How-to, Tips and Articles: The CO2-utilization Technologies That Convert CO2 Into Commercial Products via Chemical and Biochemical Reactions

Abstract

As an additional CO2-mitigation strategy to carbon capture and storage, CO2 capture and utilization (CCU) is attracting increasing interest globally. The potential applications of CCU are diverse, ranging from using CO2 in greenhouses and farming to conversion of CO2 into fuels, chemicals, polymers and building materials. CO2 has already been used for decades with mature technologies in various industrial processes such as CO2-enhanced oil recovery, the food and beverage industry, urea production, water treatment and the production of fire retardants and coolants. There are also many new CO2-utilization technologies at various stages of development and commercialization. These technologies have the potential to provide opportunities for emission savings for power and other industrial sectors by partially substituting fossil-fuel raw materials, increasing efficiency and using renewable energy, and generating revenues through producing marketable products. This paper investigates the CO2-utilization technologies that convert CO2 into commercial products via chemical and biochemical reactions with a focus on front-running technologies that are at, or close to, large-scale demonstration or commercialization. The CO2-utilization technologies are grouped according to the technological routes used, such as electrochemical, photocatalytic and photosynthetic, catalytic, biological process (using microbes and enzymes), copolymerization and mineralization. Recent developments and the status of the CO2-utilization technologies are reviewed. The environmental impact of CCU is also discussed in terms of life-cycle analysis.

Introduction

Urgent action is needed to reduce the emissions of greenhouse gases. The largest source of these emissions from human activities is from burning fossil fuels for power generation, manufacturing and transportation. Carbon capture and storage (CCS) provides a means of producing low-carbon electricity from fossil fuels and of reducing CO2 emissions from industrial processes such as gas processing, cement and steel making, where other decarbonization options are limited. Therefore, CCS is key to fulfilling the goal of the Paris Agreement to limit global warming to below 2°C. However, implementing CCS technology requires capital and operating costs. Anything that can reduce the cost of the capture process and/or can result in a value-added product could significantly improve the economics of such systems.

As an alternative to being buried underground for long-term storage, the captured CO2 can be used as a feedstock to produce marketable products. CO2 has many potential uses, either directly or indirectly by conversion. The direct use of CO2 has been practised for several decades in a wide variety of industrial processes. These processes include (but are not limited to) CO2-enhanced oil recovery (EOR), beverage carbonation (fizzy drinks), food processing, welding or as a cleaning agent in the textile and electronics industries and as a solvent (e.g. for the decaffeination of coffee and drinking-water abstraction). Typically, the scale of these applications is small, the technologies are mature and the chain of supply, production and sales is well established. Therefore, these processes are not discussed here.

CO2 can be converted into a wide variety of commercial products, such as synthetic fuels, building materials, chemicals (either as final products or intermediates) and polymers. A range of CO2-conversion technologies for producing these varied end-products are proposed and investigated [1–3]. In 2015, an international competition—the $20 million NRG COSIA Carbon XPRIZE—was launched to promote the development of technologies that convert CO2 into valuable products [4]. Ten finalists were selected in 2018. The prize will help identify the most promising pathways for CO2 conversion and prove they can be deployed at power plants and other industrial facilities. The 10 finalists must demonstrate at a scale that is at least 10 times greater than the requirements of the semfinals at one of two purpose-built industrial test sites. One is the Wyoming Integrated Test Center (USA) that is co-located with a coal-fired power plant and the other is the new carbon-conversion research hub co-located with a natural- gas-fired power plant in Calgary, Canada [4].

There are many technological routes to convert CO2 into commercial products, such as catalytic, electro- chemical, mineralization, biological (using microbes and enzymes), photocatalytic and photosynthetic processes. Electrochemical processes reduce CO2 into CO using electrolysers. H2, generally generated by water electrolysis, is a frequently used co-reactant for CO2 conversion into CH4, CH3OH, etc. Electrolysis processes are energy-intensive and have high costs. For the systems to be carbon-neutral, near-zero emission energy sources must be used. Compared to H2O electrolysis, which is well established, CO2 electrolysis is a more recent research area and work is needed to identify cheap, robust catalytic materials exhibiting high efficiency, selectivity and yield. When evaluated from a system-level perspective, energy efficiency, Faradaic efficiency, conversion rate, long-term catalyst(s) stability and durability, and process economics are five important factors to be considered for commercializing these technologies.

The main difference between photocatalytic and electrochemical CO2 reduction lies in the source of electrons, which are obtained from irradiating semiconductors under light in the former and by applying a current in the latter. A major advantage of the photocatalytic process is its direct use of photons, as opposed to initial conversion into electricity. However, such processes are complex, involving many mechanisms such as electron and proton transfer and chemical-bond formation/breaking, which are not well understood. Solar-energy-driven conversion of CO2 has attracted considerable interest worldwide and research in this field focuses primarily on the development of novel nanostructured photocatalytic materials and the investigation of the reaction mechanism on laboratory scales. For any approach using solar energy for CO2 conversion, efficiency is key for cost and scalability. Currently, the achievable CO2-conversion rates of the photocatalytic/ photothermal catalytic systems under development are often low and unfeasible for commercial-scale operations. As electrochemical or photocatalytic reduction of CO2 to produce chemicals or fuels with high specificity is rather challenging, it may be easier to use some well-established catalytic approaches to react CO2 and H2 to make carbon-based products. At the heart of these CO2-conversion technologies is the catalyst—the material that converts CO2 that needs to have high efficiency, selectivity, fast reaction rates and stability. R&D is currently being carried out world- wide to develop CO2-conversion catalysts. A number of catalysts have been engineered and tested, and they have demonstrated the ability to convert CO2 into various chemicals with high efficiency, selectivity and yield. Several reviews are available that describe the recent development in catalyst-reactor design [5–7]. More work is needed to make these catalysts more efficient, selective and stable over a long period of time. Based on these catalysts, even more work is required to develop technologically and economically viable processes for the conversion of CO2 into fuels and chemicals on a commercial scale. Also, one key technology for the market competitiveness of CO2-derived chemicals and fuels is the cheap production of carbon- free H2 [2]. In general, these processes require pure CO2, so CO2 emitted from sources such as fossil-fuel power plants, steel and cement-making needs to be purified, further increasing the costs.

