DESC:Technical Field of the invention:
The present invention relates to a process for preparing triakylphosphites. More particularly, the present invention relates to an improved process for preparing triakylphosphites with increased yield and reusable byproducts.
Background of the invention:
Trialkylphosphitesare valuable intermediates in the production of various chemicals, flame retardants, plasticizers and are also known for their role as stabilizers, as well as in the manufacture of foams and other products.
There are many methods described in the prior art to manufacture trialkylphosphites. The synthesis using phosphorus trichloride and an alcohol is the most direct and most economical to produce trialkylphosphites.
The prior art teaches the production of trialkylphosphites using phosphorus trichloride, alcohol, and a base in the presence of an inert solvent, including dilution with water or with aqueous solutions or by filtration.However, this process has a major disadvantage of including the steps of diluting the reaction mixture with water to separate the inorganic salt and the organic phase. It is known in the art that trialkylphosphite when bought in contact with water results in its degradation and thus loss of the product.
The present processes known in the art includes the use of multiple steps making the process not just expensive but also time consuming apart from causing yield losses. The yield obtained in such a process is also low, as considerable trialkylphosphite is lost when contacted with water or other aqueous based solutions. Another problem associated with the process includes choking of the columns which results in higher maintenance, increasing the cost of the process.
The processes taught in the prior art include two step processes which include the addition of the phosphorus halide at the first step of the reaction and dissolution of the amine halide with water in the second step of the process. This process increases the number of steps used and thereby increases the time required for the reaction and the cost. The increased cost is not justified by the purity of the resultant end product.
US3201435 teaches the use of a metal alcoholate or phenolate as catalysts for the transesterificaton of phosphorus trichloride to form trimethylphosphite. The use of catalysts may increase the speed of the reaction, but also increase the cost of the production; also the yield obtained is not very high to justify the cost of using the catalyst.
US5710307 teaches the production of trialkyphosphites from phosphorus trichloride and alcohol in the presence of an auxiliary base as an acid-binding agent and a solvent. However, the process uses expensive solvents and does not solve the problem of the use of multiple distillation columns. The yield obtained by this process is not remarkably different from the conventionally known processes.
The purity of the intermediates used in a process play an important role in the purity of the end product. Therefore, the trialkylphosphites used in the processes for manufacturing agrochemicals as well as other chemicals has to be of high purity and devoid of harmful impurities. The prior art teaches many methods of producing trialkylphosphitein good purity. However, a process that affords trialkylphosphites at a high yield as well as high purity has been an unmet need in the art.
There is therefore a need in the art for a process that is simple and yet eliminates the multiple steps of prior art and obtains a higher yield and good purity. The process must also generate commercially valuable byproducts which are of a high quality and are substantially pure.
US 3036110discloses a process for the preparation of trialkylphosphite esters by reacting a phosphorus halide with an alcohol in the presence of an acid binding agent, such as tertiary aliphatic amine or aniline. This patent teaches, for example at column 22:line 55, that the amine halide formed in these reactions is preferably extracted with water. This patent further teaches, for example, at page 3 opening paragraph, that trimethylphosphite is very susceptible to hydrolysis and seeks to solve this problem by extracting amine halide formed in the first stage of the reaction with water before carrying out the second stage of the reaction. The trialkylphosphite is formed only during the second stage of the reaction and does come into contact with water once it is formed. Further, during the reaction workup, this patent teaches dissolving the amine halide with water and distilling the organic phase.
This patent suggests prevention of hydrolysis of trialkylphosphites by adding a neutral diluent, such as methylene chloride, to the reaction mixture. However, despite the addition of a neutral diluent, the prevention of hydrolysis of trialkylphosphites is not always perfect.
