U.S. patent application number 09/729021 was filed with the patent office on 2002-06-06 for process for preparing phosphoric acid esters.
Invention is credited to Backer, Werner, Chrisochoou, Andreas, Hallenberger, Kaspar, Heinz, Dieter, Janke, Nikolaus, Pech, Reinhard.
Application Number | 20020068835 09/729021 |
Document ID | / |
Family ID | 7659935 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020068835 |
Kind Code |
A1 |
Janke, Nikolaus ; et
al. |
June 6, 2002 |
PROCESS FOR PREPARING PHOSPHORIC ACID ESTERS
Abstract
The present invention relates to a process for preparing
phosphoric acid esters, in particular monomeric bisaryl
diphosphates, or bridged phosphates.
Inventors: |
Janke, Nikolaus; (Dormagen,
DE) ; Pech, Reinhard; (Haan, DE) ;
Chrisochoou, Andreas; (Koln, DE) ; Heinz, Dieter;
(Levekusen, DE) ; Backer, Werner; (Wipperfurth,
DE) ; Hallenberger, Kaspar; (Leverkusen, DE) |
Correspondence
Address: |
Patent Department
Bayer Corporation
100 Bayer Road
Pittsburgh
PA
15205-9741
US
|
Family ID: |
7659935 |
Appl. No.: |
09/729021 |
Filed: |
December 4, 2000 |
Current U.S.
Class: |
558/92 |
Current CPC
Class: |
C07F 9/1406 20130101;
C07F 9/12 20130101 |
Class at
Publication: |
558/92 |
International
Class: |
C07F 009/09 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 16, 2000 |
DE |
10051191.0 |
Claims
1. Process for preparing phosphoric acid esters, characterized in
that (1) a phosphorus oxyhalide is reacted continuously,
semicontinuously or batchwise with a polyol to produce a content of
at least about 60% monomeric halophosphate intermediate, (2) the
monomeric halophosphate intermediate is reacted continuously,
semicontinuously or batchwise with an alcohol to produce the
desired phosphoric acid ester, and (3) the product from Step 2 is
worked up continuously, semicontinuously or batchwise in a phase
separator at temperatures of 50 to 120.degree. C.
2. Process according to claim 1, wherein at least one step is
carried out continuously.
3. Process according to claim 1, characterized in that all steps
are carried out continuously.
4. Process according to claim 1, wherein said reaction of a
phosphorus oxyhalide with a polyol is carried out at temperatures
of about 50 to about 250.degree. C.
5. Process according to claim 1, wherein said reaction of a
phosphorus oxyhalide with a polyol is carried out in the presence
of a catalyst.
6. Process according to claim 5, wherein said catalyst is a Lewis
acid.
7. Process according to claim 6, wherein said Lewis acid is
magnesium oxide or magnesium chloride.
8. Process according to claim 1, wherein said reaction of said
monomeric halophosphate intermediate with an alcohol is carried out
continuously.
9. Process according to claim 1, wherein said phosphorus oxyhalide
is phosphorus oxychloride.
10. Process according to claim 1, wherein said dihydric alcohol is
bisphenol A or resorcinol.
11. Process according to claim 1, wherein said alcohol is a
monohydric alcohol.
12. Process according to claim 11, wherein said monohydric alcohol
is phenol.
13. Process according to claim 1, wherein said monomeric
halophosphate intermediate is a diphosphorotetrahalidate.
14. Process according to claim 1, characterized in that the
temperature in Step 3 is between 70 and 90.degree. C.
15. Process according to claim 1, characterized in that Step 3
comprises an acidic wash and an alkaline wash.
16. Flame retardant composition, comprising a phosphoric acid ester
produced by the process of claim 1 and a polymer resin.
17. Flame retardant composition according to claim 16, wherein said
polymer resin is selected from the group consisting of
polyphenylene oxide, high-impact polystyrene, polycarbonate,
polyurethane, polyvinyl chloride, acrylonitrile-butadiene-styrene,
polybutylene terephthalate and mixtures thereof
18. Process for preparing phosphoric acid esters, characterized in
that (1) a phosphorus oxyhalide is reacted continuously,
semicontinuously or batchwise with a monohydric alcohol to produce
a normalized content of at least about 60% monohalomonophosphoric
acid diester intermediate, (2) said monohalomonophosphoric acid
diester intermediate is reacted continuously, semicontinuously or
batchwise with a polyol to produce the desired phosphoric acid
ester, (3) the product from Step 2 is worked up continuously,
semicontinuously or batchwise in a phase separator at temperatures
of 50 to 120.degree. C.
Description
PROCESS FOR PREPARING PHOSPHORIC ACID ESTERS
[0001] The present invention relates to a process for preparing
phosphoric acid esters, in particular a continuous process for
preparing monomeric bisaryl diphosphates, or bridged
phosphates.
