Life Cycle Assessment of CO₂-Based and Conventional Methanol Production Pathways in Thailand

Abstract

Methanol production through carbon capture and utilization technologies offers promising alternatives to traditional natural-gas-based methods, potentially mitigating climate change impacts and improving resource efficiency. This study evaluates four methanol production pathways: CO₂ hydrogenation, tri-reforming of methane, electrochemical CO₂ reduction, and co-electrolysis of CO₂ and water. The analysis covers 19 scenarios, combining three electricity mixes (100% Thai grid mix, 50% Thai grid mix and 50% renewable energy, and 100% renewable energy) with two hydrogen production technologies (alkaline water electrolysis and grey hydrogen). Environmental life cycle assessment results showed that most pathways perform well when using the 100% renewable energy with co-electrolysis (CE-100%) showing the most substantial reductions across all impact categories as compared conventional methanol production. Electrochemical reduction demonstrated the poorest environmental performance for all scenarios. In Thailand, implementing the CE-100% pathway could potentially yield 12.4 million tonnes of methanol annually from the cement industry’s CO₂ emissions, with an estimated value of approximately USD 5.4 billion, while reducing emissions from the industrial processes and product use (IPPU) sector by 75%. The findings provide valuable insights for policymakers, industry stakeholders, and researchers, supporting Thailand’s transition towards sustainable methanol production and broader climate goals.

1. Introduction

Fossil fuels, while currently dominant, are finite resources, and their diminishing availability has led to increased prices and economic instability in the global energy sector [1,2,3]. This scarcity not only threatens energy security but also worsens environmental concerns due to higher emissions from harder-to-reach fossil fuel reserves [4]. Compounding this issue, global energy consumption continues to rise, driven by population growth, industrialization, and improving living standards in developing countries. According to the latest OPEC World Oil Outlook, oil demand is expected to rise from approximately 97 million barrels per day (mb/d) in 2021 to around 110 mb/d by 2045 [5]. In light of these trends, the urgent need for renewable energy alternatives has become vital to address both environmental concerns and the growing energy demand [6,7].

Methanol, a versatile chemical compound, emerges as a potential solution to these energy security challenges. When produced through green pathways, methanol can serve as a carbon-neutral energy carrier and storage medium, offering a means to balance intermittent energy sources and provide a stable energy supply [8,9,10,11]. The global methanol industry is rapidly expanding, with around 90 plants producing 148 million tonnes annually as of 2019. Industry projections suggest that production capacity may increase significantly by 2030, potentially reaching 311 million tonnes per year [12]. Traditionally, methanol is produced from natural gas through a reforming process, which heavily relies on fossil fuels and contributes to greenhouse gas emissions [13,14].

As the world tackles the challenges of climate change and the need for sustainable development, alternative methods for producing methanol have gained significant attention [15]. Carbon capture and utilization (CCU) emerges as a promising approach to address these concerns [16,17,18]. By capturing carbon dioxide (CO₂) from industrial sources and utilizing it as a feedstock for methanol production, CCU not only reduces the dependence on fossil fuels but also offers a potential means of mitigating greenhouse gas emissions [19,20,21]. Carbon capture technologies, such as post-combustion capture, are integral to these pathways, enabling the extraction of CO₂ from flue gases emitted by power plants and industrial processes, which is then transformed into valuable products through CCU processes [22,23,24,25].

In the literature, several CO₂-based methanol production pathways have been explored, including CO₂ hydrogenation, tri-reforming of methane, electrochemical reduction of CO₂, and co-electrolysis. CO₂ hydrogenation involves the catalytic conversion of CO₂ and hydrogen (H₂) to methanol. This process typically employs copper-based catalysts and operates at elevated temperatures and pressures [26]. Tri-reforming of methane combines steam reforming, dry reforming, and partial oxidation of methane in the presence of CO₂ and oxygen, producing a syngas mixture suitable for methanol synthesis [12]. Electrochemical reduction of CO₂, on the other hand, utilizes renewable electricity to convert CO₂ directly to methanol in an electrochemical cell, offering the potential for a more sustainable and flexible production route [27].

Solid-oxide electrolysis (SOE) at high temperatures offers a promising solution for renewable energy storage and CO₂ conversion. This process co-electrolyzes water and CO₂ directly into syngas, achieving the desired H₂ to carbon monoxide ratio for downstream applications [28]. In comparison to low-temperature electrolysis technologies, SOE offers enhanced electrical efficiency and the capability for heat integration with subsequent synthesis processes, significantly improving overall system performance [29,30,31]. Originally proposed by the National Aeronautics and Space Administration (NASA) in the 1960s for oxygen supply and spacecraft propulsion, SOE was overlooked for many years due to inexpensive fossil fuels [32]. Nevertheless, increasing concerns regarding climate change and fossil fuel shortages have brought SOE back into focus in recent years [32].

However, to comprehensively evaluate the environmental implications of CO₂-based methanol production, conducting a life cycle assessment (LCA) that considers the entire production process, from raw material extraction to the final product, is essential [33]. LCA allows for the quantification of environmental impacts across various categories, such as global warming potential, acidification, and resource depletion, enabling a holistic comparison of different production pathways.

As a rapidly developing country with a growing chemical industry, Thailand has significant potential for implementing CO₂-based methanol production technologies [34]. To support the transition towards sustainable methanol production in Thailand, a thorough understanding of the environmental impacts associated with different production pathways is crucial. To date, life cycle assessment studies for methanol production have predominantly focused on comparing a single CO₂-based route with conventional methods, such as CO₂ hydrogenation versus steam methane reforming [13,35,36]. Recently, Rosental et al. (2020) conducted a life cycle assessment of CO₂-based production of methanol, olefins, and aromatics using CO₂ captured from industrial point sources and hydrogen derived from wind-powered electrolysis. The cradle-to-gate analysis demonstrated an 88–97% reduction in greenhouse gas (GHG) emissions compared to fossil-based production routes when wind power was employed. However, the study also noted increases in other environmental impacts, such as eutrophication and ozone depletion [35]. Similar results were reported by Hoppe et al. (2017), highlighting the potential of CO₂-based production to mitigate GHG emissions while highlighting trade-offs in resource use [33]. In addition, Win et al. (2023) explored methanol and formic acid production through CO₂ hydrogenation at a power plant. Their study found that CO₂-based methanol had higher environmental impacts in most categories compared to conventional production, while CO₂-based formic acid showed lower impacts in several categories. These studies collectively indicate that while CO₂-based processes offer substantial GHG reductions, they also present trade-offs in terms of resource use and other environmental impacts [13].

