Glycerol Acetylation Research Articles

Mesoporous phosphated and sulphated silica as solid acid catalysts for glycerol acetylation

AbstractSulphate- and phosphate-loaded silicas were synthesised using the sol-gel method with different sulphate and phosphate loadings. These catalysts were characterised using Fourier transform infrared spectroscopy (FT-IR), the Brunauer-Emmett-Teller (BET) method and X-ray photoelectron spectroscopy (XPS). Acidity was measured using the temperature-programmed desorption of ammonia (TPD-NH3) method. The results showed that glycerol esterification with acetic acid conversion decreased as follows: α(H2SO4) (100 %) > α(H3PO4) (99 %) > α(silica loaded with 20 % sulphuric acid) (SS-20; 98 %) > α(silica loaded with 20 % phosphoric acid) (PS-20; 83 %). These studies suggest that the solid acid catalytic activity in the esterification of glycerol is highly dependent on catalyst acidity strength, pore size and surface area.

A comparative study on catalytic properties of solid acid catalysts for glycerol acetylation at low temperatures

The catalytic properties of various types of solid acids, including silica–alumina, HUSY, dodecamolybdophosphoric acids supported on Nb2O5 (HPMo/Nb2O5) and mesoporous SBA-15 (HPMo/SBA-15), Amberlyst-15, sulfated ceria–zirconia (SCZ), propylsulfonic acid functionalized SBA-15 (PrSO3H-SBA-15), and sulfonic acid functionalized SBA-15 (SO3H-SBA-15) and microcrystalline cellulose (SO3H-Cell) catalysts, are studied for glycerol acetylation with acetic acid at low temperatures. Compared at the same acidity loading and similar glycerol conversion level (∼30%) below the equilibrium, the glycerol conversion turnover rate toward di- and triacetin is considerably higher on PrSO3H-SBA-15 and Amberlyst-15, with the rates shown in order as follows: PrSO3H-SBA-15>Amberlyst-15>HPMo/Nb2O5≥HPMo/SBA-15>HUSY>SCZ>SiO2–Al2O3. The catalytic properties of these solid acids are relatively stable under consecutive batch runs at 353K, whereas SO3H-SBA-15 and SO3H-Cell deactivate with a significant acidity loss due to hydrolysis of the grafted sulfonic acid groups. When similar type of the solid acids is compared, the acid strength affect the rate and selectivity, favoring a higher acid strength for the facilitation of the reactions (PrSO3H-SBA-15>Amberlyst-15; HUSY>SiO2-Al2O3; HPMo/Nb2O5≥HPMo/SBA-15). However, the proportional correlation between the acid strength and the glycerol conversion turnover rate does not hold when different types of solid acids are compared. The orders of magnitude higher glycerol conversion turnover rates with moderate Brönsted acid strength on the sulfonic acid functionalized catalysts suggest that the configuration of surface acid moieties attribute substantially to their catalytic activity for the reactions. The acid strength on SCZ is the highest, reflecting the super acidic nature of the sites formed on the sulfated metal oxide surface, but its catalytic activity for the reactions is inferior. The glycerol conversion turnover rates on the catalysts follow the Arrhenius type temperature dependence, and the characterization results indicate that the internal mass transfer resistance does not limit the reactions.

Periodic Mesoporous Organosilica Functionalized with Sulfonic Acid Groups as Acid Catalyst for Glycerol Acetylation.

A Periodic Mesoporous Organosilica (PMO) functionalized with sulfonic acid groups has been successfully synthesized via a sequence of post-synthetic modification steps of a trans-ethenylene bridged PMO material. The double bond is functionalized via a bromination and subsequent substitution obtaining a thiol functionality. This is followed by an oxidation towards a sulfonic acid group. After full characterization, the solid acid catalyst is used in the acetylation of glycerol. The catalytic reactivity and reusability of the sulfonic acid modified PMO material is investigated. The catalyst showed a catalytic activity and kinetics that are comparable with the commercially available resin, Amberlyst-15, and furthermore our catalyst can be recycled for several subsequent catalytic runs and retains its catalytic activity.

