Carbon dioxide: a renewable feedstock for the synthesis of fine and bulk chemicals

The syntheses of carbon dioxide (CO₂) based industrially important chemicals have gained considerable interest in view of the sustainable chemistry and “green chemistry” concepts. In this review, recent developments in the chemical fixation of CO₂ to valuable chemicals are discussed. The synthesis of five-member cyclic carbonates via, cycloaddition of CO₂ to epoxides is one of the promising reactions replacing the existing poisonous phosgene-based synthetic route. This review focuses on the synthesis of cyclic carbonates, vinyl carbamates, and quinazoline-2,4(1H,3H)-diones via reaction of CO₂ and epoxide, amines/phenyl acetylene, 2-aminobenzinitrile and other chemicals. Direct synthesis of dimethyl carbonate, 1,3-disubstituted urea and 2-oxazolidinones/2-imidazolidinones have limitations at present because of the reaction equilibrium and chemical inertness of CO₂. The preferred alternatives for their synthesis like transesterification of ethylene carbonate with methanol, transamination of ethylene carbonate with primary amine and transamination reaction of ethylene carbonate with diamines/β-aminoalcohols are discussed. These methodologies offer marked improvements for greener chemical fixation of CO₂ in to industrially important chemicals.     

Methodologies for chemical utilization of CO2 to valuable compounds through molecular activation by efficient catalysts

The reactions of CO₂ with oxirane to produce cyclic carbonate, and with aziridine to afford oxazolidine have been of interest as a useful method for its fixation by a chemical process. Highly efficient processes employing recyclable CO₂-phlilic homogeneous catalyst were devised for environmentally benign synthesis of cyclic carbonates and oxazolidinones under supercritical CO₂ without any organic solvent. These processes represent pathways for greener chemical fixations of CO₂ to afford industrial useful materials such as organic carbonates and oxazolidinones with great potential applications.     

Synthesis of Polycarbonate Precursors over Titanosilicate Molecular Sieves

A novel catalytic application of titanosilicate molecular sieves (TS-1 and TiMCM-41), in the synthesis of polycarbonate precursors like cyclic carbonates and dimethyl and diphenyl carbonates, avoiding toxic chemicals like phosgene or CO, is reported. Cyclic carbonates were prepared, over TS-1 and TiMCM-41, in high yields, by cycloaddition of CO₂ to epoxides, like epichlorohydrin, propylene oxide and styrene oxide, at low temperatures and pressures. Further, transesterification of the cyclic carbonates with methanol and phenol, over TiMCM-41, yielded other polycarbonate precursors like dimethyl carbonate (DMC) and diphenyl carbonate (DPC). The cyclic carbonates could also be synthesized from the olefins in the same reactor by reacting the olefins, in the presence of TiMCM-41, with a mixture of an epoxidizing agent (like H₂O₂ or tert-butyl hydroperoxide) and CO₂.     

Hydrogen bond activation strategy for cyclic carbonates synthesis from epoxides and CO2: current state-of-the art of catalyst development and reaction analysis

Chemical fixation of CO₂ into useful organic compounds has been attracting much attention from the viewpoint of CO₂ emission reduction and energy structure reformation. A useful and widely investigated chemical utilization of CO₂ is the cycloaddition of CO₂ to epoxides for the synthesis of cyclic carbonates. Efforts have been paid to the design and preparation of various catalyst systems that are active and selective to the production of the desired products under mild conditions and in green processes. This article is to review the current state of the catalyst development and the experimental and theoretical analysis of reaction mechanism for the cyclic carbonate synthesis from epoxides, one of currently important reactions involving CO₂ as a reactant with 100% atom economy. Particular attention is given to the catalysis of multifunctional catalyst systems such as metal- and hydrogen-bond donor (HBD)-based catalysts.     

A fully bio-based monomer derived from undecylenic acid,glycerol, and CO2 useful for the synthesis of polyhydroxyurethanes

Undecylenic acid, glycerol, and CO₂ were used as building blocks for obtaining a fully bio-based carbonated monomer, useful for polyurethanes. The functionality of the monomer was close to 3 cyclic carbonates/mol, located in terminal positions. In a first stage, a synthetic triglyceride was obtained with 99% selectivity by esterification of glycerol and undecylenic acid at 160°C. The triglyceride was then epoxidized using H₂O₂ and Amberlyst 15 or Amberlite IR-120 acidic exchange resins at 57°C. The selectivity to epoxide was kept constant at 98% using Amberlite IR-120. Terminal cyclic carbonates were then inserted through epoxide moieties under mild conditions by the chemical fixation of CO₂ at 80°C and 6 MPa in 6 h. A complete conversion was obtained in 6 h reaction while the selectivity to carbonate groups was near to 99% during all the reaction time. An elastomeric polyhydroxyurethane was obtained by aminolysis of the carbonated monomer with ethylenediamine at 70°C, affording a Young's modulus of 22.6 MPa and T_g of −15.2°C. The material showed a good thermal stability below 240°C.     

