A.O.I. Krause

Catalytic conversion of biomass pyrolysis vapours with zinc oxide

Conversion of pyrolysis vapours of pine sawdust was studied in micro and bench scales with zinc oxide catalyst. Three different zinc oxides were screened in a gas chromatograph system using an injection port as a fixed-bed catalytic converter in order to find appropriate reaction conditions by emphasising a high yield of bio-oil. Catalytically treated pyrolysis oils were produced in a side stream of an atmospheric fluidised bed pyrolyser (1 kg h−1) at the catalyst temperature of 400°C. The oils with silicon carbide treatment and without any catalyst were used as references. The aim was to study the catalytic effect of zinc oxide on the composition and on the stability of the oil. The pyrolysis liquids produced were homogeneous one-phase oils. The ZnO proved to be a mild catalyst and the liquid yields were not substantially reduced. It had no effect on the water-insoluble fraction (lignin-derived), but it decomposed the diethyl ether-insoluble fraction (water-soluble anhydrosugars and polysaccharides). Some indications of catalyst deactivation were observed. The oil samples were aged thermally and the variation of viscosity and water content were determined. The increase in the viscosity was significantly lower for the ZnO-treated oil (55%) than for the reference oil without any catalyst (129%). The results indicated an improvement in the stability of the ZnO-treated oil.

Effect of H2S on the stability of CoMo/Al2O3 catalysts during hydrodeoxygenation

Abstract The effect of H 2 S addition on the activity and the stability of CoMo catalyst during hydrotreating of phenol and anisole was studied. The presence of H 2 S strongly decreased the HDO activity of the sulfided catalyst, and the ratio of the HDO reaction pathways depended on the H 2 S concentration. The hydrogenolysis route to aromatics was suppressed, whereas the conversion of the hydrogenation–hydrogenolysis route to alicyclics at moderate H 2 S concentrations remained the same as in the absence of H 2 S. This clearly supports the presence of two types of active sites for HDO on the catalyst. Sulfidation of the catalyst was not a prerequisite for demethylation of anisole to phenol, though it increased the activity of the catalyst. Demethylation proceeded effectively even on the acidic sites of the Al 2 O 3 support and on the sulfhydryl groups formed on CoMo catalyst in the presence of H 2 S. In addition to desulfurization and changes in the structure of the active sulfided catalyst, the formation of coke and high molecular weight compounds on the catalyst decreased its activity but did not affect the selectivity of HDO.

Dehydrogenation of i-butane on CrOx/Al2O3 catalysts prepared by ALE and impregnation techniques

Abstract Atomic layer epitaxy (ALE), a technique relying on saturating gas–solid reactions, was applied in the preparation of CrOx/Al2O3 catalysts using Cr(acac)3 vapor and air as source materials for CrOx. Vaporized Cr(acac)3 was reacted with preheated Al2O3, and the surface complex formed was treated with air to remove the ligand residues. The Cr loading increased from 1.3 to 12.5xa0wt.% as the number of saturating Cr(acac)3 and air reactions was increased from one to 10. CrOx/Al2O3 catalysts were also prepared from solution by incipient wetness impregnation (0.3–21xa0wt.%). XPS and UV–VIS measurements of the catalysts revealed the presence of both Cr6+ and Cr3+. Although the oxidation state distribution was similar, H2-temperature programmed reduction (TPR) and solubility measurements indicated that Cr6+ surface sites were in stronger interaction with Al2O3 and more uniformly distributed in the catalysts prepared by ALE than by impregnation. On the basis of the activity of the catalysts in the dehydrogenation of i-butane, we propose that the dehydrogenation reaction uses both reduced Cr6+, i.e. redox Cr3+, and exposed non-redox Cr3+ sites. Furthermore, the dehydrogenation reaction must be insensitive to the size of the CrOx ensembles since activities were similar for the catalysts prepared by ALE and impregnation. The decay of the dehydrogenation activity in successive prereduction–reaction–regeneration cycles was attributed to a decrease in the number of redox Cr3+ sites.

