Copper/zinc methanol catalyst

Because the synthesis reactions are exothermic with a net decrease in molar volume, equiUbrium conversions of the carbon oxides to methanol by reactions 1 and 2 are favored by high pressure and low temperature, as shown for the indicated reformed natural gas composition in Figure 1. The mechanism of methanol synthesis on the copper—zinc—alumina catalyst was elucidated as recentiy as 1990 (7). For a pure H2—CO mixture, carbon monoxide is adsorbed on the copper surface where it is hydrogenated to methanol. When CO2 is added to the reacting mixture, the copper surface becomes partially covered by adsorbed oxygen by the reaction C02 CO + O (ads). This results in a change in mechanism where CO reacts with the adsorbed oxygen to form CO2, which becomes the primary source of carbon for methanol. 

A AlI lation. A number of methods are available for preparation of A/-alkyl and A[,A/-dialkyl derivatives of aromatic amines. Passing a mixture of aniline and methanol over a copper—zinc oxide catalyst at 250°C and 101 kPa (1 atm) reportedly gives /V-methylaniline [100-61-8] in 96% yield (1). Heating aniline with methanol under pressure or with excess methanol produces /V, /V-dimethylaniline [121 -69-7] (2,3). 

High pressure processes P > 150 atm) are catalyzed by copper chromite catalysts. The most widely used process, however, is the low pressure methanol process that is conducted at 503—523 K, 5—10 MPa (50—100 atm), space velocities of 20, 000-60,000 h , and H2-to-CO ratios of 3. The reaction is catalyzed by a copper—zinc oxide catalyst using promoters such as alumina (31,32). This catalyst is more easily poisoned than the older copper chromite catalysts and requites the use of sulfiir-free synthesis gas. 

Reaction with carbon monoxide using copper/zinc oxide catalyst yields methanol ... 

Liu G, et al. The rate of methanol production on a copper-zinc oxide catalyst - the dependence on the feed composition. J Catal. 1984 90(l) 139-46. 

Kniep BL, et al. Rational design of nanostructured copper-zinc oxide catalysts for the steam reforming of methanol. Angew Chem Int Ed. 2004 43(1) 112 15. 

Quantitative and qualitative changes in chemisorption of the reactants in methanol synthesis occur as a consequence of the chemical and physical interactions of the components of the copper-zinc oxide binary catalysts. Parris and Klier (43) have found that irreversible chemisorption of carbon monoxide is induced in the copper-zinc oxide catalysts, while pure copper chemisorbs CO only reversibly and pure zinc oxide does not chemisorb this gas at all at ambient temperature. The CO chemisorption isotherms are shown in Fig. 12, and the variations of total CO adsorption at saturation and its irreversible portion with the Cu/ZnO ratio are displayed in Fig. 13. The irreversible portion was defined as one which could not be removed by 10 min pumping at 10"6 Torr at room temperature. The weakly adsorbed CO, given by the difference between the total and irreversible CO adsorption, correlated linearly with the amount of irreversibly chemisorbed oxygen, as demonstrated in Fig. 14. The most straightforward interpretation of this correlation is that both irreversible oxygen and reversible CO adsorb on the copper metal surface. The stoichiometry is approximately C0 0 = 1 2, a ratio obtained for pure copper, over the whole compositional range of the... 

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... 

By far the most important synthesis gas reaction is its conversion into methanol, using copper/zinc oxide catalysts under relatively mild conditions (50 bar, 100-250°C). Methanol is further carbonylated to acetic acid (see Section 22-7), so that CH3C02H, methyl acetate, and acetic anhydride can all be made from simple CO and H2 feedstocks. Possible pathways to oxygenates in cobalt catalyzed reactions are shown in Fig. 22-6. 

Methanation as final purification for the raw gas from partial oxidation was proposed by Topsoe [739]. In this case the shift conversion is carried out in two stages with a special sulfur-tolerant shift catalyst followed by removal of hydrogen sulfide and carbon dioxide in an acid gas removal unit. Because of the potential danger of a sulfur break-through causing poisoning, the normal copper - zinc - alumina catalyst is usually not applied, which is surprising as the same risk exists in partial oxidation based methanol plants for the similarly composed methanol catalyst. 

Only a few studies of the poisoning of copper/zinc oxide catalysts have been reported (refs. 4-6). Whether copper or zinc is most su.sceptible to attack by sulfur is still a question, Tlte literature findings on the sulfur tolerance of methanol synthesis catalyst are inconsistent with industrial experience. For example, observations from indusirinl production suggest that a... 

Mueller, L.L. Griffin, G.L. Formaldehyde conversion to methanol and methyl formate on copper/ zinc oxide catalysts. J. Catal. 1987,105 (2), 352-358. 

