Compositions – Heat-exchange – low-freezing or pour point – or high boiling... – Organic components
Patent
1985-09-18
1987-03-10
Wax, Robert A.
Compositions
Heat-exchange, low-freezing or pour point, or high boiling...
Organic components
252 783, 528 10, 556449, C09K 500
Patent
active
046489827
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to stabilizers for silicates used in antifreeze compositions, and in particular, for antifreeze compositions based on alkylene glycols.
It is known that alkali metal silicates are effective corrosion inhibitors for metal alloys, e.g. aluminium alloys. It has therefore been desirable to use alkali metal silicates in antifreeze formulations. However, alkali metal silicates tend to form gels in the presence of alkylene glycols which are also normally present in antifreezes. Thus, it has been previously proposed to use a stabilizer to prevent the gelation of the alkali metal silicate in the antifreeze composition.
Several types of silicon compounds have hitherto been described as suitable stabilizers. For instance, U.S. Pat. Nos. 3,234,144 and 4,241,012 describe the use of amino-siloxanes as stabilizers; U.S. Pat. Nos. 3,312,622 and 4,241,011 discloses carboxy siloxanes as suitable stabilizers; and U.S. Pat. Nos. 3,337,496 and 4,210,548 recommend the use of hydroxyalkyl derivatives of siloxanes.
One of the major problems with the previously described stabilizers is that they do not have adequate solubility in the alkylene glycol and/or water which form the basis of the antifreeze composition.
Moreover, the low solubility of conventional stabilizers makes it particularly difficult to produce the corrosive inhibitors in concentrated form. Such concentrates, containing large amounts of inhibitors in alkylene glycol (e.g. near the solubility limits), are generally not stable from gelation over storage period of several months. Thus, it would be highly desirable to develop stabilizers which would allow the production of inhibitor concentrates which could be stored for long periods and then blended as desired into antifreeze compositions.
It has now been found that the solubility problems encountered with prior art stabilisers can be mitigated by using polyoxyalkylene derivatives of siloxanes. Moreover, by incorporating a polyalkylene oxide into the siloxane molecule, the stabilisers have improved effectiveness for retarding gelation in concentration inhibitor compositions.
Accordingly, the present invention provides a stabiliser for silicate corrosion inhibitors useful in polyalkylene glycol compositions comprising an organosiloxane containing a polyoxyalkylene end chain of the general formula:
Also provided in a separate embodiment is a organosiloxane compound of the general formula: SiO.sub.1.5 (II)
In still another embodiment, the present invention provides an antifreeze composition comprising an alkylene glycol, a silicate corrosion inhibitor and the stabiliser of formula II.
The polyoxyalkylene end chain is as illustrated in formula I where n is a number from 2 to 4, preferably 2 and x is a number from 5 to 10, preferably 6 to 9 when n is 2. Most preferred are stabilisers of formula I wherein n is 2 and x is from 6 to 9.
The stabiliser of this invention is generally prepared by reaction of appropriate polyalkylene glycol with a gamma glycidyl oxyalkyl trialkoxysilane at elevated temperatures and atmospheric pressures.
In a preferred technique, the stabiliser is prepared by reacting glycidyl oxypropyl trimethoxysilane (GOTS) with a molar excess of the appropriate polyoxyalkylene glycol, for example 1 mole of GOTS with 5.3 moles of polyethylene glycol (in excess of stoichiometric amount to avoid polymer formation). The reaction is suitably carried out in a liquid medium and in an inert atmosphere. The reaction is conducted at a temperature from 80.degree. C. to 200.degree., preferably from 100.degree. C. to 150.degree. C. and at atmospheric pressure in the presence of a hydroxide catalyst (preferably sodium or potassium hydroxide). The polyoxyalkylene derivative of GOTS so formed can be used as such, without any further treatment. GOTS is commerically available from Dynamit Nobel and Union Carbide.
The amount of the inventive stabiliser used in an antifreeze composition will depend upon the anti-corrosive formulation and in particular the amount of corrosion inhibitor but is suitabl
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BP Chemicals Limited
Wax Robert A.
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