In another conventionally known process, the organic reaction mixture and water are continuously added in a dissolver. The generated ammonium chloride in the slurry mass is extracted in water. The residence time of the slurry mixture in the dissolver is intentionally maintained to a minimum. The organic mass and aqueous amine halide mixture is then passed into a decanter for phase separation. The residence time of the mixture in the decanter cannot be controlled since a sufficient time must be allowed to pass to ensure the complete removal of water (moisture) from the organic mass. However, the residence time in the decanter allows a substantial contact period between water and the organic mass so as to cause substantial unwanted hydrolysis of the alkyl phosphites, particularly at the interface between the aqueous and organic phases. This hydrolysis has been found to be sufficient to cause the yield and/or purity of the resultant alkyl phosphites to reduce drastically. There is a need for an improved process for the preparation of trialkylphosphites that does not allow degradative interaction of the generated trialkylphosphites with water and thus leads to substantially pure product in high yield.
In this conventionally known process, the amine base, high molecular weight paraffinic solvent, ammonia, alkanol and phosphorus halide are fed to a reactor. The reaction mixture is then transferred to a holding reactor where water is added to the mixture. The reaction mixture wet cake is then fed to a decanter, which separates the reaction mass into the organic phase and the aqueous phase. This aqueous phase has been found to comprise about 17% amine halide solution in water resulting in about 5-6% yield loss occurring, in-part, due to the interaction between the trialkylphosphite and water. The amine halide solution is thereafter reacted with lime (Ca(OH)2), which produces calcium chloride and ammonia. Calcium chloride is not a commercially useful by-product, whereas ammonia produced as a by-product in this manner is two or three times more expensive than the ammonia gas that is otherwise commercially available. Therefore, it was concluded that this conventionally known process leads to commercially useless by-products, which have no market potential.
The present invention therefore aims to overcome the problems in the prior art, by providing a cost effective and high yielding process with commercially marketable by-products.
Objects of the invention:
It is an object of the present invention to provide a high-yield process for the production of substantially pure trialkylphosphites.
It is another object of the present invention to provide a process for preparing trialkylphosphitesin which the amine halide byproduct can be recovered without the need for dissolution in water.
Yet another object of the present invention is to provide a process for preparing trialkylphosphites with commercially marketable by-products.
Summary of the invention:
Therefore the present invention provides a process for preparation of trialkylphosphites of the general formula (I):

wherein R1 represents an alkyl chain having 1 to 18 carbon atoms, said process comprising centrifuging a reaction mixture comprising the reaction product of a phosphorus halide with an alkanol.
Trialkylphosphites of the general formula (I):

wherein R1 represents an alkyl chain having 1 to 18 carbon atoms, said trialkylphosphite being substantially free of dialkylphosphites.
In another aspect, the present invention provides a system for the manufacture of trialkylphosphites, said system comprising:
(a) at least one reactor into which predetermined quantities of a phosphorus halide, an alkanol and optionally an amine are fed to form a reaction mixture;
(b) at least one centrifuge which separates the reaction mixture received from the reactor into an organic mother liquor comprising trialkylphosphite and a wet cake comprising amine halide;
(c) at least one distillation column which separates out substantially pure trialkylphosphite; and
(d) at least one dryer which dries the amine halide wet cake to produce dried amine halide.
Brief Description of Accompanying drawing:
Figure 1 illustrates the apparatus for the production of trimethylphosphite and recovery of ammonium chloride.
Detailed Description:
It has been surprisingly found that the degradative interaction between trialkylphosphites and water can be effectively reduced and thus substantially pure trialkylphosphitesin high yield can be prepared if the reaction mixture comprising the reaction product of phosphorus halide with an alkanol is centrifuged. The degree of contact prevention achieved by thus centrifugation was surprisingly efficient, which improved effect could not be hitherto achieved, e.g. by use of a diluent or by decantation of the reaction mixture. This prevention of contact between water and the generated trialkylphosphite prevented the degradation of the trialkylphosphite, which thus produced a surprisingly high yield of the target trialkylphosphite.
In an embodiment, an amine may optionally be present during the reaction between phosphorus halide and alkanol.
The hydrolysis of trilalkylphosphites primarily leads to the formation of a dialkylphosphite, and eventually phosphorus acid. The presence of a dialkylphosphite has an autocatalytic effect on the reaction. Therefore, the prevention of degradative interaction between water and trialkylphosphite leads to a substantially pure trialkylphosphite product in high yield, which is substantially free of phosphorus-based impurities, preferably substantially free of a dialkylphosphite or phosphorus acid.
