CO2 Conversion

In 1989, Gadalla and Sommer (252) reported that a solid-solution NiO/MgO (1 1.35) catalyst prepared by precipitation can inhibit the carbon deposition in the CO2 reforming of methane however, they obtained a low CO2 conversion (66%), a low H2 selectivity (79%), and a low CO selectivity (77%), even at the very low WHSV of 3714 cm3 (g catalyst)-1 h-1 with a CH4/CO2 (1/1, molar) feed gas and the high temperature of 1200 K. Their relatively high CH4 conversion was partly a consequence of homogeneous gas-phase reactions that occurred under their conditions. Indeed, the authors found extensive carbon deposits plugging the reactor upstream and downstream of the reaction zone. 

The final chapter of this book is dedicated to solar energy as a source of hydrogen and for CO2 conversion. This chapter introduces the main concepts of the field and highlights the role of catalysis for using solar energy. 

Tan C-S, Chang C-F, Hsu T-J (2002) Copolymerization of carbon dioxide, propylene oxide and cyclohexene oxide by a yttrium-metal coordination catalyst system. In CO2 conversion and utilization. ACS Symp Ser 809 102-111... 

If the temperature is too low, the solid cocoa butter formed this second phase, but with higher temperatures two fluid phases are in equilibrium one is rich in CO2 and the other is rich in cocoa butter. Kokot et al. [5] showed that at 313 K and 20 MPa, the mass fractions of CO2 for these two phases are 0.44 and 0.98. When working with two fluid phases and without stirring, the results of the experiments depend on the position of the outlet pipe of the first vessel top or bottom. If the fluid is extracted from the top of the vessel, the cocoa butter powder is produced from the richest phase in CO2. Conversely, it is the cocoa butter rich phase which is extracted from the bottom. If the mixture is homogenised by... 

The capillary plasma reactor consists of a Pyrex glass body and mounted electrodes which are not in direct contact with the gas flow in order to eliminate the influence of the cathode and anode region on CO2 decomposition. Analysis of downscaling effects on the plasma chemistry and discharge characteristics showed that the carbon dioxide conversion rate is mainly determined by electron impact dissociation and gas-phase reverse reactions in the capillary microreactor. The extremely high CO2 conversion rate was attributed to an increased current density rather than to surface reactions or an increased electric field. 

The synthesis section of the Stamicarbon (STAC) process is shown in Figure 11.3. An updated version of this process, Urea 2000plus, is offered by DSM (Stamicarbon s parent company)108,110. In this process NH3 and CO2 are converted to urea via ammonium carbamate at a pressure of 140 bar and a temperature of lSt/ C to 185°C. An NH3-to-C02 molar ratio of 2.95 is used in the reactor to give a CO2 conversion of 60%, and an NH3 conversion of 41%. The reactor is lined with 316L stainless steel. It contains sieve trays to provide... 

Alternative expressions for the global rates of Reactions 14 and 16 were tried while developing the model. For the CO + CO2 conversion (Reaction 16) the overall correlation derived by Howard et al. (2) was initially used, but with this the calculated values of SL were considerably lower than the measured ones. For the methane disappearance rate (Reaction 14) the correlations proposed by Westbrook and Dryer (7) were tried, and these gave results negligibly different from those obtained by Equation 18. 

Figure 5.1.6 Comparison of the energy efficiencies and current densities for C02 reduction to formic acid, syngas, and hydrocarbons (methane and ethylene) reported in the literature with those of water electrolyzers. Efficiencies of electrolyzers are total system efficiencies, while the CO2 conversion efficiencies only include cathode losses and neglect anode and system losses. Adapted from [17],...

Urea Technologies Inc. (Maxrovic), which offers the Heat Recycle Urea Process (HRUP), whose main feature is the hot recirculation of the aqueous carbamate solution, which enhances the energy balance. This is a conventional technique, operating at 20 to 22.10 Pa absolute. 190 to 200 C, N/C ratio s 4, and once througb CO2 conversion s 71 to 72 per cent... 

Toyira, J., P. Ramirez de la Piscinal, J. L. G. Fierrob, and N. Homs, Catalytic performance for CO2 conversion to methanol of gallium-promoted copper-based catalysts influence of metallic precursors , Appl. Catal. B Environ., vol 34, Issue 4, 28 November 2001, pp 255-66. 

A series of I3-CO2 labeling studies were conducted to determine the extent of CO2 conversion to hydrocarbons in the presenee of varying quantities of CO, see Figure 11. These studies showed that no CO2 was converted in mixtures where >5% carbon atom CO was present, and that CO2 conversion to hydrocarbons did not occur until virtually all of the CO was consumed. Preliminary kinetic studies showed that product formation rates in the presence of low levels of unlabeled CO were consistent with a mechanism involving dissociative CO2 chemisorption followed by CO and sur ce C formation with hydrogeiration to hydrocarbons. Figure 12. 

Figure 5. CO2 conversion to methanol (A) and space time yield ( ) as a function of space velocity (SV).

Figure 5 shows CO2 conversion to methanol and STY at 523 K, 5 MPa as a function of space velocity ranging from 5,000 h to 20,000 h The CO2 conversion to methanol decreased with space velocity. This suggests that the methanol synthesis should be suppressed by the water produced along with methanol, as described by Saito et al. [2],... 

Among five types of species formed by CO2 adsorption on MgO, dynamic behavior of unidentate-type carbonate (species-1) upon desorption was investigated. Surface diffusion, O-exchange, and molecular substitution appreciably take place prior its desorption even below the room temperature. Since these dynamic processes necessitate bond rupture in species, MgO may be useful in CO2 conversion at low temperatures. 

The CO2 hydrogenation was carried out at 220°C under a pressure of 5.0 MPa using a reactant gas mixture composed of H2/C02/Ar=60/30/10. The flow rate of the gas mixture was adjusted to obtain the CO2 conversion in the range between 4 and 6%. The reactants and products were analyzed with on-line gas chromatographs (Shimadzu GC-4BPT, GC-7BPT, GC-8A). 

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