However, the rapid evolution of diverse and efficient pathways necessitates a more comprehensive sustainability evaluation. Although some studies have examined multiple methanol production routes, they have largely emphasized CO₂ utilization potential rather than CO₂ reduction potential [12,27]. This narrow focus leaves a critical gap in understanding the overall environmental impacts of emerging methanol production technologies. This study addresses these limitations by conducting Thailand’s first comparative LCA of four distinct CO₂-based methanol production technologies alongside the conventional route. By simultaneously evaluating multiple pathways, including scenarios utilizing wind energy as a renewable power source, this research offers a more nuanced and holistic perspective on the environmental implications of emerging methanol production methods, extending its relevance beyond Thailand. Furthermore, this study transcends the typical assessment of CO₂ reduction potential by identifying the most environmentally advantageous scenario and quantifying its CO₂ emissions reduction capability relative to traditional methanol production methods. This multifaceted approach yields invaluable insights into the comparative environmental performance of various methanol production technologies, thereby facilitating evidence-based decision making in the pursuit of more sustainable production practices. Ultimately, this comprehensive analysis contributes significantly to the body of literature surrounding sustainable methanol production, offering a robust foundation for future research and industrial applications. The objectives of this study are threefold. First, it aims to evaluate and compare the environmental impacts of four CO₂-based methanol production technologies, CO₂ hydrogenation, tri-reforming of methane, electrochemical reduction of CO₂, and solid-oxide electrolysis, with the conventional natural-gas-based methanol production method. Second, it seeks to assess the influence of different electricity sources, including renewable and Thailand’s grid mix, on the environmental performance of each CO₂-based methanol production pathway. Lastly, the study aims to examine the environmental impacts of different hydrogen production methods, specifically alkaline water electrolysis and conventional methods, within the CO₂ hydrogenation and tri-reforming pathways, to determine their contribution to the overall environmental footprint of methanol production.

By quantitatively assessing these production pathways, the study identifies the most environmentally advantageous route for methanol synthesis. The results provide critical insights into the feasibility and potential environmental impacts of implementing CO₂-based methanol production technologies in Thailand. This comprehensive analysis supports Thailand’s efforts in transitioning towards a low-carbon economy and achieving its climate goals.

2. Materials and Methods

This study employed a cradle-to-gate LCA approach following ISO 14040 and 14044 standards to ensure a rigorous and comprehensive evaluation of the environmental impacts associated with alternative and conventional methanol production [37,38].

2.1. Goal and Scope Definition

The study assesses the environmental sustainability of various methanol production routes in Thailand, focusing on CO₂-based and conventional pathways. The functional unit for this assessment is defined as one kilotonne (kt) of methanol produced. The system boundaries include all relevant stages, viz., raw material extraction, CO₂ capture, hydrogen production, and methanol synthesis.

For a comprehensive assessment, 19 scenarios (see

Table 1. Scenarios for methanol production pathways.

Scenarios	100% Renewable	50% Renewable + 50% Grid	100% Grid	Conventional Method
Hydrogenation with alkaline hydrogen	Scenario 1 (Hyd-Alk-100%)	Scenario 2 (Hyd-Alk-50%)	Scenario 3 (Hyd-Alk-Grid)	Scenario 19 (Conv-SMR)
Hydrogenation with grey hydrogen	Scenario 4 (Hyd-Grey-100%)	Scenario 5 (Hyd-Grey-50%)	Scenario 6 (Hyd-Grey-Grid)
Tri-reforming with alkaline hydrogen	Scenario 7 (Tri-Alk-100%)	Scenario 8 (Tri-Alk-50%)	Scenario 9 (Tri-Alk-Grid)
Tri-reforming with grey hydrogen	Scenario 10 (Tri-Grey-100%)	Scenario 11 (Tri-Grey-50%)	Scenario 12 (Tri-Grey-Grid)
Co-electrolysis	Scenario 13 (CE-100%)	Scenario 14 (CE-50%)	Scenario 15 (CE-Grid)
Electrochemical reduction	Scenario 16 (ER-100%)	Scenario 17 (ER-50%)	Scenario 18 (ER-Grid)

Note: Alkaline hydrogen represents hydrogen generated through water electrolysis using an alkaline electrolyte, whereas grey hydrogen represents hydrogen produced from natural gas via steam methane reforming. Hyd-Alk and Hyd-Grey refer to CO₂ hydrogenation using alkaline and grey hydrogen, respectively. Tri-Alk and Tri-Grey denote tri-reforming processes utilizing alkaline and grey hydrogen. CE stands for co-electrolysis, which generates both methanol and electricity, while ER indicates electrochemical reduction, producing methanol and hydrogen. Conv-SMR represents conventional steam methane reforming of natural gas to produce methanol, a process widely used in industry. The figure also categorizes energy sources as 100% renewable (entirely sourced from renewable energy), 50% (half renewable, half grid), and fully grid-based (relying entirely on the existing power grid).

) were developed by combining different methanol production routes, electricity mixes, and hydrogen production methods. The criteria for selecting these scenarios included: (1) inclusion of all major CO₂-based methanol production routes currently under research and development; (2) representation of varying degrees of renewable energy integration in electricity supply; (3) consideration of different hydrogen production methods for relevant pathways; and (4) inclusion of the conventional production method as a baseline for comparison. The routes assessed are CO₂ hydrogenation, tri-reforming of methane, direct electrochemical reduction of CO₂, co-electrolysis of CO₂ and H₂O in a solid-oxide electrolyzer, and the conventional natural gas reforming method. The study evaluates each production route under three distinct electricity generation scenarios: 100% Thai grid mix, a hybrid mix comprising 50% Thai grid and 50% additional renewable energy, and 100% renewable energy. For the hybrid scenario, it is assumed that half of the energy is generated by the plant itself from renewable sources, while the other half is purchased from the Thai grid mix. Additionally, the study explores hydrogenation and tri-reforming processes using two hydrogen production methods: alkaline water electrolysis and hydrogen (reformer), to identify the most environmentally sustainable methanol production route under different energy scenarios. A detailed description of all scenarios follows.

2.1.1. Route 1: Methanol Production from CO₂ Hydrogenation

This route covers the first six scenarios. Methanol production through CO₂ hydrogenation is a multistep process that begins with the capture of CO₂ from industrial sources, such as flue gas from cement plants. For hydrogen production, this case utilizes alkaline water electrolysis (AE), which was chosen for its technological maturity and lower capital cost compared to other electrolysis technologies [39]. The process employs a liquid alkaline electrolyte, commonly a 20–40 wt.% solution of potassium hydroxide, which can be highly corrosive and may lead to increased maintenance expenses [40].

