FIELD

The present disclosure relates to a process for the treatment of tail gases generated during the production of acid chlorides.

BACKGROUND

The background information herein below relates to the present disclosure but is not necessarily prior art.

Carboxylic acid chlorides are useful organic intermediates employed in the synthesis of alkyl ketene dimers, organic peroxides, surfactants, pharmaceuticals and the like. Carboxylic acid chlorides are generally prepared by a reaction of carboxylic acids with chlorinating agents such as carbonyl chloride, phosphorous chloride, thionyl chloride and the like. The use of thionyl chloride is the most preferred reagent in the process owing to the comparative ease. The use of thionyl chloride as a chlorinating agent in the reaction generates hydrogen chloride and sulfur dioxide as by-products which are continuously removed out of the reaction as a mixture of gases, known as tail gases. These tail gases, containing a mixture of the aforesaid constituent gases (HC1 and SO2), must be treated in the gas scrubbing towers to remove the constituent gases (HC1 and SO2) preventing the environmental pollution.

Conventionally, hydrogen chloride in the tail gases is recovered as concentrated hydrochloric acid and the remaining sulfur dioxide is recovered by converting it either to liquid sulfur dioxide after drying and compressing or converting to a sulphite solution by scrubbing with a dilute alkali.

In the prior art, the utilization of gas mixtures containing both hydrogen chloride and sulfur dioxide has been done to obtain hydrochloric acid and gypsum or hydrochloric acid and sodium sulfite or hydrochloric acid, phosphorous oxychloride and thionyl chloride. This process suggests utilization of gas mixtures containing both hydrogen chloride and sulfur dioxide to make chlorosulfonic acid and sulfuryl chloride. Chlorosulfonic acid is a value- added organic reagent used in the synthesis of alkyl sulphate detergents, saccharin and the like, and sulfuryl chloride is an important value added chlorinating agent in the organic synthesis. Considering the environmental hazards of tail gases and increasing demand for eco-friendly way of disposing the tail gases, there is a room for developing more eco-friendly methods of treating the tail gases with minimal environmental footprints.

There is, therefore, the present disclosure provides an alternative process for treating the tail gases that mitigates the drawbacks mentioned herein above or at least provides a useful alternative.

OBJECTS

Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:

It is an object of the present disclosure to ameliorate one or more problems of the background or to at least provide a useful alternative.

An object of the present disclosure is to provide a process for the treatment of tail gases.

Another object of the present disclosure is to provide a simple, economical, and environmentfriendly process for the treatment of tail gases generated during the production of acid chlorides.

Still another object of the present disclosure is to provide a process for the treatment of the tail gases wherein hydrogen chloride and sulfur dioxide can be converted into valuable chlorosulfonic acid and sulfuryl chloride, respectively.

Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY

The present disclosure relates to a process for the treatment of tail gases comprising hydrogen chloride and sulfur dioxide. The process comprises (step i) converting the hydrogen chloride into chlorosulfonic acid by reacting the tail gases with sulfur trioxide and (step ii) converting the sulfur dioxide into sulfuryl chloride by reacting the tail gases with chlorine gas, wherein the step (i) and the step (ii) are carried out interchangeably. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

The present disclosure will now be described with the help of the accompanying drawing, in which:

Figure 1 illustrates a schematic representation of the process of the treatment of tail gases in accordance with the present disclosure, wherein conversion of hydrogen chloride into chlorosulfonic acid is carried out followed by conversion of the sulfur dioxide into sulfuryl chloride; and

Figure 2 illustrates a schematic representation of the process of the treatment of tail gases in accordance with the present disclosure, wherein conversion of sulfur dioxide into sulfuryl chloride is carried out followed by conversion of hydrogen chloride into chlorosulfonic acid.

DETAILED DESCRIPTION

The present disclosure relates to a process for the treatment of tail gases generated during the production of acid chlorides.

Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.

Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.

The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.

Carboxylic acid chlorides are generally prepared by a reaction of carboxylic acids with chlorinating agents such as carbonyl chloride, phosphorous chloride, thionyl chloride and the like. The use of thionyl chloride is the most preferred reagent used in the process owing to the comparative ease. The use of thionyl chloride as a chlorinating agent in the reaction generates hydrogen chloride and sulfur dioxide as by products which are continuously removed out of the reaction as a mixture of gases known as tail gases. These tail gases containing a mixture of the aforesaid constituent gases (HC1 and SO2) must be treated in the gas scrubbing towers to remove the constituent gases (HC1 and SO2) for preventing the environmental pollution.

Conventionally, hydrogen chloride in the tail gases is recovered as a concentrated hydrochloric acid and the remaining sulfur dioxide is recovered by converting it either to liquid sulfur dioxide after drying and compressing or converting to a sulphite solution by scrubbing with a dilute alkali.

In the prior art, the utilization of gas mixtures containing both hydrogen chloride and Sulfur dioxide has been done to make hydrochloric acid and gypsum or hydrochloric acid and Sodium sulfite or hydrochloric acid, Phosphorous oxychloride and thionyl chloride. However, there are no disclosures wherein the tail gases i.e., a mixture of hydrogen chloride and sulfur dioxide generated during the acid chloride reaction is treated to generate chlorosulfonic acid and sulfuryl chloride respectively/individually in two serial treatments. This process suggests utilization of gas mixtures containing both hydrogen chloride and Sulfur dioxide to make Chlorosulfonic acid and Sulfuryl chloride respectively.

The present provides a process for the treatment of tail gases generated during the production of acid chlorides.

