Exploratory catalyst screening studies on the base free conversion of glycerol to lactic acid and glyceric acid in water using bimetallic Au-Pt nanoparticles on acidic zeolites

The base free oxidation of glycerol with molecular oxygen in water using bimetallic Au-Pt catalysts on three different acidic zeolite supports (H-mordenite, H-β and H-USY) was explored in a batch setup. At temperatures between 140 and 180 °C, lactic acid formation was significant and highest selectivity (60 % lactic acid at 80 % glycerol conversion) was obtained using Au-Pt/USY-600 (180 °C). A selectivity switch to glyceric acid (GLYA) was observed when the reactions were performed at 100 °C. Highest conversion and selectivity towards GLYA were obtained with Au-Pt/H-β as the catalyst (68 % selectivity at 68 % conversion).

Direct activation of microcrystalline zeolites

In this work a direct activation route of zeolites is assessed. It consists of NH4-exchanging the as-synthesized solids before removing the organic template. Calcination afterwards serves to combust the organic template and creates the Brønsted sites directly; thus applying merely a single thermal step. This method simplifies their activation and the material suffers less thermal stress. The approach was particularly effective for microcrystalline beta and ferrierite zeolites. Thorough investigation of the template content and materials' texture points out to three relevant effects that can explain the effective exchange process: partial removal of the template during exchange creates substantial microporosity (ferrierite), the remaining template is reorganized within the pores (ferrierite) and finally, void space can exist due to the non-perfect matching between the network and template (beta). This shorter method appears suited for microcrystalline zeolites; it was ineffective for crystalline MFI types. © 2013 Elsevier B.V. All rights reserved.

Evaluation of catalytic pyrolysis of cassava rhizome by principal component analysis

Rhizome of cassava plants (Manihot esculenta Crantz) was catalytically pyrolysed at 500 °C using analytical pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) method in order to investigate the relative effect of various catalysts on pyrolysis products. Selected catalysts expected to affect bio-oil properties were used in this study. These include zeolites and related materials (ZSM-5, Al-MCM-41 and Al-MSU-F type), metal oxides (zinc oxide, zirconium (IV) oxide, cerium (IV) oxide and copper chromite) catalysts, proprietary commercial catalysts (Criterion-534 and alumina-stabilised ceria-MI-575) and natural catalysts (slate, char and ashes derived from char and biomass). The pyrolysis product distributions were monitored using models in principal components analysis (PCA) technique. The results showed that the zeolites, proprietary commercial catalysts, copper chromite and biomass-derived ash were selective to the reduction of most oxygenated lignin derivatives. The use of ZSM-5, Criterion-534 and Al-MSU-F catalysts enhanced the formation of aromatic hydrocarbons and phenols. No single catalyst was found to selectively reduce all carbonyl products. Instead, most of the carbonyl compounds containing hydroxyl group were reduced by zeolite and related materials, proprietary catalysts and copper chromite. The PCA model for carboxylic acids showed that zeolite ZSM-5 and Al-MSU-F tend to produce significant amounts of acetic and formic acids.

Design and characterization of zeolite membranes for fluid separation

Experimental and theoretical methods have been used to study zeolite structures, properties and applications as membranes for separation purposes. Thin layers of silicalite-1 and Na-LTA zeolites have been synthesised onto carbon-graphite supports using a hydrothermal synthesis procedure. The separation behaviour of the composite membranes was characterized by gas permeation studies of pure, binary and ternary mixtures of methane, ethane and propane. The influence of temperature and feed gas mixture composition on the separation and selectivity performance of the membranes was also investigated. It was found that the silicalite-1 composite membranes synthesised onto the 4 hour oxidized carbon-graphite supports showed the most promising separation behaviour of all the composite membranes investigated. Molecular simulation methods were used to gain an understanding of how hydrocarbon molecules behave both within the pores and on the surfaces of silicalite-1, mordenite and LTA zeolites. Molecular dynamic simulations were used to investigate the influence of temperature and molecular loadings on the diffusional behaviour of hydrocarbons in zeolites. Both hydroxylated (surface termination with hydroxyl groups) and non-hydroxylated silicalite-1 and Na-mordenite surfaces were generated. For both zeolites the most stable surfaces correspond to the {010} surface. For the silicalite-1 {010} surface the adsorption of hydrocarbons and molecular water onto the hydroxylated surface showed a favourable exothermic adsorption process compared to adsorption on the non-hydroxylated surface. With the Na-mordenite {010} surface the adsorption of hydrocarbons onto both the hydroxylated and non-hydroxylated surfaces had a combination of favourable and non-favourable adsorption energies, while the adsorption of molecular water onto both types of surface was found to be a favourable adsorption process.

