Christoph Buttersack

THE CONCEPT OF VARIABLE ACTIVE CENTRES IN ACID CATALYSIS PART I. ALKYLATION OF BENZENE WITH OLEFINS CATALYZED BY ION-EXCHANGE RESINS

Abstract The interaction of olefins with sulfonic acid macroporous ion-exchange resins in nonpolar medium has been investigated by measuring the acidity and the catalytic activity of the adsorbed olefin towards benzene. At low olefin concentrations a sharp maximum of reactivity was found, whereas the acidity continuously decreased with increasing olefin concentration. This substrate-inhibition has been described by the model of variable active centres: The homogeneously distributed accessible acid groups form clusters surrounding the adsorbed olefin. Increasing ratios of acid groups per adsorbed olefin operate to enhance the reactivity exponentially. In the case of more polar olefins, the maximum of reactivity is sharper and shifted to lower olefin concentrations.

Measurement of acidity of polymeric solid acids

Abstract Acidity measurements using Hammett indicators have been applied to macroporous sulfonic acid ion-exchange resins in nonpolar media. The acidity was varied by partial ion-exchange. It has been proven that the adsorption of the indicator molecules is reversible in the case of a thermally pretreated resin. From the measurement of the adsorption data, the ionization ratio of the indicators can be calculated and correlated to the reactivity in the alkylation of benzene with propene and to the degree of ion-exchange. Using these correlations, a relative acidity scale can be defined. The accessibility of acid groups in different solvents must be determined as a prerequisite for the application of the theory developed in this study.

Adsorption of sucrose on zeolites

The adsorption of sucrose on FAU type zeolites was measured depending on the ratio of Si/Al and the solvent composition (ethanol–water). The maximal loading was found to be 1 sucrose molecule per α-cage. The adsorption can proceed from water on strong dealuminated zeolites and from an ethanol water mixture on aluminum rich zeolites. To recover sucrose the zeolite can be treated with ethanol–water. Alternatively the liquid is first mixed with an alcohol, sucrose is adsorbed on a hydrophilic zeolite and desorbed by the addition of water. An application is reported for the desugarization of sugar-beet molasses and process liquids of a beet sugar factory. The adsorption obeys the Langmuir isotherm and is selective compared with other saccharides. The effective diffusion coefficient of sucrose inside the zeolite pores was measured.

c,T-dependence of the self-diffusion in concentrated aqueous solutions of methyl α- and β-d-glucopyranosides

Abstract The self-diffusion coefficients D for methyl α- and β- d -glucopyranosides in aqueous solutions have been measured in the concentration range between 10% and 70% (w/w) glucoside in a wide temperature range. At higher concentrations ( c > 40%) the mobility of the water and the glucoside molecules is significantly lower in the α- d -glucoside solutions than in the corresponding mixtures containing the β-anomer.

Sulfonic acid ion-exchange resins as catalysts in nonpolar media: II. Influence of conditioning methods on the acidity and catalytic activity

Abstract The behaviour of macroporous sulfonated styrene-divinylbenzene copolymers has been investigated in relation to their acidity and catalytic efficiency in the alkylation of benzene with propene. In order to optimize catalyst activity, the following separate parameters have to be taken into account: Adsorbed water lowers the catalytic activity, but after an induction period the poisoning effect of water is at least partially offset by the interaction of the sulfonic acid groups with the olefin. The optimal drying temperature is 100°C; higher temperatures cause a sharp decrease in catalyst acidity and therefore lower catalyst activity. In addition, the perfusion of the dried resin with benzene can produce a considerable decrease in catalyst activity. The deactivation caused by elevated drying temperatures and by interaction with benzene is discussed in terms of their effect on the flexibility of the polymer backbone.

Sulfonic acid ion-exchange resins as catalysts in nonpolar media: I. Drying of the catalyst

Abstract The retention of adsorbed water upon drying of sulfonated macroporous styrene-divinylbenzene copolymers in vacuo was investigated gravimetrically and by Karl Fischer titration. The residual water content θ w decreased with increasing degree of crosslinking and was related quantitatively to the temperature, pressure and duration of drying. The increase of the drying temperature was limited with respect to the thermal stability of the resins, and the reduction of θ w was effective only down to certain values θ w . θ w was found to depend on the degree of proton exchange by K + and Ca 2+ in different ways and to decrease in the sequence La 3+ ≈ Ca 2+ > H + > K + .

Adsorption and HPLC of carbohydrates and related hydroxy compounds on zeolites

Carbohydrates, sugar alcohols, and other hydroxy compounds were separated on a HPLC-column filled with dealuminated hydrophobic Y zeolite with water as eluent. Disaccharides show a greater retention and selectivity than monosaccharides. The selectivity for monosaccharides is in the same range compared with established stationary phases but significantly greater for disaccharides and trisaccharides. When a usual hydrophilic Y zeolite is used, either exchanged by K+ or Ca++, all disaccharides are excluded from the micropores and only monosaccharides can be separated. A hydrophobic MOR type zeolite with somewhat smaller pore geometry also excludes the disaccharides while an acceptable selectivity was observed for monosaccharides and other small hydroxyl compounds. The separation can be limited by diffusion of the solutes inside the micropores. Therefore, the separation can be improved by enhancing the temperature. The linear correlation of the dynamic separation process with the static adsorption equilibrium measured after 24 h is limited to low solute–zeolite interactions.

Structure-breaking effect of metal ions influencing the acidity of an anhydrous acid

Abstract A model is proposed describing the acidity of an anhydrous acid whose protons are partially exchanged by different metal ions. The acidity is related to a defined structure-breaking effect of the ions. The ions cause a decrease in the proton activity Δ log a H+ which is related to the degree of exchange x according to Δ log a H+ = A [ K 0 -log( x /(1- x ))] where K o is a constant depending on the degree of self-ionization of the pure acid. The parameter A is proportional to the radius and inversely proportional to the valence of the metal ion. The model is applied to a sulfonic acid ion-exchange resin partially exchanged by alkali and alkaline-earth ions. The acidity is measured both using kinetic data of an acid-catalyzed model reaction and by the adsorption equilibria of basic indicators.

Correction: Adsorption of sucrose on zeolites

Correction for ‘Adsorption of sucrose on zeolites’ by Iris Fornefett et al., Green Chem., 2016, 18, 3378–3388.

Chromatography of mono- and disaccharides on granulated pellets of hydrophobic zeolites

The chromatographic response of sugars at granulated zeolite pellets in preparative scale liquid chromatography is analyzed with respect to the distribution equilibrium and mass transfer. In contrast to hydrophilic FAU type zeolites their hydrophobic dealuminated counterpart, used here, can separate disaccharides the retention of which can strongly exceed those of the monosugars. The retention is correlated with data of batch adsorption studies from the literature. Whereas the retention decreases with increasing temperature, the peak sharpness shows the opposite trend. The effective mass resistance is calculated for a series of mono- and disaccharides. It increases with the capacity factor. The diffusion coefficient of the trehalulose disaccharide is restricted by a factor of about 2 in the macropores and by a factor of more than 104 in the micropores.