Synthesis of organic carbonates from alcoholysis of urea: A review

Organic carbonates are green compounds with a wide range of applications. They are widely used for the synthesis of important industrial compounds including monomers, polymers, surfactants, plasticizers, and also used as fuel additives. They can be divided into two main classes: cyclic and linear carbonates. Dimethyl carbonate (DMC) and diethyl carbonate (DEC) are the important linear carbonates. Carbonyl and alkyl groups present in DMC and DEC make them reactive and versatile for synthesizing various other important compounds. Ethylene carbonate (EC), glycerol carbonate (GC) and propylene carbonate (PC) are well-known cyclic organic carbonates. Phosgenation of alcohols was widely used for synthesis of organic carbonates; however, toxicity of raw materials restricted use of phosgenation method. A number of new non-phosgene methods including alcoholysis of urea, carbonylation of alcohols using CO₂, oxy-carbonylation of alcohols, and trans-esterfication of alcohols and carbonates have been developed for synthesizing organic carbonates. Carbonylation of alcohols is preferred as it helps in utilization and sequestration of CO₂, however, poor thermodynamics due to high stability of CO₂ is the major obstacle in its large scale commercialization. Oxy-carbonylation of alcohols offers high selectivity but presence of oxygen poisons the catalyst. Recently, alcoholysis of urea has received more attention because of its inexpensive abundant raw materials, favorable thermodynamics, and no water-alcohol azeotrope formation. Also, ammonia evolved in this synthesis route can be recycled back to urea by reacting it with CO₂. In other words, this method is a step towards utilization of CO₂ as well. This article reviews synthesis of DMC, DEC, GC, PC, and EC from urea by critically examining various catalysts used and their performances. Mechanisms have been reviewed in order to give an insight of the synthesis routes. Research challenges along with future perspectives have also been discussed.     

Verwendung von Kohlendioxid bei technischorganischen Synthesen

Use of carbon dioxide in industrial organic syntheses . Although carbon dioxide is important as an abundant carbonaceous raw material, its utilization in chemical processes so far has been rather limited. This review covers the reactions of CO₂ employed in industry, such as the production of urea, the Kolbe-Schmitt reaction, the synthesis of cyclic organic carbonates, and the use of CO₂ in methanol synthesis. Interesting recent developments in CO₂ chemistry, especially the transition metal catalyzed reactions, are also elucidated. In addition to the synthesis of polymers and hydrocarbons, the production of oxygen-containing chemicals seems to be very profitable and attractive for future industrial applications. Not only can derivatives of formic acid and carbonic acid be formed but longer-chain carboxylic acids and their derivatives are also accessible by reactions of carbon dioxide with hydrocarbons such as alkynes, alkenes, and 1,3-dienes.     

The first synthesis of a cyclic carbonate from a ketal in SC-CO2

In this paper the synthesis of a cyclic organic carbonate by a halogen-free route is described. The ketal formed from cyclohexanone and 1,2-ethanediol was reacted with carbon dioxide, either in SC-CO₂ or in organic solvents under CO₂ pressure. Transition-metal complexes with functionalized fluorinated di-ketone ligands were used as catalyst. The synthetic methodology based on SC-CO₂ is effective for the synthesis of ethylene carbonate. The use of methanol as co-solvent in SC-CO₂ prevents the formation of the ethylene carbonate and only the alcoholysis of the ketal is observed. In organic solvents, no reaction takes place.     

ALTERNATIVE GENERATION OF H2, CO AND H2, CO2 MIXTURES FROM STEAM-CARBON DIOXIDE REFORMING OF METHANE AND THE WATER GAS SHIFT WITH PERMEABLE (MEMBRANE) REACTORS

A new process is proposed which converts CO₂ and CH₄ containing gas streams to synthesis gas, a mixture of CO and H₂ via the catalytic reaction scheme of steam-carbon dioxide reforming of methane or the respective one of only carbon dioxide reforming of methane, in permeable (membrane) reactors. The membrane reformer (permreactor) can be made by reactive or inert materials such as metal alloys, microporous ceramics, glasses and composites which all are hydrogen permselective. The rejected CO reacts with steam and converted catalytically to CO₂ and H₂ via the water gas shift in a consecutive permreactor made by similar to the reformer materials and alternatively by high glass transition temperature polymers. Both permreactors can recover H₂ in permeate by using metal membranes, and H₂ rich mixtures by using ceramic, glass and composite type permselective membranes. H₂ and CO₂ can be recovered simultaneously in water gas shift step after steam condensation by using organic polymer membranes. Product yields are increased through permreactor equilibrium shift and reaction separation process integration.

