Gaseous Carbon Waste Streams Utilization Status and Research Needs (2019) / Chapter Skim
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4 Chemical Utilization of CO2 into Chemicals and Fuels
4 Chemical Utilization of CO2 into Chemicals and Fuels
Pages 63-96
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From page 63... ...
This can often generate significant amounts of waste and can result in large greenhouse gas footprints. The grand challenge for converting CO2 waste streams into useful products is to develop processes that require minimal amounts of nonrenewable energy, are economically competitive, and provide substantial reductions in greenhouse gas emissions compared to existing technology.
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From page 64... ...
Instead in the following sections emerging technologies for the conversion of CO2 into commodity chemicals and fuels are evaluated. Initially, specific products are discussed, before a section on research challenges that extend across products.
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From page 65... ...
CHEMICAL UTILIZATION OF CO2 INTO CHEMICALS AND FUELS TABLE 4-1 Major commodity chemicals that are currently synthesized from CO2 on an industrial scale globally. Chemical Scale per yeara 30 kilotons Salicylic acid 112,000 kilotons Urea Cyclic carbonates such as 40 kilotons Ethylene carbonate Propylene carbonate 600 kilotons Polycarbonate 10 kilotons Polyether carbonate aGlobal amount produced using a process involving CO2.
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From page 66... ...
Nevertheless, due to special circumstances related to location, presently two large pilot plants for direct methanol production from CO2 are in operation. The Mitsui hemical C Company in Japan produces around 100 tons of methanol per year from CO2 (Table 4-2)
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From page 67... ...
2.4 tons Oxalic acid aAmount of product that is produced per year. b SOEC = solid oxide electrolyzer cell.
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From page 68... ...
Although this route is s calable it is not economically viable and does not involve the direct conversion of a CO2-only feedstock into dimethyl ether. Most likely research into CO2 hydrogenation to methanol will also provide insight into the formation of dimethyl ether and, if a practical catalyst for direct methanol formation is obtained, a system for dimethyl ether may follow shortly thereafter.
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From page 69... ...
The conversion of CO2 to formic acid using either H2 or protons and electrons represents an atom-economical approach to a valuable commodity chemical, which could potentially become even more important if formic acid is used as a H2 vector (PérezFortes et al., 2016a; Sordakis et al., 2018)
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From page 70... ...
at moderate to high overpotential, both in standard three-electrode electrochemical cells and in liquid electrolyte-based electrolysis flow cells, the latter at a rate of 200 mA/cm2 (Whipple et al., 2010)
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From page 71... ...
. Partial current densities for methane formation as high as 38 mA/cm2 have been reported for a Cu catalyst electrodeposited on a carbon gas diffusion electrode (Qiu et al., 2017)
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From page 72... ...
or at low temperature using a solution-phase or gas diffusion electrolysis cell. SOECs for CO2 splitting have recently been brought to market, while low-temperature systems are still in a research phase.
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From page 73... ...
Based on these prior efforts that typically employ electrodes with a geometric area of 1-2 cm2, Siemens performed experiments on a larger scale, using first 10 cm2 and then 100 cm2 gas diffusion electrodes in electrolyzer configurations with a flowing liquid electrolyte ( Jeanty et al., 2018)
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From page 74... ...
. In addition, some of the CO2 is lost by diffusion through the gas diffusion electrodes into the electrolyte, where it can react with OH– to form carbonates, which can precipitate on the electrode or migrate to the anode and release CO2 into the O2 stream.
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From page 75... ...
Strategies such as alloying silver with copper, in which the silver enhances formation of the needed CO intermediate (Hoang et al., 2018) , and precise engineering of the copper catalyst layer inside a sandwich-type gas diffusion electrode have increased Faradaic efficiencies for ethylene to 60-70 percent at rates of 160 to 250 mA/cm2 (Dinh et al., 2018)
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From page 76... ...
Potential applications for dimethylcarbonate also exist in the fuel industry where it could be blended with gasoline as an oxygenate. Historically, dimethylcarbonate was synthesized from phosgene and methanol, but now it is prepared either via trans sterification of ethylene carbonate or propylene carbonate and methanol or using CO, e methanol, and O2 as feedstocks.
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From page 77... ...
Numerous heterogeneous and homogeneous transition-metal catalysts have been developed which selectively form polycarbonates as opposed to the cyclic carbonates described earlier (see the section "Commercial echnologies T for the Chemical Utilization of Methane" in Chapter 6) from a range of comonomers including ethylene oxide, propylene oxide, cyclohexene oxide, vinyl oxide, and styrene oxide, among others (Lu and Darensbourg, 2012; Poland and Darensbourg, 2017; Qin et al., 2015)
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From page 78... ...
