FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
AND
THE PATENT RULES, 2003
COMPLETE SPECIFICATION
(See Section 10; rule 13)
"An Improved Process And Apparatus"
We , UNITED PHOSPHORUS LIMITED,
Uniphos House,
Madhu Park,l 1th Road, Khar (West),
Mumbai-400 052,
State of Maharashtra
INDIAN.
. The following specification particularly describes the invention and the manner in which it is to be performed:-

An improved process and apparatus
Field of Invention:
The present invention relates to a process and apparatus for the preparation of free flowing phosphorus pentachloride powder. More particularly, the present invention relates to a process and apparatus for the high throughput preparation of free flowing phosphorus pentachloride powder.
Background of the Invention:
Phosphorus pentachloride (PCl5) is one of the most important phosphorus halides, which finds extensive use as a chlorinating agent. It is a white to pale-yellow, water sensitive solid which is frequently contaminated with hydrogen chloride.
Phosphorus pentachloride is generally prepared by the chlorination of phosphorus trichloride (PCI3), which is an exothermic reaction producing about 124 kJ per mole of phosphorus pentachloride produced. Phosphorus pentachloride usually exists in equilibrium with phosphorus trichloride and chlorine. Therefore, the samples of phosphorus pentachloride often appear yellowish due to its contamination with chlorine.
Moreover, phosphorus pentachloride is generally considered a dangerous substance as it reacts violently with water apart from being a source of chlorine and hydrogen chloride. Accordingly, it is desirable to provide a process and apparatus for the preparation of phosphorus pentachloride that involves minimal human intervention right from the initiation of the reaction till phosphorus pentachloride is packed and shipped.
United States Patent No. 3995013 discloses a process for the preparation of high purity phosphorus pentachloride in the form of a free flowing crystalline powder. The process comprises reacting liquid phosphorus trichloride with a quantity of chlorine less than the stoichiometric quantity required to convert all of the phosphorus trichloride to phosphorus pentachloride. This invention is therefore based on the finding that phosphorus trichloride itself is a good reaction medium for the chlorination of

phosphorus trichloride to produce phosphorus pentachloride. This process leads to a flowable slurry of phosphorus pentachloride and phosphorus trichloride, which is required to be dried and purified in another provided reactor, which again required manual intervention. The phosphorus pentachloride melt dissolved in excess phosphorus trichloride, which is removed from the reactor, is required to be subjected from three further unit operations of (i) crystallization; (ii) filtration; and (iii) purification either by drying or by reacting excess phosphorus trichloride by excess chlorine, which adds to the overall cost of the product while requiring human intervention. It is desirable to provide a process and apparatus for the preparation of phosphorus pentachloride that involves minimal human intervention right from the initiation of the reaction till phosphorus pentachloride is packed and shipped. Moreover, this patent teaches maintenance of dry nitrogen atmosphere which is cumbersome and expensive.
United States Patent No. 4265865 teaches a process for the manufacture of phosphorus pentachloride by chlorination of phosphorus trichloride in the presence of a melt of phosphorus pentachloride and removing the reaction product as a melt from the reactor. The generated liquid phosphorus pentachloride is discharged from the reactor and granulated while the granulated product is removed from time to time or continuously. This patent essentially teaches a liquid phase, two step chlorination of phosphorus trichloride. However, the purity of phosphorus pentachloride produced by this process is not satisfactory, which required additional post-reaction processes such as filtration, drying etc. to produce a commercially acceptable product. These post-reaction processes substantially add to the cost of the final product, which is clearly undesirable.
An article entitled "The formation of phosphorus pentachloride from phosphorus trichloride and chlorine" by H. Austin Taylor, contribution from the Laboratory of Physical Chemistry, Princeton University, essentially teaches a laboratory scale, un-catalyzed vapor phase reaction between phosphorus trichloride and chlorine to form phosphorus pentachloride, which is usually precipitated as a cloud. This article further teaches that chlorine gas, used in the reaction, may be prepared in situ while the reaction may preferably be carried out in a nitrogen atmosphere. This references teaches merely an academic, experimental procedure which cannot be scaled to an industrial set up for

large scale manufacture of phosphorus pentachloride, which is evidenced by the use of a reactor volume of only 100 mL. Moreover, the phosphorus pentachloride formed. typically as snow flakes, as the formed vapor gives rise to an easily super-saturated vapor which is precipitated as a white cloud by some phosphorus pentachloride condensed on the condensing vessel. There is a further need in the art for an industrially applicable process for the preparation of phosphorus pentachloride that involves a vapor phase reaction between phosphorus trichloride and chlorine gas.
Indian Patent No. 172459 discloses an industrially applicable process that enables a vapor phase reaction between phosphorus trichloride and chlorine to be carried out on an industrial scale. This patent discloses a process for the production of free flowing dry phosphorus pentachloride by direct reaction between pre-heated phosphorus trichloride vapor and chlorine gas wherein phosphorus pentachloride is produced in the vapor phase. The vapor of phosphorus pentachloride is passed into a condensing chamber from where free flowing powder is scrapped, collected, packed without being exposed to the atmosphere. The apparatus disclosed in this patent comprises at least a PCI3 storage tank, PCI3 vaporizer, PC13 super-heater, chlorine introduction pipe, and jacketed reactor, conical bottom settling chamber, scrapper, screw conveyor, collection drum, outlet pipe, buffer and scrubber. However, there remains a further need in the art for an improved process and apparatus for the manufacture of phosphorus pentachloride which affords substantial plant capacity improvement to at least 4-6 tonnes per day with plant yield improvement at least from 78 to 90% on phosphorus trichloride basis.
Indian Patent No. 204970 describes an improvement to the process and apparatus disclosed and claimed in IN 172459. The disclosed improvement in the purity of the final product comprises (i) continuously maintaining a quantity of phosphorus trichloride vapor and chlorine gas at 1:1-1.1 molar raio; and (ii) continuously removing traces of impurities from the product. However, this patent does not refer to an improvement in the plant capacity to at least about 4-6 tonnes per day with plant yield improvement at least from 78 to 90%.

