Glycerol etherification

Several methods and reaction pathways have been reported for the conversion of glycerol in the literature, such as etherification, esterification [1], and oxidation [2], Via ionic dehydration acetol [3] and acrolein can be produced. The radical steps result in aldehydes, allyl alcohol, etc. [4], If the dehydration is followed by a hydrogenation step, propanediols (1,2- or 1,3-) can be obtained [5-6]. 

Etherification of glycerol with isobutene (2-methylpropene) is an acid-catalyzed reaction and produces five ethers two monoethers, two diethers and one triether (Fig. 10.2). The IUPAC names for the two monosubstituted ethers are 3-tertiary-butoxypropane-l,2-diol and 2-tertiary-butoxypropanc-1,3-diol, the two disubsti-... 

Some studies and patents related to the etherification reaction between glycerol and isobutene are available in the literature, which report the production of the ethers with various catalysts, such as zeolites [19], ion-exchange resins [20, 21] and some homogeneous catalysts, e.g., p-toluene sulfonic acid [21, 22] and methane sulfonic acid [22], Recent studies, however, have concentrated on the etherification of glycerol with isobutene on ion-exchange resins [8, 23]. 

The etherification reaction was studied in the temperature range 45-90 °C. The initial molar ratio of isobutene to glycerol varied between 1.5 and 4.5 [8, 23]. 

In a system of two parallel reactions (Fig. 10.4), selectivity is an important parameter to monitor. The measure of selectivity is defined here as the ratio of isobutene reacted to ethers / total amount of isobutene reacted . Glycerol is consumed only in the etherification reaction, so the selectivity is calculated with respect to isobutene. Depending on the extent of the reaction, the formation of an ether molecule consumes from one to three isobutene molecules, and oligomerization consumes from two to four isobutene molecules [8],... 

In the dimerization of isobutene, tertiary-butyl alcohol (TBA, 2-methyl-2-propanol) has a strong role in modifying the selectivity of the reaction to Cg hydrocarbons and limits further oligomerization to C12 and Ci6 hydrocarbons [34]. Also, in the etherification of glycerol with isobutene the addition of TBA has a clear effect on the selectivity and on hydrocarbon distribution. The selectivity to ethers increased and the fraction of the Cu and Ci6 hydrocarbons decreased while the concentration of TBA was increased from 0 to 2.6 mol.%. As a conclusion, the formation of C12 and C16 hydrocarbons can be prevented in two ways either TBA should be added to the reaction mixture or the reaction should be carried out at high temperatures [8]. 

Modifications in the production of biodiesel can result in valuable glycerol as a byproduct and in fewer separation steps. The modifications studied or considered include combining etherification of glycerol into the biodiesel production process, etherification in situ within the biodiesel process and a biodiesel process with heterogeneous catalyst. 

Acid-catalyzed glycerol etherification probably occurs via an SN1 mechanism, consisting of the consecutive formation of an oxonium and carbenium ion, and its electrophilic attack on a glycerol O atom (Scheme 11.3). 

Fig. TI.2 Sim ultaneous etherification of butadiene oligomers with glycerol. (After [41]).

Figure 2 Creep-recovery tests of chemically treated woods. U, untreated wood Fs, vapor phase formalization F, liquid phase formalization A, acetylation PO, etherification with propylene oxide MG, treatment with maleic acid and glycerol PFl, impregnation with low molecular weight phenol-formaldehyde resin PEG-ICP, impregnation with polyethylene glycol (PEG-IOOO) WPC, formation of a wood- polymer composite (PMMA) WIC, formation of a wood-inorganic material composite.

Synthesis and modification of basic mesoporous materials for the selective etherification of glycerol. 

Glycerol etherification is carried out at 260°C in a batch reactor at atmospheric pressure under N2 in the presence of 2 wt% of catalyst, water being eliminated and collected using a Dean-Stark system. Reagents and products are analysed with a GPC after silylation [5]. Batch processes are generally used in lipochemistry, especially for the esterification and transesterification reactions (except for the preparation of methyl esters). 

Such results strongly suggested that a chemioselective etherification of glycerol occurred in the porous structure of the catalyst which was not reported before. 

Another important etherification is the palladium-catalyzed telomerization of glycerol with butadiene yielding octadienyl ethers of glycerol, which can be used as starting materials for detergents [51, 52]. 

Klepaova, K. D. Mravec E. Hajekova M. Bajus Etherification of glycerol. Petroleum Coal2Wi3, 45, 54-57. 

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