Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-06-03
2001-05-15
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S208000, C526S213000, C526S315000, C526S318100, C526S318200, C526S318250
Reexamination Certificate
active
06232412
ABSTRACT:
The present invention relates to build-up suppressor agents and compositions containing such suppressor agents, which are capable of inhibiting the formation of build-up in vinyl acetate or vinyl chloride polymerization processes, or in polymerization processes utilizing a mixture thereof, with or without other vinyl monomers polymerizable therewith, which processes are effected in aqueous suspension, aqueous emulsion or in bulk.
In all the above polymerization processes, part of the formed polymer tenaciously adheres to the reactor walls, thus forming so-called “build-up” (otherwise said “scale”), with deleterious effects toward both the final product itself, due to small fragments of build-up which, by detaching from the reactor walls, can be included in the polymerized product and the safety of the reaction because the build-up slows the thermal exchange of the wall giving rise to safety problems due to overheating.
This build-up is a drawback for the polymerization operations since it is necessary to clean the walls after each repeated reaction.
This cleaning is costly as it decreases the plant output and is dangerous for the operators due to the toxicity of the monomers, particularly vinyl chloride.
A number of products and techniques have been developed to mitigate this problem, all of which are based on coating the reactor walls with products which should inhibit adhesion of the build-up or even its formation, as an example by preventing the polymerization of the monomers on the reactor walls. Phenol-formaldehyde condensation products (GB 1439339; JP 54-107991; CA 1181899; EP 0052421) or dye mixtures (alizarin, xanthones, natural flavonoids, naphthoquinones, hydroxyanthraquinones and others) with film-forming elements such as polysaccharides, polyvinyl alcohols, polyvinylpyrrolidone were proposed as reactor wall coating. See for example patents JP 04342701; JP 04154804; JP 04154801; JP 04154805; JP 04108805; JP 04159302 and JP 04031402.
EP 0 614 915 suggests the use of condensation product between quinones and heterocyclic compounds having at least two amino groups, whereas in EP 0 606 013 there are described, among others, condensation products between quinones and particular diamino-diphenyls substituted with carboxylic or sulfonic groups. Finally, in EP 0 695 761, it is described the use of products obtained by condensing a “phenol” compound, such as, for example, phenol or 1-naphthol, in the presence of an aliphatic bicarboxylic acid.
The products more widely used seem to be those described in EP 0 052 421. However, although remarkable results as to suppression of build-up formation are achieved, those agents do not allow carrying out an appreciable number of repeated polymerizations.
All these build-up suppressor agents can be applied in a number of manners, which depend on the nature of the product and on their capacity of adhering to the reactor walls.
The more common methods provide coating by painting or spraying, in which case it shall be necessary to prepare suitable solutions of the same products, for example aqueous solutions. In case of spraying, nitrogen or water vapour at 5-15 bar pressures can be used as propellant.
As said above, the performances of these products can be enhanced with the use of film-forming agents such as, for example, polysaccharides or highly hydrolyzed polyvinyl alcohols.
It has now been found, and this is an object of the present invention, that build-up suppressor agents particularly effective in polymerization processes of vinyl chloride or of vinyl acetate, or of mixtures thereof, in the presence or in absence of other monomers or polymers polymerizable with them, comprise condensation products among an aldehyde (A), a phenol compound (B) and an aromatic carboxylic acid hydroxy-substituted on the aromatic nucleus (C). These agents, as such or in the form of compositions suitable for coating, have demonstrated to be capable of suppressing in a practically complete manner, the build-up formation on the inner reactor walls and, in general, of reaction systems, also when applied in amount definitely lower than those normally used, as well as to allow the carrying out of repeated polymerizations without having to apply, each time, the agents before each run and without noticing significant variations of build-up formation between the first and the last reaction.
These agents are endowed with another favourable characteristic, i.e. they have a reduced sensitivity with respect to pH variations in polymerization processes, and possess a remarkable shelf-life.
Moreover, the polymers obtained show better physical characteristics.
Therefore, a further object of the present invention comprises compositions containing one or more of the above build-up suppressor agents.
Another object of the present invention is the use of one or more of the above build-up suppressor agents in polymerization processes of vinyl chloride or of vinyl acetate, or of their mixtures, in presence or in absence of other monomers or polymers polymerizable with them.
Still another object of the present invention is a method for suppressing build-up formation in polymerization processes of vinyl chloride or of vinyl acetate, or of their mixtures, in presence or in absence of other monomers or polymers polymerizable with them, which comprises coating the inner walls of a polymerization reactor with one or more of the above build-up suppressor agents.
The present invention further comprises a polymerization process of vinyl chloride or vinyl acetate, or their mixtures, in the presence or in absence of other monomers or polymers polymerizable with them, effected in a reactor whose inner walls are coated with one or more of the above build-up suppressor agents, and the polymers obtained by means of said process.
Finally, a further object of the present invention is a polymerization reactor whose inner walls are coated with one or more of the above build-up suppressor agents.
Compound (A) can be any aldehyde capable of condensing at the ortho- and/or para-positions with respect to a hydroxyl present on an aromatic nucleus. Many aldehydes showed themselves suitable to this purpose. Preferably, formaldehyde, or its precursors, such as paraldehyde or paraformaldehyde, aliphatic aldehydes having from 2 to 5 carbon atoms, benzaldehyde or heterocyclic aldehydes such as, for example, furfurol are used. A phenol compound (B) can be any mono- or polyhydroxylated phenol in which at least two of the ortho- and/or para-positions with respect to the hydroxy group or groups are free, for example, phenol, cresol, ethylphenol, resorcinol, pyrocathecol, hydroquinone, pyrogallol or bisphenol A, or a compound of formula (I):
wherein m is 1, 2 or 3, and R and R
1
are independently selected from the group consisting of hydrogen, halogen, (C
1-5
) alkyl, hydroxy and carbo(C
1-5
)alkoxy. Phenol, resorcinol or 1-naphthol are preferably used. Finally, compound (C) is a hydroxylated aromatic carboxylic acid of formula II:
wherein R
2
is selected from the group consisting of hydrogen, hydroxy, (C
1-5
) alkoxy, (C
1-5
) alkyl, hydroxy (C
1-5
) alkyl, halogen, phenyl and hydroxyphenyl; R
3
has the same meanings of R
2
with the exclusion of hydrogen; x and the dotted lines, taken together, represent either a divalent residue ortho-condensed with the benzene ring of formula III:
wherein p is an integer selected from 1 or 2, or they represent nothing; with the following provisos:
a) when x and the dotted lines, taken together, represent the residue of formula III, at least two of the ortho- and/or para-positions with respect to the hydroxyl group or groups must be free;
b) when x and the dotted lines, taken together, represent nothing, at least one of R
2
or R
3
represent hydroxy, and at least two of the ortho- and/or para-positions with respect to the hydroxyl group or groups must be free.
Preferably, monohydroxy benzoic acids are used such as, for example, salicylic acid and 4-hydroxy-benzoic acid, dihydroxy benzoic acids such as, for example &agr;-, &bgr;- and &ggr;-resorcylic acids, 2,3-dih
Raspanti Giuseppe
Russo Matteo Zanotti
3V Inc.
Birch & Stewart Kolasch & Birch, LLP
Harlan R.
Wu David W.
LandOfFree
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