AE systems are suitable for large-scale applications and can achieve stack efficiencies of up to 67% based on the lower heating value of the produced hydrogen [41]. These systems typically operate at temperatures ranging from 60 °C to 80 °C with electric current densities of approximately 0.2–0.4 A/cm² [42]. The overall energy consumption of the system, including both stack and peripheral components, falls within the range of 4.4−6.6 kWh per cubic meter of hydrogen produced. The resulting hydrogen gas purity exceeds 99.5%, and the operating pressure is typically maintained below 30 bar [42,43,44].

In the AE process, hydrogen is generated at the cathode, while oxygen is produced at the anode. The hydroxide ions (OH⁻) serve as the charge carriers, transporting charge from the cathode to the anode through the diaphragm separating the two electrodes. The hydrogen produced in the process is combined with captured carbon dioxide, and the resulting mixture undergoes compression and preheating to temperatures reaching 280 °C [45] (Figure 1). This heated and pressurized blend of CO₂ and H₂ is then introduced into a fixed-bed flow reactor containing a CuO/ZnO/Al₂O₃ catalyst, which is comparable to the catalyst employed in the well-established methanol synthesis process using syngas [13,19,35,45]. Within the reactor, the exothermic hydrogenation of CO₂ to methanol occurs according to the following reaction (Equation (1)):

CO₂ + 3H₂ → CH₃OH + H₂O

(1)

This reaction attains equilibrium alongside various side reactions, yielding methanol, water, and byproducts such as carbon monoxide and methane. The reactor effluent, which comprises methanol, water, unreacted gases, and byproducts, undergoes cooling to separate the liquid methanol and water from the gaseous components [45]. Subsequently, the methanol/water mixture is subjected to distillation to obtain pure methanol product, while the water can be recycled back to the electrolyzer to enhance overall efficiency.

2.1.2. Route 2: Tri-Reforming of Methane with CO₂ Utilization

Syngas production can be achieved through various methodologies; tri-reforming of methane (TRM) was selected for this study due to its superior thermodynamic efficiency and operational flexibility. TRM integrates steam reforming, partial oxidation, and CO₂ reforming in a single process, utilizing natural gas, steam, carbon dioxide, and oxygen as feedstocks (Figure 2). A key innovation in this implementation is the utilization of oxygen generated from water electrolysis, eliminating the need for an energy-intensive air separation unit. The TRM process offers precise control over the H₂/CO ratio in the produced syngas by modulating the steam and CO₂ input ratios, enabling optimization for downstream methanol synthesis [46,47]. Compared to dry reforming, which also involves CO₂ conversion, the presence of steam in TRM significantly reduces coke formation [48,49].

The primary reactor in the TRM system resembles an auto-thermal reformer and comprises three distinct reaction zones [50]. The initial zone is the burner, where the incoming feed combines within a turbulent diffusion flame. Next is the combustion zone, where a partial oxidation reaction (POX) takes place. Finally, there is the catalytic zone, where both steam reforming and dry reforming reactions occur. In this study, a commercial Ni/Al₂O₃ catalyst is utilized in the main reactor to facilitate the specified reactions [51,52,53]. To extend the operational lifespan of this type of reactor, the incoming natural gas must undergo feed preconditioning. This procedure usually involves desulfurization and prereforming processes. The unreacted gases and gaseous byproducts are also separated, recompressed, and recycled back to the reactor inlet to maximize CO₂ conversion and minimize the carbon footprint of the process. The utilization of recycling streams for both water and unreacted gases contributes to improving the efficiency and sustainability of the process, rendering it an attractive option for the production of this crucial chemical feedstock and fuel. In addition to alkaline hydrogen, grey hydrogen, which is produced from natural gas through a process called steam methane reforming, is also considered. This method is currently common and relatively inexpensive compared to AE technology.

During the desulfurization phase, hydrogen reacts with sulfur-containing compounds present in the feed, forming hydrogen sulfide, which is then removed from the primary process. This step prevents catalyst degradation in the main reactor, allowing for extended operation without the need for catalyst substitution [54]. In the prereforming stage, hydrocarbons with two or more carbon atoms are removed via reactions with steam, thus avoiding soot creation and accumulation within the main reactor. The prereformer utilizes the same nickel on alumina catalyst as the primary TRM reactor. The sources of hydrogen and methanol synthesis and purification steps are similar to the CO₂ hydrogenation pathway [55]. Heat integration is employed throughout the process to maximize energy efficiency [12]. This route includes scenarios 7 through 12: three scenarios with hydrogen generated from water electrolysis and three scenarios with grey hydrogen.

2.1.3. Route 3: Co-Electrolysis of CO₂ to Methanol

The methanol production process via co-electrolysis of CO₂ and H₂O in a solid-oxide electrolyzer (SOE) involves several key steps. Initially, CO₂ and H₂O are co-electrolyzed at 750 °C and 1.31 bar in an SOE, producing a syngas mixture of H₂, CO, and O₂ (Figure 3). The H₂-rich syngas is then compressed to 54 bars, cooled to 40 °C, and further compressed to 56 bars. In the methanol synthesis reactor, operating at 230 °C and 56 bar, the syngas is converted to methanol using a Cu/ZnO/Al₂O₃ catalyst [56,57,58]. The reaction mixture is subsequently cooled and separated, with the liquid phase containing crude methanol (91 wt%) depressurized to 4 bar and purified to 99.5 wt% in two distillation columns. This system effectively integrates heat from the exothermic methanol synthesis process, significantly enhancing overall efficiency. This route covers scenarios 13 through 15. The key chemical reactions involved in the process are as below (Equations (2)–(6)) [59,60,61,62,63]:

Electrolysis reactions:

H₂O + 2e²⁻ → H₂ + O²⁻

(2)

CO₂ + 2e²⁻ → CO + O²⁻

(3)

2O²⁻ → O₂ + 4e⁻

(4)

Methanol synthesis reactions:

CO + 2H₂ ↔ CH₃OH

(5)

CO₂ + 3H₂ ↔ CH₃OH + H₂O

(6)

2.1.4. Route 4: Direct Electrochemical Reduction of CO₂ to Methanol

The primary output is a methanol–water mixture, necessitating subsequent separation and purification to achieve commercial-grade methanol, commonly through energy-intensive distillation processes. A significant challenge in ER technology is the low methanol concentration in the cathode effluent, which necessitates extensive purification. Increasing the methanol yield at the electrolyzer output is critical for minimizing distillation energy requirements and improving the overall efficiency and economic viability of ER for industrial-scale methanol synthesis [27,64].

Concurrently, the competing hydrogen evolution reaction at the cathode produces hydrogen as a byproduct, where protons and electrons combine to form hydrogen gas (see Equations (7)–(10)). This side reaction can affect methanol yield and must be carefully managed through catalyst design and reaction conditions optimization (Figure 4). This route spans scenarios 16 through 18.