In this section we describe INS studies of molybdenum trioxide, a precmsor of molybdenum disulfide catalysts ( 7.5), and transition metal oxides which catalyse complete or partial oxidation of hydrocarbons, and copper zinc oxide catalysts, which catalyse methanol synthesis from carbon monoxide and dihydrogen ( 7.3.3). 

Copper zinc oxide catalysts—methanol synthesis... 

Nissui-Topsoe Methanol-Synthesis Process. A schematic flow diagram [29] of the process offered by Haldor Topsoe of Denmark and Nihon Suiso Kogyo Company of Japan is given in Figure 3.17. The process is based on a copper-zinc-chrome catalyst that is active at 230—280 C and at a pressures of 100-200 atm. 

Kim and Kwon described a microreactor, heated by electricity, which carried a copper/zinc oxide catalyst [46]. About 4 mL min of hydrogen was produced by the reactor. At a reaction temperature of 300 °C and an S/C ratio of 1.1, full methanol conversion was achieved. Subsequently the same group developed a chip-like... 

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]. 

Lattner and Harold [56] performed autothermal reforming of methanol in a relatively big fixed-bed reactor carrying 380 g BASF alumina-supported copper/zinc oxide catalyst modified with zirconia. The 01C ratio was set to 0.22 while the SIC ratio varied from 0.8 to 1.5. The axial temperature profile of the reactor, which had a length of 50 cm, was rather flat, the hot spot temperature did not exceed 280° C which was achieved by the air distribution system through porous ceramic membrane tubes. More than 95% conversion was achieved. Very low carbon dioxide formation was observed for this reactor only 0.4 vol.% was found in the reformate. However, the WHSV calculated from the data of Lattner and Harold [56] reveals a low value of only 6 l/(h gcat) for the highest CHSV of 10 000 h reported. 

Catillon et al. [70] investigated the performance of copper/ zinc oxide catalyst coated onto copper foams for methanol steam reforming. Significant improvement of the heat transfer by the copper and consequently higher catalyst activity was achieved compared to fixed catalyst beds. 

Copper/zinc oxide is the catalyst technology most frequently used for methanol steam reforming. Numerous pubhcations have dealt with this type of catalyst and only a few are cited here. The maximum operating temperature of copper/zinc oxide catalysts for methanol steam reforming is limited to 300 °C. 

Wiese et al. reported full conversion of methanol over a commercial copper/zinc oxide/alumina catalyst, with no further specifications given, at 280 °C and a maximum weight hourly space velocity of 5 LH2 (h gcat) in a tubular fixed bed [154]. This is within the usual range of space velocities for this type of catalyst. The power density of the fixed catalyst bed was calculated to be 12.5 kW L . The increase in carbon monoxide concentration at partial load, which is typical over copper/zinc oxide catalysts, is illustrated in Figure 4.6. Naturally, the lower the space velocity, the higher the conversion becomes. As soon as the space velocity is considerably below the value required to achieve full conversion, selectivity of the catalyst towards water-gas shift... 

Figure 4.6 Hydrogen yield versus methanol conversion and carbon monoxide content in the dry reformate for a commercial copper/zinc oxide catalyst [154],...

However, copper/zinc oxide catalysts are also active for autothermal reforming of methanol [157], the copper is then present as the oxide. Some examples will be described below. 

Palladium is the precious metal most frequently apphed for methanol steam reforming [176-178]. Despite its higher price compared with the copper-based systems, it is an attractive alternative owing to the potential for higher activity and greater robustness, which are key features for small scale reformers. The combination of palladium and zinc showed superior performance and soon the formation of a palladium-zinc alloy was identified as a critical issue for optimum catalyst performance [179]. Besides palladium/zinc oxide, palladium/ceria/zinc oxide may well be another favourable catalyst formulation [177]. However, precious metal based catalysts have a tendency to show higher carbon monoxide selectivity than copper-zinc oxide catalysts, because it is a primary product of the reforming reaction over precious metals. 

Palo et al. investigated methanol steam reforming at a 375 °C reaction temperature, applying proprietary catalyst formulations [187], which minimised the carbon monoxide concentration to 1.2 vol.%. This value was significantly lower compared with the 3 vol.% found for a copper/zinc oxide catalyst [188]. It could well be assumed that the proprietary catalyst was also a palladium/zinc oxide formulation. 

Partial oxidation of methanol is less frequently reported in the open literature. Cubeiro et al. investigated the performance of palladium/zinc oxide, palladium/ zirconia and copper/zinc oxide catalysts for partial oxidation of methanol in the temperature range between 230 and 270 °C (194j. Increasing selectivity towards hydrogen and carbon dioxide was achieved with increasing conversion, while selectivity towards steam and carbon monoxide decreased. The palladium/zinc oxide catalyst showed lower selectivity towards carbon monoxide compared with the palladium/zirconia catalyst. However, the lowest carbon monoxide selectivity was determined for the copper/zinc oxide catalyst. 

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