Catalysts for methanol synthesis

Whereas formerly zinc oxide chrome oxide catalysts were in general applied for methanol synthesis under high pressures - about 300 to 400 bar - which featured high temperature resistance and relative insensitivity to catalyst poisons, above all sulfur in many forms, today catalysts on a copper basis are used exclusively. Sometimes they are termed Blasiak catalysts in specialised literature and a number of works [3.14] exist on the first test results with this catalyst type. The copper-based catalysts permit methanol to be synthesized in an economic manner at pressures between 50 and 100 bar and temperatures around 230 to 270°C. The fact that it was first applied commercially about 1970 was mainly due to people not being in a position in the forties and fifties to obtain the necessary 

The first copper catalysts suitable for methanol synthesis on a commercial scale were developed at the end of the 60s by ICI in Billingham [3.14] and LURGI in Frankfurt [3.15]. According to the first relevant patents owned by the two companies, these catalysts had the following composition  

The question of selectivity is therefore of great importance as forming methanol from CO, CO2 and H2 is little favoured thermodynamically. The following correlations between metallic catalyst impurities or improperly applied promotors and the formation of undesirable substances accompanying the methanol are known  

The following catalyst systems are known from patents issued from 1968 to about 1975 [3.8]  

The catalysts supplied commercially these days are usually manufactured in cylindrical or tablet form measuring between 4 and 7 mm and the bulk weight is between 1.0 and 1.5kg/l. The catalysts are applied in the pressure range from SO to 100 bar and at temperatures between 230 and 280°C. At space velocities up to 12000m /h, time space yields of 0.5 to more than 1.2 kg of methanol/liter of catalyst are attained. 

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L. Ma, D.L. Trimm and M.S. Wainwright Promoted skeletal copper catalysts for methanol synthesis, in Advances of Alcohols Fuels in the World, - Proceedings of the XII International Symposium on Alcohol Fuels, Beijing, China, Tsinghua University Press, 1998, pp. 1-7. 

The same integration strategy has also been used [64] to find the optimal Cu Zn Al ratio in mixed oxide catalysts for methanol synthesis from Syngas. 

Omata et al. have investigated catalysts for methanol synthesis from C02-rich synthetic gas under pressurized conditions [22]. They tested 96 mixed-oxide catalysts composed of Cu, Zn, Al, Cr, Zr, Ga at random ratio. Each catalyst was placed in a... 

FIGURE 12 X-Ray diffraction pattern of a mixed oxide catalyst for methanol synthesis. The peaks marked C are cupric oxide Z, zinc oxide A, y-alumina. 

If catalysts are prepared by coprecipitation, the composition of the solutions determine the composition of the final product. Often the composition of the precipitate will reflect the solution concentrations, as was shown for CuO/ZnO catalysts for methanol synthesis [18], but this is not necessarily the case. For al-minum phosphates it was found that at low P A1 ratios the precipitate composition is identical to the solution composition, but if the P A1 ratio in the solution comes close to and exceeds unity, the precipitate composition asymptotically approaches a P A1 ratio of 1 [19]. Deviations from solution composition in coprecipitation processes will generally occur if solubilities of the different compounds differ strongly and precipitation is not complete or, if in addition to stoichiometric compounds, only one component forms an insoluble precipitate this the case for the aluminum phosphate. 

Kasatkin I, Kurr P, Kniep B, Trunschke A, Schlogl R. Role of lattice strain and defects in copper particles on the activity of Cu/ZnO/Al2C>3 catalysts for methanol synthesis. Angewandte Chemie, International Edition. 2007 46(38) 7324-7327. 

Baltes C, Vukojevic S, Schiith F. Correlations between synthesis, precursor, and catalyst structure and activity of a large set of CuO/ZnO/Al2C>3 catalysts for methanol synthesis. Journal of Catalysis. 2008 258(2) 334-344. 

Saito M, et al. Development of copper/zinc oxide-based multicomponent catalysts for methanol synthesis from carbon dioxide and hydrogen. Appl Catal A Gen. 1996 138(2) 311—18. 

Spencer MS. The role of zinc oxide in Cu ZnO catalysts for methanol synthesis and the water-gas shift reaction. Top Catal. 1999 8(3—4) 259—66. 

This set of experiments establishes that pure copper metal, free of surface impurities, yields less than 10 8 kg of methanol per square meter of the catalyst per hour under the standard conditions outlined above. Such a yield is far below the specific activity of supported" copper-based catalysts, e.g., 3.63 x 10 5 kg CH3OH m 2 hr-1 for the Cu/ZnO = 30/70 catalyst (39), and shows that copper metal is a very poor catalyst for methanol synthesis at 75 atm at 250°C. 