With appropriate enzymes or bacteria, CO2 can be converted into chemicals through bioreactions. One advantage of bioconversion is that it normally takes place at low temperature and pressure, so energy consumption is low. The process is, in general, simple, with mainly bioreactor(s) and a product-separation/purification process leading to low costs. The processes can take the exhaust from emission sources without the need to treat and purify the flue gas. However, bioconversion is generally a slow process. The key to bioconversion technologies is to find or engineer enzymes or bacteria to convert CO2 into the desired product with high selectivity, yield and a fast conversion rate.

CO2 can also be incorporated into various chemicals as a C1 building block, as in CO2–epoxide copolymerization. This is not thermodynamically challenging because the entirety of the CO2 molecule is used and thus the C=O bonds are not broken. Efficient and selective catalytic systems are the core technology for successful and economical CO2 copolymerization.

Ready-mixed concrete can set and harden through a carbonation process. The CO2 curing of concrete involves reactions between calcium silicate in cement and CO2 in the presence of water to form both calcium carbonate and calcium silicate hydrate gel [8]. The carbonation reactions are exothermic. The heat released will speed up the curing process, limiting the need for heat or steam, and saving energy and emissions. As many solid industrial wastes such as steel slag, cement-kiln dust, waste concrete and coal fly ash are generally alkaline, inorganic and rich in Ca or Mg, they can be used as an alternative Ca or Mg resource for carbonation by reacting with CO2 in the presence of water, to produce construction materials. This type of technology has additional environmental benefits, as it means that both solid industrial wastes and captured CO2 are used and turned into marketable products. The carbonation process converts CO2 into a solid mineral and permanently stores it within the final product. Considering that concrete is the most widely used material in the world after water, the CO2-mitigation potential of CO2-carbonation technology for building-materials production is significant. A key challenge for the industrial-scale deployment of CO2 carbonation is to accelerate the slow process of carbonation.

This paper reviews the latest development of CO2- utilization technologies that are grouped according to the technological pathways used. Due to the large and varied wealth of R&D, this review focuses on the front runners of CCU technology that have reached a commercialization or pre-commercial stage or are close to large-scale demonstration. Efforts have been made to discuss these technologies in the order of more advanced to less advanced in technological development. However, this order does not necessarily reflect the true level of development of each technology as, in most cases, little information on the processes and their performance is available for assessment and comparison of the technologies.

1. Electrochemical conversion of CO2

The electrochemical conversion of CO2 has been a dynamic field of research. Many possible routes for conversion of CO2 into products such as syngas, methane, methanol or dimethyl ether (DME) with the incorporation of renewable power in the process are being explored. A German company, Sunfire GmbH, developed a process based on high-temperature co-electrolysis of steam (H2O) and CO2 using solid oxide electrolysis cells (SOEC) to produce syngas [1]. The syngas can then be converted into synthetic fuels, such as gasoline, diesel and methane. The SOEC operate at high pressure (>1 MPa) and high temperature (>800°C). They split gaseous water (steam) rather than liquid water into H2 and O2. In addition, co-electrolysis of H2O and CO2 is more cost-effective and energy-efficient due to the fast overall electrochemical kinetics. In the Sunfire process, the syngas is converted via the Fischer–Tropsch process into long-chain hydrocarbons (-CH2-), known as Blue Crude, to produce fuels or chemicals. The Fischer–Tropsch process is exothermic and the synthesis heat released can be used to vaporize water for steam electrolysis (see Fig. 1). This makes it possible to achieve a high level of efficiency (calculated as the electric energy conversion into the heating value of the fuel produced) of ~70% [1, 10].

Sunfire GmbH built a pilot plant in Dresden, Germany that successfully produced its first batches of high-quality diesel fuel in April 2015 [11]. The 10-kW electrolyser operates at 1.5 MPa and the power can be modulated from 0 to 100% without a negative effect on the stack. The pilot plant was operated continuously for more than 1500 hours and it reached a carbon-conversion efficiency of 90%. The synthetic fuel (Audi e-diesel) has a high cetane value and therefore has excellent combustion properties [1, 11]. In July 2017, Sunfire GmbH announced that it had begun en- gineering of an industrial-scale power-to-liquid (PtL) production facility in Norway, together with a consortium of partners. Nordic Blue Crude AS, a Norwegian cleantech company, will operate the 20-MWe PtL plant that will have a production capacity of 8000 t/y Blue Crude and is expected to be operational in 2020 [12].

Another German company, ETOGAS, developed a process that uses alkaline pressurized electrolysis of H2O to produce H2, which then reacts with CO2 to form CH4 [1]. The system is developed based on the dynamic, intermittent operation of photovoltaics (PV) linked to alkaline electrolysers. The direct coupling of PV power generators with alkaline electrolysers has been successfully demonstrated in different power ranges. The catalysts for methanation consist mainly of nickel, which is the same material as used in the electrodes for the electrolysis, which may reduce the costs of materials. ETOGAS has a 25-kW pilot plant in Bad Hersfeldt for testing of biogas upgrading and a 250-kW installation in Stuttgart. ETOGAS built a 6-MWe Power-to-gas (PtG) plant for German automotive manufacturer Audi AG in Werlte, Germany that started operation in 2013. The plant consists of three 2-MWe units and has been producing synthetic methane, called Audi e-gas, since 2013 in dynamic and intermittent operation using wind power and CO2 from a biogas plant. The plant can produce about 1000 t/y of Audi e-gas, chemically binding some 2800 tCO2. The Audi e-gas has a methane content of >96% and is provided for customers of the Audi A3-tron g. The unit size can be scaled up by increasing the number of electrolyser units [1, 5, 13]. Fig. 2 shows the energy efficiency of the PtG process.

Fig. 1 Sunfire process for Blue Crude production [1]

In December 2017, Hitachi Zosen Inova AG (HZI, which acquired ETOGAS technology in 2016), together with its parent company Hitachi Zosen Corporation, was awarded the turnkey contract to build the first PtG pilot plant in Japan as part of Japan’s efforts to achieve a long-term reduction in its CO2 emissions. The plant will take fossil CO2 emissions and combine CO2 with H2 to produce CH4, which will then be fed into an existing gas grid. Hitachi Zosen Corporation will deliver a polymer-exchange membrane electrolyser for H2 production. HZI will provide the ETOGAS catalytic reactor for the methanation process. This pilot project is scheduled to be commissioned in 2018/19 [14].

