Chloride Integration

Field of Disclosure

The present disclosure relates to a method and system for producing chlorinated hydrocarbons, and in particular a method and system for producing chloromethanes.

Background

Chloromethanes (e.g., chloromethane, dichloromethane, trichloromethane and tetrachloromethane) are typically produced in a two-step process which is known in the art (see: Ullmann's Encyclopedia of Industrial Chemistry, article "Chloromethanes" and Kirk-Othmer Encyclopedia of Chemical Technology, article "Chlorocarbons and

Chlorohydrocarbons, Survey"). In the first step (the hydrochlorination process) methanol is reacted catalytically with hydrogen chloride (HC1) in the gas phase to produce chloromethane (CH ₃ CI) and water according to the following reaction equation:

CH ₃ OH + HC1 -> CH ₃ CI + H ₂ 0

where some of the water reacts with the hydrogen chloride to produce a weak

hydrochloric acid.

In the second step (the thermal chlorination process) the chloromethane is chlorinated in the gas phase to produce dichloromethane (CH ₂ CI ₂ ), trichloromethane (CHCI ₃ ) and hydrogen chloride according to the following reaction equation.

2 CH3CI + 3 Cl ₂ -> CH2CI2 +CHCI3 +3 HC1

A disadvantage of this two-step process, however, is that it produces a lot of aqueous hydrogen chloride (hydrochloric acid) while still requiring input of anhydrous hydrogen chloride. For example, when the demand for trichloromethane is low the above described two-step process produces a lot of aqueous hydrogen chloride while still being a net anhydrous hydrogen chloride importer. This problem is made worse when the chloromethanes production plant is not integrated with a hydrogen chloride producing plant.

In addition, the water produced in the hydrochlorination process is removed as hydrochloric acid, which is typically neutralized with caustic from a chlorine producing electrochemical unit. This stream of neutralized acid is then disposed of as a waste water stream, which may create an environmental concern. Furthermore the thermal chlorination process produces a waste stream rich in tetrachloromethane (CC1 ₄ ), which again has to be disposed of in a responsible manner. This is typically accomplished by incinerating the tetrachloromethane, thereby forming more hydrochloric acid that again may have to be neutralized aggravating above described disposal problems.

Summary

The present disclosure describes a method and a system that provide the required hydrogen chloride for the hydrochlorination process, while also effectively addressing the disadvantages of the traditional two-step process of forming chloromethanes (e.g., disposal of excess hydrogen chloride and undesired tetrachloromethane). The method and system of the present disclosure address these problems by recovering, recycling and reusing the hydrochloric acid streams produced in the two-step process instead of neutralizing and disposing of them as waste. Other advantages of the method and system of the present disclosure are also discussed herein.

Embodiments of the present disclosure include a method and a system for producing chloromethanes. The method includes producing dichlorine (Cl ₂ ) and dihydrogen (H ₂ ) in a chlor-alkali reactor; reacting a first portion of the dichlorine with chloromethane (CH3CI) in a thermal chlorination reactor to produce dichloromethane (CH ₂ C1 ₂ ), trichloromethane (CHCI3) and a first portion of hydrogen chloride (HC1); producing a second portion of hydrogen chloride from dihydrogen and a second portion of the dichlorine produced in the chlor-alkali reactor; and reacting methanol (CH ₃ OH) with the first portion of hydrogen chloride and the second portion of hydrogen chloride in the presence of a catalyst in a hydrochlorination reactor to produce hydrochloric acid and the chloromethane used in the thermal chlorination reactor.

The method further includes producing the second portion of hydrogen chloride by burning the second portion of dichlorine and the dihydrogen produced in the chlor- alkali reactor to produce hydrogen chloride; producing a concentrate of hydrochloric acid in an adiabatic absorber from the hydrogen chloride produced by burning the second portion of dichlorine and the dihydrogen; and desorbing hydrogen chloride from the concentrate of hydrochloric acid to produce the second portion of hydrogen chloride. The method can include supplying the chlor-alkali reactor with the concentrate of hydrochloric acid produced by the adiabatic absorber.

