Gas-phase Dehydration Of Glycerol Research Articles

Gas phase dehydration of glycerol to acrolein on an amino siloxane-functionalized MCM-41 supported Wells–Dawson type H6P2W18O62 catalyst

A novel amino siloxane-functionalized MCM-41 supported Wells–Dawson type H6P2W18O62 (D-HPW) catalyst was synthesized by a two-step method and investigated in the gas phase dehydration of glycerol to acrolein, and the yield of acrolein was obviously improved.

Gas phase dehydration of glycerol to acrolein over WO3-based catalysts prepared by non-hydrolytic sol-gel synthesis.

Solid acid catalysts based on WO3–SiO2 and WO3–ZrO2–SiO2 were prepared by one-pot non-hydrolytic sol–gel method and tested in the gas phase glycerol dehydration to acrolein. Their structural and textural characteristics were determined by X-ray diffraction (XRD), N2 adsorption, X-ray energy dispersive spectroscopy (XEDS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Their acid characteristics were studied by both temperature programmed desorption of ammonia (NH3-TPD) and FTIR of adsorbed pyridine. Under our operating conditions, all the catalysts were active and selective in the transformation of glycerol to acrolein, which was always the main reaction product. The high selectivity to acrolein is achieved on catalysts presenting a higher proportion of Brønsted acid sites. In addition, the role of oxygen in the feed on catalytic performance of these catalysts is also discussed.

Porous zirconium phosphate solid acid catalysts with variable Zr/P ratio for gas phase glycerol dehydration to acrolein

The valuation of glycerol acquired by biodiesel production is an ambitious task. Dehydration of glycerol to acrolein was experimented over porous solid acid catalysts including zirconium phosphate (ZrP) by various Zr/P molar ratios. The different characteristics of the catalysts were probed by different charecterization techniques. All the prepared catalysts were effective for conversion of glycerol (69-100%) to yield of valuable acrolein (selectivity: 26–63%). The superior performance while catalytic activity demonstrated by ZrP:12 catalyst is ascribed to the existences of moderate acidic sites with the most of them Brønsted acidic sites

Synthesis, Characterization and Catalytic Dehydration of Glycerol to Acrolein Over Phosphotungstic Acid Supported Y-Zeolite Catalysts

Vapour phase catalytic dehydration of glycerol to acrolein was studied over phosphotungstic acid (PTA) supported (with different loadings of PTA) on Y-zeolite catalysts. The active component PTA was varied between 10 and 40% w/w on the support Y-zeolite and was synthesized by the wet impregnation method. The physico-chemical characterization of the catalyst samples was investigated by X-ray diffraction (XRD), FT-IR, Raman and by the gas adsorption measurements. The XRD results showed that active component PTA is highly dispersed in an amorphous form at lower loadings of PTA and attained a crystalline state beyond 20 wt% of PTA. Both Raman and FT-IR spectra indicated that the Keggin ion structure of PTA was present in a highly dispersed state in the supported PTA/zeolite catalysts as compared to the bulk form of PTA. Temperature programmed desorption (TPD) of ammonia and FT-IR spectra of pyridine adsorption were used to determine the acidic properties of the PTA catalysts. The TPD of ammonia showed the presence of moderate acidity on the catalyst surface. The total acidity increased with raise in PTA loading up to 20 wt% and beyond this, it had decreased. The FT-IR results suggested the presence of Bronsted acidity. The Pore size increased with PTA loading until 20 wt%. Finally, the PTA/zeolite catalysts were tested for the gas phase dehydration of glycerol in a fixed-bed, micro-reactor in the temperature range between 250 and 300 °C. Among all the catalysts tested, PTA (20 wt%)/zeolite showed a total conversion of 100% glycerol and a selectivity of 79% for acrolein. These results are correlated with surface acidity, textural and structural properties of the PTA/zeolite catalysts. Glycerol dehydration products over Lewis and Bronsted acidic sites.

Heteropolyacid (H3PW12O40) supported MCM-41: An effective solid acid catalyst for the dehydration of glycerol to acrolein

The gas-phase dehydration of glycerol was conducted over HPW/MCM-41 catalysts, which were prepared by impregnation of different amount of H3PW12O40 (HPW) on the MCM-41 support. The samples were characterized by XRD, N2 physisorption, FTIR, NH3-TPD, and pyridine-FTIR measurements. N2 physisorption results suggested that the uniform framework of MCM-41 could still be well maintained after modified with HPW. Pyridine-FTIR experiments indicate that HPW modified MCM-41 can generate rich Bronsted acid sites. Moreover, Bronsted acid sites facilitated to improve acrolein selectivity. Under the optimized reaction conditions: 40wt% HPW loading, 20% glycerol concentration, and 320 °C reaction temperature, the glycerol conversion and acrolein selectivity reach 85% and 80%, respectively.

