Klaus-Joachim Jens

Hydrogen acceptor and membrane concepts for direct methane conversion

Abstract Condensation of methane in the presence of a hydrogen acceptor (titanium) to ethane and titaniumdihydride gives a thermodynamic conversion of 60% (PCH4 = 1 atm, T = 400 K). Experiments with Ti as the acceptor together with Pt/Sn, Rh or Ni catalysts, give, however, a methane conversion in the range of 1% with coke as the main product. In order to explore the possibility of methane conversion by a membrane concept , titanium and palladium as a hydrogen permeable material have also been theoretically investigated. Assuming diffusion limitation, up to 1.8 g ethane/m2·h (T = 400 K, Δx = 0.03 cm, equilibrium at p = 4 bar) may be produced in the case of palladium. Exploratory experiments show very low conversion of methane with coke as the main product.

Pulse reactor studies of catalysts for the oxidative coupling of methane

Abstract The behaviour of the catalysts MgO, Li/MgO, Li/ZnO and Mn/Na4P2O7/SiO2 are compared using a pulse reactor:. The catalysts are exposed to pulses of different gases, such as air, methane and a methane:air mixture (1:1). There is more interaction from lattice oxygen with the Mn/Na4P2O7/SiO2 and Li/MgO catalysts than with the pure MgO or Li/ZnO.

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

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.

Tailoring Cu Nanoparticle Catalyst for Methanol Synthesis Using the Spinning Disk Reactor

Cu nanoparticles are known to be very active for methanol (MeOH) synthesis at relatively low temperatures, such that smaller particle sizes yield better MeOH productivity. We aimed to control Cu nanoparticle (NP) size and size distribution for catalysing MeOH synthesis, by using the spinning disk reactor. The spinning disk reactor (SDR), which operates based on shear effect and plug flow in thin films, can be used to rapidly micro-mix reactants in order to control nucleation and particle growth for uniform particle size distribution. This could be achieved by varying both physical and chemical operation conditions in a precipitation reaction on the SDR. We have used the SDR for a Cu borohydride reduction to vary Cu NP size from 3 nm to about 55 nm. XRD and TEM characterization confirmed the presence of Cu2O and Cu crystallites when the samples were dried. This technique is readily scalable for Cu NP production by processing continuously over a longer duration than the small-scale tests. However, separation of the nanoparticles from solution posed a challenge as the suspension hardly settled. The Cu NPs produced were tested to be active catalyst for MeOH synthesis at low temperature and MeOH productivity increased with decreasing particle size.