Catalytic Dehydration Research Articles

Acid activated montmorillonite for gas-phase catalytic dehydration of monoethanolamine

The acid activated montmorillonite (Acid-Mt) was investigated for the first time as a catalyst for the gaseous-phase dehydration of monoethanolamine (MEA). A series of Acid-Mt was obtained by treating the Na-type montmorillonite (NaMt) at 104 °C in 3.2 mol L−1 HNO3 aqueous solution for 4–24 h followed by calcining at 450–1150 °C for 4 h, respectively. The Acid-Mts were characterized by X-ray diffraction, temperature programmed desorption of NH3, temperature programmed desorption of CO2, and N2 adsorption-desorption, and were evaluated as catalysts for the gaseous-phase dehydration of MEA. With increasing the activation time or calcination temperature, both the amounts of acidic and basic sites over Acid-Mt were decreased, and more pronounced extent was observed in the case of changing the calcination temperature. By correlating the catalytic results with the characterization results, the acidity of the catalyst was revealed to be the key factor in determining the MEA conversion. In contrast, a complex picture was observed in the case of the product selectivity. Generally, a higher acidity over Acid-Mt favored the intermolecular dehydration and 1,2-elimination reactions of MEA, leading to a higher selectivity of piperazine (PIP) and triethylenediamine (TEDA). When the acidity of Acid-Mt was lower, the intramolecular dehydration and deamination reactions were improved resulting in an increasing selectivity of ethyleneimine (EI). Importantly, the product distribution of the MEA dehydration was greatly regulated by the simply changing the acid activation parameters of Mt. Thus, Acid-Mt is a promising catalyst for selectively synthesizing different N-containing fine chemicals via the MEA dehydration reaction.

The phosphinoboration of 2-diphenylphosphino benzaldehyde and related aldimines

We have investigated the addition of a simple phosphinoboronate ester, Ph2PBpin (pin = 1,2-O2C2Me4), to 2-diphenylphosphinobenzaldehyde (2-Ph2PC6H4C(O)H) and related aldimine derivatives (2-Ph2PC6H4C(NR)H) as a simple and effective strategy for generating unique diphosphine ligands bearing a pendant Lewis-acid Bpin group. These reactions proceed selectively to give one new product where the phosphide fragment has added to the aldehyde (or imine) carbon atom and the electron-deficient boron group has added to the electron-rich heteroatom. Preliminary studies show these new compounds can ligate to Pd(II) and Pt(II) metal centres. These novel metal complexes, as well as the organic soluble [MCl2(coe)]2 (M = Pd, Pt, coe = cis-cyclooctene) compounds, have been shown to be effective precatalysts in the cyclisation of alkynoic acids to give the corresponding exo-dig cyclic lactones. Reactions employing these metal complexes also generated unusual endo-dig cyclic lactones not traditionally observed in these cyclisation reactions. For instance, reactions of 4-pentynoic acid also afforded significant amounts of α-angelica lactone, a biologically-important compound traditionally prepared via the catalytic dehydration and cyclisation of levulinic acid.

2,3-Butanediol dehydration catalyzed by silica-supported alkali phosphates

Characterization of acid-base centers and catalytic dehydration of 2,3-butanediol (BDO) was performed over a wide range of silica-supported alkali phosphates (M_P/SiO2; M = Na, K, Cs; M:P = 0.5–3 mol:mol). Selectivity to 1,3-butadiene (BD) and 3-butene-2-ol (3B2OL) formed by elimination correlates with the densities of conjugated acid-base pairs and increases in the order Na < K ≈ Cs. Selectivity to 2,3-epoxybutane (BTO) formed by dehydrative epoxidation increases with the M/P ratio in the order Na < K ≤ Cs. Methyl ethyl ketone (MEK) and isobutyraldyde (IBA) formed by the rearrangement are produced by isolated Brønsted acid centers. Conjugated acid-base pairs are probably composed of the end groups of polyphosphates having both acid P-OH and base PO−⋯M+ moieties. Isolated Brønsted acid centers are probably silica grafted phosphoric acid molecules at low M/P and PO(OH)2 end groups of oligophosphates at M/P > 1.5.Deactivation rate increases with the increase of M/P ratio in order Na < K < Cs. Deactivation patterns imply that sites responsible for elimination are active in dehydrative epoxidation. Dehydration of 3B2OL smoothly proceeds to BD, but the catalysts deactivate faster compared to BDO dehydration.

