Ti3C2 MXenes-based catalysts for the process of α-pinene isomerization

In this study, the catalytic performance of Ti3C2 MXene materials in the reaction of α-pinene isomerization was demonstrated. The influence of etching agents (HF, HF/H2SO4, and HF/HCl; weight ratios of mixed acids: 1 : 3, 1 : 4, and 1 : 5) on removing Al atoms from MAX phase, creation of an accordion-like structure typical for MXenes and catalytic activity of the produced samples have been revealed. The MXene HF obtained by MAX phase HF treatment exhibited the highest activity (conversion of α-pinene 74.65 mol%), while materials produced with the mixed acids (HF/H2SO4 and HF/HCl) showed a significant reduction in the conversion of α-pinene (on average about 28-fold). However, these last samples displayed an increase of about 10 mol% in the selectivity to the most desirable product-camphene. The high activity of MXene HF is a result of a high concentration of acid sites (11.62 mmol g-1) - the concentration of acid sites in the samples obtained by MAX phase mixed acids treatment was about 2.5-5.5 times smaller. This work proposes possible mechanisms for the α-pinene isomerization reaction on the MXene HF and on the MXene HF/H2SO4X : Y and MXene HF/HCl X : Y in connection with their structure.

Activated Bentonite Nanocomposite for the Synthesis of Solketal from Glycerol in the Liquid Phase

Activated bentonites are low-cost acid catalysts used in several reactions. However, their application at an industrial scale is affected by the formation of colloidal suspensions when these bentonites are in aqueous solutions. In order to overcome these limitations, this work proposes obtaining a catalyst based on a composite containing natural bentonite within a silica–resin structure, which allows separating and re-utilizing the catalyst more easily and without centrifugal filtration requirements. By means of characterization techniques, the present study determined that the activated bentonite composite presented a total specific surface area of ~360 m2 g−1, ~4 mmol of acid sites per gram of bentonite, and sites with strong acid strength, all of which bestowed activity and selectivity in the solketal synthesis reaction from glycerol and acetone, reaching equilibrium conversion within a short reaction time. Furthermore, the present work developed a Langmuir–Hinshelwood–Hougen–Watson kinetic model, achieving an activation energy of 50.3 ± 3.6 kJ mol−1 and a pre-exponential factor of 6.4 × 106 mol g−1 L−1 s−1, which are necessary for reactor design.

Reactive Distillation of Glycolic Acid Using Heterogeneous Catalysts: Experimental Studies and Process Simulation

The glycerol oxidation reaction was developed leading to selective catalysts and optimum conditions for the production of carboxylic acids such as glycolic acid. However, carboxylic acids are produced in highly diluted mixtures, challenging the recovery and purification, and resulting in high production costs, polymerization, and thermal degradation of some of the products. The protection of the acid function by esterification reaction is one of the most promising alternatives through reactive distillation (RD); this technique allows simultaneously the recovery of carboxylic acids and the elimination of most part of the water. The reactive distillation, experimental and simulation, of glycolic acid was performed, based on kinetic and thermodynamic models developed. For the thermodynamic model, binary parameters of the missing couples were determined experimentally, and the non-random two-liquid (NRTL) model was selected as the most suitable to represent the binary behavior. The kinetic study of the esterification in the presence of homogeneous and heterogeneous catalysis concluded that the heterogeneous reaction can be accurately described either by a pseudo-homogeneous model or the Langmuir–Hinshelwood (L-H) adsorption model. Reactive distillation was conducted in a distillation column filled with random packing sulfonated ion-exchange resin, Nafion NR50^®, or with extruded TiO₂-Wo_x. The conversion rate of glycolic acid in reactive distillation increases from 14% without catalyst to 30% and 36% using Nafion NR50^® and TiO₂-Wo_x, respectively. As opposed to the batch reactor study, the conversion rate of glycolic acid was better with TiO₂-Wo_x than with sulfonated ion-exchange resin. The better performance was related to an increase in the hydrodynamics inside the column. Tests using water in the feed confirm the hypothesis by increasing the conversion rate because of the decrease in the mass transfer resistance by reducing the average diffusion coefficient. The simulation of the reactive distillation column with ProSim^® Plus showed that the yield of the ester increased operating at a low feed rate with reactive stripping. In the presence of water in the feed, nonreactive stages are required, including an enrichment region to separate water vapor.

Combination of Autohydrolysis and Catalytic Hydrolysis of Biomass for the Production of Hemicellulose Oligosaccharides and Sugars

Three different types of biomass sourced from forestry waste (eucalyptus residues), agricultural waste (wheat straw), and energy crop (miscanthus) were used as starting materials to produce hemicellulosic sugars, furans (furfural and hydroxymethylfurfural), and oligosaccharides. A two-step hybrid process was implemented; biomass was first autohydrolysed without any additive to extract hemicelluloses and dissolve it in water. Then, the hydrolysate was treated with a solid acid catalyst, TiO2-WOx, in order to achieve hydrolysis and produce monomeric sugars and furans. This article investigates the role of the biomass type, autohydrolysis experimental conditions, polymerisation degree and composition of hemicelluloses on the performance of the process coupling autohydrolysis and catalytic hydrolysis. The highest global yields of both oligosaccharides and monomeric sugars were obtained from Eucalyptus (37% and 18%, respectively).