A case for renewable methanol economy and fuel cells
A more comprehensive version of this article can be found in a peer-reviewed open access publication here: A Review of The Methanol Economy: The Fuel Cell Route
- Methanol can be produced through renewable means and used as a substitute for petroleum both in the energy sector and the chemical industry
- The renewable production of methanol involves hydrogen production via water electrolysis using renewable electricity and some renewable source of CO2 via carbon capture or CO2 from biomass
- The use of methanol in high temperature PEM fuel cells for various energy applications is an interesting and efficient solution
- The cost of renewable electricity, cost of CO2 capture, and CO2 trading schemes are important factors for the economic viability of the renewable methanol economy
- By converting CO2 into liquid fuels, the harmful effects of CO2 emissions from existing industries that still rely on fossil fuels are reduced, making the transition to a more sustainable economy more feasible
A brief history of methanol
Methanol also known as wood alcohol, methyl alcohol or carbinol, is the simplest alcohol with the chemical formula CH3OH. It was first discovered in 1661 by Robert Boyle, who produced pure methanol by refining crude wood vinegar over milk of lime¹. For a long time this dry distillation of wood was the main production method for methanol until BASF started catalytic production from CO and hydrogen in the 1920s.
In the beginning of 1900s, methanol was known as heating fuel in Europe and 1920s it was used as a fuel in automobiles². The increased oil exploration in those years soon caused loss of interest and its use in automobiles did not last long, except in some performance cars for racing.
In the 1970s methanol started to become more interesting again as a feedstock in the chemical industry for the production of formaldehyde and olefins (ethylene and propylene), which are some of the most important building blocks of petrochemical and chemical synthesis processes. Since then, the global methanol production increased steadily from around 5 million metric tons in 1975 to 110 million metric tons in 2018³.
As recent as 2012, 85% of the global methanol production was used in the chemical industry¹, but this is quickly changing as its use in the energy sector has rapidly increased to more than 40% today, especially with some countries such as China pushing through policies to use methanol as a transportation fuel⁴. This along with its prominent use in the chemical industry makes methanol one of the most important chemical commodities nowadays and its demand is increasing at an average annual growth rate of more than 7%⁵ to an estimated 130.68 billion $ global methanol market by 2026⁶.
The California debacle
To combat NOx emissions and thereby fix the ozone hole, in the 1980s and 90s California embarked in a large scale trial program to test methanol as an alternative fuel for vehicles. In the trial around 15000 gasoline flex-fuel vehicles allowing up to 85% methanol in the fuel (M85) were operated⁷. While the project was technically successful, it was slowly abandoned in 2004, mainly because natural gas, which was the main source of methanol for the trials, was thought to be scarce and expensive at the time, which was later proven wrong with possibility of nowadays selling methanol from natural gas at around half the price of gasoline.
Moreover, the oil companies came up with cleaner gasoline by blending it with Methyl Tertiary Butyl Ether (MTBE) to meet California’s demands, which however required methanol for its production and diverted it from being used as a substitute to gasoline and made it more expensive⁸. So, it seems like the production of MTBE from methanol basically killed the early methanol economy by causing its scarcity and by dragging out the gasoline years by providing cleaner gasoline blend. MTBE was later banned in California and New York in 2004 and later by other states in the US as it was found in some drinking water⁸.
A similar methanol vehicles pilot program was also conducted between 2012 and 2018 in 10 Chinese cities, where more than 1000 methanol vehicles were tested. The program showed methanol’s feasibility as a viable transportation fuel with neither techno-economical nor safety issues, and today there are several hundreds of thousands of vehicles that run on pure methanol or methanol blends, including retrofitted vehicles⁹.
What is the methanol economy?
The methanol economy proposes methanol as a substitute to fossil fuels in energy storage, transportation and in the chemical industry. One of the main proponents of the methanol economy was George Olah, the Nobel prize in chemistry in 1994, who outlined the potential of a comprehensive methanol economy in his book Beyond Oil and Gas: The Methanol Economy.
The conventional methanol production process mainly comprises of three processes: synthesis gas production, methanol synthesis and methanol distillation, as shown in Fig. 1, where the synthesis gas is generally produced from fossil fuels. The produced syngas is converted into methanol using copper-based catalyst at operating pressures between 50–100 bar and operating temperatures of 200–300 ◦C, and involves the hydrogenation of CO and CO2 and reverse water–gas shift (RWGS) reactions.
To make the process renewable, the synthesis gas need to be produced by renewable means. This happens through the use of hydrogen from water via electrolysis based on renewable electricity and CO2 from carbon capture from the atmosphere or biomass sources, such as biogas and ethanol plants. A vision of the renewable methanol economy is shown in Fig. 2. The process of using electricity to produce fuels is known as Power-to-X process and in this specific case the product methanol is known as green methanol or eMethanol.
