The Vapor Phase Process

In actual practice, the temperature of reactor 6 is gradually increased from 122 C to 152 C to compensate a progressing decrease in catalyst activity due to carbonaceous deposits. A typical rate of temperature increase is 3 C/day. After ten days, when 152 C are reached, the feed is turned off, and the reactor is heated to 220 C to remove the deposits by oxidation. Then the catalyst is reactivated by hydrogenation at 160 C before a new production cycle is started at 122 C. 

The yield of the process is in excess of 92 percent. The principal by-product is 2-methyl furan. Its formation increases when the reactor temperature is raised to compensate decreasing catalyst activity. At high temperatures, commercial quantities of 2-methyl furan can be produced. 

---

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). 

The hquid-phase processes are more energy efficient than the vapor-phase processes, however, they iacur costiy high pressure equipment investment and also produce waste streams containing used catalyst (213). Both methods produce substantial quantities of by-products which cause refining difficulties. The by-products consist primarily of mesitylene [108-67-8] phorone [504-20-17, and the foUowiag xyUtone isomers (215) ... 

Substantial amounts of 3,3,6,8-tetramethyl-l-tetralone [5409-55-2] are also formed, most notably ia the vapor-phase process (216). This tetralone has been synthesized from isophorone and mesityl oxide and it can thus be assumed to be a product of these two materials ia the isophorone process (217,218). 

The vapor-phase process of SocifitH Chemique de la Grande Paroisse for production of nitroparaffins employs propane, nitrogen dioxide, and air as feedstocks (34). The yields of nitroparaffins based on both propane and nitrogen dioxide are relatively high. Nitric oxide produced during nitration is oxidized to nitrogen dioxide, which is adsorbed in nitric acid. Next, the nitric dioxide is stripped from the acid and recirculated. 

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). 

The predominant process for manufacture of aniline is the catalytic reduction of nitroben2ene [98-95-3] ixh. hydrogen. The reduction is carried out in the vapor phase (50—55) or Hquid phase (56—60). A fixed-bed reactor is commonly used for the vapor-phase process and the reactor is operated under pressure. A number of catalysts have been cited and include copper, copper on siHca, copper oxide, sulfides of nickel, molybdenum, tungsten, and palladium—vanadium on alumina or Htbium—aluminum spinels. Catalysts cited for the Hquid-phase processes include nickel, copper or cobalt supported on a suitable inert carrier, and palladium or platinum or their mixtures supported on carbon. 

Thermochemical Data. Equilibrium considerations significantly limit alcohol yield at low pressures in the vapor-phase process (116). Consequently, conditions controlling equilibrium constants have been determined and give the following relation, where Tis in K (116,117) ... 

Today, the air oxidation of toluene is the source of most of the world s synthetic benzaldehyde. Both vapor- and Hquid-phase air oxidation processes have been used. In the vapor-phase process, a mixture of air and toluene vapor is passed over a catalyst consisting of the oxides of uranium, molybdenum, or related metals. High temperatures and short contact times are essential to maximize yields. Small amounts of copper oxide maybe added to the catalyst mixture to reduce formation of by-product maleic anhydride. 

In the vapor-phase process, oxyacylation of ethylene is carried out in a tubular reactor at approximately 117°C and 5 atmospheres. The palla-... 

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. 

Polyethylene (PE) was a commercial LD type (without additives) with a density of 0.92 and polypropylene (PP) was also a commercial material with a density of 0.91. The polvolefin samples were melt pressed to 1 mm thick sheets (plates) which were wiped clean with acetone and used directly for the grafting experiments with the vapor-phase process. 

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... 

Figure 3. Reflection infrared spectra (ATR-IR) of a polypropylene-j surface before (A) and after (B) grafting with acrylamide (AM) by the vapor phase process (above). ESCA spectra of the same surface before (dotted lines) and after (full lines) the surface grafting (below).

The vapor phase process usually features dual reactors because the catalyst needs to be regenerated about every eight weeks. One reactor is offline being regenerated while the other is operating. 

Differentiate between kinetic and transport rate limitation in the vapor phase processing of ceramics. 

