Methanol as a Marine Fuel: Comparison
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Please note this is a comparison between Version 1 by Dimitrios Parris and Version 2 by Catherine Yang.

Methanol is efficient and cost-effective and excels over marine gasoil (MGO), especially in new ships. It is economically advantageous, with decreasing investment costs compared to liquefied natural gas (LNG)LNG, while providing flexibility without specialized pressure tanks. Global marine fuel trends prioritize fuel traits, accessibility, and environmental considerations, incorporating factors like policies, emissions, bunkering, and engine adaptability during transitions.

  • methanol
  • shipping
  • environmental protection
  • renewable energy
  • marine fuel

1. Introduction

Economic and demographic growth have emerged as pivotal drivers of the global energy demand, precipitating a substantial expansion in the international maritime trade and an upswing in the global fleet of ships [1]. The maritime industry shoulders the responsibility for transporting roughly 80–90% of the world’s trade [2], facilitating the movement of more than 10 billion tons of solid and liquid bulk cargo in containers every year across the planet’s oceans [3]. By the close of 2019, global trade had witnessed an 18% upswing in comparison to 2016 [4], a trajectory that is poised to result in a 50% escalation in the consumption of shipping fuel from 2012 to 2040 [5]. In this sector, fossil fuels, primarily Heavy Fuel Oil (HFO), maintain their dominance, notorious for their elevated sulfur content. Emissions stemming from a vessel operating on fuel with a sulfur content of 3.5% equate to the emissions generated by a staggering 210,000 trucks [6]. The year 2018 witnessed global shipping being accountable for over one million tons of greenhouse gases (GHG) and carbon dioxide (CO2) emissions, signifying a 9.6% and 9.3% expansion compared to levels recorded in 2012, respectively [7]. Additionally, as indicated by the United Nations, the collective greenhouse gas emissions from the global fleet experienced a 4.7% increase in 2022. Concurrently, data from the United Nations revealed that in April 2022, carbon dioxide (CO2) emissions amounted to 847 million tons, reflecting a noteworthy 23% escalation over the preceding 10 years [2]. Consequently, the maritime sector’s contribution to global anthropogenic emissions has ascended to 3,0% [8]. Disturbingly, nearly 70% of ship emissions occur within 400 km of coastlines [9][10], posing a significant hazard to the global environment and human well-being, attributable to the discharge of GHGs [11], carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), sulfur oxides (SOx) [12][13][14], nitrogen oxides (NOx) [13][14][15], and particulate matter (PM) [13][14][16][17][18][19]. The International Maritime Organization (IMO), during its third GHG study in 2014, forecasted that the growth in global trade could lead to a surge in shipping emissions ranging from 50% to 250% by 2050 [20]. Furthermore, they projected that shipping transport would be responsible for approximately 15% of global CO2 emissions during the same period [18].
This emissions scenario within the maritime transport sector poses a severe challenge to vital global emission reduction commitments, including the Paris Agreement and the Kyoto Protocol. Consequently, the IMO and the entire shipping industry play a pivotal role in mitigating their emissions. The IMO has introduced and proposed more stringent regulations for vessel operators and owners in the maritime sector to confront these challenges [18][21].

