Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 12, pp. 1814−1819.
Pleiades Publishing, Ltd., 2012.
Original Russian Text © N.V. Nikolenko, A.O. Kosynyuk, Yu.V. Kalashnikov, E.A. Cheremis, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85,
No. 12, pp. 1924−1930.
AND INDUSTRIAL INORGANIC CHEMISTRY
The Calculation of the Thermodynamic Equilibrium
O System and Determination
of Reasonable Conditions for Iron Molybdate Deposition
N. V. Nikolenko, A. O. Kosynyuk, Yu. V. Kalashnikov, and E. A. Cheremis
Ukrainian State Chemical Technology University, Dnipropetrovsk, Ukraine
Received August 22, 2011
Abstract—The thermodynamic data on the Fe
O system were analyzed. The iron(III)
molybdate precipitates were studied by the X-ray phase analysis and electron probe microanalysis. It was shown
that the content of the iron(III) oxide impurity in the precipitates depends on method and conditions of mixing of
an iron precursor solution and an molybdenum precursor solution.
The major problem in the production of formaldehyde,
urea–formaldehyde concentrate, and formaldehyde resins
concerns formaldehyde and formic acid impurities, which
are present in formalin and affect quality of the products.
In the absence of methanol, which is a stabilizer, formalin
rapidly polymerizes, which is inconvenient for transporta-
tion and storage. Abroad, the formaldehyde production and
application is realized at integrated plants within single eco-
nomic complex. The development of such plants requires
use of low power equipment for formaldehyde synthesis
with an annual capacity of 25–100 tons per year .
The most economical route to produce methanol–free
formalin with a low content of formic acid impurity is
methanol oxidation in excess air oxygen on iron mo-
lybdenum oxide catalyst . Though this catalyst is
successfully used in industry, studies on its properties
and improvement are continuing [3–7]. The iron mo-
lybdenum catalyst is iron (III) molybdate with excess of
molybdenum(VI) oxide. It is well established that one of
the main factors responsible for its selectivity in partial
oxidation of alcohols is presence of iron oxide as indi-
vidual phase [3–5]. Therefore, the industrial synthesis of
the catalyst includes prolonged (up to 48 h) annealing at
500°C as necessary stage. The solid-phase reactions pro-
ceeding between iron(III) and molybdenum(VI) oxides
upon annealing result in complete removal of impurities
of iron oxide compounds from the catalyst.
Evidently, to reduce the cost of this stage of the syn-
thesis, the content of impurities of iron oxide compounds
must be minimal even at the stage of the iron molybdate
deposition. Therefore, it is of interest to evaluate both
theoretically and experimentally the possible content of
impurity phases in relation to the deposition conditions of
The study is concerned with the thermodynamic
solubility diagrams of the precipitates (iron molybdate,
hydrated molybdenum (VI) oxide, and iron(III) hydrox-
ide) in aqueous solutions. We used in the calculations
experimental data on the concentrations of saturated
solutions and reference data on the thermodynamic equi-
librium constants for the dissolution of iron hydroxide,
complex formation between iron(III) cations and OH ions
and for the dissociation of molybdic acid. The results of
the thermodynamic equilibrium calculation in the Fe
O system are considered with due to
regard for the peculiar features of the heterogeneous pro-
cess with mass transfer as predominant mechanism. The
study performed allowed determination of the optimum
conditions of the iron molybdate deposition, providing the
lowest content of the impurity phase of iron hydroxide.
The solubility S of the iron(III) molybdate precipitate