[0002] Bisaryl diphosphates, such as bisphenol A
bis(diphenyl)phosphate and resorcinol bis(diphenyl)phosphate are
known to be effective flame retardants for polymer resins. For
example, a variety of polyphenylene oxide/high-impact polystyrene
("PPO/HIPS") and polycarbonate/acrylonitril- e-butadiene-styrene
("PC/ABS") blends can be improved with bisaryl diphosphate flame
retardants.
[0003] When using bisaryl diphosphates to impart flame retardancy
to plastics it is desired to use compounds having a high percentage
of the monomer. This is because monomeric bisaryl diphosphates
impart beneficial physical properties to the polymer, which
properties are not provided by their dimeric or polymeric
counterparts. For example, resins to which monomeric bisaryl
diphosphates have been added exhibit improved impact strength, melt
flow index, tensile properties and flexural properties when
compared to resins combined with dimeric or polymeric aryl
phosphates.
[0004] Because of their commercial utility, various processes for
the manufacture of monomeric bisaryl diphosphates have been
developed. For example, it is known that bisphenol-A
bis(diphenyl)phosphate can be obtained by catalytically reacting a
phosphorus oxyhalide with bisphenol A (BPA) and then reacting the
intermediate with phenol.
[0005] WO 99/55771 describes a process for continuously preparing
monomeric bisaryl diphosphates, which, however, are not worked up
and thus do not meet all requirements of a flame retardant for
polymer resins with regard to certain product properties (catalyst
content, acid number, hydrolysable chlorine).
[0006] It is known from EP 936243 A2 that acid components and/or
precursors thereof which, under conditions of heat and humidity,
lead to the formation of acid components, are typically present in
the bisaryl diphosphates. These impurities may originate from, for
example, catalyst residues, unreacted starting materials, such as
phosphoryl halides and/or phosphoric acid ester derivatives, or
from decomposition products of unstable phosphoric acid esters. It
has also been found that such impurities as flame retardant
additives in polymer resins compromise the hydrolytic
stability.
[0007] WO 98/47631 discloses a process for preparing aryl
diphosphate esters, which comprises a third stage of filtering off
the catalyst which is unsoluble in the reaction medium.
[0008] WO 98/35970 describes a semicontinuous process for preparing
bisaryl diphosphates using magnesium chloride as a catalyst. The
reaction product is not worked up here either.
[0009] EP 0485 807 B1 describes a process for preparing aryl
diphosphate esters in eight process steps, a workup or extraction
of the catalyst being carried out in aqueous alkaline solution.
[0010] JP-A 10/017 583 dicloses a batchwise synthesis for preparing
phosphate ester oligomers, the reaction being controlled via the
liberation rate of HCl gas. Excess phenol is removed by
distillation, whereas the catalyst, for example magnesium chloride,
is removed by washing.
[0011] Finally, JP-A 10/00 7689 discloses a process for removing
the metal chloride catalyst by means of an acidic aqueous solution
(pH.ltoreq.3) and at a temperature of at least 65.degree. C.
[0012] A disadvantage of the prior art preparation processes is
that, in the absence of a workup procedure, the desired products
can be obtained only in a form contaminated with catalyst and other
acidic minor components, or that, in the case of bridged aryl
phosphates, in particular the reaction products of bisphenol A or
resorcinol, the workup or washing prodecures suggested lead to
considerable difficulties in large-scale plants owing to the poor
phase separation between the product phase and the water phase and
to the strong hydrolysis tendency in particular in alkaline media.
At present, these difficulties prevent the realization of a
continuous and thus industrial-scale production of these
products.
[0013] The present invention therefore provides a process for
preparing phosphoric acid esters, in particular monomeric bisaryl
diphosphates or bridged phosphates, characterized in that
[0014] (1) a phosphorus oxyhalide is reacted continuously,
semicontinuously or batchwise with a polyol to produce a content of
at least about 60% monomeric halophosphate intermediate,
[0015] (2) the monomeric halophosphate intermediate is reacted
continuously, semicontinuously or batchwise with an alcohol to
produce the desired phosphoric acid ester, and
[0016] (3) the product from Step 2 is worked up continuously,
semicontinuously or batchwise in a phase separator at temperatures
of 50 to 120.degree. C.
[0017] In some preferred embodiments, the polyol in Step 1 is a
dihydric alcohol and the alcohol in Step 2 is a monohydric alcohol.
Conversely, in some preferred embodiments the phosphorus oxyhalide
is reacted with a monohydric alcohol to produce a content of at
least about 60% monohalomonophosphoric acid diester intermediate.
In a preferred embodiment, all three steps are carried out
continuously.
[0018] It is an object of the present invention to provide a method
for continuously producing phosphoric acid esters, wherein at least
one step is carried out continuously. Particularly preferably all
three steps are carried out continuously.
[0019] Another object of the present invention is to provide a
method for producing phosphoric acid esters in a continuous
reaction, wherein the monomeric halophosphate intermediate content
of a reaction between phosphorus oxyhalide and a polyol is at least
about 60%, preferably at least about 70% and particularly
preferably at least about 80%.