Danish company Haldor Topsøe developed a methanation process called TREMP™ [5]. The process consists of three adiabatic fixed-bed reactors that use home- developed methanation catalysts. The heat generated by the methanation process is recovered and used to generate high-temperature steam needed in the SOEC unit. Haldor Topsøe has built a 40-kW SOEC unit in Foulum, Demark. In 2016, they demonstrated a high-efficiency process with CH4 output of 10 m3/h, shown in Fig. 3, for biogas upgrade that converts the CO2 content (50–80%) in the biogas into pipeline-quality natural gas (methane). The overall efficiency of converting electrical power into methane is around 80% (see Fig. 4). The power consumption is thus 290 kWh/tCO2 avoided, the fresh water consumption is 1.6 t/tCO2 and there is no waste water or other emissions from the process [1, 5, 15].

Haldor Topsøe has also developed a process named eCOs™ to produce CO from CO2 and electricity using SOEC [15]. The eCOs™ process is designed as modules that can be combined into a plant with capacities from 25 to a few hundred m3 of CO/h.

Norwegian company DNV GL developed the ECFORM process to convert CO2 into formic acid and formate salts directly. The ECFORM process features a novel electrolysis reactor as illustrated in Fig. 5. It uses a proprietary tin- based alloy catalyst as cathodes to convert CO2 into for- mate salts. The reactor has a lower required cell potential and resistive losses, resulting in an increased energy efficiency of the process that makes it more economically feasible [17]. Test results show the electrodes have a selectivity of ~75% for the formate reaction and a lifetime of 1–2 years. The energy consumption of the cell is ~5.5 MWh/t and the process can run on renewable electricity [18]. DNV GL built a semi-pilot ECFORM demonstration reactor (see Fig. 6) with a 600-cm2 surface area and a capacity of reducing approximately 1 kgCO2/d. From 1 tonne of CO2, the process produces 1.04 tonnes of formic acid in the form of a minimum 85 wt% distillate, representing practically a 1:1 abatement of CO2 [1, 17]. This process is ready to scale up, but significant technological advancements are needed before large-scale production can take place.

A team at George Washington University, USA has been developing the C2CNT process, which can convert CO2 into highly valuable carbon nanofibres (CNF) and carbon nanotubes with inexpensive (nickel and steel) electrodes and low voltage. Carbon composites have a wide variety of applications, including in batteries, electronics and as lightweight alternatives to metals that are used today in aircraft, high-end sport cars and athletic equipment. In the C2CNT process, CO2 is bubbled into and dissolved in a molten carbonate bath. The CO2 is split by electrolysis at electrodes immersed in the molten bath into O2 at the anode and into carbon as pure carbon nanotubes at the cathode. By adjusting various parameters such as the addition of trace transition metals to act as CNF nucleation sites, the addition of zinc as an initiator and the control of current density, the formation of CNF or carbon nanotubes can be controlled and the product structure can be tuned and tailor-made for a specific application, such as for anodes in lithium- and sodium-ion batteries [19–21].

Fig. 2 Energy-conversion rate of the ETOGAS process [13]

Fig. 3 Haldor Topsøe’s integral SOEC and TREMP™ system [5]

Fig. 4 Exergy of Haldor Topsøe’s integral SOEC and TREMP™ system [16]

Fig. 5 ECFORM electrolysis reactor [18]

The C2CNT process can be used to capture CO2 directly from various sources such as the atmosphere, power and cement-production plants. The researchers proposed designs for fitting the system to natural-gas- and coal-fired power plants, where it would capture large amounts of CO2 and convert it into carbon nanotubes/nanofibres and pure oxygen. The oxygen could then be used to enhance combustion and the plant would have zero CO2 emissions [21]. Analyses show that production of carbon nanotubes could be more profitable for fossil-fuel power plants than generating power. For every tonne of natural gas consumed, a conventional natural-gas-fired combined cycle (NGCC) power plant produces US$909 of electricity and emits 2.74 tCO2, whilst the proposed combined NGCC and C2CNT plant would produce ~US$835 of electricity plus ~0.75 t carbon nanotubes worth ~US$225 000 at today’s price, and would emit no CO2. Using the C2CNT process, the cost of producing carbon nanotubes is estimated to be US$2000/t—less than 1% of current production costs [22]. Although the costs will be defined with the development and commercialization of C2CNT and the price will reduce when a large quantity of cheap nanotubes becomes available in the market, the profit potential exists, making this technology attractive and providing an incentive for the energy industry to reduce carbon emissions.

The C2CNT team is one of the 10 finalists to win the NRG COSIA Carbon XPRIZE [4]. At present, the researchers are working to scale up and demonstrate the C2CNT process.

The Sunfire and ETOGAS processes have been demonstrated on a pilot scale and the developers are confident to scale them up to small industrial-scale production.

ETOGAS produces CH3OH as a final product whilst the Sunfire process has the flexibility to produce various products, as it generates syngas as an intermediate. ECFORM, C2CNT and Haldor Topsøe’s processes need more R&D work and to be demonstrated on a larger scale.

Fig. 6 DNV GL’s demonstration reactor assembled in a solar-powered trailer (courtesy of DNV GL)

2. Photocatalytic and photothermal catalytic conversion of CO2

Solar-energy-driven conversion of CO2 has attracted considerable interest worldwide. A notable development is a working prototype of the ‘Sunshine to Petrol’ (S2P) reactor recently demonstrated by the Sandia National Laboratories (SNL) of US DOE [23, 24]. The S2P produces syngas (CO and H2) from CO2 and H2O using two-step metal-oxide-based thermochemical cycles. The heart of the S2P process is a unique metal-oxide-based thermochemical heat engine called the Counter-Rotating Ring Receiver Reactor Recuperator, or CR5, which features a continuous flow, spatial separation of products and thermal recuperation. Within the engine, reactive solid rings are continuously cycled thermally and chemically to produce O2 and CO from CO2 or O2 and H2 from H2O in separate and spatially isolated steps (see Fig. 7). The cylindrical metal CR5 is divided into hot and cold chambers. A solar concentrator heats the ceramic oxide reactant material on a rotating ring to ~1500°C (2700°F) and thermally reduces it, driving off some of the oxygen. The ring then rotates to a colder chamber that is filled with CO2. As it cools, the oxygen- deficient reactant material is re-oxidized by CO2 to restore it to its original state and to yield CO. This cycle repeats continuously. The same process can also produce H2 by pumping H2O instead of CO2 into the cool chamber. The H2 and CO are then mixed to make syngas, which can be turned into almost any type of hydrocarbon fuel [23].

Multi-cycle production of both H2 and CO has been demonstrated over several iron- and cerium-based compositions fabricated into monolithic pieces both in the SNL and at the National Solar Thermal Test Facility (USA). These compositions are being developed for deployment in a prototype CR5. Continued work on materials, reactor improvements and on demonstrating steady-state operation resulted in the development of the second-generation CR5, and a more compact and efficient reactor.

