Effect of the combination of copper – nickel catalyst supported on activated carbon (cu - ni/ac) and zeolite a in the direct synthesis of linear carbonates

Abstract

ABSTRACT: Direct synthesis of dimethyl carbonate (DMC) and diethyl carbonate (DEC) from CO2 and alcohol is a strongly equilibrium limited reaction that tries to find cleaner production route. Since the thermodynamic limitation the DMC and DEC yield achieved (using Cu-Ni/AC catalyst) is around 1-2% when the produced water is not removed from the system. In order to get eliminated water, dehydrating agents were used in order to shift the reaction towards a higher DMC and DEC yield. Therefore, test a novel combination of a fixed bed reactor combined with zeolite 4A is the main objective in this work. It will be analyzing the combination of the use of a dehydrative agent, such as zeolite 4A and butylene oxide with the Cu-Ni/AC catalyst at gas phase (92°C until 14 Bar) and liquid phase (92°C and 4 Bar). This unexplored option must be understood the effect of the presence of multicomponent mixtures on the adsorption capacity and kinetics of water behavior and presents the first results for the assembly zeolite 4A / Cu – Ni /AC in gas and liquid phase at same conditions. This study lets it contribute with the multicomponent adsorption determination because there are a few informations reported for this kind of systems and it proposes a simple experimental methodology that uses mass spectrometry as a new, practice and easy quantification technique in order to obtain the data. The results showed that the equilibrium conversion is strongly influenced by the pressure and temperature of the system: Conversion increases when increasing the pressure and temperature, however the water adsorption capacity of zeolite always was worse when the temperature increases and it is not affected by pressure. About the multicomponent adsorption capacity, isothermal adsorption and kinetics of water, methanol and ethanol in 4A zeolite were studied at different temperatures and different number of compounds. It has been demonstrated that adsorption of water, methanol and ethanol follow Langmuir isotherms. The mixtures of compounds show a competitive adsorption (ethanol and methanol occupy the sites) and the presence of CO2 block the access of the sites reduce the water adsorption capacity. Furthermore, the separation of water and methanol is in fact very difficult because polarities, chemical properties and even molecular sizes of water and methanol (2.6 Å and 3.6 Å) are similar. Finally, the kinetics follow by pure compounds were different when increase the number of compounds. Water, follow PFO kinetic but, in presence of methanol and CO2 presence an Elovich or IPD tendency suggest a possible chemisorption. Any catalytic activity of the Cu-Ni/AC catalyst was obtained in the liquid phase reactions at 4 Bar and 92°C. Although, it presents loss of loading by a possible leaching, it is unable to increase the yield. Regardless what dehydrating agent was used (butylene oxide or zeolite 4A) the reaction tends to zero.