Location Planning for the Production of CO₂-Based Chemicals Using the Example of Olefin Production^†

1 Introduction

Carbon dioxide (CO₂) is a greenhouse gas that is mainly produced when fossil fuels are burned. However, the use of CO₂ as a raw material is increasingly important as an option for climate protection and as an alternative raw material ^1-7. To use CO₂ as raw material, it is often captured at point sources, i.e., localized emitters from which CO₂ is produced in large quantities and at a high concentration. In the next step, the separated CO₂ is converted with hydrogen (H₂) into basic chemicals (e.g., methanol) or higher value-added chemicals (e.g., polymers). Electrochemical direct synthesis is an alternative to these thermochemical processes. During direct synthesis, CO₂ and water, e.g., are converted into C₁–C₄ alcohols in a single-stage electrochemical process. The advantages of such electrochemical processes include the completely electrically powered mode of operation, the single-stage process, and the possibility of decentralized production ⁸.

Thermochemical processes and electrochemical direct synthesis both share an increased demand for thermal and electrical energy ⁹. This is due to the thermodynamic stability and kinetic inertia of CO₂ ¹⁰. Thermochemical processes for CO₂ conversion require a reactant that is highly reactive ¹⁰. This is, e.g., H₂, which can be produced via energy-intensive processes such as water electrolysis ¹¹. In electrochemical direct synthesis, the reaction is the driver of energy intensity. Therefore, CO₂ conversion does not necessarily lead to environmental impact reduction ¹².

In view of the energy transition and the decentralized electricity supply, low-emission and, at times, inexpensive electricity is to be expected in the future ^13-15. From an environmental perspective, the local availability of CO₂ and renewable energy sources (RES) is particularly relevant for CO₂-based chemical production. This article, therefore, presents a methodology for deriving suitable locations for CO₂-based chemical production in Germany, taking into account the local availability of CO₂ and RES. The methodology is applied in an illustrative manner for CO₂-based olefin production.

The basics of carbon capture and utilization (CCU), CO₂ sources and uses, and H₂ production are presented in the following section. In Sect. 3, the methodology and procedure for identifying suitable locations and in Sect. 4, locations for CO₂-based chemical production in Germany are presented. In Sect. 5, the main results are summarized and possible limitations of the analysis as well as future research needs are discussed.

2 Carbon Capture and Utilization

According to von der Assen et al. ¹⁶, CCU involves the industrial capture of process and energy-related waste gases in order to obtain concentrated CO₂ along with the separate functional utilization of CO₂. Industrial capture comprises the capture of CO₂ directly from the atmosphere or from CO₂ point sources such as fossil fuel-based power plants. The functional utilization of concentrated CO₂ involves a recycling process that goes beyond the storage of CO₂. This can include the direct use of CO₂ as a product (e.g., as a solvent) or the conversion of CO₂ into other products such as fuels or basic chemicals. Processes that store CO₂ without further use are defined as carbon capture and storage (CCS) ¹⁷.

2.2 CO₂Utilization

The recycling of emissions containing CO₂ essentially has two positive effects. Firstly, CO₂ emissions can be retained in greenhouse gas-intensive industries. Secondly, the use of carbon emissions as a raw material may help to conserve fossil resources and establish carbon cycles by reducing the demand for carbon from fossil raw materials such as natural gas, crude oil, or coal. There is a wide range of options available for recycling CO₂. Overviews of various utilization paths based on CO₂ can be found in the literature ^35-40. CO₂ is already used in the food industry as a protective gas to preserve food or to produce carbonic acid in the beverage industry ⁴¹. Further fields of application include the agricultural industry (as fertilizer in the form of pure CO₂ or as input for urea production), the textile industry, in which CO₂ serves as a cleaning agent, and the use of CO₂ as an extinguishing agent in gas extinguishers ³, ⁴⁰, ⁴¹.

The importance of taking CO₂ as a raw material for the chemical and manufacturing industries has increased in recent decades ³², ⁴². Technologies that can be used to activate the inert molecule CO₂ and to bind it in different molecules have thus been (further) developed. An overview with a selection of possible synthesis routes, products, and their areas of application is given in Fig. 1.

The feasibility of thermo-catalytic conversions of CO₂ into basic and specialty chemicals were investigated in the work by Müller, Otto, and Peters et al. ⁶, ³⁸, ⁴³. While basic chemicals serve as a building block for a variety of downstream products and thus address a large sales market, the conversion of CO₂ into specialty chemicals is more suitable for lower plant capacities due to the often limited market for target products and higher profit margins. In order to substantially reduce fossil resource use and greenhouse gas emissions, basic chemicals should be addressed first. Besides methanol, C₂–C₄ alcohols are important building blocks of the chemical industry. Ammonia is also one of the most important basic chemicals in the chemical industry and is the building block for industrially produced nitrogen-containing compounds such as urea, ammonium salts, and nitric acid.