Fig. 7 Counter-rotating-ring receiver/reactor/recuperator (CR5) [24]

Fig. 8 Mass, energy balance and overall system efficiency of the ETL process [27]

The new reactor operated continuously, producing CO from CO2 at a peak efficiency of 1.7%, and recently achieved a H2 production rate of 2 L/h [24, 25]. However, the catalyst and construction materials developed so far are incapable of supporting efficiencies high enough for the technology to outpace other approaches such as electrolysis. Nevertheless, SNL’s work provided evidence of the potential of this technology.

Currently, extensive R&D is being carried out globally [6, 7]. Most of the work is focused on the development of efficient, selective and stable photocatalysts for the conversion of CO2 into chemicals. Various strategies such as doping, combining two or more semiconductors, synthesis of nanostructured materials, passivation layers and co-catalysts have been used so far to increase the efficiency and stability of photoactive materials.

3. Catalytic conversion of CO2

In 2012, Icelandic Carbon Recycling International (CRI) commissioned the world’s first CO2-to-methanol production facility with a current capacity of 5 million litres/y (4000 t/y) of methanol (branded Vulcanol™) [26]. Vulcanol™ is used as a blend component of gasoline and for further conversion into a diesel substitute. The CO2 is captured from flue gas released by a geothermal power plant located next to the CRI facility. The plant now recycles 5500 tCO2/y that would otherwise be released into the atmosphere. All energy used in the plant comes from the Icelandic grid, which is supplied by hydro and geothermal energy. The CRI’s patented Emissions-to-Liquids (ETL) technology consists of a low-pressure and low-temperature alkaline electrolysis system for H2 production and a catalytic fuel- synthesis process. CO2 passes a gas-conditioning system where impurities are removed to produce CO2 suitable for downstream methanol synthesis. The H2 and CO2 are mixed at a ratio of 3:1 and compressed to the target pressure followed by catalytic synthesis at an elevated temperature to produce methanol. Units can be scaled up by increasing the number of electrolysis cells. The reaction is highly exothermic and the heat is recovered and used in the downstream distillation unit, where the methanol produced is purified to a fuel grade for blending with gasoline [26, 27]. Fig. 8 shows the mass and energy balance and the overall efficiency of the ETL process.

CRI and a consortium of European industrial firms and research institutions have been awarded an €11 million grant under the EU’s Horizon 2020 programme to implement CRI’s ETL technology in a Swedish steel- manufacturing plant, demonstrating the conversion of residual blast furnace gases into liquid fuel [26]. CRI has been producing and selling Vulcanol™ in the commercial market [9]. The plant capacity is small. The competitiveness of Vulcanol™ largely depends on the oil price and is also influenced by policies.

A Canadian company, Carbon Engineering (CE), is scaling up and commercializing its Air-to-fuels (A2F) system [28]. A2F combines direct air capture (DAC) technology with water electrolysis and fuel synthesis to produce liquid hydrocarbon fuels (see Fig. 9). First, the DAC process captures CO2 from atmospheric air. The CO2 is then purified and compressed into a liquid, ready for use.

Second, clean electricity (such as solar PV) is used to electrolyse water and generate hydrogen. Third, the CO2 and hydrogen are thermo-catalytically reacted to produce syngas, which is then converted into hydrocarbons such as diesel and jet fuel.

CE has chosen the Direct Fuel Production™ platform as fuel-synthesis technology. Developed by a US company called Greyrock [29], the Direct Fuel Production™ platform, shown in Fig. 10, uses a proprietary catalyst and process to enable the transformation of a methane-rich steam (coal- mine methane, flare gas, syngas, natural gas or natural- gas liquids) into premium diesel fuel. The platinum-group metal-based catalyst can directly convert methane-rich gas into premium, ‘drop-in’ fuels, eliminating a costly refining step associated with the traditional Fischer–Tropsch process and, hence, allows the economically feasible operation of small-scale gas-to-liquid facilities [29].

Fig. 9 A diagram of CE’s A2F process [28]

Fig. 10 A diagram of CE’s A2F process [29]

Fig. 11 BSE Engineering’s methanol-synthesis process: catalytic exothermic reaction of CO2 (1.36 t/h) and H2 (0.19 t/h) to raw methanol (1.55 t/h) [30]

In 2015, CE commissioned a DAC pilot plant that captures and purifies 1 tCO2/d from the atmosphere. In 2017, a water-electrolysis and a Greyrock M-Class fuel-production plant have been installed with a capability of synthesizing roughly 1 barrel/d of fuel. In December 2017, the A2F system successfully produced its first small quantities of liquid fuels [28]. A2F process uses proven technologies and the integrated system has proven to work well on a small scale. It is anticipated that this system can be scaled up without major technical and engineering barriers. The main disadvantages are its large footprint and high costs.

BSE Engineering (Germany) has been developing a flexible and sustainable process for producing methanol from CO2 and H2 (see Fig. 11). The process uses an alkaline electrolyser and excess renewable electricity to produce H2 in a fluctuating operating mode. CO2 that is captured and purified are fed along with H2 into a reactor at the correct ratio to produce methanol via the catalytic, exothermic reaction. The reaction heat is recovered in the form of steam and is used in the methanol-purification process. The raw product from the reactor contains 64% CH3OH and 36% H2O, which is purified by distillation to a final product of >99.85 wt.% CH3OH. Both the water-electrolysis and methanol- synthesis processes have high flexibility ranging from 10 to 120% [30].

Fig. 12 LanzaTech gas-fermentation process [32]

BSE Engineering recently completed a demonstration project in which different catalysts were tested. In August 2017, BSE Engineering and BASF (Germany) signed an exclusive joint development agreement for BASF to provide custom-made catalysts for the methanol-synthesis process to enable efficient production of methanol [31]. BSE Engineering envisions the first roll-out of a 10-MW power- to-methanol plant in 2019/20 [30].

