Relative Roles of Methanol Synthesis and Solid Acid Catalysts in the Direct DME Synthesis from Syngas Heon Jung, †,‡ Seong-Min Lee, ‡ Dae-Ryook Yang, † and Kwang-Deog Jung ‡, * † Department of Chemical & Biological Engineering, Korea University, Seoul 136-701, Korea ‡ Clean Energy Research Center, Korea Institute of Science and Technology (KIST), Seoul 136-791, Korea. *E-mail: jkdcat@kist.re.kr Received September 22, 2014, Accepted December 29, 2014, Published online March 25, 2015 The Cu/ZnO/Al 2 O 3 catalysts with 13.0 and 30.6 m 2 Cu/g were designated as HM (highly active catalysts for methanol synthesis) and LM (low active catalysts for methanol synthesis), respectively. γ-Al 2 O 3 and η-Al 2 O 3 were designated as LD (low active catalysts for methanol dehydration) and HD (highly active catalysts for methanol dehydration), respectively. Four catalytic systems (LMLD, LMHD, HMLD, and HMHD) were pre- pared by admixing methanol synthesis catalysts and methanol dehydration catalysts. The syngas to dimethyl ether (DME) (STD) reaction was conducted at a GHSV of 6000 mL/g cat /h, 42 atm, and 250  C. The activity of LMLD was almost same as that of LMDH, indicating that the activity of solid acid catalysts did not influence the STD reaction on the admixed catalysts using LM. On the other hand, the activity of HMHD was much higher than that of HMLD, indicating that the solid acid catalysts controlled the STD reaction on the admixed catalysts using HM. Keywords: Direct DME synthesis, Methanol synthesis, Methanol dehydration, Effects of Cu surface area Introduction Dimethyl ether (DME) has physical properties similar to those of liquefied petroleum gas (LPG). In addition to the physical characters, DME has been known to be an environmentally clean fuel due to its low soot, NOx, and SOx emission. 1,2 From that point, DME has been considered as a substitute fuel for diesel and LPG. Because LPG fueling infrastructures were established in Asia region, attempts have been made to use DME as a car fuel mainly in Asia. Recently, some truck com- panies such as Volvo and Mack have announced the supply of DME trucks by 2015, indicating that technical issues of the DME car are almost solved. The International DME association (IDA) has reported that the heavy-duty DME- fueled vehicles have completed 100 000 km (IDA fact sheet No. 2). 3 DME has been commercially produced in two steps: (1) methanol synthesis from syngas, and (2) DME synthesis by methanol dehydration. It was reported that it is more advanta- geous to synthesize DME from syngas in one step. 4–7 Syngas to DME (STD) conversion is mainly composed of three con- secutive reactions on the mixed catalysts Cu/ZnO/Al 2 O 3 and solid acid catalysts: (1) methanol synthesis, (2) methanol dehydration, and (3) shift reaction. CO 2 + 3H 2 $ CH 3 OH + H 2 O ð1Þ 2CH 3 OH $ CH 3 OCH 3 +H 2 O ð2Þ CO + H 2 O $ CO 2 +H 2 ð3Þ The overall reaction (4a) or (4b) can be derived from reac- tions (1) depending on the H 2 /CO mole ratio. 2CO + 4H 2 $ CH 3 OCH 3 +H 2 O ð4aÞ 3CO + 3H 2 $ CH 3 OCH 3 + CO 2 ð4bÞ Steam reforming or autothermal reforming of methane gives R ratios ((H 2 -CO 2 )/(CO + CO 2 )) higher than 2.0. There- fore, methanol can be coproduced with DME if the H 2 /CO ratio is much higher than 2.0 in direct DME synthesis. Therefore, Haldor and Topsoe claimed coproduction of methanol and DME in the direct DME synthesis from methane reforming (R = 3.0). On the other hand, the molar ratio of H 2 /CO of syngas from coal gasification or biogasification was close to 1.0. In that case, it is clear that the direct DME synthesis can have an advantage over a two-step DME proc- ess, because a shift reactor is required for the two-step DME synthesis from coal gasification or biogasification to adjust the molar ratio of H 2 /CO to 2.0 in the first step (methanol synthesis). As discussed, the STD reaction requires two functionalities: (1) the hydrogenation of carbon oxides for methanol synthesis, and (2) the solid surface acidity for methanol dehydration. Several attempts have been made to give the two functional- ities of methanol synthesis and methanol dehydration in a cat- alyst preparation step, 8–10 but the admixed catalysts of methanol synthesis catalyst and solid acid catalyst showed bet- ter performances in the aspects of the apparent activity. The key reason for this behavior is the high specific Cu surface areas of the admixed catalysts. Article DOI: 10.1002/bkcs.10235 H. Jung et al. BULLETIN OF THE KOREAN CHEMICAL SOCIETY Bull. Korean Chem. Soc. 2015, Vol. 36, 1221–1225 © 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Wiley Online Library 1221