Enhanced Catalyst Activity of WO3 Using Polypyrrole as Support for Acidic Esterification of Glycerol with Acetic Acid

A series of polypyrrole supported WO3 were fabricated and characterized by FT‐IR, XRD, XPS, BET, TGA, and FESEM‐EDX. The activity of the catalysts was tested in glycerol esterification with acetic acid, and it found that WO3‐Ppy‐20 (nanocomposite with 20% WO3 loaded) showed the maximum catalyst activity with 98% and selectivity of 70% to triacetin at 110°C with a reaction duration of 10 h and also recorded the highest selectivity (75%) for acetylation of glycerol to monoacetin with about 59% conversion only. The highest acidity of WO3‐Ppy‐20 is also confirmed using TPD‐NH3 analysis. The activity and selectivity to triacetin of the catalyst were enhanced by increasing WO3 loading amount, resulting in 82% conversion for WO3‐Ppy‐5 with about 32 and 50% selectivity to monoacetin and diacetin and about 18% selectivity to triacetin; in case of WO3‐Ppy‐20, these amounts were changed to 5, 25, and 70% selectivity to monoacetin, diacetin, and triacetin, respectively with the conversion of 98%. TPD‐NH3 analysis found that polypyrrole supported WO3 increases the catalyst acidity of WO3. BET and FESEM analyses revealed that WO3 particles were well dispersed with the smallest average size in nanocomposite compared to pure WO3, which could contribute to the high activity of WO3‐Ppy catalyst for esterification of glycerol.

Screening of different solid acid catalysts for glycerol acetylation

Different solid acid catalysts, sulfonic acid functionalized amorphous and mesoporous silicas, titania doped silica HMS, sulfated zirconia and niobic acid, were synthesized, characterized and tested in the esterification reaction of glycerol. Their catalytic performance was compared with that of commercial Amberlyst-15. Fresh and spent materials were analyzed by means of X-ray photoelectron spectroscopy, N2 adsorption isotherms and acid capacity measurements. Among all the catalysts the mesoporous sulfonic silica presented the best performance in term of reactivity, with the total conversion of glycerol in 30min of reaction, and in term of stability, with no leaching of sulfonic groups of catalyst. The catalytic activity of the materials was related to their acid capacities as well as to the strength and surface density of acidic sites.

The acetylation of glycerol over amberlyst-15: Kinetic and product distribution

Glycerol is a byproduct of biodiesel synthesis and it can be converted into high value-added bioadditives. The heterogeneous acetylation of glycerol with acetic acid was conducted over Amberlyst 15 using a slurry reactor. The influence of reaction conditions such as the temperature and the molar ratio of acetic acid to glycerol (AA:G) on the product distribution was investigated. The results indicated that glycerol acetylation was a consecutive reaction. The equilibrium time for the product distribution shortened with decreasing AA:G molar ratio but with increasing temperature. It was also shown that the equilibrium conversion of glycerol as well as the combined yield of di- and triacetylated glycerols (DAG+TAG) increased with the AA:G molar ratio. Moreover, the AA:G molar ratio was the more influential factor on the yield of DAG+TAG than the temperature, although increasing the temperature might also have a positive influence on this yield. Reasonable yields of mono-, di- and triacetylated glycerols could be obtained by varying the reaction time, the AA:G molar ratio, and the temperature. The kinetic model based on homogeneous first-order consecutive reaction showed that the overall apparent rate constants (k1, k2, and k3) as well as its corresponding activation energy (E1, E2, and E3) were found to be;k1=2.07×106β0.274exp−6890T,E1=57.26kJ/molk2=18.66β1.82exp−3830T,E2=31.87kJ/molk3=1.16β−0.474exp−1670T,E3=13.90kJ/mol

Catalytic characteristics and parameters optimization of the glycerol acetylation over solid acid catalysts