Cathodic reaction:

CO₂ + 6H⁺ + 6e⁻ ↔ CH₃OH + H₂O

(7)

2H⁺ + 2e⁻ ↔ H₂

(8)

Anodic reaction:

3H₂O ↔ 1.5O₂ + 6H⁺ + 6e⁻

(9)

Overall cell reaction:

CO₂ + 2H₂O ↔ CH₃OH + 1.5O₂

(10)

2.1.5. Route 5: Conventional Method

This route begins with syngas production, where methane from natural gas undergoes a reforming process with steam and/or oxygen at elevated temperatures (800–1000 °C) and pressures (20–30 bar) in the presence of a nickel catalyst (Figure 5). This process yields syngas, a mixture of H₂ and CO. The syngas is subsequently directed to the methanol synthesis phase, where it undergoes compression and is subjected to a reaction in the presence of a copper–zinc oxide catalyst.

This process takes place at temperatures spanning from 200 °C to 300 °C and pressures ranging between 50 and 100 bar, ultimately yielding methanol as the product. In cases where the syngas has an excess of hydrogen, carbon dioxide can be introduced to adjust the composition, ensuring optimal conditions for methanol synthesis [65,66,67]. This conventional route addresses scenario 19. The reaction equation for methanol production via natural gas reforming is as follows (see Equations (11) and (12)):

1st step: CH₄ + H₂O → CO + 3H₂

(11)

2nd step: CO + 2H₂ → CH₃OH

(12)

2.2. Source of Inputs and Allocation Method

Carbon capture is a critical step in the utilization of CO₂ as a feedstock for producing valuable chemicals. The selection of an appropriate carbon capture system depends on factors such as the CO₂ source, the composition of the flue gas, and the desired CO₂ purity and pressure [68,69,70]. The study focused on a cement plant as one of the primary sources of CO₂ emissions. This sector was chosen because it is a significant contributor to Thailand’s CO₂ emissions and is considered difficult to decarbonize due to its high carbon intensity [71].

An amine-based postcombustion capture system was considered for the cement plant. Amine-based capture is a mature and widely used technology that involves the absorption of CO₂ from the flue gas using an aqueous amine solution, typically monoethanolamine [72,73,74].

The process consists of two main steps: absorption and regeneration. In the absorption step, the flue gas is in contact with the amine solution in an absorption column, where CO₂ reacts with the amine to form a carbonate salt. The CO₂-rich amine solution is then sent to a regeneration column, where it is heated to release the captured CO₂ and regenerate the amine solution [75,76]. The regenerated amine solution is cooled and recycled back to the absorption column, while the concentrated CO₂ stream is compressed and purified for utilization or storage [77]. The CO₂ point source such as cement plant was considered a separate system, with the environmental burdens associated with CO₂ production and main products allocated to the cement plant. Two pathways for hydrogen production were considered: alkaline water electrolysis and grey hydrogen from natural gas reforming, as described in Section 2.1.1.

Figure 6 delineates various process pathways for CO₂-based methanol (MeOH) production, presenting 18 distinct scenarios with their respective reactants and avoided products. The left side specifies the reactants for each pathway. For example, the Hyd-Alk pathway utilizes hydrogen from alkaline water electrolysis and CO₂, while the Hyd-Grey pathway employs grey hydrogen from natural gas reforming and CO₂. Tri-reforming pathways incorporate methane, water vapor, and oxygen, combined with either alkaline (Tri-Alk) or grey hydrogen (Tri-Grey). Co-electrolysis pathways use water to simultaneously produce methanol and electricity, whereas electrochemical reduction pathways generate methanol and hydrogen from water. The right side of the figure elucidates the avoided products and associated CO₂ emissions reductions for each scenario. Brown boxes signify the avoidance of conventional methanol production and its CO₂ emissions, applicable to scenarios such as MeOH (Hyd-Alk-100%), MeOH (Hyd-Alk-50%), and MeOH (Hyd-Alk-Grid). Purple boxes represent the combined avoidance of conventional methanol production and coal-based electricity, pertinent to co-electrolysis scenarios like MeOH (CE-100%) + electricity. Grey boxes indicate the simultaneous avoidance of conventional methanol production and fossil-based hydrogen, observed in electrochemical reduction scenarios such as MeOH (ER-100%) + hydrogen. In each pathway, the product and co-product replace their conventional counterparts. Environmental credits are assigned to each pathway based on the amount and type of conventional products replaced.

Carbon capture credits were allocated across all scenarios to account for diverted CO₂ emissions. Scenarios 1 through 12 were assigned displacement credits for substituting conventional methanol production (Figure 6).

For scenarios 13 through 15, which involve co-electrolysis, credits were allocated for both methanol production and the displacement of coal-based electricity, reflecting the dual outputs of this process. Scenarios 16 through 18 received credits for methanol production and the substitution of grey hydrogen, acknowledging the environmental benefits of replacing carbon-intensive hydrogen production methods. In the life cycle assessment of Tri-Alk scenarios, a greenhouse gas reduction credit was incorporated, equivalent to the carbon intensity of electricity consumption by an air separation unit (ASU) for producing an equivalent oxygen quantity (245 kWh/tonne oxygen) [78]. This credit accounts for the avoided emissions from conventional oxygen production. Conversely, in Tri-Grey scenarios, this ASU-related credit was omitted to accurately reflect the carbon intensity of the process. These differentiated credit allocations enable a more nuanced and comprehensive evaluation of the environmental impacts across the various methanol production pathways.

2.3. Life Cycle Inventory (LCI) and Impact Categories

The LCI phase involves collecting data for all inputs and outputs associated with the methanol production pathways. Foreground inventory data were sourced from various studies in the literature. For hydrogenation (Table S1), data came from [36,79,80,81,82]. Table S1 also provides the inventory data for tri-reforming, sourced from [12,55,81,82]. Co-electrolysis data (Table S1) were derived from [83], while electrochemical reduction data came from [27,64]. The ecoinvent 3 database was predominantly used for background inventory data, including data for the conventional methanol production process. The collected data were analyzed using SimaPro 9.5 LCA software and the ReCiPe 2016 life cycle impact assessment method to calculate environmental impacts at both midpoint and endpoint levels [84]. The analysis primarily focused on two midpoint impact categories: global warming (human health) and global warming (terrestrial ecosystems). These categories were selected due to their relevance in evaluating the performance of CCU technologies, which aim to capture and utilize CO₂, thereby potentially reducing global warming impacts. To provide a more comprehensive assessment, an endpoint analysis was also conducted, evaluating three impact categories: human health (quantified in disability-adjusted life years, DALY), ecosystem quality (expressed in Potentially Disappeared Fraction of species.m².year (species.yr)), and resource scarcity (measured in USD2013). This comprehensive approach allowed for the assessment of environmental impacts at both specific (midpoint) and broader (endpoint) levels, providing a nuanced understanding of the product’s environmental performance across different impact dimensions. The analysis was conducted using the hierarchist perspective, a consensus model frequently used in scientific studies and considered the default model in ReCiPe 2016.