The adiabatic absorber separates water from the concentrate of hydrochloric acid. This water includes the water produced in the hydrochlormation reactor. The method further includes neutralizing at least a portion of the hydrochloric acid product from each of the stripping and desorbing with the water separated from the concentrate of hydrochloric acid in the adiabatic absorber and a sodium hydroxide (NaOH) solution produced in the chlor-alkali process to produce an aqueous sodium chloride solution. The method includes providing the aqueous sodium chloride solution to the chlor-alkali reactor for producing dichlorine and dihydrogen.

The method further includes stripping the hydrochloric acid coming from the hydrochlormation reactor to recover hydrocarbons, thereby helping to purify the hydrochloric acid produced in the hydrochlormation reactor, and returning the recovered hydrocarbons to the hydrochlormation reactor. Stripping the hydrochloric acid from the hydrochlormation reactor and desorbing hydrogen chloride from the concentrate of hydrochloric acid each produce a weak hydrochloric acid product. The method includes providing the weak hydrochloric acid product from each of the stripping and desorbing to the adiabatic absorber to produce the concentrate of hydrochloric acid.

The method also includes producing tetrachloromethane in the thermal chlorination reactor and incinerating the tetrachloromethane in an incineration unit to produce a weak hydrochloric acid product. The weak hydrochloric acid is purified and supplied to the adiabatic absorber to produce the concentrate of hydrochloric acid.

The system to produce chloromethanes of the present disclosure includes a chlor- alkali reactor having an inlet for a brine that reacts in the chlor-alkali reactor to produce dichlorine and dihydrogen and a thermal chlorination reactor connected to the chlor- alkali reactor and a hydrochlormation reactor, where a first portion of the dichlorine from the chlor-alkali reactor and chloromethane from the hydrochlormation reactor react in the thermal chlorination reactor to produce dichloromethane, trichloromethane and a first portion of hydrogen chloride. The system further includes a chlorine burner connected to the chlor-alkali reactor, where the dihydrogen and a second portion of the dichlorine from the chlor-alkali reactor react in the chlorine burner to produce hydrogen chloride. An adiabatic absorber connected to the chlorine burner concentrates the hydrogen chloride produced in the chlorine burner.

A desorbing unit connected to the adiabatic absorber produces a second portion of hydrogen chloride from the hydrogen chloride concentrate coming from the adiabatic absorber. The hydrochlormation reactor is connected to the desorbing unit and the thermal chlorination reactor, where methanol (CH ₃ OH) reacts with the first portion of hydrogen chloride and the second portion of hydrogen chloride in the presence of a catalyst in the hydrochlormation reactor to produce hydrochloric acid and the

chloromethane used in the thermal chlorination reactor.

The system further includes a stripping unit connected to the hydrochlormation reactor. The stripping unit strips the hydrochloric acid from the hydrochlormation reactor to recover hydrocarbons that are returned to the hydrochlormation reactor. The desorbing unit produces hydrochloric acid, where the hydrochloric acid from the stripping unit and the desorbing unit are used in the adiabatic absorber to concentrate the hydrogen chloride produced in the chlorine burner.

The system can also include a hydrochloric neutralization unit, which is connected to the adiabatic absorber, the chlor-alkali reactor, the stripping unit and the desorbing unit. The adiabatic absorber separates water from the concentrate of hydrochloric acid, and the chlor-alkali reactor produces a sodium hydroxide (NaOH) solution, where the hydrochloric neutralization unit receives both the water and the sodium hydroxide solution. The hydrochloric neutralization unit also receives and neutralizes at least a portion of the hydrochloric acid from the stripping unit and the desorbing unit with the sodium hydroxide from the chlor-alkali reactor and the water from the adiabatic absorber.

The hydrochloric neutralization unit is also connected to the chlor-alkali reactor, where an aqueous sodium chloride solution is produced in the hydrochloric neutralization unit from the neutralization of at least a portion of the hydrochloric acid from the stripping unit and the desorbing unit with the sodium hydroxide from the chlor-alkali reactor. The aqueous sodium chloride solution produced in the hydrochloric

neutralization unit reacts in the chlor-alkali reactor to produce dichlorine and dihydrogen.

