Transhydrogenation of propyne with butane over a vanadia/θ-alumina catalyst

The transhydrogenation of propyne and butane was studied over a 1 % VO x /alumina catalyst at 873 K. In the absence of the vanadia, the alumina support was active for cracking and alkylation. However, the addition of the vanadia reduced the propensity for both cracking and alkylation and added dehydrogenation activity. When propyne and butane were co-fed over the catalyst there was a synergistic effect resulting in an increased conversion of propyne (81 cf. 26 % when fed alone); however, much of this increased conversion was converted to carbon deposited on the catalyst. Transhydrogenation of propyne to propene was detected with an enhanced yield of propene when the propane/butane mix was passed over the catalyst. Taking a yield based on propyne fed then the yield of propene increased from 1.2 to 5.0 %. The conversion of butane to value-added products was also enhanced with all the butane converted accounted for in the production of 1-butene, trans-2-butene, iso-butane and iso-butene

Deactivation and regeneration of chromia and vanadia catalysts in alkane dehydrogenation

The deactivation and regeneration of a 6 % CrOx/alumina catalyst and a 3.5 % VOx/alumina catalyst has been studied after use in butane dehydrogenation at 873 K. Both catalysts deactivate due to carbonaceous deposits and with both catalysts the isomerisation reaction from 1-butene to cis and trans-2-butene is poisoned more effectively than the dehydrogenation reaction. The chromia catalyst deactivates three times faster than the vanadia system but the total amount of carbon deposited is similar indicating that the nature of the deposit on the chromia system is much more deleterious. The vanadia catalyst can be regenerated at room temperature in a flow of oxygen by removal of reaction intermediates, which desorb as butane, butene and butadiene. Over 75 % of the activity can be retrieved and by 1 hour on stream no difference can be discerned, whereas no significant desorption is detected from the chromia catalyst at room temperature and no regeneration is observed. TPO of both systems show different profiles with the deposit on the chromia catalyst more resistant to oxidation, which suggests a more dehydrogenated or more graphitic type material, which would be in keeping with the faster deactivation. After regeneration at 873 K the chromia catalyst recovers all its activity, whereas even after 873 K regeneration the vanadia catalyst does not recover all its activity. This is likely due to a change in structure and electronic properties of the polyvanadate species

Natural rubber/organoclay nanocomposites: Effect of filler dosage on the physicomechanical properties of vulcanizates

Natural rubber/organoclay nanocomposites of varying filler loading [2 to 10 per hundred rubber (phr)] using derivative of tea (Camellia sinensis) seed oil were prepared by melt intercalation. Effects of filler dosage on the physicomechanical properties of the natural rubber (NR) vulcanizates were examined. Results of the mechanical properties indicates that tensile strength and tear properties of the modified organoclay/NR nanocomposites increases with increasing filler loading compared with the unmodified filled NR vulcanizates. Furthermore, rheological measurement showed that modified filled NR vulcanizate exhibited higher storage modulus (G I ) than the unmodified filled NR. The values of the weight-swelling ratio (Qt) of the modified filled nanocomposites decreased remarkably and are lower than the unmodified filled NR vulcanizate. The higher value of the chemical crosslink density of 0.629 at 6 phr for the organoclay/NR composite indicate better reinforcement of the filler-rubber matrix over the unmodified. The scanning electron microscopy revealed that incorporation of modified organoclay up to 6 phr has transformed the failure mechanism of the resulting NR vulcanizate compared to the unmodified. There is an indication that the optimum level of incorporation of sodium salt of tea seed oil is 6 phr