Microwave-assisted catalytic dehydration of glycerol for sustainable production of acrolein over a microwave absorbing catalyst

Uniform temperature distribution within solid catalyst particles is important to achieving low coke formation in a high-temperature reaction. However, the issue of uneven temperature distribution exists in most fixed-bed catalytic reaction systems. Here, we developed a microwave-assisted system and used it in catalytic dehydration of glycerol for sustainable production of acrolein. A coated microwave absorbing catalyst WO3/ZrO2@SiC was prepared and employed in the catalytic reactions. The effects of reaction temperature, ZrO2/SiC ratio, and weight hourly space velocity (WHSV) on glycerol conversion and arcolein selectivity were examined. Experimental results showed that the microwave heating proved to be more effective than the conventional electric heating for glycerol dehydration to acrolein at lower temperature. The acrolein selectivity reached over 70% with complete glycerol conversion at 250 ºC by microwave heating. The catalyst acidity was greatly influenced by ZrO2/SiC ratio, which in turn determined the acrolein selectivity. More importantly, much better catalyst stability was obtained in the microwave-heating process than the electric-heating process. In addition, the microwave-heating system was effective for the in-situ regeneration of deactivated catalyst.

Synergetic Effect of Brønsted/Lewis Acid Sites and Water on the Catalytic Dehydration of Glucose to 5-Hydroxymethylfurfural by Heteropolyacid-Based Ionic Hybrids.

The effective dehydration of glucose to 5‐hydroxymethylfurfural (HMF) has attracted increasing attention. Herein, a series of sulfonic‐acid‐functionalized ionic liquid (IL)–heteropolyacid (HPA) hybrid catalysts are proposed for the conversion of glucose to HMF. A maximum total yield of HMF and levoglucosan (LGA; ≈71 %) was achieved in the presence of pyrazine IL‐HPA hybrid catalyst [PzS]H2PW in THF/H2O–NaCl (v/v 5:1). The mechanism of glucose dehydration was studied by tailoring the Brønsted/Lewis acid sites of the hybrid catalysts and altering the solvent composition. It was found that water and heteropolyanions have a significant effect on the reaction kinetics. Heteropolyanions are able to stabilize the intermediates and promote the direct dehydration of glucose and intermediate LGA to HMF. A small amount of water could facilitate the conversion of glucose to LGA and suppress the dehydration of LGA to levoglucosenone. In addition, the synergetic effect of Brønsted/Lewis acid sites and a little water was conducive to accelerated proton transfer, which improved the yield of HMF from glucose dehydration.

Low-Temperature Continuous-Flow Dehydration of Xylose Over Water-Tolerant Niobia-Titania Heterogeneous Catalysts.

The sustainable conversion of vegetable biomass-derived feeds to useful chemicals requires innovative routes meeting environmental and economical criteria. The approach herein pursued is the synthesis of water-tolerant, unconventional solid acid monolithic catalysts based on a mixed niobia-titania skeleton building up a hierarchical open-cell network of meso- and macropores, and tailored for use under continuous-flow conditions. The materials were characterized by spectroscopic, microscopy, and diffraction techniques, showing a reproducible isotropic structure and an increasing Lewis/Brønsted acid sites ratio with increasing Nb content. The catalytic dehydration reaction of xylose to furfural was investigated as a representative application. The efficiency of the catalyst was found to be dramatically affected by the niobia content in the titania lattice. The presence of as low as 2 wt % niobium resulted in the highest furfural yield at 140 °C under continuous-flow conditions, by using H2 O/γ-valerolactone as a safe monophasic solvent system. The interception of a transient 2,5-anhydroxylose species suggested the dehydration process occurs via a cyclic intermediates mechanism. The catalytic activity and the formation of the anhydro intermediate were related to the Lewis acid sites (LAS)/Brønsted acid sites (BAS) ratio and indicated a significant contribution of xylose-xylulose isomerization. No significant catalyst deactivation was observed over 4 days usage.

