Reactions vapor phase processes

Alkylthiazoles can be oxidized to nitriles in the presence of ammonia and a catalyst. For example, 4-cyanothiazole was prepared from 4-methylthiazole by a one-step vapor-phase process (94) involving reaction with a mixture of air, oxygen, and ammonia at 380 to 460°C. The catalyst was M0O3 and V Oj or M0O3, VjOj, and CoO on an alumina support. 

The reaction of adipic acid with ammonia in either Hquid or vapor phase produces adipamide as an intermediate which is subsequentiy dehydrated to adiponitrile. The most widely used catalysts are based on phosphoms-containing compounds, but boron compounds and siHca gel also have been patented for this use (52—56). Vapor-phase processes involve the use of fixed catalyst beds whereas, in Hquid—gas processes, the catalyst is added to the feed. The reaction temperature of the Hquid-phase processes is ca 300°C and most vapor-phase processes mn at 350—400°C. Both operate at atmospheric pressure. Yields of adipic acid to adiponitrile are as high as 95% (57). 

In 1987, Toray Industries, Inc., announced the development of a new process for making aromatic nitriles which reportedly halved the production cost, reduced waste treatment requirements, and reduced production time by more than two-thirds, compared with the vapor-phase process used by most producers. The process iavolves the reaction of ben2oic acid (or substituted ben2oic acid) with urea at 220—240°C ia the presence of a metallic catalyst (78). 

In the Godrej-Lurgi process, olefins are produced by dehydration of fatty alcohols on alumina in a continuous vapor-phase process. The reaction is carried out in a specially designed isothermal multitube reactor at a temperature of approximately 300°C and a pressure of 5—10 kPa (0.05—0.10 atm). As the reaction is endothermic, temperature is maintained by circulating externally heated molten salt solution around the reactor tubes. The reaction is sensitive to temperature fluctuations and gradients, hence the need to maintain an isothermal reaction regime. 

Diphenylamine can also be produced by passing the vapors of aniline over a catalyst such as alumina, or alumina impregnated with ammonium fluoride (17). The reaction is carried out at 480°C and about 700 kPa (7 atm). Conversion per pass, expressed as parts diphenylamine per 100 parts of reactor effluent, is low (18—22%), and the unconverted aniline must be recycled. Other catalysts disclosed for the vapor-phase process are alumina modified with boron trifluoride (18), and alumina activated with boric acid or boric anhydride (19). 

In the direct hydration method, the reaction could be effected either in a liquid or in a vapor-phase process. The slightly exothermic reaction evolves 51.5 KJ/mol. 

Older processes still use the sulfation route. The process is similar to that used for ethylene in the presence of H2SO4, hut the selectivity is a little lower than the modern vapor-phase processes. The reaction conditions are milder than those used for ethylene. This manifests the greater ease with which an isopropyl carhocation (a secondary carhonium ion) is formed than a primary ethyl carhonium ion ... 

In the vapor-phase process, the reaction temperature and pressure are approximately 250°C and 40 atmospheres. Phosphoric acid on Kieselguhr is a commonly used catalyst. To limit polyalkylation, a mixture of propene-propane feed is used. Propylene can be as low as 40% of the feed mixture. A high benzene/propylene ratio is also used to decrease polyalkylation. A selectivity of about 97% based on benzene can be obtained. 

In the continuous process the solution of sensitizer and monomer forms a thin surface layer on the polymer in which the photoinitiated reaction takes place without affecting the bulk phase of the polymer. In the vapor phase process, the grafting reaction starts at the... 

Carbonylation of methanol to form acetic acid has been performed industrially using carbonyl complexes of cobalt ( ) or rhodium (2 ) and iodide promoter in the liquid phase. Recently, it has been claimed that nickel carbonyl or other nickel compounds are effective catalysts for the reaction at pressure as low as 30 atm (2/4), For the rhodium catalyst, the conditions are fairly mild (175 C and 28 atm) and the product selectivity is excellent (99% based on methanol). However, the process has the disadvantages that the proven reserves of rhodium are quite limited in both location and quantity and that the reaction medium is highly corrosive. It is highly desirable, therefore, to develop a vapor phase process, which is free from the corrosion problem, utilizing a base metal catalyst. The authors have already reported that nickel on activated carbon exhibits excellent catalytic activity for the carbonylation of... 

