What is required for resource-circular CO2 utilization within Mega-Methanol (MM) production?
Graphical abstract
Synopsis: A technoeconomic and environmental evaluation of achieving resource circular CO2 utilization in Mega-Methanol (MM) production.
Introduction
As the key indicator of climate change [[1], [2], [3]], the drastic increase in the atmospheric concentrations of greenhouse gases (GHGs), namely CO2 from anthropogenic sources represents a global concern [4]. Consequently, with the establishment of the Paris Agreement, greater global commitment to lowering GHG initiatives has become necessary to combat the negative environmental impacts associated with climate change. Over the last decade, the energy sector, metal and chemical industries as well as the transport sector represent the three largest contributors of CO2 emissions, accounting for a combined 87 % of total emissions [5]. Thus, GHG reduction strategies within these sectors are vital to meeting climate action goals.
With declining fossil fuel reserves and greater environmental considerations, alternative fuel sources are under investigation. Methanol has emerged as a practical solution for energy storage, having a high hydrogen content (12.6 mol%) [6]. Additionally, when used as a fuel, methanol has the potential to avoid large GHG quotas associated with fossil-fuel combustion leading to net lower CO2 emissions [7,8]. Methanol is a convenient liquid fuel substitute or additive and is also one of the most versatile chemicals as a solvent or feedstock for synthetic hydrocarbon production [9,10].
With emerging applications for methanol in transport and chemical industries, the global demand increased from 32 million metric tonnes (MT) in 2006 to 75 million MT in 2015 and is expected to increase to almost 100 million MT by 2020 [10,11], substantiating the expanding mega-methanol (MM) industry- producing upwards of 5000 MT per day [11]. Conventional methanol production is achieved via three steps: syngas production from carbon-containing feedstock, catalytic conversion of syngas to methanol and methanol purification by distillation [12,13]. As of 2014, 90 % the global methanol demand was fulfilled using natural gas feedstock [13] with syngas production achieved predominantly via steam methane reforming (SMR) [14,15].
SMR is the preferred choice for syngas generation as its economic feasibility outweighs its high GHG emission quotas-aligned to high energy requirements [[14], [15], [16], [17]]. However, as MM production capacities continue to increase up to 10,000 MT per day, energy intensive SMR operation becomes less viable [14,18]. At such large capacities, stand-alone autothermal reforming (ATR) operations are more attractive, requiring no reforming thermal energy and produce net lower CO2 emissions [10,18,19]. With technological advancement within the area improving the rigorous design of autothermal reformers, and ultimately, more control over syngas preparation [13,20], the ATR process provides a viable low cost, low carbon option for the MM process with opportunities for added heat integration lowering net energy requirements [16].
With methanol as a prime commodity for several downstream products globally, the need exists to decarbonize methanol supply chains, allowing for significant reductions in environmental burdens associated with its utilization. Thus, cleaner technologies which lowers the overall environmental burdens embodied within MM process operations can lead to more sustainable supply chain management. In an effort to encourage this sustainable transition, process design sits at the forefront of decision-making, examining areas for improvement within current MM process operations.
CO2 hydrogenation has been widely researched as an effective way to reduce emission quotas by storing carbon directly within methanol production [[20], [21], [22], [23], [24], [25]]. However, the implementation of this strategy within conventional MM production has been overlooked, as the process calls for additional hydrogen feedstocks. As global methanol producers seek to validate future MM projects, this research gap can aid in providing new avenues for increased methanol productivity and lower GHG emissions. This novel approach considers a resource-circular CO2 hydrogenation pathway- utilizing captured CO2 coupled with green hydrogen sources, directly within conventional MM production. This solution-oriented approach can become a major turning point in promoting future sustainable operations within the MM process industry aligned to clean methanol production, from cradle-to-methanol gate.
Thus, this paper investigates avenues for CO2 resource circularity within the ATR MM process design, considering multiple decision criteria through techno-economic and environmental assessments to establish informed decision-making on achieving greater sustainable operations within the MM industry.
Section snippets
Methodology
In our study, we assessed the economic and environmental performance of achieving resource-circular CO2 utilization within mega-methanol (MM) production. The modelling platform considers techno-economics and life cycle assessments, aligned to process design using Aspen Plus® V10 simulations. Guided by literature on validated process conditions [10,14], methanol production was simulated using the ATR technology coupled with: carbon capture and storage (CCS) and CO2 utilization (CCU) through CO2
Results and discussion
Our results, presented here, give insight into the overall performance of each scenario through the use of multiple decision criteria aligned to economic and environmental assessments. For each methanol production pathway investigated, process analysis was used to define set attributes which align to both economic and environmental performance. Subsequently, key performance indicators were highlighted using TAC and LCA methodologies; for which an overall sustainability analysis was carried out
Conclusions
Our study presents insights into achieving resource-circular CO2 operations within the MM process, through multiple decision criteria using techno-economics and environmental assessments. Examining current MM technologies, traditional ATR operations (BAU) were explored, alongside cleaner options such as CCS and CCU platforms employing various hydrogen supply chains governed by solar, wind and nuclear electrolysis as well as methane pyrolysis. Economically, the BAU process emerged as the most
CRediT authorship contribution statement
Johnathan Mahabir: Investigation, Writing - original draft, Writing - review & editing, Data curation. Keeara Bhagaloo: Investigation, Writing - original draft, Writing - review & editing, Data curation. Natalia Koylass: Writing - original draft, Data curation. Meethun Nathaniel Boodoo: Writing - original draft, Data curation. Rehannah Ali: Writing - original draft. Miao Guo: Validation, Writing - review & editing, Formal analysis. Keeran Ward: Supervision, Project administration, Validation,
Declaration of Competing Interest
The authors report no declarations of interest.
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These authors contributed equally to this work.