Description:Field of the invention:
The present invention generally relates processing of effluent/ residue generated during the synthesis of acrylamido tertiary butyl sulphonic acid (ATBS). More particularly, this process relates to the recovery of acrylonitrile, isolation of n-tertiary butyl acrylamide as well as preparation of various value-added products from the residual effluents generated during the synthesis of acrylamido tertiary butyl sulphonic acid (ATBS).
Background of the invention:
The acrylamido tert-butyl sulfonic acid monomer, also known as ATBS, has wide range of applications ranging from water treatment to personal care products. Thus, the need for an ATBS has surged in the last few of decades throughout the world. During ATBS manufacture, the treatment of residual effluents and side products becomes the most important assignment.
In order to synthesize acrylamido tert-butyl sulfonic acid (ATBS), excess amounts of acrylonitrile (ACRN) are combined with sulfuric acid and isobutene. The resulting reaction product includes ATBS along with substantial amounts of unreacted acrylonitrile and other by-products. ATBS can be separated away leaving the acrylonitrile along with various residual acids, acrylamides, t-butyl acrylamide and other by-product contaminants. The contaminants are present in an amount of about 5-15 percent by weight based on the weight of the filtrate composition.
Referring to the reaction scheme presented below, the acid contaminants include unreacted sulfuric acid, isobutylene monosulfonic acid (IBSA), isobutylene disulfonic acid (IBDSA), small amounts of ATBS, t-butyl acrylamide (TBA) and acrylamide (Am). If the recovered acrylonitrile along with contaminants (such as the residual acids) is used as such in the production of ATBS, the resulting product will have various undesirable impurities of acrylonitrile polymerization. The reaction scheme presented as follows shows the side product during the synthesis of ATBS.

Reaction scheme for the ATBS synthesis
The recovery of an acrylonitrile is very important factor which not only affects the impurity profile of the ATBS synthesis process but also harms the manufacturing cost. Thus, the process for the recovery of acrylonitrile is vital part in ATBS manufacturing. The process reported in patent WO 88/01263 relates to recovery and purification of excess acrylonitrile used in ATBS synthesis. Another patent, CN100402493C describes the process for the recovery of acrylonitrile using agitated thin film evaporator (ATFE). CN100402493C also discusses about the disadvantages in existing the recovery process. However, the use of ATFE sometime offers the acrylonitrile with some acidic impurities which are causing an issue in the reuse of acrylonitrile.
In brief, the recovery of an acrylonitrile is cost deciding parameter as well as helps to achieve the higher degree purity of ATBS monomer. In the distillation of acrylonitrile filtrate, continuous heating of ACRN in presence of acidic impurities results in ACRN polymerization which lowers the recovery of ACRN. In addition to that, there is probability of instantons polymerization of ACRN which may result in runaway reaction and thus making it commercially unviable.
Manufacturing unit having a zero liquid discharge is the requirement of current industrial plethora as well as for an environment. Hence, the residue recovered after ACRN recovery must be treated in ETP or need to develop a process to extract value-added compounds from it. It is worth to develop a process to isolate value-added products from residual waste obtained after ACRN recovery, this makes process more cost effective and environment-friendly. However, in the present literature, isolation of such byproducts has not explored extensively.
In the prior art, handling of effluent is not explored which is hazardous in nature for the environment. The recovery of acrylonitrile is more important and tedious job, effective distillation and storage will enhance the efficiency. Reported process also do not mention the complete overview about the effluent handling as well as the isolation/synthesis of value added product which is compulsory for industries now a day as zero discharge regulation by government.
Accordingly, it is required to provide a process of recovery of pure acrylonitrile (ACRN) and pure crystalline TBA, and to provide a method of synthesis of other value added products from the effluent/ residue generated during the synthesis of acrylamido tertiary butyl sulphonic acid (ATBS).
Objects of the invention:
The primary object of the present invention is to provide a cost-effective process with an efficient recovery and reuse of ACRN from ATBS slurry in ATBS synthesis process as well as the isolation of TBA (byproduct).
