Arenesulfonic Acid-Functionalized Bentonite as Catalyst in Glycerol Esterification with Acetic Acid

The present study is focused on the synthesis of arenesulfonic acid-functionalized bentonite as a catalyst to produce monoacetin, diacetin, and triacetin from glycerol and acetic acid using toluene as solvent and a water removing agent. The best conditions for the present reaction with acetic acid were an acetic acid:glycerol:toluene molar ratio of 7:1:1.4, 100 °C, and 0.074 wt % of catalyst (based on the total weight of glycerol). Under the reaction conditions, 96% glycerol conversion was achieved within 0.5 h from the start of the reaction. The maximum selectivity of 66% and 74% were achieved for diacetin and triacetin after 0.5 and 3 h of reaction, respectively, without formation of any byproduct. The arenesulfonic acid-functionalized bentonite was characterized by X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, N2 adsorption/desorption experiments (Brunauer, Emmett and Teller, BET, method), field emission scanning electron microscopy, and the surface acidity was determined by back titration. Without significant treatment, the catalyst was reusable for 5 consecutive runs

Synthesis of solketalacetin as a green fuel additive via ketalization of monoacetin with acetone using silica benzyl sulfonic acid as catalyst

Silica benzyl sulfonic acid (SBSA) was prepared as a catalyst for reacting monoacetin with acetone to synthesize solketalacetin as a green fuel additive. To synthesize SBSA, commercially available silica gel was functionalized with benzyl alcohol in the presence of sulfuric acid as catalyst and was then sulfonated with chlorosulfonic acid. The catalyst was characterized by FT-IR, XRD, and TGA. The catalytic activity of SBSA was compared with those of Amberlyst 36 and Purolite PD 206 as two sulfonated acidic catalysts, in a continuous flow system. The effect of different operation conditions such as acetone to monoacetin molar ratio, reaction temperature, and feed flow rate were investigated. Increasing acetone to monoacetin molar ratio increased the solketalacetin yield for the three catalysts but SBSA demonstrated the highest solketalacetin yield. Solketalacetin yield was reduced with temperature increase for all the catalysts and the maximum solketalacetin yields were recorded with Amberlyst 36 and SBSA catalyst at 20 °C and 40 °C, respectively. The catalytic activity was examined by keeping the catalysts on–stream for 25 h while the reusability tests were performed in four consecutive runs and showed that SBSA was stable up to 25 h and had the highest stability in 4 runs

Internally amplified stimulated Raman spectroscopy

Internally amplified stimulated Raman scattering is developed as a novel approach to study concentrational thresholds in stimulated Raman scattering (SRS). In the proposed physical model, amplifier molecules are used to bridge the spatial gaps among analyte molecules distributed distantly from each other throughout a dilute solution. As a result, Stokes photons can more effectively reach the next target molecules down the pump light path to sustain and amplify the desirable SRS process. The model has been verified by experimental results which give a better understanding of the threshold phenomenon in SRS. The technique of internal amplification is practically useful to lower concentrational thresholds, leading to improved detection limits in analytical SRS measurements

Continuous Synthesis of a Green Fuel Additive Mixture with Highest Quantities of Solketalacetin and Solketal and Lowest Amount of Diacetin from Biodiesel-Derived Glycerol

<div><p>This work presents a continuous, easy-to-scale-up system for glycerol conversion to a valuable fuel additive mixture such as solketalacetin ((2,2-dimethyl-1,3-dioxolan-4-yl)methyl acetate), solketal and minimum amount of diacetin with no byproducts. A two-stage reaction was conducted to synthesize the mixture. At first, glycerol was reacted with acetic acid in a continuous system to synthesize monoacetin using a small plug flow reactor and central composite design to optimize the variables related to monoacetin synthesis. Finally, an acetic acid:glycerol mole ratio of 3.7:1, a temperature of 79 °C, a flow rate of 0.9 mL min-1, and a pressure of 1 bar were determined as the optimum conditions. At the optimum condition, predicted and experimental yields of monoacetin were 63 and 62%, respectively. In the next stage, monoacetin and the residual glycerol were reacted with acetone to obtain a mixture of solketalacetin, solketal, and diacetin with the mole percentage of 62, 30, and 8%, respectively.</p></div

Optimization of Solketalacetin Synthesis as a Green Fuel Additive from Ketalization of Monoacetin with Acetone