Simultaneous hydrodesulfurization and hydrodeoxygenation : interactions between mercapto and methoxy groups present in the same or in separate molecules

Abstract Simultaneous hydrodesulfurization (HDS) and hydrodeoxygenation (HDO) of mercapto and/or methoxy group containing model compounds was studied on CoMo/γ-Al2O3 in order to find out how the interactions of the substituents affect the efficiency of hydrotreating. HDS of mercaptobenzene decreased in the presence of anisole compared to the reaction of pure mercaptobenzene and a less reactive sulfur compound, (methylmercapto)benzene, was formed via methyl transfer. Simultaneously, the cleavage of the aliphatic carbon–oxygen bond in anisole was markedly enhanced due to this methyl capture by sulfur. The apparent activation energy of phenol formation from anisole decreased, indicating as well a change in the reaction mechanism. HDO reactions of anisole were, however, suppressed in the presence of mercaptobenzene. Addition of small amounts of a sulfiding agent, CS2, to the reactor feed also had a positive effect on the total conversion of anisole, but it did not markedly affect the HDO rates. With a methoxy group present in the same molecule as a mercapto group, both the HDS rate and the reaction selectivity were dependent on the isomer structure. The HDS rate of para-mercaptoanisole was about twice as high as that of mercaptobenzene at 225°C, while the methoxy group in the ortho position did not markedly affect the rate. The HDS rate of meta-mercaptoanisole was about half of that of mercaptobenzene. Phenol was formed from ortho-mercaptoanisole, while in other mercaptoanisole isomers the methoxy group remained predominantly unchanged. HDO reactions were suppressed in the presence of a sulfur-containing substituent but methyl transfer to the benzene ring was not affected.

Liquid phase hydrogenation of tetralin on Ni/Al2O3

Abstract The kinetics of the tetralin hydrogenation in decane was studied on a Ni/ γ -Al 2 O 3 catalyst over a temperature range of 85–160°C and a pressure range of 20– 40 bar . The hydrogenation occurred by sequential steps from tetralin to cis - and trans -decalins with the formation of octalins as reaction intermediates. Besides the hydrogenation some dehydrogenation to naphthalene was observed in addition to severe catalyst deactivation. The hydrogenation followed low-order rate towards tetralin and close to first-order towards hydrogen. The proposed kinetic model based on a Langmuir–Hinshelwood-type mechanism included the tetralin hydrogenation through intermediate steps to cis - and trans -decalin. The model was able to describe the experimental results adequately and gave physically meaningful parameters.

The activity of the CoSiO2 catalyst in relation to pretreatment

Abstract The activity and characteristics of the nitrate derived Co SiO 2 were determined in relation to reductive pretreatment. With increasing reduction temperature (300–450°C), the extent of reduction increased. This increase was not, however, accompanied with increased chemisorption capacity. Namely, the hydrogen chemisorption was highest at a reduction temperature of approx. 300°C. Also, the carbon monoxide adsorption was almost constant at 200–400°C, and decreased drastically thereafter. Thus, the results suggest that cobalt agglomerated at temperatures above 400°C. The activity in toluene hydrogenation correlated well with the hydrogen uptake for reduction temperatures of above 300°C. Also, the CO hydrogenation activity of the catalyst decreased with increasing temperature of reduction (400–450°C) due to the decrease in the number of active sites.

