M.S. Wainwright

On the determination of copper surface area by reaction with nitrous oxide

Abstract The chromatographic technique for determining the specific copper surface area of catalysts by reaction with nitrous oxide has been investigated. Promotion of bulk oxidation of copper in catalysts containing oxides of chromium, zinc and aluminium led to an overestimation of the surface copper atoms. The application of a single pulse of nitrous oxide in excess of that required to oxidize an the surface copper and a temperature of 90°C has been shown to provide a reliable measurement of specific copper surface areas.

Catalysts, Kinetics and Reactor Design in Phthalic Anhydride Synthesis

Abstract Phthalic anhydride is a chemical of considerable importance and is generally produced by the vapor-phase oxidation of o-xylene or naphthalene over vanadium pentoxide catalysts according to

Kinetic study of steam reforming of methanol over copper-based catalysts

Steam reforming of methanol has been studied over various copper-based catalysts at temperatures from 443 to 533 K. Screening experiments showed that a coprecipitated CuO-ZnO-Al2O3 low-temperature methanol synthesis catalyst had the highest activity and did not deactivate with time on line. It also exhibited 100% selectivity to carbon dioxide and hydrogen (the desired reaction products). Kinetic measurements made over the coprecipitated CuO-ZnO-Al2O3 were found to fit the power law expression: rSR=k0e–105kJ/mol/RTP0.26MeOHP0.03H2OP–0.2H2 Carbon dioxide was found to have no effect on the kinetics of steam reforming of methanol. When carbon monoxide was added to the feed there was negligible influence on the steam reforming reaction with an order of 0.016 being observed.

Kinetic mechanism for the reaction between methanol and water over a Cu-ZnO-Al2O3 catalyst

Abstract The steam reforming of methanol over a Cu/ZnO/Al 2 O 3 catalyst has been investigated. The reaction yields carbon dioxide and hydrogen in the ratio of one to three, with small amounts of dimethyl ether and carbon monoxide being produced at high conversion. Comparison of the rates of methanol dehydrogenation and of steam reforming over the same catalyst indicate that steam reforming proceeds via dehydrogenation to methyl formate. Methyl formate then hydrolyses to formic acid which decomposes to carbon dioxide and hydrogen. Detailed studies of the kinetics of the reactions show that methanol dehydrogenation controls the rate of steam reforming. Langmuir-Hinshelwood modelling indicates that hydrogen extraction from adsorbed methoxy groups is rate determining to the overall processes.

Methanol synthesis over Raney copper-zinc catalysts: I. Activities and surface properties of fully extracted catalysts

The activity of fully extracted Raney copper-zinc catalysts for the methanol synthesis reaction, and the associated physical and chemical properties of these catalysts, have been examined. The Raney catalysts were prepared by leaching a series of AlCusZn alloys containing approximately 50 wt% Al and differing CuZn ratios with aqueous NaOH until complete reaction had taken place. Hydrogenation of a mixture of carbon monoxide and carbon dioxide showed that Raney catalysts prepared from alloys containing approximately 50 wt% Al, 30–36 wt% Cu, and 14–20 wt% Zn had the greatest activity for methanol synthesis. The active component for these Raney catalysts was found to be metallic copper and the activity exhibited a maximum for catalysts containing approximately 97 wt% copper. The residual zinc in these catalysts was found to provide a promotional effect to catalytic activity. The surface areas of the catalysts increased from 17 to 39 m2g−1 with increasing zinc content of the precursor alloy. The catalysts exhibited a narrow pore size distribution with the pore radius decreasing with increasing alloy zinc level. Carbon monoxide and hydrogen adsorption were used to determine the nature of the catalyst surface.

Evaluation of procedures for the estimation of dead time

Abstract In order to determine the exact retention of compounds in gas chromatographic studies some method of determining the column dead time must be employed. This paper reviews direct measurement techniques using methane injection as well as mathematical determination of dead-time from retention data for n -alkanes. A critical evaluation of these procedures is made along with recommendations concerning the choice of evaluation method to be adopted by the chromatographer.

A Review of methods for the Determination of Hold-up Volume in Modern Liquid Chromatography

Abstract Arguably, the most important parameter in modern liquid chromatography is the hold-up (or dead) volume, VM, the volume of mobile phase contained within the chromatographic system between the sample injector and the detector. Without this knowledge many dependent parameters such as capacity factor (k), selectivity (α), and resolution (Rg) cannot be computed (104, 15, 78). These data are of the utmost importance for the optimization of conditions for the separation of complex mixtures and the identification of solute bands.

Hydrogenolysis of methyl formate over copper on silica: I. Study of surface species by in situ infrared spectroscopy

The hydrogenolysis of methyl formate to methanol over silica-supported copper has been studied using in situ infrared spectroscopy coupled with simultaneous determination of rate. Under flow reaction conditions two forms of adsorbed methyl formate exist. One has a carbonyl absorption at 1726 cm−1 and is bound to the support by hydrogen bonding with a heat of adsorption of 65 kJ mol−1. The second absorbs at 1666 cm−1 and is bound to copper with an approximate heat of adsorption of 140 kJ mol−1. At 457 K the hydrogenolysis rate is directly proportional to the band intensity of the latter and hence it, or another species in equilibrium with it, is involved in the rate-determining step. Adsorption of CO from COH2 mixtures gives rise to a single infrared band at 2117 cm−1, the corresponding heat of adsorption being 60 kJ mol−1. Competitive measurements under hydrogenolysis conditions show that methyl formate will partially displace adsorbed CO and not vice versa. Nonetheless CO does reversibly inhibit the rate and this is attributed to its adsorption displacing hydrogen from the surface. The lower concentration of surface hydrogen also reduces the rate of hydrogenation of a formaldehyde intermediate leading to its deposition as a polymer as revealed by infrared bands at 1483 and 1375 cm−1. The same polymer accretes more rapidly during the reverse methanol to methyl formate reaction for which CO is a substantial by-product and hydrogen pressures are much lower than used for hydrogenolysis. Continuous deactivation of the catalyst is then observed.

Methanol synthesis and water-gas shift reactions on Raney copper catalysts

Abstract The use of Raney copper to catalyse the synthesis of methanol and the water-gas shift reaction is reviewed. The preparation of Raney copper and Raney copper-zinc alloys together with their leaching to form active catalysts is first considered. The production of methanol is promoted by copper and the major—but not the only—role of zinc oxide involves the production of higher and more stable copper surface areas. There is some evidence that the catalytic activity of both methanol synthesis and water-gas shift may be improved by events occurring at the CuZnO interface. It is now clear that carbon dioxide is the major reactant forming methanol under industrial conditions. Both in the water-gas shift and the synthesis reactions, formates appear to be the main intermediates. Raney catalysts have the advantages of high mechanical strength, of regenerability and of producing less side products during methanol synthesis—an important practical consideration. Their applicability to industrial operations would seem advantageous.

Structural and reactivity effects in the copper-catalyzed hydrogenolysis of aliphatic esters

Abstract The hydrogenolysis of a series of alkyl esters to their corresponding alcohols has been studied over a Raney copper catalyst in the temperature range 210–280 °C. Generally, the rate of hydrogen-olysis was found to increase with molecular weight while the selectivity to alcohol, derived from the acyl part of the ester, decreased due to transesterification reactions. The rate data correlated well to a Taft equation in which inductive effects were more important than steric effects, provided the equation included a term to account for the hydrogens on the α-carbon atoms. Reaction kinetics for ethyl acetate hydrogenolysis were found to be first order in hydrogen and −0.5 order in ethyl acetate.