Regeneration method for liquefied petroleum gas sweetening caustic

Abstract

A regeneration method for a liquefied gas thiol-removing alkaline solution comprising the following steps: performing an oxygenation reaction with respect to a liquefied gas thiol-removing alkaline solution and, at the same time, utilizing a high air-liquid condition to extract a disulfide and a polysulfide into a gas phase, thus completing the separation of the disulfide and the polysulfide from the alkaline solution, and implementing the regeneration of the liquefied gas thiol-removing alkaline solution.

Claims

1. A regeneration method for caustic from sweetened liquefied petroleum gas, wherein the method comprises: under the action of a sulfonated cobalt phthalocyanine-based catalyst, subjecting caustic from sweetened liquefied petroleum gas to heat exchange before pumping into the liquid inlet of a Higee reactor; entering an oxygen-containing gas into the gas inlet of the Higee reactor, and mixing together the oxygen-containing gas and the liquid comprising the caustic and the catalyst in the Higee reactor to carry out an oxidation reaction to regenerate the caustic, wherein the volume ratio of the caustic to the oxygen-containing gas is 1:100-400, and the sulfonated cobalt phthalocyanine-based catalyst is added to the caustic at a concentration ranging from 10 mg/kg to 300 mg/kg, wherein the caustic from sweetened liquefied petroleum gas comprises mercaptan sodium and sodium sulfide, and wherein the caustic from sweetened liquefied petroleum gas is the caustic obtained after liquefied petroleum gas is sweetened by alkaline washing in a refining process, wherein while the oxidation reaction is carried out by mixing the caustic and the oxygen-containing gas in the Higee reactor and contacting with the oxidation catalyst, disulfide and polysulfide generated in the oxidation reaction are extracted into the gas phase under the condition of the caustic to gas volume ratio and the gas containing the disulfide and polysulfide is removed from the Higee reactor, resulting in caustic that has been regenerated.

2. The regeneration method according to claim 1, wherein, in terms of elemental sulfur, the content of mercaptan sodium is ≤20000 mg/kg and the content of sodium sulfide is ≤10000 mg/kg in the caustic from sweetened liquefied petroleum gas.

3. The regeneration method according to claim 1, wherein the molar ratio of mercaptan sodium to sodium sulfide in the caustic from sweetened liquefied petroleum gas is 0.1-200:1.

4. The regeneration method according to claim 1, wherein the temperature of the caustic from sweetened liquefied petroleum gas after heat exchange ranges from 20° C. to 80° C.

5. The regeneration method according to claim 1, wherein the sulfonated cobalt phthalocyanine-based catalyst is sulfonated cobalt phthalocyanine, dinuclear cobalt phthalocyanine sulfonate, cobalt polyphthalocyanine or a composite catalyst thereof.

6. The regeneration method according to claim 1, wherein the sulfonated cobalt phthalocyanine-based catalyst is added in an amount of 10-100 mg/kg with respect to the caustic from sweetened liquefied petroleum gas.

7. The regeneration method according to claim 1, wherein the Higee reactor is a stator-rotor reactor, or a rotating packed bed other than one using bulk particulate packing.

8. The regeneration method according to claim 1, wherein the liquid flow in the Higee reactor is a gas-liquid countercurrent, gas-liquid co-current or gas-liquid baffling flow.

9. The regeneration method according to claim 1, wherein the pressure of the oxidation reaction ranges from normal pressure to 0.8 MPa.

10. The regeneration method according to claim 1, wherein the oxidation reaction is carried out at a rotational speed between 100 rpm and 2000 rpm.

11. The regeneration method according to claim 1, wherein the oxygen-containing gas is air or an oxygen-rich gas.

12. The regeneration method according to claim 2, wherein the content of mercaptan sodium ranges from 100 mg/kg to 20000 mg/kg and the content of sodium sulfide is 50 mg/kg to 10000 mg/kg in the caustic from sweetened liquefied petroleum gas.

13. The regeneration method according to claim 3, wherein the molar ratio of mercaptan sodium to sodium sulfide in the caustic from sweetened liquefied petroleum gas is 0.3-100:1.

14. The regeneration method according to claim 7, wherein the rotating packed bed is equipped with the packing of a structured packing or a wire mesh packing.

