Valorization of carbohydrates: dehydration of sorbitol to isosorbide in the presence of acidic zeolites

Currently, the growing interest in the use of biomass as a renewable and sustainable raw material for the production of energy, chemicals and biofuels is driving the development of new catalytic processes and technologies for its conversion. In this context, the transformation of lignocellulosic biomass can lead to a variety of platform chemicals, with a broad spectrum of applications. Sorbitol is one of the useful biomass-derived chemicals that is obtained by catalytic hydrogenation of glucose, which subsequent dehydration and intramolecular cyclization in acid medium gives rise to the formation of isosorbide. This is a high value-added chemical widely used as intermediate in the pharmaceutical industry, additive polymers such as polyethylene terephthalate (PET) and production of biodegradable polymers. Mineral acids such as sulphuric and hydrochloric acids have efficient catalytic properties for dehydration of sorbitol. However, the well-known drawbacks associated to homogeneous catalysis have promoted the studies of heterogeneous catalytic processes. Thus, solid acid catalysts such as zeolites, tetravalent metal phosphates and sulfated copper oxide have been reported as alternative solid catalysts. Nevertheless, sometimes, drastic experimental conditions are required to reach a high catalytic activity. In the present work, different commercial zeolites, in their protonic form, have been evaluated as acid solid catalysts for sorbitol dehydration, and several experimental variables have been optimizedUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Ministerio de Economía y Competitividad (CTQ2012-38204-C04-02 project), Junta de Andalucía (RNM-1565) y Fondos FEDER de la U

Characterization of rice husk-based catalyst prepared via conventional and microwave carbonisation

© 2017 Elsevier Ltd. Carbon-based sulphonated catalysts (CBSCs) were made from rice husk for biodiesel production. The CBSCs were prepared by microwave (MW) and conventional heating processes from the same feedstock. In both heating systems, the preparation was a two-step process: carbonisation and sulphonation. The aim of this study was to use MW heating to reduce the conventional CBSC preparation time and enhance the -SO 3 H group attachment to the solid catalyst. The biomass based solid acid catalysts from the two systems were characterised and compared in terms of physicochemical properties including: sulphonation, morphology, surface area and structure. The reaction times for MW assisted carbonisation and for sulphonation were significantly reduced compared to the conventional heating system; these were 30 min vs 4 h and 20 min vs 12 h, respectively. The MW prepared catalyst showed higher sulphur content (4.91%) as compared to the conventional catalyst (2.10%). The FTIR analysis showed well distinguished peaks for -SO 3 H for the MW prepared catalyst suggesting the solid catalyst was successfully sulphonated, while these peaks were very weak for the conventional catalyst. SEM analysis revealed a highly porous structure in the MW prepared catalyst, whilst a denser solid resulted for its conventionally prepared analogue, owing to the higher temperatures applied and longer sulphonation time. The surface area for the MW was higher than the conventionally prepared catalysts (43.63 m 2 /g and 37.01 m 2 /g, respectively). The structure of the samples was identified as amorphous for both catalysts as confirmed by XRD. The prepared CBSC is expected to catalyse biodiesel production reaction as evidenced by its total acidity and surface area

Mixed-metal MIL-100(Sc,M) (M=Al, Cr, Fe) for Lewis acid catalysis and tandem C−C bond formation and alcohol oxidation