2.4. Net Reduction in Life Cycle CO₂ Emissions

To estimate the net benefit of avoided CO₂ emissions for the best-case scenario, the analysis includes CO₂ emissions such as those arising from fossil fuel combustion, land transformation, as well as those avoided from the cement production process. The methodology employs a comparative assessment of the total life cycle CO₂ emissions between conventional methanol production and an alternative CO₂-based methanol production pathway as illustrated in Figure 7. This method quantifies the net climate impact, providing a clear measure of the reduction in overall CO₂ emissions attributable to the alternative production method.

The study has a few limitations worth mentioning. First, it relies on data from various literature sources rather than primary data collection, which may introduce some uncertainties. However, it must also be noted that primary data collection would also have limitation of scope and representativeness. Second, the analysis is based on current technologies and does not account for potential technological improvements which may be considered in future research.

3. Results

3.1. Midpoint Impact Categories

The analysis of global warming impacts on human health (measured in DALY) across different methanol production technologies reveals significant insights into the effectiveness of various approaches and the impact of different electricity mixes and hydrogen sources (Figure 8). For the co-electrolysis process, CE-100% is the best-performing scenario, showing a substantial reduction in global warming impacts (−2 DALY), translating to a 420% decrease compared to conventional steam methane reforming (Conv-SMR). In contrast, CE-50% and CE-Grid show increased impacts (7.00 × 10⁻¹ DALY, 11% and 3.50 DALY, 443%, respectively), emphasizing the negative effects of relying on grid electricity predominantly sourced from fossil fuels.

In the CE-100% scenario, the major contributors to the reduction in global warming impacts on human health are carbon capture (−1.21 DALY) and the displacement of conventional methanol (−6.38 × 10⁻¹ DALY). Additionally, electricity replacement from coal significantly contributes to the reduction (−3.64 × 10⁻¹ DALY). Minor contributions to the impacts include electricity use (1.64 × 10⁻¹ DALY), water use (2.55 × 10⁻³ DALY), copper oxide (4.89 × 10⁻⁴ DALY), and zinc oxide (5.76 × 10⁻⁵ DALY). These factors collectively contribute to the overall impact reduction in the CE-100% scenario. High performance in co-electrolysis of CO₂ and H₂O in SOEs is achieved through optimal electrode materials, efficient heat integration, and maintaining appropriate operating temperatures and pressures [83].

In the hydrogenation process, Hyd-Alk-100% significantly reduces global warming impacts (−1.20 DALY, −290%) compared to the conventional steam methane reforming method. However, as the renewable mix decreases, impacts for alkaline hydrogen rise sharply, with Hyd-Alk-50% and Hyd-Alk-Grid showing increased impacts (2.30 DALY, 259% and 5.80 DALY, 810%) compared to Conv-SMR. On the other hand, grey hydrogen scenarios, such as Hyd-Grey-100% (3.00 × 10⁻¹ DALY, −46%), Hyd-Grey-50% (5.00 × 10⁻¹ DALY, −25%), and Hyd-Grey-Grid (6.00 × 10⁻¹ DALY, −4%), demonstrate lower impacts compared to their alkaline counterparts in similar conditions, and they are also better than the conventional method. This indicates that while both alkaline and grey hydrogen can reduce global warming impacts compared to Conv-SMR, grey hydrogen scenarios show relatively lower impacts when partial or full grid reliance is involved.

In the Hyd-Alk-100% scenario, global warming impacts on human health are significantly mitigated by carbon capture (−1.19 DALY) and the displacement of conventional methanol (−6.38 × 10⁻¹ DALY). Major contributors to global warming include hydrogen production via alkaline water electrolysis (2.08 × 10⁻¹ DALY) and methanol from CO₂-based sources (8.35 × 10⁻² DALY). Minor impacts come from materials such as copper oxide (1.42 × 10⁻¹ DALY) and heat from steam (1.71 × 10⁻¹ DALY). The factors contributing to optimal performance in hydrogenation include high thermal efficiency, efficient integration of heat pumps and access to low-carbon or renewable electricity sources, and a substantial CO₂ utilization rate compared to other pathways [12,13,19].

For tri-reforming, Tri-Alk-100% shows a significant reduction in impacts (−4.00 × 10⁻¹ DALY, −168%) compared to both Conv-SMR and Tri-Grey-100% (9.20 × 10⁻³ DALY, −99%). However, as the renewable energy mix decreases, the impacts for Tri-Alk-50% and Tri-Alk-Grid increase (7.00 × 10⁻¹ DALY, 2% and 1.70 DALY, 173%) compared to Conv-SMR. In contrast, Tri-Grey-50% and Tri-Grey-Grid have impacts of 1.74 × 10⁻¹ DALY (−83%) and 3.39 × 10⁻¹ DALY (−63%), respectively, showing better performance than the conventional method.

In the Tri-Alk-100% scenario, global warming impacts on human health are primarily alleviated by carbon capture (−3.30 × 10⁻¹ DALY) and the displacement of conventional methanol (−6.38 × 10⁻¹ DALY). Significant contributors include methanol production from CO₂-based sources (1.80 × 10⁻¹ DALY) and natural gas (2.83 × 10⁻¹ DALY). Minor impacts come from hydrogen production via alkaline water electrolysis (5.94 × 10⁻² DALY) and other materials like copper oxide and zinc oxide. The tri-reforming process performed well because it effectively integrates steam and CO₂ reforming, improving syngas quality and overall thermal efficiency [12].

The electrochemical reduction process demonstrates the poorest performance, with ER-Grid having the highest impact (1.04 × 10³ DALY). ER-100% and ER-50% also show severe impacts (1.01 × 10³ DALY and 1.03 × 10³ DALY, respectively), indicating the inefficiency and high environmental damage when using grid electricity heavily sourced from fossil fuels. ER is less efficient due to its significantly higher energy consumption (50.5 kWh/kg) compared to alternatives. It produces a very low methanol concentration (0.05% wt.), requiring extensive purification and high steam usage. The process lacks heat integration and has a lower technological readiness level, indicating it needs substantial development to become competitive [27].

