Mitigation of CO₂by Chemical Conversion:  Plausible Chemical Reactions and Promising Products

Abstract

A critical literature analysis was conducted on the viable usage of CO 2 in the framework of the attempts to reduce the emissions of CO 2 into the atmosphere from various processes or the rate of increase of the concentration of CO 2 in the atmosphere. Applications based on the physical properties of CO 2 are summarized first. Major examples are applications in supercritical extraction, enhanced oil recovery, and use as inert gas in fire extinguishing and safety application in industry. The various possibilities of use in chemical applications are systematically discussed. CO 2 can react with several hydrocarbons and nitrogen-containing compounds (NH 3 , amines, imines). It can be used as a weak acid or as an oxidizing agent. It can be reduced electrochemically, photochemically, or chemically or by a syngas route. A variety of products can be manufactured from CO 2 , e.g., acids, alcohols, esters, lactones, carbamates, urethanes, urea derivatives, various copolymers, and polymers. In particular, polycarbonates are attractive products. Nevertheless, currently, less than 1% of the CO 2 emitted is used in chemical reactions. To reduce the emission of CO 2 substantially, only those reactions by which CO 2 is used to produce bulk chemicals are relevant, whereas those useful in the manufacture of fine chemicals are not important in this respect. CO 2 conversion to MeOH represents one of the most important options in CO 2 mitigation. MeOH can be used as additive to fuels or as a substitute for motor fuels. An increasingly important application is in the production of MTBE (methyl tert-butyl ether), DMC (dimethyl carbonate), or DME (dimethyl ether) which are major components in modern gasoline to boost octane number. An interesting application of MeOH is the usage as fuel for cars via in situ decomposition into syngas; this results in enhancement of the energy efficiency. From MeOH several useful products can be made. Another reaction of importance that has been commercialized is the so-called dry reforming in which methane reacts with CO 2 , giving synthesis gas. Some processes are commercialized and the technology is mature. An example is a process in which a mixture of biomass and fossil fuels is converted into methanol and carbon which is stored. It is obvious that thermodynamically most processes using CO 2 are not favorable for CO 2 mitigation. This does not imply that processes are never feasible. Special situations do exist where the usage of CO 2 in chemical applications is attractive. Examples are processes where CO 2 is available at a high temperature, where an external heat source is present without a good outlet for the heat, processes where CO 2 leads to the right stoichiometry or reaction environment. In these cases a high potential for an efficient process exists. An elegant example is "chemical cooling" of hot gases in the chemical process industry. A promising application is the direct substitution of certain chemicals by a reaction product of CO 2 ; an example is the replacement of the hazardous phosge...

Effects of Morphology of Cerium Oxide Catalysts for Reverse Water Gas Shift Reaction

“…Catalytic conversion of CO 2 to CO via reverse water gas shift (RWGS) reaction is a promising alternative for CO 2 utilization [1,2]. Water gas shift (WGS) and RWGS occur in all chemical processes when CO 2 and H 2 , or CO and H 2 O coexist in a reaction mixture [2].…”

Summary report : direct approaches for recycling carbon dioxide into synthetic fuel.

“…Further, the conversion chemistry that is often most fully considered is that of using CO 2 as a "green" intermediate for introducing specific functionalities into organic compounds. Although this chemistry is sometimes very elegant, the relatively small volumes that would be used render these approaches almost irrelevant from a greenhouse gas point of view [17]. Table 2 illustrates this point.…”

Green electrochemistry. Examples and challenges

“…This is one possible route for mitigation of CO 2 emissions, although only small amounts of CO 2 could be sequestered in this way [9]. Nevertheless, CO 2 reduction by electrochemical, as well as other means, is of considerable interest, and several recent works have appeared [9][10][11][12].…”

“…This is one possible route for mitigation of CO 2 emissions, although only small amounts of CO 2 could be sequestered in this way [9]. Nevertheless, CO 2 reduction by electrochemical, as well as other means, is of considerable interest, and several recent works have appeared [9][10][11][12]. For example, Li and Prentice [12] employed a high-pressure, near-critical CO 2 + water + ethanol solution, with LiCl as electrolyte and a copper cathode, to synthesize methanol by direct electrochemical reduction of CO 2 .…”