Zinc-chromium catalyst

New catalysts have helped increase the conversion and yields. The older, high-pressure processes used zinc-chromium catalysts, but the low-pressure units use highly active copper catalysts. Liquid-entrained micrometer-sized catalysts have been developed that can convert as much as 25 percent per pass. Contact of the synthesis gases with hot iron catalyzes competing reactions and also forms volatile iron carbonyl that fouls the copper catalyst. Some reactors are lined with copper. 

In this reaction a H2/CO ratio of 3 is required in the synthesis gas, and one-third of the hydrogen content is wasted in rejected steam. This reaction is carried out over a zinc/chromium catalyst and is highly exothermic. 

The pressurized gas then is led to the methanol reactor. Two different catalyst systems may be used (l) a zinc-chromium catalyst requiring gas pressures of 2000-4000 psi or (2) a copper catalyst system at 1000-2000 psi. About 95 percent of the gas is converted to methanol by this exothermic reaction ... 

This reaction is first conducted on a chromium-promoted iron oxide catalyst in the high temperature shift (HTS) reactor at about 370°C at the inlet. This catalyst is usually in the form of 6 x 6-mm or 9.5 x 9.5-mm tablets, SV about 4000 h . Converted gases are cooled outside of the HTS by producing steam or heating boiler feed water and are sent to the low temperature shift (LTS) converter at about 200—215°C to complete the water gas shift reaction. The LTS catalyst is a copper—zinc oxide catalyst supported on alumina. CO content of the effluent gas is usually 0.1—0.25% on a dry gas basis and has a 14°C approach to equihbrium, ie, an equihbrium temperature 14°C higher than actual, and SV about 4000 h . Operating at as low a temperature as possible is advantageous because of the more favorable equihbrium constants. The product gas from this section contains about 77% H2, 18% CO2, 0.30% CO, and 4.7% CH. ... 

Reforming is completed in a secondary reformer, where air is added both to elevate the temperature by partial combustion of the gas stream and to produce the 3 1 H2 N2 ratio downstream of the shift converter as is required for ammonia synthesis. The water gas shift converter then produces more H2 from carbon monoxide and water. A low temperature shift process using a zinc—chromium—copper oxide catalyst has replaced the earlier iron oxide-catalyzed high temperature system. The majority of the CO2 is then removed. 

Copper—cadmium and zinc—chromium oxides seem to provide most selectivity (38—42). Copper chromite catalysts are not selective. Reduction of red oil-grade oleic acid has been accompHshed in 60—70% yield and with high selectivity with Cr—Zn—Cd, Cr—Zn—Cd—Al, or Zn—Cd—A1 oxides (43). The reduction may be a homogeneously catalyzed reaction as the result of the formation of copper or cadmium soaps (44). 

Old processes use a zinc-chromium oxide catalyst at a high-pressure range of approximately 270-420 atmospheres for methanol production. 

Chain-growth can be initiated with high operating temperatures and pressures, in the presence of alkaHnized zinc-chromium mixed oxides (1 2) possibly modified with other metals (3)- Such promoted catalysts allowed industrial scale production of alcohol mixtures containing up to 30 wt of C alcohols. 

Such reactions comprise practically all those in which hydrogen is linked to carbon to produce of necessity hydroxy compounds, which are of industrial importance, e.g., the manufacture of methanol and higher alcohols from carbon monoxide and hydrogen in presence of catalysts, such as zinc-chromium oxides. 

C02 alternating co-polymerization aluminum catalyst system, 11, 617 asymmetric co-polyermization, 11, 618 chromium catalyst system, 11, 615 cobalt catalyst system, 11, 614 diphenoxyzinc complex, 11, 610 manganese catalyst system, 11, 617 mechanisms, 11, 609 supercritical C02, 11, 618 zinc-/3-diiminate complex, 11, 611 CO alternating co-polymerization catalysts, 11, 606 CO alternating co-polymerization mechanisms, 11, 608 homopolymerization, 11, 597... 

Methyl alcohol is obtained from synthesis gas under appropriate conditions (Fig. 1) or by the oxidation of methane (Fig. 2). This includes zinc, chromium, manganese, or aluminum oxides as catalysts, 300°C, 250 to... 

Styrene (phenyl ethylene, vinyl benzene freezing point -30.6°C, boiling point 145°C, density 0.9059, flash point 31.4°C) is made from ethylbenzene by dehydrogenation at high temperature (630°C) with various metal oxides as catalysts, including zinc, chromium, iron, or magnesium oxides coated on activated carbon, alumina, or bauxite (Fig. 1). Iron oxide on potassium carbonate is also used. 

