Dimethyl ether from syngas and effect of CO2 sorption on product distribution over a new bifunctional catalyst pair containing STA@SBA-15

Direct synthesis of dimethyl ether (DME) from syngas was investigated in the presence of a bifunctional catalyst pair containing silicotungstic acid (STA) incorporated SBA-15 (5, 10, 25% by wt. STA) for the in-situ dehydration of synthesized methanol. The methanol synthesis component of this catalyst mixture is a Cu/ZnO-based commercial (HF) catalytic material. The new STA@SBA-15 type solid acid catalysts synthesized in this study indicated ordered mesoporous structures with surface area values in the range of 493-804 m(2)/g. They possess both strong Br & oslash;nsted and Lewis acid sites. Activity tests performed at 50 bar and 275 ?C with a molar feed ratio of CO/ H-2 being 1/1 showed the highest CO conversion and DME selectivity values in the presence of HF/25STA@SBA-15 admixed catalyst, as 41.1% and 56.6%, respectively. Activity test results showed that the incorporation of STA into SBA-15 had caused a significant increase in DME selectivity and CO conversion. TGA/DTG and XRD results of the spent catalysts showed not very high coke formation (between 2.26 and 3.13%). In order to test the effect of CO2 concentration on the product distribution, a set of sorption-enhanced reaction tests were performed by in-situ removal of carbon dioxide from the reaction medium via a Huntite adsorbent. These tests showed an increase of DME selectivity to 60.3% during the first 50 min of the reaction. Another significant result obtained in the presence of Huntite was the presence of quite a high CH4 mole fraction in the product stream during the first 50 min, which decreased to less than 1% at 200 min reaction time. These results indicated the shift of reverse dry reforming and the water gas shift reactions to the product side as a result of the removal of CO2 from the reaction zone. Hence, some positive effect of CO2 sorption was observed on DME selectivity due to the appearance of CO2 in the product side of the overall DME synthesis stoichiometry. As the reaction period increased Huntite was saturated with CO2 and the effects of its sorption on product distribution diminished.

Automated summary

The direct synthesis of dimethyl ether (DME) from syngas was studied using a bifunctional catalyst containing STA@SBA-15. The results showed that incorporating STA into SBA-15 significantly improved the selectivity and conversion of DME. Furthermore, the removal of CO2 from the reaction medium further enhanced the selectivity of DME.