Major advances in the commercialization of CO₂-based syntheses are currently evident in methanol synthesis. Techno-economic studies on the operation of CO₂-based methanol synthesis can be found, among others, in Abdelaziz et al., Atsonios et al., Kar et al., and Belotti et al. ^44-47. In addition to methanol, processes for converting CO₂ and H₂ into alcohols (C₂–C₄) are also being developed. Muhler and Kaluza ⁴⁸ describe the state-of-the-art in the conversion of syngas into higher alcohols and the increase in selectivity to ethanol.

In many industrial processes, N₂ is present in the waste gas due to the supply of air and is available in the gas mixture in addition to CO₂ for further use in the post-combustion processes mentioned above. The synthesis of nitrogen into ammonia with electrochemically produced H₂ from renewable energy sources (RES) and the subsequent conversion with CO₂ into urea enables the binding of CO₂ ³², ⁴⁹. In this way, fossil raw materials, such as natural gas, could be substituted and process-related carbon-containing waste gas streams could be used.

3 Methodological Procedure

The methodological procedure for determining suitable locations is illustrated in Fig. 2.

The first criterion serves to select the CCU technology. Only CCU technologies that have already been commercially implemented are taken into consideration. A CCU technology is the conversion of CO/CO₂/H₂-containing waste gases into propene and ethene via the intermediate product methanol. Both CO₂-based methanol synthesis and the synthesis of methanol into olefins are already operated on a commercial scale and have a high degree of technological maturity ⁴⁰, ⁵⁹, ⁶⁰. Processes to produce olefins from methanol are also called methanol-to-olefins (MTO) processes ⁶¹. A special process modification with increased selectivity to the target product propene is the methanol-to-propylene (MTP™) process developed by Lurgi (now Air Liquide) ⁶². So far, commercial MTO and MTP™ plants can only be found in China. The reason for this is the high availability of cheap natural gas and coal to produce syngas. The largest MTO plants have capacities of 600–800 kt propene and ethene per year ⁶⁰. Air Liquide currently operates three MTP™ plants, each with propene capacities of around 500 kt per year ⁶⁰, ⁶².

As this technology has already been widely implemented compared to other CCU technologies, it is used for location analysis. The focus on the CO₂-based production of propene and ethene is also supported by the existing distribution infrastructure in Germany and Europe. New processes could thus be integrated more efficiently into the existing supply chains. The operating companies for the propene and ethene pipeline are the Duisburg-based companies ARG mbH & Co. KG (ethene) and PRG Propylenpipeline Ruhr GmbH & Co. KG (propene). Technical data for the pipelines can be found on the respective company websites.

Olefins are traditionally produced via rectification and the cracking of crude oil ⁶³. The crude oil is first broken into different fractions by means of atmospheric and vacuum distillation. Around 10 % of the crude oil is rectified into naphtha for the chemical industry ⁶⁴. The naphtha fraction is then converted by splitting heavy, long hydrocarbon chains into light, shorter hydrocarbon molecules (“cracking”). Detailed comparisons of the energy demands and CO₂ emissions of the various ethene and propene production processes based on crude oil, natural gas, shale gas, CO₂, and biomass are given in Zhao et al. ⁶⁵ and Ren ⁶⁶.

Large petrochemical production plants with refineries, steam crackers, and the necessary pipelines for crude oil, ethene, and propene in Germany can be found in Germany Trade & Invest ⁶⁷. To identify and evaluate possible locations to produce olefins from CO₂, the necessary mass and energy flows for the production of 1 t olefins are presented in Fig. 3 which addresses the CO₂ demand (criterion 2) and the demand for electricity from RES (criterion 3) for olefin production. The energy required for the provision of CO₂ is not included, as it depends on the CO₂ source and the respective separation process (see Sect. 2.1). In addition, life cycle assessments have shown that the greatest environmental impact is associated with the provision of H₂ ⁵⁵. Water demand and oxygen produced from electrolysis were also not taken into account in the location planning.

The electrical power demand for the production of H₂ and the operation of the plants as well as the necessary amount of CO₂ are standardized at one metric ton of olefins (the term olefins is used below to refer to the composition of 0.643 t propene and 0.357 t ethene) in order to enable a comparison with conventional production. The energy demands shown in Fig. 3 take into account the thermal and electrical energy required for the respective sub-processes. Only in the case of electrolysis, it was assumed that only electrical energy is needed.

