The utilization of CO2 as a feedstock for producing chemicals not only contributes to alleviating global climate changes caused by the increasing CO2 emissions but also provides a grand challenge in exploring new concepts and opportunities for catalytic and industrial development
The refiners in the future will use carbon dioxide as a raw material for making fuels, chemicals, and polymers/materials, and not ubiquitous crude oil. A liability now will be an asset tomorrow! The sustainability of the current generation’s high lifestyle requires a huge amount of energy which is primarily satisfied by the fossil resources: oil, natural gas, and coal.
The concentration of carbon dioxide in the atmosphere has increased from 280 ppm before the industrial revolution to 410 ppm in January 2020 to 419.8 now. The increased atmospheric CO2 concentration is arguably one of the primary causes of accelerated climate change and global warming. This supply chain from fossil feedstock cannot sustain forever as all these energy sources will diminish within three centuries. From the economic point of view, importing fossil fuel from foreign countries worth billions of dollars is a waste of foreign exchange. The Russia-Ukraine war has given a severe jolt to all oil-dependent economies.
The Government of India wants to reduce import of oil by developing new technologies including renewable resources such as solar, wind, hydro, coal to fuels and chemicals, 2G ethanol, biodiesel, etc. India accounts for more than a quarter of net global primary energy demand growth between 2017-2040 according to BP Energy; 42% of this new energy demand is met through coal, meaning CO2 emissions roughly double by 2040.
The Paris Agreement is meant to reduce the risk and impact of global warming by adopting two long term temperature goals, i.e., to check the global average temperature rise well below 2 °C above pre-industrial level, and to take more deliberate actions to limit the rise in temperature to 1.5 °C above pre-industrial levels. To achieve this goal a 20/20/20 strategy was adopted, meaning thereby, 20% decrease in CO2 emission, rise in renewable energy market share by 20%, and 20% increase in efficiency of current technology. For meeting a target of 400 GW solar power, an investment of US $500 billion is needed.
Reducing CO2 concentration in the atmosphere while meeting the energy demands of an increasing population is a formidable task for countries like India and requires long term planning and implementation of CO2 mitigation strategies. Reduction of CO2 production by shifting from fossil to renewable fuels, CO2 capture and storage (CCS), and CO2 capture and utilization (CCU) are the possible areas for systematic control and reduction of atmospheric CO2. Carbon Capture and Utilization and Storage (CCUS) is one of the key areas that can achieve CO2 emission targets while simultaneously contributing to the production of energy, fuels, and chemicals to sustain the increasing demands. In the CCU concept, carbon dioxide is captured and separated from emission gases and then converted into valuable products.
Thus, CO2 may become the future of oil through the development of synthetic fuels starting from the mixtures of carbon dioxide and hydrogen with specific catalytic chemical reactors. In that way CO2 appears as one of the possibilities for high level energy storage, including the network regulation from renewable energy production.
But, in every case, new catalytic processes and chemical plants are needed to develop this future industry. Flue gases from fossil fuel-based electricity-generating units are the major concentrated CO2 sources in India. If CO2 is to be separated, as much as 100 MW of a typical 500-MW coal-fired power plant would be necessary for today’s CO2 capture processes based on the alkanolamines absorption technologies. Therefore, it would be highly desirable if the flue gas mixtures are used for carbon dioxide conversion but without its pre-separation.
Therefore, carbon dioxide conversion and utilization should be an integral part of CO2 management. As an economical, safe, and renewable carbon source, CO2 turns out to be an attractive C1 chemical building block for making organic chemicals, materials, and carbohydrates (e.g., foods). The utilization of CO2 as a feedstock for producing chemicals not only contributes to alleviating global climate changes caused by the increasing CO2 emissions, but also provides a grand challenge in exploring new concepts and opportunities for catalytic and industrial development. CO2 can be catalytically converted to methane, methanol, dimethyl ether, liquid hydrocarbons, formic acid, gaseous hydrocarbons, urea, organic carbonates, etc. Methanol can be produced from methane either through steam reforming (SR) or direct partial oxidation (DPOM) or dry reforming (DR) with carbon dioxide.
The author is working in collaboration with the ONGC Energy Centre on green hydrogen production and CO2 conversion technologies having obtained several patents. And SR and DPOM are comparably economical, although SR is at a rather developed stage of technological maturation and expectedly has greater thermodynamic and carbon efficiencies compared to DPOM. Nevertheless, the economical use of methane as feedstock to produce methanol lays strong foundations for the future methanol economy.
Methanol can be converted into a host of valuable chemicals including olefins in promotion of the so-called methanol economy, a concept advocated by the NITI Aayog. Dimethyl ether (DME) has many fascinating attributes as a fuel which can be produced from carbon dioxide using innovative catalysts, reactors, and separators. DME is the cleanest high-efficiency compression ignition fuel as a substitute for diesel. DME’s autoignition property and high-octane number (55 to 60) are advantageous and allow DME to be used as a propane and butane substitute in LPG as a cooking fuel and the well-established LPG industry infrastructure can be used for DME.
The CO2 conversion into gaseous or liquid hydrocarbon requires high temperature (250-450 °C) and pressure (20-40 bar), but the conversion is low due to difficulty in the activation of CO2. Various catalysts need to be actively investigated to enhance CO2 conversion and to control selectivity toward specific target products.
The hydrogen production technologies are called grey, blue and green depending respectively on the source such as natural gas (with no carbon capture), natural gas or biomass with advanced carbon capture and low GHG, and electrolysis of water.