These and the other advantages apparent from the "objects" of the present invention set out hereinbelow are realized by an invention described hereinafter.
Objects of the invention:
Thus, an object of the present invention is to provide a process and an apparatus for the high throughput preparation of free flowing phosphorus pentachloride powder.
Another object of the present invention is to provide a process and an apparatus for the preparation of free flowing phosphorus pentachloride wherein the process and apparatus requires minimal human intervention right from the initiation of the reaction till phosphorus pentachloride is packed and shipped.
Another object of the present invention is to provide a process and apparatus for the preparation of phosphorus pentachloride that do not require the maintenance of an inert atmosphere during the continuance of the production.
Yet another object of the present invention is to provide a process and an apparatus for the preparation of phosphorus pentachloride which affords substantial plant capacity improvement to at least 4-6 tonnes per day with plant yield improvement at least from 78 to 90% on phosphorus trichloride basis.
Another object of the present invention is to provide a process and an apparatus for the preparation of phosphorus pentachloride that avoids the lumping or clogging of the final end product thereby avoiding the plugging of the reactor and the discharge outlets.
Yet another object of the present invention is to provide a process and an apparatus for the preparation of phosphorus pentachloride that enables maximum utilization of phosphorus trichloride and chlorine thereby leading to substantial cost savings.
These and the other advantages of the present invention are realized by an invention described hereinafter.
Summary of the invention

A process for the preparation of free flowing phosphorus pentachloride powder, said process comprising:
(a) vaporizing phosphorus trichloride at a temperature range of 76-95°C and delivering the vaporized phosphorus trichloride to a first static mixer;
(b) delivering chlorine gas into said first static mixer and allowing delivered phosphorus trichloride and chlorine vapors to blend and react to produce vapors of phosphorus pentachloride during which the temperature of the first static mixer is maintained between about 100-150°C;
(c) conveying the heated vapors of phosphorus pentachloride and any unused reactants to a provided first cooler wherein said vapors are cooled to a predetermined temperature, said cooled vapors being subsequently conveyed to a provided second static mixer;
(d) delivering chlorine gas into said second static mixer and allowing said cooled vapors delivered from said first cooler to blend and react with the delivered chlorine gas to further produce vapors of phosphorus pentachloride during which the temperature of the second static mixer is maintained between 100-150°C;
(e) conveying the heated vapors produced in said second static mixer and substantially comprising phosphorus pentachloride to a provided second cooler wherein said vapors substantially comprising phosphorus pentachloride are cooled to a predetermined temperature; and
(f) conveying said cooled phosphorus pentachloride vapors co-axially to a provided condenser thereby causing a deposition of free flowing phosphorus pentachloride powder at bottom portion of said condenser.
An apparatus for the preparation of free flowing phosphorus pentachloride powder, said apparatus comprising:
(a) at least one phosphorus trichloride vaporizer capable of receiving liquid phosphorus trichloride and vaporizing the received phosphorus trichloride at a predetermined vaporizing temperature;
(b) a plurality of static mixers, the first static mixer in each series being adapted to receive phosphorus trichloride vapors from a phosphorus trichloride vaporizer,

said plurality of static mixers adapted to receive chlorine gas from chlorine batch tanks and allow the received chlorine gas to be intimately blended with phosphorus trichloride vapors thereby causing chlorination of the received phosphorus trichloride to produce phosphorus pentachloride vapors at a predetermined temperature;
(c) a plurality of coolers placed subsequent to said plurality of static mixers, said coolers being adapted to receive, phosphorus pentachloride vapors in admixture with unreacted phosphorus trichloride or chlorine gas or both, at a predetermined temperature and cooling the said admixture of vapors to a predetermined cooled temperature, said coolers being capable of delivering the cooled admixture of gases to a static mixer provided that the last cooler in the sequence is connected to, and capable of co-axially delivering vapors substantially comprising phosphorus pentachloride to, at least one provided condenser via a delivery pipe;
(d) a plurality of delivery pipes connecting each said cooler, being placed last in the sequence of said plurality of static mixers and coolers, to a provided condenser, said plurality of delivery pipes only slightly protruding within the condenser and releasing said phosphorus trichloride vapors co-axially within said condenser such that said coaxially released phosphorus pentachloride vapors gradually condense and deposit at the bottom of said condenser; and
(e) at least one cylindrical condenser having a frustoconical bottom connected to each said cooler, being placed last in the sequence of said plurality of static mixers and coolers via a plurality of delivery pipes, said cylindrical condenser allowing the coaxially released phosphorus pentachloride vapors to condense and deposit in the frustoconical bottom of the condenser.
The above description sets forth, rather broadly, a summary of one embodiment of the present invention so that the detailed description that follows may be better understood and contributions of the present invention to the art may be better appreciated. Some of the embodiments of the present invention may not include all of the features or characteristics listed in the above summary. There are, of course, additional features of the invention that will be described below and will form the subject matter of the present