The product spectrum in the Lurgi MTP process consists of 67 % propene, 3 % ethene, 30 % liquefied petroleum gas (LPG), and light gasoline ⁶². A product distribution of the MTO process according to Jasper and El-Halwagi ⁶¹ of 64 % propene and 36 % ethene is assumed for further calculations.

In order to consider the second criterion, i.e., CO₂ sources, industrial CO₂ sources were determined with the help of a systematic literature analysis ⁶⁸, ⁶⁹. The locations, quantities, and quality of the CO₂ point sources in Germany are assessed using the European Pollutant Release and Transfer Register (E-PRTR) ²⁴. In addition, other literature sources are used for plants not subject to reporting requirements (e.g., biomethane plants) ^28-31. CO₂ sources are classified according to their CO₂ purity and CO₂ concentrations given in Tab. 1.

For the third criterion, namely, RES potentials, a technical potential is established for the provision of RES. The aim is to determine the general suitability of deploying RES-using power plants in a region. The work of Fraunhofer Institute for Environmental, Safety, and Energy Technology UMSICHT and Advanced System Technology (AST) Branch of Fraunhofer Institute of Optronics, System Technologies, and Image Exploitation IOSB will be considered for this purpose ⁷⁰, ⁷¹. The technical potential represents part of the theoretical potential, in which restrictive factors that exclude certain areas of a region are employed. To determine the technical potential, geographical conditions and topological and infrastructural land availability were taken into account as reasons for exclusion. Legal restrictions and distance regulations such as protected areas or buffer distances from settlement areas and infrastructure facilities were also included in the analysis ⁷¹. In the analysis key figures for the technical installations, which have a direct influence on the performance data, and key figures that have an effect on the placement options and space requirements of the installations, such as the hub height and rotor diameter of wind turbines, are used. A distinction is made between the installed capacity of wind turbines and photovoltaic (PV) systems and the expansion potential.

The methodology used to determine the area and potential of wind energy usually follows a fixed sequence, such as that carried out in studies commissioned by the German Wind Energy Association ⁷² or the State Agency for Nature, Environment, and Consumer Protection North Rhine-Westphalia (NRW) ⁷³. In order to determine the potential for the use of wind power, the following analyses were carried out: restriction analysis, potential wind energy analysis, and energy yield analysis. Dummy wind turbines are placed on the identified suitable areas. The respective plant parameters can be taken to calculate the number of installable plants, the installable capacity, and the associated energy yields at the wind turbine locations.

The solar potential for electricity generation takes into account the roof area and open space solar potential. To analyze potential open-space PV plants, areas were selected that are fundamentally suitable for establishing a solar park to produce eligible electricity in terms of the German Renewable Energy Sources Act (EEG). These include, e.g., edge strips along freeways and railroads, stockpiles, or even parking lots ⁷⁴. From these, areas were subsequently excluded that are not suitable as solar parks due to their specific properties, e.g., areas which are under nature protection, oriented towards the north, in the immediate vicinity of shading objects such as forest areas or buildings, or are smaller than a defined minimum size. For the remaining areas, the installable module area and the potential electricity yield are determined from information on sunshine duration or global radiation, taking into account the geographical location.

A complete individual analysis of all roof areas in Germany would be data-intensive and time-consuming. Hence, an aggregated form of analysis was applied. The potential of roof-mounted PV systems was determined based on the settlement structure. Model regions were investigated, potentials of typical settlement structures for residential, commercial, and industrial areas, city centers, and rural areas were determined, and these results extrapolated to the building stock in Germany ⁷⁴.

Applying this approach results in a total potential of 6975 TWh, which corresponds to a higher potential compared to the net electricity generation of 3000 TWh in 2050 forecasted by the German Federal Environment Agency (UBA) ⁷⁵. The calculated potentials lie above the wind potentials determined by the German Wind Energy Association (BWE) and UBA ⁷², ⁷⁶. The installable capacity of 2459 GW identified in this study is higher than the wind potential of 1188 GW determined by UBA ⁷⁶ and 1500 GW calculated by the BWE ⁷². This is due to less restrictive assumptions on the use of wind energy in forest areas, whereby the potential usable area increases to 30 % (BWE: 22 %). In addition, the potential calculated in this study includes many wind farms with densely packed plants.