The tail gases comprise hydrogen chloride and sulfur dioxide. The process for the treatment of tail gases comprises the following steps:

(i) converting the hydrogen chloride into chlorosulfonic acid by reacting the tail gases with sulfur trioxide; and (ii) converting the sulfur dioxide into sulfuryl chloride by reacting the tail gases with chlorine gas, wherein the step (i) and the step (ii) are carried out interchangeably.

In a first embodiment of the present disclosure, the process for the treatment of tail gases is carried out by the step (i) followed by the step (ii). The process comprises the following steps: a. scrubbing the tail gases with aqueous HC1 in an amount in the range of 30 ml to 100 ml per mole of the tail gases and having a concentration in the range of 15 % to 40 % in a scrubber at a first predetermined temperature to remove carryover of acid chlorides to obtain first scrubbed tail gases; b. scrubbing the first scrubbed tail gases with sulfuric acid in an amount in the range of 20 ml to 60 ml per mole of the tail gases and having a concentration in the range of 95 % to 99 % at a second predetermined temperature for removing moisture to obtain second scrubbed tail gases; c. reacting the second scrubbed tail gases with sulfur trioxide at a third predetermined temperature to obtain a mixture comprising a crude chlorosulfonic acid and an unreacted sulfur trioxide, wherein the sulfur trioxide is dissolved in a fluid medium in an amount in the range of 1 % to 35 %, wherein the sulfur dioxide gas present in the tail gases remains unreacted and exits from the scrubber along with a portion of the sulfur trioxide; d. distilling the mixture at a fourth predetermined temperature and at a first predetermined pressure to remove the unreacted sulfur trioxide to obtain a pure chlorosulfonic acid; e. scrubbing the sulfur dioxide gas from step c) with sulfuric acid in an amount in the range of 50 ml to 100 ml per mole of the tail gases and having a concentration in the range of 90 % to 98 % to remove the portion of said sulfur trioxide to obtain a scrubbed sulfur dioxide gas; f. reacting the scrubbed sulfur dioxide gas with a predetermined amount of chlorine gas in a column packed with an activated carbon at a fifth predetermined temperature to obtain a product mass comprising a crude sulfuryl chloride, unreacted sulfur dioxide and unreacted chlorine; and g. distilling the product mass at a sixth predetermined temperature and at a second predetermined pressure to remove the unreacted sulfur dioxide and the unreacted chlorine to obtain a pure sulfuryl chloride.

In a second embodiment of the present disclosure, the process for the treatment of tail gases is carried out by the step (ii) followed by step (i). The process comprises the following steps: a. scrubbing the tail gases with aqueous HC1 in the range of 30 ml to 100 ml per mole of the tail gases and having a concentration in the range of 15 % to 40 % in an amount in a scrubber at a first predetermined temperature to remove carryover of acid chlorides to obtain first scrubbed tail gases; b. scrubbing the first scrubbed tail gases with sulfuric acid in an amount in the range of 20 ml to 60 ml per mole of the tail gases and having a concentration in the range of 95 % to 99 % at a second predetermined temperature for removing moisture to obtain second scrubbed tail gases; c. reacting the second scrubbed tail gases with a predetermined amount of chlorine gas in a column packed with an activated carbon at a seventh predetermined temperature to obtain a product mass comprising a crude sulfuryl chloride, an unreacted sulfur dioxide and an unreacted chlorine, wherein the hydrochloric acid gas present in the tail gases remains unreacted in step (c); d. distilling the product mass at an eighth predetermined temperature and at a third predetermined pressure to remove the unreacted sulfur dioxide and the unreacted chlorine to obtain a pure sulfuryl chloride; e. reacting the hydrochloric acid gas from step c) with sulfur trioxide at a ninth predetermined temperature to obtain a mixture comprising a crude chlorosulfonic acid and unreacted sulfur trioxide, wherein the sulfur trioxide is dissolved in a fluid medium in an amount in the range of 1 % to 35 %; and f. distilling the mixture at a tenth predetermined temperature and at a fourth predetermined pressure to remove the unreacted sulfur trioxide to obtain a pure chlorosulfonic acid.

The tail gases are generated in a reaction between thionyl chloride and a carboxylic acid in a reactor (Rl) fitted with a stirrer.

In an embodiment of the present disclosure, the carboxylic acid can be selected from aliphatic carboxylic acids and aromatic carboxylic acids.

The aliphatic carboxylic acid can be selected from pivalic acid, valeric acid, caprylic acid, capric acid, lauric acid, myristic acid, neo heptanoic acid, neo decanoic acid, ethyl hexanoic acid, isobutyric acid, iso nonanoic acid and methoxy acetic acid.

The aromatic carboxylic acid can be selected from p-toluic acid, benzoic acid, 3,5 dimethyl benzoic acid, terephthalic acid, isophthalic acid, 4-methoxy benzoic acid, and 2-methoxy benzoic acid.

Other suitable known carboxylic acids are also used.

In an exemplary embodiment, the carboxylic acid is pivalic acid.

In accordance with an embodiment of the present disclosure, thionyl chloride is fed to the reactor (Rl) containing the carboxylic acid at a flow rate in the range of 25 moles per hour to 40 moles per hour via a flow indicator (Fl). The temperature in the reactor (Rl) is maintained in the range of 20 °C to 100 °C. In the reactor (Rl), the reaction of thionyl chloride and the carboxylic acid takes place to form acid chloride along with the generation of the tail gases. The tail gases generated in the reactor (Rl) are cooled in a cooler (Hl) to remove any carryover thionyl chloride and the acid chloride to obtain cooled tail gases. The cooled tail gases are carried to flask FL1.

In an embodiment of the present disclosure, the mole of tail gas is twice the mole of thionyl chloride reacted.

