1.CATALYTIC ETHERIFICATION OF GLYCEROL BY TERT-BUTYL
ALCOHOL TO PRODUCE OXYGENATED ADDITIVES FOR DIESEL
FUEL
III. Results and discussion
a. Effect of acidity of solid catalysts on the conversion of glycerol.
Purpose:

Collect the qualitive data approaching the equilibrium composition

Obtain a reliable comparison of the catalytic functionality.
The conversion happened:

At a prefixed time (6 h).

Using different solid acid catalysts were carried out at 0.1 MPa, 343 K, with a tert-butanolto-glycerol molar ratio (RA/G) equal to 4.
A low catalyst/glycerol ratio equivalent to 1.2 wt.% High glycerol conversion.

Using SAC-13, N-17 and HPW-17 catalysts Low glycerol conversion levels (8–15 mol.%)

The Cs-HPW and A-15 samples Higher acid capacity (Table 2)
Reaction takes place at higher ratesThe end of the reaction a glycerol conversion of 54 and
82 mol.%.
b. Effect of acid capacity on characterization of catalysts
The turnover frequency (TOF): a function of the number of acidic sites.
Determination: the initial reaction rate (glycerol conversion <5%) and normalized to the number
of acid sites.

A-15 sample: exhibit a TOF value about 3 times higher.

TOF appears to be comparable on all the systems.

Glycerol etherification (structure sensitive reaction) Considered in a reaction involving
encumbered molecules The accessibility of active sites.

A-15 catalyst An average pore diameter (APD) much higher (300 A˚)
The higher TOF of A-15 catalyst is not due to higher specific activity of acidic sites but
from the accessibility of sites which is favored using macro-porous materials like
Amberlyst.
c. Effect of temperature on glycerol conversion and products distribution
Figure 3.A:

Glycerol conversion linearity increased growing reaction temperature from 10% (303K)85% (363K).

At high temperature (363K): due to the occurrence of de-etherification reactions Glycerol
was not totally converted.
Figure 3.B:

5 different alkyl glycerol ethers could be expected: 3-tert-butoxy-1,2-propandiol (1-MBGE),
2-tert-butoxy-1,3-propandiol (2-MBGE), 1,3-di-tert-butoxy-2-propanol (1,3-DBGE), 1,2-ditert-butoxy-3-propanol (1,2-DBGE) and tri-tert-butoxy propane (TBGE).

The formation of four ethers was observed: two monosubstituted ethers (1-MBGE and/or 2MBGE) and two di-substituted ethers (1,3-DBGE and/or 1,2-DBGE).

Tri-substituted ether never formed in the whole range of temperature investigated.

Due to steric hindrance and electrostatic effects exerted by –OH groups of glycerol  The
electrophilic attack occurs on the primary carbon of glycerol.

1,3-di-tert-butoxy-2-propanol (1,3-DBGE) (the main component) concentration linearly
increased with reaction temperature.

The concentration of 1,2-di-tert-butoxy-3- propanol (1,2-DBGE) reached a maximum value
of 7% at 343 K.
d. Effect of isobutene by dehydrogenation of isobutane
Figure 4.A:

The glycerol conversion is always higher by operating at 1.0 MPa.

The most pressure effect: after 2h Glycerol conversion values increase from 53% (0.1
MPa) to 72% (at 1.0MPa).

No difference in term of glycerol conversion after 6h Reacting system reaches the
equilibrium.
Figure 4.B:

For selectivity to ethers, apart from the reaction pressure, a progressive decreasing in
MBGEs.

Due to steric hindrance No TGBE forms.

Considering the reaction at high rate under pressure Involve the electrophilic attack of a
tertiary carbocationForm ethers via the protonation of both TBA and isobutene.
e. Effect of the catalyst weight on the conversion of glycerol.

Increasing the catalyst weight Limited the growing formation of water The higher
conversion of glycerol.

Under the reaction conditions: due to tert-butanol dehydration A form amount of isobutene
(<5%).

The formation of water No formation of oligomers.
f. Effect of the reaction time on the evolution of reaction catalyst activity.

After 2 hours of reaction: glycerol was almost totally converted and the 1-MBGE was the
main product.

As the reaction proceeded MBGE concentration decreases DBGE concentration
increases.

This transformation occurred at a low rate 50% MBGE selectivity after 30 hours.
The different reaction times, the different evolution of reaction and catalyst activity.