2. Methanol as a Marine Fuel

There is a growing interest in utilizing methanol as an alternative fuel within the maritime industry, primarily spurred by increasingly stringent emission regulations. The International Maritime Organization (IMO), has implemented Tier 3 NOX emission regulations for ocean-going vessels, particularly in Emission Control Areas (ECAs), encompassing densely populated coastal zones. Concurrently, there is a reduction in the permissible sulfur content of marine fuels. To meet these more demanding regulations, diverse technologies have been introduced, including those facilitating the continued use of heavy fuel oils (HFO), such as aftertreatment systems. In addition, alternative fuels are gaining traction, with initial emphasis on liquefied natural gas (LNG). However, integrating a liquefied gas storage system, significantly impacts ship design or retrofitting. Methanol, being in liquid form at atmospheric conditions, is often deemed a more manageable fuel for various applications. It is also produced from natural gas. According to a recent technical report from the EU’s Joint Research Center, LNG and methanol stand out as the most promising alternative fuels for shipping currently, partially owing to methanol’s widespread availability in most major ports [22]. Methanol’s viability as a marine fuel is tied to its safety features, its superior emissions profile compared to bunker fuel or heavy fuel oils commonly used by large ships, and its complete miscibility in water. This miscibility allows existing vessels with double hulls to be modified for methanol storage, unlike hydrocarbons that necessitate double hulls due to their inability to mix with water. The infinite miscibility of methanol enables its storage in these voids, as any tank breach would result in the fuel dissolving. A study conducted by Malcolm Pirnie Inc. (Verbena, AL, USA) [23] determined that in the event of a methanol spill, rapid dilution occurs, preventing the attainment of dangerous concentrations. The swift dilution is further attributed to methanol’s lethal concentrations (for marine life), which are 240 times higher than diesel and 1900 times higher than gasoline. Consequently, the likelihood of reaching such concentrations is deemed highly improbable. In general, these large marine engines operate as dual-fuel diesel engines, directly comparable to dual-fuel marine engines designed for liquefied natural gas (LNG) applications, such as those found in LNG tankers. However, methanol presents distinct safety advantages over LNG due to its liquid form. Despite having a (net) volumetric Lower Heating Value (LHV), approximately 23% lower than LNG (15.9 vs. 20.5 MJ/L), methanol offers easier storage on vessels without the complexities associated with cryogenic gas storage. An important safety aspect is the considerably lower flash point of methanol compared to LNG. In fact, the flammability index of methanol, is much more akin to that of diesel. In the event of a pool fire, methanol proves significantly safer than both gases and liquid hydrocarbons [24][25][26]. According to Oloruntobi et al. (2023) [26], a rising trend in the maritime field involves the adoption of liquid low-flashpoint fuels such as methanol, for marine engines. As indicated by Ampah et al. (2021) [18], MAN’s ME-LGI system, initially integrated into Dual Fuel (DF) engines for methanol combustion in various vessels, employs high-pressure pumping and functions with a low fuel supply pressure, but it is limited within the injector [27]. Methanol represents a liquid fuel characterized by a low flashpoint, an absence of sulfur content, and ease of storage. Furthermore, it generates reduced emissions, and boasts a smaller carbon footprint when compared to traditional marine fuels. Methanol is a viable option for marine propulsion, with at least one dual-fuel marine engine available in the market that has the capability to utilize methanol [28]. As supported by research, methanol stands out as the “optimal alternative fuel” due to its “rapid availability”, utilization of existing infrastructure, cost-effectiveness, and the simplicity of both engine design and maritime technology [29]. As of now, there are 11 operational methanol-powered ships [30]. In contrast to heavy fuel oil or marine gasoline oil, the combustion of methanol in marine engines results in only a marginal reduction in carbon dioxide emissions, but significantly lowers emissions of other pollutants [31]. Methanol has the potential to be distributed to significant port terminals globally, thanks to its extensive worldwide production network. Investigating the possible applications of methanol as a marine fuel in the short, medium, and long term is a valuable pursuit given the consistent availability and broad distribution of methanol [32]. Methyl alcohol, characterized as a clear, easily flammable organic compound devoid of impurities in suspension, exhibits water miscibility at any rate. Conforming to Machiele (1987) [24][26], when not addressed, fatal quantities typically fall within the range of 1 to 2 milliliters per kilogram of body weight. This equates to 60–240 milliliters for individuals within a typical weight range. In contrast, Yaman et al. (2024) [33] support that even minimal methanol quantities prove toxic to living organisms, with a lethal dose ranging from 11.5 g to 160 g. [34]. According to Tian et al. (2022) [35], exposure to a methanol concentration between 3.913 × 103 and 6.515 × 103 g/m3 for 30–60 min poses a significant danger, surpassing the Chinese occupational health standard PC-STEL [36] of 50 mg/m3 by 768–1310 times. Notably, in the aftermath of a methanol leak, emergency repairs were carried out without protective measures, resulting in symptoms like headaches, dizziness, and fainting emerging two hours later. Furthermore, prolonged exposure to a methanol environment, ranging from 1.2 × 103 to 8.3 × 103 ppm (equivalent to 1.56 × 103–1.079 × 104 mg/m3) has been reported to cause visual impairment [35][37][38]. Methanol, widely recognized as CH3OH and commonly denoted as MeOH [39], plays a pivotal role in the chemical and pharmaceutical sectors [40] as well as in the synthesis of artificial hydrocarbons. It is noted that global methanol production has reached approximately 90 million tons per year, with approximately 65% originating from natural gas through steam methane reforming and the remaining 35% derived from coal via gasification procedures [41][42][43]. This versatile compound is acknowledged as a sustainable and eco-friendly energy source, with significant potential for reducing emissions in internal combustion engines [38][44]. In the context of maritime applications, methanol bears similarities to LNG, with the advantage of it being in liquid form at a standard temperature and pressure, making it more manageable [45][46]. As reported by Tian et al. (2022) [35], vaporizing