The system further includes an incineration unit connected to the thermal chlorination reactor and a purifying unit connected to the incineration unit. The thermal chlorination reactor produces tetrachloromethane that is incinerated in the incineration unit to produce a weak hydrochloric acid product. The weak hydrochloric acid product is purified in the purifying unit to a weak hydrochloric acid that is supplied to the adiabatic absorber to produce the concentrate of hydrochloric acid. The chlor-alkali reactor is connected to the adiabatic absorber, where the concentrate of hydrochloric acid produced by the adiabatic absorber is used in the chlor-alkali reactor to produce the dichlorine and dihydrogen.

Definitions

As used herein dichlorine (Cl ₂ ) is a compound that is in a gas phase at standard temperature and pressure of 0 °C and an absolute pressure of 100 kPa (IUPAC).

As used herein dihydrogen (H ₂ ) is a compound that is in a gas phase at standard temperature and pressure of 0 °C and an absolute pressure of 100 kPa (IUPAC).

As used herein, "chlorinated hydrocarbons" are defined as compounds that include chlorine, carbon and hydrogen.

As used herein, "chloromethanes" are defined as compounds that include chloromethane (CH ₃ C1); dichloromethane (CH ₂ C1 ₂ ); trichloromethane (CHCI3) and tetrachloromethane (CC1 ₄ ).

As used herein, "hydrogen chloride" is a compound that is in a gas phase at standard temperature and pressure of 0 °C and an absolute pressure of 100 kPa (IUPAC).

As used herein, "hydrochloric acid" is an aqueous solution of hydrogen chloride that is in a liquid phase at standard temperature and pressure of 0 °C and an absolute pressure of 100 kPa (IUPAC).

As used herein, "brine" is a solution of sodium chloride in water.

As used herein, "caustic" is a solution of sodium hydroxide (NaOH) in water. As used herein, a "weak hydrochloric acid" is a solution of hydrogen chloride in water that contains 10 to 15 weight percent (wt.%) hydrogen chloride (HC1). As used herein, a "concentrate of hydrochloric acid" is a solution of hydrogen chloride in water that contains 30 to 36 weight percent (wt.%) hydrogen chloride (HCl).

As used herein, "°C" is a symbol for degrees Celsius.

As used herein, "Pa" is a symbol for a pascal.

As used herein, "a," "an," "the," "at least one," and "one or more" are used interchangeably. The term "comprises", and variations thereof, does not have a limiting meaning where this term appears in the description and claims.

As used herein, the term "and/or" means one, more than one, or all of the listed elements.

Also herein, the recitations of numerical ranges by endpoints include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

Brief Description of Drawings

Figure 1 provides a schematic of a system for producing chloromethanes according to an embodiment of the present disclosure.

Figure 2 provides a schematic of a system for producing chloromethanes according to an embodiment of the present disclosure.

Detailed Description

Embodiments of the present disclosure provide for a method and system for producing chloromethanes. The process and system of the present disclosure uniquely integrate a chlor-alkali electrolysis process with a two-step chloromethane process. The chlor-alkali electrolysis process produces dichlorine and dihydrogen that are used in a hydrochlorination reactor and a thermal chlorination reactor of the two-step

chloromethanes process to produce, among other things, chloromethane (CH ₃ C1), dichloromethane (CH ₂ CI ₂ ) and trichloromethane (CHCI ₃ ). As discussed herein, integrating these processes according to the present disclosure can help to both minimize chloromethane waste and by-product streams, while using the starting and intermediate products from these reactors in an efficient manner.

Specifically, the problem of having to dispose of "waste" hydrochloric acid as is encountered in other systems and methods has been addressed in the present invention. Specifically, the method and system of the present disclosure help to reduce the amount of waste water by up to 60 percent and the amount of caustic used by as much as 80 percent as compared to traditional low-integrated chloromethane processes. The method and system of the present disclosure address these problems by recovering, recycling and reusing the hydrochloric acid streams produced in the two-step process instead of neutralizing and disposing of them. As discussed more fully herein, the present disclosure teaches the recovery, recycle and reuse of hydrogen chloride produced in the thermal chlorination reactor and the hydrochlorination reactor to produce hydrochloric acid that is used in the hydrochlorination reactor.

