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As early as in 1931, Adkins [12] discovered a copper-
ratio composition used to give the final synthesis catalyst is
Cu:Zn = 3:2. After dissolving Cu(NO3)2ꢀ3H2O and
Zn(NO3)2ꢀ6H2O in 500 mL of de-ionized water, a desired
amount of aqueous solution of Na2CO3 was added under
vigorous stirring at 50 °C. The resulting precipitate was
washed repeatedly with de-ionized water after the filtration
of the suspension. After overnight drying at 110 °C, the
solid was crushed and pelleted by adding 2 wt% of
graphite. The pellet was reduced under 10 mL/min of
hydrogen by heating to 240 °C at a rate of 5 °C/h and then
cooled to room temperature under the atmosphere of
hydrogen. The obtained catalyst was then transferred in
nitrogen atmosphere and stored in dodecyl methyl ester
before use.
chromium (Cu/Cr) catalyst for hydrogenation of ethyl
ester. Similar catalysts are still frequently used for hydro-
genation of fatty ester [13–15]. Nowadays, the catalysts
containing chromium is not environmentally benign
because of the releasing of environmental hazard Cr6? in
the process of the Cu/Cr catalyst preparation. Researches
were therefore focused on the replacement of chromium by
zinc [16], manganese [17], iron [18] or other promoters
[19, 20]. Cu/Zn catalyst is the commonly used one among
those catalysts. However, natural oils, the best alternative
to the raw materials for preparation of FOH, always contain
various impurities which are harmful to the catalyst per-
formance and difficult to be removed from fatty esters.
Some of the impurities are from the growing process of the
plants or usage of pesticides, and others may from the
process of fatty ester preparation [9, 21]. Even trace of
these impurities in the feedstock may act as the catalyst
poisons, which would cause catalyst deactivation and
shorten the lives of the catalyst, e.g., typical operating lives
of Cu/Zn catalysts in large plants varies from 3 to 6 months
depending on the process concerned and the actual plant
configuration [21, 22]. Catalyst deactivation is a problem
of great and continuing concern in the practice of industrial
FOH processes. Costs to industry for catalyst replacement
and process shutdown total millions of dollars per year.
Chlorides are known to be a particularly virulent poison
for Cu catalysts [4], and this is important with catalysts for
the low-temperature water–gas shift reaction. In practice,
the only halide usually encountered in hydrogen and
ammonia plants is chloride in the form of HCl. To the best
of our knowledge, little is known about the nature of the
chlorides present in fatty methyl ester feedstocks prepared
from natural fats and oils, possible candidates are mono-
and dialkyl chlorides [23–25].
2.2 Catalytic Reactions
Catalyst deactivation experiments were carried out in a 1-L
stirred autoclave reactor. The experimental conditions,
such as the effects of agitation rate, reaction time, catalyst
load in FAME, reaction temperature, and hydrogen pres-
sure were systematically optimized during preliminary
tests. Results indicated that mass transfer resistance could
be eliminated with an agitation rate over 600 rpm, the best
performance of Cu/Zn catalyst could be reached at the
reaction temperature of 240 °C and at the hydrogen pres-
sure of 21 MPa, and the conversion of methyl laurate, as
well as the selectivity of methyl laurate to lauryl alcohol,
increased with reaction time (from 0 to 5 h) and catalyst
added in FAME substrate (from 0 to 2.5 wt%), respec-
tively, and then kept stable with further increment of
reaction time and catalyst load in FAME. Therefore,
experimental runs typically consisted of charging the
reactor with about 400 g catalyst-ester slurry with a weight
ratio of 0.025 and varying amount of chlorides, followed
by purging the autoclave three times with hydrogen and
raising the pressure to about 4 MPa. The reactor temper-
ature was then raised to 240 °C and the hydrogen pressure
was increased to 21 MPa with continuous supply of
hydrogen. After reaction with the agitation of 750 rpm for
300 min, the heater was removed and the temperature
decreased rapidly with the reactor cooled to room tem-
perature, then the gas was released slowly. The liquid
samples were analyzed by a GC equipped with a flame
ionization detector (FID), where 1-octanol was used as the
internal standard compound for analysis. All reactants were
identified by Micromass GCTTM GC-mass spectroscopy.
The reaction equation can be generalized according to:
In this work, the effects of mono- and dialkyl chlorides
on the physical and chemical properties of Cu/Zn catalyst,
prepared by co-precipitation method, were investigated.
This kind of information is of pivotal importance for the
design of deactivation-resistant catalysts, the operation of
industrial chemical reactors, and the study of specific
reactivating procedures. The hydrogenation of methyl
laurate to dodecanol was taken as a model reaction.
2 Experimental
2.1 Catalyst Preparation
R-COOCH3 þ 2H2 ! R-CH2OH þ CH3OH
where R represents CH3(CH2)10.
ð1Þ
The copper zinc catalyst was prepared by parallel co-pre-
cipitation method according to the literature [21]. Mole
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