An evaluation of global warming impacts on terrestrial ecosystems (measured in species.yr) across methanol production technologies unveils considerable differences attributable to varying electricity mixes and hydrogen sources (Figure 9). Within this context, CE-100% emerges as particularly effective, achieving a substantial impact reduction (−6.16 × 10⁻³ species.yr). This represents a 420% decrease compared to Conv-SMR. Conversely, CE-50% and CE-Grid exhibit increased impacts (2.14 × 10⁻³ species.yr, 11% and 1.05 × 10⁻² species.yr, 443%), indicating the negative influence of grid electricity predominantly sourced from fossil fuels. Similarly, in the hydrogenation process, Hyd-Alk-100% shows a substantial reduction in global warming impacts (−3.66 × 10⁻³species.yr, −290%) compared to Conv-SMR.

The major contributors to the reduction in global warming impacts for the CE-100% scenario include carbon capture, which accounts for a significant reduction of −3.65 × 10⁻³ species.yr. The shift from conventional methanol contributes −1.93 × 10⁻³ species.yr, and electricity replacement from coal adds another −1.10 × 10⁻³ species.yr. Smaller contributions come from electricity use (4.96 × 10⁻⁴ species.yr), copper oxide (1.48 × 10⁻⁶ species.yr), zinc oxide (1.74 × 10⁻⁷ species.yr), and water use (7.69 × 10⁻⁶ species.yr). These factors collectively result in a total net reduction of −6.16 × 10⁻³ species.yr for global warming impacts in terrestrial ecosystems.

For the Hyd-Alk-100% scenario, the main drivers for the reduction in global warming impacts (species.yr) are carbon capture (−3.60 × 10⁻³ species.yr) and the shift from conventional methanol (−1.93 × 10⁻³). Hydrogen production via alkaline water electrolysis (6.27 × 10⁻⁴ species.yr), copper oxide (4.29 × 10⁻⁴ species.yr), and heat from steam (5.15 × 10⁻⁴ species.yr) contribute positively but are outweighed by the larger reductions. Smaller contributions include methanol (CO₂-based) (2.52 × 10⁻⁴ species.yr), zinc oxide (1.90 × 10⁻⁵ species.yr), aluminum oxide (1.47 × 10⁻⁵ species.yr), and electricity (1.18 × 10⁻⁵ species.yr). These combined elements result in a total net reduction of −3.66 × 10⁻³ species.yr.

For tri-reforming, Tri-Alk-100% shows a significant reduction in impacts (−1.32 × 10⁻³ species.yr, −168%) compared to both Conv-SMR and Tri-Grey-100% (2.60 × 10⁻⁵ species.yr, −100%). However, as the renewable energy mix decreases, impacts rise for Tri-Alk-50% and Tri-Alk-Grid (1.97 × 10⁻³ species.yr, 2% and 5.26 × 10⁻³ species.yr, 173%) compared to Conv-SMR. In contrast, Tri-Grey−50% and Tri-Grey-Grid show reductions in impacts (5.24 × 10⁻⁴ species.yr, −73% and 1.02 × 10⁻³ species.yr, −47%), demonstrating better performance than both their alkaline counterparts and the conventional method. In the Tri-Alk-100% scenario, the most significant contributors to reducing global warming impacts (species.yr) are carbon capture (−9.94 × 10⁻⁴ species.yr) and the transition from conventional methanol (−1.93 × 10⁻³ species.yr). The use of CO₂-based methanol (5.43 × 10⁻⁴) and natural gas (8.56 × 10⁻⁴) adds to the impact but is offset by the larger reductions. Other contributions come from hydrogen produced via alkaline water electrolysis (1.79 × 10⁻⁴) and electricity (1.96 × 10⁻⁵). Smaller contributions are from materials such as copper oxide (6.70 × 10⁻⁸), zinc oxide (5.27 × 10⁻⁹), aluminum oxide (9.24 × 10⁻⁸), and nickel (1.43 × 10⁻⁷) (Table S2).

3.2. Endpoint Impact Categories

Figure 10 presents the human health impacts, measured in DALY, for various methanol production technologies. The data illustrate significant differences in health implications across production methods, influenced by the choice of electricity mix and hydrogen source. In different scenarios, CE-100% and Tri-Alk-100% exhibit the most substantial reductions in DALY, demonstrating decreases of −2.25 DALY (−322%) and −3.91 × 10⁻¹ DALY (−138%), respectively. These findings emphasize the critical role of utilizing 100% renewable energy sources to optimize environmental performance. Conversely, the electrochemical reduction scenarios consistently show the highest DALY impacts, regardless of the energy mix. The ER-Grid scenario, in particular, demonstrates a concerning increase to 1.27 × 10³ DALY compared to the conventional method. The ER-100% scenario shows an increase to 1.22 × 10³ DALY, and the ER-50% scenario indicates a rise to 1.25 × 10³ DALY. These results highlight the inefficiency and high environmental cost associated with this technology, indicating that ER is currently the least viable option for sustainable methanol production, primarily due to its high electricity consumption and low technological maturity. The impact of hydrogen technologies varies significantly with the energy source. Hydrogenation with alkaline hydrogen performs well with 100% renewable energy, showing a reduction of 7.17 × 10⁻¹ DALY (−29%). However, impacts increase drastically with grid reliance, reaching 1.14 × 10¹ DALY. In comparison, hydrogenation with grey hydrogen scenarios, although less effective with renewable energy (2.54 DALY, 150%) as compared to the alkaline pathway, demonstrate more resilience to grid reliance, with impacts ranging from 2.75 DALY (over 170% higher than the conventional method) to 2.95 DALY (191%). Tri-reforming with grey hydrogen also consistently reduces DALY impacts across all energy mixes, with reductions of 1.30 × 10⁻¹ DALY (−87%) for 100% renewable energy, 3.24 × 10⁻¹ DALY (−68%) for 50% renewable, and 5.18 × 10⁻¹ DALY (−49%) for grid reliance, outperforming Tri-Alk when partial or full grid reliance is involved. This suggests that while renewable pathways are ideal, grey hydrogen pathways offer lower impacts when grid electricity is used.

Figure 11 displays the ecosystem impacts, quantified in species.yr, for different methanol production technologies. The results demonstrate notable variations in environmental consequences, reflecting the effects of diverse electricity sources and hydrogen production methods. Among the scenarios, CE-100% and Tri-Alk-100% exhibit the most substantial reductions in species.yr, with CE-100% showing a significant decrease of −6.49 × 10⁻³ species.yr (−357%) and Tri-Alk-100% demonstrating a reduction of −1.30 × 10⁻³ species.yr (−151%), emphasizing the effectiveness of utilizing 100% renewable energy sources to minimize ecosystem impacts. Conversely, electrochemical reduction scenarios consistently show the highest impacts on ecosystems, with the ER-Grid scenario displaying a dramatic increase to 3.47 species.yr, markedly higher than the conventional method, indicating a stark increase in ecosystem impacts due to high electricity consumption and low efficiency associated with ER technology. ER-100% and ER-50% scenarios also exhibit similarly high impacts, with values of 3.35 and 3.41 species.yr, respectively. Hydrogenation technologies present varying impacts depending on the hydrogen source and energy mix. Hydrogenation with alkaline hydrogen performs well with 100% renewable energy, showing a reduction of 4.41 × 10⁻⁴ species.yr (−82%). However, ecosystem impacts increase significantly with grid reliance, reaching 2.71 × 10⁻² species.yr (975%).