The method and system of the present disclosure also address the problem of what to do with impurities that are normally present in the hydrochloric acid produced in the thermal chlorination reactor and the hydrochlorination reactor. The reaction of hydrogen chloride and methanol produces water which is typically removed as weak hydrochloric acid from the hydrochlorination reactor. This weak hydrochloric acid from the hydrochlorination reactor is also contaminated with chloromethane. Using both a desorption process and an adiabatic absorption process the contamination in the hydrochloric acid stream coming from the hydrochlorination reactor is removed, thereby allowing the hydrochloric acid to be reused. Specifically, purifying the weak

hydrochloric acid from the hydrochlorination reactor allows its reuse in forming a concentrated hydrochloric acid in the adiabatic absorption process and in forming hydrogen chloride in desorption process that is then recycled back to and used in the hydrochlorination reactor. Other advantages of the method and system of the present disclosure are also discussed herein.

The figures herein follow a numbering convention in which the first digit or digits correspond to the drawing figure number and the remaining digits identify an element or component in the drawing. Similar elements or components between different figures may be identified by the use of similar digits. For example, 110 may reference element "10" in Fig. 1, and a similar element may be referenced as 210 in Fig. 2. As will be appreciated, elements shown in the various embodiments herein can be added, exchanged, and/or eliminated so as to provide any number of additional embodiments of the present disclosure. In addition, as will be appreciated the proportion and the relative scale of the elements provided in the figures are intended to illustrate the embodiments of the present invention, and should not be taken in a limiting sense.

Referring now to Fig. 1, there is shown a system 100 to produce chloromethanes according to an embodiment of the present disclosure. The system 100 includes a chlor- alkali reactor 102, as are known, having an inlet for a brine 104 that reacts in the chlor- alkali reactor 102 to produce dichlorine (Cl ₂ ) 106 and dihydrogen (H ₂ ) 108. The reaction of the brine is through the electrolysis of water (H ₂ 0) and sodium chloride (NaCl), to produce the dichlorine, dihydrogen and a sodium hydroxide (NaOH) solution 123.

A thermal chlorination reactor 110 is connected to the chlor-alkali reactor 102 and a hydrochlorination reactor 112. In the hydrochlorination reactor 112, methanol

(CH ₃ OH) 138 reacts with hydrogen chloride (HC1) to form chloromethane (CH ₃ CI) and water (H ₂ 0). Inside the hydrochlorination reactor 112 hydrochloric acid is also formed from the hydrogen chloride and the water. A portion of the chloromethane 116-1 can be removed from the hydrochlorination reactor 112, as needed for market demands, while the remaining portion of the chloromethane 116-2 from the hydrochlorination reactor 112 is chlorinated in the thermal chlorination reactor 110.

In the thermal chlorination reactor 110 the chloromethane 116-2 from the hydrochlorination reactor 112 reacts with a first portion 114 of the dichlorine 106 from the chlor-alkali reactor 102 to produce dichloromethane (CH ₂ C1 ₂ ) 118, trichloromethane (CHCI ₃ ) 120 and a first portion of hydrogen chloride (HC1) 122. Some

tetrachloromethane (CC1 ₄ ) 151 can also be produced in the thermal chlorination reactor 110. As discussed herein, the tetrachloromethane can be incinerated in an incineration unit with dihydrogen from the chlor-alkali reactor 102 (see Fig. 2) to produce a weak hydrochloric acid. As discussed for FIG. 2, the weak hydrochloric acid from the incineration unit can be recycled for eventual use in the hydrochlorination reactor.

The hydrochlorination can be done in a liquid phase with or without a catalyst (e.g., ZnCl ₂ ). Temperatures for the liquid phase reactions can range from 120 °C to 160 °C. The hydrochlorination can also be done in the gas phase with, for example, a AI ₂ O ₃ catalyst. Gas phase reaction pressures are typically from 0.3 MPa to 0.6 MPa, with reaction temperatures of 280 °C to 350 °C. Thermal chlorination typically is done in the gas phase without catalyst at a pressure of 0.8 Mpa to 1.5 Mpa and at a temperature of 350 °C to 400 °C. Chloromethane can be chlorinated in the liquid phase at 60 °C to 100 °C using radical producing agents like azodiisobutyronitrile.