The acetylation of glycerol over different solid acid catalysts were investigated using a slurry reactor. Amberlyst-15 showed high activity as well as high selectivity towards diacetin and triacetin. The different catalytic activities between various catalysts were explained in terms of acid sites, pore diameter, and hydrophilic properties. The consecutive reaction of glycerol acetylation and the “steric effect” for the products was confirmed. Both the molar ratio of acetic acid to glycerol (AA/G molar ratio) and the temperature had positive effects on the glycerol conversion and the selectivity towards higher esters. However, the AA/G molar ratio was the more influential factor than the temperature, especially for improving the combined selectivity of diacetin and triacetin. At the optimal operating conditions (AA/G molar ratio 9/1 and 110°C), the glycerol conversion predicted by the nonlinear models is 98.47%, and the corresponding selectivity is 8.65%, 46.56%, 44.79%, and 91.35% towards MAG, DAG, TAG, and DAG+TAG, respectively, all of these values are close to the experimental data.

Glycerol acetylation catalysed by ion exchange resins

Five types of ion exchange resins (Amberlyst 15, Ambertlyst-36, Dowex 50Wx2, Dowex 50Wx4 and Dowex 50Wx8) have been compared in glycerol acetylation carried out at 378K and atmospheric pressure. The glycerol:acetic acid molar ratio was set to 8:1. In these conditions the best performances were exhibited by Amberlyst-36 and Dowex-2. The effects of catalyst loading and the pre-treatment were also studied for the latter catalysts, showing that the use of 6.25g of dry catalyst/l of glycerol resulted in the optimal conditions for our reaction. The catalytic performances of the resins were unaltered after washing with distilled water in a Soxhlet apparatus, showing that sulphonic species were not removed by leaching. Recyclability tests showed that these solids are directly reusable up to 4–5 esterification runs. No homogeneous catalysis was detected in the filtered liquid media obtained after contact with the solids. Resins are not deactivated by the presence of water in the reaction medium.

Chemical Kinetics for Synthesis of Triacetin from Biodiesel Byproduct

The reaction kinetic of the glycerol acetylation with acetic acid catalyzed by sulfuric acid has been studied in the frame of continuous triacetin production. Glycerol, acetic acid and sulfuric acid catalyst were reacted in a batch reactor, in order to get reaction kinetics data. The mole ratio of catalyst to glycerol and temperature were studied during the experience. This study concluded that the selectivity of triacetin increased with increase in mole ratio of catalyst to glycerol. Increasing temperatures lead to increase selectivity of triacetin. It will decreased at the time of acetic acid has begun to evaporate. Triacetin synthesis is an exothermic reaction, a higher reaction temperature will cause in shifting the balance toward formation of reactants. This needs to be anticipated by taking one of the products so that the equilibrium shifting toward product formation.

Selective acetylation of glycerol over CeO2–M and SO42−/CeO2–M (M = ZrO2 and Al2O3) catalysts for synthesis of bioadditives

The feasibility of acetylation of glycerol with acetic acid was investigated employing CeO2–ZrO2, CeO2–Al2O3, SO42−/CeO2–ZrO2, and SO42−/CeO2–Al2O3 solid acid catalysts to synthesize monoacetin, diacetin and triacetin having interesting applications as bioadditives for petroleum fuels. Intensive physicochemical and surface characterization of the prepared catalysts were performed using XRD, BET surface area, ammonia-TPD and Raman spectroscopy techniques. Characterization results revealed that impregnated sulfate ions strongly influence the physicochemical characteristics of the investigated mixed oxide catalysts. Among various catalysts investigated, the SO42−/CeO2–ZrO2 combination catalyst exhibited superior catalytic activity under mild conditions. The effect of various parameters such as reaction temperature, molar ratio of acetic acid to glycerol, catalyst wt% and time-on-stream were studied over the SO42−/CeO2–ZrO2 catalyst to optimize the reaction conditions. Catalyst reusability was also carried out to understand its stability.