[0020] A further object of the invention is to provide a method for
producing monomeric phosphoric acid ester products which can be
used as flame retardants, for example, in plastics.
[0021] Further objects and advantages of the present invention will
be apparent from the following description.
[0022] The term continuous as used herein means that the reactants
are fed into the apparatus at a constant flow rate and the reaction
mixture is removed in an equally continuous manner. All reaction
parameters are kept constant over time.
[0023] The term semicontinuous as used herein means that one
reactant is introduced into the apparatus whereas another reactant
is added slowly and continuously.
[0024] The term batchwise or discontinuously as used herein means
that the reactants are introduced together into the apparatus,
where they remain for a defined reaction time under set reaction
conditions.
[0025] For the purposes of promoting an understanding of the
principles of the invention, reference will now be made to
preferred embodiments and specific language will be used to
describe the same. It will nevertheless be understood that no
limitation of the scope of the invention is thereby intended, such
alterations and further modifications in the illustrated methods,
and such further applications of the principles of the invention as
illustrated therein, being contemplated as would normally occur to
one skilled in the art to which the invention relates.
[0026] Preferably, the present invention relates generally to a
continuous process for producing phosphoric acid esters, wherein
all three steps are run continuously, so that a product can be
produced which has a high monomeric halophosphate intermediate
content relative to dimeric halophosphate intermediate content,
along with high productivity, when the reaction is carried out in a
continuous reactor system, such as a continuous stirred tank
reactor (CSTR). The intermediate can be used, in certain
embodiments, to form a desired monomeric phosphoric acid ester,
including BPA bis(diphenyl)phosphate.
[0027] The preferred reactor design (i.e., a continuous reactor)
allows the production of product ratios otherwise unattainable in
commercial quantities at high productivity.
[0028] The degree of oligomerization or polymerization can further
be controlled to some extent by the degree of reaction completion
in individual stages of a multiple stage continuous reactor
series.
[0029] In one aspect of the invention, phosphoric acid esters are
continuously produced by a two step process. In the first step, a
content of at least about 60% monomeric halophosphate intermediate,
preferably a bis(dichlorophosphate), is formed by continuously
reacting a phosphorus oxyhalide with an alcohol, preferably a diol
or other polyol. After preferably removing the excess phosphorus
oxyhalide, the monomeric halophosphate intermediate is reacted with
another alcohol, preferably a monohydric alcohol such as a phenol,
to produce a desired phosphoric acid ester. The phosphorus
oxyhalide, which has been removed for example by distillation, can
be returned to the process, i.e. re-used for preparing the
halophosphate intermediate.
[0030] The products of the Step 1 reaction are predominantly
monomeric, and, as the monomeric product is used as a reactant in
Step 2, the product of the Step 2 reaction will likewise be
predominantly monomeric. However, it is recognized that, should one
desire an oligomeric or polymeric component after forming the
monomeric product from Step 1, the monomeric product from Step 1
may be reacted with a polyol in Step 2 and the resultant product
may be further processed as desired.
[0031] In yet another aspect of the invention, the desired
phosphoric acid esters are produced by continuously reacting
phosphorous oxyhalide with a monohydric alcohol to produce a
content of at least about 60% monohalomonophosphoric acid diester
intermediate. The intermediate is then reacted with a polyol,
preferably a dihydric alcohol, to produce the desired phosphoric
acid ester.
[0032] Further describing one embodiment of the processes of the
present invention, Step 1 of a process for preparing phosphoric
acid esters preferably includes continuously reacting an
appropriate alcohol with phosphorus oxyhalide in the presence of a
Lewis acid catalyst. The phosphorus oxyhalide used in the present
invention is generally of the formula POX.sub.n where X is a
halide, including chloride or bromide, and n is preferably 3.
Phosphorus oxychloride, POCl.sub.3, is the most preferred
phosphorus oxyhalide.
[0033] Step 1 produces a monomeric halophosphate intermediate when
a polyhydric alcohol, such as a dihydric alcohol, is used. In that
embodiment, the Step 1 reaction proceeds, diagrammatically, as
follows:
HO--R--OH+2 POX.sub.3.fwdarw.X.sub.2OP--O--R--O--POX.sub.2 (I)+2
HX
[0034] Any unreacted POX.sub.3 is removed by distillation under
reduced pressure, leaving the Step 1 intermediate product I. In the
above diagram, R is the carbon chain portion (i.e. the aromatic,
aliphatic, alicyclic portion or a combination thereof) of the
alcohol, X is a halide as previously mentioned and compound I is
the monomeric halophosphate intermediate product of Step 1.