4. Bioconversion of CO2

Several interesting bioconversion routes using CO/CO2 are also under development, some on an industrial scale. LanzaTech developed a biological gas-fermentation process that uses exhaust gases from industrial processes to produce fuels and chemicals [32]. The process uses microbes that grow on gases (rather than sugars, as in traditional fermentation) to transform CO-rich waste gases and residues into chemicals in a continuous process. LanzaTech’s proprietary bacteria is a naturally occurring organism in the acetogens family or gas-fermenting organisms that can digest a wide variety of carbon-rich wastes to produce fuels and chemicals such as ethanol and 2,3-butanediol at high selectivity and yields. The process can consume H2-free CO-only gas streams due to the highly efficient biological water gas shift reaction occurring within the acetogenic microbes. This reaction allows the bacteria to compensate for any deficit of H2 in the input gas stream by catalysing the release of H2 from water using the energy content of CO. As a result, the LanzaTech process is feedstock-flexible and can deal with flue gas with a range of CO and H2 compositions [1, 32]. The LanzaTech process is simple (see Fig. 12) and operates at close to ambient temperature and atmospheric pressure, resulting in reduced CO2 emissions and minimized heating and cooling costs. It uses two sources of energy: steam for the separation/ purification of the end-product and electricity to run the process equipment such as pumps and compressors.

LanzaTech started pilot-scale ethanol production with a capacity of 56.8 m3/y using off-gas exhaust from a steel mill in 2008. In November 2012, LanzaTech started a 380-m3/y demonstration plant with China’s largest steel producer, Baogang in Shanghai, converting CO-rich flue gas from Baogang’s steel mill into ethanol. A second demonstration plant of the same size has been built at Shougang’s steel mill in Beijing and has been operational since 2013. This facility runs on a flue gas that contains a high proportion of CO and no H2, and it achieved >1000 hours of continuous operation at a production rate of 400 m3/y. An additional facility fed with steel-mill off-gas with a capacity of 46.2 m3/y ethanol entered operation in 2014 in Kaoshiung, Taiwan. In 2013, LanzaTech commissioned a demonstration plant in Georgia (USA) using syngas from biomass gasification to produce ethanol. In 2014, LanzaTech, with Japan’s Sekisui Chemical, successfully demonstrated ethanol production from municipal solid waste (MSW)-derived syngas using the LanzaTech process. The Sekisui MSW processing plant is a commercial plant that gasifies unsorted, non-recycled, non-compostable MSW and the resultant syngas is burned to generate electricity. A slip stream of the syngas containing H2:CO at a 1:1 ratio was fed to a LanzaTech bio- reactor to produce ethanol continuously that exceeded the target production rates several times over a period of 12 months. These facilities have demonstrated different key aspects of the LanzaTech process [32, 33]. LanzaTech’s first commercial facility converting waste emissions from steel production into ethanol with a capacity of 60 567 m3/y started operation in May 2018 in China, and several more commercial-steel off-gas-to-ethanol plants are planned or under construction in China and Belgium (90 850 m3/y). A LanzaTech plant converting ferroalloy exhaust into ethanol with a capacity of 53 212 m3/y is scheduled to start operation in 2019 in South Africa [32, 33].

LanzaTech is also developing a fermentation process that can use CO2 as a carbon source. Currently, they are working with the Indian Oil Corporation (IndianOil) to construct the world’s first refinery off-gas-to-bioethanol production facility. The 40 000-m3/y (35 000-t/y) demonstration facility will be installed at IndianOil’s Panipat Refinery, at an estimated cost of 350 crore rupees (US$55 million). It will be integrated into the existing site infra- structure and will be LanzaTech’s first project capturing refinery off-gases [33]. The refinery exhaust contains almost equal amounts of CO and CO2, and has a high H2 content (H2:CO ratio is 5:1). Fifty per cent of carbon in the ethanol product will come directly from CO2. The plant is scheduled to come online in 2019 [33]. As described above, the LanzaTech process has been successfully demonstrated on a pre-commercial scale using syngas or CO-rich gas from various sources. Several commercial projects are under construction and planned. Work is ongoing to develop a system that can convert CO2 efficiently and economically.

An American company, Joule Unlimited Technologies Inc., engineered microbes such as genetically modified cyanobacteria that harness the sun’s energy to convert CO2 and H2O directly into ethanol or hydrocarbon fuels in a continuous, single-step conversion process. The technology was facilitated by Joule’s patented SolarConverter system, which made use of interconnected circulation modules in the form of thin and standard capsules filled with its proprietary microorganisms, non-potable water and micro- nutrients. The cyanobacteria were grown in non-potable water and waste CO2 sourced from the local industrial flue-gas streams and fertilizer was fed into the capsules to promote growth. The microorganisms were kept in motion to enable them to receive maximum exposure to sunlight, driving photosynthesis. The microorganisms charged by sunlight absorbed the CO2 and produced fuel molecules that were transferred to the medium on a continuous basis. The medium circulated through a separator extracting the end-product, which was finally sent to the central plant for separation and purification to fuel grade [34]. The process took up to 8 weeks, after which the modules were flushed and cleaned on a rotational basis. The process was designed to convert CO2 emitted from power plants and industrial processes in the presence of a catalyst into a specific molecule of interest, including ethanol and hydrocarbons comprising diesel, jet fuel and gasoline.

No pre-treatment of the waste CO2 flue gas was required [34, 35]. Joule completed 2-year pilot testing of diesel and ethanol (trademarked Sunflow-D and Sunflow-E, respectively)-production processes and received approval from the US Environmental Protection Agency (EPA) for the Sunflow-E as an advanced biofuel in 2016 [34].

Joule’s technology targeted a price point of 0.32 $/L ($1.20 per gallon) or $50 per barrel for both Sunflow-E and Sunflow-D products [35]. When it was first demonstrated, these prices were competitive with conventional fuels and attracted many interested investors around the world. Joule had ambitious plans to commercialize its technology by building a number of commercial plants at multiple locations worldwide. However, the investors later withdrew and Joule Unlimited collapsed during 2016–17, but the developers believe that the technology is worthy of continued developing [36].

Interesting developments are also underway in the area of engineered bacteria and enzymes for bioconversion of CO2. Scientists at the University of Dundee (UK) recently developed a process that enables the Escherichia coli (E. coli) bacterium to act as an efficient carbon-capture device and convert CO2 into formic acid [37]. US scientists created a novel enzyme, formolase, using a computational protein design programme, which can convert formaldehyde into dihydroxyacetone—a reaction not known to occur naturally. This allows the development of a unique CO2-fixation pathway that will feed directly into E. coli’s central metabolism. Strains expressing this pathway can be modified for the conversion of CO2 into fuels such as ethanol [38]. Although still in the early stage of development, this approach opens a way to alternative CO2-conversion pathways using microbial biotechnology.