CO and H₂ can be combined in first step to be used for chemical synthesis or as fuel in power generation cycles. Mixtures of CO₂ and H₂ in second step can be used for synthesis as well (e.g., alternative methanol synthesis) and as direct feed in molten carbonate fuel cells. Pure H₂ from the above processes can be used also for synthesis or as fuel in power systems and fuel cells. The overall process can be considered environmentally benign because it offers an in-situ abatement of the greenhouse CO₂ and CH₄ gases and related hydrocarbon-CO₂ feedstocks (e.g., coal, landfill, natural, flue gases), through chemical reactions, to the upgraded calorific value synthesis gas and H₂, H₂ mixture products.     

Direct conversion of CO2 with diols,aminoalcohols and diamines to cyclic carbonates,cyclic carbamates and cyclic ureas using heterogeneous catalysts

CO₂ has a large effect on global warming by greenhouse gases, and development of an effective technique for the reduction of CO₂ is a crucial and urgent issue. From the chemical viewpoint, CO₂ is regarded as a stable, safe and abundant C1 resource, and the transformation of CO₂ to valuable chemicals is promising not only for reduction of CO₂ but also for production of useful chemicals. This mini‐review focuses on the direct conversion of CO₂ with diols, aminoalcohols and diamines to cyclic compounds such as cyclic carbonates, cyclic carbamates and cyclic ureas, and in particular discusses the mechanisms for these reactions over heterogeneous catalysts. © 2013 Society of Chemical Industry     

Use of carbon dioxide in industrial organic syntheses

Although carbon dixoide is important as an abundant carbonaceous raw material, so far, its utilization in chemical processes has been rather limited. This review covers the reactions of CO₂ employed in industry, such as the production of urea, the Kolbe-Schmitt reaction, the synthesis of cyclic organic carbonates and the use of CO₂ in methanol synthesis. Interesting recent developments in CO₂ chemistry, such as the reactions catalyzed by transition metals, are also described. Apart from the synthesis of polymers and hydrocarbons, the production of oxygen-containing substances appears to be very profitable and attractive for future industrial applications. Not only can derivatives of formic and carbonic acids be produced but also longer-chain carboxylic acids and their derivatives by reactions of carbon dioxide with hydrocarbons such as alkynes, alkenes and 1,3-dienes.     

Synthesis of cyclic carbonates from urea and diols over metal oxides

Several metal oxides were used for synthesis of ethylene carbonate from urea and ethylene glycol. ZnO showed high activity towards the reaction. TPD, FTIR and reaction test indicated that the catalysts with appropriate acid and base properties were favorable to the synthesis of cyclic carbonate. Furthermore, the reaction of urea with various diols revealed that the selectivity of five-membered cyclic carbonates was higher than that of six-membered cyclic carbonates.     

Use of carbon dioxide as feedstock for chemicals and fuels: homogeneous and heterogeneous catalysis

CO₂ is considered to play a key role in an eventual climate change, due to its accumulation in the atmosphere. The control of its emission represents a challenging task that requires new ideas and new technologies. The use of perennial energy sources and renewable fuels instead of fossil fuels and the conversion of CO₂ into useful products are receiving increased attention. The utilization of CO₂ as a raw material for the synthesis of chemicals and fuels is an area in which scientists and industrialists are much involved: the implementation of such technology on a large scale would allow a change from a linear use of fossil carbon to its cyclic use, mimicking Nature. In this paper the use of CO₂ as building block is discussed. CO₂ can replace toxic species such as phosgene in low energy processes, or can be used as source of carbon for the synthesis of energy products. The reactions with dihydrogen, alcohols, epoxides, amines, olefins, dienes, and other unsaturated hydrocarbons are discussed, under various reaction conditions, using metal systems or enzymes as catalysts. The formation of products such as formic acid and its esters, formamides, methanol, dimethyl carbonate, alkylene carbonates, carbamic acid esters, lactones, carboxylic acids, and polycarbonates, is described . The factors that have limited so far the conversion of large volumes of CO₂ are analyzed and options for large‐scale CO₂ catalytic conversion into chemicals and fuels are discussed. Both homogeneous and heterogeneous catalysts are considered and the pros and cons of their use highlighted. © 2013 Society of Chemical Industry     