[0035] Examples of appropriate alcohols include polyols, such as
polyphenols, and including dihydric alcohols such as biphenols,
bisphenol A, tetrabromobisphenol A, bisphenol S, bisphenol F,
ethylene glycol, 1,4-butanediol, 1,2-hexanediol, resorcinol,
catechol, hydroquinone and trihydric alcohols such as glycerol as
well as other polyols. The aromatic and alicyclic portions of the
alcohols may be alkyl or halo-substituted. The aliphatic portion of
the alcohol may also be halo-substituted. The alkyl substituent
comprises saturated or unsaturated aliphatic hydrocarbon groups
which may be either straight-chain or branched and have a carbon
chain length of from 1 to 18. For example, the alkyl group includes
methyl, ethyl and structural isomers of propyl, butyl, pentyl,
hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl,
tetradecyl, pentadecyl, hexadecyl, heptadecyl and octadecyl. The
halo substituent is preferably chlorine and/or bromine. It is
further preferred that there is no more than one substituent ortho
to each hydroxyl group on an aromatic alcohol.
[0036] The catalyst may be any Lewis acid capable of promoting the
reaction. Examples include, but are not limited to, AlCl.sub.3,
ZnCl.sub.2, CaCl.sub.2, MgO or MgCl.sub.2, preferably MgO or
MgCl.sub.2. The catalyst is used in an amount sufficient to allow
the reaction to proceed smoothly. The amount of catalyst used in
Step 1 is typically in the range of about 100 ppm to about 5000 ppm
(relative to the other reagents added to the first reactor),
preferably 100 ppm to about 1000 ppm and most preferably about 300
ppm to about 700 ppm.
[0037] The reaction temperature in Step 1 will depend on the
specific polyol reacted, but generally can be controlled over a
wide range, from about 50.degree. C. to about 250.degree. C., and
the process may be operated at atmospheric pressure, at a reduced
pressure, or at an elevated pressure. However, a temperature of
about 50.degree. C. to about 200.degree. C. is preferred, a
temperature of about 80.degree. C. to about 140.degree. C. is
particularly preferred, and a temperature of about 85.degree. C. to
about 100.degree. C. in the first stage and second stage and about
100.degree. C. to about 120.degree. C. in subsequent stages is most
preferred.
[0038] In the first step, the process may be operated with a
sufficient excess of POX.sub.3 to yield a workable reaction mass at
the reaction temperature, or an unreactive solvent may be used. The
phosphorus oxyhalide/polyol mole ratio is typically about 2.5:1 to
about 10:1, preferably about 3:1 to about 6:1 and most preferably
about 4:1 to about 5:1. The residence time in each reactor may vary
from 0.25 hours to about 6 hours.
[0039] As mentioned above, the degree of oligomerization or
polymerization can further be controlled to some extent by the
degree of reaction completion in individual stages of a multiple
stage continuous reactor series. The degree of reaction completion
in Stage 1 of Step 1 is typically about 10 to about 100%, and about
20% to about 100% in subsequent stages. However, it is preferred
that the degree of reaction completion in Stage 1 be about 30% to
about 80% and in subsequent stages about 50% to about 100%. It is
most preferred that the degree of reaction completion in Stage 1 be
about 30% to about 50%, in Stage 2 about 70% to about 100% and in
subsequent stages about 85% to about 100%.
[0040] The reaction of Step 1 is carried out by continuous,
semicontinuous or batchwise, preferably continuous reaction of the
above-described reagents. As used herein, the term "continuously
reacting" means that at least one step, such as Step 1 or 2 or 3,
can be carried out at least partly continuously (i.e. the step can
be divided into various stages and at least one stage is carried
out continuously) or the entire step can be carried out
continuously. The number of stages may range from about 1 to about
5, preferably from about 1 to about 3 and most preferably from
about 2 to about 3.
[0041] However, it is also possible to carry out Step 1 and Step 2
in continuous or semicontinuous mode and only Step 3 in batchwise
mode. Alternatively, it is also possible to carry out only Step 2
and Step 3 in continuous or semicontinuous mode and only Step 1 in
batchwise mode.
[0042] It is likewise possible to use any combination of
continuous, semicontinuous or batchwise operation of the individual
steps, including batchwise operation of all Steps 1, 2 and 3.
[0043] The term "continuous reactor" as used herein refers to a
vessel where raw materials or a feed stream containing unreacted or
partially reacted material is added continuously or essentially
continuously while material is being removed from the vessel to
maintain an essentially constant reactor volume, and where
conditions in the vessel are such that a finite degree of reaction
occurs.
[0044] As indicated above, the selection of reactor design to
accomplish the continuous portion of the reaction in either Step 1
or Step 2 or Step 3 plays an important role in determining the
degree of oligomerization or polymerization and the quality of the
product. Examples of commercially available reactors that might be
used to practice the invention, and that one skilled in the art is
familiar with, include falling film or thin film reactors,
continuously stirred tank reactors (CSTRs), tube reactors and
packed column reactors. Although a wide variety of reactors may be
used to practice the invention, CSTRs are preferred.
[0045] A series of continuous reactors may employ the same type, or
a different type, of reactor. It is further preferred that a CSTR
be used in Stage 1 of a step and then either another CSTR may be
used or a batch reactor may be used. It is most preferred to use a
series of CSTRs or, alternatively, a series of CSTRs, the final
stage being carried out in a batch reactor.
