A PROCESS FOR PREPARING EPICHLOROHYDRIN

Field of invention

The present invention relates to preparation of epoxides.

More particularly, the present invention relates to a process for the preparation of epichlorohydrin.

Background and prior art

Epichlorohydrin (also known as l,2-epoxy-3-chloropropane or 2- chloromethyl oxirane) is a useful raw material in the manufacturing of resins. The largest use of Epichlorohydrin is in the manufacture of Epoxy Resins, which find applications in surface coatings. A number of surface active agents are also being made from Epichlorohydrin which is used as detergents, demulsifiers, phenoxy resins, synthetic rubbers, glycidyl ethers, amine adducts and the like. It is also used as a stabilizer for chlorinated rubbers and as a solvent for cellulose, resins and paints. However, a significant fraction of epichlorohydrin (ECH) produce goes in the manufacture of glycerin. Epichlorohydrin also finds applications in the preparation of a number of pharmaceuticals, textile conditioners, dyes, paper sizing agents and the like. It is used as a solvent (e.g. for cellulose acetate) as a stabilizer for polyvinyl chloride, chlorinated rubbers and several chlorine containing insecticides, and as an additive to lubricating oil greases.

Epichlorohydrin is industrially manufactured by chlorination of Allyl chloride, which is obtained, by high-temperature chlorination of propylene. By-products of chlorination are cis- and trans-l,3-dichloropropene and 1,2- dichloropropane. Glycerol dichlorohydrin are made from Allyl chloride with 1, 2, 3-trichloropropane being the by-product. Finally, Epichlorohydrin is

produced from the glycerol-dichlorohydrin mixture by treatment with base. The main disadvantages are,

1) The process uses lime/CaO, water and extra chlorine, resulting in high cost.

2) Expenses on the utilities involving steam, electricity, cooling water and air/N2 arevery high.

3) Generation of effluents, which are of the order of 15-20 tons per ton of ECH product, is major problem in terms of operation cost and the statutory requirements.

Conventionally, epichlorohydrin is manufactured by reacting allyl chloride with chlorine in an aqueous acidic medium, neutralizing the resulting acidic medium containing the product, separating and purifying epichlorohydrin from the resulting solution.

United States Patent no. 6380407 discloses a process for the manufacturing of an epoxide, in which an olefin reacts with a peroxide compound in the presence of a zeolite-based catalyst and in the presence of a solvent in a reactor in the liquid phase. Gaseous compound was introduced continuously into the reactor at a flow rate which was sufficient to entrain at least some of the epoxide produced, which is recovered along with the gaseous compound at the point at which it leaves the reactor. Some of the draw backs are use of gaseous compound for carrying out the reaction which results in consumption of extra energy in preheating the compound and also for maintaining the fluidization of the solid catalyst.

United States Patent No. 4,113,746 discloses a continues process for the manufacture of epichlorohydrin comprising reacting chlorine and allyl chloride in an aqueous acidic medium; neutralizing the resulting hydrochloric acid containing glycerol dichlorohydrin with an alkaline

solution of CaCO ₃ and Ca(OH) ₂ to form a solution containing epichlorohydrin, saponifying the neutralized solution with slaked lime. Epichlorohydrin is then separated by azeotropic distillation. A large amount of calcium chloride slurry formed during neutralization is further recycled in the process.

United States Patent No. 4,634,784 discloses a process for preparing epichlorohydrin by reacting allyl alcohol with chlorine at a temperature of about -30 to 20 ⁰ C under a pressure of 0 to 10 atm in an aqueous hydrochloric acid solution to form 2,3-dichloro-l-propanol; separating a portion of the hydrogen chloride by heating the reaction mixture to recover the hydrogen chloride gas; cooling the reacting mixture after separating the HCl gas to a temperature of 40 ⁰ C or less and reacting it with an alkaline solution or suspension at 40"C to recover epichlorohydrin.

The main disadvantages of above mentioned conventional manufacturing process of epichlorohydrin are: formation of large amount of calcium chloride as slurry, use of corrosive acid (hydrochloric acid or chlorine gas) and formation of diols as by-products. One way to obviate these problems is through preparing epichlorohydrin by reacting allyl chloride with hydrogen peroxide in a liquid medium preferably an aqueous alcohol in presence of a catalyst. The epichlorohydrin is obtained as a product along with the mixture of alcohol-water, unconverted allyl chloride and possibly certain impurities from reactants and various by products. However, the key issues in such hydrogen peroxide mediated process include isolation of final product, epichlorohydrin. Typically, the reaction mass comprises multiple binary hetero azeotropes, which do not allow easy separation of the product

epichlorohydrin and the reactant allyl chloride from the reaction crude. These binary hetero azeotropes hamper the distillation process.

The prior art processes, as disclosed in United States Patent No. 6,288,248 and 6,350,888 disclose liquid extraction using dichlorobenzene using excess of extraction solvent (more than 30 tons per ton of epichlorohydrin), further adding to the cost of purification of thus obtained epichlorohydrin. Moreover, further treatment of the raffinate is difficult.

The gross production cost of epichlorohydrin by hydrogen peroxide process is higher compared to conventional process, mainly due to the processing of methanol-water mixture. If methanol quantity could be further reduced, it is certain that the energy cost will be reduced consequently. Hence there is a need for an improved process for the manufacture of epichlorohydrin in which minimum epichlorohydrin is lost into the aqueous layer and to increase the percentage yield by cascade reactions. The objects of the present invention address such needs.

Objects of the invention

It is an object of the present invention to provide a continuous process for the preparation of high purity epichlorohydrin.

It is another object of the present invention to provide a continuous process for preparing epichlorohydrin using cascade or split reactor system.

It is a further object of the present invention to provide a method for efficient separation of epichlorohydrin from the reaction mass by extraction.

Yet another object of the present invention is to prepare pure epichlorohydrin without any side products.

It is a still further object of the present invention is to provide a clean, cost effective, eco-friendly process for the formation of epichlorohydrin.

Summary of the invention

In accordance with this invention there is provided a process for preparing epichlorohydrin comprising the following steps:

(a) reacting allyl chloride with an inorganic peroxide compound in the presence of at least one solvent at a temperature of about 40 to 50 degree C in atleast one reactor containing a catalyst bed to obtain a resultant mixture of epichlorohydrin, unreacted allyl chloride, solvent and water;

(b) extracting, in at least one extractor by water from the resultant mixture to form an organic phase stream and mainly comprising epichlorohydrin, unreacted allyl chloride, solvent and traces of water an aqueous phase stream comprising water, solvent and traces of allyl chloride and epichlorohydrin;

(c) separating and recovering the solvent and water individually from the aqueous phase via at least one distillation column;

(d) separating and recovering unreacted allyl chloride and epichlorohydrin individually from the organic phase via at least one distillation column;

(e) recycling the recovered water from step (c) to the extractor for step

(b);

(f) recycling the recovered allyl chloride from step (d);

(g) recycling the recovered solvent from step (c) to the reactor for step (a); and (h) collecting and purifying the recovered epichlorohydrin by distillation.

In accordance with one of the embodiment of the present invention, the reactors are arranged in parallel.

In an alternate embodiment, the reactors are arranged in series and the resultant mixture of one reactor is used as a partial feed for the next reactor in series.

Typically, the reactants are premixed before feeding the mixture to the reactor.

Typically, the reactants are fed separately to the reactor.

Typically, the molar ratio of allyl chloride to peroxide at the inlet of the reactor is 9:1 and allyl chloride to solvent weight ratio is 2:1.

Preferably, the extraction step includes the step of addition of ally chloride for phase shifting of the separation towards the organic phase.

Typically, the inorganic peroxide is at least one peroxide selected from a group consisting of hydrogen peroxide, acetone triperoxide, hexamethylene triperoxide diamine, sodium peroxide, barium peroxide, calcium peroxide, strontium peroxide, carbamide peroxide, magnesium peroxide and benzoyl peroxide.

Typically, the solvent is at least one solvent selected from a group consisting of methanol, ethanol, 1-propanol, 1-butanol, acetic acid and acetone.

Typically, the extraction step further comprises the step of recycling the recovered unreacted allyl chloride to the extraction step.

Brief description of the drawing

FIG 1: represents the schematic diagram for the process of the present invention; and

FIG 2: represent the flow diagram of an extractor involved in the said process of the present invention as shown in FIG 1.

Detailed description of the invention

In accordance with the present invention, there is provided an improved process for the preparation and purification of epichlorohydrin wherein a reaction mixture of allyl chloride (ALC), solvent, water and 50% inorganic peroxide compound is fed to a reactor system in an up-flow manner, wherein the reactor system is either arranged in series or parallel. The reactants can be fed separately to the reactor system or can be premixed. The reactor system comprises at least one reactor containing catalyst to form a resultant mixture of epichlorohydrin, unreacted allyl chloride, solvent and water. Preferably, the reactors are arranged in series wherein the resultant mixture from the first reactor forms a partial feed for the second. The reaction temperature was maintained around 40 - 50 degree C.

The resultant mixture, after exiting the first reactor, enters the next reactor and the subsequent reactors. Each subsequent reactor contains catalyst and is fed with additional peroxide compound. The peroxide compound is fed into each reactor for efficient utilization of the catalyst activity and high

percentage conversion of the reactants. The amount of peroxide compound added depends upon several factors such as number of reactors, temperature, and amount of the catalyst in the reactor, catalyst activity and stoichiometric conversion in each reactor. All the reactors are maintained at predetermined temperature and pressure. The composition of the effluent stream from each reactor is continuously analyzed by gas chromatography.

The product stream from the last reactor is fed to an extractor for extraction with cold water at 0-5 degree C and separation of the resultant mixture into aqueous phase and organic phase. The aqueous phase containing un-reacted allyl chloride, water and solvent is fed to a first distillation column, wherein un-reacted allyl chloride and solvent are collected at the top of the distillation column as vapors and are sent back to the main reactor for reaction therein. The water obtained is discharged out and can be used further for horticulture purposes. The lighters coming out of this distillation column are used as combustion fuel whereas the leftover distillation mass is sent back to the Extractor.

The organic phase after extraction is fed to a second distillation column. In another embodiment, fresh allyl chloride is added to this second distillation column for phase shifting of the separation towards the organic phase. The vapor stream consisting mainly of allyl chloride and methanol from the top of the second distillation column is fed back to the main reactor. The extraction step further comprises recycling of the recovered ally chloride for extraction. The epichlorohydrin from the distillation column is further distilled to obtain epichlorohydrin of about 99 % purity and yield of about 96%. This is collected at the base of the distillation column.

Typically, the inorganic peroxide is at least one peroxide selected from a group consisting of hydrogen peroxide, acetone triperoxide, hexamethylene triperoxide diamine, sodium peroxide, barium peroxide, calcium peroxide, strontium peroxide, carbamide peroxide, magnesium peroxide and benzoyl peroxide.

Typically, the solvent is at least one solvent selected from a group consisting of methanol, ethanol, 1-propanol, 1-butanol, acetic acid and acetone.

The invention will now be described with reference to the accompanying schematic drawing, FIG. 1, which illustrates a flow diagram of typical embodiments of a process in accordance with this invention.

Description of figure 1 :

In accordance with the present invention, figure 1 discloses one of the embodiments where in, the catalytic oxidation of allyl chloride takes place in reactors (Rl and R2) containing packed catalyst. Inlet stream (IS) containing the reactants, allyl chloride (ALC), methanol (MeOH) and one part of fresh hydrogen peroxide (HP) is passed into the reactor Rl, and the second part of fresh Hydrogen Peroxide is passed into the second Reactor (R2).

As shown in Figure 1, Reactor 1 (Rl) is a first reactor containing catalyst. In this reactor, catalytic oxidation of Allyl chloride takes place with hydrogen peroxide (50 %) to form epichlorohydrin. Methanol is added to the reactor for homogenization of the liquid media. The molar ratio of Allyl chloride to hydrogen peroxide at the inlet of the reactor is typically 9:1 and allyl chloride to methanol weight ratio is typically 2:1. The reaction mass exiting the first reactor contains about 7-8 % of epichlorohydrin along with unreacted allyl chloride, methanol and water. This reaction mass is then fed

to a second reactor (R2) also containing catalyst. A calculated amount of hydrogen peroxide is added again to the reactor (R2). The flow rate of feed entering the second reactor is maintained typically at 50 - 65 gm/hr.

After the completion of the reaction, an outlet stream (OS) from the reactor R2, containing epichlorohydrin (ECH), unreacted allyl chloride, methanol and water is transferred to a holding tank (Tl). The effluent stream (ES) from the holding tank (Tl) is then mixed with process water (PW) and then fed to an extraction chamber (ECl). The organic phase (OP) and aqueous phase (AP) get separated in the extraction chamber (ECl). The aqueous phase (AP) from the ECl is passed into the EC2, in which second time extraction of ECH takes place by adding fresh ALC to the extraction chamber EC2. The OP from the ECl and EC2 is passed into the distillation column C2; however the AP from the EC2 is passed to the distillation column Cl. The recovered ALC, MeOH from the Cl and C2 are recycled and reused. The process water from Cl and ETP is recycled to T2 via RPW. The crude ECH obtained from the C2 is fed to a C3 to obtain pure ECH and heavies. The mass flow rate of ES/PW is maintained in the range of 0.2 to 0.7.

Typically, the extraction chambers (EC) consist of three separate units: a premixer (M), a cold extractor (CE) and a Decanter settler (DS) as shown in FIG. 2.

The premixer M is a preferred embodiment for proper mixing of two streams. The premixer M comprises glass beads wherein streams from Tl and T2 are thoroughly mixed before flowing downstream to a cold extractor CE. The two streams from Tl and T2 is typically water and/or ally chloride in the desired ratios.

The cold extractor (CE) is a coil type of cooler in which the reactor effluent and the process water is led through the coil and coolant is circulated through the coolant inlet in the shell to bring down the temperature of the mixture in the coil to 8 to 4 degree C and exits at the outlet. The residence time of the mixture in the extractor ranges between 45 to 150 minutes. From the cold extractor the mixture of the reactor effluent and the process water is led to the decanter settler (DS) placed below the cold extractor (CE) in the extraction chamber EC, where the temperature of the mixture is maintained at about 8 to 4 degree C. The separation of organic and aqueous phase takes place by difference in densities of the two phases, in which the organic phase settles to the bottom of the decanter settler (DS) and is extracted through the outlet of the decanter settler (DS) through organic outlet. The resident time of the split phase content and the levels of the two phases are carefully controlled. The aqueous phase is let off from the aqueous outlet of the decanter settler (DS).

The aqueous phase after the EC typically consists of mainly water and methanol with some quantities of unreacted allyl chloride and some traces of ECH. The organic phase obtained from the column Cl and C2 typically consists of epichlorohydrin, unreacted allyl chloride, and Methanol with some traces of water. The organic phase is led to the distillation column (C2) where the crude epichlorohydrin is obtained and is led to the distillation column (C3) to obtain high purity epichlorohydrin. The recovered ALC and MeOH from the distillation column Cl and C2 is recycled and mixed with the inlet stream (IS) of the reactor (Rl). The aqueous stream is led to the distillation column (Cl) where essentially, methanol and allyl chloride and water get separated. The recovered ALC, MeOH and water from distillation column Cl is sent back to the inlet of Reactor Rl and to the inlet of cold Extraction unit respectively.

The conversion of hydrogen peroxide is around 99% with 98.18% selectivity to epichlorohydrin.

A split reactor system in accordance with this invention was tested for the preparation of epichlorohydrin by continuous reaction between allyl chloride and hydrogen peroxide using aqueous alcohol as solvent and observed to fulfill the objects of the present invention.

The use of split reactor system (at least two reactors in sequence) has shown some advantages like:

1. Concentration of epichlorohydrin in the reactor effluent stream is more by 67-72 % than the conventional single reactor system leading to consequent increase in space time yield of epichlorohydrin;

2. Reaction goes smoothly without any hassle at lower temperatures of about 42 to 46 ⁰ C;

3. No side products like diols were observed during reaction;

4. Catalyst shows better activity even after 60 hrs, and;

5. Better separation was achieved at distillation train Dl and D2 by using cold water (0-5 ⁰ C) and allyl chloride respectively,

Advantageous features of the present invention

1. A simple sequence of at least two reactors, extractor and distillation coulmn.

2. Extraction is carried out using cold water; water effluent can be used for horticulture purposes.

3. No organic/ inorganic effluent formation during the reaction.

4. No diol formation.

5. No use of strong, corrosive acid like hydrochloric acid or chlorine gas.

6. Overall use of methanol is reduced by 30-35 % without affecting the selectivity to epichlorohydrin.

7. Very clean route compared to conventional routes for the preparation and separation of epichlorohydrin.

The invention will now be described with respect to the following examples which do not limit the invention in any way and only exemplify the invention.

Examples 1:

A combined feed at a rate of 60 gms/hr containing excess Allyl chloride was reacted with one part of Hydrogen Peroxide in presence of Methanol as a solvent using 15 gms of TS-I catalyst packed in the first reactor, on a continuous basis to produce Epichlorohydrin. The stream at the exit of first reactor mainly consisted of un reacted Allyl chloride (32.36 mole%), Methanol (52.05 mole%), Epichlorohydrin (3.97 mole%), & Water (11.57 mole%), which was mixed with the second part of Hydrogen Peroxide and was fed into the second reactor, containing 15 gms of catalyst on a continuous basis to produce Epichlorohydrin. The stream at the exit of second reactor mainly contains Allyl chloride (25.39 mole %), Methanol (46.11 mole %), Epichlorohydrin (7.54 mole %), & Water (20.91 mole %). The second reactor effluent, at a rate of 46 gms/hr was mixed with water which was chilled to 5 degree C, in specially designed extractor equipment. The weight ratio between process stream and water was maintained at 0.4. Sufficient residence time of 100 minutes was provided in the settler, to separate the organic and the aqueous phase. The bottom organic layer was withdrawn at a rate of 28.09 gms/hr containing Allyl chloride (59.80 mole %), Methanol (11.51 mole %), Epichlorohydrin (24.68 mole %), & Water (4.00 mole %). The top aqueous layer was further extracted with fresh quantity of allyl chloride at 5 degree C. The two layers obtained were further

subjected to fractionation and pure Epichlorohydrin was recovered by further distillation at the rate of 9.02 gms/hr with an overall yield of 96.45% and purity of 99%. The water, methanol and allyl chloride from the two layers were recovered and recycled to the first reactor.

Example 2

A combined feed at a rate of 2100 gms/hr containing excess Allyl chloride was reacted with one part of Hydrogen Peroxide in presence of Methanol as a solvent using 800 gms of TS-I catalyst packed in the first reactor, on a continuous basis to produce Epichlorohydrin. The stream at the exit of first reactor mainly consisted of un reacted Allyl chloride (35.36 mole %), Methanol (45.87 mole %), Epichlorohydrin (4.25 mole %), & Water (14.48 mole %), which was mixed with the second part of Hydrogen Peroxide and was fed into the second reactor, containing 800 gms of catalyst on a continuous basis to produce Epichlorohydrin. The stream at the exit of second reactor mainly contains Allyl chloride (26.17 mole %), Methanol. (46.16 mole %), Epichlorohydrin (8.06 mole %), & water (19.57 mole %). The second reactor effluent, at a rate of 2020 gms/hr was mixed with water which was chilled to 5 degree C, in specially designed extractor equipment. The weight ratio between process stream and water was maintained at 0.4. A sufficient residence time of 100 minutes was provided in the settler, to separate the organic and the aqueous phase. The bottom organic layer was withdrawn at a rate of 1233.52 gms/hr containing Allyl chloride (62.39 mole %), Methanol (14.25 mole %), Epichlorohydrin (19.93 mole %), & water (3.42 mole %). The top aqueous layer was further extracted with fresh quantity of allyl chloride at 5 degree C. The two layers obtained were further subjected to fractionation and pure Epichlorohydrin was recovered by further distillation at the rate of 331.73 gms/hr with an overall yield of 96.69 %. The

water, methanol and allyl chloride from the two layers were recovered and recycled to the first reactor.

Example 3

A combined feed at a rate of 60 gms/hr containing excess Allyl chloride was reacted with one part of Hydrogen Peroxide in presence of Methanol as a solvent using 15 gms of TS-I catalyst packed in the first reactor, on a continuous basis to produce Epichlorohydrin. The stream at the exit of first reactor mainly consisted of un reacted Allyl chloride (32.51 mole%), Methanol (52.16 mole %), Epichlorohydrin (3.95 mole %), & Water (11.55 mole %), which was mixed with the second part of Hydrogen Peroxide and was fed into the second reactor, containing 15 gms of catalyst on a continuous basis to produce Epichlorohydrin. The stream at the exit of second reactor mainly contains Allyl chloride (25.54 mole %), Methanol (46.22 mole %), Epichlorohydrin (7.52 mole %), & Water (20.89 mole %). The second reactor effluent, at a rate of 46 gms/hr was mixed with water which was chilled to 5 degree C, in specially designed extractor equipment. The weight ratio between process stream and water was maintained at 0.41. A sufficient residence time of 120 minutes was provided in the settler, to separate the organic and the aqueous phase. The bottom organic layer was withdrawn at a rate of 27.52 gms/hr containing Allyl chloride (59.83 mole %), Methanol (11.49 mole %), Epichlorohydrin (24.47 mole %), & Water (4.21 mole %). The top aqueous layer was further extracted with fresh quantity of allyl chloride at 5degree C. The two layers obtained were further subjected to fractionation and pure Epichlorohydrin was recovered by further distillation at the rate of 9.02 gms/hr with an overall yield of 95.61% and 99% purity. The water, methanol and allyl chloride from the two layers were recovered and recycled to the first reactor.

Example 4

A combined feed at a rate of 2100 gms/hr containing excess Allyl chloride was reacted with one part of Hydrogen Peroxide in presence of Methanol as a solvent using 800 gms of TS-I catalyst packed in the first reactor, on a continuous basis to produce Epichlorohydrin. The stream at the exit of first reactor mainly consisted of un reacted Allyl chloride (35.96 mole %), Methanol (45.27 mole %), Epichlorohydrin (4.31 mole %), & Water (14.42 mole %), which was mixed with the second part of Hydrogen Peroxide and was fed into the second reactor, containing 800 gms of catalyst on a continuous basis to produce Epichlorohydrin. The stream at the exit of second reactor mainly contains Allyl chloride (26.43 mole %), Methanol (46.22 mole %), Epichlorohydrin (8.99 mole %), & water (19.64 mole %). The second reactor effluent, at a rate of 2020 gms/hr was mixed with water which was chilled to 5 degree C, in specially designed extractor equipment. The weight ratio between process stream and water was maintained at 0.41. A sufficient residence time of 120 minutes was provided in the settler, to separate the organic and the aqueous phase. The bottom organic layer was withdrawn at a rate of 1268.52 gms/hr containing Allyl chloride (65.39 mole %), Methanol (13.87 mole %), Epichlorohydrin (19.76 mole %), & water (3.32 mole %). The top aqueous layer was further extracted with fresh quantity of allyl chloride at 5 degree C. The two layers obtained were further subjected to fractionation and pure Epichlorohydrin by further distillation was recovered at the rate of 328.40 gms/hr with an overall yield of 95.72 %. The water, methanol and allyl chloride from the two layers were recovered and recycled to the first reactor.

While considerable emphasis has been placed herein on the specific steps of the preferred embodiment, it will be appreciated that many alterations can be made and that many modifications can be made in the preferred embodiment

without departing from the principles of the invention. These and other changes in the preferred embodiment as well as other embodiments of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.