Description

DESCRIPTION OF EMBODIMENTS

(1) In order to provide a better understanding of the technical features, objects, and advantages of the present invention, the technical solutions of the present invention are described in detail below as examples, which cannot be construed as limitation to the scope of the invention.

(2) Here, at the presence of a sulfonated cobalt phthalocyanine-based catalyst, the liquefied petroleum gas sweetening caustic containing both mercaptan sodium and sodium sulfide undergoes heat exchange before being pumped into the liquid inlet of a Higee reactor. The liquid is sheared and divided into tiny droplets, liquid filaments, and liquid membrane by a high-speed rotating rotor, providing a large specific surface area for interphase mass transfer and a rapidly renewing interphase surface. An oxygen-containing gas is metered through a flow meter and enters the gas inlet, and the gas and liquid are mixed in the rotor of a rotating packed bed or in the stator-rotor structure where an intense gas-liquid mass transfer process takes place. The oxidation reaction of mercaptan sodium and sodium sulfide as well as the separation of the generated disulfide and polysulfide from the caustic are then accomplished, thereby completing the regeneration of the liquefied petroleum gas sweetening caustic. The regenerated caustic and the oxidized off-gas containing disulfide and polysulfide are discharged from the liquid outlet and gas outlet of the Higee reactor, respectively. The regenerated caustic after deoxidation is returned to a sweetening unit for reuse, and the oxidized off-gas containing disulfide and polysulfide is sent to an off-gas treatment unit.

(3) The concentration of mercaptan sodium (NaSR) and sodium sulfide in the regenerated caustic is determined by potentiometric titration. The method for the determination of the concentration of disulfide and polysulfide (collectively referred to as sulfides R.sub.1S.sub.mR.sub.2, m≥2, in the following tables) in the regenerated caustic is as follows: after the caustic is extracted three times with n-hexane, the extractant is analyzed by a coulometric analyzer. The method for the determination of the sodium thiosulfate concentration in the regenerated caustic includes: acidification to pH 6 by acetic acid, introducing nitrogen gas to eliminate the interference of hydrogen sulfide and mercaptan, and adding formaldehyde to eliminate the interference of sulfite ions, followed by determination with the iodometric method.

(4) Here, R, R.sub.1 and R.sub.2 are alkyl groups, and R, R.sub.1 and R.sub.2 may be the same or different and may be a methyl group, an ethyl group, a propyl group or the like.

EXAMPLE 1

(5) This example provides a one-step complete regeneration method for liquefied petroleum gas sweetening caustic, comprising the following steps:

(6) Under the condition of a sulfonated cobalt phthalocyanine catalyst having a concentration of 300 mg/kg, the liquefied petroleum gas sweetening caustic containing both mercaptan sodium and sodium sulfide was heat exchanged to a temperature of 55° C. and pumped into the liquid inlet of a Higee reactor using wire mesh packing. The liquid was sheared and divided into tiny liquid membranes, filaments and droplets by a high-speed rotating rotor, providing a large specific surface area for interphase mass transfer and a rapidly renewing interphase surface. Air was metered through a flow meter and entered the gas inlet, and the gas and liquid were mixed in the rotor of the Higee reactor where an intense gas-liquid mass transfer process took place. The oxidation reaction of mercaptan sodium and sodium sulfide as well as the separation of the formed disulfide and polysulfide from the caustic were then accomplished, thereby completing the regeneration of the liquefied petroleum gas sweetening caustic. The regenerated caustic and the oxidized off-gas containing disulfide and polysulfide were discharged at the liquid outlet and gas outlet of the Higee reactor, respectively. The regenerated caustic after deoxidation was returned to a sweetening unit for reuse, and the oxidized off-gas containing disulfide and polysulfide was sent to an off-gas treatment unit. In the Higee reactor, the gas-liquid ratio was 300:1 (v/v), the rotational speed was 1100 rpm, and the operating pressure was 0.15 MPa. The caustic compositions before and after the reaction are shown in Table 1.

