(60r) A Hybrid Catalytic Route to Ethanol from Residue Gases Via the Dimethyl Ether and Methyl Acetate Synthesis: Process Design and Techno-Economic Analysis

The production of ethanol from unconventional sources has recently attracted great attention as a promising alternative energy production option. Ethanol is considered an attractive fuel because it can be cleaner burning fuel, which reduces harmful emissions such as carbon monoxide and volatile organic compounds that contribute to air pollution and climate change. The innovation of cost-effective ethanol production processes is critical to meet the growing demand for sustainable energy system. This study proposes a novel ethanol production process from residue gas, via a three-step catalytic conversion involving dimethyl ether (DME) synthesis, DME carbonylation and methyl acetate (MA) hydrogenation. The proposed process aimed to address the economic challenges associated with ethanol production pathways, particularly residue gas from steel industries. The proposed residue gas upgrading process offers several advantages over traditional ethanol production pathways. Firstly, it utilizes residue gas, a low-value byproduct that would otherwise be disposed or flared. By utilizing residue gas as a feedstock for ethanol production, the proposed process has not only economic benefits but also environmental advantages (e.g., reducing greenhouse gas emissions) as well as advantages as a sustainable path in the circular economy. In addition, because the proposed route does not rely on conventional energy sources, various issues related to energy production (e.g., energy security and diversity) can be avoided: especially, compared to biomass-driven ethanol such as water depletion, land use, and food security.

The proposed route to ethanol from residue gas was simulated using Aspen Plus and validated using experimental data from the literature. The proposed simulation model estimated mass and energy information, as well as sizing and costing data (such as capital and operating costs). Heat integration was also achieved through the design of the optimal heat exchange network using the Aspen Plus heat exchange network design tool. In order to identify economic feasibility of process model, techno-economic evaluation of the proposed process was carried out, which showed that the unit production cost (UPC) of ethanol and process energy efficiency (EEF) was estimated. For the major cost drivers, sensitivity analysis was performed to investigate the economic effects of different technological improvements under various market scenarios. Especially, comparative analysis with different ethanol prices was also conducted to establish economically viable strategy of the proposed route in the global market.

In this study, the ethanol production process simulation model is developed with the 100,000 ton/year of ethanol production rate. The first step of the proposed process is DME synthesis, which converts carbon monoxide and hydrogen in the residue gas into DME. This step is carried out in experimental data using a copper-based catalyst under specific reaction conditions, including temperature, pressure, and gas flow rate. The resulting DME product is then subjected to the second step, DME carbonylation, which involves the reaction of DME with carbon monoxide to produce methyl acetate. The DME carbonylation is simulated using FER catalyst, with the CO/DME ratio to 9. The final reaction step of the process consists of the hydrogenation of MA to produce ethanol, which is carried out using Cu/ZnO/Al₂O₃ catalyst. In addition to this, sub reaction process was selected to enhance the yield of ethanol production using methanol produced in the MA hydrogenation process. The methanol produced through the hydrogenation was then used for additional DME production through the methanol to DME process, and the total ethanol production was greatly improved by using it for the carbonylation reactor. To develop the process steps described above, the selection and allocation of complex separation processes is crucial to design cost- and energy-efficient ethanol production. One of the major challenges of this process is how to treat off-gases from DME synthesis and MA hydrogenation sections. To address this issue, methanol solvent-based gas separation has been employed, which has shown promising results in the separation of carbon monoxide and hydrogen from other materials. Additionally, distillation columns have been used to separate various reaction products, including DME, MA,and ethanol, which are substances requiring purification. While these separation processes add complexity to the overall process, they are necessary to achieve the high purity levels required for ethanol production. Overall, the successful integration of these separation processes into the production process has resulted in a highly efficient and economically viable method for ethanol production from residue gas.

To improve the proposed process's energy efficiency, we developed a heat exchange network using Aspen Plus heat exchange network design tool. Heat exchange network is one of the crucial components in a variety of chemical process industries, playing a key role in heat recovery and energy conversation. The design of an efficient heat exchange network can help to minimize energy consumption and reduce the overall cost of operation. The Aspen Plus software has been widely used for the design of heat exchange networks. It provides a comprehensive set of tools to model and simulate heat exchangers and optimize their performance. The heat exchange network synthesis process involves several steps, including stream data collection, heat transfer equipment selection and sizing, and network optimization. Overall, the design of the heat exchange network provides significant benefits for industrial processes, including improved energy efficiency, reduced operating costs, and enhanced sustainability. We achieved 29.3% reduction in energy consumption, an 11.4% reduction in utility costs, and 7.5% increase in process equipment costs as a result of the heat exchange network synthesis.

The proposed process was evaluated for its economic feasibility using the UPC of the ethanol. The UPC includes the annualized capital investment (ACI), variable operating cost (VOC), and fixed operating cost (FOC). The ACI is specified as the total capital investment (TCI) with depreciation considered. The TCI is estimated based on the purchase equipment cost calculated using the cost data of the Aspen process economic analyzers. The purchase equipment cost is multiplied by a Lang factor, which includes installation, instrumentation, piping, control costs and indirect cost. The VOC includes the utility cost and raw material cost, and FOC includes labor, maintenance, operating supplies and plant overheads. The UPC is expressed as the ratio of combined ACI, VOC, FOC and annual ethanol production rate. As a result of the economic evaluation, the UPC of ethanol was found to be 1.45 USD/kg. Among them, raw material cost contributed the most with 69.7% f the total production cost. In addition, utility cost and ACI were found to contribute about 21% and 8% respectively.

In this study, we performed the sensitivity analysis for the ethanol production process to derive the major cost-driver and determine economic feasibility. First, the change in process economic performance was analyzed considering the 20% change in process economic factors such as interest rate, process life time, utility and raw material cost. As a result of the analysis, it was found that the cost of carbon monoxide and methanol had the greatest effect on process economics among raw materials. Since the economic feasibility of the proposed ethanol production process is sensitive to global market conditions, an analysis of the global ethanol market was also conducted. As a result of comparing the economic feasibility of the proposed process with respect to ethanol prices in each country, it was found to have price competitiveness in countries such as Europe and Japan. However, in countries where the cost of biomass raw materials is cheap due to their large land area, the proposed process is still insufficient to secure economic feasibility.

In conclusion, this study proposed a novel process for ethanol production from residue gas, and analyzed the economic feasibility of the process. The ethanol production process via three catalytic conversion processes (DME synthesis, DME carbonylation and MA hydrogenation) shows the ethanol production cost of 1.45 USD/kg. As a result of analyzing the contribution for each cost factor, it was confirmed that the cost contribution for raw material was the largest, followed by carbon monoxide and methanol. In addition, an analysis was conducted on how economically feasible the ethanol produced through proposed process was in the global ethanol market.

In this study, the process design development and analysis of the ethanol production process from residue gas were performed. As a future work, we perform the task of enhancement of economic and environmental performance for global ethanol market competitiveness. For instance, another applicable unit process can be synthesized and ethanol production strategies will be derived by applying scenario-based assessment.