In an embodiment of the present disclosure, the acid chloride is pivaloyl chloride. In accordance with the first embodiment of the present disclosure, the process for the treatment of tail gases is carried out by the step (i) followed by the step (ii).

Figure 1 illustrates a schematic representation of the process of the treatment of tail gases in accordance with the first embodiment of the present disclosure, wherein the conversion of hydrogen chloride into chlorosulfonic acid is carried out followed by the conversion of sulfur dioxide into sulfuryl chloride.

The process is described in detail herein below.

Step-(a): The tail gases are scrubbed with an aqueous HC1 to remove any carryover of acid chlorides to obtain first scrubbed tail gases.

In accordance with an embodiment of the present disclosure, the tail gases comprising hydrogen chloride and sulfur dioxide are cooled in the cooler Hl and entered in a flask FL1 comprising aqueous hydrochloric acid in an amount in the range of 30 ml to 100 ml per mole of the tail gases and having a concentration in the range of 15 % to 40 %. During the scrubbing process, the aqueous HCL in the flask FL1 is circulated through a column Cl by using a pump Pl. The tail gases are scrubbed in the flask FL1 and the column Cl at a first predetermined temperature to remove the carryover acid chlorides from the tail gases to obtain first scrubbed tail gases.

In an embodiment of the present disclosure, the first predetermined temperature is in the range of 50 °C to 120 °C. In an exemplary embodiment, the first predetermined temperature is 100 °C. In another exemplary embodiment, the first predetermined temperature is 90 °C. The temperature of the column Cl is adjusted in such a way that there is no hydrogen chloride absorption takes place.

The columns Cl, C2, C3 and C4 are packed with a material selected from glass raschig rings, pall rings, Berl saddles and Intalox saddles.

In commercial plants, the columns may be packed with structured packings (corrugated sheets or corrugated wire mesh) or random packings (Raschig rings, Pall rings, Berl saddles, Intalox saddles), the packings being made of suitable materials namely metals such as stainless steel and hastelloy, or plastics such as teflon and polypropylene.

In accordance with an embodiment of the present disclosure, the concentration of the aqueous hydrochloric acid (HCL) is in the range of 15% to 40%. In an exemplary embodiment of the present disclosure, the concentration of the aqueous hydrochloric acid is 20%. In another exemplary embodiment, the concentration of the aqueous hydrochloric acid is 28%. The concentration of the aqueous hydrochloric acid (HCL) is adjusted depending upon the operating pressure of the column ensuring there is no net change in HC1 concentration in FL1.

In accordance with an embodiment of the present disclosure, the amount of the aqueous hydrochloric acid (HCL) is in the range 30 ml to 100 ml. In an exemplary embodiment, the amount of the aqueous hydrochloric acid is 90 ml per mole of the tail gases. In another exemplary embodiment, the amount of the aqueous hydrochloric acid is 50 ml per mole of the tail gases.

The first scrubbed gases obtained from column Cl are cooled in a cooler H2 and are entered into a flask FL2.

Step-(b): The first scrubbed tail gases obtained in step (a) are scrubbed with sulfuric acid to remove moisture to obtain second scrubbed tail gases.

In accordance with an embodiment of the present disclosure, the first scrubbed gases obtained from the first column Cl are cooled in the cooler H2 and entered into the flask FL2 comprising sulfuric acid in an amount in the range of 20 ml to 60 ml per mole of the tail gases and having a concentration in the range of 95 % to 99 %. During the scrubbing process, sulfuric acid in the flask FL2 is circulated through a column C2 by using a pump P2. The first scrubbed tail gases are scrubbed in the flask FL2 and the column C2 at a second predetermined temperature to remove the moisture from the first scrubbed tail gases to obtain second scrubbed tail gases.

In an embodiment of the present disclosure, the second predetermined temperature is in the range of 20 °C to 100 °C. In an exemplary embodiment, the second predetermined temperature is 25 °C. In another exemplary embodiment, the second predetermined temperature is 50 °C.

In an embodiment of the present disclosure, the concentration of sulfuric acid is in the range of 95% to 99%. In an exemplary embodiment, the concentration of sulfuric acid is 98%.

In an embodiment of the present disclosure, the amount of sulfuric acid is in the range of 20 ml to 60 ml per mole of the tail gas. In an exemplary embodiment, the amount of sulfuric acid is 60 ml per mole of the tail gas. In another exemplary embodiment, the amount of sulfuric acid is 30 ml per mole of the tail gas.

The second scrubbed gases obtained from the column C2 are cooled in a cooler H3 and are entered into a flask FL3.

Step-(c): The second scrubbed tail gases obtained in step (b) are reacted with sulfur trioxide dissolved in a fluid medium to obtain a mixture comprising a crude chlorosulfonic acid and an unreacted sulfur trioxide.

In accordance with an embodiment of the present disclosure, the second scrubbed tail gases obtained from the column C2 are cooled in the cooler H3 and entered into the flask FL3 comprising sulfur trioxide dissolved in the fluid medium. During the reaction, sulfur trioxide dissolved in the fluid medium is circulated through a column C3 by using a pump P3. HC1 in the second scrubbed tail gases reacts with sulfur trioxide at a third predetermined temperature to obtain a mixture comprising crude chlorosulfonic acid and an unreacted sulfur trioxide. The sulfur dioxide present in the tail gases remains unreacted and passes on to the next step along with a portion of sulfur trioxide.

In an embodiment of the present disclosure, the third predetermined temperature is in the range of 20 °C to 90 °C. In an exemplary embodiment, the third predetermined temperature is 50 °C. In another exemplary embodiment, the third predetermined temperature is 30 °C.