invention. In this respect, before explaining at least one preferred embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of the construction and to the arrangement of the components set forth in the following description or as illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.
Brief description of the drawings
Fig.l is a flowchart depicting the process for the preparation of phosphorus pentachloride according to the present invention.
Fig. 2 is a schematic representation of the apparatus for the preparation of phosphorus pentachloride according to the present invention.
Fig. 3 is a schematic representation of the drying and cooling means included within the apparatus of the present invention.
DetaiJed description of the invention:
Accordingly, in one aspect, the present invention provides an improved process for the preparation of free flowing phosphorus pentachloride powder.
The process comprises vaporizing liquid phosphorus trichloride at a temperature range of from about 76°C to about 95°C in at least one provided vaporizer. Preferably, only one vaporizer is provided although in alternate embodiments, more than one vaporizer may also be provided.
Preferably, liquid phosphorus trichloride is stored in a phosphorus trichloride storage tank; which is connected to a phosphorus trichloride charging tank. The phosphorus trichloride storage tank is utilized to store the entire inventory of phosphorus trichloride, which is regularly fed to the batch tank with the progress of the reaction and consumption of phosphorus trichloride during the reaction.

In another embodiment, several phosphorus trichloride charging tanks may be provided, which may be individually connected to provided plurality of vaporizers via connecting delivery pipes.
Subsequent to vaporization, phosphorus trichloride vapor is delivered from said vaporizer or from a plurality of said vaporizers to at least one static mixer or to a plurality of such static mixers.
Preferably, liquid chlorine may stored in a chlorine storage tank connected to a chlorine charging tank or it may be continuously generated and delivered to the chlorine charging tank during the progress of the reaction via a chlorine delivery pipe. The chlorine charging tank is connected to a static mixer or to a plurality of static mixers through another chlorine delivery pipe or through a plurality of such delivery pipes. In this embodiment, the chlorine storage tank is utilized to store the entire inventory of chlorine, which is regularly fed to the chlorine batch tank with the progress of the reaction and consumption of chlorine during the reaction.
In an embodiment, several chlorine storage tanks may be provided, which may be individually connected to the provided plurality of static mixers via connecting chlorine delivery pipes.
In a preferred embodiment, said phosphorus trichloride batch tanks have individual capacities of 50 L each, which may in turn be connected to larger phosphorus trichloride storage tanks respectively. In this embodiment, the larger storage tanks may be connected to the smaller batch tanks to continuously replenish the same during the operation of the process according to the present invention.
T +
Therefore, according to the present invention, phosphorus trichloride vapor and chlorine gas are simultaneously delivered to a first static mixer. The static mixer allows the

delivered vapors to blend and react to produce vapor of phosphorus pentachloride, during which the temperature of the mixer is maintained between about 100-150°C.
The chlorination of phosphorus trichloride is an exothermic reaction. The production of phosphorus pentachloride vapor releases a large amount of heat. Accordingly, the static mixer may be optionally provided with an external cooling means which maintains the temperature of the static mixer in the range of about 100-150°C. Preferably, the static mixer is provided with an external jacketed cooler provided with cold water circulation to maintain a desired temperature.
It has been surprisingly found that a maximum yield of phosphorus pentachloride powder is achieved when the temperature in the static mixer is maintained in the range of about 100-150°C. It was found that the percentage conversion of phosphorus trichloride to phosphorus pentachloride fell rapidly when the temperature was allowed to rise beyond 150°C while at temperature below 100°C, the lumping characteristic of phosphorus pentachloride increased substantially leading to consequent nozzle choking. Percentage conversion is shown below:

S No. Temperature maintained in the static mixers (°C) Percentage conversion PC13 to PC15 of
1 100 98.0
2 105 97.2
3 110 96.2
4 120 93.3
5 125 91.5
6 130 89.2
7 135 86.7
8 140 83.8
9 145 80.5
10 150 77.0
11 170 59.9

Accordingly, in this embodiment, the temperature within the static mixers is preferably maintained between 100°C to about 150°C.
A static mixer is a device consisting of mixer elements contained in a cylindrical or squared housing. The mixing elements of a static mixer comprise a series of baffles that are made of a metal or plastic. The delivered vapors are made to flow through the static mixer wherein the provided baffles continuously blend the vapors.
Preferably, the static mixer according to an embodiment includes a series of fixed baffles enclosed within a tubular housing, wherein the geometrical design of the baffles produces patterns of flow division and radial mixing of the vapors.
The residence time of the vapors within the static mixer depends, inter alia, on the number of striations provided in the static mixer. Typically, the residence time may be upto about 1 minute although residence time periods of about 2 seconds are almost sufficient to enable complete reaction between vapor of phosphorus trichloride and chlorine gas.
Subsequently, the vapor exiting the first static mixer, containing phosphorus pentachloride substantially along with small quantities of phosphorus trichloride or chlorine or both, is passed to a first cooler which cools the delivered vapor to a temperature range of, preferably about 100°C to about 105°C.
The cooled vapor is subsequently delivered to a second static mixer to which chlorine gas is again delivered. The cooled vapor exiting the first cooler is allowed to blend and react with the delivered chlorine gas to further produce phosphorus pentachloride vapor. The temperature of the second static mixer is preferably maintained between 100°C to about
150°C.
In an embodiment, a series of such static mixers and coolers may be placed alternately till end phosphorus pentachloride product of desired purity is obtained. In another embodiment, two to eight series, more preferably about four to six series, most preferably, about four series of two alternately placed static mixers and coolers may be