Thermo-kinetic and diffusion studies of glycerol dehydration to acrolein using HSiW-γ-Al2O3 supported ZrO2 solid acid catalyst

The thermo-kinetic study of gas-phase glycerol dehydration reaction using a supported γ-Al2O3 nanoparticle based solid catalyst (SiW20-Al/Zr10) has been investigated. The kinetic model was established based on the reaction mechanism, taking into account two parallel reactions of glycerol degradation into acrolein or acetol. Reaction rate constants and activation energies for all the products in the glycerol dehydration reaction were determined at various reaction temperatures (280–340 °C). The first-order kinetic model and the experimental data fitted-well. Also, based on thermodynamic analysis the values of ΔH‡, ΔS‡, and ΔG‡ for all the endothermic reactions were determined by Eyring equation. Finally, the absence of internal and external diffusions were confirmed by Weisz-Prate Criterion (CWP <1) and Mear's Criterion (CM < 0.15), respectively for pellet diameters less than dP < 5 μm. The results from this study are useful for future reactor modeling and simulation work.

Kinetic Study on Catalytic Conversion of Glycerol to Renewable Acrolein

Biodiesel is a suitable alternative to gasoline and diesel since it emits less carbon emission. There has been a surplus of glycerol in the market due to biodiesel production. Glycerol may be a good source of bio-based feed since it is from a renewable source. The kinetic study of gas-phase glycerol dehydration reaction using a supported ?-Al2O3 nanoparticle based solid heteropoly acid catalyst (SiW20-Al/Zr10) has been investigated. A kinetic model was established, based on the reaction mechanism, taking into account two parallel reactions of glycerol degradation into acrolein or acetol. All the reaction rate constants and activation energies were determined at various reaction temperatures (280 – 340 °C). The first-order kinetic model and the experimental data fitted-well. Results revealed that all the rate constants increased with temperature, and the activation energies of glycerol dehydration to acrolein and acetol were 46.0 and 53.3 kJ/mol. The results from this study are useful for simulation and process modelling of a bio-refinery for sustainable production of bio- based chemicals.

Dehydration of glycerol to acrolein over Wells–Dawson and Keggin type phosphotungstic acids supported on MCM-41 catalysts

Gas phase dehydration of glycerol to acrolein was studied using the Wells–Dawson and Keggin type phosphotungstic acids supported on MCM-41 catalysts. The samples were characterized using XRD, FTIR, pyridine-FTIR, UV–Vis, N2 adsorption, NH3-TPD, ICP, SEM and elemental analysis. FT-IR and UV–Vis spectra results confirmed the presence of Wells–Dawson and Keggin type phosphotungstic acids on the support. XRD results suggested that the active phases were highly dispersed on MCM-41. N2 adsorption results showed that the mesoporous structure of MCM-41 was retained after loading of phosphotungstic acids. H3PW12O40/MCM-41 showed higher total acid sites than H6P2W18O62/MCM-41, but the number of Brønsted acid sites on H6P2W18O62/MCM-41 was higher than that of H3PW12O40/MCM-41. Glycerol conversion increased with the total amount of acid sites. The acid type also influenced catalytic performance. The selectivity to acrolein increased with increasing the ratio of Brønsted and Lewis acid, and lower value of Brønsted/Lewis acid favored the production of hydroxyacetone. H6P2W18O62/MCM-41 owned more Brønsted acid sites, the dehydration reaction was more likely to occur via the Brønsted acid sites dehydration route, thus generating more acrolein and formaldehyde. Meanwhile, H3PW12O40/MCM-41 exhibited more Lewis acid sites, the dehydration reaction was more likely proceeding via the Lewis acid sites dehydration route and generating more hydroxyacetone and acetaldehyde. Furthermore, we concluded that the reasons for decrease of catalytic performance in glycerol conversion were leaching of HPW and coke deposition.

Effect of Nb doping in WO3/ZrO2 catalysts on gas phase dehydration of glycerol to form acrolein

Gas-phase dehydration of glycerol to produce acrolein was investigated over tungstated zirconia catalysts with and without niobium doping, in order to correlate the catalytic activity and life-stability with the acid/base properties of the catalysts.