The concentration of the sulfur trioxide in the circulating fluid medium is maintained in the range of 1 % and 35 % by adding sulfur trioxide to the circulating fluid medium. In an exemplary embodiment of the present disclosure, the concentration of sulfur trioxide is 30%. In another exemplary embodiment, the concentration of sulfur trioxide is 17%.

The fluid medium can be selected from the group consisting of chlorosulfonic acid, oleum, sulfuric acid and sulfuryl chloride. In an exemplary embodiment, the fluid medium is chlorosulfonic acid.

The fluid medium is present in an amount in the range of 30 ml to 100 ml per mole of the tail gas. In an exemplary embodiment, the amount of the fluid medium is 95 ml per mole of the tail gas. In another exemplary embodiment, the amount of the fluid medium is 60 ml per mole of the tail gas. Step-(d): The mixture obtained in step (c) is distilled at a fourth predetermined temperature and a first predetermined pressure to remove the unreacted sulfur trioxide to obtain a pure chlorosulfonic acid.

The mixture containing chlorosulfonic acid obtained from the flask FL3, which contains the unreacted sulfur trioxide and some dissolved sulfur dioxide, is first distilled to remove the dissolved sulfur dioxide and sulfur trioxide and then further distilled at a first pressure at a fourth temperature to obtain a pure chlorosulfonic acid. This distillation also removes color if any present in the crude chlorosulfonic acid.

In an embodiment of the present disclosure, the fourth predetermined temperature is in the range of 80 °C to 150 °C. In an exemplary embodiment, the fourth predetermined temperature is 90 °C to 120 °C.

In an embodiment of the present disclosure, the first pressure is in the range of 20 mmHg to 100 mmHg. In an embodiment of the present disclosure, the first pressure is 50 mmHg.

In accordance with an embodiment of the present disclosure, the distillation of the crude chlorosulfonic acid can be carried out in a wiped film reactor to overcome foaming, during the distillation.

The yield of the pure chlorosulfonic acid obtained after distillation is in the range of 80% to 99%. In an exemplary embodiment of the present disclosure, the yield of pure chlorosulfonic acid is 85%. In another exemplary embodiment, the yield of pure chlorosulfonic acid is 98%.

The unreacted sulfur trioxide present in the tail gases obtained from the column C3 is cooled in a cooler H4 and entered into a flask FL4.

Step-(e): The sulfur dioxide obtained in the step (c) is scrubbed with sulfuric acid to remove the portion of sulfur trioxide to obtain a scrubbed sulfur dioxide gas.

In accordance with an embodiment of the present disclosure, the sulfur dioxide gas obtained in the step (c) from the column C3 is cooled in the cooler H4 and entered into the flask FL4 comprising sulfuric acid. During the scrubbing process, sulfuric acid in the flask FL4 is circulated through a column C4 by using a pump P4. Sulfur dioxide in the tail gas is scrubbed in the flask FL4 and the column C4 with sulfuric acid having a concentration in the range of 90 % to 98 % in an amount in the range of 50 ml to 100 ml per mole of the tail gases at a temperature in the range of 20 C to 50 C to remove the portion of sulfur trioxide to obtain a scrubbed sulfur dioxide gas.

In an exemplary embodiment the temperature is 25 C.

In an exemplary embodiment, the concentration of the sulfuric acid is in the range of 95 %.

In an exemplary embodiment, the amount of sulfuric acid is 60 ml per mole of the tail gas.

The scrubbed sulfur dioxide gas obtained from the column C4 is cooled in a cooler H5 and passed on to the next step.

Step-(f): The scrubbed sulfur dioxide gas obtained in step (e) is reacted with chlorine gas to obtain a product mass comprising a crude sulfuryl chloride, unreacted sulfur dioxide and unreacted chlorine.

In accordance with an embodiment of the present disclosure, the scrubbed sulfur dioxide obtained from the column C4 is first cooled in the cooler H5 to a temperature in the range of 5 °C to 25 °C and mixed with chlorine gas in a predetermined molar ratio in a static mixercooler SI to obtain a gas mixture. This is done by monitoring the sulfur dioxide rate by using a flow indicator F2 and adjusting the chlorine gas by using a flow indicator F3. The gas mixture (scrubbed sulfur dioxide gas with chlorine gas) is passed through a column C5 packed with an activated carbon at a fifth predetermined temperature to obtain a product mass comprising a crude sulfuryl chloride, an unreacted sulfur dioxide and an unreacted chlorine.

In an embodiment, a stream of liquid sulfuryl chloride can be circulated in the column C5 and the reaction between the sulfur dioxide gas and chlorine gas can be carried out over the activated carbon to obtain the product mass comprising the crude sulfuryl chloride, the unreacted sulfur dioxide and the unreacted chlorine which is dissolved in the circulating stream of liquid sulfuryl chloride and collected in a flask FL5.

The predetermined molar ratio of sulfur dioxide to the chlorine gas is in the range of 1:2 to 2:1. In an exemplary embodiment, the predetermined molar ratio of sulfur dioxide to the chlorine gas is 1:1.

In an embodiment of the present disclosure, the fifth predetermined temperature is in the range of -10 °C to 30 °C. In an exemplary embodiment, the fifth predetermined temperature is 15 °C. In another exemplary embodiment, the fifth predetermined temperature is 5 °C. The product mass collected in the flask FL5 is cooled in a cooler H6 and is taken for distillation.

Step-(g): In a seventh step, the product mass obtained in the step (f) is distilled at a sixth predetermined temperature at a second predetermined pressure to remove the unreacted sulfur dioxide and the unreacted chlorine to obtain a pure sulfuryl chloride.