Aside from the recently described Cu/Th02 catalysts, copper on chromia and copper on silica have been reported to catalyze methanol synthesis at low temperatures and pressures in various communications that are neither patents nor refereed publications. It is not feasible to critically review statements unsupported by published data or verifiable examples. However, physical and chemical interactions similar to those documented in the copper-zinc oxide catalysts are possible in several copper-metal oxide systems and the active form of copper may be stabilized by oxides of zinc, thorium, chromium, silicon, and many other elements. At the same time it is doubtful that more active and selective binary copper-based catalysts than... 

With adjustment of the steam/methane ratio, the reactor can produce a synthesis gas with CO/H2 = 1/2, the stoichiometric proportions needed for methanol production. This mixture at approximately 200 atm pressure is fed to the methanol unit where the reaction then proceeds at 350°C. Per pass conversions range from 30 to 50 over the catalyst— typically a supported copper oxide with a zinc, chromium, or manganese oxide promoter 3... 

The hydrogenation of an unsaturated ester to an unsaturated alcohol may be possible over zinc-chromium oxide as catalyst, although the catalyst is known to be much less active for the usual ester hydrogenations than copper-chromium oxide. Ethyl or butyl (eq. 10.25) oleates were hydrogenated to octadecenol in yields of over 60% with a zinc-chromium oxide at 280-300°C and 20 MPa H2.16 The butyl ester was much preferred to the ethyl ester, since it was difficult to separate the ethyl ester from the alcohol product because of their similar boiling points. 

The decarbonylation of furfural to give furan is best carried out at rather high temperatures. The following catalysts have been described Pd or Pd on charcoal,30 calcium oxide,31 32 zinc and iron chromite,33 or zinc, chromium, and manganese oxide (from ammonium chromate and manganese nitrate).34 The optimum reaction temperature with... 

In the traditional plant concept, the gas from the secondary reformer, cooled by recovering the waste heat for raising and superheating steam, enters the high-temperature shift (HTS) reactor loaded with an iron - chromium catalyst at 320 - 350 °C. After a temperature increase of around 50 - 70 °C (depending on initial CO concentration) and with a residual CO content of around 3 % the gas is then cooled to 200-210 °C for the low-temperature shift (LTS), which is carried out on a copper - zinc - alumina catalyst in a downstream reaction vessel and achieves a carbon monoxide concentration of 0.1-0.3 vol%. 

Heterogeneity of the surfaces of oxide catalysts such as chromium oxide, zinc oxide, and zinc-chromium oxide has been postulated by H. S. Taylor (75) on the basis of adsorption studies. In the author s view, Taylor s experimental observations may be also explained without assuming a heterogeneous character of the oxide surfaces. 

Iron-chromium oxide catalysts, reduced with hydrogen-containing in the conversion plants, permit reactions temperatures of 350 to 380°C (high temperature conversion), the carbon monoxide content in the reaction gas is thereby reduced to ca. 3 to 4% by volume. Since, these catalysts are sensitive to impurities, cobalt- and molybdenum-(sulfide)-containing catalysts are used for gas mixtures with high sulfur contents. With copper oxide/zinc oxide catalysts the reaction proceeds at 200 to 250°C (low temperature conversion) and carbon monoxide contents of below 0.3% by volume are attained. This catalyst, in contrast to the iron oxide/chromium oxide high temperature conversion catalyst, is, however, very sensitive to sulfur compounds, which must be present in concentrations of less than 0.1 ppm. 

By hydrogenation at high pressure of lauric acid in the presence of a zinc-copper-cadmium-chromium catalyst. Lazier, U. S. pat. 1,839,974. 

The efficiency of zinc-chromium and vanadium-magnesium oxide catalysts in the reaction of butanediol dehydrogenation has been established. The optimum reaction conditions in butadione synthesis providing high yields and selectivity have been found. Experimental substantiation of principles for the purposeful synthesis of the catalytic systems mentioned above is considered. The catalysts were prepared based on these principles. 

We have investigated a series of the dehydrogenating catalysts for this reaction. Our attention was focused on two of them. Further study of 2,3-butanediol dehydrogenation and oxidative dehydrogenation to butadione was performed using zinc-chromium oxide catalysts and vanadium-magnesium oxide catalysts as well. 

Figure 1. Dehydrogenation of acetoin (to the left, pale dots) and of 2,3-butanediol (to the right) on zinc- chromium oxide catalyst, LHSV=1.6 h" 2, acetoin (as initial material) 3, butadione 1, butanediol (as initial material) 2, acetoin (formed as intermediate from butanediol) 3,butadione.

Zinc-chromium oxide catalysts were prepared by co-precipitation from aqueous solutions of corresponding nitrates with aqueous ammonia. The precipitated hydroxo-compounds mixed with ZnO were dried at 120°C and the slightly wet product was then molded by squeezing out through orifices with diameter of 4 mm [6]. 

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