Liquid-phase adsorption of n-paraffins on type 5A molecular sieves

As a basis for the commercial separation of normal paraffins a detailed study has been made of factors affecting the adsorption of binary liquid mixtures of high molecular weight normal paraffins (C12, C16, and C20) from isooctane on type 5A molecular sieves. The literature relating to molecular sieve properties and applications, and to liquid-phase adsorption of high molecular weight normal paraffin compounds by zeolites, was reviewed. Equilibrium isotherms were determined experimentally for the normal paraffins under investigation at temperatures of 303oK, 323oK and 343oK and showed a non-linear, favourable- type of isotherm. A higher equilibrium amount was adsorbed with lower molecular weight normal paraffins. An increase in adsorption temperature resulted in a decrease in the adsorption value. Kinetics of adsorption were investigated for the three normal paraffins at different temperatures. The effective diffusivity and the rate of adsorption of each normal paraffin increased with an increase in temperature in the range 303 to 343oK. The value of activation energy was between 2 and 4 kcal/mole. The dynamic properties of the three systems were investigated over a range of operating conditions (i.e. temperature, flow rate, feed concentration, and molecular sieve size in the range 0.032 x 10-3 to 2 x 10-3m) with a packed column. The heights of adsorption zones calculated by two independent equations (one based on a constant width, constant velocity and adsorption zone and the second on a solute material balance within the adsorption zone) agreed within 3% which confirmed the validity of using the mass transfer zone concept to provide a simple design procedure for the systems under study. The dynamic capacity of type 5A sieves for n-eicosane was lower than for n-hexadecane and n-dodecane corresponding to a lower equilibrium loading capacity and lower overall mass transfer coefficient. The values of individual external, internal, theoretical and experimental overall mass transfer coefficient were determined. The internal resistance was in all cases rate-controlling. A mathematical model for the prediction of dynamic breakthrough curves was developed analytically and solved from the equilibrium isotherm and the mass transfer rate equation. The experimental breakthrough curves were tested against both the proposed model and a graphical method developed by Treybal. The model produced the best fit with mean relative percent deviations of 26, 22, and 13% for the n-dodecane, n-hexadecane, and n-eicosane systems respectively.

The adsorptive separation of aromatic hydrocarbon mixtures

A detailed study has been made of the feasibility of adsorptive purification of slack waxes from traces of aromatic compounds using type 13X molecular sieves to achieve 0.01% aromatics in the product. The limited literature relating to the adsorption of high molecular weight aromatic compounds by zeolites was reviewed. Equilibrium isotherms were determined for typical individual aromatic compounds. Lower molecular weight, or more compact, molecules were preferentially adsorbed and the number of molecules captured by one unit cell decreased with increasing molecular weight of the adsorbate. An increase in adsorption temperature resulted in a decrease in the adsorption value. The isosteric heat of adsorption of differnt types of aromatic compounds was determined from pairs of isotherms at 303 K to 343 K at specific coverages. The lowest heats of adsorption were for dodecylbenzene and phenanthrene. Kinetics of adsorption were studied for different aromatic compounds. The diffusivity decreased significantly when a long alkyl chain was attached to the benzene ring e.g. in dodecylbenzene; molecules with small cross-sectional diameter e.g. cumene were adsorbed most rapidly. The sorption rate increased with temperature. Apparent activation energies increased with increasing polarity. In a study of the dynamic adsorption of selected aromatic compounds from binary solutions in isooctane or n-alkanes, naphthalene exhibited the best dynamic properties followed by dibenzothiophene and finally dodecylbenzene. The dynamic adsorption of naphthalene from different n-alkane solvents increased with a decrease in solvent molecular weight. A tentative mathematical approach is proposed for the prediction of dynamic breakthrough curves from equilibrium isotherms and kinetic data. The dynamic properties of liquid phase adsorption of aromatics from slack waxes were studied at different temperatures and concentrations. The optimum operating temperature was 543 K. The best dynamic performance was achieved with feeds of low aromatic content. The studies with individual aromatic compounds demonstrated the affinity of type NaX molecular sieves to adsorb aromatics in the concentration range 3% - 5% . Wax purification by adsorption was considered promising and extension of the experimental programme was recommended.