Additionally, research into the copolymerization of CO2 with aziridines to produce polycarbamates and oxetanes is also only at an early stage and should also be encouraged as it may lead to polymers with different properties than those currently available. Carboxylic Acid Production Carboxylic acids comprise a broad class of commodity chemicals that are used as solvents, reagents, and monomers for polymer production, among other applications.
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From page 79... ...
Below, an assessment is provided about the current state of research toward a number of c arboxylic acid targets. Acrylic and Methacrylic Acid Production Acrylic acid (5.8 million tons were produced in 2014; Limbach, 2015)
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From page 80... ...
Further research is needed to uncover strategies for avoiding stoichiometric reagents altogether. Oxalate and Oxalic Acid Production Oxalates and oxalic acid, while not commodity chemicals, are still produced at a scale of 120,000 tons per year (Qiao et al., 2014)
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From page 81... ...
In early research (prior to 2000) , Pb and other catalysts were used to generate oxalic acid in electrochemical cells with Faradaic efficiencies in the 70-98 percent range, but this was only done at low rates in a standard electrochemical cell (Rudolph et al., 2000; Shoichiro et al., 1987)
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From page 82... ...
Although carbon nanotubes are a valuable item, at this stage their range of applications is limited compared to conventional carbon fibers. The carbon nanotubes that have been pro 82
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From page 83... ...
Similarly, the utilization of CO2 from gaseous waste streams would be aided by improving the interface between CO2 capture and conversion. There are relatively few catalysts for CO2 conversion which have been utilized in conjunction with systems for CO2 capture and this could play a key role in developing efficient approaches to utilize CO2 from waste streams.
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From page 84... ...
. The overall process is effectively the combustion reaction in reverse, with electric power providing the energy input.
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From page 85... ...
High synthesis rates require effective mass transport of CO2 to the catalyst aterial m while maintaining high ionic conductivity. These requirements have been met by using gas diffusion electrodes, which are used in commercial technologies such as fuel cells and 85
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From page 86... ...
Some gains can still be made by reducing the overpotential of the various cathode catalysts. However, those potential gains are small compared to the energy requirements of an overall electrolysis process that typically couples the CO2 electroreduction at the cathode to the highly energy intense oxygen evolution reaction (OER)
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From page 87... ...
A RESEARCH AGENDA FOR CHEMICAL UTILIZATION OF CARBON DIOXIDE Stages of development and key barriers for various chemical utilization approaches are shown in Figure 4-1 and Table 4-3. Priority Research Areas In previous sections of this chapter specific challenges related to converting CO2 to certain products, general challenges related to CO2 conversion regardless of the product, and the technological barriers to commercialization have been described.
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From page 88... ...
Coupling Oxidation and Reduction Reactions The focus of most CO2 electroreduction efforts has been on improving the cathode in its efficiency and activity in converting CO2 to a desired product. Typically the overall process requires stoichiometric amounts of water for the oxygen evolution reaction on the anode, with that reaction requiring more than 85 percent of the total electrical energy input.
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From page 89... ...
could allow for CO2 conversion with lower energy demand and generate a more valuable co-product than O2. Conclusion 4-1 The grand challenge for converting CO2 waste streams into useful products is to develop processes that require minimal amounts of nonrenewable energy, are economically competitive, and provide substantial reductions in greenhouse gas emissions compared to existing technology.
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From page 90... ...
Recommendation 4-4 Researchers should increase attention to CO2 conversion processes that produce nontraditional targets, especially those with C–C bonds, to have transformative impacts. Recommendation 4-5 Researchers should explore processes that combine CO2 reduction with the oxidation of substrates from other waste streams (e.g., agricul tural or biomass waste or industrial by-products)
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From page 91... ...
2018. Upscaling and continuous operation of electrochemical CO2 to CO conversion in aqueous solutions on silver gas diffusion electrodes.
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From page 92... ...
Angewandte Chemie International Edition 56(38)
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From page 93... ...
1987. Selective formation of formic acid, oxalic acid, and carbon m onoxide by electrochemical reduction of carbon dioxide.
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2016. The effect of electrolyte composition on the electroreduction of CO2 to CO on Ag based gas diffusion electrodes.
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From page 95... ...
2017. Electrochemical reduction of CO2 in solid oxide electrolysis cells.
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