Three scenarios were developed for the location analysis for CO₂-based olefin production (see Tab. 2). In scenario 1, locations are sought where the plant network of methanol and MTO plants is supplied with sufficient CO₂ and RES for the production of 800 kt of olefins per year. Scenario 2 examines existing refineries and their potential production volumes of CO₂-based olefins. The advantage of integration into existing refineries is that the infrastructure needed to distribute the olefins is already in place. In scenario 3, the substitution of petroleum-based olefin production by CO₂-based olefin production throughout Germany is investigated. An annual production volume of ethene and propene in Germany is 9094 kt ⁷⁷.

Using geographic information systems (GIS) and taking into account the amount of CO₂ available regionally, potentially suitable locations for MTO plants are identified according to the scenario-specific data from Tab. 2 and the regional potential availability of RES. For this purpose, the CO₂ point sources and the RES potential are spatially aligned at the level of the energy regions. The classification according to energy regions is carried out as in the Fraunhofer Institute for Environmental, Safety, and Energy Technology UMSICHT and AST Branch of Fraunhofer Institute of Optronics, System Technologies and Image Exploitation IOSB ⁷⁰. In addition to settlement density, this is based on the degree of centralization. In total, 146 energy regions were defined in Germany. Other location factors such as the availability of labor are not considered but would have to be taken into account in the case of specific location analysis.

4 Results and Discussion

To analyze the distribution of industrial CO₂ sources and to conduct location planning for future chemical plants with CO₂ use, two overview maps of the CO₂ point sources were developed (see Fig. 4). The maps provide an overview of the spatial distribution of the CO₂ point sources and the available CO₂ quantities. The overview map of point sources with a low CO₂ concentration in flue gas (≤ 35 %) for lignite-fired power plants, coal-fired power plants, natural gas-fired power plants, refineries, steel mill gas power plants, waste incineration, steel and iron production, cement production, lime production, and pulp and paper production is based on the data from operators subject to mandatory reporting from the E-PRTR for the reference year 2015 ²⁴. The European Union ⁷⁸ requires all operators of facilities above an emission threshold of 100 kt CO₂ per year to report to their competent authority. In 2015, this included 397 emitters from 41 different economic sectors ²⁴. The number of emitter types was reduced to 20 different CO₂ point source types and 351 emitters based on the minimum contribution of 1 % to the total emissions.

Fig. 4 (right) summarizes the corresponding distribution of industrial CO₂ point sources with a low concentration (≤ 35 %) for Germany. The figure shows that in Germany CO₂ emissions from lignite-fired power plants (162 105 kt a⁻¹ CO₂) and hard-coal-fired power plants (96 246 kt a⁻¹ CO₂) dominate in terms of volume, although CO₂ is present in low concentrations in the flue gas of these plants. It can also be concluded that the majority of emitters with low CO₂ flue gas concentrations are located in NRW, both in terms of quantity (187 283 kt a⁻¹ CO₂) and number (104 emitters). CO₂ use is, therefore, a particularly interesting option for NRW, as CO₂ emitters and consumers are located in close proximity ⁶⁴. There are also plants in which CO₂ separation takes place due to the primary production, e.g., CO₂ separation in ammonia production ⁷⁹.

In addition to process-related CO₂ separation in ammonia plants, biomethane, ethylene oxide, and H₂ production, CO₂ is obtained in high purity as a by-product. According to the Industrieverband Agrar e.V. (IVA) ²⁸, ammonia was produced at four sites in Germany in 2015. Actually, 189 biogas plants with gas processing exist in Germany ²⁹. Rebsdat and Mayer ³⁰ identified four ethylene oxide production plants and Maisonnier et al. ³¹ 28 plants where H₂ is produced from methane by means of steam reforming. The locations of the CO₂ point sources with high CO₂ content are indicated in Fig. 4a. An extensive distribution of CO₂ point sources with high CO₂ content (100 %) is evident. In particular, the high density of CO₂ point sources in Lower Saxony (34 plants) and Saxony-Anhalt (33 plants) should be highlighted. H₂ plants (2996 kt a⁻¹), ammonia plants (2175 kt a⁻¹), and biomethane plants (1153 kt a⁻¹) represent the highest contributions to the total CO₂ emissions (6609 kt a⁻¹) from sources with high CO₂ concentrations.