In comparison, hydrogenation with grey hydrogen scenarios are more resilient to grid reliance, with impacts ranging from 6.09 × 10⁻³ species.yr (141%) to 7.12 × 10⁻³ species.yr (182%). Tri-reforming with grey hydrogen consistently reduces ecosystem impacts across all energy mixes, with reductions of 3.09 × 10⁻⁴ species.yr (−87%) for 100% renewable energy, 7.92 × 10⁻⁴ species.yr (−68%) for 50% renewable, and 1.27 × 10⁻³ species.yr (−49%) for grid reliance. These results indicate that grey hydrogen pathways are more robust and have lower impacts under grid electricity conditions compared to their alkaline counterparts.

Figure 12 shows the resource scarcity impacts, expressed in USD2013, associated with various methanol production technologies. The analysis reveals the economic implications of resource depletion, highlighting the influence of electricity mix and hydrogen source choices on long-term resource availability. Co-electrolysis and hydrogenation with alkaline hydrogen continue to demonstrate substantial reductions in resource costs. CE-100% achieves a notable decrease of −2.43 × 10⁵ USD2013, while Hyd-Alk-100% shows a reduction of −1.97 × 10⁵ USD2013 compared to the conventional method. These findings underscore the effectiveness of utilizing 100% renewable energy in minimizing resource scarcity impacts. Conversely, electrochemical reduction scenarios remain the most resource intensive, with the ER-Grid scenario seeing a dramatic increase to 1.37 × 10⁸ USD2013, significantly surpassing the conventional method. ER-100% and ER-50% scenarios also show considerable impacts, with values of 1.35 × 10⁸ USD2013 and 1.36 × 10⁸ USD2013, respectively.

Comparing alkaline and grey hydrogen technologies reveals further insights. For hydrogenation, Hyd-Alk is highly effective with 100% renewable energy, however, its impact rises with grid reliance, peaking at 3.58 × 10⁵ USD2013. Conversely, hydrogenation with grey hydrogen consistently shows reductions across all energy mixes: −8.93 × 10⁴ USD2013 for 100% renewable energy, −7.86 × 10⁴ USD2013 for 50% renewable, and −6.79 × 10⁴ USD2013 for grid reliance, indicating superior performance under less favorable energy conditions as compared to alkaline counterparts. Similarly, tri-reforming technologies display varied performance. Tri-reforming with alkaline hydrogen reduces impacts by −7 × 10⁴ USD2013 using 100% renewable energy but shows increased impacts under grid reliance, rising to 1 × 10⁵ USD2013.

In comparison, tri-reforming with grey hydrogen achieves reductions in resource scarcity across all energy mixes, with −3.92 × 10⁴ USD2013 for 100% renewable, −2.91 × 10⁴ USD2013 for 50% renewable, and −1.91 × 10⁴ USD2013 for grid reliance. These results indicate that grey hydrogen pathways generally offer a more balanced performance with lower resource scarcity impacts, particularly when grid electricity is used, compared to their alkaline counterparts.

In the literature, various studies have reported that CO₂ hydrogenation for methanol production outperforms conventional methods in terms of reducing greenhouse gas emissions [35,36,85]. This process has garnered significant attention as a promising strategy for mitigating climate change. However, a closer examination of endpoint impacts unveils a more complex pattern in its environmental performance. This divergence between midpoint and endpoint results necessitates a comprehensive analysis of various methanol production methods, including tri-reforming, co-electrolysis, and electrochemical reduction of CO₂.

Table 2. Advantages and disadvantages of the four alternative methanol production routes.

Technologies	Advantages	Disadvantages
Hydrogenation	Established process High product purity High CO2 reduction potential with renewable H2 Moderate energy requirements Environmental impacts depend on hydrogen source (better with renewable hydrogen)	Requires separate H2 source
Tri-reforming	High product purity Moderate CO2 reduction potential with renewable H2 Moderate energy requirements Syngas ratio can be adjusted Moderate environmental impacts (due to natural gas usage)	Emerging process Uses natural gas (fossil fuel) Requires separate H2 source
Co-electrolysis	High product purity High CO2 reduction potential with renewable energy Moderate energy requirements Does not require separate H2 source Low environmental impacts with 100% renewable energy	Emerging technology
Electrochemical reduction	In situ H2 generation Potential for high CO2 reduction	Low product purity Extensive purification needed Emerging technology Higher environmental impacts compared to other methods

presents a comparative analysis of the advantages and disadvantages for the four alternative methanol production routes considered.

The results demonstrate significant differences in environmental performance between hydrogenation and tri-reforming processes for methanol synthesis, primarily attributed to their respective energy and resource requirements. Hydrogenation, particularly when utilizing alkaline electrolysis (Hyd-Alk scenarios), exhibits high sensitivity to the electricity mix composition. While Hyd-Alk-100% shows substantial reductions in global warming potential at the midpoint level, its performance at the endpoint level is less favorable compared to Tri-Alk-100%. This discrepancy is attributed to the higher energy demands of the hydrogenation process. CO₂ hydrogenation necessitates approximately 0.21 kWh of electricity per kg of methanol produced [80]. Additionally, green hydrogen production via alkaline water electrolysis is energy-intensive, consuming 52 kWh per kg of hydrogen [81].

The elevated energy requirements of hydrogenation corroborate the findings of Win et al. (2023), who observed that CO₂-based methanol production resulted in higher environmental impacts across multiple categories due to its energy-intensive nature [13]. This elucidates why hydrogenation, despite its potential benefits in CO₂ utilization, can result in higher impacts for certain environmental indicators, particularly when considering endpoint categories. Conversely, tri-reforming exhibits superior overall environmental performance across various energy scenarios. Tri-Alk-100% demonstrates significant reductions in global warming potential for both human health and ecosystem endpoints. The enhanced performance of tri-reforming can be attributed to its lower resource and energy requirements. Tri-reforming integrates dry reforming of methane with steam reforming and partial oxidation, resulting in more efficient resource utilization. Notably, tri-reforming requires lower CO₂ and hydrogen inputs compared to hydrogenation, translating to reduced overall energy demands [12].