The authors thank Johnson Matthey and the EPSRC for an Industrial CASE award to L.M. We gratefully acknowledge the IAESTE UK for a scholarship to B.E. They also thank the Leverhulme Trust (F/00 268/BJ), EPSRC (EP/J501542/1), and the EaStCHEM Research Computing Facility.The trivalent metal cations Al3+, Cr3+, and Fe3+ were each introduced, together with Sc3+, into MIL-100(Sc,M) solid solutions (M=Al, Cr, Fe) by direct synthesis. The substitution has been confirmed by powder X-ray diffraction (PXRD) and solid-state NMR, UV/Vis, and X-ray absorption (XAS) spectroscopy. Mixed Sc/Fe MIL-100 samples were prepared in which part of the Fe is present as α-Fe2O3 nanoparticles within the mesoporous cages of the MOF, as shown by XAS, TGA, and PXRD. The catalytic activity of the mixed-metal catalysts in Lewis acid catalysed Friedel–Crafts additions increases with the amount of Sc present, with the attenuating effect of the second metal decreasing in the order Al>Fe>Cr. Mixed-metal Sc,Fe materials give acceptable activity: 40 % Fe incorporation only results in a 20 % decrease in activity over the same reaction time and pure product can still be obtained and filtered off after extended reaction times. Supported α-Fe2O3 nanoparticles were also active Lewis acid species, although less active than Sc3+ in trimer sites. The incorporation of Fe3+ into MIL-100(Sc) imparts activity for oxidation catalysis and tandem catalytic processes (Lewis acid+oxidation) that make use of both catalytically active framework Sc3+ and Fe3+. A procedure for using these mixed-metal heterogeneous catalysts has been developed for making ketones from (hetero)aromatics and a hemiacetal.Peer reviewe

Sub- and supercritical esterification of palm fatty acid distillate with carbohydrate-derived solid acid catalyst

The esterification of palm fatty acid distillate (PFAD) in supercritical methanol was investigated by using carbohydrate-derived solid acid catalyst. The catalysts were prepared by sulfonation of incomplete carbonized glucose and starch, which had been coded as sulfonated-ICG and sulfonated-ICS, respectively. The contents of fatty acid methyl ester (FAME) and its yield were determined by using gas chromatography techniques. The effects of sub- and supercritical operating conditions such as methanol/PFAD molar ratio, catalyst amount, reaction temperature and reaction time were analyzed to determine their optimum operating conditions. At optimum reaction temperature of 290 °C, methanol/PFAD molar ratio of 6/1, catalyst amount of 1 wt.% and 5 min reaction time, the esterification of PFAD in supercritical methanol with the presence of sulfonated-ICS and -ICG catalysts resulted 97.3% and 95.4% of FAME; both catalysts yield significantly higher percentages compared to uncatalyzed reaction. Alongside of its potential in enhancing the efficiency of production process, the utilization of carbohydrate-derived solid acid catalyst in supercritical methanol method had also resulting fast reaction and energy saving

New heterogeneous catalysts for trans-esterification of triglycerides

This paper describes preliminary work done towards the development of new metallic heterogeneous catalysts to be used in the transesterification reaction of triglycerides, which is of considerable interest in the production of biodiesel. Biodiesel, is a mixture of mono-alkyl esters of fatty acids, and is currently manufactured by transesterification of triglycerides with methanol using NaOH or KOH as liquid base catalyst. Catalysts as such are corrosive to the equipment, and as these catalysts are in liquid phase must be neutralized after the completion of the reaction, typically using HCl, thus producing salt streams. Moreover, due to the presence of free fatty acids it reacts to form soaps as unwanted by-products, hence requiring more expensive separation processes. Therefore, there is a great need on the development of industrial processes for biodiesel production using solid acid catalysts. The key benefit of using solid acid catalysts is that no polluting by-products are formed and the catalysts do not have to be removed since they do not mix with the biodiesel product

Development of covalent triazine frameworks as heterogeneous catalytic supports

Covalent triazine frameworks (CTFs) are established as an emerging class of porous organic polymers with remarkable features such as large surface area and permanent porosity, high thermal and chemical stability, and convenient functionalization that promotes great potential in heterogeneous catalysis. In this article, we systematically present the structural design of CTFs as a versatile scaffold to develop heterogeneous catalysts for a variety of chemical reactions. We mainly focus on the functionalization of CTFs, including their use for incorporating and stabilization of nanoparticles and immobilization of molecular complexes onto the frameworks