Profiling the short-lived cationic species generated during catalytic dehydration of short-chain alcohols

Short-chain alcohols are important products of biomass conversion and can be further converted into platform chemicals via catalytic dehydration. Although cationic species are believed to be intermediates in the alcohol-to-hydrocarbon processes, directly observing them is still a challenge due to the lack of efficient tools to deal with their instability and short lifetimes. Here we integrate a micro catalytic reactor onto the ion inlet of an Orbitrap mass spectrometer for high-speed, high-sensitivity, and high-throughput detection of the short-lived cationic species generated during dehydration of short-chain alcohols over heterogeneous catalysts. Hundreds of cationic species can be feasibly observed within the catalytic alcohol dehydration on acidic zeolites H-Beta and H-ZSM5. It is demonstrated that these cationic species may feasibly reveal the catalytic reaction activity and selectivity. This strategy has the potential to inform catalyst development and to help refine reaction conditions in the future.

Catalytic Conversion of Carbohydrates into 5‐Ethoxymethylfurfural by a Magnetic Solid Acid Using γ‐Valerolactone as a Co‐Solvent

AbstractSelective conversion of carbohydrates to fuels and fine chemicals is of great importance for biorefinery. However, development of efficient solid acidic catalysts which perform stably for this process is still challenging. Herein, we reported a novel carbon‐based solid acidic catalyst, prepared via hydrothermal carbonization of glucose followed by magnetization of Fe3O4 and sulfonation of H2SO4, which can serve as an efficient and recyclable catalyst in the catalytic dehydration of fructose to 5‐hydroxymethylfurfural (HMF) and subsequent etherification of 5‐ethoxymethylfurfural (EMF) with ethanol from various carbohydrates. The effects of reaction conditions (temperature, time, solvents, catalyst amount, and γ‐valerolactone (GVL) concentration) were optimized affording to a maximum EMF yield of 67.4 % at 120 °C, 55 wt % catalyst loading based on starting fructose and 60 vol.% of GVL in ethanol after 24 h of reaction. Noticeably, GVL promotes the formation of EMF and HMF reducing the extent of side reactions. Recycling experiments showed that the catalyst could be easily separated with a magnet and reused up to 4 consecutive times without significant loss of activity. The present work opens a way to synthesize reusable and cost‐effective solid acidic catalysts from biomass wastes and may contribute to a holistic approach for biomass valorization.

Dehydration of Ethanol to Ethylene on Ring- and Trilobe-Shaped Catalysts

The indicators of ethanol to ethylene catalytic dehydration process on trilobe- and ring-shaped samples of an alumina catalyst were compared at the fixed parameters: thermal agent temperature and catalyst load. Experiments were performed in a flow-through reactor of a laboratory setup and in a tubular reactor of a pilot installation. The use of the less active ring-shaped catalyst ensures higher values of ethanol conversion, ethylene yield, and catalyst performance and significantly lower hydraulic resistance, compared to the more active trilobe-shaped catalyst. This is caused by lower intensity of the heat absorption on the less active catalyst and, correspondingly, to the higher temperature in the ring bed due to higher bed porosity.

Catalytic dehydration of hexose sugars to 5‐hydroxymethylfural

AbstractThe catalytic conversion of cellulosic biomass to downstream products provides a viable solution to alleviate the energy crisis and global warming. This article provides a relatively comprehensive review of the dehydration of glucose (the monomer of cellulose) and fructose considering various catalyst and solvent systems. Biphasic solvents and heterogeneous systems are recommended from the point of view of industrial applications. A two‐step catalytic conversion of glucose via fructose has been envisaged: first, isomerization of glucose to fructose, which has been extensively discussed in this review, and then transformation of fructose to downstream products. Two‐step tandem catalytic reactions from glucose to downstream products (i.e., one‐pot synthesis via fructose) are also attractive for industrial applications and should be given more attention. © 2018 Society of Chemical Industry and John Wiley &amp; Sons, Ltd

Dehydration of sorbitol into isosorbide over silver-exchanged phosphotungstic acid catalysts

