Vol. 28, No. 12 (2016)
Hydrogenolysis of Glycerol using Fe-Fe/Al2O3 Complex Catalyst 2597
other metal-acid bifunctional catalyst systems. In spite of
several research efforts, drawbacks of existing technologies
for production of 1,2-propane diol have been limited to the
laboratory scale only. The hydrogenolysis of dilute solutions
of glycerol (10-30 % w/w) has been carried out in a pressure
range of 10-32 MPa and temperature range of 200-350 °C
and the reaction gave low selectivity towards propylene glycol.
High selectivity towards ethylene glycol and other byproducts
like lactic acid, acetol, acrolein and degradation products like
propanol, ethanol, methanol and methane is reported in the
literature. Among the metals used as catalyst, copper has been
effective in reducing the reaction temperature and pressure.
Dasari et al. [10] found Raney Ni with copper to be an efficient
catalyst. They also suggested that high concentration of
glycerol in feed gives higher conversion of glycerol and higher
yield of 1,2-propanediol. Miyazawa et al. [12] have shown
that higher concentration of glycerol in feed would give more
waste products and smaller conversion of glycerol on hydro-
genolysis over Ru/C. The literature suggested that the following
metals are of prime importance viz., nickel, copper, platinum,
palladium and ruthenium. Platinum, palladium and ruthenium
being noble metals, their use would greatly alter the economics
of the process, hence in this, work homonuclear bimetallic
complex catalyst Fe-Fe/L1 was prepared and catalytically
tested.
(645 mL). 160 mL acetic acid is taken in a 3-necked reactor
vessel of 2 L volume, which is equipped with a stirrer, an
addition funnel and a water-cooled reflux condenser. The
sodium dichromate is dissolved in remaining acetic acid (485
mL) and introduced through the addition funnel drop wise
with stirring for about 40 min at 110 °C. The reaction mixture
is cooled, filtered and washed with water to get green coloured
crystals of tosylated dialdehyde.
Tosylated dialdehyde (250 g) is taken in a 5 L beaker
and 900 mL of H2SO4 is added. This mixture is stirred for 1 h
and ice-water slurry is added till the volume becomes 4 L. The
precipitated material is collected by vacuum filtration, washed
with water and dried. This is dissolved in toluene and the liquid
is recrystallized which yields brownish yellow coloured needle
like crystals (Scheme-I). The product obtained is 2,6-diformyl-
4-methylphenol. The melting point of this compound was
determined to be 130 °C.
Synthesis of Fe-Fe complex: The complex is synthesized
in three steps. In the first step, in a 250 mL conical flask 2,6-
diformyl-4-methylphenol (0.95 g, 0.012 mol) and N,N-dimethyl
formamide (50 mL) are taken in a 250 mL conical flask and
1,2-phenylenediamine (0.65 g, 0.006 mol) is added. To this
solution ferric nitrate (0.65 g, 0.006 mol) is added and the
solution is stirred till the entire ferric nitrate dissolves comp-
letely. The solution is kept for 1 h and diethyl ether is added
later in it. Precipitation begins and the precipitate is filtered
and dried. In the second step, this dried material (2.14 g, 0.005
mol) and cupric acetate (1.597 g, 0.008 mol) are taken in a
250 mL conical flask and dissolved in 20 mL methanol. The
solution is stirred for 0.5 h and crystals of complex appear.
These are collected by filtration and washed with diethyl
ether and dried. The dried material (1.871 g, 0.0036 mol) is
then dissolved in 30 mL methanol and 1,2-phenylenediamine
(0.336 g, 0.336 mol) is added to it. A brown precipitate is
formed which is washed with diethyl ether and dried in a
vacuum desiccator (Scheme-II).
Loading of Fe-Fe complex on alumina: The aluminum
oxide (approximately) 9 g is dissolved in 20 mL of deionized
water. 1 g of powdered catalyst is then mixed with the resulting
aqueous alumina solution and is stirred in magnetic stirrer at
80 °C for 0.5 h. The resulting mixture is then dried at 160 °C
in oven for 4 h, followed by calcinations at 320 °C for 3 h.
Reaction procedures: A high pressure batch reactor made
of stainless steel (300 mL) is used for carrying out the hydro-
genolysis reactions. The reactor is equipped with a pressure
gauge, a thermocouple, gas delivery system and provision for
sampling. An on/off controller is used for controlling the
temperature with a chrome alloy thermocouple for temperature
sensing. The reactor was operated in batch wise mode with
initial feeding of glycerol solution, hydrogen gas and the
catalyst before heating is started.
EXPERIMENTAL
The chemicals sodium dichromate, p-cresol, 4-toluene
sulfonyl chloride, sodium azide, benzene, benzoyl chloride,
anhydrous diammonium hydrogen orthophosphate and
m-phenylene diamine were purchased from Loba Chemie,
Mumbai. Sodium hydroxide, sodium chloride, toluene, isopro-
panol, glycerol, methanol, formaldehyde, N,N-dimethyl form-
amide and 1,2-dichloroethane were procured from Qualigens
Fine Chemicals, Mumbai. Analytical grade of anhydrous
ammonium molybdate [(NH4)2Mo7O24·4H2O] was purchased
from Samir Tech-Chem Pvt. Ltd., Vadodara, ferric nitrate
[Fe(NO3)3] from Ranbaxy Fine Chemicals Ltd.
Preparation of 2,6-diformyl-4-methylphenol: About
33 % NaOH solution is prepared by dissolving 100 g of NaOH
in 400 mL water and 126 g (2 mol) of p-cresol is added which
forms a golden yellow coloured product.A 37 % formaldehyde
solution is added to this mixture and stirred for 0.5 h and left
for 24 h at ambient temperature (35 °C). This mixture is filtered
by vacuum filtration and the filtrate obtained is washed with
saturated solution of sodium chloride. The product obtained
is 2,6-dimethylol-4-methyl phenol. A 1300 mL water and
130 mL of 33 % NaOH are added to 2,6-dimethylol-4-methyl
phenol taken in a round-bottomed flask and stirred. A 494 g
(2.6 mol) of p-toluene sulfonyl chloride dissolved in toluene
is added to the above and stirred for 20 h at room temperature.
An aqueous and emulsified phase is formed. This mixture is
kept in an ice bath and toluene is added till solids are formed.
A white solid is called tosylated phenol is formed which is
separated by vacuum filtration and washed with toluene and
dried, forming 272 g of product (m.w. 338).
The reactor is initially charged with 200 mL of aqueous
glycerol and 2 g of catalyst. It is then pressurized with 0.35 MPa
of hydrogen gas and then heated to the required temperature
for the desired reaction time. Every reaction is carried out for
8 h. The product samples are withdrawn at regular intervals of
0.5 h by means of a needle valve. The quantity withdrawn
is less than 1 mL so that the total change in volume can be
The tosylated phenol (272 g, 0.8 mol) is now oxidized
with sodium dichromate (208 g, 0.69 mol) and acetic acid
Lal, Sunder