The butane isomerization process developed by the Universal Oil Products Co. is shown in Figure 4. In this process (3), the feed is maintained essentially in the liquid phase under pressure. Part of the feed is by-passed through a saturator, where it dissolves aluminum chloride. The feed later picks up hydrogen chloride and passes through the reactor, which is packed with quartz chips. Some insoluble liquid complex is formed, and this adheres to the quartz chips. The aluminum chloride in the feed is preferentially taken up by the complex, which thus maintains an active catalyst bed. The complex slowly drains through the reactor, losing activity en route. It arrives at the bottom in essentially spent condition and is discarded. Aluminum chloride carried overhead in the reactor products is returned to the reactor from the bottom of the recovery tower. The rest of the process is the same as in the vapor-phase processes. 

Detailed studies on the vapor-phase process for the manufacture of chlorofluoroethanes showed the striking influence of the catalyst composition on the product distribution.17... 

The crystalline inorganic monopropellants decompose directly from the solid to the vapor phase and are approximately described by the above mentioned theoretical work, in spite of the fact that the gas phase processes are simplified. However, the double-base propellants and other organic materials liquefy before vaporizing. In their combustion, so-called foam and fizz zones occur before the vapor phase processes. Much work has been done attempting to apply the conservation equations to the series of processes. This work forms the basis for the summary by Geckler (G3). It is the viewpoint of this author that too many parameters are determined empirically in this application of the theory, so that useful extrapolations are not possible. One must admire the manipulative skill of the early workers in this field and also their determination to formulate a complete theory. When and if the rate parameters become available, a useful theory will be developed with the aid of this early work. 

In the EBMax process, benzene is fed to the bottom of the liquid-filled multibed reactor. Ethylene is co-fed with the benzene and also between the catalyst beds. Polyethylbenzenes, which are almost exclusively diethylbenzenes, undergo transalkylation with benzene in a second reactor. Mobil-Badger offers both liquid phase and vapor phase transalkylation processes. The vapor phase process removes benzene feed coboilers such as cyclohexane and methylcyclopentane as well as propyl and butylbenzenes. Because the EBMax process produces very low levels of propyl and butylbenzenes, for most applications, the more energy efficient liquid phase process is preferred. Worldwide, there are currently ten licensed EBMax units with a cumulative ethylbenzene production capacity of five million metric tons per year. 

For the growth of group 13-15 compounds, the general embodiment of the vapor-phase process is that liquid... 

The detailed operating conditions are shown in Table IV. Because of the greater tolerance in feed impurities, the catalyst consumption was slightly higher than in the vapor-phase processes and amounted to 50-120 gallons of isobutane per pound of aluminum chloride. 

The vapor-phase processes gave the least trouble (3). All maj or equipment in vapor-phase plants was made of carbon steel. Alloys were used only in such applications as trim on pumps and valves. 

To oxidize ethylene to acetaldehyde technically, two major approaches seem feasible (a) vapor-phase heterogeneous catalysis, and (b) liquid-phase homogeneous catalysis. The most pertinent references on the vapor-phase process are summarized in Table VI. However, neither this approach nor the electrolytic oxidation of ethylene (14) appears to have gained any commercial importance. Liquid-phase homogeneous catalysis is the approach practiced commercially, and this is understood when one talks about the Wacker process. The latter has been carried out in two principal ways ... 

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. 

The first commercial plant based on the Mobil/Badger vapor phase technology was commissioned in 1980. From 1980 until the early 1990s, use of the vapor phase process gained in popularity because it offered several advantages over the aluminum chloride process. A major benefit of the vapor phase process was the use of a zeolite catalyst that eliminated the issues associated with corrosion and waste disposal of aluminum chloride. 

Despite its better performance than the vapor phase process, Gulf type oxychlorination remains subject to the use of highly corrosive reactants, resulting in. high capital expenditures. 

The vapor phase process makes it possible to regenerate the solid catalyst continuously by controlled combustion of coke deposits. This operation takes place in a second... 

Although this type of reaction, was initially developed in the liquid phase (1912), it is mainly the vapor phase processes, developed in particular by Wacko- (1930), that have been industrialized. Until I960, all existing manufacturing facilities worldwide employed this synthesis method. A number of these plants are still in operation, particularly in Western Europe. 

---