Gas phase dehydration of glycerol to acrolein: Coke on WO3/TiO2 reduces by-products

Glycerol is a renewable feedstock for specialty chemicals that is co-produced when oil and fats are transesterified to biodiesel or hydrolysed to fatty acids. Acrolein is a target specialty chemical but catalysts deactivate with time due to coke and thus require frequent regeneration cycles to maintain activity. WO3/TiO2 catalyst dehydrated glycerol for 14h while the acrolein selectivity increased as coke formed on the catalyst. After the first hour of reaction the acrolein selectivity was 36% and it reached steady state after 6h at a selectivity of 73%. The major by-products were acetone, propanaldehyde, acetaldehyde, acetol and formic acid. Coke selectivity dropped from 50% in the first hour to 9% after 14h. Elemental analysis (CHNS/O) of the catalyst withdrawn from the reactor during the experiments confirmed that polyaromatics formed on the surface. Based on NH3 and SO2 adsorption calorimetry the number of strong acid sites remained constant during 14h, while the number of the weak and medium acid sites dropped. The basic sites disappeared after 2h; coincidentally, less by-products (acetone) formed. Samples treated with pyridine, were analysed by FT-IR and they had fewer Brønsted sites but no Lewis acid sites. Carbon deposited on walls of the cylindrical pores (based on Barrett–Joyner–Halenda method) and reduced the pore diameter.

Sulfonic functionalized SBA-15 catalysts in the gas phase glycerol dehydration. Thermal stability and catalyst deactivation

The catalytic conversion of glycerol to acrolein was studied using sulfonic functionalized mesoporous silica SBA-15. The catalysts were prepared by the co-condensation method, conducting the silica synthesis and functionalization of its surface with thiol-propyl groups in the same stage. In a next step, the oxidation of thiol groups to sulfonic groups was made varying the concentration of H2O2 in order to obtain catalysts with different levels of acidity on the surface. The solids were characterized by BET, SEM, FTIR, XPS, and potentiometric titration with n-butilamine. The thermal stability was analyzed by thermogravimetry (TGA) and temperature-programmed desorption (TPD). The reaction tests were performed at different temperatures between 275 °C and 350 °C, and under feed flow conditions that allowed the study of the deactivation phenomena by coke deposition. The best temperature in order to maximize the acrolein yield was 300 °C. Higher temperatures led to a rapid deactivation by a combined effect of coke deposition and decomposition of functional groups.

Pd-H3PW12O40/Zr-MCM-41: An efficient catalyst for the sustainable dehydration of glycerol to acrolein

The gas-phase dehydration of glycerol was investigated over H3PW12O40/MCM-41, H3PW12O40/Zr-MCM-41 and Pd-H3PW12O40/Zr-MCM-41 mesoporous molecular sieves catalysts. MCM-41, Zr-MCM-41 and Pt-H3PW12O40/Zr-MCM-41 were also examined for comparison. The catalysts were characterized by X-ray diffraction, nitrogen adsorption–desorption, NH3-TPD, pyridine-FTIR and thermogravimetric analysis measurements. Compared with MCM-41, Zr-MCM-41 catalyst showed higher acidity and better catalytic performance in glycerol dehydration to acrolein. Compared to Zr-MCM-41, the acidity of H3PW12O40/Zr-MCM-41 catalyst significantly increased and the catalyst showed an enhanced glycerol conversion and acrolein selectivity. In order to improve the stability of H3PW12O40/Zr-MCM-41 catalyst, a small amount of platinum group metals (Pd) was doped. The nitrogen adsorption–desorption results revealed that mesoporous structure of the Pd-H3PW12O40/Zr-MCM-41 catalyst remained almost unchanged, and the specific surface area, pore volume and pore size decreased. In comparison with H3PW12O40/Zr-MCM-41, the total acidity of Pd-H3PW12O40/Zr-MCM-41 catalyst did not show any obvious change, but the number of the Brønsted acid sites increased, the amount of the Lewis acid sites decreased. The Pd-H3PW12O40/Zr-MCM-41 catalyst exhibited significantly higher selectivity for the formation of acrolein, relatively lower coke deposition and excellent catalyst stability. After 50h of reaction, the conversion of glycerol decreased from 100% to 55% over H3PW12O40/Zr-MCM-41 catalyst, while the conversion of glycerol reduced from 97% to 87% over Pd-H3PW12O40/Zr-MCM-41 catalyst. A drastic decrease in conversion after 35h over Pt-H3PW12O40/Zr-MCM-41 catalyst was also observed. Moreover, Pd-H3PW12O40/Zr-MCM-41 catalyst was completely regenerated under the regeneration conditions and exhibited excellent reusability in the dehydration of glycerol to acrolein.