Transformation of renewable biomass into chemicals has attracted much attention recently. Efficient catalytic dehydration of biomass-derived sorbitol into isosorbide over solid acid catalysts under moderate reaction conditions is still a technical challenge. A series of silver-exchanged phosphotungstic acid catalysts were prepared by an ion-exchanged process, and dehydration of sorbitol into isosorbide was performed under solvent-free conditions. More than 99% conversion of sorbitol was obtained with 83% selectivity of isosorbide over Ag1H2PW catalyst at 140 °C within 1 h, which are comparable with that using a homogeneous phosphotungstic acid (HPW) catalyst. The silver-exchanged phosphotungstic acid catalysts were characterized by various techniques such as XRD, FT-IR, Raman, NH3-TPD and Py-IR to build a relationship between the catalytic activity and their natures. Ag1H2PW exhibited much higher activity for catalytic dehydration of sorbitol to isosorbide compared with Ag2H1PW and Ag3PW under the same reaction conditions, which was attributed to the stronger acidity and higher amount of Brönsted acid sites. Moreover, Ag1H2PW could be easily regenerated by 65% HNO3 solutions and used repeatedly at least 3 times without obvious loss of catalytic activity.

The Effect of Cofed Species on the Kinetics of Catalytic Methyl Lactate Dehydration on NaY

The catalytic dehydration of biomass-derived methyl lactate to acrylic acid is a renewable route to a high-value, high-volume monomer, but achieving high selectivity and production rates remains challenging. One roadblock is that the role of the species cofed with methyl lactate, typically water, in the dehydration mechanism over alkali-metal-exchanged zeolites remains unclear. In this study, we determined the effects of protic and aprotic cofed species, including water, methanol, and methyl acetate, on the rate and selectivity of methyl lactate dehydration over NaY via kinetic and spectroscopic investigations. We show that water plays multiple competing roles in the mechanism: (1) generating the unselective Brønsted acid sites on NaY leading to acetaldehyde and coke formation; (2) suppressing the activity of the Lewis acid sites responsible for lactate dehydration; and (3) facilitating the displacement of adsorbed sodium acrylate by lactate, leading to the formation of acrylic acid. The first process increases the rate of side product formation, while the second and third processes decrease and increase the dehydration rate, respectively. As a result of these competing roles, the rate-limiting step of methyl lactate dehydration shifts from acrylate product recovery to sodium lactate dehydration as the concentration of water increases.

Catalytic dehydration of ethanol to ethylene and diethyl ether over alumina catalysts containing different phases with boron modification

The catalytic ethanol dehydration of ethanol over the solvothermal-derived alumina catalysts was investigated in this study. First, alumina catalysts were synthesized by the solvothermal methods to obtain three different phase composition of alumina catalysts including γ-phase (G–Al), χ-phase (C–Al) and equally mixed χ–γ phases (M–Al). Then, all catalysts were modified with boron (G–Al–B, C–Al–B and M–Al–B). It was found that the boron modification increased the amounts of total acid sites and the ratio of weak to strong acid sites (WSR). The catalytic activity and product selectivity of six catalysts via catalytic ethanol dehydration at 200, 300, and 400 °C were measured. For all catalysts, it revealed that ethanol conversion increased with increased temperatures from 200 to 400 °C. At 200–300 °C, the unmodified catalysts tended to exhibit the higher catalytic activity than the boron-modified catalysts. However, at high temperature (400 °C), the boron modification tended to increase the catalytic activity, especially for the M–Al–B catalyst (complete ethanol conversion at 400 °C). Considering ethylene production, the M–Al–B exhibited the highest ethylene yield among other catalysts with 92% at 400 °C. For diethyl ether, it was observed that the M–Al catalyst gave the highest diethyl ether yield of 57% at 300 °C. This is because the boron modification increased the amounts of total acid sites, which can promote the production of ethylene, while this is not preferable for diethyl ether production, which is favored by weak acid sites.