Therefore, in an aspect, the present invention provides a process for preparation of trialkylphosphites of the general formula (I):

wherein R1 represents an alkyl chain having 1 to 18 carbon atoms, said process comprising centrifuging a reaction mixture comprising the reaction product of a phosphorus halide with an alkanol.
In an embodiment, the centrifugation according to the present invention separates the centrifuged reaction mixture into an organic mother liquor comprising trialkylphosphite and a wet cake comprising an amine halide, which are processed separately.
In an embodiment, the phosphorus halide is selected from phosphorus trifluoride, phosphorus trichloride, phosphorustribromide or phosphorus triiodide.
In an embodiment, the suitable phosphorus halides include those halides wherein one or more halogen atoms are replaced with an aliphatic, araliphatic or aromatic radical. In this embodiment, the phosphorus halide may preferably be selected from methyl phosphorus dichloride, diethyl phosphorus chloride, ethyl phosphorus dichloride, dimethyl phosphorus chloride, methylethyl phosphorus chloride, phenyl phosphorus dichloride, diphenyl phosphorus chloride, butyl phosphorus dichloride, ethylphenyl phosphorus chloride and the corresponding compounds wherein the chloride moiety is replaced with bromide or iodide moiety.
However, in a preferred embodiment, the preferred phosphorus halide is phosphorus trihalide described hereinabove.
In an embodiment, R1 represents an alkyl chain having from 8 to 16 carbon atoms.
In an embodiment, R1 represents an alkyl chain having from 9 to 15 carbon atoms.
In an embodiment, R1 represents an alkyl chain having from 10 to 13 carbon atoms.
In an embodiment, R1 represents an aromatic group having from about 6 to about 16 carbon atoms.
In an embodiment, when the alkyl substituent R1 represents an aromatic group, the centrifuged reaction mixture is the reaction product of phosphorus halide, an alkanol and an amine. For example, an amine may be used when the target trialkylphosphite is an aromatic compound.
In an embodiment, the alkanol is an aliphatic alcohol having from 1 to 18 carbon atoms, preferably from 8 to 16 carbon atoms.
In another embodiment, the alkanol is an aliphatic alcohol having from 9 to 15 carbon atoms, preferably from 10 to 13 carbon atoms.
In the embodiment where the preferred alkyl substituent is an aromatic group, the preferred alkanol may be the corresponding phenolic compound. For example, for illustrative purposes only, where the trialkylphosphite is triphenylphosphite, the corresponding alkanol may be phenol. Such minor variations are within the realm of a person skilled in the art and ought to be considered within the scope of the present invention.
In another embodiment, the alkanol may be a straight or branched aliphatic alcohol selected from methanol, ethanol, propanol, secondary butanol, tertiary butanol and ethylhexanol; cycloaliphatic alcohols such as cyclohexanol and cyclohexyl propanol; and aliphatic alcohols including an aromatic substituent such as benzyl alcohol.
In an embodiment, the alkyl chain may be substituted or unsubstituted, and when substituted, the substituent may be selected from alkoxy, halo or an aromatic substituent. The preferred alkoxy, halo or aromatic substituent is not particularly limiting and may be selected by a skilled artisan on the basis of the target trialkylphosphite required.
In an embodiment, the alkyl chain may be selected from methyl, ethyl, propyl, isopropyl, butyl, pentyl, mexyl, heptyl, octyl, isooctyl, ethyl-hexyl, decyl, butoxyethyl, 2-fluoroethyl, 2-chloroethyl, 2-bromoethyl, 3-trichloroethyl, 3-trifluoroethyl, 3-tribromoethyl, benzyl, m-chlorobenzyl, m-bromobenzyl, m-fluorobenzyl or ethylphenyl.
The term “substantially free of” is intended herein to denote trialkylphosphites being completely free of, or comprises less than 100 ppm of, dialkylphosphites, phosphorus acid or phosphorus based impurities. The term “phosphorus-based impurities” denotes all compounds, including dialkylphosphites and phosphorus acid, that are derivable from unwanted hydrolysis of trialkylphosphites.