Hydroxylated magnesium fluorides as environmentally friendly catalysts for glycerol acetylation

The increase of biodiesel production during the next years will result in an overproduction, and therefore, an accumulation of glycerol on the market. The use of glycerol-based additives to improve the properties of biodiesel or gasoline is one of the possibilities currently being explored to utilize this renewable feedstock. In this context, partly hydroxylated magnesium fluorides have demonstrated catalytic activity in the esterification of glycerol with acetic acid to yield diacetylglycerine (DAG) and triacetylglycerine (TAG). The catalytic activity depends on the density of acid sites at the external catalytic surface while the selectivity to different acylated products is influenced by the nature of the acid sites (Lewis and/or Brønsted). Using non-conventional activation methods of the reactant molecules, as microwave or ultrasound irradiation, optimal glycerol conversions (>90%) and selectivities to the desired compounds (over 85%) were obtained. The activities and selectivities achieved using partly hydroxylated fluorides as catalysts are comparable or even superior to those displayed by conventional oxide based acid catalysts under thermal activation.

Acetylation of glycerol to biofuel additives over sulfated activated carbon catalyst

Oxygenated fuel additives can be produced by acetylation of glycerol. A 91% glycerol conversion with a selectivity of 38%, 28% and 34% for mono-, di- and triacetyl glyceride, respectively, was achieved at 120°C and 3h of reaction time in the presence of a catalyst derived from activated carbon (AC) treated with sulfuric acid at 85°C for 4h to introduce acidic functionalities to its surface. The unique catalytic activity of the catalyst, AC-SA5, was attributed to the presence of sulfur containing functional groups on the AC surface, which enhanced the surface interaction between the glycerol molecule and acyl group of the acetic acid. The catalyst was reused in up to four consecutive batch runs and no significant decline of its initial activity was observed. The conversion and selectivity variation during the acetylation is attributed to the reaction time, reaction temperature, catalyst loading and glycerol to acetic acid molar ratio.

Glycerol acetylation on sulphated zirconia in mild conditions

This work focuses on the role of the hydrolysis ratio over the physicochemical properties of sulphated zirconia (SZ) obtained by the sol–gel method. The solids obtained were tested in the esterification of acetic acid diluted in glycerol, the latter being used both as reactant and solvent. The acidic properties of the SZ samples and their performances in the acetylation reaction have been successfully correlated. The recyclability has also been studied: sample SZ-1 (sulphated zirconia prepared with a hydrolysis molar ratio=1) shows a progressive deactivation in successive tests due to sulphur leaching which induces an activity in the homogeneous phase.

Acetylation of glycerol over heteropolyacids supported on activated carbon

Abstract The acetylation of glycerol was carried out over dodecatungstophosphoric acid (PW) supported on activated carbon, being the monoacetin, diacetin and triacetin the reaction products. A series of catalysts, with different heteropolyacid loading (from 3.5 to 6.5 wt.%), were prepared. It was observed that the catalytic activity increases with the amount of PW immobilized on the activated carbon, being the PW2_AC (with 4.9 wt.%) the most active sample. However, at high loading of heteropolyacid on the activated carbon, a decrease on the catalytic activity was observed, which can be probably explained due to some hindrance in the activated carbon porous system. All catalysts exhibited good values of selectivity to the diacetin. Catalytic stability of the PW2_AC was also studied by performing consecutives batch runs with the same catalyst sample. After the third batch, it was observed that the catalytic activity stabilized.

Synthesis of bio-additives: Acetylation of glycerol over zirconia-based solid acid catalysts

Acetylation of glycerol with acetic acid was investigated over ZrO2, TiO2–ZrO2, WOx/TiO2–ZrO2 and MoOx/TiO2–ZrO2 solid acid catalysts to synthesize monoacetin, diacetin and triacetin having interesting applications as bio-additives for petroleum fuels. The prepared catalysts were characterized by means of XRD, BET surface area, ammonia-TPD and FT-Raman techniques. The effect of various parameters such as reaction temperature, molar ratio of acetic acid to glycerol, catalyst wt.% and time-on-stream were studied to optimize the reaction conditions. Among various catalysts investigated, the MoOx/TiO2–ZrO2 combination exhibited highest conversion (~ 100%) with best product selectivity, and a high time-on-stream stability.

