Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
2000-05-16
2003-12-02
Silverman, Stanley S. (Department: 1754)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C210S690000, C210S691000, C210S906000, C588S249000
Reexamination Certificate
active
06656363
ABSTRACT:
The present invention relates to a process for the disposal of organophosphorus compounds contained in an industrial charge.
It is known to use organophosphorus compounds as catalysts, in particular as catalyst ligands. However, during the step in which these catalysts are employed, it is often found that they become partially degraded, with the result that traces of these catalysts are present in the reaction products. This is the case, for example, during the dimerization reaction of acrylonitrile to form 1,4-butenedinitrile, as described in patent U.S. Pat. No. 4,952,541.
Depending on the way in which these products will later be used, it is often preferable to dispose of the catalyst residues which they contain. This is because these residues may, for example, poison and therefore deactivate the catalysts used in later reaction steps.
It may also be recommended to dispose of these residues in such a way that they do not lead to the release of environmentally controlled compounds into the atmosphere or into residual water and/or solvents.
It is also known to use organophosphorus compounds as extracting agents during purification operations involving liquid/liquid extraction: the product to be purified, initially in aqueous solution with the impurities, is transferred into the extracting solvent based on these organophosphorus compounds, while the impurities remain in the aqueous phase. This gives rise to a purified product in the organic phase which is then back-extracted into the aqueous phase. During this back-extraction, some of the organophosphorus-based organic phase can enter the aqueous phase. The product which is obtained, although purified, then contains undesirable organophosphorus traces.
One conventional way of purifying the products consists in distilling the medium containing the phosphorus residues, but an operation of this type is expensive in terms of investment and operation. Furthermore, it is not always possible and, lastly, decomposition of the products to be purified is sometimes found to occur.
In certain cases, an additional liquid/liquid extraction may be carried out, but the solvent enriched with phosphorus compounds then needs to be treated before being discharged or re-used.
It has also been proposed to use ion-exchange resins, such as for example in patent GB-A-2,212,155. These resins have the drawback of being expensive, as well as of exhibiting acidity which may lead to undesired degradation.
In patent U.S. Pat. No. 4,952,541, the phosphorus compounds are disposed of by bringing the reaction medium into contact with an oxidizing agent. However, depending on the nature of the medium to be treated, it may become degraded by the oxidizing agent.
One object of the present invention is therefore to provide a novel process for the disposal of organophosphorus compounds contained in a liquid or gaseous medium.
Another object is to provide a process of this type which does not degrade a liquid or gaseous medium.
To this end, the invention relates to a process for disposing of trivalent and/or pentavalent organophosphorus compounds which comprise at least one carbon atom and are contained in a gas or a liquid, in which the said gas or, liquid is brought into contact with alumina and/or titanium oxide.
The process of the invention therefore consists in bringing the organophosphorus compounds into contact either with alumina or with titanium oxide, or with a mixed compound of alumina and titanium oxide. The reaction involved is an adsorption and/or uptake reaction.
According to a first embodiment, the process employs an adsorbant solely based on alumina.
The invention preferably excludes those processes for the disposal of organophosphorus compounds contained in a gas or liquid with the aid of alumina for which the organophosphorus compounds are phosphites and the gas or liquid is a charge of ethylenically unsaturated monomers, in particular the processes as defined in French patent application No. 97 00623.
The alumina may be in a variety of forms, and may for example be in the form of powders, beads, extrudates, in crushed form or monolith form. If the alumina which is used is in the form of beads, these beads may result from formation by rotary technology or by drop coagulation (referred to as the oil drop method).
The alumina which is used generally has a specific surface of at least 10 m
2
/g, preferably at least 30 m
2
/g, even more preferably at least 70 m
2
/g.
This specific surface is a surface area measured by the BET method. The term surface area measured by the SET method is intended to mean the specific surface determined by the adsorption of nitrogen, in accordance with standard ASTM D 3663-78, drawn up on the basis of the BRUNAUER-EMMETT-TELLER method described in the periodical “The Journal of the American Society”, 60, 309 (1938).
This alumina also generally has a total pore volume (TPV) of at least 0.1 cm
3
/g, preferably at least 0.3 cm
3
/g, even more preferably at least 0.5. This total pore volume is measured in the following way: the values of the grain density and the absolute density are determined: the grain density (Dg) and absolute density (Da) are measured by the picnometry method, respectively with mercury and helium, the TPV is given by the formula:
1
Dg
-
1
Da
.
The processes for preparing aluminas having the total pore volume and specific surface characteristics needed for implementing the process according to the invention are known to the person skilled in the art.
As regards the specific surface, this may in particular be controlled by the temperature at which the alumina is calcined (or activated) after it has been formed.
As regards the pore volume, control over it derives essentially from the selection of the initial alumina used to form it, and the operating conditions under which the alumina is formed. The person skilled in the art will know these conditions.
It is possible to use an alumina comprising at least one compound of an element selected from the group comprising the alkaline metals and the alkaline-earth metals, in particular Na
2
O, but it is preferable for the proportion of this compound to be at most 5% by weight, and preferably at most 2. This is because it has been found that the adsorption may be less efficient when the alumina comprises these alkali or alkaline-earth metals in too high a proportion.
According to a first preferred variant, the alumina is in the form of beads manufactured by rotary technology, or in a crushed form in which the pore volume corresponding to a diameter in excess of 100 Å (V
100 Å
) is at least 0.05 cm
3
/g, preferably at least 0.2 cm
3
/g, and even more preferably at least 0.35 cm
3
/g.
The volume V
100 Å
is measured by the mercury penetration technique in which Kelving's law is applied.
Formation by rotary technology involves aggregation of alumina carried out by contact and rotation of alumina by itself. Examples of machines which may be used for this purpose include rotary granulators and rotating drum machines.
This type of process makes it possible to obtain beads having controlled dimensions and pore distributions, these dimensions and distributions being in general created during the aggregation step.
The porosity can be created in various ways, for example selection of the particle size distribution of the alumina powder or the aggregation of several alumina powders with different particle size distributions. Another method consists in mixing a so-called pore-forming compound with the alumina powder before or during the aggregation step, this compound disappearing completely as a result of heating and thus creating porosity in the beads.
As examples of pore-forming compounds which may be used, mention may be made of wood flour, charcoal, sulphur, tars, plastics or emulsions of plastics such as polyvinyl chloride, polyvinyl alcohols, naphthalene or the like. The amount of pore-forming compounds added is dictated by the desired pore volume.
The alumina powder used as a starting material can be obtained by conventional processes such as th
Laucher Dominique
Nedez Christophe
Rhodia Chimie
Silverman Stanley S.
Vanoy Timothy C.
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