Hydrogen chloride needed for the method and system of the present disclosure can be produced in a chlorine burner 124 connected to the chlor-alkali reactor 102 and adiabatic absorber 130. So, for example, the dihydrogen 108 and a second portion of the dichlorine 126 from the chlor-alkali reactor 102 react in the chlorine burner 124 to produce a second portion of hydrogen chloride 128. The dihydrogen 108 and a second portion of the dichlorine 126 can be fed to the chlorine burner 124, where the dihydrogen 108 can be in a slight stoichiometric excess to better ensure a complete hydrogen chloride synthesis. So, producing the second portion of hydrogen chloride 128 includes burning the second portion of dichlorine 126 and the dihydrogen 108 produced in the chlor-alkali reactor 102 to produce hydrogen chloride. General operating conditions for the chlorine burner 124include an operating pressure of about 100 kPa (1 Bar(g)) and an operating temperature in the burning chamber of about 2000 °C.

The second portion of hydrogen chloride 128 from the chlorine burner 124 flows into the adiabatic absorber 130 where it is concentrated to form a concentrate of hydrochloric acid 132. The adiabatic absorber 130 in addition to producing the concentrate of hydrochloric acid 132 also separates water 131 from the concentrate of hydrochloric acid 132 using the heat generated in the absorption process. As discussed herein, make-up "water" for the adiabatic absorber 130 is provided in the form of a weak hydrochloric acid 150, which is produced in a desorbing unit 134 and a stripping unit 142. In this way, the weak hydrochloric acid from these units, as discussed herein, is recycled and reused. General operating conditions for the adiabatic absorber 130 include an operating pressure of about 100 kPa (1 Bar(g)) and an operating temperature of 80 °C to 120 °C. General operating conditions for the desorbing unit 134 include an operating pressure of 500 kPa (5 Bar(g)) to 1 MPa (10 Bar(g)) and an operating temperature of 160 °C to 190 °C.

The desorbing unit 134 is connected to the adiabatic absorber 130, where the desorbing unit 134 produces a second portion 136 of hydrogen chloride from the concentrate of hydrochloric acid 132 formed from the hydrogen chloride concentrated in the adiabatic absorber 130. The second portion 136 of hydrogen chloride from the concentrate of hydrochloric acid 132 is used in the hydrochlorination reactor 112 in forming the chloromethane, as discussed herein. The desorbing unit 134 also produces a weak hydrochloric acid 135. The weak hydrochloric acid 135 produced by the desorbing unit 134 is joined with weak hydrochloric acid 148 produced in the stripping unit 142.

As illustrated, the stripping unit 142 is connected to the hydrochlorination reactor

112. The stripping unit 142 uses steam 144 to strip the hydrochloric acid 140 from the hydrochlorination reactor 122 to recover hydrocarbons 146 (e.g., methanol and chloromethane), which can be returned to the hydrochlorination reactor 112. Stripping unit 142 also produces a weak hydrochloric acid 148. The steam used in the stripping unit 142 adds to the water produced in the hydrochlorination reactor 112 and further increases the flow-rate of the weak hydrochloric acid 148.

The desorbing unit 134 produces hydrochloric acid 135, where the hydrochloric acid 148 from the stripping unit 142 and the desorbing unit 134 are used, as discussed herein, in the adiabatic absorber 130 to concentrate the hydrogen chloride 132 produced in the chlorine burner 124. As illustrated, the weak hydrochloric acid 148 from the stripping unit 142 and the weak hydrochloric acid 135 from the desorbing unit 134 are provided to the adiabatic absorber 130 via line 150. For the various embodiments, the stripping unit 142 can operate at a pressure of 0.7 MPa to 1.2 MPa and a temperature of 175 °C to 195 °C.

As illustrated, the hydrochlorination reactor 112 is connected to the desorbing unit

134 and the thermal chlorination reactor 110, where methanol 138 reacts with the first portion 122 of hydrogen chloride and the second portion 136 of hydrogen chloride in the presence of a catalyst in the hydrochlorination reactor 112 to produce hydrochloric acid 140 and the chloromethane 116 used in the thermal chlorination reactor 110.