5. Copolymerization of CO2

Polymers have traditionally been derived primarily from petrochemicals. The ring-opening copolymerization of CO2 and epoxides for the synthesis of a range of aliphatic polycarbonates was discovered in the 1960s and is now considered to be practical for scaled production and application. The Asahi Kasei Corporation (Japan) has developed a process for polycarbonate production from CO2 without using toxic phosgene and CH2Cl2 (and hence it is non-corrosive) [39]. The process uses ethylene oxide, its by-product CO2 and bisphenol-A as starting materials to produce two important products: polycarbonate and monoethylene glycol. The catalysts have high activity and selectivity, resulting in high purity and high yields of the products, and therefore separation and purification of the products are unnecessary. Also, there are no wastes for disposal or treatment. The developers claim that the Asahi Kasei process has lower capital costs than the traditional phosgene process [39]. Since the first commercial polycarbonate production started in Taiwan (China) in 2002, several Asahi Kasei process plants have been built or are under construction in South Korea, Russia and Saudi Arabia under licence agreement. Asahi Kasei has sold a license for this process to six companies with a total polycarbonate production capacity of 1.07 Mt/y by 2019, meaning that 0.185 MtCO2/y can be fixed in the products [40] [41].

In the Production Dreams project, Covestro (Germany) and its partners developed a process that uses up to 20% of CO2 as a feedstock to produce polyether-polycarbonate polyols (cardyon™ polyols). The catalyst developed for this process has a high selectivity and, therefore, the formation of undesirable by-products is avoided. Also, the cardyon™ polyols possess the properties required for polyurethane foam application [1]. Since June 2016, Covestro has been operating a production plant in Dormagen, Germany to manufacture the cardyon™ polyols for flexible polyurethane foams for use in mattresses and upholstered furniture. The plant has a capacity of 5000 t/y and the CO2 processed is a waste product from a neighbouring chemical facility [42].

Novomer Inc. (USA) developed a catalytic process to produce polypropylene carbonate polyols containing up to 50 wt.% of CO2. Its trademark Converge® polyols are used primarily in polyurethane formulations targeted at coatings, adhesives, sealants, elastomers, and flexible and rigid foams. The company’s initial products (1000 and 2000 molecular weight grade diols) are manufactured at a multi-thousand-tonne commercial- scale toll facility in Houston (USA). Novomer claims that incorporating these new polyols into existing formulations yields final products with improved performance, strength and weatherability. At costs of less than 200 US$/t, CO2 is cheaper than conventional petroleum-based raw materials and, hence, Converge® polyols would cost less than conventional polyols when produced on a full commercial scale [1, 43]. In November 2014, Novomer announced that Jowat AG, a supplier of industrial adhesives headquartered in Germany, would be the first to commercially adopt Novomer’s new Converge® polyols for use in polyurethane hot melt adhesive applications. In 2016, Novomer announced that it had successfully completed commercial-scale rigid foam trials using two unique polyols blends. Both polyol blends were processed on full-scale continuous lamination lines. Combining Converge® polyols with a recycled polyethylene tereph- thalate (r-PET) polyol, the optimized polyol blends enable foam manufacturers to produce polyisocyanurate foams using traditional equipment and processing conditions and reduce the total petrochemical feedstock content and polyols costs [43]. In 2016, US automaker Ford announced that, using Converge® polyols produced with CO2 captured during its operations, it had created and tested new foam and plastic components for applications such as seat cushions and the new materials would go into production vehicles within 5 years [44].

There are many other companies and institutes that are actively developing and producing CO2-based polymers. In China, Nanyang Zhongju Tianguan Low Carbon Technology Company says it has developed a catalyst system for the copolymerization of propylene oxide and CO2 (a by-product of its ethanol-production process) to produce biodegradable polypropylene carbonate. In 2015, it had a production capacity of 25 000 t/y and a new 100 000-t/y production facility was under construction [45]. Other Chinese CO2 based polymers producers include Jinlong Green Chemical Company that produces aliphatic polycarbonate polyols from CO2 and ethylene oxide using a polymer-supported bimetallic compound as a catalyst and biodegradable polyurethane foam [46] and Inner Mongolia Mengxi High-Tech Group Company that produces 3000 t/y aliphatic polycarbonate using CO2 from its cement kiln [47].

Newlight Technologies (USA) developed a biological system to produce plastics trademarked AirCarbon [48]. This process has three steps: capture, extraction and polymerization. First, concentrated CH4 or CO2 emissions from sources are directed into a bioconversion reactor. These carbon emissions are combined with Newlight’s biocatalyst, which pulls carbon out of the CH4 or CO2. Finally, carbon, oxygen and hydrogen are re-assembled to form a biodegradable long-chain thermopolymer, AirCarbon. AirCarbon is made of approximately 40 wt.% oxygen from air and 60 wt.% carbon and hydrogen from captured carbon emissions. It is a high-performance thermoplastic and can be used as a substitute for oil-derived plastics. The developers claim that an independent life-cycle analysis (LCA) has verified that AirCarbon is a carbon-negative (net negative avoided CO2 emissions) material. Moreover, AirCarbon is cheaper than its oil-based counterparts due to the highly efficient biocatalyst developed by Newlight Technologies [48].

The AirCarbon-production process achieved commercial scale in 2013 and it is currently used for packaging by companies including Dell and the Body Shop. In July 2015, Newlight Technologies signed a 20-year off-take agreement with Vinmar International Limited, a major player in the global petrochemicals industry, to sell 100% of AirCarbon PHA (Polyhydroxyalkanoates) from Newlight’s planned 22 680-t/y production facility for 20 years. The contract also covers 100% of the output from two AirCarbon-production facilities for a total of >8.6 Mt over 20 years. Newlight Technologies also signed a 4.5-Mt Production License Agreement with IKEA in 2016 and a 15-year Production License Agreement with Paques Holdings bv [48].

Econic Technologies (UK) has developed two homogeneous catalyst systems: alternating-catalyst systems and tunable catalyst systems [49, 50]. Alternating-catalyst systems enable the polymerization of epoxides and CO2 to produce polycarbonate polyols with the maximum possible CO2 content (see Fig. 13). These polyols have excellent properties for some high-performance applications, but they have a higher viscosity than their traditional petrochemical-based counterparts, which limits their use in other areas. Tunable catalyst systems overcome this limitation by allowing the amount of CO2 incorporated into the polyols to be tailored according to the performance requirements of an application. The polyols are reacted with di-isocyanates to make polyurethanes, which can be used for a variety of applications such as foams for mattresses or car seats and resistant coatings in paints. The developers claim that both the catalyst systems can operate efficiently in existing polymer-manufacturing plants without the formation of significant by-products [49]. Tests conducted using CO2 captured from the UK’s first CCS pilot project at Ferrybridge coal-fired power station showed that the catalysts were robust enough to deal with the impurities contained in the captured CO2, producing the same polymer as that resulting from using pure CO2 [50]. Econic Technologies has recently opened a demonstration plant comprising all elements of the industrial production process, integrated from reaction through to final product treatment [49].