Results of these investigations demonstrate that changes of the reactor surface can be an effective method for directing chemical reactions. Thus, developing a theory of how heterogeneous factors influence liquid-phase chain reactions is one of the important lines of advancement in this area. Only a few years ago it was thought, almost a priori, that there are practically no heterogeneous factors in liquid-phase oxidation and that liquid-phase processes differ from vapor-phase processes in this respect. 

Fredenhagcn and Cadenbach reacted fluorine with organic vapors within the mesh of a metal gauze. Though some of their reactions must have involved liquid films, this became a standard vapor-phase process. 

For example, the most economical pressure range for typical vapor-phase processes is between about five and thirty atmospheres, based on both equipment and energy costs. Similarly, the reaction temperature should permit the heat of reaction to be recovered as steam at pressures between perhaps 3 and 45 atmospheres, corresponding roughly to 134 and 258°C. 

HPAs, however, is their solubility in polar solvents or reactants, such as water or ethanol, which severely limits their application as recyclable solid acid catalysts in the liquid phase. Nonetheless, they exhibit high thermal stability and have been applied in a variety of vapor phase processes for the production of petrochemicals, e.g. olefin hydration and reaction of acetic acid with ethylene [100, 101]. In order to overcome the problem of solubility in polar media, HPAs have been immobilized by occlusion in a silica matrix using the sol-gel technique [101]. For example, silica-occluded H3PW1204o was used as an insoluble solid acid catalyst in several liquid phase reactions such as ester hydrolysis, esterification, hydration and Friedel-Crafts alkylations [101]. HPAs have also been widely applied as catalysts in organic synthesis [102]. 

The three processes differ by the operating conditions as reaction temperature, type of heat control and degree of system heterophasicity. Moreover, different processes could bring about also different thermal effects inside the polymer particle The solution process mainly yields polyethylene with a medium to very narrow (Q values of 2 or 3) MWD, while both slurry and vapor phase processes give... 

Catalytic reactions can take place in either the liquid or vapor phase. Liquid phase reactions can be run in either a continuous manner or as a batch process while vapor phase reactions are run only in a continuous mode. In a batch reaction the catalyst, reactants, and other components of the reaction mixture are placed in an appropriate reaction vessel, the reaction is run and the products removed from the vessel and separated from the catalyst. In a continuous system the reactants are passed through the catalyst and the products removed at the same rate as the reactants are added. The applicability of vapor phase processes is limited by the volatility and thermal stability of the reactants and products so such processes are not commonly involved in the preparation of even moderately complex molecules. Because of this, primary attention will be placed here on liquid phase processes with vapor phase systems of secondary importance. A discussion of the different types of reactors used for each of these processes is found in the following chapter. The present discussion is concerned with the effect that the different reaction parameters can have on the outcome of a catalytic reaction. 

In addition to these mass transport steps, heat conduction can also be important in heterogeneously catalyzed processes. For exothermic reactions the heat generated at the catalytic site must be dissipated away from the catalyst and into the reaction medium while heat must be supplied to the active sites for endothermic reactions. In liquid phase processes heat transport is generally not a significant factor since the liquid tends to equalize the temperature throughout the reaction medium and, thus, facilitate temperature control. In vapor phase processes, however, heat transport can be a significant problem. 

It was pointed out already in the chapters 17.1 and 17.3 that 2-methylfiiran appears as an unwanted by-product when fiirfuryl alcohol is made from lurfiiral by the vapor phase process at 135 °C, using a copper chromite catalyst, and that the relative quantity of 2-methylfiiran increases when the reaction temperature is raised to compensate the gradual reduction of catalyst activity. 

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