Referring now to Fig. 2, there is shown a system 201 to produce chloromethanes according to an embodiment of the present disclosure. The system 201 includes a chlor- alkali reactor 202, as are known, having an inlet for a brine 204 that reacts in the chlor- alkali reactor 202 to produce dichlorine 206 and dihydrogen 208. The reaction of the brine is through the electrolysis of water and sodium chloride, to produce the dichlorine, dihydrogen and a sodium hydroxide solution 223. A thermal chlorination reactor 210 is connected to the chlor-alkali reactor 202 and a hydrochlorination reactor 212. In the hydrochlorination reactor 212, methanol 238 reacts with hydrogen chloride to form chloromethane and water. Inside the

hydrochlorination reactor 212 hydrochloric acid is also formed from the hydrogen chloride and the water. A portion of the chloromethane 216-1 can be removed from the hydrochlorination reactor 212, as needed for market demands, while the remaining portion of the chloromethane 216-2 from the hydrochlorination reactor 212 is chlorinated in the thermal chlorination reactor 210.

In the thermal chlorination reactor 210 the chloromethane 216-2 from the hydrochlorination reactor 212 reacts with a first portion 214 of the dichlorine 206 from the chlor-alkali reactor 202 to produce dichloromethane 218, trichloromethane 220 and a first portion of hydrogen chloride 222. Tetrachloromethane 251 is an

unavoidablebyproduct in the thermal chlorination reactor 210.

Both of the thermal chlorination reactor 210 and the hydrochlorination reactor 212 can operate at pressures and temperatures as discussed herein. Hydrogen chloride needed for the method and system of the present disclosure can be produced in a chlorine burner 224 connected to the chlor-alkali reactor 202 and adiabatic absorber 230. So, for example, the dihydrogen 208 and a second portion of the dichlorine 226 from the chlor- alkali reactor 202 react in the chlorine burner 224 to produce a second portion of hydrogen chloride 228. The dihydrogen 208 and a second portion of the dichlorine 226 can be fed to the chlorine burner 224, where the dihydrogen 208 can be in a slight stoichiometric excess to better ensure a complete hydrogen chloride synthesis takes place. The general operating conditions for the chlorine burner 224 include those discussed herein.

The second portion of hydrogen chloride 228 from the chlorine burner 224 flows into the adiabatic absorber 230. The second portion of hydrogen chloride 228 produced in the chlorine burner 224 is concentrated in the adiabatic absorber 230 to form a concentrate of hydrochloric acid 232. The general operating conditions for the adiabatic absorber 230 include an operating pressure of about 100 kPa (1 Bar(g)) and an operating temperature of 80 °C to 120 °C. The second portion of hydrogen chloride 228 from the chlorine burner 224 flows into the adiabatic absorber 230 where it is concentrated to form a concentrate of hydrochloric acid 232. The adiabatic absorber 230 in addition to producing the concentrate of hydrochloric acid 232 also separates water 231 from the concentrate of hydrochloric acid 232 using the heat generated in the absorption process. As discussed herein, make-up "water" for the adiabatic absorber 230 is provided in the form of a weak hydrochloric acid 250. The weak hydrochloric acid 250 is produced in a desorbing unit 234, in a stripping unit 242 and in an incineration unit 252. In this way, the weak hydrochloric acid from these units, as discussed herein, is recycled and reused.

As illustrated, the chlor-alkali reactor 202 is connected to the adiabatic absorber

230, via a storage unit 262, where the concentrate of hydrochloric acid 232 produced by the adiabatic absorber 230 can be used in the chlor-alkali reactor 202 to produce the dichlorine and dihydrogen. For example, a portion of the concentrate of hydrochloric acid 232 is diverted to the chlor-alkali reactor 202 via line 260 from the storage unit 262. The portion of the concentrate of hydrochloric acid 260 can be used to, among other things, help control the pH of the electrolysis cells in the chlor-alkali reactor 202.

The desorbing unit 234 is connected to the adiabatic absorber 230, where the desorbing unit 234 produces a second portion 236 of hydrogen chloride from the concentrate of hydrochloric acid 232 formed from the hydrogen chloride concentrated in the adiabatic absorber 230. The second portion 236 of hydrogen chloride from the concentrate of hydrochloric acid 232 is used in the hydrochlorination reactor 212 in forming the chloromethane 216, as discussed herein. The desorbing unit 234 also produces a weak hydrochloric acid 235. The weak hydrochloric acid 235 produced by the desorbing unit 234 is joined with weak hydrochloric acid 248 produced in a stripping unit 242 in storage unit 264. General operating conditions for the desorbing unit 234 include an operating pressure of 500 kPa (5 Bar(g)) to 1 MPa (10 Bar(g)) and an operating temperature of 160 °C to 190 °C. The general operating conditions for the stripping unit 242 include those previously discussed.