The term “substantially pure” trialkylphosphite of the present invention denotes the trialkylphosphite prepared by the process of the present invention having a purity of at least about 98%, preferably between 99% to about 99.9% and still more preferably, having a purity of about 99.5%.
In an embodiment, the term “high yield” in relation to the yield of trialkylphosphitedenotes from about 90% to 99% yield. These yields had never been achieved by the conventional processes and were a significant finding of the present invention.
In an embodiment, the amine may be preferably a secondary aliphatic amine.
In an embodiment, the amine may be selected from dimethylamine, diethylamine, methylethylamine, diisobutylamine and diisopropylamine.
Thus, in embodiment, a reaction mixture comprising the reaction product of a phosphorus halide with an alkanoloptionally in the presence of an amine is centrifuged.
In an embodiment, the reaction mixture is preferably in the form of a slurry. The slurry is prepared in a reactor and continuously transferred into a holding vessel. The slurry is then fed into a provided centrifuge.
In an embodiment, the centrifuge is a peeler centrifuge.
In an embodiment, the centrifugation according to the present invention separates the centrifuged reaction mixture into an organic mother liquor comprising trialkylphosphite and a wet cake comprising an amine halide, which are processed separately.
The supernatant containing trialkylphosphiteis then transferred to a distillation tower for removal of the high boiling solvent, and preferably to another distillation column to separate the target product and the solvent. The solvent extraction leads to a high yield of substantially pure trialkylphosphite in high yield. The recovered solvent is recycled.
The wet cake comprising the amine halide is transferred via a screw feeder to a dryer, preferably a hot air dryer. In the dryer, hot air is passed over the amine halide wet cake to afford substantially pure amine halide, which is a commercially useful by-product.
In an embodiment, the centrifuge is a peeler centrifuge, which is operated at 700 to 1000 rpm, preferred being 800 to 1000 rpm and most preferred being 900 to 1000 rpm.
In an embodiment, the slurry comprising the reaction mixture of phosphorus halide, alkanol and an amine is prepared according to a predetermined process.
In an embodiment, the phosphorus halide is reacted with an alkanoloptionally in the presence of an amine and an inert solvent in a reactor. This reaction leads to a slurry comprising the trialkylphosphite and amine halide. This slurry is thereafter transferred to a holding reactor and subsequently to a centrifuge.
In an embodiment, the reaction between phosphorus halide, alkanol and the amine may be carried out in a single step. In this embodiment, the phosphorus halide,alkanol, amine, an inert solvent and a scavenging agent are added to a reactor. The reaction between phosphorus halide and the alkanolresults in the formation of trialkylphosphite and hydrogen halide. The scavenging agent reacts with hydrogen halide forms an intermediate compound which then reacts with the amine to give amine halide as a byproduct.
In an embodiment, the reaction is exothermic and instantaneous and may therefore be carried out in a continuous manner. In order to control the reaction temperature, the reaction mixture includes an inert solvent which has a high boiling point and which may be added to moderate the heat generated.
Alternatively, the reaction mass may be surrounded on the outside with external heat exchanger. Alternatively, a combination of the two may also be employed to control reaction temperature.
In an embodiment, the alkanol may be present in from about a stoichiometric amount to a molar excess amount relative to the amount of phosphorus halide. However, the precise quantity of molar excess of the alkanol is not particularly limiting and may be readily determined by a skilled artisan.
In an embodiment, the trialkylphosphite produced in the process of the present invention may be used for manufacture of agrochemicals.
In an embodiment, the trialkylphosphite produced in the process of the present invention may be used for manufacture of organophosphorus agrochemicals.
The process of the present invention has numerous advantages over the prior art. The process is low cost and less time consuming. The one step process is continuous, thereby increasing manufacturing output and decreasing time of production. The yield of trialkylphosphite obtained is substantially higher than that of the existing processes known in the art. The process eliminates the use of water and yet recovers ammonium halide of high purity and without any significant yield losses. Importantly, the recovered amine halide is commercially marketable and thus useful by-product, which has not been made possible hitherto.
In an embodiment, the inert high boiling solvent may be selected from, but is not limited to solvents such as heavy normal paraffin.