[0046] It is noted that, along with the monomeric product produced
in the Step 1 reaction diagrammed above, dimeric, other oligomeric
or polymeric products may be formed. For example, referring to the
diagram of the Step 1 reaction above, compound I may react with
Step 1 reactants (i.e., with the dihydric alcohol and POX.sub.3) to
form the following dimeric component:
X.sub.2OP--O--R--O--POX--O--R--O--POX.sub.2
[0047] The above dimeric component may also be produced by reaction
of the following reactants and intermediates from the reaction of
Step 1:
[0048] (1)
HO--R--O--POX.sub.3+HO--R--OH.fwdarw.HO--R--O--POX--O--R--OH+HX
[0049] (2)
X.sub.2OP--O--R--O--POX.sub.2+HO--R--OH.fwdarw.HO--R--O--POX--O-
--R--POX.sub.2+HX
[0050] (3)
HO--R--O--POX.sub.3+HO--R--O--POX.sub.2.fwdarw.HO--R--O--POX--O-
--R--O--POX.sub.2+HX
[0051] It is obvious that the product formed from (1)-(3) above
must be further reacted with POX.sub.3 to form the dimeric
component.
[0052] A suitable methode for determining the relative amounts of
monomer, dimer and further homologues of Step 1 is liquid
chromatography (GPC) using an RI detector.
[0053] The reaction of Step 1 preferably forms a content of at
least about 60% monomeric halophosphate intermediate. It is further
preferred that the reaction of Step 1 forms a content of at least
about 70%, particularly preferably at least about 80%, monomeric
halophosphate intermediate.
[0054] Referring now to Step 2 of the process, the product of Step
1 is reacted with an alcohol, such as a monohydric alcohol
including phenol, in a similar way using a Lewis acid catalyst. In
one embodiment, Step 2 may be depicted diagrammatically as
follows:
X.sub.2OP--O--R--O--POX.sub.2+4
R'OH.fwdarw.(R'O).sub.2OP--O--R--O--PO(OR'- ).sub.2+4HX
[0055] X and R are as defined above for Step 1 and
X.sub.2OP--O--R--O--POX- .sub.2 is a monomeric halophosphate
intermediate. R'OH is the monohydric alcohol, R' being the carbon
chain portion (i.e., the aromatic, aliphatic, alicyclic, portion or
a combination thereof) of the alcohol, and
(R'O).sub.2OP--O--R--O--PO(OR').sub.2 is the desired phosphoric
acid ester product. When R'OH includes an aromatic or alicyclic
ring, the aromatic or alicyclic ring may be alkyl- or
halo-substituted as discussed above for the dihydric alcohol in
Step 1. The aliphatic portion of the alcohol may also be
halo-substituted as discussed above. It is further preferred that
there is no more than one substituent ortho to each hydroxyl group
on an aromatic alcohol. Examples of the alcohol that may be reacted
in Step 2 include, but are not limited to, phenol, xylenols,
tribromophenol, methanol, t-butanol, cyclohexanol and
phenol/formaldehyde condensates. It is preferred to carry out Step
2 by reacting the halophosphate intermediate product of Step 1 with
phenol using magnesium chloride as a catalyst.
[0056] As in the first step, the phenol (or other alcohol) and the
product of Step 1 can be continuously fed to a CSTR in Step 2.
Alternatively, the phenol (or other alcohol) can be added as a
single charge to the product of Step 1, and the resulting mixture
can be fed continuously to the reactor.
[0057] The discharge from the first continuous reactor may be fed
to a second continuous reactor where the material is held at
125-250.degree. C. for a residence time of about 0.25-6 hours. The
total phenol charge may be added to the first reactor or split such
that part of the total phenol charge is added to the first reactor
and the remainder added to the second reactor.
[0058] The discharge from the second reactor is fed to a buffer
tank. The buffer tank is used to feed a continuous or batch vacuum
stripper adapted to remove excess alcohol from Step 2, such as
phenol. The alcohol, for example phenol, excess which has been
removed can be returned to the process, i.e. reused for carrying
out Step 2. A catalyst is used as in the reaction of Step 1.
[0059] The reaction of Step 2 is typically performed at a
temperature sufficient to convert the halophosphate intermediate to
the desired phosphoric acid ester product. Although this
temperature may vary depending on the reagents used and the desired
product, the temperature of the material in the reactor
advantageously ranges from 50.degree. C. to about 250.degree. C.,
but preferably from about 125.degree. C. to about 250.degree. C.
The volume of the reactor is preferably adjusted so that the
residence time ranges from about 0.25 to 6 hours.
[0060] The alcohol/monomeric halophosphate intermediate mole ratio
is typically about 4:1 to about 5:1, but preferably about 4.04:1 to
about 4.40:1, and most preferably about 4.04:1 to about 4.12:1. As
in the first step, an excess of the alcohol may be used to improve
the ease of processing, or an unreactive solvent may be
employed.