The hydrochlorination reactor 212 is connected to the desorbing unit 234 and the thermal chlorination reactor 210, where the methanol 238 reacts with the first portion 222 of hydrogen chloride and the second portion 236 of hydrogen chloride in the presence of a catalyst in the hydrochlorination reactor 212 to produce hydrochloric acid 240 and the chloromethane 216 used in the thermal chlorination reactor 210.

As illustrated, the stripping unit 242 is connected to the hydrochlorination reactor 212. The stripping unit 242 uses steam 244 to strip the hydrochloric acid 240 from the hydrochlorination reactor 212 to recover hydrocarbons 246 (e.g., organic by-products from the chlorination reactions), which can be returned to the hydrochlorination reactor 212. Stripping unit 242 also produces the weak hydrochloric acid 248. The desorbing unit 234 produces weak hydrochloric acid 235, where the hydrochloric acid 248 from the stripping unit 242 and the desorbing unit 234 are used, as discussed herein, in the adiabatic absorber 230 to concentrate the hydrogen chloride 232 produced in the chlorine burner 224. As illustrated, the weak hydrochloric acid 248 from the stripping unit 242 and the weak hydrochloric acid 235 from the desorbing unit 234 are provided to the adiabatic absorber 230 via line 250.

Referring again to the thermal chlorination reactor 210, the tetrachloromethane 251 is incinerated with dihydrogen 208 from the chlor-alkali reactor 202 in the incineration unit 208. General operating conditions for the incineration unit 208 include an operating pressure of about 100 kPa (1 Bar(g)) and an operating temperature of around 2000 °C for reaction, with a cooled down in a range of 50 °C to 90 °C. The incineration process produces hydrogen chloride which is absorbed with water 254 to form a weak hydrochloric acid product 256. From the weak hydrochloric acid product 256 produced in the incineration unit 252, a portion 266 of the weak hydrochloric acid is neutralized with the sodium hydroxide solution 223 produced in the chlor-alkali reactor 202 in a hydrochloric neutralization unit 268. The hydrochloric neutralization unit 268 of the system 200 is connected to the adiabatic absorber 230, the chlor-alkali reactor 202, the stripping unit 242 and the desorbing unit 234. The hydrochloric neutralization unit 268 receives and neutralizes at least a portion 270 of the weak hydrochloric acid from the stripping unit 242 and the desorbing unit 234, via the storage unit 264, with the sodium hydroxide solution 223 from the chlor-alkali reactor 202 and the water 231 from the adiabatic absorber 230.

The neutralization of the weak hydrochloric acid and water streams produces an aqueous sodium chloride solution 272 from the neutralization of at least a portion of the hydrochloric acid from the stripping unit 242 and the desorbing unit 234 with the sodium hydroxide solution 223 from the chlor-alkali reactor 202. The aqueous sodium chloride solution 272 is fed to a brine unit 274. In addition to receiving the aqueous sodium chloride solution 272, the brine unit 274 can also receive water 276 and sodium chloride 278 with which to form the brine 204 that reacts in the chlor-alkali reactor 202.

The weak hydrochloric acid product 256 produced in the incineration unit 252 is also supplied to a purifying unit 280 via line 282. The purifying unit 280 purifies the weak hydrochloric acid product 256 by removing organic and inorganic by-products from the incineration to produce a weak hydrochloric acid 284. Different devices can be used for the purifying unit 280. For example, the purifying unit 280 can be a steam stripper that uses steam to purify the weak hydrochloric acid product 256. Alternatively, the purifying unit 280 could be a multiple effect evaporation unit. Examples of such a multiple effect evaporation unit can be found in U.S. Pat. No. 5,174,865 to Stultz et al., which is incorporated herein by reference in its entirety. Other means are known in the art. The weak hydrochloric acid 284 is supplied to storage unit 264, where it joins the weak hydrochloric acid from both the desorbing unit 234 and the stripping unit 242. From the storage unit 264, the weak hydrochloric acid is supplied to the adiabatic absorber 230 to produce the concentrate of hydrochloric acid 232.