methanol poses challenges, but its ability to be stored in plastic containers adds convenience to transportation, filling, storage, and utilization. In any case, the findings of a 2015 study, executed by Ellis and Tanneberger, suggest that methanol holds an edge over LNG when it comes to onboard containment because of its liquid form. However, incorporating it into marine fuel systems demands modifications to existing setups and an infrastructure upgrade to facilitate regular bunkering [27][47]. Additionally, due to its non-static nature, methanol easily dissolves in water and can be extinguished using water in the event of a fire [38]. Methanol’s appeal as an alternative fuel stems from its clean-burning qualities, characterized by the absence of sulfur and carbon-to-carbon bonds. This trait contributes to a reduction in SOx and PM emissions, while its lower adiabatic flame temperature has the potential to restrict NOx formation during combustion, as highlighted by Glaude et al. (2010) [47]. Aabo (2020) [48] and Korberg et al. (2021) [49] underscore findings from MAN Energy Solutions research, indicating that the introduction of water to methanol can effectively control NOx formation in combustion [49][50]. This outcome enables the engine to comply with Tier III NOx regulations, negating the need for Selective Catalytic Reduction (SCR) or Exhaust Gas Recirculation (EGR) systems [27]. It has demonstrated the potential for lower emissions of sulfur oxides (SOx), nitrogen oxides (NOx), and particulate matter (PM) in marine engines, further underscoring its environmental advantages. For instance, NOx emissions were significantly reduced when using methanol as fuel compared to marine gas oil (MGO) [51]. Moreover, PM, SOx, and carbon dioxide (CO2) emissions were substantially lower with methanol use, making it compliant with Emission Control Area regulations [18]. However, it is important to note that greenhouse gas (GHG) emissions from non-renewable methanol sourced from natural gas are slightly higher than those from heavy fuel oil (HFO) and marine diesel oil (MDO) [46]. Conversely, the utilization of renewable methanol derived from biomass feedstock can lead to a GHG impact approximately 56% lower than HFO [18][51]. As reported by the Methanol Institute (2023) [52], compared to conventional fuels, the use of renewable methanol leads to a remarkable reduction in carbon dioxide emissions by as much as 95%, significantly lowers nitrogen oxide emissions by up to 80%, and completely eliminates emissions of sulfur oxide and particulate matter [53]. Methanol as a fuel offers notable advantages in terms of economy, safety, environmental friendliness, reliability, and versatility, positioning it as an excellent alternative to conventional internal combustion (IC) engines for energy needs [44]. In comparison to traditional gasoline and diesel fuels, methanol fuel, with its single carbon atom composition, is less prone to soot formation post-combustion. Owing to its elevated oxygen content, methanol proves well-suited for lean combustion, leading to a reduction in cylinder combustion temperatures, thereby impeding the generation of NOx. If methods can be devised to enable the compression ignition of methanol in diesel engines, the potential elimination of the need for diesel particulate filters (DPF) and selective catalytic reduction (SCR) becomes feasible. This, in turn, would curtail operational costs and exhaust emissions, thereby fostering the global IC engine industry’s progression towards low carbon and environmental sustainability [38][44]. Reviewing the literature that explores the application of methanol in diesel engines [54], the analyses regarding how methanol’s application leads to a decrease in particulate matter (PM) emissions can be classified into three distinct categories: (1) Methanol’s lower carbon fraction helps prevent the generation of aromatics, thereby minimizing soot formation [55][56]. (2) The presence of the -OH group and the low cetane number of methanol result in an extended ignition delay [57][58], fostering greater premixed fuel vaporization and consequently reducing local rich combustion zones, ultimately lowering soot formation [54][59]. (3) The oxygenated nature of methanol provides an additional oxygen supply, facilitating combustion promotion [57] and carbon oxidation [60][61]. According to Wang et al. (2023) [62], methanol as a Liquid Hydrogen Carrier (LHC) can be transported using standard methods, without requiring compression or cryogenic conversion, utilizing existing energy infrastructure. Upon reaching the delivery sites, hydrogen (H2) is extracted from these carriers for utilization. The liquid carriers are subsequently recycled and ready for another delivery [53]. Additionally, certain characteristics specific to methanol, could enhance its practicality. For instance, methanol has the potential to directly fuel a fuel cell, resulting in CO2 production that is comparatively easier to capture and store [63][64]. Several demonstration projects have been actively exploring the implementation of methanol as a fuel for shipping, with two prominent examples being the conversion of the Stena Germanica 1500 passenger ferry which occurred in 2015 [65][66], and the operation of Waterfront Shipping’s 50,000 deadweight tonnage methanol tanker vessels [67]. These initiatives involve the practical use of methanol in these vessels [26]. Ampah et al. (2021) [18] agree with this, stating that over the last two decades, various projects have explored methanol utilization in marine vessels; among others, they included the METHAPU project from 2006 to 2009 [51], the SUMMETH project in 2018 [47][68], and the launch of the world’s first methanol-powered ferry, the Stena Germanica, by Stena Line in 2015 [22]. By 2018, seven methanol-fueled vessels were operational worldwide [69]. Xing et al. (2021) recommend considering methanol as a potential energy source for marine fuel cells, even in the absence of established international maritime regulations for fuel cell power systems [68]. Additionally, Ni et al. (2020) suggest using methanol in waste heat recovery systems, offering potential fuel savings of up to 9% [18][70]. For the Stena Germanica project, Wärtsilä enhanced medium-speed four-stroke marine diesel engines with specialized injectors, enabling the separate direct injection of methanol and pilot fuel (marine gasoil, MGO). In the case of the Waterfront Shipping tankers, MAN low-speed two-stroke engines are utilized, featuring a separate direct injection system for methanol and pilot fuel (MGO or HFO). However, detailed measurement data for these engines are currently limited, with only a few results provided by the manufacturers. Despite the limited data, the available information suggests that the engines comply with emission regulations and exhibit efficiencies comparable to those achieved with diesel fuel [26].