Another object of the present invention is to provide a method of synthesis of value-added products from the effluent/ residue generated during the synthesis of acrylamido tertiary butyl sulphonic acid (ATBS).
Still another object of the present invention is to provide process for the recovery of pure ACRN for recycling of the ACRN for synthesizing ATBS.
Yet another object of the present invention is to inhibit polymerization of pure acrylonitrile in a process of recovery of acrylonitrile from ATBS slurry.
Summary of the invention
The present invention provides a method of recovery of ACRN, recovery of tert-butyl acrylamide (TBA) and synthesis of polymeric salts from an effluent generated during synthesis of acrylamido tertiary butyl sulphonic acid (ATBS). The method of the present invention provides a zero liquid discharge method for ATBS synthesis, since reusable ACRN is recovered in the process along with other value-added products. ATBS is synthesized by reacting mixture of excess acrylonitrile and sulphuric acid with isobutene and separating the ATBS particles by filtration. The method comprises inhibiting polymerization of ACRN by adding polymerization inhibitor to the effluent and distilling the effluent over a continuous distillation equipment to recover acrylonitrile and collecting a viscous residue from a bottom tank of the distillation equipment. The recovered ACRN is reused in the ATBS synthesis process while the viscous residue is further processed to recover tert-butyl acrylamide (TBA) and to polymerize the residual monomeric impurities like isobutylene monosulfonic acid (IBSA), isobutylene disulfonic acid (IBDSA), small amounts of ATBS, t-butyl acrylamide (TBA) and acrylamide (Am). TBA, insoluble in water is separated by adding water to the viscous residue and filtering out the precipitated of TBA, while the filtrate contains unreacted sulfuric acid and monomeric impurities. In next step, the filtrate is neutralized by using an inorganic base and the sulphate salt is filtered out. Further, the water filtrate from the neutralized filtrate is reduced to a predefined level using a suitable technique selected from distillation and evaporation and the resultant aqueous filtrate is subjected to polymerization by adding a polymerization initiator and a deoxygenating catalyst and heating the mixture at a temperature ranging from 40ºC to 60ºC to get liquid salt of a polymeric material. The aqueous filtrate can also be co-polymerized using suitable and optimal polymerization conditions by using an additional co-monomer. The liquid salt of the polymeric material is the spray dried to remove water content and to get a solid salt of polymeric material.
Detailed description of the embodiments:
The foregoing objectives of the invention are accomplished and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention described in the present embodiments.
If the specification states a component or feature "may' can", "could", or "might" be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
As used in the description herein and throughout the claims that follow, the meaning of "a, an," and "the" includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of "in" includes "in" and "on" unless the context clearly dictates otherwise.
List of abbreviations used throughout the complete specification:
ATBS: Acrylamido tertiary butyl sulphonic acid
IB: Isobutylene
ACRN: Acrylonitrile
IBSA: Isobutylene sulphonic acid
IBDSA: Isobutylene disulfonic acid,
TBA: tert-butyl acrylamide
Am: Acrylamide
AMPDSA: Acrylamido methyl propane disulphonic acid
H2SO4: Sulphuric acid
The present invention provides a method for value added processing of an effluent, generated during synthesis of ATBS. The value added processing involves recovery of acrylonitrile, isolation of tert-butyl acrylamide as well as preparation of various industrially useful polymeric salts from the effluent generated during ATBS synthesis. In order to synthesize acrylamido tert-butyl sulfonic acid (ATBS), excess amounts of acrylonitrile are combined with sulfuric acid and isobutene. Specifically, 6:1 to 16:1 mixture of acrylonitrile and sulphuric acid is reacted with isobutene to get a resulting reaction product including ATBS along with substantial amounts of unreacted acrylonitrile and other by-products. The ATBS is separated by filtration, leaving an effluent containing acrylonitrile along with various residual acids, acrylamides, tert-butyl acrylamide and other by-product contaminants. The contaminants are present in an amount of about 5-15% by weight based on the weight of the filtrate composition.