(7) TABLE-US-00001 TABLE 1 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 20000 10000 0 0 Product  350  250 9 1

EXAMPLE 2

(8) This example provides a one-step complete regeneration method for liquefied petroleum gas sweetening caustic, comprising the following steps:

(9) Under the condition of a dinuclear cobalt phthalocyanine sulfonate catalyst having a concentration of 100 mg/kg, the liquefied petroleum gas sweetening caustic containing both mercaptan sodium and sodium sulfide was heat exchanged to a temperature of 45° C. and pumped into the liquid inlet of a Higee reactor using monolithic foamed silicon carbide as structured packing. The liquid was sheared and divided into tiny liquid membranes, filaments and droplets by a high-speed rotating rotor, providing a large specific surface area for interphase mass transfer and a rapidly renewing interphase surface. An oxygen-rich gas (having an oxygen content of 35%) was metered through a flow meter and entered the gas inlet, and the gas and liquid were mixed in the rotor of the Higee reactor where an intense gas-liquid mass transfer process took place. The oxidation reaction of mercaptan sodium and sodium sulfide as well as the separation of the formed disulfide and polysulfide from the caustic were then accomplished, thereby completing the regeneration of the liquefied petroleum gas sweetening caustic. The regenerated caustic and the oxidized off-gas containing disulfide and polysulfide were discharged at the liquid outlet and gas outlet of the Higee reactor, respectively. The regenerated caustic after deoxidation was returned to a sweetening unit for reuse, and the oxidized off-gas containing disulfide and polysulfide was sent to an off-gas treatment unit. Here, in the Higee reactor, the gas-liquid ratio was 250:1 (v/v), the rotational speed was 900 rpm, and the operating pressure was 0.6 MPa. The caustic compositions before and after the reaction are shown in Table 2.

(10) TABLE-US-00002 TABLE 2 Content (in terms mercaptan sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 10000 3000 0 0 Product  140  70 4 2

EXAMPLE 3

(11) This example provides a one-step complete regeneration method for liquefied petroleum gas sweetening caustic, comprising the following steps:

(12) Under the condition of a sulfonated cobalt phthalocyanine catalyst having a concentration of 10 mg/kg, the liquefied petroleum gas sweetening caustic containing both mercaptan sodium and sodium sulfide was heat exchanged to a temperature of 55° C. and pumped into the liquid inlet of a Higee reactor using a stator-rotor structure. The liquid was sheared and divided into tiny liquid membranes, filaments and droplets by a high-speed rotating rotor, providing a large specific surface area for interphase mass transfer and a rapidly renewing interphase surface. Air was metered through a flow meter and entered the gas inlet, the gas and liquid were mixed in the stator-rotor reactor where an intense gas-liquid mass transfer process took place, thus the oxidation reaction of mercaptan sodium and sodium sulfide as well as the separation of the formed disulfide and polysulfide from the caustic were accomplished, thereby completing the regeneration of the liquefied petroleum gas sweetening caustic. The regenerated caustic and the oxidized off-gas containing disulfide and polysulfide were discharged at the liquid outlet and gas outlet of the Higee reactor, respectively. The regenerated caustic after deoxidation was returned to a sweetening unit for reuse, and the oxidized off-gas containing disulfide and polysulfide was sent to an off-gas treatment unit. Here in the Higee reactor, the gas-liquid ratio was 100:1 (v/v), the rotational speed was 500 rpm, and the operating pressure was 0.1 MPa. The caustic compositions before and after the reaction are shown in Table 3.

(13) TABLE-US-00003 TABLE 3 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 100 50 0 0 Product  <8 <4 <1  <1 

EXAMPLE 4

(14) This example provides a one-step complete regeneration method for liquefied petroleum gas sweetening caustic, comprising the following steps:

(15) Under the condition of a cobalt polyphthalocyanine catalyst having a concentration of 200 mg/kg, the liquefied petroleum gas sweetening caustic containing both mercaptan sodium and sodium sulfide was heat exchanged to a temperature of 55° C. and pumped into the liquid inlet of a Higee reactor using wire mesh packing. The liquid was sheared and divided into tiny liquid membranes, filaments and droplets by a high-speed rotating rotor, providing a large specific surface area for interphase mass transfer and a rapidly renewing interphase surface. Air was metered through a flow meter and entered the gas inlet, and the gas and liquid were mixed in the rotor of the Higee reactor where an intense gas-liquid mass transfer process took place. The oxidation reaction of mercaptan sodium and sodium sulfide as well as the separation of the formed disulfide and polysulfide from the caustic were thus accomplished, thereby completing the regeneration of the liquefied petroleum gas sweetening caustic. The regenerated caustic and the oxidized off-gas containing disulfide and polysulfide were discharged at the liquid outlet and gas outlet of the Higee reactor, respectively. The regenerated caustic after deoxidation was returned to a sweetening unit for reuse, and the oxidized off-gas containing disulfide and polysulfide was sent to an off-gas treatment unit. Here in the Higee reactor, the gas-liquid ratio was 150:1 (v/v), the rotational speed was 1000 rpm, and the operating pressure was 0.3 MPa. The caustic compositions before and after the reaction are shown in Table 4.

