ARTICLE | doi:10.20944/preprints202206.0055.v1
Subject: Chemistry And Materials Science, Organic Chemistry Keywords: Sulfonated silica catalyst (SiO2-SO3H); methyl salicylate; green chemistry; methylating agent; deacetylation (acyl nucleophilic substitution); solid acid catalyst
Online: 6 June 2022 (03:45:09 CEST)
SiO2-SO3H, with a surface area of 115 m2/g, pore volume of 0.38 cm3g-1 and 1.32 mmol H+/g, was used as a 20% w/w catalyst for the preparation of methyl salicylate (Wintergreen oil or MS) from acetylsalicylic acid (ASA). A 94% conversion was achieved in a microwave reactor during 40.0 minutes at 120 oC in MeOH. The resulting crude product was purified by flash chromatography. The catalyst could be re-used three times.
ARTICLE | doi:10.20944/preprints202201.0013.v1
Subject: Chemistry And Materials Science, Applied Chemistry Keywords: hydrophilic sulfonated silica catalyst; Aliquat 336; tetrabutylammonium tetrafluoroborate; transesterification; fatty acid methyl esters, DMSO.
Online: 4 January 2022 (15:24:55 CET)
Triglycerides of waste cooking oil reacted with methanol in refluxing toluene to yield mixtures of diglycerides, monoglycerides and fatty acid methyl esters (FAMEs) in the presence of 20% (w/w) catalyst/oil using the hydrophilic sulfonated silica (SiO2-SO3H) catalyst alone or with the addition of 10% (w/w) co-catalyst/oil [(Bun4N)](BF4) or Aliquat 336]. The addition of the ammonium salts to the catalyst lead to a decrease in the amounts of diglycerides in the products, but the concentrations of monoglycerides increased. Mixtures of [(Bun4N)](BF4)/catalyst were superior to catalyst alone or Aliquat 336/catalyst for promoting the production of mixtures with high concentrations of FAMEs. The same experiments were repeated using DMSO as the solvent. The use of the more polar solvent resulted in excellent conversion of the triglycerides to FAME esters with all three-catalyst media. A simplified mechanism is presented to account for the experimental results.
ARTICLE | doi:10.20944/preprints201909.0110.v1
Subject: Chemistry And Materials Science, Applied Chemistry Keywords: solid acid; sulfonated carbon; high voltage; biodiesel; oleic acid
Online: 10 September 2019 (11:59:30 CEST)
Sulfonated carbon was used as an efficient and reusable heterogeneous solid acid catalyst for the synthesis of biodiesel via esterification of oleic acid with methanol under high voltage conditions. Using an inexpensive and reusable catalyst, environmental benignity, excellent yields in short times, synthesis in atmospheric pressure and low temperature conditions are some of the important features of this protocol. In the final results were confirmed by GC.
ARTICLE | doi:10.20944/preprints202307.1088.v1
Subject: Engineering, Chemical Engineering Keywords: Chitosan; Fuel Cell; Water Uptake; Proton Conductivity; Silica, Sulfonated
Online: 17 July 2023 (09:19:49 CEST)
The purpose of this study is to identify the steps involved in fabricating silica/chitosan composite membranes and their suitability in fuel cell application. It also intends to identify the physical characteristics of chitosan composite membranes, including their degree of water absorption, proton conductivity, methanol permeability, and functional groups. In this investigation, composite membranes were fabricated using the solution casting method with chitosan content of 5 g and silica variations dosage of 2% and 4% while stirring at a constant speed for 2h. According to the findings, the analysis of composite membranes produced chitosan membranes that were successfully modified with silica. The optimum membrane was found to be 4% s-SiO2 from the Sol-gel method with composite membrane's optimal condition of 0.234 cm/s proton conductivity, water uptake of 56.21%, and reduced methanol permeability of 0.99 × 10 -7 cm2/s in the first 30 minutes and 3.31 × 10-7 in the last 150 minutes. Maintaining lower water uptake capacity at higher silica content is still a challenge that needs to be addressed. However, the fabricated membranes showed exceptional results in terms of proton conductivity and methanol permeability.
ARTICLE | doi:10.20944/preprints202104.0675.v1
Subject: Chemistry And Materials Science, Biomaterials Keywords: Carbon nanotubes; Functionalization; Sulfonated Poly-Ether-Ether-Ketone; FTIR
Online: 26 April 2021 (13:29:14 CEST)
.Functionalization of multi-walled carbon nanotubes (MWNTs) surface with sulfonated poly(ether ether ketone) SPEEK chains using hexane diamine (HAD) as the interlinking molecule was investigated. MWNTs were first oxidized by nitric acid to generate carboxyl groups on their surface. Grafting of SPEEK chains on the MWNTs surface was achieved using hexane diamine as a cross-linking molecule. The attachment took place after the reaction of amine groups with carboxyl groups of oxidized MWNTs and sulfonate groups of SPEEK as confirmed by infrared (FTIR) analysis. Scanning electron microscopy (SEM) showed that MWNTs were packed into a dense and compact structure. Transmission electron microscopy (TEM) showed that the nanotubes were wrapped by polymer chains and arranged in a bundle like structure. These observations reveal that some of MWNTs were interconnected by SPEEK chains.
ARTICLE | doi:10.20944/preprints202308.0792.v1
Subject: Chemistry And Materials Science, Polymers And Plastics Keywords: Sulfonated poly(ether ether ketone); degree of sulfonation; electron beam irradiation
Online: 10 August 2023 (10:19:46 CEST)
The aim of this study is to compare different methods used for determination of the DS for sulfonated membranes before and after high dose irradiation. Commercial PEEK was homogenously sulfonated up to DS of 60-90% and the membranes were prepared using solvent casting method. Part of the samples were irradiated with 10 MeV electron beam up to 500 kGy dose to assess the ionising radiation induced effects. Both non-irradiated and irradiated membranes were characterized by Fourier Transformation infrared (FT-IR) spectrometry, thermogravimetric analysis (TGA), proton nuclear magnetic resonance (1H-NMR), electrochemical impedance analysis and for the first time for non-irradiated membranes by spectrophotometric analysis with Cr(III). Comparison of the above-mentioned methods for application for DS assessment was done. It was observed that irradiated membranes presented a higher value of DS. Appearance of different new signals in 1H-NMR and FT-IR spectra of irradiated membranes indicated the effects of radiation induced changes in the structure of SPEEK materials. It was determined that the novel method with Cr(III) is applicable for the determination of SPEEK DS under 80%.