Solventless transacetalization of solketal over Amberlyst catalysts into valuable bio‐based chemicals

Abstract

BACKGROUND In addition to being a greener synthetic approach, the production of value‐added chemicals from bio‐based glycerol is highly appealing owing to its nontoxicity, renewability and availability. The current work reports solventless transacetalization of solketal with benzaldehyde in the presence of heterogeneous Amberlyst® catalysts (A15 dry, A15 wet, A36 and A46). RESULTS Effects of several reaction parameters on the transacetalization of solketal also were investigated and optimized to attain maximum conversion and yield. This reaction, however, is accompanied by concurrent hydrolysis of solketal to form the side product glycerol. Of all solid acid catalysts investigated, A15 dry (10 wt%) gave the highest conversion (88%) under optimized reaction conditions of 60 °C, 5:1 (solketal/benzaldehyde) and 30 min duration. The A15 dry is reusable and recyclable with only 8% reduction in conversion after five consecutive cycles. The approach was extended to other aldehydes including furfural and phenylacetaldehyde to produce, respectively, a highly value‐added fuel additive intermediate and hyacinth fragrance. CONCLUSION The transacetalization of solketal with less reactive aldehyde into cyclic glycerol acetal was achieved in an efficient, feasible and green manner. A15 was the most reactive catalyst of all Amberlyst® catalysts investigated. This approach also provided effective utilization of waste of biodiesel production – glycerol – for transformation into value‐added products. © 2021 Society of Chemical Industry (SCI).

Characterization of crude glycerol and glycerol pitch from palm-based residual biomass

“…On top of the availability and low value of CG, there has been extensive interest in this by-product due to the prospect of purification to pure glycerol that has three reactive hydroxyl groups for transformation into highly value-added intermediates, chemicals, and products such as glycerol acetal [ 6 , 7 ], glycerol ether [ 8 ], and glycerol carbonates [ 9 ]. Glycerol has found applications in many high value–added industries such as personal care, cosmetics, pharmaceutical, and food industries which require high-purity glycerol as feedstock.…”

Synthesis of Solketal Ethers as Cold Flow Improver for Palm‐Based Biodiesel

“…Two‐step synthesis of SE from glycerol using homogeneous [26] and heterogeneous acid catalysts [15,27,28] has been previously reported. However, in acid‐catalyzed reactions of solketal, the yield was greatly reduced by inevitable side reactions such as hydrolysis of the acetal moiety [12,29] …”

“…[6] Nevertheless, the hydroxyl groups in glycerol must first be transformed into other derivatives to improve their miscibility and compatibility with fuel. In addition to glycerol ethers, [7] glycerol acetal/ketal such as solketal is another derivative that can be easily synthesized, [8][9][10][11][12] is commercially available, and exhibits potential as a fuel additive. Solketal has been shown to improve the octane number, [13] viscosity, [14] antiwear properties, [15] and cold flow properties [16][17][18] of gasoline or biodiesel while reducing gum formation and emission of carbon monoxide and hydrocarbon.…”

“…However, in acid-catalyzed reactions of solketal, the yield was greatly reduced by inevitable side reactions such as hydrolysis of the acetal moiety. [12,29] Base-catalyzed etherification has been widely studied for production of polyglycerol [30] using catalyst such as metal oxide, [31,32] carbonate [33] and alkali metal acetate salts. [34] In an earlier work, formation of SE as intermediate has been reported in the preparation of monoether using classic Williamson etherification in the presence of strong base, NaH.…”