In first step, the method of the present invention comprises adding 100 ppm to 200 ppm of a polymerization inhibitor to the effluent, and distilling the effluent over a continuous distillation equipment to recover acrylonitrile and collecting a viscous residue from a bottom tank of the distillation equipment. In an embodiment, the polymerization inhibitor is monomethyl ether hydroquinone (MEHQ).
As explained in the background art, in the distillation of acrylonitrile filtrate, continuous heating of ACRN in presence of acidic impurities results in ACRN polymerization which lowers the recovery of ACRN. In addition to that, there is probability of instantons polymerization of ACRN which may result in runaway reaction and thus making it commercially unviable. It is observed that the addition of polymerization inhibitor and continuous distillation process at lower temperature helps in getting the desired purity with efficient recovery of ACRN. Various continuous distillation equipment e.g. agitated thin film evaporator (ATFE), rising film evaporator (RFE), short path distillation unit (SPDU), wiped film evaporator (WFE) help to get the efficient recovery of ACRN. However, the combination of two or more distillation equipment offers more efficient recovery and high purity of ACRN. During continuous distillation, the residual material becomes more viscous thus making recovery less efficient. This problem can be resolved using the combination of two or more distillation equipment.
Analysis of the viscous residue collected from the bottom tank of the distillation equipment shows that it contains mainly TBA along with water soluble impurities such as IBSA, IBDSA, Am, AMPDSA and unreacted sulfuric acid. Tert-butyl acrylamide (TBA) is a monomer which is used to synthesize various polymers as well as an important intermediate in organic chemical synthesis. Also, the polymer of TBA has a wide application in paper industries, as a thickener, personal care products etc.
The method of the present invention in next step involves adding 1.5 to 2 volumes of water to the viscous residue and heating the water-residue mixture at a temperature ranging from 70ºC to 80ºC to precipitate out tert-butyl acrylamide (TBA). tert-butyl acrylamide residue is filtered out to get a filtrate containing unreacted sulfuric acid and aforementioned monomeric water soluble impurities. The crude TBA is purified by recrystalisation using suitable organic solvent. The washed cake is subjected to drying in the vacuum oven at a temperature ranging from 40ºC to 70ºC under reduced pressure to obtain more than 99.5% pure TBA.
The method of the present invention in next step involves removal of unreacted sulphuric acid by neutralizing the filtrate using an inorganic base and filtering out the sulphate salt formed, using a suitable solid-liquid separation technique. In an embodiment, the inorganic base is selected from: sodium hydroxide, potassium hydroxide, lime, ammonia, magnesium hydroxide, ammonium hydroxide and mixtures thereof.
An isolation and separation of the monomeric water-soluble impurities was proved difficult. However, the common functionality among these impurities is a monomeric unit which can be easily polymerized by using various radical initiators and suitable conditions. The quantity of solid content in water filtrate or the concentration of monomeric impurities finds vital role which decides the final application of the polymer. The viscosity of polymer affects the end use such as melting temperature, density and thus efficacy. Therefore, optimal viscous polymer provides the better quality and handling to end use. If the solid content of the residue is on higher side, then there is formation of polymer with high viscosity and density, which fails in the end use poses handling challenges. Generally, the optimal quantity of solvent in the solution polymerization has great impact on the polymerization. The impact is mainly due to having better heat transfer, preventing auto-acceleration and help to get desired polymer property. Hence, to match the desired solid content in aqueous filtrate, the removal of water to a predefined scale is essential.
Hence, the method of present invention in the next step involves removal of water content from the neutralized filtrate to a predefined level using a suitable technique, before subjecting the neutralized water filtrate to polymerization. In an embodiment, the suitable technique is selected from distillation, continuous distillation, distillation with short path distillation unit (SPDU) and evaporation techniques like multi-effect evaporation (MEE), agitated thin film evaporation (ATFE), rising film evaporation (RFE), wiped film evaporation (WFE), etc.