In an embodiment, the scavenging agent may be selected from but is not limited to secondary amines. In an embodiment, the scavenging agent is diethylamine.
It has been surprisingly found that the degradative interaction between trialkylphosphites and water can be effectively reduced and thus substantially pure trialkylphosphites can be prepared in high yield if the reaction mixture comprising the reaction product of phosphorus halide with an alkanoloptionally in the presence of an amine is centrifuged. Therefore, the prevention of degradative interaction between water and trialkylphosphite leads to a substantially pure trialkylphosphite product, which is substantially free of phosphorus-based impurities, preferably substantially free of a dialkylphosphite or phosphorus acid.
Thus, in an aspect, the present invention provides trialkylphosphites of the general formula (I):

wherein R1 represents an alkyl chain having 1 to 18 carbon atoms, said trialkylphosphite being substantially free of dialkylphosphites.
In an embodiment, R1 represents an alkyl chain having from 8 to 16 carbon atoms.
In an embodiment, R1 represents an alkyl chain having from 9 to 15 carbon atoms.
In an embodiment, R1 represents an alkyl chain having from 10 to 13 carbon atoms.
In an embodiment, the alkyl chain may be substituted or unsubstituted, and when substituted, the substituent may be selected from alkoxy, halo or an aromatic substituent. The preferred alkoxy, halo or aromatic substituent is not particularly limiting and may be selected by a skilled artisan on the basis of the target trialkylphosphite required.
In an embodiment, the alkyl chain may be selected from methyl, ethyl, propyl, isopropyl, butyl, pentyl, mexyl, heptyl, octyl, isooctyl, ethyl-hexyl, decyl, butoxyethyl, 2-fluoroethyl, 2-chloroethyl, 2-bromoethyl, 3-trichloroethyl, 3-trifluoroethyl, 3-tribromoethyl, benzyl, m-chlorobenzyl, m-bromobenzyl, m-fluorobenzyl or ethylphenyl.
The term “substantially free of” is intended herein to denote trialkylphosphites being completely free of, or comprises less than 100 ppm of, dialkylphosphites, phosphorus acid or phosphorus based impurities. The term “phosphorus-based impurities” denotes all compounds, including dialkylphosphites and phosphorus acid that are derivable from unwanted hydrolysis of trialkylphosphites.
The term “substantially pure” trialkylphosphite of the present invention denotes the trialkylphosphite prepared by the process of the present invention having a purity of at least about 98%, preferably between 99% to about 99.9% and still more preferably, having a purity of about 99.5%.
In an embodiment, the substantially pure trialkylphosphite produced in the present invention may be used for manufacture of agrochemicals, preferably organophosphorus agrochemicals.
In an embodiment, the substantially pure trialkylphosphite produced in the present invention may be used as plasticizer.
In another aspect, the present invention provides a system for the manufacture of trialkylphosphites, said system comprising:
(a) at least one reactor into which predetermined quantities of a phosphorus halide , an alkanol and optionally an amine are fed to form a reaction mixture;
(b) at least one centrifuge which separates the reaction mixture received from the reactor into an organic mother liquor comprising trialkylphosphite and a wet cake comprising amine halide;
(c) at least one distillation column which separates out substantially pure trialkylphosphite; and
(d) at least one dryer which dries the amine halide wet cake to produce dried amine halide.
It has been seen, as above, that the degradative interaction between trialkylphosphites and water can be effectively reduced and thus substantially pure trialkylphosphites can be prepared in high yield if the reaction mixture comprising the reaction product of phosphorus halide with an alkanoloptionally in the presence of an amine is centrifuged. Surprisingly, a system for the manufacture of trialkylphosphite, wherein the system comprises a centrifuge has not been hitherto provided. Therefore, the system of the present invention leads to a substantially pure trialkylphosphite product, which is substantially free of phosphorus-based impurities, preferably substantially free of a dialkylphosphite or phosphorus acid.
In an embodiment, the reactor produces a slurry upon reaction of alkyl halide with alkanol. The slurry is thereafter conveyed to a centrifuge.