(16) TABLE-US-00004 TABLE 4 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 5000 1000 0 0 Product  28  16 2 <1 

EXAMPLE 5

(17) This example provides a one-step complete regeneration method for liquefied petroleum gas sweetening caustic, comprising the following steps:

(18) Under the condition of a composite catalyst of sulfonated cobalt phthalocyanine and dinuclear cobalt phthalocyanine sulfonate (sulfonated cobalt phthalocyanine:dinuclear cobalt phthalocyanine sulfonate=1:1 w/w) having a concentration of 100 mg/kg, the liquefied petroleum gas sweetening caustic containing both mercaptan sodium and sodium sulfide was heat exchanged to a temperature of 50° C. and pumped into the liquid inlet of a Higee reactor using wire mesh packing. The liquid was sheared and divided into tiny liquid membranes, filaments and droplets by a high-speed rotating rotor, providing a large specific surface area for interphase mass transfer and a rapidly renewing interphase surface. Air was metered through a flow meter and entered the gas inlet, the gas and liquid were mixed in the rotor of the Higee reactor where an intense gas-liquid mass transfer process took place, and the oxidation reaction of mercaptan sodium and sodium sulfide as well as the separation of the formed disulfide and polysulfide from the caustic were then accomplished. A flow of oxygen-containing gas was introduced into the gas inlet via a flow meter, and the gas and liquid were mixed in the Higee reactor, thereby completing the regeneration of the liquefied petroleum gas sweetening caustic. The regenerated caustic after deoxidation was returned to a sweetening unit for reuse, and the oxidized off-gas containing disulfide and polysulfide was sent to an off-gas treatment unit. Here, in the Higee reactor, the gas-liquid ratio was 300:1 (v/v), the rotational speed was 1000 rpm, and the operating pressure was 0.5 MPa. The caustic compositions before and after the reaction are shown in Table 5.

(19) TABLE-US-00005 TABLE 5 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 2000 1800 0 0 Product  48  31 4 2

EXAMPLE 6

(20) This example provides a one-step complete regeneration method for liquefied petroleum gas sweetening caustic, comprising the following steps:

(21) Under the condition of a dinuclear cobalt phthalocyanine sulfonate catalyst having a concentration of 100 mg/kg, the liquefied petroleum gas sweetening caustic containing both mercaptan sodium and sodium sulfide was heat exchanged to a temperature of 50° C. and pumped into the liquid inlet of a Higee reactor using wire mesh packing. The liquid was sheared and divided into tiny liquid membranes, filaments and droplets by high-speed rotating rotor, providing a large specific surface area for interphase mass transfer and a rapidly renewing interphase surface. Air was metered through a flow meter and entered the gas inlet, the gas and liquid were mixed in the rotor of the Higee reactor where an intense gas-liquid mass transfer process took place, and the oxidation reaction of mercaptan sodium and sodium sulfide and the separation of the formed disulfide and polysulfide from the caustic were thus accomplished. A flow of oxygen-containing gas was introduced into the gas inlet via a flow meter, and the gas and liquid were mixed in the Higee reactor, thereby completing the regeneration of the liquefied petroleum gas sweetening caustic. The regenerated caustic after deoxidation was returned to a sweetening unit for reuse, and the oxidized off-gas containing disulfide and polysulfide was sent to an off-gas treatment unit. Here in the Higee reactor, the gas-liquid ratio was 150:1 (v/v), the rotational speed was 300 rpm, and the operating pressure was 0.3 MPa. The caustic compositions before and after the reaction are shown in Table 6.