In an embodiment of the present disclosure, the sixth predetermined temperature is in the range of 25 °C to 100 °C. In an exemplary embodiment of the present disclosure, the sixth predetermined temperature is 69 °C to 80 °C.

In an embodiment of the present disclosure, the second predetermined pressure is in the range of 200 mmHg to 900 mmHg abs. In an exemplary embodiment of the present disclosure, the second pressure is 760 mmHg abs (atmospheric pressure).

The yield of the pure sulfuryl chloride is in the range of 70% to 95%. In an exemplary embodiment of the present disclosure, the yield of the pure sulfuryl chloride is 80%. In another exemplary embodiment, the yield of the pure sulfuryl chloride is 95%.

The present disclosure further provides an alternative route for treating the tail gases by first reacting sulfur dioxide with chlorine gas prior to the reaction of hydrogen chloride with sulfur trioxide.

In accordance with the second embodiment of the present disclosure, the process for the treatment of tail gases is carried out by using step (ii) following step (i).

Figure 2 illustrates the schematic representation of the process of the treatment of tail gases in accordance with the second embodiment of the present disclosure, wherein a step of converting the sulfur dioxide into sulfuryl chloride is followed by a step of converting hydrogen chloride into chlorosulfonic acid.

The process is described in detail.

Step-(a): The tail gases are scrubbed with an aqueous HC1 to remove any carryover of acid chlorides to obtain first scrubbed tail gases.

Step-(b): The first scrubbed tail gases obtained in step (a) are scrubbed with sulfuric acid to remove moisture to obtain second scrubbed tail gases. Step-(a) and step-(b) are same as in the first embodiment.

Step-(c): The second scrubbed tail gases obtained in step (b) are reacted with chlorine gas to obtain a product mass comprising a crude sulfuryl chloride, an unreacted sulfur dioxide and unreacted chlorine.

In accordance with the present disclosure, the second scrubbed tail gases obtained from column C2 is first cooled in a cooler H7 to a temperature in the range of 5 °C to 25 °C and mixed with chlorine gas in a predetermined molar ratio in a static mixer-cooler S2 to obtain a gas mixture. This is done by monitoring and estimating the sulfur dioxide gas rate in the second scrubbed tail gases by using a flow indicator F4 and adjusting the chlorine gas by using a flow indicator F5. The gas mixture (scrubbed sulfur dioxide gas with chlorine gas) is passed through a column C6 packed with an activated carbon at a seventh predetermined temperature to obtain a product mass comprising a crude sulfuryl chloride, an unreacted sulfur dioxide and an unreacted chlorine.

The hydrogen chloride present in the tail gas remains unreacted and passes on to the next step.

In an embodiment, the reaction between the sulfur dioxide gas and chlorine gas is carried out over the activated carbon in the column C6 to obtain the product mass comprising the crude sulfuryl chloride, the unreacted sulfur dioxide and the unreacted chlorine which is dissolved in the circulating stream of liquid sulfuryl chloride and collected in a flask FL6.

The predetermined molar ratio of sulfur dioxide to the chlorine gas is in the range of 1:2 to 2:1 in . In an exemplary embodiment, the predetermined molar ratio of sulfur dioxide to the chlorine gas is 1:1.

In an embodiment of the present disclosure, the seventh predetermined temperature is in the range of -10 °C to 30 °C. In an exemplary embodiment, the seventh predetermined temperature is 5 °C.

The product mass collected in the flask FL6 is taken for distillation.

Step-(d): The product mass obtained in the step (c) is distilled at an eighth predetermined temperature at a third predetermined pressure to remove the unreacted sulfur dioxide and the unreacted chlorine to obtain a pure sulfuryl chloride. In an embodiment of the present disclosure, the eighth predetermined temperature is in the range of 25 °C to 100 °C. In an exemplary embodiment of the present disclosure, the sixth predetermined temperature is 69 °C to 80 °C.

In an embodiment of the present disclosure, the third pressure is in the range of 200 mmHg to 900 mmHg abs. In an exemplary embodiment of the present disclosure, the third pressure is 760 mmHg abs.

The yield of the pure sulfuryl chloride is in the range of 70% to 95%. In an exemplary embodiment of the present disclosure, the yield is 92%.

The unreacted hydrogen chloride present in the tail gases obtained from the column C6 is cooled in a cooler H8 and entered into a flask FL7.

Step-(e): The unreacted hydrogen chloride gas present in tail gases obtained in the step (c) is reacted with sulfur trioxide to obtain a mixture comprising a crude chlorosulfonic acid and unreacted sulfur trioxide.

In accordance with an embodiment of the present disclosure, the unreacted hydrogen chloride present in the tail gases obtained from the flask FL6 is cooled in the cooler H8 and entered into the flask FL7 comprising sulfur trioxide dissolved in the fluid medium. During the reaction, sulfur trioxide dissolved in the fluid medium is circulated through a column C7 by using a pump P5. HC1 in the tail gases reacts with sulfur trioxide at a ninth predetermined temperature to obtain a mixture comprising crude chlorosulfonic acid and an unreacted sulfur trioxide.

In an embodiment of the present disclosure, the ninth predetermined temperature is in the range of 20 °C to 90 °C. In an exemplary embodiment, the ninth predetermined temperature is 30 °C.

The concentration of the sulfur trioxide in the circulating fluid medium is maintained in the range of 1 % and 35 % by adding sulfur trioxide to the circulating fluid medium. In an exemplary embodiment of the present disclosure, the concentration of sulfur trioxide is 17%.