In an embodiment, the slurry is conveyed to the centrifuge via a provided holding reactor. The holding reactor continuously receives the slurry from the reactor and conveys the received slurry batchwise to a centrifuge in a feeding cycle.
In an embodiment, the centrifuge is a peeler centrifuge. A peeler centrifuge is per se known in the art and may be used as available in this embodiment of the invention.
In an embodiment, the centrifuge is adapted to separate the reaction mixture slurry into an organic mother liquor comprising trialkylphosphite and a wet cake comprising an amine halide. The organic mother liquor is transferred to a distillation tower while the amine halide wet cake is transferred to a dryer.
In an embodiment, the mother liquor is fed to a distillation column via a provided stripping column. The stripping column receives the mother liquor from the centrifuge, strips out the alkanol from the organic mass and transfers the resultant organic mass to a distillation column.
In an embodiment, the distillation column separates the high boiling paraffinic solvent and pure trialkylphosphite.
In another embodiment, the high boiling paraffinic solvent is recovered from the bottom of the distillation column and recycled via a provided recycle tank.
In an embodiment, the wet cake of amine halide received from the centrifuge is fed to a hot air dryer via a provided cake collector. The hot air dryer dries the wet cake of amine halide by passing stream of hot air to provide dried amine halide.
In an embodiment, the wet cake of amine halide is received from the centrifuge into a cake collector. The cake collector continuously receives the wet cake from the centrifuge and continuously feeds the received wet cake to the hot air dryer via a screw feeder. The screw feeder receives the wet cake from the collector and conveys the received wet cake at a predetermined rate to the hot-air dryer.
In an embodiment, the centrifuge is a peeler centrifuge adapted to operate at 700 to 1000 rpm, preferably at 800 to 1000 rpm and most preferably at 900 to 1000 rpm.
In an embodiment, the centrifuge is provided with a scrapper, which scraps the amine halide sticking to the centrifuge walls, if any.
In an embodiment, the distillation column is preferably adapted to operate under vacuum and reflux conditions to separate the trialkylphosphite from the high boiling paraffinic solvent.
Thus, in another aspect, the present invention provides a system for the manufacture of trialkylphosphites, said system comprising:
(a) at least one reactor into which predetermined quantities of a phosphorus halide, an alkanol and optionally an amine are fed to form a reaction mixture;
(b) at least one holding reactor which is adapted to continuously receive the slurry from the reactor and convey the received slurry batchwise to a centrifuge;
(c) at least one centrifuge which separates the reaction mixture received from the holding reactor into an organic mother liquor comprising trialkylphosphite and a wet cake comprising amine halide;
(d) at least one stripping column adapted to receive the organic mother liquor from the centrifuge and separate the unreacted alkanol from the mother liquor to a resultant organic mass and to convey the resultant organic mass to a provided distillation column;
(e) at least one distillation column which separates out substantially pure trialkylphosphite from the supplied organic mass separating high boiling paraffinic solvent therefrom;
(f) at least one recycle tank, adapted to receive the high boiling paraffinic solvent generated from the distillation column and recycle the received high boiling paraffinic solvent to the reactor;
(g) at least one cake collector adapted to continuously receive the wet cake from the centrifuge and continuously feed the received wet cake to a provided screw feeder;
(h) at least one screw feeder adapted to receive the wet cake from the cake collector and to convey the received wet cake at a predetermined rate to a provided hot-air dryer; and
(i) at least one dryer which dries the amine halide wet cake to produce dried amine halide.
Description of a preferred embodiment:
An apparatus (figure 1) was provided for the production of trimethylphosphite and recovery of ammonium chloride. The apparatus included a reactor (1), a holding reactor (2), a peeler centrifuge (3), a cake collector (4), a stripper column (5), a distillation column (6), a solvent recycle tank (7), a screw feeder (8) and dryer (9). The raw materials phosphorus trichloride, methanol, ammonia, paraffinic high boiling solvent and diethylamine were continuously supplied to the reactor (1). The quantity of the raw material introduced was based on the flow rate of phosphorus trichloride, which was introduced at the rate of 1800 kg/hr to 2300 kg/hr. During the reaction, phosphorus trichloride reacted with methanol to form trimethylphosphite and hydrogen chloride. The scavenging agent reacted immediately with the formation of hydrogen chloride to form an indeterminate intermediate compound, which upon reaction with ammonia afforded ammonium chloride as a by-product. The use of paraffinic solvent moderated the heat produced in the reaction and the organic mass was produced in a slurry form. The organic mass was continuously circulated through the spiral heat exchanger. After completion of the reaction, the slurry comprising about 12% amine halide solution and the trialkylphosphitewas continuously transferred to the holding reactor (2).