Methanol can be divided into three categories based on the feedstock for the synthesis gas production: black methanol when fossil fuels are used, grey methanol when municipal solid wastes that are not entirely renewable are used, and green methanol when hydrogen from renewable electricity and renewable CO2 are used.
Once produced, methanol has a plethora of chemical derivatives and products that can serve several sectors of our modern economy. A value chain for methanol with some of its derivatives and their application are given in Fig. 3.
The way forward with power-to-X (PtX)
Renewable energy sources such as wind and solar are characterized by intermittency, meaning that there are periods of high and low production due to their dependency on weather conditions. This leads to a mismatch between the energy production and demand, which causes instability of the grid both due to frequency imbalance in the short-term (hourly and daily basis) and on a seasonal basis calling for high costs of grid balancing services.
Therefore, for successful integration of renewable energy sources, storage solutions are necessary so that excess electricity produced can be used at a later stage when the demand is low or to create value for other applications. While batteries are excellent and ubiquitous electricity storage solutions for our day to day electronics applications and for electric vehicles, the scale of global transition towards renewable electricity requires more practical solutions.
Hydrogen production from renewable electricity via water electrolysis (a process by which water is split into hydrogen and oxygen) is one such solution. The electrolyzer can be connected to the electricity grid and produce hydrogen from excess electricity, which can then be use either directly in fuel cells to produce electricity that can be fed back to the grid or can be stored and transported for other uses, including transportation and chemical synthesis.
Additionally, the electrolyzer can be paired with a methanol plant to produce liquid and easier to handle fuel than hydrogen. This process requires CO2 source that can be obtained renewably from CO2 capture from the atmosphere or other sources, such biofuel and biogas plants, which at moment emit their CO2 byproduct into the atmosphere. There are also CO2 intensive industries, such as cement factories, which maybe interested in such a solution to reduce their carbon footprint while also producing a valuable liquid fuel in the process.
Even though CO2 is emitted when using methanol for energy production, be it in fuel cells or in internal combustion engines, the CO2 cycle for green methanol is closed. This means that it is the CO2 that was used during its production that is emitted, and therefore, no new CO2 is emitted into the atmosphere. Moreover, when CO2 from industrial processes is used, the fact that the produced methanol replaces the consumption of fossil fuels for transportation or chemical processes avoids further CO2 emissions. Therefore, a renewable methanol can be considered as a carbon sink (absorbs more carbon than it releases) compared to the current state of affairs as CO2 that would otherwise be simply emitted into the atmosphere could be used in transportation and chemical processes that currently run on fossil fuels.
Methanol in fuel cells
Fuel cells are electrochemical devices like batteries with electrodes and electrolytes, but unlike batteries instead of storing electricity, they produce it continuously as long as they are fed with a fuel (hydrogen or hydrogen rich mixtures and compounds). So, one could say that functionally, they take from both the worlds of batteries and combustions engines, where they produce clean electricity directly like batteries as long as they are fed with fuel like combustion engines.
While there are several types of fuel cells with different materials used for the electrolyte and electrodes, the most common ones are polymer electrolyte membrane (PEM) fuel cells. These are the same types of fuel cells that one can find in most of the commercial fuel cell vehicles (Toyota Mirai, Hyundai Nexo, Honda Clarity, Nikola semi-truck, ..etc.). These operate at temperatures below 100 degree Celsius (typically at 80 degree Celsius), as they depend heavily on the presence of liquid water for the proton conduction between the electrodes, which is an important part of the electrochemical process that produces electricity. Due to these low operating temperatures they also tend to be prone to degradation by impurities in the hydrogen fuel feed. Therefore, they have to be fed with pure hydrogen or if hydrogen sources such as methanol are used gas purification is needed before the gas mix can enter the fuel cell.
Consequently, methanol is best used in a variant of the PEM fuel cell that operates at higher temperatures and can tolerate more impurities. To achieve this a phosphoric acid-doped polymer electrolyte called polybenzimidazole (PBI) is used, which allows to conduct protons in the absence of liquid water. These fuel cells typically operate at temperatures of around 160 degree Celsius, and due to this higher operating temperature they are known as high temperature PEM fuel cells, to distinguish them from the more common lower temperature counterparts.