According to the Hydrogen Council and McKinsey report large scale renewable hydrogen production costs are expected to fall faster to lower than USD 2.3 per kilogram and the low-carbon hydrogen can break even with grey hydrogen between 2028 to 2034 at a cost of about US $35-50 per ton of carbon dioxide equivalent. The US Department of Energy has stated that a price of around US $2.5 will be the most economical for the hydrogen economy.
In fact, hydrogen will play an important role in all these chemicals. Hydrogen is regarded as an energy carrier, and it can only be produced by using energy from other sources. The ICT, in collaboration with OEC has developed a novel Cu-Cl cycle for thermochemical hydrogen production. This closed loop Cu-Cl cycle is a green and zero discharge process capable of producing hydrogen on a large scale. The hydrogen produced by this promising process can be utilized in the hydrogenation of carbon dioxide to fuels and chemicals.
Carbon Dioxide Refinery Concept and Processes Developed by the Author’s Lab
Steel making releases more than 3 billion metric tons of CO2 each year, having the biggest climate impact. To help limit global warming, the steel industry will need to shrink its carbon footprint significantly.
Thus, hydrogen can substitute fossil fuels in some carbon intensive industrial processes, such as steel, chemical, and allied industries. It can present solutions for difficult dues, etc. Another incentive for using gaseous biofuels for transport applications is the prospect to diversify feedstock sources.
Biomethane, also called renewable natural gas (RNG), or sustainable natural gas (SNG), which is separated from biogas, is the most efficient and clean burning biofuel available today. Biomethane is upgraded to a quality like fossil natural gas, having a methane concentration of 90% or greater, by which it becomes possible to distribute the gas to customers via the existing gas grid within existing appliances.
Furthermore, it is very promising to use biogas containing carbon dioxide as the co-reactant for methane conversion in the so-called dry reforming process, since carbon dioxide can provide extra carbon atoms for methane conversion, while carbon dioxide also serves as a better oxidant, compared to oxygen or air. The cofeed of carbon dioxide will also increase the methane conversion and the yield of objective products. In addition to syngas, gaseous hydrocarbons (C2 to C4), liquid hydrocarbons (C5 to C11+) and oxygenates can be produced in methane conversion with the co-feed of carbon dioxide. The liquid hydrocarbons are highly branched, representing a high-octane number, while oxygenates mainly consist of a series of alcohols and acids. It is also important to note that carbon should not be used as a source of fuel but for making chemicals and materials and all non-carbon sources of energy such as solar, wind, geothermal, tidal, and nuclear and above all hydrogen from water splitting will meet the requirements of the Paris Agreement.
Plastics refining is greenhouse-gas intensive. Carbon dioxide emissions from ethylene production are projected to expand by 34% between 2015 and 2030. For instance, polyvinylchloride (PVC) is a widely used thermoplastic polymer due to its stability, affordability, and workability. It is a versatile general plastic widely used in construction, civil material, and many other consumer goods. PVC polymer is highly polar and thus has a good insulation property, but it is inferior to non-polar polymers like polypropylene (PP) and polyethylene (PE). PVC, PE and PP are commonly used in piping, water sanity, and medical industries, etc. whereas PP is extremely thermal resistant and can tolerate much higher temperatures than PVC. These polymers contribute to carbon footprint and global warming.
PVC is shown to have higher energy consumption and CO2 gas emission that shows its high potential in global warming than other plastics. Likewise, the recycling of PVC has shown substantial contributions in lowering the effect on climate change. PVC can improve its production scale but also reduce global warming. Among all three types of polymers, PVC has more energy consumption and CO2 gas emission. Thus, it has a more contribution to global warming in comparison to other types of polymers. It was also revealed that recycling and non-recycling products have the same quality of products.
Worldwide, about 40% of plastics are used as packaging. Typically, packaging is meant for a single use (SUP), so there is a fast turnaround to disposal. The packaging can be handled in three different ways: landfill, incineration, or recycling. Waste incineration has the biggest climate impact of the three options. As per the CIEL report, U.S. emissions from plastics incineration in 2015 were 5.9 million metric tons of CO2 equivalent whereas the World Energy Council predicts that if plastics production and incineration increase as anticipated, GHG will increase to 49 million metric tons by 2030 and 91 million metric tons by 2050.
Landfilling has a much lower climate impact than incineration. But the location of landfills can be associated with similar environmental injustices. Recycling is a different ball game with an entirely different set of problems. Compared to the low costs of virgin materials, recycled plastics are high cost with low commercial value. This makes recycling profitable only rarely, so it requires considerable government subsidies. However, so called chemical recycling of polymers including depolymerization and hydrogenation.
Ellen MacArthur Foundation suggests that only 2% of plastics are recycled into products with similar functionality. Another 8% are “downcycled” to something of lower quality. The rest of plastic is landfilled, goes into the environment, or incinerated. Eventually, cutting emissions associated with plastics may require an all-of-the-above strategy: reducing waste, retaining materials by refurbishing or remanufacturing, and recycling. Chemical recycling comprises three mechanisms by which the polymer is purified from plastics without changing its molecular structure, is depolymerised into its monomer building blocks, which in turn can be repolymerised, and is converted into chemical building blocks and can thus be used to produce new polymers.
Hydrogen and methane production from styrofoam waste using an atmospheric-pressure microwave plasma reactor is reported. Polymer upcycling such as SUP conversion into new products is all now worthy of practice. If government-established recycling targets are to be attained, the relationships between consumers, municipalities, and petrochemical production must be enhanced.
After all, public opinion is moved by media images of an endangered planet and eco system. Only through the collaboration of people, municipalities, and industry - supported by improved technology along the recycled plastics supply chain a solution for this global crisis can be achieved.
Carbon dioxide refineries are not far away to be seen and to be believed. Net zero should happen much before 2050 during the lifetime of many readers.
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