[0061] In a preferred embodiment of the first aspect of the
invention, BPA is continuously added to magnesium chloride and
phosphorus oxychloride in a dissolution vessel at a temperature of
about 50.degree. C. The relative feed rates are such that the
phosphorous oxychloride/BPA mole ratio is about 5:1. The reaction
mixture is then fed to a first CSTR at a temperature of about
90.degree. C. The volume of the reactor is maintained to give a
residence time of about 1 hour.
[0062] The contents of the first reactor are continuously removed
and transferred to further CSTRs arranged in series, successively
increasing the temperature to about 100.degree.C. and finally
120.degree. C. The feed and discharge rates from the reactor are
such that the residence time is about 1 hour in each case.
[0063] The discharge from the last reactor is fed to a buffer tank,
which is maintained at about 90.degree. C. while being filled. The
filled buffer tank is used to feed a continuous distillation to
remove the excess POCl.sub.3 from the product of Step 1.
[0064] The product of Step 1 is then reacted with phenol using
magnesium chloride as a catalyst.
[0065] As briefly mentioned above, the inventive continuous process
may be operated such that part of the first step or second step is
performed in a continuous reactor with the rest of the reaction
being completed in a batchwise reactor or reactors. Similarly, an
entire step may be performed in a continuous reactor or series of
continuous reactors, while the other step is carried out in batch
reactors. The steps may be carried out so as to maximize production
of monomeric halophosphate intermediate product and, consequently,
monomeric phosphoric acid ester product.
[0066] The monomer content of the reaction product of Step 2
depends on the presence of a high percentage of monomeric
halophosphate intermediate which acts as a reactant in Step 2.
Thus, if a large amount of monomeric halophosphate intermediate is
produced in Step 1 relative to the dimeric component, the monomer
content of the reaction of Step 2 will also be relatively large.
That is, relatively large amounts of the monomeric phosphoric acid
ester product of Step 2 will be formed compared to dimeric,
oligomeric or polymeric phosphoric acid ester product.
[0067] Parameters that can affect the properties and quality of the
products of Step 1 and Step 2 include catalyst selection and amount
of catalyst used, and phosphorus oxyhalide/alcohol ratio. Each of
these parameters has an optimum range to give a flame retardant
material exhibiting the desired properties. In addition, the
moisture content of each starting material has an effect on the
final product quality. For example, if the moisture content of the
reactants is kept low, a larger amount of monomeric product can be
obtained.
[0068] When Step 1 or Step 2 are performed in a series of reactors,
at least one of which is a continuous reactor, the raw materials,
such as solvent, catalyst, phosphorus oxyhalide, alcohol (i.e.
phenol or polyol, such as a diol) may be added to just the first
reactor in the series or to downstream reactors in addition to the
first. This can be done to improve the ease of processing, to
control product quality and/or to obtain the desired product or
mixture of products.
[0069] In an alternative embodiment, a process for preparing
phosphoric acid esters is provided which is characterized in
that
[0070] (1) a phosphorus oxyhalide is reacted continuously,
semicontinuously or batchwise with a monohydric alcohol to produce
a content of at least about 60% monohalomonophosphoric acid diester
intermediate,
[0071] (2) said monohalomonophosphoric acid diester intermediate is
reacted continuously, semicontinuously or batchwise with a polyol
to produce the desired phosphoric acid ester,
[0072] (3) the product from Step 2 is worked up continuously,
semicontinuously or batchwise in a phase separator at temperatures
of 50 to 120.degree. C., preferably 70 to 90.degree. C.
[0073] In this second aspect of the invention, the products from
this step are then reacted with the chosen alcohol selected from
the alcohols described above, preferably a polyol, such as a diol,
to give the desired phosphoric acid ester. This route also utilizes
Lewis acid catalysts and continuous addition of reactants as
described for the other embodiments. Step 2 product composition and
properties are similar to those obtained in the previously
described route. The inventive continuous process may be operated
in a similar fashion as described above. For example, in certain
embodiments the reaction of the intermediate with the polyol may
also be performed in a continuous reactor. Alternatively, the first
reaction may be performed in a batch reactor and the second
reaction may be performed continuously.
[0074] Referring more specifically to the above alternative
embodiment, the Step 1 reaction of the monohydric alcohol with the
phosphorus oxyhalide may be diagrammed as follows:
POX.sub.3+2R'OH.fwdarw.(R'O).sub.2POX (II)+2HX
[0075] R'OH and X are as previously defined and compound II is the
monohalomonophosphoric acid diester intermediate.
[0076] The specific catalyst and the quantity used are the same as
in the previous embodiments discussed.
[0077] The reaction temperature in Step 1 of the alternative
embodiment can likewise be controlled over a wide range, from about
50.degree. C. to about 250.degree. C., and the process may
similarly be operated under various pressures. However, a
temperature of 50.degree. C. to about 200.degree. C. is preferred,
and a temperature of about 90.degree. C. to about 140.degree. C. is
particularly preferred. Moreover, residence times are typically
about 0.25 hours to about 6 hours.
