INTEGRATION OF METHANOL SYNTHESIS AND ITS DEHYDRATION TO DIMETHYL ETHER FROM SYNTHESIS GAS AT A LOW PRESSURE REACTOR USING MIXED BED CATALYST

• Main Author: Ardy, Aisyah
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/62655
• Institution: Institut Teknologi Bandung

The Government of Indonesia through Presidential Regulation of the Republic of Indonesia Number 22 of 2017 concerning the General National Energy Plan (RUEN) has planned for dimethyl ether (DME) as household fuel, and its use will begin in 2022. Currently, DME is produced commercially by dehydrating methanol. Generally, methanol is produced by synthesis gas from natural gas. Several developments on direct synthesis of DME from synthesis gas are still being carried out due to some challenges in the operation process. The cost of the direct synthesis of DME is expected to be lower than that through methanol. In this research, the direct synthesis of DME has been successfully carried out at low pressure (about 20 bar) and low temperature (200-280 ?). The pressure in this research was lower than the commercial methanol synthesis of 50-100 bar. The direct synthesis of DME is the integration of the consecutive reactions of synthesis of methanol from synthesis gas and its dehydration into DME. At low pressure, methanol formation is low, but methanol is directly dehydrated to DME. In this study, the direct synthesis of DME was carried out using a mixed catalyst that was selective for the respective reactions, namely the synthesis of methanol and its dehydration into DME. Both catalysts have been tested for their activity in each reaction. These two catalysts have similar compositions: 63% Cu, 26-27% Zn, and 9% Al. But each has different pore properties as follows: (i) surface area 54.8 m2/g (catalyst M151) and 110.0 m2/g (catalyst XAB); (ii) pore volume 0.22 mL/g (M151) and 0.29 mL/g (XAB). The activity test of each catalyst was carried out at 240 ? and 20 bar, and the feed was composed of 65% H2, 28% CO, and 7% N2. The XAB catalyst gave CO conversion of 30%, and methanol yield of 1.2%. The M151 catalyst gave CO conversion of 74%, and DME yield of 1.8% without the methanol product. The M151 catalyst also accommodates the dehydration of methanol to DME, because M151 has an acid site. The original ?-Al2O3 catalyst has too high acidity, so the dehydration reaction proceed further to produced small molecules, rather than the main product of DME. To overcome this, the ?-Al2O3 catalyst was modified with phosphorus (P/Al) impregnation. The ?-Al2O3 catalyst with 5% phosphorus (5P/Al) has low-medium acidity which was good for dehydration of methanol to DME. The results of the 5P/Al catalyst activity test at 1 bar and 240 ? gave methanol conversion of 42%, DME yield of 18%, and DME selectivity of 75%. The 5P/Al catalyst was more selective to produce DME than the original ?-Al2O3 catalyst. The direct synthesis of DME was carried out using a mixed catalyst (XAB):(5P/Al) and ratio (1:1), in continuous, batch, and repeated batch processes. The experiments were carried out with a modified Carberry reactor which provided good contact between the synthesis gas and the catalyst. The feed synthesis gas has a composition of 65% H2, 28% CO, and 7% N2. The direct synthesis of DME was carried out in batches at an initial pressure of 15-23 bar and a temperature of 200- 280 ?. Mixed catalyst (XAB):(5P/Al) gave good activity: CO conversion of 70%, and DME yield of 37% in the batch process at a pressure of 20 to 15 bar (P20-15), and temperature of 240 ?. At the same temperature 240, and lower initial pressure of 17 bar (P17-12) has given CO conversion of 50% and DME yield of 31.2%. At an initial pressure of 23 bar (P23-18) and a temperature of 260 ?, the catalyst (XAB):(5P/Al) gave CO conversion of 75%, and DME yield of 60.5%. In the repeated batch process at an initial pressure of 20 bar (P20-15) and 23 bar (P23-18), the mixed catalyst (XAB):(5P/Al) still showed a good activity even though it had been used up to six times (± 2 hours/ batch). At 240 ?, the performance of mixed catalyst (XAB):(5P/Al): an initial pressure of 20 bar (P20-15) resulted in CO conversion of 65%, with DME yield of 40%, and an initial pressure of 23 bar (P23- 18) resulted in CO conversion of 67%, with DME yield of 44%. Performance increases with temperature: at an initial pressure of 23 bar (P23-18) and temperature of 260 ?, CO conversion increased to 75%, and yield of DME to 60%. These results indicated that the reaction rate of direct synthesis of DME was more influenced by temperature than pressure. The main novelty of this doctoral research is the proof that the direct synthesis of DME from synthesis gas could be carried out at a pressure of about 20 bar and a temperature of 240-260 ?, through shifting the equilibrium reaction of methanol synthesis and its dehydration. This direct synthesis at low pressure was carried out with a mixed catalyst of XAB and 5P/Al, with a ratio of 1:1 (lower than other researchers which generally reached 5/1). The success of this research is expected to facilitate further development in a larger scale experiments, considering that XAB catalyst for methanol synthesis is available in the open market, and the use of modified ?-Al2O3 with 5% phosphorus for dehydration of methanol to DME.