(386c) Techno-Economic Analysis of Shale Gas-to-Dimethyl Ether (DME) Process Via Direct Synthesis

Due to the volatile oil market and uncertainty in the crude oil supply in the future, it is necessary to develop cleaner and more carbon efficient non-petroleum based transportation fuels.¹ In the recent years, the use of dimethyl ether (DME) as an alternative transportation fuel is being strongly investigated. DME is used as a high quality fuel and has the potential to replace diesel due to its high cetane number (55-60).² DME can be produced by indirect and direct synthesis of syngas. The direct synthesis route has higher productivity compared to the indirect route but it has not been commercialized yet. Countries in the Asia-Pacific regions use coal to produce DME and are currently the largest consumers of DME. With low cost shale gas being abundantly available in the United States, DME can be produced from shale gas with less CO₂ emission and capital investment. Even though several studies have been conducted to developing catalysts and reactors for direct syngas-to-DME processes and plant-wide analysis of coal-to-DME processes, there is hardly any study in the open literature on a shale gas-to-DME process. With this motivation, we will present a techno-economic study of a shale gas-to-DME plant via direct synthesis using the process model developed in Aspen Plus^® and economic model developed in Aspen Plus Economic Analyzer(APEA^®).

In this work, a technically-feasible shale gas-to-DME process is synthesized first. Shale gas is first converted to syngas via pre-reformer and autothermal reformer and then converted to DME via direct synthesis. In the syngas production unit, a pre-reformer is required to convert the heavy hydrocarbons and prevent coking in the autothermal reformer. The raw syngas is sent to an acid gas removal unit to separate CO₂. The clean syngas is then sent to the DME production unit. The effluent of the DME reactor is then fed to a separation section where the unconverted syngas, DME, CO₂, water, and methanol are separated. A portion of the CO₂ recovered in the separation section is utilized by recycling to the syngas production unit.

The presentation will focus on the following aspects: (1) development of kinetic models for pre-reformer, autothermal reformer, and DME synthesis reactor using the rate parameters regressed from experimental data, (2) development of a low cost novel separation system to separate unconverted syngas, DME, CO₂, water and methanol using DME as solvent, (3) development of the plant-wide model of a shale gas-to-DME process in Aspen Plus^® and validation of plants section for which experimental data exist, (4) techno-economic analysis in APEA using the model developed in Aspen Plus^®, (5) sensitivity study to analyze the effect of key design parameters on the main economic measures (i.e. net present value, internal rate of return, payback period), including design parameters such as steam to carbon ratio and oxygen to carbon ratio in the autothermal reformer, H₂/CO ratio in the DME synthesis reactor, technologies for acid gas removal (chemical or physical absorption), extent of CO₂ recycle, and utilization.

Reference

1. Azizi, Z.; Rezaeimanesh, M.; Tohidian, T.; Rahimpour, M. R. Dimethyl Ether: A Review of Technologies and Production Challenges. Chemical Engineering and Processing: Process Intensification. 2014, 82, 150â??172.
2. Ogawa, T.; Inoue, N.; Shikada, T.; Inokoshi, O.; Ohno, Y. Direct Dimethyl Ether (DME) Synthesis from Natural Gas. Studies in Surface Science and Catalysis Natural Gas Conversion VII, Proceedings of the 7th Natural Gas Conversion Symposium. 2004, 379â??384.