2.1. Use of Methanol in Diesel Engines

However, the majority of internal combustion engines have used methanol as an additional fuel and not as the main fuel, until this moment. Diesel engines are widely recognized for their attributes such as high thermal efficiency, substantial torque, low pollution emissions, and high reliability, making them prevalent in both commercial and passenger vehicles. The utilization of methanol fuel in diesel engines is particularly meaningful for reducing diesel consumption and curbing pollutant emissions. Presently, the primary approaches to integrate methanol fuel into diesel engines involve direct mixing, port injection, and in-cylinder direct injection, as detailed in reference [38][71].

2.2. Blending Diesel and Methanol Directly

The direct mixing method combines methanol and diesel, but requires costly co-solvents due to their incompatible properties. Conversely, Methanol-to-Diesel (MTD), synthesized from methanol, is a liquid mixture blended with diesel. Guo et al.’s study [71] found that a 20–30% MTD blend with diesel, showed comparable power but a 14% increase in fuel consumption and significantly reduced exhaust emissions, establishing MTD as a cost-effective, environmentally friendly diesel additive. Soni and Gupta (2021) [72] and Soni and Gupta (2021) [73] found that increasing methanol in diesel from 10% to 30 significantly reduced NO, CO, and HC emissions by 65%, 68%, and 56%, respectively. They also advocated for adding water to the fuel to further decrease emissions [72][73]. In experiments by Jamrozik, up to 30% methanol positively affected the engine thermal efficiency without significant IMEP changes. However, exceeding 30% resulted in reduced CO emissions, but caused significant CO2 and THC emission changes, alongside a notable drop in cylinder pressure, leading to engine instability [74]. Huang (2004) [75] demonstrated that higher methanol fractions enhance combustion characteristics, such as engine thermal increases and BSFC decreases with greater oxygen or methanol fractions. CO and smog in exhaust gas are substantially reduced, but NOx increases, particularly at high loads. The NOx–soot balance curve remains relatively flat during diesel–methanol mixed fuel operations [75]. Despite direct application benefits, challenges persist due to methanol and diesel immiscibility, requiring costly co-solvents. Blending ratios are limited due to cold start issues and oil separation, restricting the full potential of methanol fuel in direct mixing methods [38][76][77][78][79].

2.3. Methanol Injection through the Port, Coupled with Direct Injection of Diesel

In the port injection method, methanol is injected into the intake port during the intake process, forming a combustible mixture with fresh air. Diesel is then directly injected into the cylinder near the top dead center, leading to the ignition of the methanol/air mixture through the spontaneous combustion of diesel. However, the considerable latent heat released during methanol evaporation, when sprayed into the inlet, absorbs a substantial amount of heat, resulting in a significant reduction in the inlet temperature. This phenomenon can pose challenges such as engine cold start difficulties or idle misfires [80]. To overcome this issue, Professor Yao from Tianjin University introduced the diesel/methanol combined combustion (DMCC) concept. Under the DMCC system, diesel engines operate in two combustion modes: diesel diffusion combustion and diesel pilot air/methanol mixed combustion. Pure diesel combustion is employed during an idling speed and low load, while the DMCC combustion mode is activated when the engine load, cooling water temperature, and engine speed meet the specified values [81]. According to Yao et al. (2008) [82], DMCC combustion in a direct-injection diesel engine reduces soot and NOx emissions, but increases HC and CO emissions, compared to the original diesel engine. Combining DMCC with an oxidation catalyst mitigates CO, HC, NOx, and soot emissions [82]. Cheng et al.’s study on methanol fumigation revealed that increasing fumigated methanol decreases the brake thermal efficiency (BTE) at low loads, but increases it at high loads. Methanol fumigation increases HC, CO, and NO2 emissions but reduces the NOx concentration, smoke opacity, and particulate matter mass concentration. Combining fumigated methanol with a diesel oxidation catalyst, reduces CO, HC, NO2, particulate matter mass, and numbers [54]. Geng et al. (2014) [83] observed that, under low and medium loads, DMDF combustion significantly reduces dry soot emissions before the diesel oxidation catalyst (DOC), with a slight increase under high loads. DOC significantly reduces the particulate matter mass and number concentration under all engine loads. An increased methanol injection decreases the intake air temperature, leading to a lower particulate matter mass and number concentration in the DMDF mode [83]. Wei et al. (2015), found that a high premixed ratio of methanol (PRm) in a dual-fuel diesel engine leads to prolonged ignition delay, shortened combustion duration and altered emissions, disrupting the traditional NOx-soot trade-off [84]. Diesel oxidation catalyst (DOC) application post-PRm combustion effectively reduces HC, CO, and formaldehyde emissions. Liu et al. (2015) observed that in the Dual Fuel-Diesel Methanol Fumigation (DMDF) mode, a low injection pressure yields a lower indicated mean effective pressure (IMEP) than pure diesel combustion [81]. Higher injection pressures in the DMDF mode enhance combustion characteristics and reduce brake-specific fuel consumption (BSFC), with NOx and smoke emissions lowered, but HC, CO, and NO2 emissions increased compared to pure diesel combustion. The port injection of methanol is favored over direct mixing for its flexibility in controlling methanol ratios, achieving higher substitution rates, and improving fuel economy and emissions [38][81][84].