Influence of confining environment polarity on ethanol dehydration catalysis by Lewis acid zeolites

Lewis acidic Sn centers isolated within Beta zeolite frameworks catalyze bimolecular ethanol dehydration to diethyl ether, yet with kinetic behavior sensitive to the hydrophobic character of their confining microporous voids. Sn sites in open ((HO)-Sn-(OSi)3) and closed (Sn-(OSi)4) configurations, quantified from infrared spectra of adsorbed CD3CN before and after reaction, convert to structurally similar intermediates during ethanol dehydration catalysis (404 K) and revert to their initial configurations after regenerative oxidation treatments (21% O2, 803 K). Dehydration rate data (404 K, 0.5–35 kPa C2H5OH, 0.1–50 kPa H2O) measured on ten low-defect (Sn-Beta-F) and high-defect (Sn-Beta-OH) zeolites were described by a rate equation that was derived from mechanisms identified previously by density functional theory calculations and simplified using microkinetic modeling to identify kinetically-relevant pathways and intermediates. Polar hydroxyl defect groups located in the microporous environments that confine Sn sites preferentially stabilize reactive (ethanol-ethanol) and inhibitory (ethanol-water) dimeric intermediates over monomeric ethanol intermediates. As a result, equilibrium constants (404 K) for ethanol-water and ethanol-ethanol dimer formation are 3–4× higher on Sn-Beta-OH than on Sn-Beta-F, consistent with insights from single-component (302 K) and two-component (303 K, 403 K) ethanol and water adsorption measurements. Intrinsic dehydration rate constants (404 K) were identical, within error, among Sn-Beta-OH and Sn-Beta-F zeolites; thus, measured differences in dehydration turnover rates solely reflect differences in prevalent surface coverages of inhibitory and reactive dimeric intermediates at active Sn sites. The confinement of Lewis acidic binding sites within secondary microporous environments of different defect density confers the ability to discriminate surface intermediates on the basis of polarity, providing a design strategy to accelerate turnover rates and suppress inhibition by water.

Coking of Catalysts in Catalytic Glycerol Dehydration to Acrolein

Catalytic glycerol dehydration provides a sustainable route to produce acrolein because glycerol is a bioavailable platform chemical. However, in this process catalysts are rapidly deactivated due to coking. This paper examines and discusses recent insights into coking of catalysts during catalytic glycerol dehydration. The nature and location of coke and the rate of coking depend on feedstock, operating conditions, and the acidity and pore structure of the solid catalysts. Several methods have been suggested for inhibiting the coking and slowing the deactivation of catalyst, including (1) cofeeding of oxygen, (2) tuning of the pore size of the solid acid catalysts, (3) doping noble metals (Ru, Pt, Pd) into the solid acid catalysts, and (4) designing new reactors. The present methods for inhibiting coking are still unsatisfactory. The deactivated catalysts can be regenerated by removing coke. Nevertheless, the rapid deactivation of the regenerated catalyst remains problematic. The literature survey indica...

Particle filter-based monitoring scheme for simulated bio-ethylene production process

ABSTRACTThe use of biomass has been promoted to meet the need for sustainable production of ethylene, which is the most used petroleum-derived in the polymer industry. Ethanol is an alternative feedstock to yield the so-called bio-ethylene through catalytic dehydration in fixed-bed reactors. As the reaction system is strongly endothermic, it is very important to know accurately the reactor temperature to assure the process performance. However, in the industrial context, the process measurements are often uncertain and not all variables can be directly measured online. In this regard, this paper analyses the mathematical modelling and numerical simulation of the ethanol catalytic dehydration and contributes with a monitoring scheme using the Bayesian method known as particle filter. Numerical simulations helped understanding the process behaviour and locating the best position for the temperature sensor in the reactor. From temperature measurements, the proposed inferential tool estimates hidden state variables and unmeasured disturbances, using Sequential Importance Resampling algorithm for the particle filter. The proposal is investigated according to the number of particles and the criterion total error reduction. The results show that the monitoring scheme is able to estimate satisfactorily the process variable profiles, as the temperature and chemical conversion, along the reactor length.

