Aisyah Ardy

DME has been acknowledged as an environmentally friendly household fuel. DME and LPG have similar characteristics, both chemical and physical properties, so tha

National Plan on Energy of Indonesia 2017 states that dimethyl ether (DME, CH₃OCH₃) will be used as partial substitution of LPG for household fuel. Methanol dehydration using a solid catalyst is a common technology to produce DME. In this research, a catalyst γAl₂O₃ prepared in our laboratory has been characterized. This catalyst had a surface area of 194.4 m²/g, a total pore volume of 0.55 mL/g, and an average pore diameter of 112, 3 A˙. This catalyst had medium and high acidity sites. Activity tests of this catalyst were carried out in a fixed bed reactor at temperatures of 240, 260 and 280°C. The gas flow rates were related to the gas hourly space velocity of 1500, 2142 and 3000 h⁻¹. Experimentally, the conversions of methanol were closed to that of thermodynamic conversions, i.e about 90% depending on the reaction temperature. The outlet gas was found to contain H₂ up to 2% indicating that there were side reactions besides the dehydration of methanol to DME.

National General Energy Plan of Indonesia 2017 (RUEN 2017) stated that dimethyl ether (DME) is appointed as a blending of LPG to reduce LPG imports. DME can be made with two reaction pathways, namely direct synthesis and indirect synthesis. The objective of this study was to determine the effect of pressure and syngas composition on the direct synthesis of DME using dual fixed bed catalyst. The research was carried out with two types of catalyst: M-xxx as a commercial catalyst for methanol synthesis and γ-Al2O3 as catalyst for dehydration of methanol to DME. The later was prepared in our Laboratory of Chemical Reaction Engineering and Catalysis, ITB. The dual catalyst experiment was carried out at 5 and 7 bars, and a fixed temperature of 240oC. The mass ratio of the M-xxx to γ-Al2O3, so-called M/D ratios, were varied from 1/9 to 9/1. Two type of syngas were used, i.e. SA containing only H2 and CO with a SN of 2,3 and SB containing 4% CO2 with SN of 1,8. The dual bed with a M/D ratio of 1/4 gave a CO conversion up to 62% at 5 bars and 240oC (SA). As pressure increased, the conversion of CO and H2 increases to 85% and 83% at 7 bar and 240oC (SA). The presence of CO2 (SB) decreases catalyst activity, as indicated by the decrease in conversion of CO and H2 to 56% and 54%, at 7 bar and 240oC.

Direct synthesis of DME catalyst was prepared using the co-precipitation method. The catalyst contained CuO/ZnO/Al₂O₃ about 40/27/33 (%-wt). Two types of catalyst were prepared, i.e. CZMA0 (Mg 0%-wt) and CZMA20 (Mg 20%-wt). Both of catalysts were activated using reducing gas (5% H₂ and N₂). The activity test was conducted by syngas model which contained (%-mole) 65% H₂, 28% CO and 7% N₂. The reaction was carried out in a fixed bed reactor at 5 bar, and temperature of 240, 250 and 260°C. Synthesis shown CZMA20 catalyst gave the highest catalytic activity with 73% of CO conversion and 66% of H₂ conversion (5 bar and 260°C). Direct synthesis of DME was also carried out using a dual-catalyst, i.e. catalyst for methanol synthesis (M151, the commercial catalyst of methanol synthesis) and methanol dehydration (γ-Al₂O₃-ITB). The activity of dual catalyst shown 93% of CO conversion and 91% of H₂ conversion. This activity was more stable than two other catalysts (CZMA0 and CZMA20).

The increase of Liquid Petroleum Gas (LPG) import in Indonesia made the government promote Dimethyl Ether (DME) as partial substitution of LPG as written in the General Planning of National Energy (RUEN) 2017. DME can be produced from biomass which abundantly exists in Indonesia. Such biomass is especially oil palm empty fruit bunches (EFB) that consist of 49.07% C, 6.48% H, 0.70% N, 38.29% O, and 5.36% Ash. Techno-economic analysis of this bio-DME production plant was conducted based on literature data. The direct synthesis of DME was applied in this study, instead of using methanol as an intermediate product. Result calculated from mass and energy balance simulation was 4.1 EFB/DME. Thus, 1,090 ton per day of DME can be produced from EFB with a collecting radius of 100 km in Riau Province. Assuming 20 years plant operation with DME selling price of IDR 145,000/12-kg-LPG-equivalent and EFB price of 300 IDR/kg, economic evaluation showed that this business was economically feasible with 10.08% IRR generated. The CAPEX of this plant was 990.4 million USD and the OPEX was IDR 7,143 IDR/kg-LPG-equivalent. DME production from EFB will give the positive economics and environmental effects. Therefore, support and synergy from government, industries, and academics are needed to realize this business.

A research on the production of dimethyl ether (DME) at lower pressure has been conducted in related to the national program on the partial substitution of LPG with DME in the near future (RUEN 2017). DME may be liquefied at a pressure of about 6 atm (25°C), or a temperature of -25°C (1 bar). Burning of DME may produce a cleaner flue gas than LPG. Experiments on dehydration of methanol to produce DME were carried out at a atmospheric pressure (1 bar) and a temperature of 240°C. The experiment was conducted in a tubular reactor with a diameter of 20 mm. and three types of catalyst, i.e. g-Al₂O₃ (from our laboratory), and two commercial catalysts namely catalyst A and catalyst B. The γ-Al₂O₃ catalyst had a surface area of 194.4 m²/gram, an average pore diameter of 11.2 nm, and a total pore volume of 0.546 mL/gram. Methanol concentration in the influent of the reactor was 0.02 mol/L, 0.05 or 0.07 mol/L. It was found that g-Al₂O₃ catalyst had a better activity than the two commercial catalysts. A stable conversion of methanol of 72% was obtained on g-Al₂O₃ catalyst for the on-stream time of 6 to 10 hour. Kinetics of dehydration of methanol to DME on γ- Al₂O₃ catalyst could be represented as a first order reaction with an activation energy Ea of 256.6 kJ/mol and a frequency factor k_o of 8·10⁺²⁸.