Operation with Copper Catalysts

It is clear that the mixed copper oxide/zinc oxide/alumina formulation is an excellent catalyst in the low-pressure methanol process. There has been much debate in explaining the role of copper in the reaction and how methanol is pro-dnced. The group that invented the catalyst examined a number of possibih- 

It has been concluded from experimental work with catalysts containing alumina that methanol forms from carbon dioxide and that the catalyst activity is proportional to the copper metal surface area. The presence of carbon dioxide in the gas increases the synthesis rate. The zinc oxide and alumina play little part in the actual reaction apart from stabihzing the reduced copper and protecting it from the effect of any poisons. On the other hand, with catalysts containing chromia, the carbon dioxide leads to a decrease in the reaction rate.  

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The Rh2(OAc)+-catalyzed reaction between crotyl bromide and ethyl diazoacetate at or below room temperature follows the pathway 129 - 131 - 132 exclusively. At higher temperature, when ethyl bromoacetate and increasing amounts of the [1,2] rearrangement product 126 are found additionally, the 129 -> 130 - 132 -f 133 route becomes a competing process. With copper catalysts, this situation may be applicable at all temperatures, but it has been suggested that the route via complex 130 operates solely, when copper bronze is the catalyst154). 

Wacker (1) A general process for oxidizing aliphatic hydrocarbons to aldehydes or ketones by the use of oxygen, catalyzed by an aqueous solution of mixed palladium and copper chlorides. Ethylene is thus oxidized to acetaldehyde. If the reaction is conducted in acetic acid, the product is vinyl acetate. The process can be operated with the catalyst in solution, or with the catalyst deposited on a support such as activated caibon. There has been a considerable amount of fundamental research on the reaction mechanism, which is believed to proceed by alternate oxidation and reduction of the palladium ... 

Lindstrom et al. [55] developed a fixed-bed autothermal methanol reformer designed for a 5 kW fuel cell operated with copper/zinc oxide catalyst doped with zirconia. The system was started without preheating from ambient temperature by methanol combustion in a start-up burner, which was operated at sixfold air surplus to avoid excessive temperature excursions. Because significant selectivity toward carbon monoxide was observed for the autothermal reforming process, a WGS stage became mandatory [55]. 

The Dow Chemical Company in the mid-1920s developed two processes which consumed large quantities of chlorobenzene. In one process, chlorobenzene was hydrolyzed with ammonium hydroxide in the presence of a copper catalyst to produce aniline [62-53-3J. This process was used for more than 30 years. The other process hydrolyzed chlorobenzene with sodium hydroxide under high temperature and pressure conditions (4,5) to product phenol [108-95-2]. The LG. Earbenwerke in Germany independentiy developed an equivalent process and plants were built in several European countries after World War II. The ICI plant in England operated until its dosing in 1965. 

In the 1930s, the Raschig Co. in Germany developed a different chlorobenzene-phenol process in which steam with a calcium phosphate catalyst was used to hydrolyze chlorobenzene to produce phenol (qv) and HCl (6). The recovered HCl reacts with air and benzene over a copper catalyst (Deacon Catalyst) to produce chlorobenzene and water (7,8). In the United States, a similar process was developed by the BakeHte Division of Union Carbide Corp., which operated for many years. The Durez Co. Hcensed the Raschig process and built a plant in the United States which was later taken over by the Hooker Chemical Corp. who made significant process improvements. 

Catalyst composition also depends on the type of reactor used. Fixed-bed iron catalysts are prepared by precipitation and have a high surface area. A silica support is commonly used with added alumina to prevent sintering. Catalysts for fluidized-bed application must be more attrition-resistant. Iron catalysts produced by fusion best satisfy this requirement. The resulting catalyst has a low specific surface area, requiring higher operating temperature. Copper, another additive used in the preparation of precipitated iron catalysts, does not affect product selectivity, but enhances the reducibility of iron. Lower reduction temperature is beneficial in that it causes less sintering. 

Supported palladium and copper catalysts are usually used. A serious problem of this reaction is that palladium forms a complex with vinylacetylene below 100°C. This complex is soluble in the hydrocarbon mixture undergoing hydrorefining and, consequently, palladium is eluted from the catalyst. Operating at temperatures above 100°C or the use of bimetallic palladium catalysts310 solves this problem. 

In particular, 85% of the 5p isomer with respect to the 5a one represents the highest observed value which can not be obtained with gaseous H2 either changing operative conditions (T and P) or the nature of the copper catalyst. 

If a Low Temperature Shift (LTS) converter is installed (see Figure 5.35), the gas from the HTS is cooled to increase the conversion, and then it is passed through the LTS converter. The LTS converter is fdled with a catalyst containing copper oxide, zinc oxide, and aluminum oxide. It operates at about 200-220°C. The residual CO content in the converted gas is about 0.2% to 0.4% (on a dry gas basis)53. Some LTS reactors operate with an inlet temperature of 190-210°C and reduce the CO level to 0.1 to 0.2 mole % (dry). Again, the catalyst takes the reaction to equilibrium at as low a temperature as possible because this favors the hydrogen production70. 

The gas from the HTS is cooled to increase the conversion, and then it is passed through the low temperature shift (LTS) converter. The LTS converter is filled with copper oxide/zinc oxide-based catalyst and operates at about 200-220°C. The residual CO content is about 0.2 to 0.4 percent (on a dry gas basis).53... 

Conversion of the CuHM catalyst (58%) in the absence of SOj is constant with time (Figure IB) while conversion decreases from 58 to 35% after 13 h of operation with SOj. A more rapid loss of NO removal activity is evident for this catalyst relative to the copper-free catalyst. 

Formaldehyde is nowadays one of the major produced chemicals due to its uses in many fields of chemical industry [1]. The commercial production started in 1890 using metallic copper catalysts. In 1910 copper catalysts were replaced by silver catalysts with higher yields [2]. Although the first report of the excellent catalytic behavior of iron molybdates in selective oxidation of methanol to formaldehyde is of 1931, the related industrial process based on them only went into operation in 1940-50 [1]. A recent report [3] shows that iron molybdates and silver catalysts are nowadays equally used as industrial catalysts for formaldehyde production. 

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