commercially used to prepare phosphorus pentachloride of desired purity and at a desired yield.
In one embodiment, each series may be provided with an exclusive phosphorus trichloride vaporizer which supplies vapor of phosphorus trichloride to that particular series may be used.
The heated phosphorus pentachloride vapor produced in the static mixer that is placed last in each sequence is delivered to a cooler that is placed subsequent to the last placed static mixer. The temperature of the phosphorus pentachloride vapor is thereafter cooled to a temperature range of less than about 110°C).
The process of the present invention comprises delivering the phosphorus pentachloride vapor cooled in said last placed cooJer to a condenser. The deiivery pipe connecting said last placed cooler protrudes slightly into said condenser and releases phosphorus pentachloride vapor in a coaxial direction i.e. parallel to the central axis of the cylindrical condenser.
It has been found that releasing the phosphorus pentachloride vapors coaxially within said condenser and close to lateral internal surface of the cylindrical condenser causes the released phosphorus pentachloride vapor to condense gradually and deposit on the floor of the frustoconical bottom of the condenser without sticking to the walls of the condenser. In another embodiment, the external side walls of the condenser may be hard tapped with a hammering means which causes small amount of powdered phosphorus pentachloride sticking to the walls of the condenser to deposit at the bottom of said condenser.
Optionally, the internal side walls of the condenser may be provided with a scrapping means to scrap any phosphorus pentachloride powdery material sticking to the internal wall of the condenser and cause it to settle at the bottom of the condenser.

In an embodiment, the deposited phosphorus pentachloride powder is delivered to a drying and cooling means, while the undeposited vapor within the condenser is passed into a scrubbing means.
The scrubbing means according to the present invention is capable of removing the 'unreacted chlorine or phosphorus trichloride from the gas stream. In a preferred embodiment, excess chlorine gas with fine particulates of phosphorus pentachloride may be vented out of the condenser. The vented vapor may be subjected to washing and/or neutralization with an alkali in an absorption system subsequent to being passed through a buffer. Preferably, the buffer may be constructed of lead or nickel, which prevents any carry-over of particulate phosphorus pentachloride into the fluid stream. A subsequently placed absorption system comprising a dilute alkali solution flowing counter-currently to the contaminated vapor absorbs any unreacted chlorine gas. The preferred alkali solution may comprise sodium hydroxide, sodium bicarbonate, lime or soda ash.
In an embodiment wherein the vapor exiting the condenser comprises a substantial quantity of phosphorus trichloride, excess trichloride is removed from the vapor using a trombone cooler.
The process of the present invention additionally comprises drying and cooling the deposited phosphorus pentachloride powder in a provided drying and cooling means.
The drying means comprises passing the powdered phosphorus pentachloride through a cylindrical shaft having a plurality of impeller blades provided therein. The shaft having a plurality of impeller blades provided therein is placed within a hollow cylindrical shell. Hot water is allowed to circulate externally to said cylindrical shell to cause the phosphorus pentachloride powder to be heated and dried. The hollow cylindrical jacket has a hot water supply port at one end and a hot water return port to exit the hot water coming out of the cylindrical shell. A series of such dryers may be placed in sequence to achieve a desired purity of phosphorus pentachloride. Preferably, two to four such dryers may be placed in a sequence to achieve a desired purity of phosphorus pentachloride.

In a preferred embodiment, the dried phosphorus pentachloride powder is passed through a cooling shell. Preferably, the cooling shell is similar in construction to the drying shell with cold water replacing the hot water of the drying shells.
In an embodiment, the cooling shell has an inert atmosphere of nitrogen maintained therein.
In one embodiment, the material exiting the drying and cooling means is collected into carboys, sieved using a vibro-machine and packed into weight adjusted packets.
In another aspect, the present invention provides an apparatus for the preparation of free flowing phosphorus pentachloride powder. The apparatus comprises at least one phosphorus trichloride vaporizer, a plurality of static mixers, a plurality of coolers, a plurality of delivery pipes and at least one cylindrical condenser.
The phosphorus trichloride vaporizer vaporizes liquid phosphorus trichloride at a temperature range of from about 76°C to about 95°C. Preferably, only one vaporizer is provided although in alternate embodiments, more than one vaporizer may also be provided.
Preferably," liquid phosphorus trichloride is stored in a phosphorus trichloride storage tank, which is connected to the vaporizer or to a plurality of such vaporizers through a phosphorus trichloride delivery pipe or pipes.
In an embodiment, said phosphorus trichloride vaporizer receives liquid phosphorus trichloride from phosphorus trichloride batch tank, converts the received liquid phosphorus trichloride to vapor at said predetermined temperature.
In an embodiment, the preferred phosphorus trichloride is a mild steel vaporizer having a 50 L volume, which is capable of vaporizing about 35 to 60 kg of vaporizer per hour.
In another embodiment, several phosphorus trichloride storage tanks may be provided, which may be individually connected to provided plurality of vaporizers via connecting delivery pipes.

The vaporized phosphorus trichloride is delivered from said vaporizer or from a plurality of said vaporizers to at least one static mixer or to a plurality of such static mixers.
Preferably, liquid chlorine may stored in a chlorine storage tank connected to a chlorine charging tank or it may be continuously generated and delivered to the chlorine charging tank during the progress of the reaction via a chlorine delivery pipe. The chlorine charging tank is connected to a static mixer or to a plurality of static mixers through another chlorine delivery pipe or through a plurality of such delivery pipes. In this embodiment, the chlorine storage tank is utilized to store the entire inventory of chlorine, which is regularly fed to the chlorine batch tank with the progress of the reaction and consumption of chlorine during the reaction.
In an embodiment, several chlorine storage tanks may be provided, which may be individually connected to the provided plurality of static mixers via connecting chlorine delivery pipes.
In a preferred embodiment, said phosphorus trichloride batch tanks have individual capacities of 50 L each, which may in turn be connected to larger phosphorus trichloride storage tanks respectively. However, individual capacities of larger or smaller volumes are not excluded and may be selected based on the capacity of the desired plant/ apparatus. In this embodiment, the larger storage tanks may be connected to the smaller batch tanks to continuously replenish the same during the operation of the process according to the present invention.
The apparatus of the present invention comprises a plurality of static mixers. The first provided static mixer receives phosphorus trichloride and chlorine vapors generated by the provided phosphorus trichloride and chlorine vaporizers and allow the received vapors to blend intimately and react to produce phosphorus pentachloride vapors. The said plurality of static mixers is maintained at a temperature from about 100°C to about 150°C during the generation of phosphorus pentachloride vapors.