[0078] The alcohol/phosphorus oxyhalide mole ratio is
advantageously from about 1.5:1 to about 3:1, and particularly
preferably from about 1.75:1 to about 2.25:1.
[0079] Reaction of phosphorus oxyhalide with a monohydric alcohol
may yield the following undesired compounds:
(R'O)POX.sub.2 (III)
(R'O).sub.3PO (IV)
[0080] Compound III is a dihalomonophosphoric acid monoester
intermediate and Compound IV is a phosphoric acid triester.
Compound IV is undesired as this compound can no longer react with
a polyol in Step 2 to produce a desired phosphoric acid ester
product. Compound III is undesired because it has the potential of
reacting with the reactants and intermediates formed in the
reaction of Step 2, and can thus lead to formation of dimeric,
oligomeric or polymeric products in Step 2. As one skilled in the
art is aware of the specific undesired reactions that may proceed
and products that may be produced, it is not necessary to describe
them here.
[0081] The reaction between phosphorus oxyhalide and the monohydric
alcohol will typically produce a content of at least about 60%
monohalomonophosphoric acid diester. It is further preferred that
at least about 70%, particularly preferably at least about 80%, of
the monohalomonophosphate diester is produced. Step 2 of the
alternative embodiment may be diagrammed as follows:
2
(R'O).sub.2POX+HO--R--OH.fwdarw.(R'O).sub.2OP--O--R--O--PO(OR').sub.2+2H-
X
[0082] R'and X are as defined above. The reaction of Step 2
produces the desired monomeric phosphoric acid ester product,
(R'O).sub.2OP--O--R--O--- PO(OR').sub.2.
[0083] The specific catalyst and the quantity used is the same as
in the embodiments discussed previously.
[0084] The reaction temperature in Step 2 of the alternative
embodiment can also be controlled over a wide range, from about
50.degree. C. to about 250.degree. C., and the process may
similarly be operated under various pressures. However, a
temperature of about 125.degree. C. to about 250.degree. C. is
preferred. Moreover, residence times are typically about 0.25 hours
to about 6 hours.
[0085] The polyol/monohalomonophosphoric diester intermediate mole
ratio is advantageously from about 0.3:1 to about 0.8:1, and
particularly preferably from about 0.4:1 to about 0.6:1. The
preferred degrees of reaction completion in Step 1 are similar to
those described above.
[0086] The alternative process variants comprise a subsequent third
step of working up.
[0087] The present invention shows that a significant improvement
in phase separation can be achieved when aqueous workup is
performed in a temperature range from 50 to 120.degree. C.,
preferably between 70 and 90.degree. C., whereas the hydrolysis
reaction is not yet relevant at the residence times required for
the separation. To achieve a sufficient and reproducible product
quality (which is a necessary prerequisite for a continuous
technical process that must be met), the process of the invention
additionally comprises using specific phase separators. At least, a
gravitational separator equipped with knits, lamellae or coalescing
aids should be used, but a particularly good separation in the
alkaline range is achieved by using centrifugal liquid-liquid
separators.
[0088] The workup of Step 3 comprises both an acidic wash and an
alkaline wash, which can likewise be operated in continuous,
semicontinuous or batchwise mode, preferably in continuous
mode.
[0089] Any aqueous acid can be used for the acidic wash, for
example HCl, H.sub.2SO.sub.4, H.sub.3PO.sub.4, CH.sub.3COOH.
Particular preference is given to aqueous HCl, in particular in a
concentration range from 0.5 to 10%. Any conventional basic salt
can be used for the alkaline wash, for example NaOH,
Na.sub.2CO.sub.3, NaHCO.sub.3, sodium acetate and corresponding
potassium salts. Particular preference is given to Na salts, in
particular NaOH in a concentraion range from 0.5 to 10%.
[0090] The process of the invention is particularly suitable for
continuously preparing bisphenol A diphosphate (BDP) or resorcinol
diphosphate (RDP), in which case the polyol used is resorcinol.
[0091] The phosphoric acid esters prepared by the methods of the
present invention can be utilized as flame retardants in resin
compositions. The resin may be a polymer and may include
polyphenylene oxide, high-impact polystyrene, polycarbonate,
polyurethane, polyvinyl chloride, acrylonitrile-butadiene-styrene,
polybutylene terephthalate and mixtures thereof A wide variety of
other polymer resins may also be used.
[0092] The examples which follow illustrate the invention. The
resulting bisaryl phosphate is characterized with regard to monomer
content, acid number, hydrolysable chlorine and magnesium content
(catalyst). The characteristic parameters are determined by
well-known methods:
[0093] The monomer content is determined by liquid chromatography
(reverse phase HPLC) using a UV detector at 254 nm.
[0094] The acid number is determined by titration with KOH in
ethanol.
[0095] Residual hydrolyzable chlorine is analysed by hydrolyzing
the chlorine attached to phosphorus with sodium methoxide in
methanol followed by titration of chloride with silver nitrate.