WO3 supported on Zr doped mesoporous SBA-15 silica for glycerol dehydration to acrolein

Glycerol dehydration to acrolein is one of the most promising routes to valorize the surplus of such by-product of the biodiesel industry. In this context, a family of solid acid catalysts based on tungsten oxide supported over zirconium doped mesoporous SBA-15 silica has been synthesized and the influence of phosphoric acid treatment on the catalytic behavior has been also evaluated. These catalysts have been characterized by using the following techniques: XRD, N2 adsorption-desorption at −196°C, NH3–TPD, pyridine adsorption coupled to FT-IR spectroscopy, X-ray photoelectron spectroscopy, Raman and diffuse reflectance UV–visible spectroscopies, and they have been tested in the gas-phase dehydration of glycerol. Under the operating conditions assayed, all catalysts were active and acrolein was always the main product. The catalytic performance of support was enhanced when WO3 was supported and after treatment with H3PO4. The best catalytic results were achieved for 20W catalyst which showed values of glycerol conversion and acrolein yield of 97% and 41%, respectively, after 2h on stream at 325°C, and this activity was even maintained after 8h. Moreover, the treatment with phosphoric acid improved the acrolein yield at 2h on stream, but the deactivation of these catalysts was more pronounced probably because of the deterioration of textural and acid properties.

MWW-type catalysts for gas phase glycerol dehydration to acrolein

The materials derived from MWW layered precursor (MCM-22, MCM-36 and ITQ-2) were synthesized with molar ratio SiO2/Al2O3=30, characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), textural analysis by N2 physisorption, temperature programmed desorption of ammonia (NH3-TPD) and diffuse reflectance infrared spectroscopy (DRIFTS) of adsorbed pyridine and evaluated in gas phase glycerol dehydration to acrolein. The delaminated material (ITQ-2) has presented better catalytic performance than MCM-22 zeolite or MCM-36 pillared material, in both glycerol conversion and acrolein selectivity. These results were interpreted based on the textural properties and acidity changes. ITQ-2 excellent performance is due to higher accessibility and improved acidity when compared to pillared MCM-36 or parent MCM-22 zeolite. Long-term stability under either nitrogen or air co-feeding was investigated for ITQ-2.

Gas phase selective conversion of glycerol to acrolein over supported silicotungstic acid catalyst

Gas phase dehydration of glycerol to acrolein over a series of supported HSiW on ZrO2 and nano-sized γ-Al2O3 catalyst has been investigated. The characterization results revealed that impregnation of γ-Al2O3 nanoparticles increased the specific surface area, pore diameter, and thermal stability of the supported catalysts. The highest acrolein selectivity of 88.5% at 97.0% glycerol conversion was achieved over 0.5g 30HZ-20A catalyst in 3h at glycerol feed concentration of 10wt%, temperature=300̊C and TOF=136h−1. The coke deposition has no significant effect on the activity of 30HZ-20A catalyst. Indeed, the catalyst was stable even after 40h.

Structural, textural, and acid–base properties of layered Mg–Al oxides modified with a tungstate or phosphate and their activity and selectivity in gas-phase glycerol dehydration

The effect of the nature of the anion (WO2- 4, [H2W12O40]6–, HPO2- 4) introduced into the interlayer space of Mg–Al hydroxides with Mg/Al = 3 on their structural, textural, acid–base, and catalytic properties has been investigated. The synthesized materials are layered Mg–Al hydroxides with a hydrotalcite-like structure. Heat treatment of these hydroxides at 450–600°C yields a MgO-based solid solution, which turns into a mixture of MgO and MgAl2O4 phases on being heat-treated at 900°C. The samples modified with the [H2W12O40]6– and HPO2- 4 anions additionally contain MgWO4 and Mg3(PO4)2 phases, respectively. The OH groups of the materials examined do not show pronounced Bronsted acidity. (NH4)2HPO4 introduced into the interlayer space of the Mg–Al hydroxide is the most effective modifier enhancing the surface acidity, while the highest basicity is attained by introducing the Na2WO4 modifier. Glycerol dehydration at 275–350°C, involving acid sites of the surface, yields a wide variety of products containing 2 to 12 carbon atoms per molecule. A correlation has been established between the amount of glycerol dehydration products (acrolein + acetol) and the number of strong Lewis acid sites (νCO = 2177–2195 cm–1). The presence of basic sites varying in strength and concentration on the catalyst surface is favorable for condensation, cyclization, and oligomerization reactions yielding a wide range of C4+ products.