Pathways for CO2 Formation and Conversion During Fischer–Tropsch Synthesis on Iron-Based Catalysts

CO₂ reaction and formation pathways during Fischer–Tropsch synthesis (FTS) on a co-precipitated Fe–Zn catalyst promoted with Cu and K were studied using a kinetic analysis of reversible reactions and with the addition of ¹³C-labeled and unlabeled CO₂ to synthesis gas. Primary pathways for the removal of adsorbed oxygen formed in CO dissociation steps include reactions with adsorbed hydrogen to form H₂O and with adsorbed CO to form CO₂. The H₂O selectivity for these pathways is much higher than that predicted from WGS reaction equilibrium; therefore readsorption of H₂O followed by its subsequent reaction with CO-derived intermediates leads to the net formation of CO₂ with increasing reactor residence time. The forward rate of CO₂ formation increases with increasing residence time as H₂O concentration increases, but the net CO₂ formation rate decreases because of the gradual approach to WGS reaction equilibrium. CO₂ addition to synthesis gas does not influence CO₂ forward rates, but increases the rate of their reverse steps in the manner predicted by kinetic analyses of reversible reactions using non-equilibrium thermodynamic treatments. Thus the addition of CO₂ could lead to the minimization of CO₂ formation during FTS and to the preferential removal of oxygen as H₂O. This, in turn, leads to lower average H_2/CO ratios throughout the catalyst bed and to higher olefin content and C₅₊ selectivity among reaction products. The addition of ¹³CO₂ to H₂/¹²CO reactants did not lead to significant isotopic enrichment in hydrocarbon products, indicating that CO₂ is much less reactive than CO in chain initiation and growth. We find no evidence of competitive reactions of CO₂ to form hydrocarbons during reactions of H₂/CO/CO₂ mixtures, except via gas phase and adsorbed CO intermediates, which become kinetically indistinguishable from CO₂ as the chemical interconversion of CO and CO₂ becomes rapid at WGS reaction equilibrium.     

Reactions of glycerol with poly(ethylene ether carbonate) polyols

Poly(ethylene ether carbonate) polyols can be modified by chemical reactions with polyglycol modifiers under conditions of elevated temperatures and reduced pressures. The modifier becomes chemically incorporated into the modified polyol and is used to control properties such as moisture sensitivity, CO₂ content, T_g, density, etc. in the resultant polyol. However, glycerol cannot be used as a modifier for poly(ethylene ether carbonate) polyols under the same conditions since it reacts with poly(ethylene ether carbonate) polyols by a transesterification reaction sequence to form glyceryl carbonate. As the temperature is increased, the glyceryl carbonate decomposes to yield glycidol and carbon dioxide. These reactions are conveniently followed by ¹³C-NMR. The preparation of glyceryl carbonate by this process has not been previously reported.     

Adsorption and electrooxidation of ethylene glycol and its C2 oxidation products on a carbon-supported Pt catalyst: A quantitative DEMS study

Aiming at a better understanding of ethylene glycol oxidation, the adsorption and oxidation of ethylene glycol and its incomplete C₂ oxidation products glycol aldehyde, glyoxal, glycolic acid, glyoxylic acid and oxalic acid on carbon supported Pt catalysts were investigated by on-line differential electrochemical mass spectrometry (DEMS) under continuous electrolyte flow. This includes adsorption transients at different, constant potentials, oxidative removal (‘stripping’) of the resulting adsorbates, and potentiodynamic bulk oxidation/reduction of the respective molecules. The data show a pronounced influence of the different functional groups on the adsorption and oxidation characteristics, with hydroxyl and carboxylic functions resulting in lower adsorption rates and pronounced potential effects, while aldehyde functions lead to high adsorption rates at all potentials. The potential effects in the adsorption rate are mainly ascribed to surface blocking by H_upd species. For aldehydes and acids, CO₂ formation occurs already at potentials below the onset of OH_ad formation, which is ascribed to the decomposition of the carboxylic group or of the diol groups of hydrated aldehydes. The contributions of different reaction pathways, including: (i) ‘direct’ oxidation to CO₂, (ii) indirect oxidation to CO₂ via formation and further oxidation of CO_ad, and (iii) incomplete oxidation to more highly oxidized C₂ species, with the possibility of their further reaction via re-adsorption and reaction along (i)–(iii), are discussed.     