2.4. Injecting Methanol and Diesel Directly

In agreement with the literature review, both methanol and diesel utilize in-cylinder direct injection, enhancing the replacement rate to improve fuel efficiency and decrease emissions, thereby expanding methanol’s usage in compression ignition engines [38][85]. In a heavy-duty diesel engine, separate injections of diesel and methanol effectively overcome the NOx-soot trade-off, showcasing the successful integration of methanol into high-pressure diesel injection systems [85]. Research by Jia and Denbratt (2018) indicates that a direct methanol injection efficiently reduces total hydrocarbon (THC) and CO emissions in a heavy-duty diesel/methanol engine [86]. Two primary in-cylinder direct injection approaches involve adding a separate fuel injection system for methanol in larger engines or using a single injector for both fuels, addressing spatial constraints, but presenting developmental challenges [87][88][89].

3. E-Methanol’s Production and Infrastructure

Methanol is traditionally derived from natural gas and coal, yet diverse sources like wood, agricultural and domestic wastes, renewable sources, and even CO2 are recognized as viable alternatives [46][89][90][91][92][69][110][111][112][113]. However, the use of fossil fuels results in pollution and CO2 emissions, hindering efforts to combat global climate change and build a sustainable, low-carbon society [38][63]. Therefore, the practical importance of advancing renewable alternative fuels is crucial. CO2 utilization for methanol synthesis not only mitigates the greenhouse effect but also produces various chemical products and clean fuels. This innovative approach, highlighted by Nguyen and Zondervan (2019) and Battaglia et al. (2021) [63][114][115], achieves multiple goals simultaneously. However, methanol production from coal or coke oven gas poses environmental challenges, generating wastewater, waste gas, and substantial CO2 emissions. The technology for CO2 hydrogenation to methanol involves heterogeneous catalysts, facilitating a reduction reaction using CO2 and H2—commonly known as direct hydrogenation. Despite evolving from the CO hydrogenation process and some industrial development, direct hydrogenation has drawbacks like harsh conditions and low methanol selectivity. To address this, researchers have introduced a homogeneous catalyst based on the direct hydrogenation method to enhance the efficiency of CO2 hydrogenation to methanol.

3.1. Methanol’s Infrastructure

Methanol's chemical prominence stems from a substantial global production of around 70 million metric tons in 2015, with a capacity of approximately 110 million metric tons [52][52][75]. It plays a vital role in the petrochemical industry, contributing to the synthesis of various chemicals and materials [25][93][94][52][136][141]. China leads methanol production, meeting half of its road transport fuel needs, while the U.S. doubled its production in 2015, surpassing China as the leading low-cost producer due to shale rock gas [52][94][95][52][141][142].

Compared to traditional oil refining, a modern methanol facility can produce around 20,000 barrels per day, showcasing its significance. Despite higher specific fuel consumption, methanol remains cost-effective compared to MGO, even with a higher crude price than LNG [92][92][96][113][22][143]. Although 38.6% cheaper per metric ton than diesel, annual fuel costs rise by 28.16%, necessitating a 28% reduction in ship speed to maintain consistent fuel costs [92][97][43][113].

In new ship construction, methanol propulsion systems offer economic advantages with lower investment costs than LNG, expected to decrease with growing experience [12][46][89][12][69][110]. Andersson, Lundgren, and Marklund (2014) demonstrated an 11–18 EUR/MWh cost reduction and a 7% increase in plant efficiency through integration with existing industries [98][144].

3.1.1. Substantial Ships Engaged in Global Commerce

Global acceptance of marine fuels for trading ships necessitates an extensive bunkering network. Adaptations for alternative fuels like methanol and LNG are needed, with LNG requiring specialized storage and fuel systems. Methanol, due to its liquid state, requires fewer modifications and utilizes well-established technology components in the maritime industry. Its flexibility in storage, with existing tanks easily adapted, makes it a practical choice [76][97]. This is in contrast to conventional oil and gaseous fuels, which pose challenges for volume-critical ships [89][99][110,145].