Fig. 13 Econic catalyst systems [51]

CO2-copolymmerization technologies are fast advancing. Some companies have been commercially producing CO2-based polymers for years whilst others are marketing their products. It can be expected that more CO2-based polymer products will emerge in the commercial market in the near future.

6. Mineral carbonation

A CO2 concrete-curing process developed by CarbonCure Technologies (Canada) injects liquid CO2 delivered in a pressurized tank into wet concrete while it is being mixed [8]. The CO2-curing process takes place under atmospheric pressure and without the need for special curing chambers.

The concrete products have the same or better quality compared to those produced using conventional methods. The curing time is significantly reduced, leading to cost reduction. However, the cost savings are offset to some extent by the use of liquid CO2 for the curing process. Once injected, the CO2 becomes chemically converted into a solid mineral and permanently stored within the concrete. It was estimated that the efficiency of CO2 absorption into the concrete is about 50–80%. A cubic metre of concrete can take up to around 3.5 kg of CO2 [8, 52]. A preliminary analysis shows that CO2 curing has a lower cost compared to the use of a non-chloride accelerator [52]. The process can be integrated into the concrete producer’s batching system and has no impact on normal operations. The CarbonCure process has already been adopted in a number of ready-mix concrete plants owned by several producers with 25 masonries and 45 ready-mix installations, mainly in North America, and there are plans to retrofit more [53]. In January 2018, CarbonCure announced that it had led a team of five companies to demonstrate its technology to convert CO2 emissions from cement production into value-added concrete for construction projects. CO2 emissions from the Argos Roberta cement plant near Calera, Alabama (USA) will be captured, transported and reused in Argos’s Glenwood (USA) concrete operations equipped with the CarbonCure process. This concrete cured with captured CO2 is then used in a local construction project [53]. CarbonCure is one of the 10 finalists for the NRG COSIA Carbon XPRIZE.

Solidia Technologies (USA) is currently commercializing its cement- and concrete-making technology. During the Solidia Technologies’ Concrete™ curing process, concrete ready-mix is poured and vibrated in moulds to achieve concrete consolidation. The raw concrete is then removed from moulds and loaded into a curing chamber. CO2 is injected into the curing system, which is then sealed until the curing process is complete [54]. The developer claims that the technologies can ease production, reduce costs with improved performance of cement and concrete, while reducing the carbon footprint of Solidia Concrete™ by up to 70% and water consumption by 60–80%. It is estimated that up to 300 kgCO2 can be absorbed by each tonne of Solidia Cement™ used to make concrete. The Solidia Concrete™ curing process is adaptable to a wide variety of concrete formulations, production methods and standards while using manufacturers’ existing batching/mixing equipment. The concrete reaches full strength in 24 hours compared to the up to 28 days required for traditional concrete products [54]. Solidia Technologies is now commercializing its technologies.

In 2012, Carbon8 Systems (UK) successfully put its patented Accelerated Carbonisation Technology (ACT) into commercial operation to produce carbon-negative aggregate. The ACT uses captured CO2 to treat a wide range of thermal wastes such as cement dusts, steel slags, oil-shale ash, incinerator ash or paper ash and contaminated soils [55, 56]. Fig. 14 shows the flowchart of the ACT process. The waste is blended with a precisely controlled quantity of liquid CO2 and water in the pre-treatment mixer for carbonation. The carbonated waste is sent to the batch mixer, where fillers and binders are added. The mixture is then delivered to the pelletizer, where gaseous CO2 is injected to accelerate the cementation process to form rounded aggregates. Screening and storing the aggregates complete the process [57]. Rainwater is collected and used in the process and there is no solid, liquid or gaseous waste discharged. The process is exothermic and hence it does not require heat. Only electricity is consumed to move materials through the system. Consequently, the process fixes more CO2 in the aggregate than the CO2 emitted so it is carbon-negative.

The first ACT plant at Brandon in Suffolk (UK) was commissioned in early 2012 and it now produces over 65 000 t/y of carbonated lightweight aggregate (or 30 000 t/y APCR) from MSW incineration air-pollution control residues (APCR). The final product derived from hazardous APCR has been designated as ‘end-of-waste’ by the UK Environment Agency. In February 2016, a second plant with a capacity of 100 000 t/y was commissioned in Avonmouth and three more UK plants of a similar size or larger were expected to be operational in 2018 [55, 57].

Researchers in the UCLA (University of California, Los Angeles, USA) Carbon Upcycling team have been working on a unique process that converts CO2 emissions from power plants and industrial facilities into a near CO2- neutral building material, called CO2NCRETE. Their approach is based on the integration of several technologies into a closed-loop process, to utilize flue gas exhausted from point source emitters by efficiently recovering waste heat and enriching CO2 present in the gas stream to fabricate CO2NCRETE. A novel binder system based on calcium hydroxide (Ca(OH)2) is mixed with aggregates and admixtures to form a CO2NCRETE building element in the desired shape. The final, and key, step lies in combining the captured CO2 with the CO2NCRETE element via a carbonation reaction to form a solid building component. As a construction material, CO2NCRETE is suitable for various formulations and can be made into different shapes. These elements can be used like Legos to rapidly assemble buildings, bridges and other infrastructures traditionally constructed using concrete [58]. Carbon Upcycling’s process allows for CO2 borne in the flue gas of power and industrial plants to be captured and converted at its source. It is capable of handling flue gas from various sources containing varying CO2 concentrations without the need for pre-treatment [59]. The UCLA Carbon Upcycling team is another finalist for the NRG COSIA Carbon XPRIZE.

Carbstone Innovation NV of Belgium and Canadian company CarbiCrete independently developed a cement- free concrete-making process using steel slag by CO2 carbonation [60]. The Carbstone Process uses an innovative grinding mill to grind coarse slag into fine particles that are used as fillers. Two mixers blend the various raw materials (fillers and various slag sands) with water. The par- ticle size of the raw materials and the quantity of water are precisely controlled for an optimal carbonation process. In the next step, the moist mixture is hydraulically pressed into the required shape such as large bricks, which may be either hollow or solid. The carbonation is carried out in an autoclave under high pressure and temperature [60]. The Carbonation Activation process developed by CarbiCrete uses steel slag to replace cement and CO2 is injected into wet concrete to carbonate it and to give it its strength. The process can be implemented in any concrete-producing plant with virtually no process-flow disruption [61]. CarbiCrete estimates that the production of a standard-sized concrete block (often referred to as a cinder block that weighs 18 kg) using this process would result in 2 kgCO2 emission savings and 1 kgCO2 would be absorbed by a cinder block during the curing process [62].

