Carbon Dioxide Utilisation
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Indian Journal of Chemistry Vol. 51A, Sept-Oct 2012, pp. 1252-1262 Carbon dioxide utilisation Carbon dioxide – A potential raw material for the production of fuel, fuel additives and bio-derived chemicals Sivashunmugam Sankaranarayanan & Kannan Srinivasan* Discipline of Inorganic Materials and Catalysis, CSIR-Central Salt and Marine Chemicals Research Institute, Gijibhai Bhadheka Marg, Bhavnagar 364 002, India Email: [email protected]/ [email protected] Received 12 July 2012; revised and accepted 18 August 2012 Amongst the various greenhouse gases emitted into the atmosphere, carbon dioxide emission is the highest in terms of tonnage and has been identified as a predominant source contributing to climate change. Owing to its abundance through anthropogenic sources, it is highly desirable to utilize CO 2 to produce valuable products, in particular fuels and large volume chemicals, and thereby mitigate significantly its environmental impact. This review aims to cover the attempts made in utilizing CO 2 for the production of fuels, fuel additives and bio-derived chemicals, in particular organic carbonates. Although this review does not intend to encompass the literature in the holistic manner, it does endeavor to provide recent approaches, difficulties, challenges and offer perspective in the years to come on this important area of research. Keywords : Carbon dioxide utilization, Raw material for fuel production, Syngas, Methane, Dimethyl carbonate, Fatty cyclic carbonate, Glycerol carbonate Carbon dioxide (CO 2) is a greenhouse gas and occupies International Energy Outlook 2011, world’s energy the top position (more than 80 % in terms of amount related CO 2 emission is estimated to increase from for USA) in the overall emissions amongst other gases 30.2 billion metric tons (BMT) in 2008 to 35.2 and 5 such as carbon monoxide (CO), methane (CH 4), 43.2 BMT in 2020 and 2035 respectively. chlorofluorocarbons (CFC’s), etc. Increase in the In the current scenario, decreasing the CO 2 amount emission of greenhouse gases makes significant in the atmosphere is the biggest challenge and needs climate changes and will lead to consecutive effects new ideas and technologies. Possible ways to reduce such as increase in global temperature and changes in the CO 2 concentration in the atmosphere are using wind patterns. China occupies the top position in CO 2 renewable fuels instead of fossil fuels and by emissions with 24 % of world emissions, followed by converting the emitted CO 2 into useful products by United States (18 %), while India contributes around chemical transformations. Although sincere efforts 1 5 %. Longer estimated life time of CO 2 in are being made for replacing fossil fuels by renewable the atmosphere (50-200 years) and a profound surge energy, 6 there are several practical difficulties and in the human related emissions in recent decades limitations. Although a single solution is not going to cause serious concerns on its emission and impact on the environment. Sources of CO 2 emissions can be broadly classified into three categories, namely, stationary, mobile and natural sources. Generally, industrial emissions belong to stationary sources, emissions from vehicles are classified as mobile sources, and emission from volcano are natural sources. 2 Figure 1 shows the different anthropogenic sources of CO 2 and their sinks (based on 2010 data). 3 Burning of fossil resources such as petroleum and coal contributes significantly to CO 2 emission whose rate are estimated at 22.29 and 4 24.65 kg C/GJ, respectively. According to the Fig. 1 − Anthropogenic sources of CO 2 and their sinks. SIVASHUNMUGAM & KANNAN: CO 2 AS POTENTIAL RAW MATERIAL FOR FUEL PRODUCTION 1253 solve such a mega problem, an alternative approach to by its utilization as a source for fuel production. This reduce CO 2 emission is by its value addition to will be advantageous not in terms of value but also in produce large quantities of useful products. Such an significantly curbing its emission, which in turn will approach would also create new opportunities that are mitigate greenhouse effect. hitherto not realized or known. Utilization of biomass for energy and chemical High abundance and low cost are the production is an active research domain currently main advantages of CO 2 as a promising feedstock pursued all over the world because of its ecological 7,8 11 in organic synthesis. CO 2 is an interesting and economic gains. CO 2 is also gaining C1 building block and can be an apt replacement significance in the biorefining processes of biomass to for hazardous molecules like phosgene in many value-added bio-derived chemicals. Herein, recent industrial processes. Efforts have been made to attempts in the use of CO 2 as a raw material for fuel, utilize CO 2 in commercial applications such as food fuel additives and bio-derived chemicals, in particular processing and carbonated beverages. In recent organic carbonates is reviewed (Fig. 3). years, CO 2 has attracted the attention of chemical industries as it can be categorized as a sustainable raw CO 2 for the Production of Fuels material that can be used to produce diverse products Products obtained from CO 2 have applications as through a variety of chemical transformations. fuels and fuel additives. Figure 4 shows the schematic Despite such practices, currently in industries, only representation of production of fuel and fuel 110 million metric tons (MMT) of CO 2 are used for additives from CO 2. Carbon dioxide is in the highly chemical transformation which is less than 1 % of oxidized form, and hence reduction process is largely global emissions. 