The importance of bunkering facilities is emphasized for LNG, and uncertainties about long-term fuel availability act as obstacles to new fuel adoption [96][100][143,146]. The significant fuel demands of large container ships highlight the need for substantial capacities [101][147].

Considering methanol as a fuel, particularly from fossil feedstock, is globally accessible, providing an interim solution until renewable methanol production scales up [89][102][110,148]. Existing infrastructure for methanol storage and distribution in chemical industries can be adapted for marine fuel with minor adjustments, making its development a relatively minor obstacle compared to some alternative fuels [46][89][102][69,110,148].

3.1.2. Ships Involved in Short-Distance, Coastal, and Domestic Trade

In smaller vessels navigating confined areas like short sea shipping, bunkering opportunities are limited. Skold and Styhre (2017) highlight that conventional oil bunker fuel provision in Sweden is primarily handled by a few major companies [103][150]. For vessels like ferries operating between two ports, bunkering services typically occur at one port, exemplified by the Stena Germanica ferry bunkering methanol in Gothenburg every four to six days [104][151].

Bunkering operations, whether offshore, at anchor, or alongside, involve fuel transfer from sources like road tankers or bunker barges [105][152]. Despite diverse providers, the procedural steps remain consistent, with bunkering being a high-risk activity due to potential pollution, financial penalties, or imprisonment. In the absence of dedicated bunker barges for methanol, converting an existing one is cost-effective at EUR 1.5 million [102][148]. In Sweden, smaller vessels like road ferries are bunkered by trucks using existing transportation systems for methanol [106][153].

3.1.3. The Availability of Fuel and the Competition from Other Consumers

Ship owners, as highlighted by Svanberg et al. (2018), demand assurance on long-term fuel availability before committing to a switch, factoring in investments in adapting fuel systems and engines [89][110]. Careful evaluation, considering factors like fuel availability, cost, and adherence to environmental mandates, is essential when retrofitting vessels for alternative fuels [107][154].

Transitioning to environmentally superior fuels, like methanol, involves considerations such as environmental policies, customer expectations, and corporate branding. Compliance with emissions reduction regulations requires evaluating bunkering processes, infrastructure adequacy, modification costs, potential cost disparities, and adaptability of ship engines [89][110]. For reducing greenhouse gas emissions with renewable methanol, the outlook depends on production and demand, with limited quantities currently used in fuel blending to meet European Commission objectives [100][146].

Methanol quality considerations, per Svanberg et al. (2018), include potentially lower purity in diesel combustion engines compared to typical International Methanol Consumers and Producers Association (IMPCA)-quality methanol. Tests show that methanol with 90% purity performs well as fuel [89][108][109][110,155,156]. High-purity methanol standards exceeding 95%, as outlined by Seddon (2011), are suitable for marine use, reducing competition and having a lower environmental impact than IMPCA grade [110][157].

3.2. Comparison of Bunkering Cost between Methanol, E-Methanol, and Conventional Fuels

Methanol's adaptability, cost-effective bunkering, and economic advantages in new ship construction position it favorably against conventional fuels [12][77][102][12,98,148]. Despite higher specific fuel consumption, methanol proves cost-effective compared to MGO and diesel, with a potential return on investment within three years [46][89][92][97][111][22,43,69,110,113]. Utilizing various feedstocks, including carbon capture and utilization, methanol production faces challenges due to its lower heating value compared to Heavy Fuel Oil [112][113][158,164].

Investing in methanol production is economically viable, with returns within three years and competitive costs compared to exhaust gas treatment and LNG investments. Bio-methanol production costs vary based on feedstock and processes, with potential reductions through adjustments [92][96][114][113,143,167].

Integration with other industries and using residual heat can decrease costs, while evaluating environmental externalities highlights Natural Gas (NG) methanol's competitiveness with Heavy Fuel Oil (HFO) for various ships. Policymakers must urgently address maritime emissions, incorporating incentives and comprehensive assessments for effective mitigation strategies [98][112][144,158].

3.3. The EU ETS and Fuel EU Regulations

The IMO and EPA's measures for gradual greenhouse gas reduction have been adopted by the European Union. Regulations issued by the EU now mandate the reduction and neutralization of fuels by 2050. The monitoring–record–verifying (MRV) system, initiated by European Regulation EU 757/2015 [115][171], requires ships in European ports to record and annually report fuel consumption and carbon dioxide emissions. The EU has also introduced two additional regulations, the EU Emission Trading System (EU ETS) and the Fuel EU Regulation encoded by Regulation EU 2023/1805.

