2.1.4. Esterification
The fatty acids recovered as described in Section 2.1.3 were
esterified using p-toluene sulphonic acid dissolved in methanol
as catalyst. The reaction was conducted at 60 C with vigorous stirring
for 135 min. The ethanol/oil ratio loaded in the reactor was selected
depending on the initial acidity of the raw material. In the
case of the fatty acids recovered from the glycerine phase, the following
conditions were used for soybean oil and beef tallow,
respectively: 60% and 40% v/v of ethanol (referred to the volume
of oil), and 0.66% and 0.56% v/v of p-toluene sulphonic acid (relative
to the total volume loaded into the reactor, i.e. ethanol plus
oil). After esterification, the system was allowed to settle. The
upper phase containing mainly ethanol, p-toluene sulphonic acid
and water, was fed to the ethanol recovery step. The lower phase
was a mixture of ethyl esters and glycerides. This product was
mixed with the feed of the transesterification reactor, in which
the acylglycerides fraction was converted into ethyl esters. The
acidity was measured as a function of time in small aliquots of
the reaction mixture retrieved from the reaction vessel. The acidity
was determined as prescribed in European standard EN 14104,
after the sample was washed with cold water and centrifuged at
3500g for 2 min, in order to eliminate the catalyst. Measurements
were carried out in duplicate, and fell within a 15% interval of the
average value. Two analysis of acidity determined on the same
sample did not differ by more than 5%.
2.1.4. Esterification
The fatty acids recovered as described in Section 2.1.3 were
esterified using p-toluene sulphonic acid dissolved in methanol
as catalyst. The reaction was conducted at 60 C with vigorous stirring
for 135 min. The ethanol/oil ratio loaded in the reactor was selected
depending on the initial acidity of the raw material. In the
case of the fatty acids recovered from the glycerine phase, the following
conditions were used for soybean oil and beef tallow,
respectively: 60% and 40% v/v of ethanol (referred to the volume
of oil), and 0.66% and 0.56% v/v of p-toluene sulphonic acid (relative
to the total volume loaded into the reactor, i.e. ethanol plus
oil). After esterification, the system was allowed to settle. The
upper phase containing mainly ethanol, p-toluene sulphonic acid
and water, was fed to the ethanol recovery step. The lower phase
was a mixture of ethyl esters and glycerides. This product was
mixed with the feed of the transesterification reactor, in which
the acylglycerides fraction was converted into ethyl esters. The
acidity was measured as a function of time in small aliquots of
the reaction mixture retrieved from the reaction vessel. The acidity
was determined as prescribed in European standard EN 14104,
after the sample was washed with cold water and centrifuged at
3500g for 2 min, in order to eliminate the catalyst. Measurements
were carried out in duplicate, and fell within a 15% interval of the
average value. Two analysis of acidity determined on the same
sample did not differ by more than 5%.
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