The CE-100% scenario emerges as the optimally performing option among all scenarios examined. This superior performance is attributed to multiple factors. Primarily, the co-electrolysis process requires lower energy input compared to the hydrogenation method (Table S1). Additionally, it eliminates the necessity for external hydrogen production, a significant energy-intensive step in alternative processes. While CO₂ utilization in co-electrolysis is comparable to the hydrogenation process, a key advantage is the generation of electricity as a co-product [13,83]. These factors synergistically contribute to the enhanced environmental performance of the CE-100% scenario.

The current performance of electrochemical reduction of CO₂ to methanol is suboptimal when compared to alternative methods due to several critical limitations. These include low methanol concentration (0.05% wt compared to the desired 40–67% wt), high energy demand (50.5 kWh/kg MeOH versus 0.21 kWh/kg in hydrogenation method), substantial steam consumption for purification (>10,000 MJ/kg versus 1.44 MJ/kg in hydrogenation method), and low technological readiness level [13,27,80]. Enhancing ER efficiency necessitates advancements in electrocatalyst design for improved selectivity and efficiency, reactor configuration and reaction condition optimization, integration of renewable energy and process heat, and Faradaic efficiency improvements coupled with reduced cell potential. Achieving a minimum methanol concentration of 40% wt at the reactor output is crucial for ER to become a competitive low-carbon solution for methanol production [27]. However, substantial research and development efforts are imperative to address these challenges and elevate ER to industrial viability.

3.3. Application of Best-Case Scenario

Thailand’s energy landscape is evolving rapidly, as outlined in the 2024 Power Development Plan [86]. While natural gas and coal dominated the electricity generation mix in 2020, their roles are set to diminish substantially by 2037. The plan projects a decrease in natural gas usage from 57% to 41% and coal from around 20% to 7%, while renewable energy is expected to surge to 51% of the total energy mix [86]. Carbon capture and utilization technologies for coal and natural gas plants may offer limited long-term benefits, as the energy sector increasingly shifts toward renewable sources. However, CCU remains crucial for hard-to-decarbonize industries such as cement production.

The cement industry in Thailand is a significant contributor to the country’s greenhouse gas emissions, with approximately more than 18 million tonnes of CO₂ emitted in 2019 [71]. This substantial carbon footprint presents both a challenge and an opportunity for innovative solutions in Thailand’s transition towards sustainability. The concept of CCU technology, specifically co-electrolysis, to convert these emissions into methanol offers an attractive pathway for emissions reduction and value creation.

While traditional methanol production relies heavily on fossil fuels and generates substantial life cycle CO₂ emissions, the CE-100% approach utilizes CO₂ from cement plants as a feedstock. This innovative method can avoid approximately 1.96 kt of CO₂ per kt of methanol produced. This approach addresses three critical environmental concerns simultaneously: it mitigates emissions from cement production and avoids the associated emissions from conventional methanol production and coal-based electricity generation. By repurposing industrial CO₂ emissions and decreasing reliance on fossil fuels, the CE-100% technology represents a significant step towards more sustainable industrial practices and circular economy principles.

Ideally, the full conversion of cement industry emissions could yield an impressive 12.4 million tonnes of methanol annually, while simultaneously reducing CO₂ emissions by approximately 24.3 million tonnes per year, equivalent to a 75% reduction of emissions from the industrial processes and product use (IPPU) sector. This methanol production capacity, however, far exceeds Thailand’s projected domestic demand of 800,000 tonnes by 2034 [87], potentially positioning the country as a significant methanol exporter. Methanol’s versatility as a fuel additive, chemical feedstock, and industrial solvent further enhances its appeal as a CCU product. The economic implications of such a transformation are also substantial with potential annual revenue reaching USD 5.4 billion (assuming a conservative methanol price of USD 440 per tonne) [88]; this approach could significantly impact Thailand’s trade balance, shifting the country from a methanol importer to a major exporter. However, the practical implementation of this ambitious plan faces considerable challenges. It would require extensive infrastructure development, including large-scale CO₂ capture facilities at cement plants, electrolysis plants for hydrogen production, methanol synthesis plants, and associated transportation and storage systems. The necessary technology investments are substantial, containing not only CCU-specific equipment but also significant upgrades to the power grid to accommodate the increased renewable energy capacity required to power the CE process.

Market dynamics present another crucial consideration. While Thailand’s domestic methanol demand is growing, absorbing the potential excess production would necessitate developing new international markets and competing with established methanol producers. This may also involve creating new domestic applications for methanol to increase local consumption. Regulatory support would play a vital role in making this vision a reality. Implementing carbon pricing mechanisms, providing subsidies or tax incentives for CCU and methanol production, mandating methanol blending in fuels, and streamlining permitting processes for new facilities would all be essential steps in creating a favorable environment for this transition. Despite these challenges, the potential benefits are compelling. This approach could lead to a significant reduction in industrial CO₂ emissions, create a new sustainable industry and export market, support Thailand’s transition to a low-carbon economy, generate jobs in CCU and related sectors, and reduce dependence on fossil fuel imports.

4. Conclusions

Carbon capture and utilization (CCU) for methanol production offers a promising solution to address greenhouse gas emissions and reduce fossil fuel dependence in the chemical sector. This research employed a comprehensive life cycle assessment to evaluate the environmental impacts of CO₂-based and conventional methanol production methods in Thailand, focusing on CCU technologies. Among the 19 evaluated pathways, co-electrolysis of CO₂ and water using solid-oxide electrolyzers demonstrated the most substantial environmental benefits, particularly under a 100% renewable energy scenario (CE-100%). This process showed the highest reductions across all impact categories compared to conventional steam methane reforming (Conv-SMR), attributed to its high electrical efficiency and effective heat integration.

CO₂ hydrogenation using hydrogen from alkaline water electrolysis (Hyd-Alk-100%) also showed significant benefits when powered by renewable energy, though its advantages diminish with grid electricity use. Tri-reforming of methane, especially Tri-Alk-100%, presented a balanced and robust performance across various scenarios. In contrast, electrochemical reduction of CO₂ consistently exhibited the worst environmental performance due to high energy consumption and poor methanol yield. Implementing CE-100% methanol production using CO₂ emissions from Thailand’s cement industry could potentially produce 12.4 million tonnes of methanol annually, valued at approximately USD 5.4 billion, while reducing CO₂ emissions by 24.3 million tonnes per year. This represents a 75% reduction in emissions from the industrial processes and product use (IPPU) sector. This study provides crucial insights for policymakers, industry stakeholders, and researchers, aiding Thailand’s transition to greener methanol production and advancing its climate change goals. Carbon capture and utilization for the production of bulk chemicals is an emerging field with significant potential. To make informed decisions, future research should incorporate economic assessments to identify cost-effective solutions for sustainable methanol production.