Kinetic Modeling, Thermodynamic, and Mass-Transfer Studies of Gas-Phase Glycerol Dehydration to Acrolein over Supported Silicotungstic Acid Catalyst

The kinetics of gas-phase glycerol dehydration in a packed-bed reactor over a highly active and stable supported silicotungstic acid catalyst with zirconium oxide and nanosized aluminum oxide (30HZ-20A) was investigated. The kinetic study is based on the optimal reaction conditions determined by response surface methodology. The reaction rate followed first-order kinetics with the activation energy and frequency factor, E = 27.5 kJ/mol and A = 5.35 × 105 s–1, respectively. Based on thermodynamic analysis, the values of ΔH° and ΔS° of the endothermic reaction were 14.70 and 0.09 kJ/(mol K), respectively, and ΔG° = −12.12 kJ/mol. The mass-transfer analysis revealed the pellet sizes of dp < 1 μm proceeded under reaction-limiting conditions. Experimental results confirmed high efficacy of the tested catalyst due to unity effectiveness factor and very low Thiele modulus.

Theoretical and experimental evaluation of mass transfer limitation in gas phase dehydration of glycerol to acrolein over supported HSiW catalyst

Experimental and theoretical studies were performed to evaluate the existence of internal and external mass transfer limitations in the gas phase glycerol dehydration to acrolein over supported HSiW catalyst. In the experimental method, the internal and external diffusions were determined by varying the gas mass flow-rate (mg), catalyst pellet size (dp), and catalytic bed volume (Vcat). In the theoretical approach the dimensionless parameters such as effectiveness factor (η), Thiele modules (φ1), and overall effectiveness factor (Ω) were calculated. The experimental results indicated no external mass transfer limitation due to constant glycerol conversion (94–97%) at various conditions. In addition, both the theoretical and experimental approaches confirmed no internal mass transfer limitation in glycerol dehydration reaction with catalyst pellet sizes of dp = 2–4 and 5–7 µm due to effectiveness factor equal to 1 (η = 1). Calculation of the overall effectiveness factor (Ω) also confirmed the absence of external and internal diffusion in presence of catalysts with pellet size of dp < 13–17 µm.

Gas-phase dehydration of glycerol over calcined tungsten-modified Zn–Al–O hydrotalcite-type catalysts

Zinc aluminum (ZA) samples with the ratio of Zn/Al>2 prepared by deposition of a mixed solution of aluminum and zinc nitrates with an aqueous solution of precipitant and varied by the method of modification with tungsten-containing component were characterized by XRD, FTIR, and adsorption methods and tested in the reaction of glycerol dehydration. The properties of samples were studied depending on Zn/Al ratio (ZA-2, ZA-3), the nature of precipitant: NaOH (ZA-2) or NH4OH (ZA-2a), and the method of modification by introducing the [W12O41]10− anion into the interlayer space [ZA-2 (W), ZA-2a (W)] or by deposition of PW (SiW) heteropoly acid on the surface [PW (SiW)/ZA-2 (ZA-2a)]. It was shown that dried ZA-2 sample represented a layered Zn–Al hydroxide with a structure similar to hydrotalcite; ZA-2a and ZA-3 samples contained ZnO in addition to mentioned phase. The modification of ZnAl samples with W-containing component did not change the phase composition but reduced the degree of crystallinity. The thermal treatment of the samples in the interval of 450–600°C promoted the formation of a solid solution based on ZnO which transformed after the calcination at 900°C into mixture of ZnO and ZnAl2O4 phases. It was found that the surface of the studied samples contained both Bronsted (BAS) and Lewis acid sites (LAS). BAS concentration referred to m2 of the surface increased in the row: ZA-2a<ZA-2a(W)<SiW/ZA-2a, while the concentration of LAS decreased in the same row. The correlation between the amount of acrolein formed and BAS content on the sample surface, on the one hand, and between the ratio of acrolein/acetol and BAS/(sumLAS+BAS) ratio, on the other hand, was revealed.

Deactivation study of a heteropolyacid catalyst for glycerol dehydration to form acrolein

Gas-phase glycerol dehydration to form acrolein over a heteropolyacid catalyst has been studied to understand the rapid deactivation process. The decrease in the conversion as a function of time was observed depending on operating conditions. The experiments were performed in an isothermal fixed bed reactor for eight hours. The influence of temperature, residence time, glycerol concentration, water concentration and oxygen concentration was studied. Next, a global kinetic equation for the deactivation was proposed for the studied experimental conditions.