An economical and easy to scale up method for glycerol conversion to solketalacetin (i.e., (2,2-dimethyl-1,3-dioxolan-4-yl)­methyl acetate) as a valuable fuel additive is described, for the first time. Monoacetin was synthesized by reacting glycerol with acetic acid, and then solketalacetin was produced from the reaction of monoacetin with acetone using Purolite PD 206 as a catalyst. The central composite design was employed for the experimental design and then response surface methodology was used for the optimization of variables for the second stage of the reaction. The optimum operating conditions for the second stage of the reaction were as follows: acetone to monoacetin mole ratio, 5; reaction temperature, 20 °C; pressure, 45 bar; flow rate, 0.2 mL·min^–1; and catalyst, 2.0 g. Yield of the second stage of the reaction at the experimental design conditions and at the acetone to monoacetin mole ratio of 9 was obtained as 69% and 100%, respectively

Glycerol transesterification with ethyl acetate to synthesize acetins using ethyl acetate as reactant and entrainer

Transesterification of glycerol with ethyl acetate was performed over acidic catalysts in the batch and semi-batch systems. Ethyl acetate was used as reactant and entrainer to remove the produced ethanol during the reaction, through azeotrope formation. Since the azeotrope of ethyl acetate and ethanol forms at 70 oC, all the experiments were performed at this temperature. Para-toluene sulfonic acid, sulfuric acid, and Amberlyst 36 were used as catalyst. The effect of process parameters including ethyl acetate to glycerol molar ratio (6-12), reaction time (3-9 h), and the catalyst to glycerol weight (2.5-9.0%), on the conversion and products selectivities were investigated. Under reflux conditions, 100% glycerol conversion was obtained with 45%, 44%, and 11% selectivity to monoacetin, diacetin, and triacetin, respectively. Azeotropic reactive distillation led to 100% conversion of glycerol with selectivities of 3%, 48% and 49% for monoacetin, diacetin, and triacetin. During the azeotropic reactive distillation, it was possible to remove ethanol to shift the equilibrium towards diacetin and triacetin. Therefore, the total selectivity to diacetin and triacetin was increased from 55% to 97% through azeotropic distillation

Stimulated Raman scattering activity of organic compounds

The stimulated Raman scattering (SRS) activity of over one hundred organic compounds was investigated at room temperature. Spectra were obtained successfully for the colourless neat liquids but not for the solid chemicals in solution, and their SRS shifts were measured systematically. The results confirmed that SRS Stokes shifts are usually the same as those observed in spontaneous Raman scattering, with occasional differences in frequency from the strongest spontaneous Raman bands. Empirical trends have been observed in functional group recognition, compound classification, degenerate vibrational modes, substituent group effects, hydrogen bonding and concentration threshold. Other new observations such as multiple peaks, exceptional SRS activity and distributed spectra are also reported. SRS offers several advantages over normal Raman spectroscopy in industrial process monitoring, and a potentially interesting scope of analytical utility is discussed

Valorization of Biodiesel Derived Glycerol to Acetins by Continuous Esterification in Acetic Acid: Focusing on High Selectivity to Diacetin and Triacetin with No Byproducts

This work presents a continuous, easy-to-scale-up esterification system with 100% conversion of glycerol in acetic acid with a high selectivity to DA and TA and no byproducts under industrially applicable reaction conditions. The main emphasis is to obtain TA from glycerol esterification in acetic acid without using any acetic anhydride or harsh conditions. The effects of reaction parameters, including the acetic acid-to-glycerol mole ratio (1–9), temperature (66–134 °C), and pressure (1–199 bar) with a 0.5 mL·min^–1 feed flow rate, on the glycerol conversion and selectivities to monoacetin, diacetin, triacetin, and byproducts were investigated. Under the optimum conditions of an acetic acid-to-glycerol mole ratio of 7, a temperature of 100 °C, and a pressure of 1 bar, over 3 g of Amberlyst 36, the glycerol conversion and monoacetin, diacetin, and triacetin selectivities reached 100%, 43%, 44%, and 13%, respectively. The formation of byproducts was not detected under these optimum conditions. Amberlyst 36 remained stable after 25 h on-stream. The recovered catalyst was reused with no significant deactivation after three cycles. This continuous system also can be used for monoacetin synthesis with 85% selectivity and 95% glycerol conversion with an acetic acid-to-glycerol mole ratio of 1, a temperature of 100 °C, and a pressure of 100 bar