The method of present invention in the next step involves subjecting the resultant aqueous filtrate (obtained after the adjusting of predefined solid content) to polymerization at temperature ranging from 40ºC to 60ºC by adding 0.5 to 1.0% by wt of a polymerization initiator and 0.5 to 1.0% by wt of a deoxygenating agent. The auto generated temperature of the reaction ranges from 70ºC to 90ºC and a salt of a polymeric material is formed in liquid state. Spray drying of the liquid salt of the polymeric material to remove water content gives the final solid of polymeric material. The inorganic base used for neutralization of filtrate and removal of unreacted sulphuric acid decides the properties of end polymer, like water solubility and binding ability of the desired polymer.
In an embodiment, the polymerization initiator is selected from: peroxodisulphate, peroxides, hydroperoxides and peresters, azo compounds and redox systems with organic and inorganic components. Specifically, the polymerization initiator is sodium per sulphate. The presence of free oxygen would inhibit the polymerization reaction and will not initiate the reaction, therefore the suitable deoxygenating agent is the necessity for such reactions. In an embodiment, the deoxygenating agent is selected from sodium sulphite, zinc, iron, calcium carbide and sodium metabisulhite (SMBS). In a preferred embodiment, the deoxygenating agent is sodium metabisulphite (SMBS).
Alternately, the aqueous filtrate obtained after the adjusting of predefined solid content is subjected to polymerization with another co-monomer in order to get various co-polymers having properties which are depending on selected co-monomer. In an embodiment, the co-monomer is selected from various active monomers such as acrylic acid, methyl acrylic acid, vinyl derivatives. In a preferred embodiment, the co-monomer is acrylic acid co-monomer. The resulting co-polymer has found applications in numerous fields.
The polymers and co-polymer produced from the mixtures of monomeric impurities can be utilized as an additive in the various industries such as chemical, infrastructure, leather, etc.
The method of recovery of acrylonitrile, isolation of tert-butyl acrylamide as well as preparation of various value added products from the effluents generated during ATBS synthesis, is further explained by way of illustrative examples. The examples are given by way of illustration and should not be construed to limit the scope of present invention.
Experimental examples:
Acrylamido tertiary butyl sulfonic acid (ATBS) was synthesized by reacting isobutene with 6:1 to 16:1 mixture of excess amounts of acrylonitrile and sulfuric acid. ATBS was separated by filtration. 100 ppm to 200 ppm of a polymerization inhibitor (MEHQ) was mixed with the filtrate containing acrylonitrile along with other contaminants and the filtrate was subjected to distillation over a continuous distillation equipment to recover acrylonitrile. After recovering the acrylonitrile, the viscous residue was collected from bottom tank of the distillation equipment.
Example 1: Isolation of tert-butyl acrylamide (TBA):
250 gm of the residue obtained after recovery of ACRN, was taken in 2 liter round bottom flask and 2 vol of water was added while maintaining the temperature between 70ºC to 80ºC to get the white precipitation of TBA. The solid-liquid separation was carried out by using any filtration device to get the wet cake of crude TBA. The wet cake was washed with fresh water (1 volumes with respect to wet cake). The crude TBA was taken for further purification by recrystalisation using methanol (0.5-3 volumes). The washed cake was subjected to drying in the vacuum oven. The drying was carried out at a temperature ranging from 40ºC to 70ºC under reduced pressure to obtain desired quality of TBA (50 g). The purity of TBA was more than 99.5% by GC and impurities were found within the specifications.
Example 2: Removal of sulphuric acid
The water filtrate obtained in Example 1 contains a mixture of impurities such as unreacted sulfuric acid, IBSA, IBDSA, acrylamide and AMPDSA. 1 kg of the filtrate was taken in RBF and neutralized using 89 g of Calcium hydroxide while maintaining the teperature between 20ºC and 30ºC, to precipitate out calcium sulphate. The solid-liquid separation was carried out by using continuous centrifuge filtration device to get a wet cake of crude calcium sulfate. The wet cake was washed with minimum amount of fresh water. The crude calcium sulfate was subjected to drying to get 150 g pure calcium sulphate.
