John van der Schaaf

Fructose Dehydration to 5-Hydroxymethylfurfural over Solid Acid Catalysts in a Biphasic System

Different acidic heterogeneous catalysts like alumina, aluminosilicate, zirconium phosphate, niobic acid, ion-exchange resin Amberlyst-15, and zeolite MOR have been studied in fructose dehydration to 5-hydroxymethylfurfural (HMF). The acidity of these materials was characterized using temperature-programmed desorption of NH₃ and IR spectroscopy of adsorbed pyridine. The nature and strength of acid sites was shown to play a crucial role in the selectivity towards HMF. Brønsted acid sites in the case of zeolites and ion-exchange resin led to high selectivities in the dehydration of fructose with an increase in selectivity with the addition of an organic phase. Lewis acidity in the case of phosphate and oxides resulted in the intensive production of humins from fructose at the initial stages of the process, whereas organic phase addition did not affect selectivity.

“Hairy Foam”: carbon nanofibers grown on solid carbon foam. A fully accessible, high surface area, graphitic catalyst support

This paper describes the synthesis of carbon nanofibers (CNFs) on solid carbon foam (“Hairy Foam”) by catalytic decomposition of ethylene. The effect of nickel loading on fiber diameter and morphology, CNF coverage, and fiber layer thickness is studied using SEM and N2/Kr-physisorption. The surface area increased from 0.12 m2support g−1support for reticulated vitreous carbon (RVC) to 146 m2support g−1support for “Hairy Foam”. A nickel concentration of 0.5 gNig−1RVC results in fibers with a diameter of 30 to 90 nm. Increasing the nickel concentration results in fiber diameters of 30 to 1100 nm. Complete CNF coverage is obtained for a nickel deposition time ≥240 min and a nickel concentration ≥2.5 gNig−1RVC.

Glucose Dehydration to 5-Hydroxymethylfurfural in a Biphasic System over Solid Acid Foams

A solid acid foam-structured catalyst based on a binderless zirconium phosphate (ZrPO) coating on aluminum foam was prepared. The catalyst layer was obtained by performing a multiple washcoating procedure of ZrPO slurry on the anodized aluminum foam. The effect of the pretreatment of ZrPO, the concentration of the slurry, and the amount of coating on the properties of the foam was studied. The catalytic properties of the prepared foams have been evaluated in the dehydration of glucose to 5-hydroxymethylfurfural (HMF) in a biphasic reactor. The catalytic behavior of ZrPO foam-based catalysts was studied in a rotating foam reactor and compared with that of bulk ZrPO. The effect of a silylation procedure on the selectivity of the process was shown over bulk and foam catalysts. This treatment resulted in a higher selectivity due to the deactivation of unselective Lewis acid sites. Addition of methylisobutylketone leads to extraction of HMF from the aqueous phase and stabilization of the selectivity to HMF over bulk ZrPO. A more intensive contact of the foam with the aqueous and organic phases leads to an increase in the selectivity and resistance to deactivation of the foam in comparison with a bulk catalyst.

Hydrogen Production through Aqueous‐Phase Reforming of Ethylene Glycol in a Washcoated Microchannel

Aqueous-phase reforming (APR) of biocarbohydrates is conducted in a catalytically stable washcoated microreactor where multiphase hydrogen removal enhances hydrogen efficiency. Single microchannel experiments are conducted following a simplified model based on the microreactor concept. A coating method to deposit a Pt-based catalyst on the microchannel walls is selected and optimized. APR reactivity tests are performed by using ethylene glycol as the model compound. Optimum results are achieved with a static washcoating technique; a highly uniform and well adhered 5 μm layer is deposited on the walls of a 320 μm internal diameter (ID) microchannel in one single step. During APR of ethylene glycol, the catalyst layer exhibits high stability over 10 days after limited initial deactivation. The microchannel presents higher conversion and selectivity to hydrogen than a fixed-bed reactor. The benefits of using a microreactor for APR can be further enhanced by utilizing increased Pt loadings, higher reaction temperatures, and larger carbohydrates (e.g., glucose). The use of microtechnology for aqueous-phase reforming will allow for a great reduction in the reformer size, thus rendering it promising for distributed hydrogen production.