Methyl chloride purification for the silicone industry

This study experimentally investigated methyl chloride (MeCl) purification method using an inhouse designed and built volumetric adsorption/desorption rig. MeCl is an essential raw material in the manufacture of silicone however all technical grades of MeCl contain concentrations (0.2 - 1.0 % wt) of dimethyl ether (DME) which poison the process. The project industrial partner had previously exhausted numerous separation methods, which all have been deemed not suitable for various reasons. Therefore, adsorption/desorption separation was proposed in this study as a potential solution with less economic and environmental impact. Pure component adsorption/desorption was carried out for DME and MeCl on six different adsorbents namely: zeolite molecular sieves (types 4 Å and 5 Å); silica gels (35-70 mesh, amorphous precipitated, and 35-60 mesh) and granular activated carbon (type 8-12 mesh). Subsequent binary gas mixture adsorption in batch and continuous mode was carried out on both zeolites and all three silica gels following thermal pre-treatment in vacuum. The adsorbents were tested as received and after being subjected to different thermal and vacuum pre-treatment conditions. The various adsorption studies were carried out at low pressure and temperature ranges of 0.5 - 3.5 atm and 20 - 100 °C. All adsorbents were characterised using Brunauer Emmett Teller (BET), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDXA) to investigate their physical and chemical properties. The well-known helium (He) expansion method was used to determine the empty manifold and adsorption cell (AC) regions and respective void volumes for the different adsorbents. The amounts adsorbed were determined using Ideal gas laws via the differential pressure method. The heat of adsorption for the various adsorbate-adsorbent (A-S) interactions was calculated using a new calorimetric method based on direct temperature measurements inside the AC. Further adsorption analysis included use of various empirical and kinetic models to determine and understand the behaviour of the respective interactions. The gas purification behaviour was investigated using gas chromatography and mass spectroscopy (GC-MC) analysis. Binary gas mixture samples were syringed from the manifold iii and AC outlet before and after adsorption/desorption analysis through manual sample injections into the GC-MS to detect and quantify the presence of DME and ultimately observe for methyl chloride purification. Convincing gas purification behaviour was confirmed using two different GC columns, thus giving more confidence on the measurement reliability. From the single pure component adsorption of DME and MeCl on the as received zeolite 4A subjected to 1 h vacuum pre-treatment, both gases exhibited pseudo second order adsorption kinetics with DME exhibiting a rate constant nearly double that of MeCl thus suggesting a faster rate of adsorption. From the adsorption isotherm classification both DME and MeCl exhibited Type II and I adsorption isotherm classifications, respectively. The strength of bonding was confirmed by the differential heat of adsorption measurement, which was found to be 23.30 and 10.21 kJ mol-1 for DME and MeCl, respectively. The former is believed to adsorb heterogeneously through hydrogen bonding whilst MeCl adsorbs homogenously via van der Waal’s (VDW) forces. Single pure component adsorption on as received zeolite 5A, silica gels (35-70, amorphous precipitated and 35-60) resulted in similar adsorption/desorption behaviour in similar quantities (mol kg-1). The adsorption isotherms for DME and MeCl on zeolite 5A, silica gels (35-70, amorphous precipitated and 35-60) and activated carbon 8-12 exhibited Type I classifications, respectively. Experiments on zeolite 5A indicated that DME adsorbed stronger, faster and with a slightly stronger strength of interaction than MeCl but in lesser quantities. On the silica gels adsorbents, DME exhibited a slightly greater adsorption capacity whilst adsorbing at a similar rate and strength of interaction compared to MeCl. On the activated carbon adsorbent, MeCl exhibited the greater adsorption capacity at a faster rate but with similar heats of adsorption. The effect of prolonged vacuum (15 h), thermal pre-treatment (150 °C) and extended equilibrium time (15 min) were investigated for the adsorption behaviour of DME and MeCl on both zeolites 4A and 5A, respectively. Compared to adsorption on as received adsorbents subjected to 1 h vacuum the adsorption capacities for DME and MeCl were found to increase by 1.95 % and 20.37 % on zeolite 4A and by 4.52 % and 6.69 % on zeolite 5A, respectively. In addition the empirical and kinetic models and differential heats of adsorption resulted in more definitive fitting curves and trends due to the true equilibrium position of the adsorbate with the adsorbent. Batch binary mixture adsorption on thermally and vacuum pre-treated zeolite 4A demonstrated purification behaviour of all adsorbents used for MeCl streams containing DME impurities, with a concentration as low as 0.66 vol. %. The GC-MS analysis showed no DME detection for the tested concentration mixtures at the AC outlet after 15 or 30 min, whereas MeCl was detectable in measurable amounts. Similar behaviour was also observed when carrying out adsorption in continuous mode. On the other hand, similar studies on the other adsorbents did not show such favourable MeCl purification behaviour. Overall this study investigated a wide range of adsorbents (zeolites, silica gels and activated carbon) and demonstrated for the first time potential to purify MeCl streams containing DME impurities using adsorption/desorption separation under different adsorbent pre-treatment and adsorption operating conditions. The study also revealed for the first time the adsorption isotherms, empirical and kinetic models and heats of adsorption for the respective adsorbentsurface (A-S) interactions. In conclusion, this study has shown strong evidence to propose zeolite 4A for adsorptive purification of MeCl. It is believed that with a technical grade MeCl stream competitive yet simultaneous co-adsorption of DME and MeCl occurs with evidence of molecular sieiving effects whereby the larger DME molecules are unable to penetrate through the adsorbent bed whereas the smaller MeCl molecules diffuse through resulting in a purified MeCl stream at the AC outlet. Ultimately, further studies are recommended for increased adsorption capacities by considering wider operating conditions, e.g. different adsorbent thermal and vacuum pre-treatment and adsorbing at temperatures closer to the boiling point of the gases and different conditions of pressure and temperature.