The slurry was continuously received in the holding vessel, from which a specified batch size (3100 kg/batch to 3400 kg/batch) of slurry was fed to the peeler centrifuge(3) in the feeding cycle. Subsequent to the completion of the feeding cycle, the centrifuge was run at 940 rpm for the separation of mother liquor from the ammonium chloride wet cake. After the recovery of mother liquor from the cake, the wet cake of ammonium chloride was removed using the scrapper. After the filtration, the mother liquor collected from the centrifuge was continuously fed to the stripper (5) and distillation column (6). The wet cake containing ammonium chloride was collected in a cake collector (4) and sent for drying.
The stripping column (5) was operated under vacuum to strip out excess methanol from the organic mass. The organic mass containing trimethylphosphite was fed to the mid-portion of the distillation column (6). The distillation column was operated under vacuum and reflux conditions. Trimethylphosphite(99.5% purity) was collected from the top of the distillation column and the high boiling paraffin solvent was recovered from the bottom of the distillation column and recycled via a provided solvent recycle tank (7).
The wet cake received in the cake collector (4) has a loss-on-drying profile of about 10-15%. The wet cake was continuously fed to a screw feeder (8), which in turn fed the wet cake to a hot-air dryer (9). The dried ammonium chloride was collected, blended and packed.
The process of the present invention demonstrates several advantages over the conventional process used in the prior art. The process of the present invention is a high yield process. The process is also a zero waste process which generates useful by-products of commercial importance. The process of the present invention also decreases the number of steps of the invention as compared to the prior art, resulting in decreased footprint of the process. The process of the present invention is safer than inventions of the prior art, wherein, the pressure required to in the process of the prior art was 17 times more than the atmospheric pressure, making it a safety hazard, the present invention eliminates the need for such high pressure making it safer than those process of the prior art. Another advantage of the present invention is the substantially increased yields obtained through the process of the present invention.
These and other advantages of the invention may become more apparent from the examples set forth herein below. These examples are provided merely as illustrations of the invention and are not intended to be construed as a limitation thereof.
Examples:
Example 1 – Preparation of trimethylphosphite.
Phosphorus trichloride at the rate of 1800 kg/hrwas added to methanol, ammonia, paraffinic high boiling solvent and diethylaminein a reactor. The organic mass wascontinuously circulated through a spiral heat exchanger. After completion of the reaction, the slurry comprising about 12% ammonium chloride solution and the trimethylphosphitewas transferred to a holding reactor.
The slurry wasthen fed to a peeler centrifuge. The centrifuge was run at 940 rpm for the separation of mother liquor from the ammonium chloride wet cake. After the recovery of mother liquor from the cake, the wet cake of ammonium chloride was removed using the scrapper. After the filtration, the mother liquor was collected from the centrifuge and continuously fed to a stripper and distillation column. The wet cake containing ammonium chloride was collected in a cake collector and sent for drying. The organic mass containing trimethylphosphitewas fed to a mid-portion of the distillation column. The distillation column was operated under vacuum and reflux conditions. Trimethylphosphite (99.5% purity) was collected from the top of the distillation column and the high boiling paraffin solvent was recovered from the bottom of the distillation column and recycled via a provided solvent recycle tank.
The invention has been described above by way of illustration, and the specific embodiment disclosed is not intended to limit the invention to the particular forms disclosed. For example, the embodiments described in the foregoing were directed to providing a clear idea about the preferred modes, including the best mode, of making and using the present invention. However, in alternate embodiments, those skilled in the art may implement the invention without deviating from the central idea of the invention. The invention therefore covers all modifications, equivalents, and alternatives falling within the spirit and scope of the description of the invention.