3.3.1. EU ETS Regulation

The EU Emission Trading System (EU ETS) enforces an annual 'cap and trade' system, reducing emissions by 37% since 2005. Tradable allowances quantify emissions on the EU carbon market, with companies facing fines for insufficient surrender. The declining cap ensures market value, encouraging cost-effective emission reductions. Revenues exceeding EUR 152 billion since 2013 support national budgets, renewable energy, and low-carbon initiatives. The EU ETS applies to all EU nations, Iceland, Liechtenstein, Norway, covering around 40% of EU emissions, extending to maritime transport emissions from 2024 [116][117][172,173].

Non-compliance with EU MRV requirements for ships may lead to expulsion and trade prohibition within the EU. Failure to submit allowances incurs an excess emissions penalty of EUR 100 per ton of CO2, with persistent non-compliance risking denial of entry into the EU for all ships under a company's jurisdiction [116][117][172,173].

3.3.2. Fuel EU Regulation (EU 2023/1805)

The Fuel EU Maritime Regulation, complementing the EU ETS, gradually reduces shipping sector fuel emissions. Adopted on 13 September 2023, it takes effect by 1 January 2025, covering CO2 emissions from large ships until 1 January 2024. Ambitious targets aim for a 2% decrease in 2025 to 80% by 2050, including methane and nitrous oxide emissions. Following the Well to Wake principle, it mandates zero-emission measures at berth to reduce air pollution in ports. With a flexible, technology-neutral approach, the regulation introduces voluntary pooling and applies to vessels above 5000 gross tonnage at EEA ports. Reporting through THETIS MRV from 2025 aligns with the EU's goals of a 55% net emissions reduction by 2023 and climate neutrality by 2050 [115][116][117][171][172][173].

3.4. Methanol and E-Methanol Affection by the International Regulations

Renewable methanol derived from biomass exhibits a 56% lower GHG impact than heavy fuel oil [18][51][18][74]. Adopting renewable methanol results in significant reductions, including a 95% cut in CO2 emissions and an 80% decrease in nitrogen oxide emissions [52][53][75][76]. Innovative synthesis approaches using CO2 not only counteract the greenhouse effect, but also offer diverse chemical products and clean fuels [38][118][119][63,114,115]. Despite challenges like wastewater, hydrogenating CO2 for methanol aligns with carbon neutrality goals [41][46]. Industrial synthesis consumes about 110 million metric tons of CO2 annually [120][119], addressing the greenhouse effect and producing chemical products [120][119]. Experimental evidence supports using trace CO2 for an up to 79% methanol yield [121][125]. Catalyst technologies like N-heterocyclic olefin catalysts contribute to carbon neutrality [121][122][125][126]. In essence, renewable methanol, especially from innovative sources, stands out for substantial GHG reduction and sustainable energy practices [52][53][118][75,76,114]. It is premature to draw conclusions about how methanol will be affected by the implementation of international regulations. However, its properties such as CO2 sequestration during production—especially when derived from renewable sources and carbon dioxide hydrogenation—as well as its low emissions compared to conventional fuels make it an environmentally friendly fuel. It seems likely to meet the conditions for achieving greenhouse gas emission reduction goals. Considering additional measures outlined in the regulations to propel shipping into the new era of fuels, such as carbon taxation on conventional fuels, investments in methanol infrastructure, and strict penalties for non-compliant vessels [123][124][174,175], itwe can assume that this particular fuel will likely be positively impacted by the European Union’s new regulations. Future research will confirm these assumptions.

4. Challenges of Using Methanol as a Marine Fuel

Literature consistently highlights methanol's potential as a marine fuel, but challenges include supply, infrastructure, and bunkering processes. Critical evaluations are needed for bunkering facilities, fuel supply systems, onboard containment, and vessel engines [89][125][110][176]. Proper ventilation and open deck locations are crucial for bunkering stations, with existing infrastructure potentially sufficient but additional terminals may be needed [126][177]. Methanol's non-cryogenic nature simplifies handling and transportation, aligning with familiar procedures of conventional bunker vessels [46][69]. Operational experiences from Platform Supply Vessel (PSV) and Offshore Support Vessel (OSV) fleets provide valuable insights [127][128][178,179].

Methanol, with its global ubiquity, emerges as a promising ship bunker fuel, especially for short-sea vessels that can adapt to more frequent bunkering [129][180]. However, larger vessels face challenges in redesigning ships to accommodate low-energy-content fuels like methanol [130][181]. Compliance with regulations, including MSC.1/Circ.1621, poses concerns, emphasizing the need for sustainable production methods like biomass or renewable electricity to reduce CO2 emissions [66][130][88,181].