Example 3: Polymerization of monomeric impiurities.
After separation of calcium sulphate, the filtrate (937 g) was transferred to a round bottom flask and maintained at room temprature followed by addition of 0.66 g MEHQ. The solid content was then adjusted around 40% in water filtrate by using rota evaporation or multi-effect evaporation (MEE) technique. Nitrogen bubler was inserted in the flask for nitrogen purging for 10 min and temprature was allowed to increase between 50ºC to 55ºC. 3.3 g sodium metabisulphite powder and 3.3 g sodium persulphate was added while maintaining the temperature between 50ºC to 55ºC. During the polymerisation the temprature of reaction mixture rises to between 80ºC and 85ºC in 10-15 min. The reaction mixture was then cooled to 30ºC to get the off-white to dark brown coloured liquid polymer. Subsequently the liquid was transferred for spray drying to remove all water to get the off-white to brown solid calcium salt of polymeric material (110 g).
Example 4: Removal of unreacted sulfuric acid using sodium hydroxide and Polymerization of monomeric impiurities.
The experimental procedure in example 1, example 2 and example 3 was repeated using 25-100% sodium hydroxide in example 2, as the inorganic base for neutralisation of filtrate/ removal of unreacted sulfuric acid. The set of experiment offered sodium sulphate and sodium salt of polymeric material.
Example 5: Removal of unreacted sulfuric acid using magnessium hydroxide and Polymerization of monomeric impiurities.
The experimental procedure in example 1, example 2 and example 3 was repeated using magnessium hydroxide in example 2, as the inorganic base for neutralisation of filtrate/ removal of unreacted sulfuric acid. The set of experiment offered magnessium sulphate and magnessium salt of polymeric material.
Experimental results:
Viscosity and density of the polymer formed depends on the solid content of the residue. If the solid content of the residue is on higher side, then there is formation of polymer with high viscosity and density which fails in the end use as well as poses a handling challenge. The relation of polymer properties and the solid content of the neutralized filtrate is explained in Table 1 below:
Table 1:
Sr. No. Base Solid content Temp Initiator pH Viscosity (10% aqueous sol.) density
1. NaOH 30 50 SPS 6-7 2.1 0.30
2. NaOH 40 50 SPS 6-7 2.5 0.36
3. NaOH 50 50 SPS 6-7 3.3 0.42
4. NaOH 60 50 SPS 6-7 6.5 0.48
5. NaOH 40 40 SPS 6-7 3.1 0.31
6. NaOH 40 60 SPS 6-7 3.3 0.29
7. NaOH 40 70 SPS 6-7 2.9 0.30
8. NaOH 40 50 PPS 6-7 3.2 0.35
9. Ca(OH)2 40 50 SPS 6-7 3.4 0.38
Example 6: Preparation of co-polymer
The experimental procedure in example 1 and example 2 was repeated using 25-100% sodium hydroxide in as the inorganic base for neutralisation of filtrate/ removal of unreacted sulfuric acid. 450-500 g of the neutral filtrate was transferred to the RBF and maintained the room temprature then added acrylic acid (144 g). The reaction mixture becomes acidic (pH-3.0). The reaction mixture was the neutralized to pH 7 by using sodium hydroxide. The solid content was adjusted around 50-55% by evaporation of water using rota evaporation. The nitrogen bubller was inserted for nitrogen purging for 10 min and tempratue was allowed to increase between 50-55°C. 3.3 g sodium metabisulphite powder and 3.3 g sodium persulphate werethen added at 50-55°C. During the polymerisation the temprature of reaction mixture rose to 85°C in 10-15 min.. The reaction mixture was cooled to 30°C to get the off-white to dark brown coloured liquid sodium salt of co-polymer. Table 2 below shows the visosity and density of the resultant copolymenrs obtained using varying percentage of acrylic acid co-monomer.