9 applicable to produce fuel and fuel additives. In redox Sakakura et al. 10 categorized a variety of reactions reactions, high energy substances or electro-reductive using CO 2 as a potential starting material resulting in processes are needed because of high thermodynamic 12 many products. Figure 2 summarizes the possible stability and lower reactivity of CO 2. Chemical reactions and some important chemicals derived using reduction routes are being explored for the reduction CO 2. Production of chemicals like urea and processes. Very recently, a research group carbonates using CO 2 is well-known and has been from University of California at Los Angeles commercialised. Besides chemicals, energy products reported a method wherein genetically engineered from CO 2 would make a considerable impact on its microorganism was deployed for the successful emission. The worldwide requirement of fuels is conversion of CO 2 into fuels such as iso -butanol and nearly two orders of magnitude higher than that of 3-methyl-1-butanol. 13 Carbon Sciences, a California- chemicals. CO 2 emission can be effectively reduced based company is developing a bio-catalytic Fig. 3 − Overall scheme for the utilization of CO 2 for the Fig. 2 − Possible reactions and important chemicals from CO 2. production of fuel, fuel additives and bio-derived chemicals. 1254 INDIAN J CHEM, SEC A, SEPT-OCT 2012 Fig. 5 − Hydrogenation of CO 2. [Adapted from Ref. 15 with permission from Elsevier, Amsterdam, The Netherlands]. Carbon monoxide Conversion of CO 2 via reverse water gas shift (RWGS) reaction is the most lucrative route for the production of CO (Eq. 1) that can further be used in Fischer-Tropsch (FT) process to produce hydrocarbons. Fig. 4 − Schematic representation of fuel and fuel additives …(1) production from CO 2. process for converting CO 2 into hydrocarbons such as The equilibrium can be shifted towards the right by methane, ethane and propane, which can be utilized (a) increasing the CO 2 concentration, (b) operating at 14 instead of gasoline and jet fuels. Generally, high H 2 concentration, and, (c) removing the product biocatalytic routes are more expensive and time (water) from the system. 17 Different metals such as Cu, consuming than other catalytic routes. Highly active Zn, Fe and Ce containing catalysts are well known for metal catalysts have been investigated for the the WGS reaction and these catalysts can effectively hydrogenation of CO 2 in homogenous or carry out RWGS reaction also. Apart from these, heterogeneous forms. Pt catalyst was also studied for RWGS reaction with 18,19 20 Hydrogenation of CO 2 results in various products different catalyst supports. Recently, Rosen et al. of C 1-type and higher chain length hydrocarbons reported electroreduction of CO 2 to CO below depending upon the reaction conditions. Hydrogen is overpotential using ionic liquid as electrolyte and generally obtained either from fossil sources or silver cathode as catalyst. through water splitting. Development of various The formation of CO in RWGS reaction is catalyst systems and surface science techniques has explained by two models, namely, redox mechanism created interest in the hydrogenation of CO 2 and formate decomposition mechanism. In the case of in recent years. Direct hydrogenation of CO 2 redox mechanism it was suggested that reduction of and hydrogenation of CO obtained from CO 2 are CO 2 and oxidation of H 2 that result in the formation of 21 among the two possible ways for producing CO and H 2O, occur due to the metal species. In the fuels. Some of the previous studies 15 have case of formate decomposition mechanism, it was suggested that CO 2 hydrogenation proceeds via the suggested that association of H 2 with CO 2 results in dissociative adsorption of CO 2 to form CO and O formate species as intermediate which decomposes to atoms on the surface, which on further give CO. 22 hydrogenation renders products as shown in Fig. 5. Even at 400 °C, due to the low equilibrium Several routes can be proposed for the use of CO 2 in constants, it requires hydrogen-rich or carbon dioxide- hydrogen reduction such as (i) conversion to rich reactant mixtures to yield acceptable results. products via synthesis gas, (ii) direct hydrogenation Otherwise the operating temperature needs to be into useful products, and, (iii) reactions to other increased to around 750 °C.