The amount of the fluid medium is present in an amount in the range of 30 ml to 100 ml per mole of the tail gas. In an exemplary embodiment, the amount of the fluid medium is 60 ml per mole of the tail gas. The fluid medium can be selected from the group consisting of chlorosulfonic acid, oleum, sulfuric acid and sulfuryl chloride. In an exemplary embodiment, the fluid medium is chlorosulfonic acid.

Step-(f): The mixture obtained in step (e) is distilled at a tenth predetermined temperature and a fourth predetermined pressure to remove the unreacted sulfur trioxide to obtain a pure chlorosulfonic acid.

The mixture containing chlorosulfonic acid obtained from the flask FL7, which contains the unreacted sulfur trioxide and some dissolved sulfur dioxide, is first distilled to remove the dissolved sulfur dioxide and sulfur trioxide and then further distilled at a third pressure at a tenth temperature to obtain a pure chlorosulfonic acid. This distillation also removes color if any present in the crude chlorosulfonic acid.

In an embodiment of the present disclosure, the tenth predetermined temperature is in the range of 80 °C to 150 °C. In an exemplary embodiment of the present disclosure, the tenth predetermined temperature is 90 °C to 120 °C.

In an embodiment of the present disclosure, the fourth predetermined pressure is in the range of 20 mmHg to 100 mmHg. In an exemplary embodiment of the present disclosure, the fourth predetermined is 50 mmHg.

The yield of the pure chlorosulfonic acid obtained after distillation is in the range of 70% to 98%. In an exemplary embodiment of the present disclosure, the yield of the pure chlorosulfonic acid is 97%.

In an embodiment of the present disclosure, during the formation of chlorosulfonic acid, some unreacted gases such as sulfur dioxide, chlorine and sulfur trioxide remain in the stream of column C7.

The unreacted gases (sulfur dioxide, chlorine and sulfur trioxide) from the column C7 are cooled in a cooler H9 and carried to a flask FL8 comprising sulfuric acid, wherein scrubbing of the unreacted gases take place. During the scrubbing process, sulfuric acid in the flask FL8 is circulated through a column C8 by using a pump P6. Sulfur dioxide in the unreacted gases is scrubbed in the flask FL8 and the column C8 with sulfuric acid having a concentration in the range of 90 % to 98 % in an amount in the range of 50 ml to 100 ml per mole of the tail gases at a temperature in the range of 20 °C to 50 °C to remove the portion of sulfur trioxide to obtain a scrubbed unreacted gases comprising sulfur dioxide.

The unreacted gases comprising sulfur dioxide and chlorine are cooled in a cooler H10 and are passed through a polishing column C9 packed with activated carbon which converts any unconverted sulfur dioxide and chlorine to sulfuryl chloride. In an embodiment, still remaining gases are cooled in a cooler Hl 1 to remove sulfuryl chloride traces and further sent to an alkali scrubber.

In accordance with an embodiment of the present disclosure, the crude sulfuryl chloride from FL9 are distilled along with the crude sulfuryl chloride obtained from the FL6 to remove excess sulfur dioxide and/or chlorine to obtain a pure sulfuryl chloride.

The process of the present disclosure produces chlorosulfonic acid, which is a value-added reagent used in the synthesis of alkyl sulphates detergents, saccharin and the like.

The process of the present disclosure produces sulfuryl chloride, which is an important value added chlorinating agent in the organic synthesis/reactions.

The process of the present disclosure is simple, economical, and environment-friendly.

The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.

The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.

EXPERIMENTAL DETAILS

Experiment 1: Process for the treatment of tail gases to produce chlorosulfonic acid and sulfuryl chloride in accordance with the first embodiment of the present disclosure. 40 kg of Pivalic acid was taken in a reactor R1 fitted with a stirrer, a catalyst was added and thionyl chloride was pumped at 3.8 kg per hour via a flow indicator (Fl) into the reactor R1 at 40°C. In the reactor (Rl), thionyl chloride was reacted with the Pivalic acid to form pivaloyl chloride along with the generation of the tail gases, HC1 and SO2. The tail gases generated in the reactor (Rl) were cooled in a cooler (Hl) to 10 °C to remove any carryover thionyl chloride and the pivaloyl chloride to obtain cooled tail gases. The cooled tail gases were carried to a flask FL1 for treatment process to produce chlorosulfonic acid and sulfuryl chloride.

Example 1 : Process for the treatment of tail gases to produce chlorosulfonic acid and sulfuryl chloride (Figure 1)

Step-(a): The cooled tail gases containing hydrogen chloride and sulfur dioxide generated during the acid chloride reaction were passed from the cooler Hl into a flask FL1 comprising 90 ml of 20 % aqueous hydrochloric acid/mole of the tail gases. During the scrubbing process, the aqueous HCL in the flask FL1 was circulated through a column Cl by using a pump Pl. The tail gases were scrubbed in the flask FL1 and the column Cl at 100 °C to remove the carryover pivaloyl chlorides from the tail gases to obtain first scrubbed tail gases.

Step-(b): The first scrubbed tail gasses from the column Cl were cooled in a cooler H2 to 10 °C and entered into a flask FL2 comprising 60 ml 98% sulfuric acid/mole of the tail gases. During the scrubbing process, sulfuric acid in the flask FL2 was circulated through a column C2 by using a pump P2. The first scrubbed tail gases were scrubbed in the flask FL2 and the column C2 at 25°C to remove the moisture from the first scrubbed tail gases to obtain second scrubbed tail gases.