Catalytic acetylation of glycerol with acetic anhydride

We studied the acetylation of glycerol with acetic anhydride using different solid acid catalysts. The results indicated that at 60 °C, zeolite Beta and K-10 Montmorillonite showed 100% selectivity to triacetin within 20 min, with a molar ratio of 4:1. Amberlyst-15 acid resin yielded 100% triacetin after 80 min, whereas niobium phosphate gave diacetin and triacetin in 53% and 47% selectivity, respectively. All catalysts were more selective to triacetin than the uncatalyzed reaction. By contrast, zeolite Beta gave poor yield of triacetin when acetic acid was used as acetylating agent. The different behavior was explained in terms of the stabilization of the acylium ion intermediate.

Acetylation of glycerol to synthesize bioadditives over niobic acid supported tungstophosphoric acid catalysts

Acetylation of glycerol to yield mono, di and triacetin (acetylated glycerol) was carried over niobic acid supported tungstophosphoric acid (TPA) catalysts. The catalysts with varying TPA content were prepared and characterized by different techniques. The characterization results reveal the presence of well-dispersed Keggin ion on support. The results suggest that the glycerol conversion and selectivities depend on the acidity of the catalysts, which in turn is related to the content of TPA on niobic acid. The change in conversion and selectivities during the acetylation also is attributed to the reaction time, catalyst concentration and glycerol to acetic acid molar ratio.

Glycerol acetylation over dodecatungstophosphoric acid immobilized into a silica matrix as catalyst

The esterification of glycerol with acetic acid was carried out over dodecatungstophosphoric acid (PW) immobilized into a silica matrix. The products of glycerol acetylation were monoacetin, diacetin and triacetin. The immobilization of PW into silica was carried out by two different techniques: sol–gel and impregnation methods. The catalysts prepared by sol–gel method will be denoted as PW-in-S while the catalysts prepared by impregnation will be denoted as PW-on-S. The catalysts were characterized by nitrogen adsorption at 77K, FTIR, XDR and ICP-AES. A series of PW immobilized into silica with different PW loading were prepared. It was observed that the catalytic activity increases with the amount of PW immobilized into silica, either by the sol–gel method or by the impregnation method.High values of selectivity to diacetin were obtained with all catalyst.The effect of various parameters, such as, reaction temperature, catalyst loading, molar ratio of glycerol to acetic acid and reusability of PW-in-S2 were studied to optimize the reaction conditions.The catalytic stability of the PW-in-S2 was evaluated by performing consecutives batch runs with the same catalyst sample. It was observed a stabilization of the catalytic activity.

Esterification of glycerol with acetic acid over dodecamolybdophosphoric acid encaged in USY zeolite

Abstract The esterification of glycerol with acetic acid was carried out over dodecamolybdophosphoric acid (PMo) encaged in the USY zeolite. The products of glycerol acetylation were monoacetin, diacetin and triacetin. A series of PMo encaged in the NaUSY zeolite with different PMo loading from 0.6 to 5.4 wt.% were prepared. It was observed that the catalytic activity increases with the amount of PMo immobilized in the NaUSY zeolite, being the PMo3_NaUSY (with 1.9 wt.%) the most active sample. However, at high loading of heteropolyacid encaged in the NaUSY zeolite, a decrease on the catalytic activity was observed, which can be explained, probably, due to the internal diffusion limitations. Good values of selectivity to diacetin were obtained with all the catalyst. Catalytic stability of the PMo3_NaUSY was evaluated by performing consecutives batch runs with the same catalyst sample. After the second batch, it was observed a stabilization of the catalytic activity.

Acetylation of glycerol catalyzed by different solid acids

This work describes the acetylation of glycerol with acetic acid catalyzed by different solid acids. Reactions were carried out in batch mode under reflux. The kinetics of glycerol transformation and selectivity to the products, notably mono, di and triacetyl esters, were determined within 30 min of reaction time to observe the primary products. The results showed that the acid exchange resin, Amberlyst-15, was the most active catalyst, achieving 97% conversion in this period, followed by K-10 montmorillonite, niobic acid, HZSM-5 and HUSY. The selectivity varied for each catalyst and conversion degree, but the yield of di and triacetylated products increased with increasing conversion and reaction time. In all cases, the formation of α-hydroxy-acetone (acetol) was observed and associated with the glycerol dehydration. The poor performance of the zeolites might be related to diffusion problems of the acetylated esters inside the cavities.