,CLAIMS:1. A process for preparation of trialkylphosphites of the general formula (I):

wherein:
R1 represents an alkyl or an aromatic group having 1 to 18 carbon atoms,

said process comprising centrifuging a reaction mixture comprising the reaction product of a phosphorus halide with an alkanol,

wherein the phosphorus halide is selected from methyl phosphorus dichloride, diethyl phosphorus chloride, ethyl phosphorus dichloride, dimethyl phosphorus chloride, methylethyl phosphorus chloride, phenyl phosphorus dichloride, diphenyl phosphorus chloride, butyl phosphorus dichloride, ethylphenyl phosphorus chloride and the corresponding compounds wherein the chloride moiety is replaced with bromide or iodide moiety, and

thealkanol is an aliphatic alcohol having from 1 to 18 carbon atoms.

2. ATrialkylphosphite of the general formula (I):

wherein
R1 represents an alkyl or an aromatic group having 1 to 18 carbon atoms, said trialkylphosphite being substantially free of dialkylphosphites.
3. A system for the manufacture of trialkylphosphites, said system comprising:
a. at least one reactor into which predetermined quantities of a phosphorus halide , an alkanol and optionally an amine are fed to form a reaction mixture;
b. at least one centrifuge which separates the reaction mixture received from the reactor into an organic mother liquor comprising trialkylphosphite and a wet cake comprising amine halide;
c. at least one distillation column which separates out substantially pure trialkylphosphite; and
d. at least one dryer which dries the amine halide wet cake to produce dried amine halide.
4. The system as claimed in claim 3 wherein said reactor produces slurry upon reaction of alkyl halide with alkanol, which slurry is conveyed to the centrifuge via a provided holding reactor, which continuously receives the slurry from the reactor and conveys the received slurry batchwise to a centrifuge in a feeding cycle.
5. The system as claimed in claim 3 wherein the centrifuge is a peeler centrifuge.
6. The system as claimed in claim 3 or claim 5 wherein the centrifuge is adapted such that the reaction mixture slurry is separated into an organic mother liquor comprising trialkylphosphite and a wet cake comprising an amine halide.
7. The system as claimed in claim 3 additionally comprising a stripping column which receives the mother liquor from the centrifuge, strips out the alkanol from the organic mass and transfers the resultant organic mass to a distillation column.
8. The system as claimed in claim 3 additionally comprising a cake collector which receives the wet cake of amine halide from the centrifuge in a continuous manner and feeds the said wet cake to a hot air dryer via a provided screw feeder which receives the wet cake from the collector and conveys the received wet cake at a predetermined rate to the hot-air dryer.
9. The system as claimed in claim 3 wherein the centrifuge is adapted to operate at 700 to 1000 rpm.
10. A system for the manufacture of trialkylphosphites, said system comprising:
a. at least one reactor into which predetermined quantities of a phosphorus halide, an alkanol and optionally an amine are fed to form a reaction mixture;
b. at least one holding reactor which is adapted to continuously receive the slurry from the reactor and convey the received slurry batchwise to a centrifuge;
c. at least one centrifuge which separates the reaction mixture received from the holding reactor into an organic mother liquor comprising trialkylphosphite and a wet cake comprising amine halide;
d. at least one stripping column adapted to receive the organic mother liquor from the centrifuge and separate the unreacted alkanol from the mother liquor to a resultant organic mass and to convey the resultant organic mass to a provided distillation column;
e. at least one distillation column which separates out substantially pure trialkylphosphite from the supplied organic mass separating high boiling paraffinic solvent therefrom;
f. at least one recycle tank, adapted to receive the high boiling paraffinic solvent generated from the distillation column and recycle the received high boiling paraffinic solvent to the reactor;
g. at least one cake collector adapted to continuously receive the wet cake from the centrifuge and continuously feed the received wet cake to a provided screw feeder;
h. at least one screw feeder adapted to receive the wet cake from the cake collector and to convey the received wet cake at a predetermined rate to a provided hot-air dryer; and
i. at least one dryer which dries the amine halide wet cake to produce dried amine halide.