Synthesis of diethyl carbonate from ethanol through different routes: A thermodynamic and comparative analysis

In this study, thermodynamic analysis of various possible synthesis routes of diethyl carbonates (DEC), a benign organic carbonate, was carried out and a comparative analysis was performed. Chemical equilibrium constants at standard conditions were calculated using Gibbs free energy of the system. The Benson group contribution method was used to estimate standard heat of formation and standard entropy change of some raw materials/components like dimethyl carbonate. Variation of heat capacity (C_p) with temperature was estimated for different components from the Rozicka‐Domalski model. Variation of chemical equilibrium constants with temperature and pressure was studied for various routes. Synthesis of DEC from ethylene carbonate (EC) was also found to be better considering equilibrium constants at room temperature. The CO₂ route was found to be the most unfavourable route for DEC synthesis due to stability of CO₂ molecules. Moreover, DEC synthesis through the urea route was found to be best at high temperatures since the equilibrium constants were found to increase exponentially. Experiments were conducted for DEC synthesis using the EC route at two temperatures. Activity coefficients were calculated using the UNIFAC model. Experimentally and theoretically determined chemical equilibrium constant values were found to be similar. PRO/II was also used to minimize Gibbs free energy of the system and estimate the equilibrium constants and the results were comparable with those obtained by the equilibrium constant method and the trend was found to be the same for both the methods.     

Catalysed carbon gasification with Ba13CO3

The interaction of barium carbonate with carbon black was studied to understand catalysed CO₂ gasification of carbon. Temperature-programmed reaction with isotopic labelling of the carbonate and the carbon showed that carbon dramatically accelerated the rate of BaCO₃ decomposition to form BaO and CO₂, which rapidly gasified carbon to form CO. Pure BaCO₃ was observed to exchange carbon dioxide with the gas-phase, and the exchange rate was increased significantly by carbon at higher temperatures, due to formation of a carbon-carbonate complex. The interaction of BaCO₃ and C to form a complex occurred well below gasification temperatures, and BaCO₃ did not decompose until after gasification began and the gas phase CO₂ concentration was low. During catalysed gasification, formation of gaseous CO from a surface oxide is shown directly to be the slow step in the reaction. The active catalyst appears to cycle between BaCO₃ and BaO (both of which interact with carbon). The rates of carbonate decomposition, catalytic gasification, and exchange with gaseous CO₂ are all slower for BaCO₃ than for K₂CO₃, indicating the large differences in carbonate-carbon interaction between alkali carbonates and alkaline earth carbonates. The two carbonates apparently follow different reaction mechanisms.     

Synthesis of glycerol carbonate by direct carbonatation of glycerol in supercritical CO2 in the presence of zeolites and ion exchange resins

Glycerol carbonate is a key bifunctional compound employed as solvent, additive, monomer, and chemical intermediate. We have synthesized it on a pilot scale in the laboratory in cyclic or alicyclic organic carbonate medium. In this study, we examined the use of supercritical CO₂ as a reaction medium and as a source of carbonate for carbonatation of glycerol. Glycerol carbonate could be obtained by direct reaction of carbon dioxide with an organic carbonate in the presence of heterogeneous catalysts. Carbonatation of glycerol into glycerol carbonate went to equilibrium in supercritical CO₂ medium. This revised version was published online in July 2006 with corrections to the Cover Date.     

Zirconium-based isoreticular metal-organic frameworks for CO<Subscript>2</Subscript> fixation via cyclic carbonate synthesis

Two highly stable isoreticular metal-organic frameworks comprising chains of zirconium coordinated with linkers of 1,4-H₂BDC (1,4-benzenedicarboxylic acid) and 4,4′-H₂BPDC (4,4′-biphenyldicarboxylic acid), denoted as MIL-140A and MIL-140C, were synthesized. The catalytic activity of these frameworks was studied for the coupling reaction of CO₂ and epoxides to produce cyclic carbonates under solvent-free conditions. Excellent activity was observed for both catalysts: they yielded high epoxide conversion with >99% selectivity toward the cyclic carbonate, and were fully reusable even after four cycles without any considerable loss of initial activity. The enhancement in the catalytic activity was explained based on acidity/basicity studies. The influence of various reaction parameters such as catalyst amount, reaction time, reaction temperature, and CO₂ pressure was also investigated. Reaction mechanism was proposed on the basis of experimental evidence and our previous DFT (density functional theory) studies.