Carbon dioxide (C02), is a colorless and odorless gas that occurs in nature and serves as a source of carbon for photosynthesis in all plants and crops. CO2 utilization’ refers to its use at concentrations above atmospheric levels, directly or as a feedstock in industrial or chemical processes, to produce valuable carbon-containing products. Energy utilization is based on the combustion of carbonaceous fuels, which are dominated by the three fossil fuels-coal, petroleum, and natural gas. While the amount of CO2 consumption for organic chemicals is relatively small as compared to the CO2 emitted from fossil fuel combustion, CO2 conversion and utilization should be an integral part of carbon management, given that CO2 is a greenhouse gas (GHG) and its concentration in the atmosphere significantly contributes to global warming. There is great interest worldwide in reducing the emission of greenhouse gases. The proper use of CO2 in chemical processing adds value by making industrially useful carbon-based products. Studies on converting CO2 into carbon-based chemicals and materials continue to be important as we strive for sustainable development. CO2 conversion and utilization is the first step in CO2 recycling and resource conservation. While carbon capture and storage (CCS) has been somewhat struggling to make economic sense over the past few decades, research and industry are now working together to find ways that CO2 sequestration will be a good value proposition.
The 2015 Paris Global Climate agreement focused the world’s attention on CO2 utilization and emissions and has given a new imperative to efforts to mitigate the impact of the use of hydrocarbon fuels in both government and corporate boardrooms. Global emissions of CO2 were 33.4 billion tons in 2011. Given a cost target of about $23-$60 per ton, the value of the market is over a trillion dollars per year. Spending on carbon capture technology already exceeds $400 million per year, with an annual projected growth rate of 6%. In that current political environment mandates were being enforced which threaten the coal and other fossil fuel industries. CO2 mitigation is also a key factor in the lifecycle analysis and value proposition for many biofuel processes. This created a great opportunity for new and improved technologies. Reports of laboratory-scale breakthroughs and commercialization efforts are constantly appearing. Techno-economic evaluation of these technologies for specific applications requires an independent multi-disciplined team with a broad range of skills and experience. There are a large number of methods for CO2 mitigation, including pre-combustion and post-combustion treatments either commercialized or in the last stages of development.1 The post-combustion methods include chemical adsorption, membrane separations, and absorption. A large number of projects in various stages have been announced. A list of these is reported in the MIT Carbon Capture and Sequestration Database. All of these technologies add significant costs to the primary process and produce a waste stream that does not have significant value.
Unfortunately, President Trump announced in June 2017 his intent to withdraw the United States from the Paris Agreement. However, it is not that easy as the withdrawal process requires that the agreement is in force for three years before any country can formally announce its intention to drop out, and then such a country would have to wait a year before actually leaving the pact. This is interpreted to mean that while the United States could officially exit on November 4, 2020 (which would be a day after the presidential election), the withdrawal would not be permanent, as a future president could rejoin in as short as a month’s time.
All this has led to great interest in finding uses for CO2 that add value. Private equity, philanthropy, and governments are funding development projects. Efforts include a privately funded competition with a $20 million prize for the best use of carbon dioxide. This interest has led to a significant effort to commercialize processes that convert CO2 to chemicals.
The key problem with CO2 utilization is the thermodynamics of the process. No matter the route, sufficient energy must be supplied in some form to promote the required chemistry Any proposed technology must explain the source of the energy or avoid conversion of the carbon/oxygen bonds. The processes that make the most sense are those where waste heat available can be supplemented by a renewable source or when bond breaking is kept to a minimum. There are locations where excess thermal heat or electrical power is available from nuclear or geochemical sources. For example, there is an operating plant in Iceland using geothermal power to generate hydrogen which is then used in a CO2 to fuels process. It should be noted that this process uses fossil carbonates as the CO2 source. Where excess energy is not available, processes that sequester the CO2 in platform chemicals and structural materials have a great advantage. Another challenge is the collection, concentration and purification of the CO2. This can add significant cost and complexity to any technology solution. An example of a commercially proven technology for accomplishing this for mixed CO/CO2 streams is UOP’s selexol process.
A third challenge is that the quantities of CO2 available are huge. The economics of the chemical market will likely be drastically affected by the influx of large quantities of specific products so the chemicals may have less than fuel value. The use of current prices does not reflect the ultimate processing economics.
A number of companies are commercializing CO2 utilization technologies. Some have demonstrated the use of biobased CO2 utilization. There is a lot of waste heat that can be used in the pyrolysis process which could be directed to this process. Approaches that directly capture the carbon dioxide without needing a high energy conversion step are very attractive. A wide variety of these will be needed because the scale of polymer production is not matched with the amount of CO2 which needs to be sequestered. Any product could potentially flood the market. The cost of process integration costs and/or CO2 collection need to be considered.
Sorting out the various technologies and evaluating the claims of various commercialization groups is a difficult task. Large renewable energy and biochemical consulting firms certainly have experts in these biotechnologies, as well as the more common areas like bio and renewable fuels, biomass and biomass power, feedstocks, biomaterials, and biochemicals. These larger groups will also have expertise in other technologies like agitation systems, anaerobic digestion, beverage fermentation, bio-oil extraction, bioreactors, carbon capture, carbon storage, carbonization, catalysis, cellulosic ethanol, cleantech, combined heat and power, direct combustion, enzyme technologies, fermentation, Fischer-Tropsch, gasification, genetic engineering, hydrothermal, nanotechnology, organosynthesis, power generation, pyrolysis, renewable technology due diligence, synthetic biology, thermochemical conversion, torrefaction, water treatment, and waste management.
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