As discussed herein, the system of the present disclosure allows for a method of producing chloromethanes that includes producing dichlorine and dihydrogen in the chlor-alkali reactor, where a first portion of the dichlorine is reacted with chloromethane in the thermal chlorination reactor to produce dichloromethane, trichloromethane and the first portion of hydrogen chloride. The second portion of hydrogen chloride is produced from dihydrogen and the second portion of the dichlorine produced in the chlor-alkali reactor. Methanol is reacted with the first portion of hydrogen chloride and the second portion of hydrogen chloride in the presence of a catalyst in the hydrochlorination reactor to produce hydrochloric acid and the chloromethane used in the thermal chlorination reactor.

The method further includes, for producing the second portion of hydrogen chloride, burning the second portion of dichlorine and the dihydrogen produced in the chlor-alkali reactor to produce hydrogen chloride. The concentrate of hydrochloric acid is produced in the adiabatic absorber from the hydrogen chloride produced by burning the second portion of dichlorine and the dihydrogen, where the hydrogen chloride is desorbed from the concentrate of hydrochloric acid to produce the second portion of hydrogen chloride.

The method can further include supplying the chlor-alkali reactor with the concentrate of hydrochloric acid produced by the adiabatic absorber, as illustrated and discussed in Fig. 2. The adiabatic absorber also acts to separate water from the concentrate of hydrochloric acid in the adiabatic absorber. The water from the adiabatic absorber, along with at least a portion of the hydrochloric acid product from each of the stripping unit and desorbing unit can be neutralized with the sodium hydroxide solution produced in the chlor-alkali process to produce an aqueous sodium chloride solution. The aqueous sodium chloride solution can be provided to the chlor-alkali reactor, as discussed herein, for use in producing the dihydrogen and dichlorine.

The method also includes using the stripping unit to strip the hydrochloric acid coming from the hydrochlorination reactor so as to recover hydrocarbons, which are returned to the hydrochlorination reactor. Stripping the hydrochloric acid from the hydrochlorination reactor and desorbing hydrogen chloride from the concentrate of hydrochloric acid each produce a hydrochloric acid product, where the hydrochloric acid product from each of the stripping and desorbing is provided to the adiabatic absorber to produce the concentrate of hydrochloric acid.

As discussed, tetrachloromethane is also produced in the thermal chlorination reactor. The tetrachloromethane is incinerated in the incineration unit to produce the weak hydrochloric acid product. The weak hydrochloric acid product is purified, as discussed herein, to produce a weak hydrochloric acid. The weak hydrochloric acid is supplied to the adiabatic absorber to produce the concentrate of hydrochloric acid.

In contrast to the method and system of the present disclosure, the weak hydrochloric acid produced in the hydrochlorination reactor of a traditional low- integrated chloromethane process is neutralized with the caustic produced in a chlor- alkali reactor. The chlor-alkali reactor also produces dihydrogen, which in the traditional low-integrated chloromethane process is used in an incineration process to convert tetrachloromethane, produced in the thermal chlorination reactor, to additional weak hydrochloric acid. This weak hydrochloric acid is also neutralized with caustic produced in the chlor-alkali reactor of the traditional low-integrated chloromethane process.

The method and system of the present disclosure, in contrast, recover, recycle and reuse the hydrochloric acid instead of neutralizing and disposing of it. This helps to reduce the amount of waste water that is produced in the weak hydrochloric acid neutralization process of the traditional low-integrated chloromethane process by up to 60 percent. In addition, recovering, recycling and reusing the hydrochloric acid according to the present disclosure allows for a reduction in the amount of caustic used by as much as 80 percent as compared to traditional low-integrated chloromethane processes.

As will be apparent to one skilled in the art, the weak hydrochloric acid of the system and method of the present disclosure is effectively recovered, recycled and reused. In addition, the system and method of the present disclosure also allow for about an 80 percent reduction in caustic use due to this efficient recovery, recycling and reuse of the weak hydrochloric acid. Finally, the amount of waste water generated in the present system and method can also be reduced by more than 60% as compared to the prior art systems for producing similar amounts and type of chloromethanes.