(22) TABLE-US-00006 TABLE 6 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 2500 400 0 0 Product  28  16 2 1

EXAMPLE 7

(23) This example provides a one-step complete regeneration method for liquefied petroleum gas sweetening caustic, comprising the following steps:

(24) Under the condition of a cobalt polyphthalocyanine catalyst having a concentration of 100 mg/kg, the liquefied petroleum gas sweetening caustic containing both mercaptan sodium and sodium sulfide was heat exchanged to a temperature of 45° C. and pumped into the liquid inlet of a Higee reactor using a stator-rotor structure. The liquid was sheared and divided into tiny liquid membranes, filaments and droplets by a high-speed rotating rotor, providing a large specific surface area for interphase mass transfer and a rapidly renewing interphase surface. Air was metered through a flow meter and entered the gas inlet, and the gas and liquid were mixed in the stator-rotor reactor where an intense gas-liquid mass transfer process took place. The oxidation reaction of mercaptan sodium and sodium sulfide and the separation of the formed disulfide and polysulfide from the caustic were then accomplished, thereby completing the regeneration of the liquefied petroleum gas sweetening caustic. The regenerated caustic and the oxidized off-gas containing disulfide and polysulfide were discharged at the liquid outlet and gas outlet of the Higee reactor, respectively. The regenerated caustic after deoxidation was returned to a sweetening unit for reuse, and the oxidized off-gas containing disulfide and polysulfide was sent to an off-gas treatment unit. Here in the supergravity reactor, the gas-liquid ratio was 200:1 (v/v), the rotational speed was 600 rpm, and the operating pressure was 0.2 MPa. The caustic compositions before and after the reaction are shown in Table 7.

(25) TABLE-US-00007 TABLE 7 Content (in terms of Mercaptan Sodium Sodium elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 3000 700 0 0 Product 110 33 3 2

EXAMPLE 8

(26) This example provides a regeneration method for liquefied petroleum gas sweetening caustic, comprising the following steps:

(27) With 300 mg/kg of sulfonated cobalt phthalocyanine, the liquefied petroleum gas sweetening caustic was subjected to heat exchange to reach a temperature of 60° C. and pumped into the liquid inlet of a Higee reactor; a flow of oxygen-containing gas entered the gas inlet via a flow meter, and the gas and the liquid were mixed in the Higee reactor to complete the regeneration of the liquefied petroleum gas sweetening caustic, with a gas-liquid ratio of 500:1 (v/v), a rotational speed of 2000 rpm, and an operating pressure at atmospheric pressure. The caustic compositions before and after the reaction are shown in Table 8.

(28) TABLE-US-00008 TABLE 8 Content (in terms of elemental Mercaptan Sodium Sodium sulfur) sodium sulfide Sulfides thiosulfate mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 20000 10000 0 0 Product 300 200 4 <1

EXAMPLE 9

(29) This example provides a regeneration method for liquefied petroleum gas sweetening caustic, comprising the following steps:

(30) With 100 mg/kg of sulfonated cobalt phthalocyanine, the liquefied petroleum gas sweetening caustic was subjected to heat exchange to reach a temperature of 40° C. and pumped into the liquid inlet of a Higee reactor; a flow of oxygen-containing gas entered the gas inlet via a flow meter, and the gas and the liquid were mixed in the Higee reactor to complete the regeneration of the liquefied petroleum gas sweetening caustic, with a gas-liquid ratio of 400:1 (v/v), a rotational speed of 1000 rpm, and an operating pressure at 0.8 MPa. The caustic compositions before and after the reaction are shown in Table 9.

(31) TABLE-US-00009 TABLE 9 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 10000 3000 0 0 Product 100 50 2 <1

EXAMPLE 10

(32) This example provides a regeneration method for liquefied petroleum gas sweetening caustic, comprising the following steps:

(33) With 10 mg/kg of sulfonated cobalt phthalocyanine, the liquefied petroleum gas sweetening caustic was subjected to heat exchange to reach a temperature of 20° C. and pumped into the liquid inlet of a Higee reactor; a flow of oxygen-containing gas entered the gas inlet via a flow meter, and the gas and the liquid were mixed in the Higee reactor to complete the regeneration of the liquefied petroleum gas sweetening caustic, with a gas-liquid ratio of 50:1 (v/v), a rotational speed of 300 rpm, and an operating pressure at atmospheric pressure. The caustic compositions before and after the reaction are shown in Table 10.

