Projects about renewable methanol synthesis in research and

later course of the process. The design of this reactor is shown in Figure 2.1 b). As a modification, it is also possible to pass the reaction mixture through the catalyst on the housing side and to flow the cooling medium through the tubes. In this configuration, gas is often used as cooling medium instead of steam. A further modification is to use double tubes through which the reaction mixture first flows on the inside for heating and then flows back through the outer tube filled with the catalyst, whereby steam is used on the housing side (OTT et al., 2012, p. 10f). The advantages of the isothermal reactor are optimal temperature control, the generation of a small amount of by-products, lower operating costs compared to the adiabatic reactor, and a longer catalyst service life. Disadvantages are that, compared to the adiabatic reactor, the maximum production capacity is lower due to the large total reactor volume through tubes and casings and these reactors are also more expensive to invest due to their more elaborate design (HANSEN et al., 2008, p.

2939).

2.1.3 Projects about renewable methanol synthesis in research and industry

The first pilot plant was commissioned by MCI (Mitsui Chemicals Inc.) in 2009. It produces 100 t/a of methanol with CO2 from industrial waste gases and H2, which is produced by photolysis of water (MITSUI CHEMICALS INC., 2008). In 2011, CRI (Carbon Recycling International) commissioned the "George Olah Renewable Methanol Plant". Here, CO2 from a geothermal energy plant was initially used on a pilot scale to synthesise methanol. In the meantime, the production capacity has been increased to 4000 t/a, which corresponds to a recycling of 5,500 t/a of CO2

emissions. The CO2 comes from the waste gas of an adjacent geothermal plant, which would otherwise be released into the atmosphere. It must first be treated so that it can be used in the methanol plant. The required H2 is produced by electrolysis. In the end, geothermal steam is used as a heat source for separation of water from methanol by distillation. The only by-products are H2O from distillation and pure O2 from electrolysis. The plant is modularly designed, so that an enlargement as well as an adaptation to different locations is possible. CRI claims that they were the first to produce fuels based on CO2 on an industrial scale. Over 90% of CO2 emissions in the entire life cycle can be saved with this process compared to the production with fossil energy sources (CARBON RECYCLING INTERNATIONAL, 2020).

The EU is also committed to producing methanol using industrial waste gases.

Therefore, the EU-funded MefCO2 project was launched in 2015. This project uses CO2 from exhaust gases together with H2, which is produced by electrolysis with surplus energy from, e.g., WTGs to produce methanol. The pilot-scale plant was completed in June 2019 after four and a half years and now produces 1 t/d of methanol. This means that more than 1.5 t/d of CO2 is separated from flue gas. This pilot plant is currently one of the largest plants for production of methanol using CO2 from exhaust gases in the EU. This plant is also modular with the aim of adapting it to different plant sizes and gas compositions of the waste gases (MEFCO₂, 2016). Meanwhile, many large companies from the energy and chemical industries have entered the research and production of renewable methanol.

Companies active in the global renewable methanol market include Advanced Chemical Technologies, BASF, CRI, Enerkem, Fraunhofer, Innogy, Nordic Green, OCI N.V., Serenergy A/S and Sodra (ALLIED MARKET RESEARCH, 2020).

There is also interest in small-scale renewable methanol production plants in research and industry. As early as 1998, USHIKOSHI et al. (1998) investigated the general functionality of the process for methanol synthesis from CO2 and H2 in a test plant with a production capacity of 50 kg/d of methanol. Here, it can be shown that the production rate of methanol increases with an increase in pressure and that the optimum reaction temperature for this process setup is 270°C. Furthermore, a

very high selectivity can be demonstrated and a purity of 99.9% of the produced methanol is achieved. In 2016, RIVAROLO et al. (2016) published the results of a feasibility study and an economic analysis for a methanol plant with a production volume of 100 kg/h. Two different plant concepts were investigated; one separates the CO2 by treating biogas and the other obtains the CO2 from an external source.

In both cases, the required H2 is produced by means of an alkaline electrolyser (AEL) which obtains electricity from a renewable energy source. If this is not available, the electricity is taken from the grid. The authors showed that there is great potential for methanol production from renewable sources. In his master's thesis, DE JONG (2018) also investigated a small-scale methanol plant. The objective was to design a container-scale plant which can be operated automatically in order to be used even in remote locations. The main focus is on adapting the various components of the plant to the size of containers. The author developed a concept where the system fits into three of them. As a CO2 source, ambient air is used. Sea water, on the other hand, is used for electrolysis. The required electricity is generated by a PV system.

There are several companies in the industry dealing with small-scale plants for renewable methanol synthesis. For example, Thyssenkrupp sells small plants with production volumes of 10 to 200 t/d methanol, which can be operated with renewable H2 and CO2 from industrial waste gases or biogas plants. These plants were developed together with SLF (Swiss Liquid Future) and the process is called

"SLF/Uhde Methanol Process". The electricity is generated from hydropower, wind power or solar energy. The electrolysis plant was developed by Thyssenkrupp itself. This plant is known as a "Green Methanol Plant" and has a modular design.

The structure of the overall concept is shown in Figure 2.2 (THYSSENKRUPP INDUSTRIAL SOLUTIONS AG, 2020). Moreover, bse engineering already produces small plants for methanol synthesis under the name "FlexMethanol".

Here, only H2 from surplus electricity together with CO2 from exhaust gases is used for methanol production. The "FlexMethanol 10" process produces 8200 t/a methanol, whereby it is stated that the process is scalable according to the needs of the buyer. In this process an AEL cell is used to produce the H2. For methanol synthesis, a tube bundle reactor is used, which is operated at 240°C and 40 bar.

Investment costs of less than 3000 €/kW are given (BSE ENGINEERING, 2020).

Founded in 2014, Ineratec manufactures modular chemical plants for PtX and gas-to-liquid (GtL) applications using innovative reactor concepts, including reactors for methanol synthesis. These are compact reactors with microstructure technology, which can be used in container-scale modular designs (INERATEC, 2017).

Figure 2.2: Process design of the “Green Methanol Plant” developed by the Thyssenkrupp Industrial Solutions AG.

Caption: THYSSENKRUPP INDUSTRIAL SOLUTIONS AG (2020).

There is already a general interest in producing methanol from renewable sources and thus ensure a reduction in CO2 emissions. However, the current focus of research is rather on large plants, which can be operated in combination with CO2

from industrial waste gases. So far, there are no investigations corresponding to the plant concept of the methanol synthesis in combination with small-manure plants.

The research concentrating on the connection with biogas plants, is primarily based on the production of synthesis gas from which methanol or other liquids are produced (BOZZANO et al., 2017, CLAUSEN et al., 2010, HUISMAN et al., 2011, SWANSON et al., 2010). This process is called Biomass-to-Liquid (BtL). There are also a few studies on methanol synthesis, where the CO2 is captured from larger biogas plants and used as an educt (DECKER et al., 2019, RIVAROLO et al., 2016, SCHORN et al., 2020).