Dermot J. Collins

Denitrogenation of piperidine on alumina, silica, and silica-aluminas: The effect of surface acidity

Abstract Alumina, silica, and three silica-aluminas having 10, 50 and 90 wt% SiO 2 were prepared and characterized for the total acidity, acid strength distribution, and Bronsted/Lewis acidity. The characterization involved the techniques of ammonia chemisorption, temperature-programmed desorption (TPD), and FT-IR spectroscopy. The effect of surface acidity on denitrogenation selectivity was studied by means of the reactions of piperidine in a continuous-flow fixed-bed reactor operated at atmospheric pressure and 320–340°C. The overall piperidine conversion to various products increases with the total acidity of the catalysts. However, the denitrogenation selectivity depends only on the concentration of Bronsted acid sites, demonstrating the participation of those sites in the deamination mechanism and hence showing evidence for the Hofmann elimination pathway. The other important reactions of piperidine were alkylation, condensation, disproportionation, and dehydrogenation, to yield alkylpiperidines, 2,3,4,5-tetrahydropyridine, pyridine, 1,2,3,4-tetrahydroquinoline, 1,2,3,4-tetrahydro-3-methylquinoline, 5,6,7,8-tetrahydroquinoline, and decahydroquinoline.

Xylene isomerization and disproportionation over lanthanum Y catalyst

Xylenes have been converted using a LaY zeolite catalyst at a temperature, 350 °C, where transalkylation, as well as isomerization, occurs. The relative rates of the isomerization reactions were calculated using the Wei-Prater method. Relative selectivities calculated from the relative rates (Wei-Prater) agree very well with those calculated from rates obtained by extrapolation to low conversions. The trimethylbenzenes obtained at low conversions are those expected from methyl-group-directing influence for the ortho-xylene and para-xylene reactants; however, with meta-xylene an equilibrium trimethylbenzene composition was obtained even at very low conversions. The results are consistent with a series reaction path for the isomerization reaction.

Isomerization and disproportionation of trimethylbenzenes with LaY zeolite catalyst

Abstract Trimethylbenzenes undergo both disproportionation and isomerization during conversion over LaY zeolite catalysts. Isomerization occurs primarily by a series of 1,2-methyl shifts. Disproportionation appears to occur by removal of a methyl group from one trimethylbenzene prior to its isomerization to other trimethylbenzenes; the methyl group is transferred to another trimethylbenzene as predicted for the ortho-para directing influence of the methyl groups already on the ring. A set of relative rate constants for isomerization, calculated using the Wei-Prater procedure, obtained for xylene and trimethylbenzene isomerization has a similar pattern.

Catalytic conversion of alcohols: role of sodium in altering the alkene products obtained with alumina catalysts

In order to study the catalytic conversion of alcohols to alkenes, catalysts were prepared by impregnating Degussa aluminum oxide C with aqueous NaNO/sub 3/ and then drying and calcining the catalysts. The alcohols studied were 2-butanol and 2-octanol; but since a serious secondary isomerization effect present when 2-butanol is converted is eliminated when a mixture of the two alcohols is converted, the mixture was used for this study. The results indicated that two types of dehydration sites must occur on the alumina catalyst. One type designated A is more active for dehydration, and their selectivity from 1-butene and cis-2-butene in about equal amounts with only a small fraction of trans-2-butene. The other type of sites, B sites, form isomers in nearly equal amounts.

Isomerization and disproportionation of xylenes with an aluminum chloride catalyst

Abstract Xylenes undergo both isomerization and disproportionation with AlCl 3 - HCl catalyst. The six relative rate constants for xylene isomerization calculated using the Wei-Prater procedure agree with those claculated using classical kinetic methods. Thus, the Wei-Prater method is advantageous since absolute rates for the conversion of each of the three xylene reactants are not required, as is the case when using the classic kinetic method. Initial trimethylbenzene products, formed by disproportionation, are consistent with a transalkylation mechanism where the selectivity is controlled by alkyl group directing effects. However, these trimethylbenzenes poison the catalyst. Poisoning is consistent with, but does not require, the formation of a complex of two AlCl 3 catalyst molecules with each 1,3,5-trimethylbenzene; this complex is an inactive catalyst for the xylene iso-merization reaction.

Side reactions in quinoline hydrodenitrogenation

Abstract The mechanism for hydrodenitrogenation (HDN) of quinoline to propylbenzene, propylcyclohexene and propylcyclohexane is well established. In this paper the formation of substantial amounts of species formed from HDN intermediates is reported for a cobalt-molybdenum/alumina catalyst. As many as eighteen species were found in reaction mixtures at concentration levels greater than 1%, with indoline and hydrindane being the most significant. The results suggest that Bronsted acidity may be responsible for the formation of indoline and hydrindane.

Nitrobenzene hydrogenation: poisoning effect of tin dichloride on a platinum catalyst

Abstract Tin chloride acts as a poison when added at levels of Sn/Pt⩾1. Ammonium chloride, when added prior to stannous chloride, eliminates the poisoning effect, presumably by converting SnCl2 to the SnCl3− anion. Poisoning by SnCl2 decreases exponentially with the Sn/Pt ratio.

The hydrogenation behavior of various Kentucky coals

Abstract Kentucky coals numbers 6, 9 and 11 and Illinois coal number 6 were hydrogenated with and without a hydrodesulphurization catalyst in a 0.3-liter autoclave. Reaction conditions simulated the syncrude mode of the H-Coal process (pressure of 14 MPa, temperature of 725 K). Conversion of all coals to oil plus asphaltenes was in the 80–85% range, irrespective of seam, mine, use of catalyst or time. Reaction to preasphaltenes was minimal in runs which used a catalyst, except for KY no. 6 coal. Without catalyst about 4% preasphaltenes were isolated in the product. Sulphur balances indicated that the catalyst, Cyanamid HDS-2A, was effective at keeping sulphur in the solid residue. Between 75 and 95% of the sulphur stayed in the residue for catalyzed reaction as opposed to 25 to 45% for the uncatalyzed cases. Actual conversion values were consistently lower than those predicted based on petrographic data. This is postulated as being due to the reaction conditions.