Aqueous phase reforming in a microchannel reactor: the effect of mass transfer on hydrogen selectivity

Aqueous phase reforming of sorbitol was carried out in a 1.7 m long, 320 μm ID microchannel reactor with a 5 μm Pt-based washcoated catalyst layer, combined with nitrogen stripping. The performance of this microchannel reactor is correlated to the mass transfer properties, reaction kinetics, hydrogen selectivity and product distribution. Mass transfer does not affect the rate of sorbitol consumption, which is limited by the kinetics of the reforming reaction. Mass transfer significantly affects the hydrogen selectivity and the product distribution. The rapid consumption of hydrogen in side reactions at the catalyst surface is prevented by a fast mass transfer of hydrogen from the catalyst site to the gas phase in the microchannel reactor. This results in a decrease of the concentration of hydrogen at the catalyst surface, which was found to enhance the desired reforming reaction rate at the expense of the undesired hydrogen consuming reactions. Compared to a fixed bed reactor, the selectivity to hydrogen in the microchannel reactor was increased by a factor of 2. The yield of side products (mainly C3 and heavier hydrodeoxygenated species) was suppressed while the yield of hydrogen was increased from 1.4 to 4 moles per mole of sorbitol fed.

Advances in continuous crystallization : toward microfluidic systems

Abstract Continuous crystallization methods are reported in this review, with a particular focus on microfluidic systems. Advances in the nonmicrofluidic crystallization systems include multistage crystallization and intensifying the mixing of plug flow devices and generally improve the product quality and yield but do not resolve the scale-up issues. Microfluidic systems lead to an extremely reproducible particle production with numbering-up possibilities for large-scale applications. An overview of microfluidic devices is reported, focusing on the points of improvement and the challenges that still remain.

Zirconium Phosphate Coating on Aluminum Foams by Electrophoretic Deposition for Acidic Catalysis

The electrophoretic deposition method has been applied for the formation of an amorphous zirconium phosphate layer on the surface of open‐cell aluminum foam. The aluminum foam was fully and uniformly covered by the zirconium phosphate layer with a good mechanical adherence to the support. The obtained composites were characterized by using XRD, SEM and nitrogen adsorption. The coated aluminum foams showed high catalytic activity in the dehydration of fructose to 5‐hydroxymethylfurfural. This method of foam coating is much more convenient and effective than the traditional washcoating procedure, avoiding the anodization pretreatment of the foam to increase adherence.

Micromixing in a Rotor–Stator Spinning Disc Reactor

This paper presents the micromixing times in a rotor–stator spinning disc reactor. Segregation indices are obtained at different rotational speeds performing the Villermaux–Dushman parallel-competitive reaction scheme. Consequently, the corresponding micromixing times are calculated using the engulfment model, while considering the self-engulfment effect. It was found that the segregation index decreases with an increasing disc speed. Furthermore, for the investigated operational conditions, the estimated micromixing times are in the range of 1.13 × 10–4 to 8.76 × 10–3 seconds, in agreement with the theoretical dependency on the energy dissipation rate of ε–0.5. In a rotor–stator spinning disc reactor it is thus possible to further continue the theoretical trend of decreasing micromixing times with very high levels of energy dissipation rates that are unattainable in traditional types of process equipment.

Adsorptive Water Removal from Dichloromethane and Vapor-Phase Regeneration of a Molecular Sieve 3A Packed Bed

The drying of dichloromethane with a molecular sieve 3A packed bed process is modeled and experimentally verified. In the process, the dichloromethane is dried in the liquid phase and the adsorbent is regenerated by water desorption with dried dichloromethane product in the vapor phase. Adsorption equilibrium experiments show that dichloromethane does not compete with water adsorption, because of size exclusion; the pure water vapor isotherm from literature provides an accurate representation of the experiments. The breakthrough curves are adequately described by a mathematical model that includes external mass transfer, pore diffusion, and surface diffusion. During the desorption step, the main heat transfer mechanism is the condensation of the superheated dichloromethane vapor. The regeneration time is shortened significantly by external bed heating. Cyclic steady-state experiments demonstrate the feasibility of this novel, zero-emission drying process.

Selective production of methane from aqueous biocarbohydrate streams over a mixture of Platinum and Ruthenium catalysts

A one-step process for the selective production of methane from low-value aqueous carbohydrate streams is proposed. Sorbitol, used herein as a model compound, is fully converted to methane, CO2 , and a minor amount of H2 by using a physical mixture of Pt and Ru (1:5 in mass basis) at 220 °C and 35 bar. This conversion is the result of hydrogenolysis of part of the sorbitol over Ru and the in situ production of H2 through the aqueous-phase reforming of the remaining carbohydrate over Pt. A synergistic effect of the combination of these two catalysts results in the rapid and highly selective conversion of the carbohydrate to methane. This process offers the possibility of upgrading a low-value carbohydrate stream into a valuable fuel with no addition of H2. Exergy analysis reveals that nearly 80 % of the exergy of the reactant is recovered as methane.