Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-07-12
2001-11-06
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S721000, C568S722000, C568S723000, C568S724000, C568S725000, C568S774000, C568S776000, C568S779000
Reexamination Certificate
active
06313355
ABSTRACT:
OTHER COMMONLY-OWNED COPENDING APPLICATIONS
Reference is also made to other commonly-owned copending U.S. application Ser. Nos. 09/288,195, filed Apr. 8, 1999 and 09/407,314, filed Sep. 28, 1999.
TECHNICAL FIELD
This invention relates to novel, highly efficient processes for the preparation of tetrabromobisphenol-A.
BACKGROUND
Tetrabromobisphenol-A is one of the most widely used brominated flame retardants in the world. It is used extensively to provide flame retardancy for styrenic thermoplastics and for some thermoset resins.
Processes used for producing tetrabromobisphenol-A generally fall into three categories. The first category includes processes in which substantial amounts of methyl bromide are co-produced along with the tetrabromobisphenol-A. Generally, up to 40-50 pounds of methyl bromide can be expected per 100 pounds of tetrabromobisphenol-A produced. In most cases, the processes within this first category feature reacting bisphenol-A and bromine in methanol. The ring-bromination of the bisphenol-A is a substitution reaction which generates one mole of HBr per ring-bromination site. Thus, for the production of tetrabromobisphenol-A, four moles of HBr are generated per mole oftetrabromobisphenol-A produced. The HBr in turn reacts with the methanol solvent to produce the methyl bromide co-product. After the bisphenol-A and bromine feed are finished, the reactor contents are cooked for one to two hours to complete the reaction. At the end of the reaction, water is added to the reactor contents to precipitate out the desired tetrabromobisphenol-A product.
The second category of processes features the production of tetrabromobisphenol-A without the co-production of substantial amounts of methyl bromide and without the use of oxidants to convert the HBr to Br
2
. See for example U.S. Pat. No. 4,990,321; U.S. Pat. No. 5,008,469; U.S. Pat. No. 5,059,726; and U.S. Pat. No. 5,138,103. Generally, these processes brominate the bisphenol-A at a low temperature, e.g., 0 to 20° C., in the presence of a methanol solvent and a specified amount of water. The water and low temperature attenuate the production of methyl bromide by slowing the reaction between methanol and HBr. The amount of water used, however, is not so large as to cause precipitation of the tetrabromobisphenol-A from the reaction mass during the bromination reaction. Additional water for that purpose is added at the end of the reaction. This type of process typically uses a fairly long aging or cook period after the reactants have all been fed, and requires additional process time for the final precipitation of tetrabromobisphenol-A via the last water addition.
In the third category are those processes which feature the bromination of bisphenol-A with bromine in the presence of a solvent and, optionally, an oxidant, e.g., H
2
O
2
, Cl
2
, etc. See for example U.S. Pat. No. 3,929,907; U.S. Pat. No. 4,180,684; U.S. Pat. No. 5,068,463 and Japanese 77/034620 B4 77/09/05. The solvent is generally a water-immiscible halogenated organic compound. Water is used in the reaction mass to provide a two-phase system. As the bisphenol-A is brominated, the tetrabromobisphenol-A is formed in the solvent. The co-produced HBr is present in the water. When used, the oxidant oxidizes the HBr to Br
2
, which in turn is then available to brominate more bisphenol-A and its under-brominated species. By oxidizing the HBr to Br
2
, only about two moles of Br
2
feed are needed per mole of bisphenol-A fed to the reactor. To recover the tetrabromobisphenol-A from the solvent, the solution is cooled until tetrabromobisphenol-A precipitation occurs. The cooling of the solution to recover tetrabromobisphenol-A entails additional expense and process time.
Process technology for producing tetrabromobisphenol-A is described in commonly-owned U.S. Pat. Nos. 5,527,971, 5,723,690, 5,847,232, 6,002,050, 6,084,136, and 6,084,137, and in commonly-owned U.S. patent application Ser. Nos. 09/288,195, filed Apr. 8, 1999, 09/329,374, filed Jun. 10, 1999, 09/407,314, filed Sep. 28,1999, and 09/416,855, filed Oct. 12, 1999.
THE INVENTION
This invention makes it possible to produce tetrabromobisphenol-A on a continuous basis wherein the use of bromine feeds can be eliminated or at least greatly minimized, wherein steady state operation can be rapidly achieved after plant startup, and wherein such steady state operation can be maintained with minimal process controls. At the same time these objectives can be achieved without sacrifice of other advantageous features of the commonly-owned technology, such as forming during the bromination precipitated tetrabromobisphenol-A that is highly pure, of minimal, if any, color, readily recoverable, and formed in high yield based on the bisphenol-A fed to the reaction.
The processes of this invention thus feature the efficient production of high-quality, low-color tetrabromobisphenol-A in high yields under operating conditions that avoid localized concentrations of bromine in the reaction mass and that make possible the maintenance of a bromination reaction mass of substantially uniform composition throughout substantially the entire bromination reaction. Although the processes of this invention can be run in a semi-continuous mode, the greatest benefits are achievable when the operation is conducted in a continuous mode. When run in a semi-continuous mode, process efficiency is enhanced due to relatively short reaction times and the absence of a need for a time-consuming one hour plus post-reaction cook period or a post-reaction tetrabromobisphenol-A precipitation step. The use of a continuous process for the production of tetrabromobisphenol-A is a rarity in itself and is made possible by the short reaction and tetrabromobisphenol-A precipitation times which are features of processes of this invention. In the continuous mode, reactor size can be substantially reduced without a loss in product output.
In addition to the above reaction efficiencies, the processes of this invention are capable of producing high yields of tetrabromobisphenol-A in a methanol- or ethanol-based solvent without the substantial concomitant production of methyl bromide or ethyl bromide, e.g., as little as 0.2 to 1.0 lbs (ca. 0.09 to ca. 0.45 kg) of methyl bromide or ethyl bromide per 100 lbs (ca. 45.4 kg) of tetrabromobisphenol-A product. Even further, it is possible to obtain high yields of almost pure white tetrabromobisphenol-A even though excess unreacted bromine is present in the reaction mass during substantially all of the time steady state bromination conditions have been established.
Pursuant to this invention there is provided in one of its embodiments a process of producing tetrabromobisphenol-A, which process comprises:
a) concurrently feeding to a reactor (i) a first continuous feed stream composed of bisphenol-A and/or underbrominated bisphenol-A and a water-miscible organic solvent, (ii) a second continuous feed composed of gaseous hydrogen bromide and/or aqueous hydrobromic acid, and (iii) a third continuous feed composed of aqueous hydrogen peroxide, at relative rates that maintain in the reactor during at least a substantial portion of such concurrent feeding, a reaction mass having a liquid phase containing from above about 15 to about 85 wt % water, and preferably in the range of about 30 to about 85 wt % water, the wt % being based upon the amount of water and water-miscible organic solvent in the liquid phase of the reaction mass;
b) during at least a substantial portion of the concurrent feeding in a), maintaining the temperature of the reaction mass within the range of about 30 to about 100° C.;
c) during at least a substantial portion of the concurrent feeding in a), providing the continuous feeds at relative rates (i) that maintain in the liquid phase of the reaction mass an amount of unreacted bromine that is in excess over the stoichiometric amount theoretically required to convert the bisphenol-A and/or underbrominated bisphenol-A to tetrabromobisphenol-A, and to continuously form during substantially all of the time th
Barton Randall S.
Holub Richard A.
Manimaran Thanikavelu
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