265119 Production of Hydrogen From Dimethyl Ether Over Promoted Bifunctional Catalysts

Tuesday, October 30, 2012: 1:30 PM
321 (Convention Center )
Changfeng Yan1,2, Juan Li3,4, Weimin Luo3, Rongrong Hu3,4, Zhiwei Yao3, Changqing Guo3 and Wenbo Li3, (1)Hydrogen Production Lab., Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Beijing, China, (2)Hydrogen Production Lab., Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou, China, (3)Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou, China, (4) Graduate University of Chinese Academy of Sciences, Beijing, China

Hydrogen fuel cells generating electricity from hydrogen and oxygen show higher energy efficiency than Carnot cycle, which the byproduct is only water. Its main fuel is hydrogen or hydrogen-rich gas. Dimethyl ether (DME) is an ideal liquid fuel as hydrogen carrier due to its high H/C ratio, high energy density and ease storage and transportation. Furthermore, DME is inert, non-carcinogenic, non-mutagenic, non-corrosive, and virtually non-toxic. It can also be conveniently stored and handled because its physical properties are very similar to those of LPG. DME will, therefore, play an important role in the future's energy supply system.

Steam reforming (SR) of DME is a distinguished process to produce hydrogen, and is an attractive route to provide hydrogen for fuel cells on a small/medium scale. In this work we investigate the hydrogen production from the DME SR over catalyst Z417 and the self-made catalysts Cu/-Al2O3 prepared by the impregnation coupling intermittent microwave heating method (imp-IMH) or the sole impregnation method (imp). Hydrogen production from DME SR on the commercially catalyst Z417 and self-made catalysts Cu/-Al2O3 was investigated under different conditions in a bench-scale fixed-bed reactor. Catalyst Z417 was chosen for steam reforming of DME at high-temperature of > 350 ºC and catalysts Cu/-Al2O3 were used for low-temperature of <350 ºC. The hydrogen yield and the DME conversion over catalyst Z417 increased greatly with increasing temperature, which reached the maximum value of 66.4% and 91.8%, respectively at 500 ºC. The catalysts Cu/-Al2O3 made by the impregnation coupling with imp-IMH and the imp were performed on the SR of DME at 350 ºC. The hydrogen yield was just 33.7% over 12wt% Cu/-Al2O3 (imp-IMH) with 8.6% higher than that over 12wt% Cu/-Al2O3 (imp) after the catalyst keeps stable, and the DME conversion was just 45.1% with 4.6 % higher than that over 12wt% Cu/-Al2O3 (imp). The selectivity of CO is lower and the selectivity of CO2 over 12wt% Cu/-Al2O3 (imp-IMH) is higher than that over 12wt% Cu/-Al2O3 (imp). This phenomenon might be explained that imp-IMH can control heating method to adjust crystalline structure and grain size of catalyst, which may be easily led to carry water gas shift reaction.

According to the SEM images, the copper particles in the Cu/-Al2O3 prepared with impregnation coupling with intermittent microwave heating method were finer and more uniform distributed than that in the Cu/-Al2O3 prepared with impregnation method. Cu/-Al2O3 (imp) consisted of large particles (about 5 µm and above) with a platelike morphology. In addition, it also could be found that the surface of carriers -Al2O3 prepared by the imp-IMH method was less smooth, which may be attributed to that the frequency of microwave radiation ranging from 0.3 to 300 GHz could make the ions migrate and the dipolar molecules rotate. Therefore, microwave heating is more interesting method to prepare catalyst as compared to conventional heating. The catalysts made by imp-IMH had the higher hydrogen yield and DME conversion, and the better stability.

Fig.1 DME steam reforming over Cu/-Al2O3 (a) the hydrogen yield and DME conversion, and

(b) Ci selectivity (Steam to DME ratio of 5:1, 350 ºC, total gas flow rate of 9900 ml g-1h-1).

     

Fig.2 SEM images of the catalysts 12wt% Cu/-Al2O3 prepared with (a) impregnation method, and (b) impregnation coupling with intermittent microwave heating method.


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