Base Co-monomer (%) Viscosity density
NaOH Acrylic acid (10%) 40 1.01
NaOH Acrylic acid (15%) 75 1.33
NaOH Acrylic acid (20%) 94 1.21
Advantages of the invention:
? The present invention provides a detailed description for the isolation of byproduct and to get the value added products from the effluent generated during the synthesis of ATBS.
? The present invention also provides a zero liquid discharge method for synthesis of ATBS providing recycle, reuse and management of the effluent generated in the ATBS synthesis.
? The present invention also provides strategy to make the process of ATBS more cost-effective and industrially viable by reducing the effluents and by getting the value added products additionally.
? The developed invention additionally incorporates a greener feature into ATBS synthesis, making the protocol more environmentally friendly.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, and to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but such omissions and substitutions are intended to cover the application or implementation without departing from the scope of the claims of the present invention.

, Claims:We claim

1. A method for value-added processing of an effluent generated during synthesis of acrylamido-2-tert-butylsulphonic acid (ATBS), wherein ATBS is synthesized by reacting 6:1 to 16:1 mixture of acrylonitrile and sulphuric acid with isobutene and separating the acrylamido-2-tert-butylsulphonic acid particles by filtration, the method comprising the steps of:
adding a polymerization inhibitor to the effluent and distilling the effluent using either a continuous distillation equipment or a combination of continuous distillation equipment to recover acrylonitrile and collecting a viscous residue from a bottom tank of the distillation equipment;
adding 1.5 to 2.5 volumes of water to the viscous residue and heating the mixture at a temperature ranging from 60ºC to 80ºC to precipitate out crude tert-butyl acrylamide;
filtering out the tert-butyl acrylamide residue to get a filtrate containing unreacted sulfuric acid and monomeric impurities;
neutralizing the filtrate using an inorganic base and filtering out the sulphate salt;
removing water content from the neutralized filtrate till a solid content of the neutralized filtrate is in a range from 30% to 80% by weight, using a technique selected from a distillation, an evaporation and a combination thereof;
subjecting the resultant aqueous filtrate to polymerization by adding 0.5% to 1.0% by wt of polymerization initiator and 0.5% to 1.0% by wt of deoxygenating agent and heating the mixture at a temperature ranging from 50ºC to 80ºC to get liquid salt of a polymeric material;
drying the liquid salt of the polymeric material to remove water content to get a solid salt of polymeric material.
2. The method as claimed in claim 1, wherein the monomeric impurities are isobutylene monosulfonic acid (IBSA), isobutylene disulfonic acid (IBDSA), small amounts of ATBS, t-butyl acrylamide (TBA) and acrylamide (Am).
3. The method as claimed in claim 1, wherein the polymerization inhibitor is monomethyl ether hydroquinone (MEHQ).
4. The method as claimed in claim 1, wherein the continuous distillation equipment is a one selected from an agitated thin film evaporator, a rising film evaporator, a short path distillation unit and a wiped film evaporator.
5. The method as claimed in claim 1, wherein the inorganic base is selected from: sodium hydroxide, potassium hydroxide, lime, ammonia, magnesium hydroxide, ammonium hydroxide and mixtures thereof.
6. The method as claimed in claim 1, wherein the polymerization initiator is selected from: peroxodisulphate, peroxides, hydroperoxides and peresters, azo compounds and redox systems with organic and inorganic components.
7. The method as claimed in claim 1, wherein the polymerization initiator is sodium per sulphate.
8. The method as claimed in claim 1, wherein the deoxygenating catalyst is sodium metabisulhite (SMBS).
9. The method as claimed in claim 1, wherein the crude tert-butyl acrylamide is purified by recrystalisation using methanol or using any suitable solvent.
10. The method as claimed in claim 1, wherein the aqueous filtrate obtained after the adjusting the solid content is subjected to polymerization with a co-monomer selected from acrylic acid, methyl acrylic acid, vinyl derivatives.