Kinetics of catalytic cracking with short contact times

Abstract A novel isothermal pulse reactor was used to study the kinetics of gas oil cracking on a FCC equilibrium catalyst with short contact times. The feed was a lighter gas oil than typically used in FCC-units. Experiments were carried out by varying the catalyst-to-oil ratio, volume of the oil pulse, temperature and residence time. After each hydrocarbon pulse the catalyst was regenerated by introducing several oxygen/nitrogen pulses through the catalyst bed. The amounts of carbon monoxide and carbon dioxide formed were measured and the amount of coke on the catalyst was calculated. The reproducibility of the experiments was excellent. A kinetic model that included five lumps, namely, gas oil, gasoline, liquefied petroleum gas (LPG), dry gas and coke with five cracking reactions was developed first and its kinetic parameters were determined from the experimental results. The data could be best described by the model wherein the rate of cracking of gas oil to gasoline and to LPG were both approximated as second order dependency and the rate of cracking of gas oil to dry gas and to coke as first order dependency on the gas oil concentration. The five-lump model was further enlarged by dividing the gasoline fraction into paraffins, olefins, naphthenes and aromatics resulting in an eight-lump model with eight reactions. In addition, changes in the activity of the catalyst during one experiment was accounted for by using two exponential activity functions, one for catalytic cracking reactions and the other for coke formation. The formation of dry gas was considered to be the product of a thermal reaction only. The kinetic parameters of the Arrhenius’ law and the deactivation parameters were estimated by a non-linear regression program. In the five-lump model 12 parameters and in the eight-lump model 18 parameters (rate coefficients, activation energies and deactivation parameters) were obtained. The kinetic parameters of the Arrhenius’ law were statistically significant in both models.

Ethene hydroformylation on Co/SiO2 catalysts

The results from ethene hydroformylation at 173°C showed that a Co(acac)3/SiO2 catalyst prepared from Co(acac)3 precursor by gas‐phase deposition was three times as active as a catalyst prepared by impregnation from cobalt nitrate, but oxo‐selectivities were similar. The high propanal selectivities on the Co(acac)3/SiO2 seem to be related to the presence of highly dispersed active sites favouring CO insertion. As dispersion is decreased from 23 to 8% due to increasing metal content (from 5 to 16 wt%), oxo‐selectivity decreased from 39 to 25%. The activity of Co(acac)3/SiO2 remained unchanged during 68 h on stream. The gas‐phase deposition technique described here is a promising method for the preparation of active, selective and stable heterogeneous hydroformylation catalysts.

The effect of the precursor on the characteristics of Co/SiO2 catalysts

Abstract The effect of the precursor on the characteristics of the Co/SiO 2 catalysts prepared from Co(NO 3 ) 2 , Co 2 (CO) 8 and Co 4 (CO) 12 was determined. The near-surface reduction was clearly lower for the Co 2 (CO) 8 derived catalyst than for the Co 4 (CO) 12 based one. The hydrogen chemisorption, CO desorption, XRD and XPS measurements indicated that the dispersion of the metallic species decreased in the precursor order Co 2 (CO) 8 > Co 4 (CO) 12 ≫ Co(NO 3 ) 2 . The TPD studies showed that CO was more strongly adsorbed on catalysts derived from carbonyls than on those based on nitrate, resulting in greater initial activity in CO hydrogenation. In pulsed CO hydrogenation reactions, the selectivity of the Co 2 (CO) 8 derived catalyst differed from the other two. Thus, despite the well documented transformation of the Co 2 (CO) 8 to Co 4 (CO) 12 on the silica support, the supported catalysts derived from these two precursors exhibited distinct characteristics and reactivity.

The long-term performance of Co/SiO2 catalysts in CO hydrogenation

The activity in terms of conversion of carbon monoxide was determined for Co/SiO2 catalysts in CO hydrogenation over a reaction time of 120 h. The catalysts were prepared from nitrate (N) and carbonyl (CO) precursors. The conversion decreased rapidly during the first five hours, and thereafter moderately at a rate related to dispersion, i.e. the higher the dispersion the higher the rate of decrease. The active sites were blocked by wax and coke formed in the reaction, although some agglomeration of particles probably took place on the Co(CO)/SiO2 catalysts. More carbon was accumulated on Co(CO)/SiO2 than on Co(N)/SiO2 during the reaction suggesting a need for frequent regeneration. The reduction-oxidation-reduction treatments indicated, however, that the regenerability of the Co(CO)/SiO2 in terms of hydrogen uptake is poor, although the amounts adsorbed still remained higher than those for Co(N)/SiO2.