Preparation of Phosphotungstic Acid Ionic Liquid Catalyst

With the shortage of fossil energy, rising oil prices and increasing environmental pollution caused by vehicle emissions, there is an urgent need to find new alternative energy sources. Among them, biodiesel has attracted people's attention because of its renewability and low emission.

Biodiesel is a fatty acid methyl ester fuel obtained by transesterification of oil plants, animal fats and waste cooking oils. Heterogeneous inorganic acids and bases are generally employed as catalysts for the transesterification reaction. Although inorganic acids such as inorganic acids and inorganic bases have price advantages and high product yields, they all have problems such as equipment corrosion and wastewater pollution. In addition, bio-enzyme catalysts have appeared in the market, but the enzymes of this type have high prices, long reaction times, and low reaction yields.

In recent years, heteropolyacid catalysts represented by phosphotungstic acid have been widely popular, and they have good catalytic performance, and have not only acid catalytic properties but also redox catalytic properties. In addition, the heteropoly acid structure is stable, can be used in a homogeneous or heterogeneous catalytic environment, can also be used together with a phase transfer catalyst, has no pollution to the environment, and is less corrosive to equipment, and is a promising green catalyst. Many researches and applications are based on the synthesis of phosphotungstic acid, such as a phosphotungstic acid ionic liquid catalyst proposed by some scholars. The catalyst can be used to prepare biodiesel, the process comprising:

1. The 1,3-propane sultone is dissolved in acetone, the mass ratio of 1,3-propane sultone to acetone is 1:5, and the mixture is stirred in the reactor with a dropping funnel under ice bath conditions. The morphine was added dropwise, and the white solid formed after 1 h of reaction was washed three times with solvent acetone and dried to give the intermediate 1-(3-sulfopropyl)morpholine. The intermediate 1-(3-sulfopropyl)morpholine is added to the aqueous solution of phosphotungstic acid, and the molar ratio of 1-(3-sulfopropyl)morphinphyline to phosphotungstic acid is 3:1, and the reaction is carried out at room temperature for 24 hours. The product was distilled under reduced pressure to remove water, and the remaining solid was placed in a vacuum oven to dry to constant weight to give the final product 1-(3-sulfopropyl)morpholine phosphotungstate.

2. Soybean oil and methanol were added to a three-necked flask equipped with a reflux condenser in a molar ratio of 1:14, and then a 5% phosphotungstic acid ionic liquid having a mass of soybean oil was added. The reaction was carried out at a reaction temperature of 65 ° C under normal pressure for 8 hours. After the reaction was completed, the mixture was transferred to a separatory funnel, and the mixture was allowed to stand for separation and liquid separation. The upper layer is mainly biodiesel, the biodiesel is washed with water, dried to constant weight, and then its composition is analyzed by gas chromatography and the biodiesel yield is calculated to be 96.4%.

Heteropolyacid salts are very easy to recycle and catalyst regeneration due to their heterogeneous catalytic reaction during the reaction. Combining the advantages of ionic liquids and heteropolyacids, combining the anions of heteropolyacids with the groups of ionic liquids not only adjusts the catalytic performance of heteropolyacids, but also overcomes the difficulty in recovering expensive heteropolyacid homogeneous catalysts and is easy to lose. The environmental pollution caused by it and the unfavorable problems in industrial production applications, and its application in transesterification to prepare biodiesel have great industrial application prospects.

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