The plurality of static mixers is preferably provided with external cooling means. The external cooling means is preferably a jacketed cooler, which allows cold water to flow through it thereby effectively cooling, without causing deposition, of the generated phosphorus pentachloride vapor. The provided external cooling means is adapted to maintain the temperature within said plurality in the range of about 100-150°C.
In an embodiment, said plurality of static mixers comprises mixer elements contained in a cylindrical or squared housing. The mixing elements preferably comprise a series of baffles that are made of a metal or plastic. The received vapors of phosphorus trichloride and chlorine flow through the static mixer wherein the provided baffles continuously blend the vapors thereby leading to the formation of phosphorus pentachloride vapor.
Preferably, the static mixer according to an embodiment includes a series of fixed baffles enclosed within a tubular housing, wherein the geometrical design of the baffles produces patterns of flow division and radial mixing of the vapors. Preferably, the internal lining of each static mixer may be made of PTFE,
In an embodiment, each static mixer is constructed of stainless material, preferably SS316. The provided baffles are preferably made from polytetrafluoroethylene (PTFE).
The apparatus of the present invention comprises a first cooler disposed subsequent to said first static mixer. The first cooler receives the vapor exiting the first static mixer, which substantially comprises phosphorus pentachloride along with small quantities of unreacted phosphorus trichloride or chlorine or both. The first cooler cools the received vapor to a temperature range of from about 80°C to 120oC, more preferably from about 85°C to about 95°C.
The apparatus of the present invention comprises a second static mixer, which receives the cooled vapor exiting the first cooler. The second static mixer comprises a second feed pipe for delivering chlorine gas into it, which is intimately blended and further reacts with the cooled vapor exiting the first cooler. The second reaction between the cooled vapor and chlorine gas further produces substantially pure phosphorus pentachloride vapor.

However, the substantially pure phosphorus pentachloride vapor may still comprise trace amounts of unreacted phosphorus trichloride or chlorine vapors, which may be subjected to further reaction steps in subsequently placed cooler and static mixer sequences.
Thus, in this embodiment, a plurality of static mixers and a plurality of coolers may be alternately placed to produce an optimum yield for the process. For example, in one embodiment, a static mixer is first placed which receives vapors of phosphorus trichloride and chlorine. The reaction vapor exiting the first static mixer is then cooled in the subsequently provided cooler. The cooled vapor exiting the first cooler is again fed to a second static mixer to which again chlorine gas is passed. The reaction vapor from the second static mixer is again passed to a second cooler. The vapor exiting the second cooler is thereafter passed into a condenser. In an embodiment, instead of two static mixers and two coolers, a plurality of static mixers and coolers may be alternatively placed to achieve an optimum yield of the process.
In an embodiment, several such series of alternatively placed plurality of static mixers and coolers may be conveniently employed in the apparatus according to the present invention. Preferably, four to eight such series of alternatively placed plurality of static mixers and coolers may be conveniently employed in the apparatus according to the present invention.
In an embodiment, the temperature in the static mixers comprised within the apparatus of the present invention is preferably maintained between 100°C to about 150°C.
In this embodiment, each said static mixer and cooler series may be provided with an exclusive phosphorus trichloride vaporizer which supplies vapor of phosphorus trichloride to that particular series may be used. Additionally, each said static mixer and cooler series may be provided with chlorine vaporizer for supplying pre-heated chlorine gas to that particular series.

In an embodiment wherein the apparatus comprises four series of two static mixers and two coolers, the second static mixer in each said series may be connected to the last cooler positioned in said series.
The vapor exiting each said last placed cooler in the series is delivered to a condenser via a delivery pipe. The delivery pipe connecting said last placed cooler protrudes only slightly into the condenser and releases phosphorus pentachloride vapor in an axial direction that is parallel to the central axis of the cylindrical condenser. In this embodiment, the phosphorus pentachloride vapor is released axially such that the released vapors travel in a direction that is close to and parallel to the lateral surface of the condenser.
It has been found that releasing the phosphorus pentachloride vapors axially within said condenser causes the released.phosphorus pentachloride vapor to condense gradually and deposit on the floor of the frustoconical bottom of the condenser without sticking to the walls of the condenser.
Preferably, the condenser of a desired size may be selected made up of a material selected from mild steel, explobonded Nickel or other such material that are conventionally used in the art.
In a preferred embodiment, the apparatus of the present invention comprises a hammering means disposed externally on the lateral surface of the condenser. The hammering means is adapted to tap the external lateral surface of the condenser thereby causing a small amount of phosphorus pentachloride powder sticking to the internal walls of the container to deposit at the bottom of the condenser.
Alternatively to the hammering means, the apparatus of the present invention comprises a scrapping means adapted to scrap any phosphorus pentachloride powdery material sticking to the internal lateral wall of the condenser and cause it to settle at the bottom of the condenser.