Copper and zinc containing mesoporous molecular sieves AIMCM-41 have been studied by MAS NMR, electron spin resonance, nitrogen and carbon monoxide adsorption and temperature programmed reduction. AlMCM-41 materials with ns,/nAi = 15, 30 and x have been synthesized in the presence of copper and zinc Carbon monoxide adsorption shows the presence of Cu ions after mild activation, but Zn ions have not been detected indicating that only a ZnO phase is formed Temperature programmed reduction reveals the presence of CuO clusters of various size depending on the on the ns./n ij ratio and the zinc concentration The results of this study allow the preparation of mesoporous molecular sieves with remarkable redox properties, which are potential model catalyst for methanol synthesis... 

Methanol synthesis from H2/CO2 has been studied so feir in relation to that from H2/C0.[2,3] One of the reasons studied before is due to an interesting phenomenon that an addition of small amoimt CO2 into H2/CO feed improves methanol 5deld significantly in the industrial process.[2] The role of added CO2 was noted. Rozovskii showed by tracer analysis study that carbon species of produced methanol originated from CO2 in the H2/CO feed, suggesting methanol was produced via C02.[4] Recent researches have been aiming at the development of highly efficient catalysts for methanol synthesis for the industrial process. 

Development of high performance Raney copper-based catalysts for methanol synthesis from CO2 and H2... 

In previous studies the authors have reported that metals oxides such as GaaOa, AI2O3, Zr02 and Cr203 contained in Cu/ZnO-based catalysts have an important role to improve simultaneously the activity and the selectivity[1, 2]. Unlike Cu/ZnO-based catalysts, Raney copper catalysts have not been widely reported in the literature as practical catalysts for methanol synthesis. However, 20 years ago Wainwright and co-workers have been the first to report the potentiel use of Raney Cu and Raney Cu-Zn as catalysts to produce methanol from syngas to use as synthetic liquid fuel [3]. Recent works of Wainwright et al. on methanol synthesis... 

Figure 1 shows the activity of the multicomponent catalyst compared with the activities of Cu/ZnO, Cu/Zn0/Ah03 and a commercial catalyst for methanol synthesis from syngas. 

Figure 3. Activity of a Cu/Zn0/Zr02/ A1203/Ga203 catalyst for methanol synthesis Reaction conditions catalyst loading = 3 1, temperature = 523 K, pressure = 5 MPa,...

The selectivity of the multicomponent catalyst for methanol synthesis was extremely high. Accordingly, the purity of methanol produced was 99.9%. 

New preparation method of Cu/ZnO catalysts for methanol synthesis from carhon dioxide hydrogenation hy mechanical alloying... 

Methanol synthesis by catalytic hydrogenation of carbon dioxide is evaluated as one of the most promissing processes for conversion of carbon dioxide into valuable chemicals[l]. While various catalysts for methanol synthesis from carbon dioxide and hydrogen have been investigated, their durability - an important factor for evaluating their practicability-have not been reported[2,3,4,5]. The authors prepared CuO-ZnO-AI 2 O 3 catalysts for methanol synthesis from carbon dioxide and examined their activities and durabilities. 

Hong Chuanqing, Study and Development of C30I Catalyst for Methanol Synthesis, Natural Gas Chemical Industry (Chinese), 15(3)(1990) 31—36. 

Liu, X. Recent advances in catalysts for methanol synthesis via hydrogenation of CO and C02. Industrial Engineering Chemistry Research, 2003, 42, 6518. 

The activity of supported Pt catalysts for methanol synthesis from C0-H2 is considerably enhanced when the metal is supported on oxides which exhibit themselves appreciable activity for MeOH synthesis. Furthermore it is found that the rate of methanol formation on Pt-supported catalyst is increased when Th02, Ce02 were mechanically mixed with the Pt catalyst. Such behaviour is typical for bifunctional catalysts. It has already been reported that Th02, Ce02 adsorb carbon monoxide without dissociation. Such activated CO can be hydrogenated to form a formyl species, the formyl species interacting with lattice oxygen will produce a formate intermediate. 

A formate specifically bonded to the Cs+ ions is documented by the comparison of the spectrum in Fig. 2b with reference spectra of HCOOCs (ref. 36). The facile formation of surface HCOOCs from CsOH and CO led the author and coworkers to the probing of CsOH/Cu/ZnO and later HCOOCs/Cu/ZnO catalysts for methanol synthesis (ref. 37) and the WGS reaction (ref. 38). The promotion by Cs of the Cu/ZnO catalyst for methanol is shown in Figure 3. 

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