AUTHOR=Ahoba-Sam Christian , Olsbye Unni , Jens Klaus-Joachim 

TITLE=The Role of Solvent Polarity on Low-Temperature Methanol Synthesis Catalyzed by Cu Nanoparticles

JOURNAL=Frontiers in Energy Research

VOLUME=Volume 5 - 2017

YEAR=2017

URL=https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2017.00015

DOI=10.3389/fenrg.2017.00015

ISSN=2296-598X

ABSTRACT=Methanol syntheses at low temperature in a liquid medium presents an opportunity for full syngas conversion per pass. The aim of this work was to study the role of solvents polarity on low temperature methanol synthesis (LTMS) reaction using 8 different aprotic polar solvents. A ‘once through’ catalytic system, which is composed of Cu nanoparticles and sodium methoxide, was used for methanol synthesis at 100 oC and 20 bar syngas pressure. Solvent polarity rather than the 7-10 nm Cu (and 30 nm Cu on SiO2) catalyst used dictated trend of syngas conversion. Diglyme with a dielectric constant (ɛ) = 7.2 gave the highest syngas conversion among the 8 different solvents used. Methanol formation decreased with either increasing or decreasing solvent ɛ value of diglyme (ɛ = 7.2). To probe the observed trend, possible side reactions of methyl formate, the main intermediate in the process, were studied. Methyl formate was observed to undergo two main reactions; (i) decarbonylation to form CO and MeOH and (ii) a nucleophilic substitution to form dimethyl ether and sodium formate. Decreasing polarity favoured the decarbonylation side reaction while increasing polarity favoured the nucleophilic substitution reaction. In conclusion, our results show that moderate polarity solvents, e.g. diglyme favour MF hydrogenolysis and hence, methanol formation, by retarding the other two possible side reactions.