Process Modeling and Simulation of an Industrial-Scale Plant for Green Ethylene Production

Catalytic dehydration of ethanol is a key step in the production of polyethylene from renewable raw materials. Obtaining a mathematical model to optimize the ethanol-to-ethylene reactor setup is of great interest to the industry, allowing the optimal design of larger plants and improvements to existing plants. This work presents a phenomenological model of an ethanol dehydration reactor that takes into account 8 chemical reactions and 10 chemical species, considering nonidealities in the reaction rates and axial catalyst activity profile. Additionally, the axial variation of pressure, velocity, and thermodynamics properties are considered in the proposed model. Model validation at different operating conditions shows that the predicted temperature and composition profiles match the data from an industrial plant with relative deviations below 5% and from a pilot plant with relative deviation below 0.4%.

Catalytic dehydration of sorbitol and fructose by acid-modified zirconium phosphate

Zirconium phosphate, a typical metal phosphate material, is characteristic in the design of structures and active sites, which has received widespread attention as solid acid catalysts in biomass conversion. In this work, the acid-modified zirconium phosphate catalyst was synthesized and characterized by the methods of XRD, TGA, FT-IR, NH3-TPD, pyridine-adsorbed FT-IR, SEM, TEM and 31P MAS NMR. Subsequently, the as-obtained material has been employed for the dehydration of sorbitol and fructose, which can be converted into isosorbide (ca. 73.6% selectivity) and 5-hydroxymethylfurfural (ca. 73.4% selectivity), respectively under optimal reaction conditions. It was found that the modification of oleum enhanced both the amounts and strength of Brönsted and Lewis acidic sites, and also improved the dispersity by “exfoliating” zirconium phosphate, resulting in the formation of very thin nanosheets instead of original amorphous structure and thus exposing more active sites for catalytic reaction. These effects were favorable for improving the catalytic dehydration activity and selectivity of sorbitol and fructose significantly. Meantime, the acidic sites of the acid-modified zirconium phosphate catalyst is highly leaching-resistant in dehydration reaction and the catalyst can be recycled up to five times without any considerable loss of activity.

Vapor phase selective tetrahydrofuran production from dehydration of biomass derived 1,4-butanediol using ecofriendly red brick catalyst

Vapor phase catalytic dehydration of 1,4-BDO to tetrahydrofuran was investigated over activated red brick as green catalyst at 375 °C, exhibited highest THF selectivity 100% at complete conversion of 1,4-BDO under atmospheric pressure. The intrinsic catalytic activity of red brick catalyst was attributed to the synergy of higher Bronsted acidic sites and moderate Lewis acidic sites of SiO2 and Fe2O3, as confirmed by Pyridine FT-IR and NH3-TPD. The physico-chemical properties were evaluated from XRD, SEM-EDX, FT-IR, UV–vis DRS, ICP-MS and XRF techniques. The high catalytic efficiency was confirmed through steady time-on-stream and activity comparison studies against conventional catalysts.

Synthesis of HMF from fructose using Purolite® strong acid catalyst: Comparison between BTR and PBR reactor type for kinetics data acquisition

5-hydroxymethyl-2-furfural (HMF) is an important furanic compound that can be obtained from renewable raw materials. HMF has wide application in the industry, acting as an intermediate in the production of fine chemicals, polymer, biofuels, and pharmaceuticals. In this research, HMF was obtained from the catalytic fructose dehydration. Purolite® SGC650H, a gel-type strongly acidic resin, was applied as a catalyst using dimethylsulfoxide (DMSO) as a solvent. All experiments were carried out in a batch reactor (BTR) and a continuous packed bed reactor (PBR). The reactor performance data showed that increase in temperature resulted in higher HMF yield. In contrast, the higher the fructose concentration, the lower the HMF conversion. The HMF production rates in the PBR were higher because of the concentration of the catalyst. The rate constants were calculated by means of a pseudo-first-order reaction model, and the Arrhenius kinetic parameters obtained changed with regards to the reactants concentrations. The kinetic parameters displayed linear correlation in the Cremer-Constable diagram, which means that the system was under a kinetic compensation effect (KCE); therefore, the model was not suitable to represent the reaction. Langmuir-Hinshelwood (LHHW) models for rate equation were also tested. However all of them failed to adjust to the data, and thus a rate law was not determined. Due to the observed KCE, it was believed that there is at least a set of parallel dehydration reactions initiated from the different fructose isomers which has an influence on kinetic parameters.