Fig. 14 Carbon8 Systems’ ACT process [56]

CO2-mineralization processes for manufacturing of inorganic chemicals have also been investigated. The SkyMine process [63], developed by Carbonfree Chemicals (formerly Skyonic), both captures and utilizes CO2. The process can remove CO2 and acid gases such as SO2 and NOx as well as heavy metals from exhaust gases from power and other industrial plants and transform them into marketable products, such as sodium bicarbonate or baking soda, water-based HCl solution, sodium hydroxide or caustic soda and bleach. It uses an electrochemical method to make a low-concentration NaOH solution from salt and water. This solution is then used to scrub CO2 and other chemicals from a flue gas and can ultimately produce high-purity NaHCO3. The electrolysis also produces hydrogen and chlorine gases. The patented SkyMine process can be applied to new and existing stationary emitting sources such as refineries, power plants and steel mills. The first SkyMine facility was built at Capitol Aggregates cement plant in San Antonio, Texas (USA) and it began operation in March 2015. It was estimated that a 15% CO2 emissions reduction could be achieved at the plant, which was equivalent to annual savings of 83 000 tonnes of CO2 [63].

7. Life Cycle Assessment (LCA)

The CO2 savings of CCU depend largely on the utilization option. To assess and estimate the full range of benefits such as the net CO2 emissions avoided, the length of time the CO2 is stored in the product and the potential market value of a use, it is essential to apply sound analytical methodologies. LCA considers the entire life cycle of products and processes from raw-materials extraction and transport via production and product use to recycling and final disposal of wastes. However, many CCU technologies are under development and the data are not yet available for a full LCA. Nevertheless, several LCAs have been conducted for different CCU processes based largely on assumptions. These results may not be accurate and reliable, but could provide some indicative comparisons.

Using the data provided by Joule Technologies, the US EPA’s analysis determined that Joule Technologies’ Sunflow-E, ethanol produced from bioconversion of CO (as described in Section 4), could achieve an 85.1% life-cycle greenhouse gas emission reduction when compared to baseline fossil-fuel-based gasoline [34]. Cuéllar-Franca and Azapagic [64] compared 16 LCA studies of different CCU pathways published in the literature. They recalculated some results for comparison purposes, as shown in Fig. 15. Thirteen of the studies considered fossil-fuel power plants as a source of CO2, with the rest using CO2 from chemical plants such as ammonia and hydrogen production. The results suggested that mineral carbonation could reduce the global-warming potential (GWP) by 4–48% compared to not having CCU. The estimated GWP ranged from 524 kg CO2 equivalent for each tonne of CO2 removed directly from a power plant to 1073 kg CO2-eq/t removed when the CO2 is captured using monoethanolamine (MEA). Utilizing CO2 for the production of chemicals, specifically, dimethyl car- bonate could reduce the GWP by 4.3 times compared to the conventional dimethyl carbonate process from phosgene (31 rather than 132 kg CO2-eq/kg dimethyl carbonate). CO2- EOR had a GWP 2.3 times lower than releasing the CO2 into the atmosphere. Capturing CO2 by microalgae to produce biodiesel had a GWP 2.5 times higher than fossil diesel.

A ‘cradle-to-gate’ (including production and all upstream processes) analysis of polyols for polyurethane production using CO2 (captured from a lignite power plant) was conducted using data from a real industrial pilot plant [65]. The analysis indicated that the production of polyols with 20 wt.% CO2 in the polymer chains resulted in up to 3 kg CO2-eq emission savings per kg CO2 utilized. The use of fossil-fuel resources could be reduced by 13–16% and emissions of other air pollutants were also lowered.

A preliminary LCA of the CarbonCure process (see Table 1) shows that the CO2 concrete-curing process can have a net CO2 emissions reduction of ~18 kg/m3 concrete [66].

Fig. 15 Comparison of GWP of different CCU options [64]

Table 1 LCA of the CarbonCure process for concrete production [66]

8. Conclusions

The utilization of CO2 as a feedstock to produce a wide variety of chemicals and materials poses a challenge but also provides new opportunities to diverse industries. CCU covers a number of technologies and products, and involves a wide range of new players and industries. Various technology pathways are being explored. In recent years, CCU technologies have made rapid advances. Several technologies for the production of fuels or chemicals by catalytic, electrochemical and bioconversion of CO2 or CO2-derived polymers via CO2 copolymerization are already in commercial operation and more are emerging in the commercial market. At the heart of these technologies is the catalyst that converts CO

Extensive R&D is ongoing worldwide. A number of catalysts (and microbes) have been engineered and tested, and they have demonstrated the ability to convert CO2 into various chemicals with high efficiency, selectivity and yield. Most of the investigations are still at a very early stage of development and more work is needed to develop technologically and economically viable processes for the conversion of CO2 into fuels and chemicals on a commercial scale.

The developments of technologies for producing construction and other materials through CO2 carbonation such as CO2-cured concrete and accelerated carbonation of wastes for carbonated aggregate production are more advanced and several processes are being commercialized. These technologies are easy to install or retrofit in the current production systems and are economically competitive with relatively low costs. The products produced have qualities similar to, or better than, those traditionally produced and can store the CO2 permanently. Therefore, they are expected to be one of the first CCU technologies to achieve widespread deployment.

LCA of CCU processes shows that CO2-derived polymers and CO2-cured concrete have a better environmental performance and a smaller carbon footprint than traditionally produced counterparts. LCA also indicates that fuels such as methanol produced from CO2 have environmental benefits when renewable energy is used for their production.

Looking ahead, CCU will continue its progression in the short to medium term, especially in areas that are technologically more advanced, such as CO2-derived polymers, CO2 carbonation and methanol production. In the long term, CCU will become a key element in a circular carbon economy with sustainable low-carbon chemical and energy production.

Source: Qian Zhu - The IEA Clean Coal Centre

Advertisement

The 10 largest coal producers and exporters in Indonesia:

Click Here for Top World Clean Coal Technologies Contractors

Wednesday, February 5, 2020

The CO2-utilization Technologies That Convert CO2 Into Commercial Products via Chemical and Biochemical Reactions