Methanol production has wide applications for electricity generation and hydrogen transportation. In addition, methanol has many applications including dimethyl carbonate and dimethyl ether production [1]. Recently, methanol production from syngas through catalytic Fischer-Tropsch synthesis, which is not fully carbon-neutral, has raised environmental concerns. Production of methanol from biomass generates many benefits such as sustainability and commercial viability [2]. Green methanol can be generated from different bio-based resources and clean technologies including gasification, reforming, stripper-off gas and power-to-liquid (Figure 1). On the other hand, biomethanol refers to green methanol produced from bio-based sources through bioprocesses with the involvement of microorganisms and enzymes. As shown in Figure 1, e-methanol represents green methanol which is produced from CO₂ capture as a byproduct of the electrolysis process to generate hydrogen. AlNouss et al. [3] developed the gasification of palm wastes for methanol production and investigated a techno-economic and environmental analysis. The focus of the study is CO₂ capture by deploying CaO to maximize methanol production and profit. It is widely acknowledged that fuels derived from biomass resources can reduce CO₂ emissions and partially replace fossil fuels. Regarding the economic aspect, the project life, methanol and dimethyl ether prices affected the economic feasibility of the biomass conversion process [4]. In consideration of the current energy consumption trends, efficient utilization of biomass resources has increased in both the industrial and academic sectors. Galusnyak et al. [5] examined a new membrane process design from secondary biomass for biomethanol production. As the results show, the utilization of exhausted olive pomace as a biomass source would enhance the detailed distribution of the global warming potential impact category.

Commonly, methanol, one of the ‘mega’ industrial platform chemicals, is produced from different feedstocks such as natural gas or coal. From Figure 2, the current worldwide methanol production capacity is 198 Mt/year, which is mostly employed for producing formaldehyde and plastics. Methanol is mainly produced from syngas (H₂ and CO) via steam reforming of natural gas as well as coal gasification. The coal-to-methanol process significantly increases the energy consumption and CO₂ emission to co-produce syngas and hydrogen ^[6][7]. The naval industry is also another fast-growing sector to consume methanol. Methanol production is predicted to follow the increasing trend up to 2050 since green methanol is attracting great interest as a sustainable energy carrier ^[7][6]. Chen et al. [8] proposed a novel hybrid process of coal gasification and coking to produce methanol. They investigated the effect of the coke gasification reaction and carbon tax on the integrated process economy. According to a detailed techno-economic analysis, the internal rate of return for coal gasification is 22.5% with more economic benefits in comparison with the coal-to-methanol process.

The conventional synthesis of methanol is based on the reforming of fossil sources, which has raised environmental issues due to greenhouse gas emissions. Hence, it is important to generate methanol from biomass feedstocks and thermochemical processes. Kasmuri et al. [9] investigated the production of methanol from renewable sources via a thermochemical reaction. The dynamic control system was employed to maintain a high yield of methanol production in pyrolysis.

2. Potential of Methanol as a Renewable Energy Carrier

2.1. Industrial Applications of Methanol

Methanol has a variety of industrial applications in chemical industries, such as supplementing fuel oil, acting as an antifreeze agent in pipelines, and being used as fuel cells. Moreover, methanol is the simplest organic liquid hydrogen carrier and acts as an energy storage system for a variety of portable power applications. In terms of the transportation sector, Table 1 makes a comparison of biodiesel and gasoline (hydrocarbon fuel) in terms of energy density and average octane numbers. Methanol shows a wide range of downstream applications such as the substrate for producing biodiesel through transesterification and organic solvents. As shown in Figure 3 methanol can be suggested as a promising substrate in various sectors such as the generation of fuel, chemicals and light olefins.

2.2. Techno-Economic Analysis of Methanol Production

Table 2 shows a list of some reported thermochemical and biological processes for methanol production. ] conducted a TEA on the hybrid steam reforming reaction, which involved the co-utilization of glycerol and natural gas to generate synthesis gas under reforming conditions. The resulting compressed synthesis gas was subsequently converted into green methanol, and the capital cost investment was assessed considering the overall equipment expenses. The study concludes that green methanol is not economically competitive with conventional methanol unless specific measures or corrections are implemented. In developing countries, producing green methanol as a new renewable energy source by using biomass feedstock leads to economic savings. As stated by Zhang et al. ^[13][17] methanol production via steam gasification of lignocellulosic biomass and biochar seems to be the most efficient raw material to produce methanol. The outcome of the techno-economic analysis (TEA) revealed that the internal rate of return obtained in the biochar scenario is higher than using pine biomass at the same plant scales. The authors concluded that methanol produced from waste biomass is unfortunately not commercially competitive with the traditional methods of producing methanol. The detailed distribution of total product costs affected by feedstock at different scales is displayed in Figure 4. Choe et al. ^[14][18] investigated the production of methanol by considering different landfill gas management pathways. TEA was performed to find out the most reliable process for methanol production from an economic perspective. It was proved that the operating expenditure reduction, particularly hydrogen cost and unit electricity price reduction, must be determined to be economically feasible. Table 3 represents current studies about techno-economic assessment for sustainable methanol production. Ramachandran et al. ^[15][1927] investigated biodiesel production from Jatropha oil for damage categories of climate change and ecosystem quality. The authors showed that the production process from Jatropha oil has fewer environmental side effects than that from the waste cooking oil process. Sills et al. ^[24][28] quantified the environmental performance of algal biofuels to estimate ranges of expected values of LCA metrics. The ranges of reported LCA impact categories showed that global warming potential values aligned with algal biofuel production together with anaerobic digestion are quite uncertain. Table 4 compares biochemical and thermochemical routes in terms of environmental impacts and economic indicators.

2.3. Lifecycle Assessment of Methanol

Biofuels are alternatives to fossil fuels and their environmental impacts over the entire production chain are evaluated by lifecycle assessment (LCA). The main objective is to analyze existing LCA studies and highlight key methodological approaches to critically evaluate existing biomass to biofuel pathways. Morales et al. ^[20][24] also investigated a consequential LCA of biofuel generation in Denmark considering two cases. The authors concluded that seaweed production was recognized as the most energy-sensitive processing part and the system has the potential for technological development. Mu et al. ^[21][25] evaluated a well-to-wheel LCA on algal biofuel production to identify key parameters that determine nutrient use. The authors revealed that most synthetic fertilizer inputs are eventually discharged within wastewater to the environment. LCA of macroalgae cultivation for producing biofuel was studied by Aitken and co-authors ^[22][26]. The investigation aims to identify energy conservation and environmental effects of the cultivation and processing of bioethanol production from marine macroalgae and biogas. As the authors point out, the impact of CO₂ emission reduction can be limited unless industrial-scale models are used. Sajid et al. ^[23][