4.1. Advantages of Using Methanol

Methanol's light, colorless, and flammable properties make it a feasible transportation fuel with substantial production capacity [25][46][91][92][52][69][112][113]. Reported advantages include a significant evaporation temperature, decreased air/fuel ratio, increased energy ratio, swift flame speed, molar expansion, moderate flame temperature, and substantial H/C ratio [25][52]. Methanol's liquid state, reduced viscosity, and adaptability to existing infrastructure and LNG gas tanks ease integration [16][92][131][16][113][166]. Despite high production costs, bunkering is straightforward, but economic barriers hinder widespread adoption in shipping [131][166]. Methanol engines match or exceed traditional fuels in efficiency, especially at low loads, attributed to its high-octane number and evaporative cooling [25][102][111][132][133][134][135][22][52][137][148][183][185][186]. Combustion characteristics align with diesel, surpass gasoline, and fit Otto engines due to high auto-ignition resistance [25][89][92][111][22][52][113][110].

4.2. Disadvantages of Using Methanol

While methanol presents promising aspects as a future clean fuel with potential for large-scale production, distribution, and storage in the supply chain, there are notable drawbacks associated with its physicochemical properties and toxicity. These disadvantages primarily impact human health, including ship crews, and pose challenges related to material compatibility during combustion in internal combustion engines and fire initiation and treatment.

4.3. Potential Hazards and Factors to Take into Account When Bunkering Methanol

In conclusion, while methanol holds promise as a future clean fuel, its use poses challenges. Safety assessments by Pearson, Turner, and Bromberg suggest inherent hazards, but studies indicate that alcohols, including methanol, can be safer than gasoline. Methanol's low flash point, toxicity, and corrosiveness raise concerns for human health, demanding cautious handling and safety measures [136][137][187,188]. Gerba (2019) emphasizes careful handling during spills or leaks, and Van Hoecke et al. (2021) highlight the need for detection and ventilation systems [123][126][174,177]. Methanol's potential for evaporation, its near-invisible flames, and its flammability in specific concentrations add complexity. Hughes (2021) notes slower evaporation than liquefied gas, and Shamsul et al. (2014) specify the flammable range of methanol vapor. Precautions are necessary in manifold, P/V relief valve, and ventilation systems to avert sparks or ignition [25][26][138][139][52][53][190][191]. Concerns extend to engine modifications due to corrosion and the unsuitability of methanol for diesel engines. The need for safety measures during operation, given its low flash point, presents additional challenges. The corrosive nature of methanol interacting with CO2 emphasizes the importance of avoiding inert gases containing carbon dioxide [26][66][89][92][134][140][141][53][88][110][113][185][192][193].

4.4. Environmental Impact of Using Methanol

The environmental assessment of methanol as a marine fuel necessitates considering life cycle greenhouse gas (GHG) emissions. Methanol derived from natural gas shows varied GHG impacts, with biomass-sourced methanol demonstrating lower emissions [17][44][89][142][17,24,68,110]. Its low GHG and emission levels, attributed to a high hydrogen-to-carbon ratio and absence of sulfur, make methanol a favorable option [25][143][144][145][43,52,194–196]. Dual-fuel studies indicate reduced emission rates with increasing methanol percentages [97][43]. Methanol's usage results in a 30% reduction in NOx formation and emissions, supporting compliance with IMO Tier III restrictions [25][82][146][147][148][149][52,103,198,199,200,201]. However, conflicting views exist, with some studies refuting these claims [89][149][110,201]. Employing methanol reportedly leads to a 7% reduction in CO2 emissions compared to Marine Gas Oil (MGO) [46][69]. Nevertheless, a study suggests a 10–25% reduction in CO2 per ton-nautical mile at lower engine loads, accompanied by increased CO and HC emissions [22][25][22,52]. Methanol's impact on Specific Fuel Oil Consumption (SFOC) and formaldehyde formation is noted, indicating potential challenges [22][44][46][92][150][151][22,48,68,69,113,202]. In terms of ocean protection, methanol's swift dispersion in water upon leakage prevents hazardous concentrations, but potential harm may persist regionally until adequate dilution is achieved [44][46][92][150][48,68,69,113].

5. Conclusions

In conclusion, methanol stands out as a transformative solution for the maritime energy landscape, aligning with emission reduction targets and the imperative for sustainable fuels amid global shipping demands. Its liquid form, advantageous properties, and existing infrastructures in key ports position it favorably. However, safety concerns, lower flash points, and health risks require careful consideration. Despite challenges, utilizing intermittent sustainable energy sources for methanol production shows promise. Advancements in synthesis methods and existing infrastructure enhance its economic viability, environmental benefits, and technological adaptability. Future research should focus on operational studies, bunkering processes, infrastructures, and financial implications for a successful transition. Global collaboration is crucial for integrating methanol as a sustainable alternative fuel. The industry's response to universal demand, coupled with the implementation of ESG criteria, can drive adoption, investments, research, and positive environmental impacts, reducing carbon footprints and emissions of SOx, NOx, and PMs.

 
 
 
 
 
 
 

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