Mesoporous sulfonic acid silicas for pyrolysis bio-oil upgrading via acetic acid esterification

Propylsulfonic acid derivatised SBA-15 catalysts have been prepared by post modification of SBA-15 with mercaptopropyltrimethoxysilane (MPTMS) for the upgrading of a model pyrolysis bio-oil via acetic acid esterification with benzyl alcohol in toluene. Acetic acid conversion and the rate of benzyl acetate production was proportional to the PrSO3H surface coverage, reaching a maximum for a saturation adlayer. Turnover frequencies for esterification increase with sulfonic acid surface density, suggesting a cooperative effect of adjacent PrSO3H groups. Maximal acetic acid conversion was attained under acid-rich conditions with aromatic alcohols, outperforming Amberlyst or USY zeolites, with additional excellent water tolerance.

Progress in the development of mesoporous solid acid and base catalysts for converting carbohydrates into platform chemicals

This chapter provides a general overview of recent studies on catalytic conversion of fructose, glucose, and cellulose to platform chemicals over porous solid acid and base catalysts, including zeolites, ion-exchange resins, heteropoly acids, as well as structured carbon, silica, and metal oxide materials. Attention is focused on the dehydration of glucose and fructose to HMF, isomerization of glucose to fructose, hydrolysis of cellulose to sugar, and glycosidation of cellulose to alkyl glucosides. The correlation of porous structure, surface properties, and the strength or types of acid or base with the catalyst activity in these reactions is discussed in detail in this chapter.