Novel "green" catalysts for controlled ring-opening polymerization of lactide

Syntéza polylaktidu (PLA) polymerací za otevření kruhu cyklického monomeru (ROP) může být uskutečněna různými způsoby. Literatura uvádí více než 100 katalytických systémů, jejichž pomocí lze polylaktid a jiné biodegradabilní alifatické polyestery získat. Například organokovové katalyzátory na bázi Sn, Zn, Al atd. se po splnění své polymerační funkce stávají kontaminanty a pro humánní implantáty je použití takového materiálu diskutabilní. V současné době jsou v centru výzkumné pozornosti nové N-heterocyklické karbenové katalyzátory. Tyto „metal-free“ katalytické struktury jsou schopné reprodukovatelně řídit syntézu polymerů předem definované molekulové hmotnosti s definovanými koncovými skupinami a nízkou polydisperzitou, která je charakteristická pro živý průběh polymerace. Nabízí se možnost syntézy blokových kopolymerů a různorodých makromolekulárních architektur. Předložená diplomová práce se zabývá studiem polymerace cyklického monomeru D,L-laktidu katalyzované N-heterocyklickým karbenem. Polymerace byly vedeny v přítomnosti benzylalkoholu jako iniciátoru v roztoku THF. Byl sledován vliv složení reakčního systému monomer – iniciátor – katalyzátor. Dále byly připraveny polymery opticky čistého L-laktidu s makroiniciátory PEG s Mn = 1000 a 2000 g/mol. Střední číselná molekulová hmotnost (Mn) a polydisperzita (PDI) byly stanoveny pomocí GPC. Definovatelnost koncových skupin vybraných polymerů byla prokázána pomocí 1H NMR.The synthesis of polylactide (PLA) by ring-opening polymerization (ROP) of cyclic monomer can be realized by different routes. More than 100 catalysts for the synthesis of polylactide and other biodegradable aliphatic polyesters are published in the literature. For example organometallic catalysts based on Sn, Zn, Al etc. after finishing polymerization function became contaminants and using obtained polymer material in human body is controversial. At present, the research is focused on novel N-hererocyclic carbene catalysts. These metal-free catalysts are able to produce polymers with controlled molecular weight, narrow polydispersity, end-group fidelity with high reproducibility as well as to synthesize the block copolymers and complex macromolecular architectures, which is characteristic for living polymerization system. This diploma thesis is focused on study of polymerization of cyclic monomer D,L-lactide catalyzed by N-hererocyclic carbene. Polymerizations were carried out at the presence of benzylalcohol as initiator at THF. We were focused on the influence of composition of reaction system monomer – initiator – catalyst. Polymers of optically pure L-lactide with macroinitiators PEG with Mn of 1000 a 2000 g/mol were prepared as well. Number average molecular weight (Mn) and polydispersity index (PDI) was determined by GPC. 1H NMR was used to prove end-group fidelity.

Hydrogen production by methanol steam reforming on NiSn/MgO-Al 2O3 catalysts: The role of MgO addition

The effect of the magnesia loading on the surface structure and catalytic properties of NiSn/MgO-Al2O3 catalysts for hydrogen production by methanol steam reforming has been investigated. The catalysts have been obtained by impregnation of γ-Al2O3 by the incipient wetness method, with variation of the MgO content. X-ray diffraction (XRD), BET surface area and H2-temperature programmed reduction (TPR) have been used to characterise the prepared catalysts. From this, it has been concluded that the incorporation of MgO results in the formation of MgAl 2O4 spinel, which modifies the acid-base properties of the catalysts. The formation of Ni-Sn alloys after the reductive pre-treatment has also been evidenced. The influence of the temperature of reaction and of the MgO loading on the hydrogen production by reforming of methanol has been established. Moreover, tests of catalytic stability have been carried out for more than 20 h. The carbonaceous deposits have been examined by temperature-programmed oxidation (TPO). The analysis of the catalysts after reaction has confirmed the low level of carbon formation on these catalysts. In no case, carbon nanotubes have been detected on the solids.Junta de Andalucía TEP106Ministerio de Ciencia e Innovación ENE2009-14522-C05-0