The use of pure CO₂, which is obtained during ammonia, ethylene oxide, biomethane, and H₂ production, makes sense from both an ecological and an economic viewpoint, since expensive processing steps, which are associated with increased energy demands, are avoided. However, the quantitative share of industrial CO₂ sources with a high concentration of all CO₂ point sources is only 1.46 %. The currently largest point source with highly concentrated CO₂ (ammonia plant) emits up to 850 kt a⁻¹ CO₂ and thus allows for the production of 270 kt a⁻¹ olefins. Compared to commercially established MTO plants with a production capacity of approx. 800 kt a⁻¹ olefins, these smaller plants would probably not be competitive in standalone operation, as an analysis of existing plants in China demonstrates ⁶⁰. For this reason, only CO₂ point sources with low CO₂ concentrations are taken into account in the identification of locations in the scenarios examined. The three scenarios (see Tab. 2) investigated for the assessment of possible locations for CO₂-based syntheses are presented and evaluated below.

4.1 Scenario 1: 800 kt MTO Plant

The locations for the potential plants producing 800 kt olefins per year are indicated in Fig. 5 with green dots. Only locations where the aggregated amount of CO₂ and the RES potential in the energy region are sufficient to cover the specific CO₂ and H₂ demands of the currently largest installed MTO plant (800 kt a⁻¹ olefins) are marked. In addition to these locations, the ethene (red) and propene (yellow) pipelines are also shown. Furthermore, the green shades in the figure reflect the H₂ supply potential in predefined energy regions. A dark green shade indicates a greater potential for H₂ production. The potentially producible amount of H₂ was examined and it was found that in all German energy regions the demanded amount of H₂ can be provided for the olefin synthesis if the use of RES by other sectors and for other purposes is excluded.

Locations where the olefin production potential is high and where there is a connection to the ethene and propene pipeline (see scenario 2) are interesting. These requirements are met by the sites located in NRW. Examples include the production plants of ThyssenKrupp Steel Europe AG in the north of Duisburg, the Oxea GmbH plants in Oberhausen, Ruhr Oel GmbH in Gelsenkirchen, INEOS Köln GmbH, and the Basell Polyolefine GmbH plants in Wesseling. Only the H₂ supply potential there is lower than, e.g., in most RES regions in northern Germany. Locations near Hamburg, such as the Vattenfall Moorburg power plant and Holborn Europa Raffinerie are interesting as well. Good distribution channels are available for these locations via the pipeline and there is a connection with an energy region with high H₂ supply potential.

4.2 Scenario 2: Refineries

Suitable locations for the production of olefins in the immediate vicinity of existing refineries are marked with blue triangles in Fig. 6. Only the CO₂ generated in the refineries is taken into account for the potential production of olefins. This results in plant capacities of less than 800 kt. The potentially producible amount of H₂ was examined and it was shown that in all energy regions the required amount of H₂ can be provided for the olefin synthesis if the use of RES by other sectors and for other purposes is excluded.

In particular, preference should be given to refineries where the olefin production potential is high. Connection to the ethene and propene pipelines is present at all but two of the identified locations. The refineries north of Cologne, in particular, emit large amounts of CO₂ and are therefore particularly suitable for the CO₂-based production of olefins. In Lower Saxony and Brandenburg each is one site that is not in the immediate vicinity of the ethene and propene pipelines. If CO₂-based olefins were to be produced, a pipeline connection would first have to be established. The location in Brandenburg would be particularly interesting due to the high potential olefin production capacities.

Refineries are CO₂ point sources with a lower concentration of CO₂ in the flue gas. For this reason, the energy demand for the capture of CO₂ from the flue gas must be taken into account in the specific location planning. If necessary, the energy demand could be covered by using excess heat at the plant.

5 Summary and Outlook

The analysis did not consider that, in addition to CO₂ separation and purification, it might be necessary to transport CO₂ present in the region due to differences in the spatial distribution of CO₂ emitters and consumers. CO₂ can be transported by pipeline, ship, rail, or truck. In order to reduce transport costs, CO₂ can be compressed ⁸⁰. The compression of CO₂ is also necessary for methanol synthesis due to the production process. Possible compression steps are environmentally relevant as they are associated with increased electricity demand. Other studies have shown that CO₂-based polymer production saves greenhouse gas emissions, but is associated with increased raw material costs ⁸¹.

Further restrictions will have to be investigated in future research. This applies, in particular, to economic considerations, especially taking rapidly changing framework conditions into account (e.g., prices of CO₂ certificates). Current studies demonstrate that CO₂-based polymer production is not economically competitive ⁸². In a large-scale implementation, the effects on the existing energy network and production structures must be investigated ⁸³. The planning of specific plant concepts requires further region-specific investigations, which are currently being developed in various projects by Fraunhofer UMSICHT. It should also be noted that some of the considered CO₂ point sources would play a tangential role in the future, such as coal-fired power plants due to the approaching phase-out of coal as an energy source.

Abbreviations