1、PDF外文：http:/ 1 中文 3825 字 A New Low-Temperature Synthesis Route of Methanol: Catalytic Effect of the Alcoholic Solvent 1. Introduction Gas-phase methanol is being produced industrially by 30-40 million ton per year around the world, from CO/ CO2/H2 at a temperature range of 523-573 K and
2、 a pressure range of 50-100 bar, using copper-zinc-based oxide catalyst. Under these extreme reaction conditions, the efficiency of methanol synthesis is severely limited by thermodynamics as methanol synthesis is an extremely exothermic reaction.1,2 For example, at 573 K and 50 bar, it is calculate
3、d by thermodynamics that theoretic maximum one-pass CO conversion is around 20% for flow-type reactor when H2/CO=2. Also it is reported that the one-pass CO conversion in the industrial ICI process is between 15 and 25%, even if H2-rich gas is used (H2/CO =5,523-573 K).3 Therefore, developing a low-
4、temperature process for methanol synthesis, which will greatly reduce the production cost and utilize the thermodynamic advantage at low temperature, is challenging and important.3 If conversion is high enough in methanol synthesis, recycling of the unreacted syngas can be omitted and air can be use
5、d directly in the reformer, instead of pure oxygen. Generally, low-temperature methanol synthesis is conducted in the liquid phase. The BNL method first reported by Brookhaven National Laboratory (BNL), using a very strong base catalyst (mixture of NaH, acetate), realized this continuous liquid-phas
6、e synthesis in a semi-batch reactor at 373-403 K and 10-50 bar. However, a remarkable drawback of this process is that even a trace amount of carbon dioxide and water in the feed gas or reaction system will deactivate the strongly basic catalyst soon,4,5 resulting in high cost coming from the comple
7、te purification of the syngas from reformer, and reactivation of the deactivated catalyst. This is the main 外文资料原文 2 reason stopping the commercialization of this low-temperature methanol synthesis method. Liquid-phase methanol synthesis from pure CO and H2 via the formation of methyl formate
8、 has been widely studied, where carbonylation of methanol and successive hydrogenation of methyl formate were considered as two main steps of the reaction.6-13 Palekar et al. used a potassium methoxide/copper chromite catalyst system to conduct this liquid-phase reaction in a semi-batch reacto
9、r at 373-453 K and 30-65 bar.6 Although the mechanism of BNL method is still controversial, a lot of researchers think that it is similar to the mechanism above.3 However, similar to that in the BNL method, in this process CO2 and H2O act as poisons to the strong base catalyst (RONa, ROK) as well an
10、d must be completely removed from syngas, making commercialization of low-temperature methanol synthesis difficult. Tsubaki et al. proposed a new method of low-temperature synthesis of methanol from CO2/H2 on a Cu-based oxide catalyst using ethanol as a kind of “catalytic solvent”, by which methanol
11、 was produced in a batch reactor at 443 K and 30 bar.14 This new process consisted of three steps: (1) formic acid synthesis from CO2 and H2； (2) esterification of formic acid by ethanol to ethyl formate； and (3) hydrogenation of ethyl formate to methanol and ethanol. Considering that the water-gas
12、shift reaction at lower temperature is easily con-ducted on Cu/ZnO catalyst,15-25 a new route of methanol synthesis from CO/H2 containing CO2, as a more practical way of methanol synthesis, is proposed. It consists of the following fundamental steps: As formic acid was not detected in the prod
13、ucts, we suggested the reaction path as step (2). Tsubaki et al. investigated the synthesis reaction of methanol from CO/CO2/H2, using ethanol as reaction medium in a batch reactor and found high 外文资料原文 3 selectivity for methanol formation at temperature as low as 423-443 K.26 In this communi
14、cation, the catalytic promoting effects of different alcohols on the synthesis of methanol from CO/ CO2/H2 on Cu/ZnO catalyst were investigated. High yields of methanol were realized while some alcohols were utilized. 2. Experimental Section The catalyst was prepared by the conventional coprecipitat
15、ion method. An aqueous solution containing copper, zinc nitrates (Cu/Zn in molar ratio=1), and an aqueous solution of sodium carbonate were added simultaneously with constant stirring to 300 mL of water. The precipitation temperature and pH value were maintained at 338 K and 8.3-8.5, respectively. T
16、he resulting precipitate was filtrated and washed with distilled water, followed by drying at 383 K for 24 h and calcination at 623 K for 1 h. This precursor was then reduced by a flow of 5% hydrogen in nitrogen at 473 K for 13 h and successively passivated by 2% oxygen diluted by argon. The BET sur
17、face area for the catalyst was 59.4 m2/g. The catalyst here is denoted as Cu/ZnO (A). In the experiments using reactant gas of different composition, a commercially available ICI catalyst (ICI 51-2) was also used through the same reduction pretreatment, denoted here as Cu/ZnO (B). The BET surface ar
18、ea for Cu/ZnO (B) was 20.1 m2/g. To confirm the influence of the catalyst passivation, a tailor-made reactor where in situ reduction of the catalyst before ethanol introduction was available, was used to perform the catalyst reduction and reaction； but no difference in reaction behavior was observed
19、. So using passivated catalyst reduced separately had no influence. In the reaction, a closed typical batch reactor with inner volume of 80 mL and a stirrer was used. The stirring speed of the propeller-type stirrer was carefully checked to eliminate the diffusion resistance between gas, liquid, and solid phases. A desired amount of solvent and catalyst was added into the reactor. Then the reactor was