Step-(c): The second scrubbed tail gases from the column C2 were cooled in a cooler H3 to 20 °C and entered into a flask FL3 comprising 30% sulfur trioxide dissolved in 95 ml of chlorosulfonic acid/mole of the tail gases. During the reaction, sulfur trioxide dissolved in chlorosulfonic acid was circulated through a column C3 by using a pump P3. HC1 in the second scrubbed tail gases were reacted with sulfur trioxide at 50°C to obtain a mixture comprising crude chlorosulfonic acid and 5% unreacted sulfur trioxide.

The sulfur dioxide present in the tail gases remains unreacted and passes on to the next step along with a portion of sulfur trioxide. Step-(d): The mixture containing chlorosulfonic acid obtained from the flask FL3, (which contains the unreacted sulfur trioxide and some amount of dissolved sulfur dioxide), was distilled to remove first the dissolved sulfur dioxide and sulfur trioxide and then further distilled at 50 mmHg at 90 °C to 120 °C to obtain a pure chlorosulfonic acid having 99% purity (yield= 85%).

Step-(e): The sulfur dioxide gas obtained in the step (c) from the column C3 was cooled in a cooler H4 to 10 °C and entered into a flask FL4 comprising 60 ml of 95% sulfuric acid/mole of the tail gases. During the scrubbing process, sulfuric acid in the flask FL4 was circulated through a column C4 by using a pump P4. Sulfur dioxide in the tail gas was scrubbed in the flask FL4 and the column C4 with sulfuric acid at 25 °C to remove the portion of sulfur trioxide to obtain a scrubbed sulfur dioxide gas.

Step-(f): The scrubbed sulfur dioxide obtained from the column C4 was first cooled in a cooler H5 to 15 °C and mixed with chlorine gas in a molar ratio of 1:1 in a static mixercooler SI to obtain a gas mixture. This was done by monitoring the sulfur dioxide rate by using a flow indicator F2 and adjusting the chlorine gas by using a flow indicator F3. The gas mixture (scrubbed sulfur dioxide gas with chlorine gas) was passed through a column C5 packed with an activated carbon where a stream of liquid sulfuryl chloride was also circulated at 15 °C to obtain a product mass comprising a crude sulfuryl chloride, an unreacted sulfur dioxide and an unreacted chlorine which dissolved into the circulating stream of the liquid sulfuryl chloride.

Step-(g): The product mass obtained in the step (f) was distilled at 69 °C to 80 °C at 760 mmHg abs to remove the unreacted sulfur dioxide and the unreacted chlorine to obtain a pure sulfuryl chloride having 99% purity (yield 80%).

Example 2: Process for the treatment of tail gases to produce chlorosulfonic acid and sulfuryl chloride (Figure 1)

Step-(a): The cooled tail gases containing hydrogen chloride and sulfur dioxide generated during the acid chloride reaction were passed from the cooler Hl at 10 °C into a flask FL1 comprising 50 ml of 28 % aqueous hydrochloric acid/mole of the tail gases (total 25.6 liters). During the scrubbing process, the aqueous HCL in the flask FL1 was circulated through a column Cl by using a pump Pl. The tail gases were scrubbed in the flask FL1 and the column Cl at 90 °C to remove the carryover pivaloyl chlorides from the tail gases to obtain first scrubbed tail gases.

Step-(b): The first scrubbed tail gasses from the column Cl were cooled in a cooler H2 to 20 °C and entered into a flask FL2 comprising 30 ml 98% sulfuric acid/mole of the tail gases (total 15.5 liters). During the scrubbing process, sulfuric acid in the flask FL2 was circulated through a column C2 by using a pump P2. The first scrubbed tail gases were scrubbed in the flask FL2 and the column C2 at 50 °C to remove the moisture from the first scrubbed tail gases to obtain second scrubbed tail gases.

Step-(c): The second scrubbed tail gases from the column C2 were cooled in a cooler H3 to 20 °C and entered into a flask FL3 comprising 17 % sulfur trioxide dissolved in 60 ml of chlorosulfonic acid/mole of the tail gases (total 30.7 liters of chlorosulfonic acid containing 17 % SO3). During the reaction, sulfur trioxide dissolved in chlorosulfonic acid was circulated through a column C3 by using a pump P3. HC1 in the second scrubbed tail gases were reacted with sulfur trioxide at 30 °C to obtain a mixture comprising a crude chlorosulfonic acid and 5% unreacted sulfur trioxide.

The sulfur dioxide present in the tail gases remained unreacted and was passed on to the next step along with a portion of sulfur trioxide.

Step-(d): The mixture containing chlorosulfonic acid obtained from the flask FL3, (which contains the unreacted sulfur trioxide and some dissolved sulfur dioxide), was distilled to remove first the dissolved sulfur dioxide and sulfur trioxide and then further distilled at 50 mmHg at 90 °C to 120 °C to obtain a pure chlorosulfonic acid having 99% purity (yield= 98 %).

Step-(e): The sulfur dioxide gas obtained in the step (c) from the column C3 was cooled in a cooler H4 to 10 °C and entered into a flask FL4 comprising 60 ml of 95% sulfuric acid/mole of the tail gases (total 30.7 liters). During the scrubbing process, sulfuric acid in the flask FL4 was circulated through a column C4 by using a pump P4. Sulfur dioxide in the tail gas was scrubbed in the flask FL4 and the column C4 with sulfuric acid at 25 °C to remove the portion of sulfur trioxide to obtain a scrubbed sulfur dioxide gas.

Step-(f): The scrubbed sulfur dioxide obtained from the column C4 was first cooled in a cooler H5 to 15 °C and mixed with chlorine gas in a molar ratio of 1:1 in a static mixercooler SI to obtain a gas mixture. This was done by monitoring the sulfur dioxide rate by using a flow indicator F2 and adjusting the chlorine gas by using a flow indicator F3. The gas mixture (scrubbed sulfur dioxide gas with chlorine gas) was passed through a column C5 packed with an activated carbon at 15 °C to obtain a product mass comprising a crude sulfuryl chloride, an unreacted sulfur dioxide and an unreacted chlorine which dissolved into the circulating stream of the liquid sulfuryl chloride.