The apparatus of the present invention preferably comprises a scrubbing means. The provided scrubbing means is capable of removing the unreacted chlorine or phosphorus trichloride from the gas stream exiting the condenser. In a preferred embodiment, excess chlorine gas with fine particulates of phosphorus pentachloride may be vented out of the condenser. The scrubbing system according to the present invention comprises a buffer and an absorption system.
The buffer is preferably constructed of lead or nickel and prevents any carry-over of particulate phosphorus pentachloride into the fluid stream.
The absorption system comprises a dilute alkali solution flowing counter-currently to the contaminated vapor and absorbs any unreacted chlorine gas. The preferred alkali solution may comprise sodium hydroxide, sodium bicarbonate, lime or soda ash. The vented vapor may be subjected to washing and/or neutralization with an alkali in an absorption system subsequent to being passed through a buffer. Preferably, a 5% caustic solution in water is used as a preferred scrubbing liquid.
Optionally, the apparatus of the present invention comprises a trombone cooler to condense phosphorus trichloride when present in excess in the vapor exiting the condenser.
In an embodiment wherein the vapor exiting the condenser comprises a substantial quantity of phosphorus trichloride, excess trichloride is removed from the vapor using a trombone cooler.
The apparatus of the present invention comprises a drying and cooling means.
The drying means comprises a cylindrical shaft having a plurality of impeller blades . provided therein. The shaft having a plurality of impeller blades provided therein is placed within a hollow cylindrical shell. Hot water is continuously circulated outside the hollow cylindrical shell, but within the drying means, to raise the temperature of the powdery phosphorus pentachloride material flowing through said drying means to cause the volatile trace impurities of phosphorus trichloride and chlorine to evaporate.

The drying means of the present invention is preferably provided with a hot water supply port at one end and a hot water return port to provide an exit to the hot water exiting the drying means.
In a preferred embodiment, a series of such drying means may be placed in a sequence to achieve a desired purity of phosphorus pentachloride. Preferably, about four such dryers may be placed in a sequence to achieve a desired purity of phosphorus pentachloride.
In another embodiment, the apparatus of the present invention additionally comprises a cooling shell disposed subsequent to said plurality of drying means. Preferably, the cooling shell is similar in construction to the drying means wherein cold water replaces the hot water that is circulated through the drying means.
In an embodiment, the cooling shell has an inert atmosphere of nitrogen maintained therein.
Preferably, several carboys are disposed at the exit of the cooling means to collect the dried and cooled phosphorus pentachloride powder. The collected is shaken using a vibro-shaker machine that is conventionally available to fine-settle the product. The settled product is packed into weight adjusted packs.
Preferably, the packing may be done in an online packing assembly wherein continuous packing of dried, cooled and fine-settled powder occurs.
Detailed description of the drawings
Figure 1 is a flowchart depicting a process for the preparation of free flowing phosphorus pentachloride according to a preferred embodiment of the present invention. The process essentially comprises vaporizing liquid phosphorus trichloride at a temperature range of from about 76°C to about 95°C in at least one provided vaporizer (SI). The vaporized phosphorus trichloride is delivered to at least one static mixer or to a plurality of such static mixers (S2). Subsequently, the vapor exiting the first static mixer, containing

phosphorus pentachloride substantially along with small quantities of phosphorus trichloride or chlorine or both, is passed to a first cooler (S3). The cooled vapor is subsequently delivered to a second static mixer (S4) to which chlorine gas is again delivered (S5). The heated phosphorus pentachloride vapor produced in the second static mixer is delivered to a second cooler (S6). The cooled vapor exiting the second cooler and substantially containing phosphorus pentachloride vapor is delivered to a condenser (S7), wherein powdered crystalline phosphorus pentachloride is allowed to deposit at the floor of the condenser. The deposited phosphorus pentachloride is thereafter delivered (S8) to a drying and cooling means. The undeposited vapor within the condenser is passed into a scrubbing means (S9). The scrubbing means removes the unreacted chlorine or phosphorus trichloride from the gas stream. The deposited phosphorus pentachloride is dried and cooled in the provided drying and cooling means. The phosphorus pentachloride exiting the drying and cooling means is collected into carboys (S10), sieved using a vibro-machine shaker (SI 1) and packed into weight adjusted packets (S12).
Turning to figure 2, described is an apparatus (1) for the preparation of free flowing phosphorus pentachloride. The apparatus comprises phosphorus trichloride vaporizers (2) and chlorine vaporizers (not shown). The vaporized phosphorus trichloride is delivered from the vaporizer (2) and chlorine gas is supplied from chlorine vaporizer to static mixers (3). The static mixers (3) receives phosphorus trichloride and chlorine vapors generated by the provided phosphorus trichloride and chlorine vaporizers and allows the received vapors to blend intimately and react to produce phosphorus pentachloride vapors. The vapor exiting the static mixer is delivered to a subsequently placed cooler (4). The cooler cools the received vapor to a temperature range of from about 80°C to about 100°C. The second static mixer (4') comprises a second feed pipe (5) for delivering chlorine gas into it, which is intimately blended and further reacts with the cooled vapor exiting ihe first cooler. The vapor exiting each said last placed cooler in the series is delivered to a condenser (6) via a delivery pipe. The delivery pipe connecting said last placed cooler (7) protrudes only slightly into the condenser and releases phosphorus pentachloride vapor in an axial direction that is parallel to the central axis of the

