摘要:

Nitration of aromatics is a key process in the catalytic manufacturing of semiproducts for the synthesis of drugs, pesticides, and dyes. However, the large-scale synthesis, involving the concentrated mineral acids used as catalysts, makes nitration one of the most environmentally harmful processes, producing huge amounts of organic wastes, exhausted acids, and the products of their neutralization. A search for environmentally safer catalysts and nitrating agents appears to be an actuality. Numerous data concerning the aromatics nitration in homogeneous media have been summarized in a set of books and reviews [l-41. Recent papers are of considerable interest, since they reflect the attempts to perform nitration on heterogeneous catalysts, for example, zeolites [5–8]. The data on aromatic nitration on the surface of solid acids [9, 111 and in the gas phase [12–14] allowed us to clarify the role of intermediate Tand a-complexes, estimate the substrate and position selectivity, and elucidate the main approaches of nitration mechanism in various media. In this review the data concerning nitration on solid catalysts are summarized. We hope this information will make it possible to estimate the perspectives of heterogeneous catalyst application on a large scale.

ISSN:0161-4940    

DOI:10.1080/01614949508007095

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Three-phase slurry bubble column reactors have been used extensively in a number of chemical, petrochemical, and biochemical process engineering applications. For the success of these operations and their large scale industrial exploitation, it is essential that their transport and chemical characteristics be adequately understood on a mechanistic basis so that appropriate design criteria and optimum operating conditions can be established. It is the purpose of this review to present such available knowledge in relation to chemical catalytic operations. The mass transfer characteristics, catalytic activity, and mixing patterns of different phases necessitate a detailed understanding of the hydrodynamic behavior and catalyst dispersion in slurry bubble column reactors. The current status of these aspects is presented, discussed, and assessed in this review. Chemical and biochemical reactions are exothermic in nature and hence efficient heat removal devices must be installed in the reactor to preserve its isothermal behavior and chemical catalytic activity by avoiding temperature runaway. Extensive work recently conducted from this heat transfer viewpoint is reviewed and appraised. The bubble dynamics, and slurry mixing and movement characteristics of such baffled bubble columns are significantly different from those of unbaffled bubble columns. Very limited information is available on baffled bubble column operations and this is reviewed and critically examined. An important application of the slurry bubble column is in the synthesis of fuel gases on suspended catalyst particle surface to produce chemicals. One such example is the Fischer-Tropsch synthesis of hydrogen and carbon monoxide in what is referred to as indirect coal liquefaction technology. Pilot plant efforts of this nature and their successes are briefly mentioned. Mathematical details and models developed from time to time to characterize catalytic bubble column operations are briefly described and discussed. In the context of available information and its integration presented here, the specific needs for future experimental and theoretical research work are pointed out.

ISSN:0161-4940    

DOI:10.1080/01614949508007096

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Catalysis by heteropoly acids (HPAs) and related compounds is a field of growing importance, attracting increasing attention worldwide, in which many new and exciting developments are taking place in both research and technology [1–111, HPAs are polyoxometalates incorporating anions (heteropolyanions) having metal-oxygen octahedra as the basic structural units [ll-141. Among a wide variety of HPAs those belonging to the so-called Keggin series are the most importance for catalysis. They include heteropolyanions (HPANs)

ISSN:0161-4940    

DOI:10.1080/01614949508007097

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0161-4940    

DOI:10.1080/01614949508007098

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor