DESC:Field of the invention
The present invention relates to a process for the preparation of alkyl bromide from alcohol isolated from a waste stream of the isopropanol manufacturing plant.

Background of the invention
The background information herein relates to the present invention but is not necessarily prior art.

There are various technologies commercially available for the production of isopropanol (IPA), including methods such as utilizing sulfuric acid or phosphoric acid, directly hydrating propylene using an ion-exchange catalyst and employing the acetone route. In the direct hydration process, the raw material used is refinery-grade propylene, which has a purity ranging from 60% to 90% depending on the configuration of the sourcing refinery. Isopropanol (IPA) is generated through a chemical reaction between propylene and water at a temperature ranging from 180? to 200?, and at a pressure of 30 bar to 50 bar in the presence of phosphoric acid in the vapor phase. Using the direct hydration process, the percentage of IPA converted is around 4% to 5%. The propylene that hasn’t undergone a reaction is retrieved and reused within the process, thereby boosting the overall conversion rate of the process to exceed 90%. The initial IPA with a crude composition ranging from 12% to 20% strength undergoes a process where it is passed into a sequence of distillation columns which results in the separation of undesired byproducts like ether, acetone, n-propanol (NPA), hexanol, hexane, and water, ultimately resulting in the production of pure IPA, which is the primary goal of the IPA plant. As a result, there hasn’t been much focus on utilizing the by-product streams like n-propanol (NPA), diisopropyl ether, acetone and the like. Among all the by-products obtained from the IPA plant, NPA is generated with organic impurities, IPA, water etc., at a rate that amounts to 1% to 2% of the IPA production rate. Conventionally, there is no such process known in the prior art that employs or utilizes the waste stream from the isopropanol manufacturing plant which is rich in n-propanol to prepare alkyl bromide such as propyl bromide.
Therefore, a need exists to provide a process for the preparation of alkyl bromide from n-propanol recovered from the waste stream of the isopropanol manufacturing plant that is suitable for various applications.

Summary of the invention
In an aspect, the present invention relates to a process for preparation of propyl bromide from n-propanol. The process comprises:
(a) recovering n-propanol from a waste stream of an isopropanol manufacturing plant; and
(b) treating n-propanol with a brominating agent in presence of a catalyst.

In an aspect, the invention relates to a process for recovery of n-propanol from waste stream of isopropanol manufacturing plant. The process comprises:
i. collecting n-propanol (NPA-rich) waste stream from isopropanol manufacturing plant by azeotropic distillation, wherein the waste stream includes an organic phase and an aqueous phase; and
ii. adding a solvent to the organic phase followed by distillation to recover n-propanol.

Detailed description of the invention
In an embodiment, a process for preparation of alkyl bromide such as propyl bromide from n-propanol comprises of recovering n-propanol (NPA) from an NPA rich waste stream of an isopropanol manufacturing plant. The recovered NPA is treated with a brominating agent in the presence of a catalyst to obtain alkyl bromide.

In an embodiment, a process for recovery of n-propanol (NPA) from waste stream of an isopropanol (IPA) manufacturing plant comprises the steps of collecting n-propanol (NPA-rich) waste stream from an isopropanol manufacturing plant by azeotropic distillation. The waste stream includes an organic phase and an aqueous phase. The organic phase is treated with a solvent and subjected to distillation for recovering n-propanol. The detailed process of recovering n-propanol is explained in Stage 1.

In accordance with the embodiments of the present disclosure, the process for the preparation of alkyl bromide such as propyl bromide from n-propanol (NPA) recovered from the isopropanol (IPA) manufacturing plant comprises two stages:
Stage 1: recovering n-propanol from an isopropanol (IPA) manufacturing plant waste stream; and
Stage 2: treating the recovered n-propanol of stage 1 with a brominating agent in the presence of a catalyst to obtain alkyl bromide such as propyl bromide.

The process is described in detail below:

Stage 1: Recovering n-propanol (NPA).
In an isopropanol (IPA) manufacturing plant, n-propanol (NPA) rich waste stream is produced and collected by azeotropic distillation. The NPA rich waste stream includes an organic layer and an aqueous layer. A solvent is added to the organic layer, which is subjected to distillation to recover NPA. Though, the solvent can be added without separation of the organic layer and aqueous layer, preferably, the aqueous layer is separated to avoid processing load on downstream equipment before adding the solvent to the organic layer.

Azeotropic distillation is carried out in suitable distillation column(s).

The solvent includes but is not limited to entrainers such as at least one of cyclohexane, ethyl acetate, n-heptane, and methyl isobutyl ketone. Other suitable similar solvents can be used. The amount of the solvent ranges from 8% to 12%.

The distillation after adding the solvent is carried out at a temperature in a range of 90°C to 130 oC. Suitable distillation column(s) were utilized to conduct distillation.
Different distillation columns were utilized to collect NPA, organic impurities, solvent with water, and only water via fractionation distillation as follows:
In first fractionation distillation, water is collected at a temperature in a range from 90°C to 96°C.
In the second fractionation distillation, solvent and water are collected at a temperature of 110°C.
In the third fractionation distillation, n-propanol is recovered with an increase in temperature from 110°C to 130°C and high boiling impurities present in the distillation pot were settled down.

The solvent is further separated from water and recycled back to the distillation column.

The NPA rich waste stream constitutes around 70% of an organic layer and 30% of an aqueous layer. The organic layer comprises of NPA in a range of around 30% to 40%, water in a range of 15% to 25%, and balance organic impurities which can include, but is not limited to 3-methyl 3-pentanol, 2-methyl pentanol, 4-methyl 2-pentanol, IPA, dimethyl butanol, and ethyl methyl pentene.

The amount of NPA recovered is in high amount of 75% to 80%. The recovered NPA has a high purity in a range of 96% to more than 99%. It was found that around 75% to 80% of the NPA could be recovered from the waste stream of the IPA manufacturing plant, which otherwise conventionally would have been disposed of or lost. NPA is used across many industries in many chemical reactions. Therefore, recovery of the NPA from an IPA manufacturing plant is economically valuable and helps to sustain the other downstream processes. An example is the utilization of the recovered NPA in a process of manufacturing alkyl bromide such as propyl bromide. Further, the disposal of waste streams from an IPA manufacturing plant without removal of NPA could pose an environmental concern. This invention addresses such problems and provides an effective means to recover and utilize NPA in other processes.
Stage 2: Preparing alkyl bromide from recovered n-propanol (NPA).
The recovered n-propanol (NPA) from Stage 1 is treated with a brominating agent
in the presence of a catalyst. The brominating agent is selected from hydrogen bromide, liquid bromine, N-bromo succinimide or mixtures thereof. Preferably, 48wt% of hydrogen bromide or 62% of hydrogen bromide or only liquid bromine is used. The brominating agent and n-propanol is present in a molar ratio of 0.2:1 to 4:1.

The catalyst is selected from a sulfur or sulfur-containing reagent. The sulfur containing agent is preferably sulfuric acid. The amount of the catalyst is in a range from 2% to 5%.

The brominating agent and n-propanol are stirred in a reactor and heated to a temperature in a range from 120°C to 130°C. The brominating agent and n-propanol are continuously fed via pumps in equimolar quantities, while simultaneously removing n-propyl bromide and water formed in the process through distillation.

a. Forming propyl bromide by using hydrogen bromide
The recovered n-propanol (NPA) of Stage 1 is treated with hydrogen bromide in the presence of a catalyst at an ambient temperature in a molar ratio of hydrogen bromide to n-propanol ranging from 2:1 to 4:1 to obtain propyl bromide. The amount of hydrogen bromide is in a range of 45wt.% to 65wt.%.

The catalyst includes but is not limited to sulfuric acid, and sulfur. The catalyst promotes the reaction and acts as a dehydrating agent. The amount of the catalyst is in a range from 2% to 5%.

The mixture is heated to 61°C to 66°C for 3 hours, cooled and separated at 30°C to form an upper phase and a lower phase.

The upper phase consisting of propyl bromide was extracted.
The lower (aqueous) phase consists of hydrogen bromide and a minor quantity of propyl bromide dissolved in it. The lower phase is heated up to 125°C to recover the dissolved propyl bromide by evaporation.

Propyl bromide obtained from the lower phase is combined with the upper phase.

Propyl bromide is washed with alkali and dried over anhydrous sodium carbonate. The alkali is selected from sodium carbonate, caustic soda (sodium hydroxide), etc. in an amount from 2% to 3%.

The method described herein can be used to prepare other alkyl bromides including but not limited to, methyl bromide, ethyl bromide, and propyl bromide.

b. Forming propyl bromide by using liquid bromine.
Propyl bromide is produced by reacting n-propanol with liquid bromine at a temperature in a range of 62°C to 65°C in the presence of a catalyst at a residence time ranging from 1 hour to 5 hours. Propyl bromide is neutralized or washed or polished by adding a soda ash solution.

The molar ratio of bromine to n-propanol is in a range of 0.2:1 to 0.6:1.

The catalyst can include but is not limited to sulfur, and sulfuric acid. Sulfur acts as an electrophile and promotes the reaction rate as it acts as a dehydrating agent. The amount of the catalyst is in a range from 2% to 5%.

The yield of the propyl bromide is in a range of 94% to 99%.

The purity of n-propyl bromide is in a range of 94% to more than 99 %.

The process for the preparation of n-propyl bromide is performed either in batch mode or in continuous mode.
The propyl bromide is recovered through phase separation in batch mode or by overhead condensation in continuous mode.

The final product stream contains 96% to 99% of n-propyl bromide, purity of 99+ % and isopropyl bromide in a range of 0.5% to 1.5%.

The scheme of the present invention to prepare n-propyl bromide using hydrogen bromide and/or liquid bromine is as follows:
1) HBr + C3H7OH ? C3H7Br + H2O
2) Br2+ 2C3H7OH ? 2C3H7 Br + ½ O2

The use of propyl bromide includes but is not limited to vapor degreasing, metal cleaning, dry cleaning, as a solvent carrier in adhesives, and as a chemical intermediate in organic synthesis and in the manufacture of agrochemicals and pharmaceuticals, pigments and dyes, disinfectants, antiseptics, aerosols, coating & inks, etc.

The process is environment friendly and highly efficient as it provides higher yield and purity of n-propyl bromide from waste stream of isopropanol manufacturing plant. Recovering n-propanol from the waste stream and recycling the solvent provides a cost-efficient process.

Experimental details

The following examples are illustrative and not limiting to the invention.

Example 1: Recovery of n-propanol (NPA) from the isopropanol (IPA) manufacturing plant waste stream
The waste stream of isopropanol (IPA) manufacturing plant from azeotropic distillation column rich in NPA was collected. An approximate 2040 gm of NPA-rich waste stream was allowed to form an organic and an aqueous layer. Approximately 30% of waste was removed from the 2040 gm NPA-rich waste stream by separating the aqueous layer for a time of 15 minutes to 30 minutes. The remaining organic layer consists of 30% n-propanol (NPA), 20% water and balance organic impurities. 10% of cyclohexane was added to the batch of organic layer. The temperature of the distillation pot was kept in a range from 120°C to 130?. Initially, water was flashed out of the waste stream. Around 410 gm of water was collected at 90°C to 96?. The second fractionation was rich in cyclohexane and around 242 gm of water was collected at 110?. With a further increase in temperature from 110°C to 130?, 335 gm of n-propanol (NPA) was recovered and collected in a separate bottle and high boiling impurities were settled in the distillation pot. Cyclohexane was further separated from water and recycled back to the distillation column feed.

Thus overall, 75% to 80% of n-propanol (NPA) was recovered from the waste stream. Results of gas chromatography for the recovered n-propanol (NPA) was 99+ % pure.

The n-propanol (NPA) was recovered in high amount by the above process.

Example 2: Production of n-propyl bromide using 62% of hydrogen bromide solution
62% of hydrogen bromide (HBr) solution was reacted with pure n-propanol (NPA) obtained from the fraction process of Example 1. 6331 gm of hydrogen bromide and 1000 gm of n-propanol having a molar ratio of HBr/n-propanol 2.9: 1.0 was fed into a reactor at an ambient temperature. Sulfuric acid was added into the reactor as a catalyst. The mixture was stirred and heated to 61°C to 66°C for 3 hours. After cooling, two phases i.e., upper phase and lower phase were separated at 30°C. The lower phase consists of 48 wt% of hydrogen bromide (HBr) along with a minor amount of n-propyl bromide dissolved in the lower phase. The upper phase consists of n-propyl bromide. The lower (aqueous) phase was heated up to 125°C to recover the dissolved n-propyl bromide by evaporation. N-propyl bromide recovered from the lower phase was combined with the upper phase to obtain the final product. N-propyl bromide was washed with 2% to 3% of sodium carbonate and dried over anhydrous sodium carbonate. Overall, 1931 gm of n-propyl bromide was obtained in the reaction. The yield of n-propyl bromide was 94% to 96% having 99% purity along with 0.14% of isopropyl bromide.
Table 1:
Sr. No. Raw materials Molecular weights Quantity
(gm) Purity
(%) Purity based on 100% Number of moles
(gm/mol) Molar ratio (M/R)
1 n-propanol (NPA) 60 1000 99 990.00 16.5 1
2 Hydrogen bromide (HBR) 81 6331 62 3925.2 48.46 2.94
3 n-propyl bromide 122.9 1931 99 1911.35 15.55 0.94

Example 3: Production of n-propyl bromide using liquid bromine
500 gm of n-propanol (NPA) and 666 gm of bromine (Br2) were fed to a glass reactor in a molar ratio of 0.5:1. Sulfur was added to the reactor as a catalyst. The reaction temperature was maintained at 62°C to 65? for a residence time of 1 hour to 5 hours. N-propyl bromide was recovered through the continuous overhead condenser. N-propyl bromide was neutralized or washed or polished with a soda ash solution.
Table 2:
Sr. no. Raw materials Molecular weights Quantity
(gm) Purity on 100% gm/mol Molar ratio (M/R)
1 n-propanol
(NPA) 60 500 99 495.00 8.25 1
2 Bromine (Br2) 159.8 666 99 659.32 4.13 0.50
3 n-propyl bromide 122.9 973 99 963.63 7.84 0.95

It is clear from the results that n-propanol can be recovered from an IPA manufacturing plant in high amount and can be efficiently used in further processes to provide alkyl bromide in high yield and purity.
The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to a person skilled in the art, the invention should be construed to include everything within the scope of the disclosure.

CLAIMS:

1. A process for preparation of propyl bromide from n-propanol comprising:
(a) recovering n-propanol from a waste stream of an isopropanol manufacturing plant; and
(b) treating n-propanol with a brominating agent in presence of a catalyst.

2. The process as claimed in claim 1, wherein, the step (a) comprises:
i. collecting n-propanol (NPA-rich) waste stream from isopropanol manufacturing plant by azeotropic distillation, wherein the waste stream includes an organic phase and an aqueous phase; and
ii. adding a solvent to the organic phase followed by distillation to recover n-propanol.

3. The process as claimed in claim 2, wherein the organic phase is separated from the waste stream before adding the solvent.

4. The process as claimed in claim 2, wherein, the waste stream comprises 70% of the organic phase and 30% of the aqueous phase.

5. The process as claimed in claim 4, wherein, the organic phase comprises n-propanol in a range of 30% to 40%, water in a range of 15% to 25% and organic impurities selected from 3-methyl 3-pentanol, 2- methyl pentanol, 4-methyl 2-pentanol, isopropanol, dimethyl butanol and ethyl methyl pentene.

6. The process as claimed in claim 2, wherein, the solvent is added in an amount of 8% to 12% and is selected from cyclohexane, ethyl acetate, n-heptane, methyl isobutyl ketone and mixtures thereof.

7. The process as claimed in claim 2, wherein, the distillation is carried out at a temperature in a range of 90? to 130?.
8. The process as claimed in claim 1, wherein, the brominating agent is selected from hydrogen bromide, liquid bromine, N-bromo succinimide or mixtures thereof.

9. The process as claimed in claim 1, wherein, the brominating agent and n-propanol is present in a molar ratio of 0.2:1 to 4:1.

10. The process as claimed in claim 1, wherein, the catalyst is present in a range of 2% to 5% and is selected from sulfur or sulfur-containing reagent.

11. The process as claimed in claim 10, wherein, the sulfur containing reagent is selected from sulfuric acid.

12. The process as claimed in claim 1, wherein, the step (b) is carried out at a temperature in a range of 61? to 66? for a residence time in a range from 1 hour to 5 hours.

13. The process as claimed in claim 1, wherein, the step (b) is carried out in a batch mode or in a continuous mode.

14. A process for recovery of n-propanol from waste stream of isopropanol manufacturing plant, the process comprising:
a. collecting n-propanol (NPA-rich) waste stream from isopropanol manufacturing plant by azeotropic distillation, wherein the waste stream includes an organic phase and an aqueous phase; and
b. adding a solvent to the organic phase followed by distillation to recover n-propanol.