cylindrical condenser. It was observed that releasing the phosphorus pentachloride vapors axially within said condenser causes the released phosphorus pentachloride vapor to condense gradually and deposit on the floor of the frustoconical bottom (not shown) of the condenser without sticking to the walls of the condenser. The collected phosphorus pentachloride powder is dried and cooled in a drying and cooling means (8) and packed into weighed packets.
Turning to figure 3, illustrated is an exemplary drying and cooling means preferable in an embodiment of the present invention. The drying means (8) of the present invention additionally comprises a blender (9) in addition to the dryers (10). The dryers (10) comprise a cylindrical shaft (11) having a plurality of impeller blades (12) provided therein. The dryers are preferably provided with a hot water supply port (13) at one end and a hot water return port (14) to provide an exit to the hot water exiting the drying means. The apparatus of the present invention additionally comprises a cooling shell (15) disposed subsequent to said plurality of drying means. The cooling shell comprises a cold water input port (16) and outlet-port (17) for circulating cold water through the cooling means to ensure sufficient cooling of the powdered phosphorus pentachloride. The cooled phosphorus pentachloride is collected into a plurality of carboys (18), fine-settled using a vibro-shaker machine (19) and packed. Preferably, the carboys are disposed at the exit of the cooling means to collect the dried and cooled phosphorus pentachloride powder. The collected is shaken using a vibro-shaker machine that is conventionally available to fine-settle the product. The settled product is packed into weight adjusted packs.
It was surprisingly found that the final phosphorus trichloride content of the phosphorus pentachloride powder obtained by the process of the present invention was at most 0.1%, whereas the conventional processes lead to a phosphorus trichloride content as much as about 5%.
Example 1
Liquid phosphorus trichloride was allowed to flow from phosphorus trichloride storage tank to the vaporizer at a flow rate of 40 kg per hour while chlorine gas flow rate was

maintained at 18 kg per hour. Liquid phosphorus trichloride was thus vaporized at 90°C and provided to the first static mixer. The vapor exiting the first static mixer was passed to the first cooler. The cooled vapor was further passed to a second static mixer where further chlorine gas at 18 kg per hour was delivered. The heated product vapor was fed to a second cooler. The cooled vapor exiting the second cooler was fed to a condenser (S7), wherein powdered crystalline phosphorus pentachloride is allowed to deposit at the floor of the condenser. The deposited phosphorus pentachloride was thereafter delivered to a drying and cooling means. The deposited phosphorus pentachloride was dried and cooled in the provided drying and cooling means. The product, powdered phosphorus pentachloride, was obtained at 47.2 kg per hour. The final product was thus obtained at an average yield of 89.4% based on the quantity of chlorine with a purity of about 99.4%. The free-flowing product had phosphorus trichloride content maximum of about 0.17%.
Example 2
Liquid phosphorus trichloride was allowed to flow from phosphorus trichloride storage tank to the vaporizer at a flow rate of 30 kg per hour while chlorine gas flow rate was maintained at 13.5 kg per hour. Liquid phosphorus trichloride was thus vaporized at 90°C and provided to the first static mixer. The vapor exiting the first static mixer was passed to the first cooler. The cooled vapor was further passed to a second static mixer where further chlorine gas at 13.5 kg per hour was delivered. The heated product vapor was fed to a second cooler. The cooled vapor exiting the second cooler was fed to a condenser, wherein powdered crystalline phosphorus pentachloride is allowed to deposit at the floor of the condenser. The deposited phosphorus pentachloride was thereafter delivered to a drying and cooling means. The deposited phosphorus pentachloride was dried and cooled in the provided drying and cooling means. The product, powdered phosphorus pentachloride, was obtained at 36.13 kg per hour. The final product was thus obtained at an average yield of 91.2% based on the quantity of chlorine with a purity of about 99.3%. The free-flowing product had phosphorus trichloride content maximum of about 0.10%.
The invention has been described above with reference to the specific examples. It should be noted that the example(s) appended above illustrate rather than limit the invention, and

that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. Other than in the operating examples provided hereinbefore or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions are to be understood as being modified in all instances by the term "about".

WE CLAIM:
1. A process for the preparation of free flowing phosphorus pentachloride powder, said process comprising:
(a) vaporizing phosphorus trichloride at a temperature range of 76-95°C and delivering the vaporized phosphorus trichloride to a first static mixer;
(b) delivering chlorine gas into said first static mixer and allowing delivered phosphorus trichloride and chlorine vapors to blend and react to produce vapors of phosphorus pentachloride during which the temperature of the first static mixer is maintained between about 100-150°C;
(c) conveying the heated vapors of phosphorus pentachloride and any unused reactants to a provided first cooler wherein said vapors are cooled to a predetermined temperature, said cooled vapors being subsequently conveyed to a provided second static mixer;
(d) delivering chlorine gas into said second static mixer and allowing said cooled vapors delivered from said first cooler to blend and react with the delivered chlorine gas to further produce vapors of phosphorus pentachloride during which the temperature of the second static mixer is maintained between 100-150°C;
(e) conveying the heated vapors produced in said second static mixer and substantially comprising phosphorus pentachloride to a provided second cooler wherein said vapors substantially comprising phosphorus pentachloride are cooled to a predetermined temperature; and
(f) conveying said cooled phosphorus pentachloride vapors co-axially to a provided condenser thereby causing a deposition of free flowing phosphorus pentachloride powder at bottom portion of said condenser.