[0096] The magnesium content of the phosphoric acid ester is
measured by means of conventional atomic absorption methods.
EXAMPLES
[0097] Example 1: Preparation of bisphenol A
bis(diphenylphosphate)
[0098] Experiments were conducted in a tank battery consisting of 4
1 1reactors equipped with a stirrer, thermocouple, condenser, and
heating mantle. The reaction mixture is kept constant at 1 1 by
means of an overflow. The reaction temperature is set separately
for each reactor via a separate thermostat.
[0099] Stage 1
[0100] The reaction mixture (POCl.sub.3/BPA mole ratio =5.0,
MgCl.sub.2 7 mmol/mol BPA) is introduced into an interchangeable
receptacle at 50.degree. C. and transferred to the first reactor by
means of a pump. Hydrochloric acid liberated in the reaction is
vented and absorbed in water. The following temperature profile is
set for the tank battery 82/86/105/120.degree. C. The flow rate is
1.5-2.0 l/h, resulting in an average residence time of 2-2.5 h.
[0101] After the reaction, excess POCl.sub.3 is continuously
distilled off in a falling film evaporator and returned to the
reaction.
[0102] Cl content: 29.4%
[0103] Stage 2
[0104] The intermediate from Stage 1 is introduced into a
receptacle and admixed with the desired amount of phenol at
50.degree. C. (8 mol% excess based on the Cl content of the
intermediate). The reaction mixture is transferred to the first
reactor by means of a pump. The following temperature profile is
set: 135/160/190/210.degree. C. The flow rate is 1.0-1.3 l/h. The
average residence time is 3-4 hours.
[0105] After the reaction, excess phenol is continuously distilled
off in a falling film evaporator and returned to the reaction.
[0106] The resulting BDP had the following properties:
1 Monomer content: 80.5% Acid number: 1.2 mg KOH/g Hydrolyzable
chlorine: 757 ppm Mg content: 260 ppm
EXAMPLE 2
[0107] BDP prepared as decribed in Example 1 was used for the
workup.
[0108] The product was washed with 1% strength HCl and then washed
neutral with deionized water, followed by a 2-stage alkaline wash
using 2% strength NaOH. Finally, the product was again washed
neutral with deionized water and then dried by simple continuous
evaporation until a water content of <500 ppm was reached.
[0109] Step 3 was carried out as a multistage procedure at 1 bar
and at a temperature of 85.degree. C. under a nitrogen blanket.
[0110] A feed of 0.9 l/h of the product of Step 2 was subjected to
an HCl wash with 1% strength HCl (feed rate 450 ml/h) in Stage 1, a
water wash (feed rate 250 ml/h) in Stage 2, an alkaline wash (feed
rate 300 ml/h of 2% strength NaOH) in Stages 3 and 4 and a final
water wash (feed rate 250 ml/h) in Stages 5 and 6 and finally fed
to a centrifuge in Stage 7.
[0111] Final drying of the product at 60 mbar and 120.degree. C.
gave the desired product which had an Mg content of 30 ppm, an acid
number of 0.12 mg KOH/g and a chlorine content of 52 ppm.
[0112] The following apparatuses were used in Step 3:
2 Stage Mixer Phase separation Acidic wash: Stirred tank
Gravitational separator equipped with PTFE knit Water wash Mixing
pump Gravitational separator equipped with PTFE knit Alkaline wash
Stirred tank Gravitational separator equipped with coalescing aid
(5.mu. metal fibre) Mixing and phase separation in V2 centrifuge
from CINC, Nevada, USA Water wash Stirred tank Gravitational
separator equipped with coalescing aid (5.mu. metal fibre) Stirred
tank Gravitational separator equipped with coalescing aid (5.mu.
metal fibre) Centrifuge Subsequent separation in V2 centrifuge
CINC, Nevada, USA
EXAMPLE 3
[0113] BDP was prepared as described in Example 1 in a continuous
laboratory scale apparatus using MgCl.sub.2 catalyst and
continuously introduced into the washing step.
3 Stage 1 Acidic wash: Feed rate of 1% strength HCl: 440 ml/h Stage
2 Water wash: Feed rate: 270 ml/h Stage 3 + 4 Alkaline wash: Feed
rate of 2% strength NaOH: 300 ml/h Stage 5 Water wash: Centrifuge
feed rate: 270 ml/h Apparatuses in Example 3 Stage Mixer Phase
separation 1 Stirred tank Gravitational separator equipped with
PTFE knit 2 Mixing pump Gravitational separator equipped with PTFE
knit 3 Stirred tank Gravitational separator equipped with
coalescing aid (5.mu. metal fibre) 4 Mixing and phase separation in
V2 centrifuge from CINC, Nevada, USA 5 Mixing and phase separation
in V2 centrifuge from CINC, Nevada, USA
[0114] Drying at 60 mbar and 120.degree. C. yields an optically
clear product having an acid number of 0.06 mg KOH/g, an Mg content
of 18 ppm and a chlorine content of 20 ppm.
* * * * *