An Overview of the Production of Oxygenated Fuel Additives by Glycerol Etherification, Either with Isobutene or tert-Butyl Alcohol, over Heterogeneous Catalysts

Abstract

Biodiesel production has considerably increased in recent decades, generating a surplus of crude glycerol, which is the main drawback for the economy of the process. To overcome this, many scientists have directed their efforts to transform glycerol, which has great potential as a platform molecule, into value-added products. A promising option is the preparation of oxygenate additives for fuel, in particular those obtained by the etherification reaction of glycerol with alcohols or olefins, mainly using heterogeneous catalysis. This review collects up-to-date research findings in the etherification of glycerol, either with isobutene (IB) or tert-Butyl alcohol (TBA), highlighting the best catalytic performances reported. Furthermore, the experimental sets employed for these reactions have been included in the present manuscript. Likewise, the characteristics of the glycerol ethers–(bio)fuel blends as well as their performances (e.g., quality of emissions, technical advantages or disadvantages, etc.) have been also compiled and discussed.

Effect of Preparation Method on the Catalytic Property of Calcined Ca–Al Hydrotalcite for the Synthesis of Ethyl Methyl Carbonate

“…As an important class of solid base catalysts, calcined hydrotalcite has the advantages of strong alkalinity, high surface alkali content, low cost, and easy separation. − It is widely used in alkali-catalyzed reactions such as transesterification of biodiesel and organic carbonates. − Compared with the commonly calcined Mg–Al hydrotalcite, the calcined Ca–Al hydrotalcite shows higher alkali strength. Nowadays, calcined Ca–Al hydrotalcite with a Ca/Al ratio of 2 is more commonly used in the field of catalysis by previous literature works. − …”

Synthesis and Properties of 1,2,3-Triethoxypropane: A Glycerol-Derived Green Solvent Candidate

“…Driven by the need to boost the use of glycerol, a number of value-added glycerol derivatives have been developed for various applications using different methods including carboxylation, pyrolysis, esterification, transesterification, etherification, hydrolysis, and oxidation. − Glycerol etherification is a favorable way among these applicable directions mainly because it can directly produce oxygenated fuel additives with appropriate alkylation agents such as 1-butene and t -butanol. − Apart from fuel additives, small-molecule glycerol ether derivatives are believed to be competitive candidates for next-generation CO 2 capture solvents due to the concentrated ether functional groups, which have been proven to have high CO 2 affinity in other physical solvents − or polymer membranes for gas separation. − Despite a wide range of catalysts (acidic or basic, homogeneous, or heterogeneous) applied in the fabrication of fuel additives, these reactions usually experience oligomerization or equilibrium between mono-, di-, and triethers of glycerol, which are difficult to separate and might introduce extra cost and impact the efficiency of CO 2 removal. , One example is dimethyl ethers of polyethylene glycol (DMPEG) which comprises a family of dimethyl ethers of the formula CH 3 (OCH 2 CH 2 ) n OCH 3 produced from methanol, methyl chloride, and ethylene oxide, with an average n = 6, but with a distribution of n = 4–10 . Because DMPEG synthesis is an oligomerization reaction, the product is not uniform.…”

Zeolite-based catalysis for isobutene conversion into chemicals and fuel additives. A review

“…The reaction between glycerol and isobutene is a Brönsted acid catalyzed reaction and produces a large game of mono-, di-and tri-ethers (Scheme 6) [96]. By-products like isobutene oligomers and tert-butyl alcohol can be also formed.…”