the rate compared with conventional operation by a factor of 10 due to a combination of mass transfer area and kinetics [29]. Thus the old question of aqueous-biphase hydroformylation "Where does the reaction takes place " - i.e., at the interphase or the bulk of the liquid phase [23,56h] - is again questionable, at least under the conditions (packed tubular reactors, other hydrodynamic conditions, in mini plants, and in the unusual,and costly presence of ethylene glycol) and not in harsh industrial operation. The considerable reduction of the laminar boundary layer in highly loaded packed tubular reactors increases the mass transfer coefficients, thus Oxeno claim the successful hydroformylation of 1-octene [25a,26,29c,49a,49e,58d,58f], The search for a new reactor design may also include operation in microreactors [59]. 

As outlined in Chapter 5, Section 5.2.3.2 various approaches to overcoming the low rates of the hydroformylation of long chain alkenes in aqueous biphasic systems have been proposed. Some of these, such as the use of microemulsions [24-26] or pH dependent solubility [27], have provided improvements often at the expense of complicating the separation process. Perhaps the most promising new approaches involve the introduction of new reactor designs where improved mixing allows for... 

Tibbetts, G.G., Gorkiewicz, D.W., and Alig, R.A. A new reactor for growing carbon fibers from liquid- and vapor-phase hydrocarbons, Carbon, 1993, 31 (5), 809 814. 

The design problem usually fits into the spectrum ranging from (1) the rational design of a completely new reactor for a new process, to (2) the analysis of performance of an existing reactor for an existing process. A common situation, between these extremes, even for a new plant, is the modification of an existing type of reactor, the design of which has evolved over time. 

In this chapter, we consider nonideal flow, as distinct from ideal flow (Chapter 13), of which BMF, PF, and LF are examples. By its nature, nonideal flow cannot be described exactly, but the statistical methods introduced in Chapter 13, particularly for residence time distribution (RTD), provide useful approximations both to characterize the flow and ultimately to help assess the performance of a reactor. We focus on the former here, and defer the latter to Chapter 20. However, even at this stage, it is important to realize that ignorance of the details of nonideal flow and inability to predict accurately its effect on reactor performance are major reasons for having to do physical scale-up (bench —> pilot plant - semi-works -> commercial scale) in the design of a new reactor. This is in contrast to most other types of process equipment. 

New reactor technologies are currently under development, and these include meso- and micro-structured reactors or the use of membranes. Among meso-structured reactors, monolithic catalysts play a pre-eminent role in environmental applications, initially in the cleaning of automotive exhaust gases. Beside this gas-solid application, other meso-structures such as membranes [57, 58], corrugated plate or other arranged catalysts and, of course, monoliths can be used as multiphase reactors [59, 60]. These reactors also offer a real potential for process intensification, which has already been demonstrated in commercial applications such as the production of hydrogen peroxide. 

In one of her most difficult moments Barbara vowed that when she retired she would devote herself to increasing awareness of environmental health issues to improve conditions for others in similar situations. Today she is keeping her word with a burning passion. She is on the board of directors of the Environmental Health Network (EHN) based in Larkspur, California. She is editor of the EHN newsletter—New Reactor—maintains a Web page, and helps to field calls on the EHN support and information hotline. She has worked with San Francisco city officials to develop a sustainable city plan. She was one of the authors of a fragrance-free resolution adopted by the Sierra Club. 

Three Mile Island and Chernobyl occurred more than 20 years ago and the nuclear power freeze is beginning to thaw. High priced oil and natural gas make atomic energy appear cheap by comparison. Global-warming concerns are pushing a new interest in nuclear power. After a decade where no nuclear power plants came online in the United States, 31 new reactors are planned. 

Nuclear power is quietly reappearing in the United States and around the world. Major U.S. utilities have applied for site permits for new reactors, and interest is also growing through Europe. 

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