Step-(g): The product mass obtained in the step (f) was distilled at 69 °C to 80 °C at 760 mmHg abs to remove the unreacted sulfur dioxide and the unreacted chlorine to obtain a pure sulfuryl chloride having 99% purity (yield 95 %).

Experiment 2: Process for the treatment of tail gases to produce chlorosulfonic acid and sulfuryl chloride in accordance with the second embodiment of the present disclosure.

Example 3: Process for the treatment of tail gases to produce chlorosulfonic acid and sulfuryl chloride (Figure 2)

Step-(a): The cooled tail gases containing hydrogen chloride and sulfur dioxide generated during the acid chloride reaction were passed from the cooler Hl at 10 °C into a flask FL1 comprising 50 ml of 28 % aqueous hydrochloric acid/mole of the tail gases (total 25.6 liters). During the scrubbing process, the aqueous HCL in the flask FL1 was circulated through a column Cl by using a pump Pl. The tail gases were scrubbed in the flask FL1 and the column Cl at 90 °C to remove the carryover pivaloyl chlorides from the tail gases to obtain first scrubbed tail gases.

Step-(b): The first scrubbed tail gasses from the column Cl were cooled in a cooler H2 to 20 °C and entered into a flask FL2 comprising 30 ml 98 % sulfuric acid/mole of the tail gases (total 15.5 liters). During the scrubbing process, sulfuric acid in the flask FL2 was circulated through a column C2 by using a pump P2. The first scrubbed tail gases were scrubbed in the flask FL2 and the column C2 at 50 °C to remove the moisture from the first scrubbed tail gases to obtain second scrubbed tail gases.

Step-(c): The second scrubbed tail gases obtained from the column C2 was first cooled in a cooler H7 to 5 °C and mixed with chlorine gas in a molar ratio of 1 : 1 in a static mixer-cooler S2 to obtain a gas mixture. This was done by monitoring and estimating the sulfur dioxide gas rate in the second scrubbed tail gases by using a flow indicator F4 and adjusting the chlorine gas by using a flow indicator F5. The gas mixture (scrubbed sulfur dioxide gas with chlorine gas) was passed through a column C6 packed with an activated carbon at 5 °C where the sulfur dioxide and chlorine reacted to obtain a product mass comprising a crude sulfuryl chloride, an unreacted sulfur dioxide and unreacted chlorine which were collected in a Flask FL6.

The hydrogen chloride present in the tail gas remained unreacted and was passed on to the next step.

Step-(d): The product mass obtained in the step (c) was distilled at 69 °C to 80 °C at 760 mmHg to remove the unreacted sulfur dioxide and the unreacted chlorine to obtain a pure sulfuryl chloride.

Step-(e): The unreacted hydrogen chloride present in the tail gases obtained in step (c) from the flask FL6 was cooled in a cooler H8 to 5 °C and entered into a flask FL7 comprising 17 % sulfur trioxide dissolved in 60 ml of chlorosulfonic acid/mole of the tail gases (total 30.7 liters of chlorosulfonic acid containing 17 % SO3). During the reaction, sulfur trioxide dissolved chlorosulfonic acid was circulated through a column C7 by using a pump P5. HC1 in the tail gases reacted with sulfur trioxide at 30 °C to obtain a mixture comprising a crude chlorosulfonic acid and 5 % unreacted sulfur trioxide.

Step-(f): The mixture containing chlorosulfonic acid obtained from the flask FL7, (which contains 5% unreacted sulfur trioxide and some dissolved sulfur dioxide), was distilled to remove first the dissolved sulfur dioxide and sulfur trioxide and then further distilled at 50 mmHg at 90 °C to 120 °C to obtain a pure chlorosulfonic acid having 99% purity (yield= 97 %).

Further, the unreacted gases such as sulfur dioxide, chlorine and Sulfur trioxide stream from the column C7 were cooled in a cooler H9 and passed through a Flask FL8 containing 60 ml 95% sulfuric acid/mole of the tail gases (total 30.7 liters). During the scrubbing process, sulfuric acid in the flask FL8 was circulated through a column C8 by using a pump P6. Sulfur dioxide in the unreacted gases were scrubbed in the flask FL8 and the column C8 with sulfuric acid at 25 °C to remove the portion of sulfur trioxide to obtain a scrubbed unreacted gases comprising sulfur dioxide and chlorine.

The unreacted gases comprising sulfur dioxide and chlorine were cooled in a cooler H10 to 10 °C and were passed through a polishing column C9 packed with activated carbon which converts any unconverted sulfur dioxide and chlorine to sulfuryl chloride. Any remaining gases were cooled in a cooler Hl l to remove sulfuryl chloride traces and further sent to an alkali scrubber.

The crude sulfuryl chloride from FL6 and FL9 was distilled together to remove excess sulfur dioxide and/or chlorine to obtain a pure sulfuryl chloride having 99% purity (Yield = 92%).

TECHNICAL ADVANCEMENTS

The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for the treatment of tail gases, that:

- is simple and environment-friendly; produces chlorosulfonic acid, which is a value-added reagent used in the synthesis of alkyl sulphates detergents, saccharin and the like; and produces sulfuryl chloride, which is an important value added chlorinating agent in the organic synthesis/reactions.

The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

The foregoing description of the specific embodiments so fully reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications of such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.

Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure 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 disclosure and not as a limitation.