1、外文资料原文 1 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 a pressure range of 50-100 b
2、ar, 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 calculated by thermodynamics that theo
3、retic 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-temperature process for metha
4、nol 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 used directly in the reformer, i
5、nstead 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-phase synthesis in a semi-batch r
6、eactor 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 complete purification of the syngas
7、 from reformer, and reactivation of the deactivated catalyst. This is the main 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 has been widely studied, where carbonylation
8、 of methanol and successive hydrogenation of methyl formate were considered as two main steps of the reaction.6-13 外文资料原文 2 Palekar et al. used a potassium methoxide/copper chromite catalyst system to conduct this liquid-phase reaction in a semi-batch reactor at 373-453 K and 30-65 bar.6 Although th
9、e 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 and must be completely removed from syngas,
10、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 was produced in a batch reactor at 443 K
11、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 shift reaction at lower temperature is eas
12、ily 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 products, we suggested the reaction path as step (2)
13、. 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 selectivity for methanol formation at temperature as low as 423-443 K.26 In this communication, the catalytic promoting effects of different alcohols on
14、 the synthesis of methanol from CO/ CO2/H2 on Cu/ZnO catalyst were investigated. High yields of 外文资料原文 3 methanol were realized while some alcohols were utilized. 2. Experimental Section The catalyst was prepared by the conventional coprecipitation method. An aqueous solution containing copper, zinc
15、 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. The resulting precipitate was filtrated and washed with
16、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 surface area for the catalyst was 59.4 m2/g. The catalyst
17、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 area for Cu/ZnO (B) was 20.1 m2/g. To confirm the influen
18、ce 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. So using passivated catalyst reduced separately had n
19、o 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
20、 was added into the reactor. Then the reactor was closed and the air inside the reactor was purged by reactant gas. A pressurized mixture gas of CO (31.90%), CO2 (5.08%), and H2 (60.08%) was introduced and then the reaction took place at the desired temperature. Ar of 2.94% in the feed gas was used
21、as inner standard. After reaction, the reactor was cooled by ice-water and then the gas inside the reactor was released very slowly and collected in a gas-bag for analysis. The standard reaction conditions were as follows: catalyst=1.0 g； solvent=20 mL； reaction temperature=443 K； initial pressure=3
22、0 bar. At the standard reaction temperature of 443 K, the pressure was calculated to be 55 bar, including the vapor pressure of about 10 bar from ethanol.27 All products were confirmed on GC-MS (Shimadzu GCMS 1600) and analyzed by two gas chromatographs (Shimadzu GC-8A/FID for liquid products, and GL Science GC-320/TCD for gas products). Conversion or yield was calculated on the basis of all carbon in the feed gas. In the experiments using reactant gas of different composition, where Cu/ZnO (B) was employed, a conventional magnetically stirred batch reactor was used. The