To use methanol in these fuel cells, it has to first be converted in a hydrogen-rich gas mixture via a process called reforming in a catalytic reactor at temperatures of around 250–350 degree Celsius. This is usually integrated in a system with the fuel cell, where via a smart heat integration some of the heat produced in the fuel cell is used to heat an evaporator that feed the reformer and excess hydrogen-rich gas is returned back from the fuel cell to the reformer to provide heat for the reforming process via a burner unit. The overall system electrical efficiency in this case is around 40% and if the released heat is also used in combined heat and power application (CHP) the overall system efficiency can be significantly higher. The modularity of such a systems allows it to fit several applications, including in the automotive and stationary applications.
Aalborg: the methanol hub
There are several initiatives around the world at all levels of the methanol economy as can be seen in the interactive map here. In Denmark, counting on the high wind energy penetration of around 47%⁹ (2019) of the electricity consumption currently and future plans to further expand this, several PtX projects are demonstrating the possibility of replacing fossil fuels with sustainable alternatives. Aalborg, in the north of Denmark is increasingly becoming the methanol hub with several private companies driving innovation in the entire value chain of PtX, from renewable methanol synthesis plants to the use of methanol in fuel cells for various applications.
REintegrate ApS, a spin-off company from Aalborg University is developing facilities for the PtX process based on hydrogen from electrolysis and CO2 recycling from biogas plants. The Green Methanol Infrastructure Consortium, a cooperation between Danish petrol company OK a.m.b.a., Hamag and Serenergy A/S opened the first methanol refuelling station in Europe in Aalborg in 2015. To complete the methanol value chain Serenergy A/S and Blue World Technologies ApS, also located in Aalborg, are developing fuel cell systems that operate on reformed renewable methanol for various applications, both for transportation and stationary applications.
Additionally, a new project in Aalborg called GreenCem is investigating a carbon capture facility at the Aalborg Portland cement plant and a PtX facility that will recycle the captured CO2 to produce green methanol through a reaction with hydrogen. Since the adoption of carbon pricing schemes is challenging for carbon-intensive industries, such as cement factories, equipping them with PtX facility to take advantage of their high concentration CO2 emissions, can contribute not only to minimize their emissions but also provide valuable transportation fuels and raw materials for the chemical industry by producing methanol via PtX.
Therefore, with the complete value chain of green methanol strategically placed in Aalborg, it will be interesting to see how in the coming years innovation will push the commercialization of the involved technologies. Cost of renewable electricity is decreasing every year with increased penetration and consequently the cost of green hydrogen is falling and the maturity of electrolyzers is also contributing to lower CAPEX of PtX plants.
That being said, while carbon capture is relatively inexpensive for pure streams of CO2 such as those in biofuel plants, where CO2 concentration can reach up to 90 vol%, the cost is still too high for a commercially viable implementation of green methanol production from atmospheric CO2 capture. Therefore, more work is needed to reduce the cost of CO2 capture in order to drive down the cost of green methanol. At the moment, PtX plants will have to rely on high CO2 concentration sources, such as biogas and biofuel plants and carbon-intensive industries, such as cement factories.
References
¹ Ott, J.; Gronemann, V.; Pontzen, F.; Fiedler, E.; Grossmann, G.; Kersebohm, D.B.; Weiss, G.; Witte, C. Methanol. In Ullmann’s Encyclopedia ofIndustrial Chemistry; Wiley-VCH Verlag GmbH& Co. KGaA:Weinheim, Germany, 2012; doi:10.1002/14356007.a16_465.pub3.
² El-Zeftawy, A.M. Focus on the Chemical Value of Methanol. J. Univ. Eng. Sci. 1995, 7, 209–254, doi:10.1016/S1018–3639(18)31058–4.
³ Dalena, F.; Senatore, A.; Basile, M.; Knani, S.; Basile, A.; Iulianelli, A. Advances in Methanol Production and Utilization, with Particular Emphasis toward Hydrogen Generation via Membrane Reactor Technology. Membranes 2018, 8; doi:10.3390/membranes8040098.
⁴ Kai Zhao. A Brief Review of China’s Methanol Vehicle Pilot and Policy; Technical report; Methanol Institute: Alexandria, VA, USA, 2019.
⁵ Alvarado, M. The Changing Face ofthe Global Methanol Industry; Technical report; IHS: London, UK, 2016
⁷ Verhelst, S.; Turner, J.W.; Sileghem, L.; Vancoillie, J. Methanol as a fuel for internal combustion engines. Prog. Energy Combust. Sci. 2019, 70, 43–88, doi:10.1016/J.PECS.2018.10.001.
⁸ Fuel freedom foundation. When California had 15,000 methanol cars — Fuel Freedom Foundation.
⁹ Jacob Gronholt-Pedersen, Denmark sources record 47% of power from wind in 2019. Reuters.