2. The process as claimed in claim 1, comprising delivering phosphorus trichloride vapors from a plurality of said vaporizers to a plurality of static mixers.
3. The process as claimed in claim 1 or claim 2, comprising simultaneously cooling the static mixers during the reaction using an external cooling means which maintains the temperature of the static mixer in the range of about 100-150°C.
4. The process as claimed in any preceding claim, wherein the residence of the reacting vapor within said plurality of static mixers is upto about 1 minute.
5. The process as claimed in claim 4, wherein said residence time is about 2 seconds.
6. The process as claimed in any preceding claim, wherein two to eight series of alternatively placed plurality of static mixers and plurality of coolers are positioned around said condenser, wherein the exit of each last placed cooler opens into said condenser.
7. The process as claimed in claim 6, wherein each series is provided with an exclusive phosphorus trichloride vaporizer which supplies vapor of phosphorus trichloride to that particular series.
8. The process as claimed in any preceding claim comprising removing the unreacted chlorine or phosphorus trichloride from the gas stream using a scrubbing means.
9. The process as claimed in any preceding claim comprising scrubbing the vented vapor by washing and/or neutralization with an alkali in an absorption system subsequent to being passed through a buffer.
10. The process as claimed in any preceding claim comprising removing excess phosphorus trichloride in the vented vapor using a trombone cooler.

11. The process as claimed in any preceding claim comprising drying and cooling the deposited phosphorus pentachloride powder in a provided drying and cooling means.
12. The process as claimed in any preceding claim comprising collecting the material exiting the drying'and cooling means into carboys, sieving using a vibro-machine shaker and packing into weight adjusted packets.
13. An apparatus for the preparation of free flowing phosphorus pentachloride powder, said apparatus comprising:

(a) at least one phosphorus trichloride vaporizer capable of receiving liquid phosphorus trichloride and vaporizing the received phosphorus trichloride at a predetermined vaporizing temperature;
(b) a plurality of static mixers, the first static mixer in each series being adapted to receive phosphorus trichloride vapors from a phosphorus trichloride vaporizer, said plurality of static mixers adapted to receive chlorine gas from chlorine batch tanks and allow the received chlorine gas to be intimately blended with phosphorus trichloride vapors thereby causing chlorination of the received phosphorus trichloride to produce phosphorus pentachloride vapors at a predetermined temperature;
(c) a plurality of coolers placed subsequent to said plurality of static mixers, said coolers being adapted to receive, phosphorus pentachloride vapors in admixture with unreacted phosphorus trichloride or chlorine gas or both, at a predetermined temperature and cooling the said admixture of vapors to a predetermined cooled temperature, said coolers being capable of delivering the cooled admixture of gases to a static mixer provided that the last cooler in the sequence is connected to. and capable of co-axially delivering vapors substantially comprising phosphorus pentachloride to. at least one provided condenser via a delivery pipe;

(d) a plurality of delivery pipes connecting each said cooler, being placed last in the sequence of said plurality of static mixers and coolers, to a provided condenser, said plurality of delivery pipes only slightly protruding within the condenser and releasing said phosphorus trichloride vapors co-axially within said condenser such that said coaxially released phosphorus pentachloride vapors gradually condense and deposit at the bottom of said condenser; and
(e) at least one cylindrical condenser having a frustoconical bottom connected to each said cooler, being placed last in the sequence of said plurality of static mixers and coolers via a plurality of delivery pipes, said cylindrical condenser allowing the coaxially released phosphorus pentachloride vapors to condense and deposit in the frustoconical bottom of the condenser.

14. The apparatus as claimed in claim 13 wherein said plurality of static mixers is maintained at a temperature from about 100°C to about 150°C during the generation of phosphorus pentachloride vapors.
15. The apparatus as claimed in claims 13-14 wherein said plurality of static mixers is preferably provided with external cooling means..
16. The apparatus as claimed in claims 13-15 wherein said static mixer comprises a series of baffles contained in a cylindrical housing.
17. The apparatus as claimed in claims 13-16, wherein static mixer is constructed of stainless steel material, preferably SS316 and is internally lined with PTFE.
18. The apparatus as claimed in claims 13-17, wherein said baffles are made of polytetrafluoroethylene (PTFE).
19. The apparatus as claimed in claims 13-18 wherein a plurality of static mixers and coolers are placed alternatively.
20. The apparatus as claimed in claim 19, wherein a plurality of such series are positioned around the condenser.
21. The apparatus as claimed in claim 20 wherein four series of two static mixers and two coolers are placed in sequence.

22. The apparatus as claimed in claims 13-21, wherein the vapor exiting each said last placed cooler in the series is delivered to a condenser via a delivery pipe.
23. The apparatus as claimed in claims 13-22, wherein said delivery pipe connecting said last placed cooler protrudes slightly into the condenser and releases phosphorus pentachloride vapor in an axial direction that is parallel to the central axis of the cylindrical condenser.
24. The apparatus as claimed in claim 23, wherein phosphorus pentachloride vapor is released coaxially such that the released vapors travel in a direction that is close to and parallel to the lateral surface of the condenser.
25. The apparatus as claimed in claims 13-24 comprising a scrubbing means such as herein described.
26. The apparatus as claimed in claims 13-25 comprising a trombone cooler to condense phosphorus trichloride when present in excess in the vapor exiting the condenser.
27. The apparatus as claimed in claims 13-26 comprising a drying and cooling means such as herein described,
28. The apparatus as claimed in claims 13-27 comprising a plurality of carboys, at least a vibro-shaker means and a plurality of weight-adjusted packets.
29. A process for the preparation of free flowing phosphorus pentachloride powder substantially as described herein with reference to the examples and accompanying drawings.
30. An apparatus for the preparation of free flowing phosphorus pentachloride powder substantially as described herein with reference to the examples and accompanying drawings.