(34) TABLE-US-00010 TABLE 10 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 100 50 0 0 Product <10 <5 <1 <1

EXAMPLE 11

(35) This example provides a regeneration method for liquefied petroleum gas sweetening caustic, comprising the following steps:

(36) With 200 mg/kg of sulfonated cobalt phthalocyanine, the liquefied petroleum gas sweetening caustic was subjected to heat exchange to reach a temperature of 50° C. and pumped into the liquid inlet of a Higee reactor; a flow of oxygen-containing gas entered the gas inlet via a flow meter, and the gas and the liquid were mixed in the Higee reactor to complete the regeneration of the liquefied petroleum gas sweetening caustic, with a gas-liquid ratio of 100:1 (v/v), a rotational speed of 800 rpm, and an operating pressure at 0.3 MPa. The caustic compositions before and after the reaction are shown in Table 11.

(37) TABLE-US-00011 TABLE 11 Content (in terms of Mercaptan Sodium Sodium elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 5000 1000 0 0 Product 30 20 3 <1

EXAMPLE 12

(38) This example provides a regeneration method for liquefied petroleum gas sweetening caustic, comprising the following steps:

(39) With 100 mg/kg of sulfonated cobalt phthalocyanine, the liquefied petroleum gas sweetening caustic was subjected to heat exchange to reach a temperature of 45° C. and pumped into the liquid inlet of a Higee reactor; a flow of oxygen-containing gas entered the gas inlet via a flow meter, and the gas and the liquid were mixed in the Higee reactor to complete the regeneration of the liquefied petroleum gas sweetening caustic, with a gas-liquid ratio of 300:1 (v/v), a rotational speed of 1200 rpm, and an operating pressure at 0.4 MPa. The caustic compositions before and after the reaction are shown in Table 12.

(40) TABLE-US-00012 TABLE 12 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 2000 1800 0 0 Product 50 30 3 <1

EXAMPLE 13

(41) This example provides a regeneration method for liquefied petroleum gas sweetening caustic, comprising the following steps:

(42) With 100 mg/kg of sulfonated cobalt phthalocyanine, the liquefied petroleum gas sweetening caustic was subjected to heat exchange to reach a temperature of 55° C. and pumped into the liquid inlet of a Higee reactor; a flow of oxygen-containing gas entered the gas inlet via a flow meter, and the gas and the liquid were mixed in the Higee reactor to complete the regeneration of the liquefied petroleum gas sweetening caustic, with a gas-liquid ratio of 150:1 (v/v), a rotational speed of 400 rpm, and an operating pressure at 0.1 MPa. The caustic compositions before and after the reaction are shown in Table 13.

(43) TABLE-US-00013 TABLE 13 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 2500 400 0 0 Product 30 15 2 <1

COMPARATIVE EXAMPLE 1

(44) In this comparative example, 300 mL of caustic containing mercaptan sodium and sodium sulfide was added to a 500 mL glass flask, and air was introduced through an air duct at the bottom of the flask. Under a nitrogen flow rate of 150 L/h, a reaction was carried out for 1 h at a temperature of 60° C. and a stirring speed of 2000 rpm, with 300 mg/kg of sulfonated cobalt phthalocyanine. The operation was performed under atmospheric pressure. The caustic compositions before and after the reaction are shown in Table 14.

(45) TABLE-US-00014 TABLE 14 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 20000 10000 0 0 Product 3500 1800 650 8500

COMPARATIVE EXAMPLE 2

(46) In this comparative example, 300 mL of caustic containing mercaptan sodium and sodium sulfide was added to a 500 mL glass flask, and air was introduced through an air duct at the bottom of the flask. Under a nitrogen flow rate of 15 L/h, the reaction was carried out for 1 h at a temperature of 20° C. and a stirring speed of 300 rpm, with 10 mg/kg of sulfonated cobalt phthalocyanine. The operation was performed under atmospheric pressure. The caustic compositions before and after the reaction are shown in Table 15.

(47) TABLE-US-00015 TABLE 15 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 100 50 0 0 Product 28 15 11 57

COMPARATIVE EXAMPLE 3

(48) In this comparative example, 300 mL of caustic containing mercaptan sodium and sodium sulfide was added to a 500 mL glass flask, and air was introduced through an air duct at the bottom of the flask. Under an oxygen-containing gas flow rate of 150 L/h, the reaction was carried out for 1 h at a temperature of 60° C. and a stirring speed of 1200 rpm, with a sulfonated cobalt phthalocyanine catalyst having a concentration of 10 mg/kg. The operation was performed under atmospheric pressure. The caustic compositions before and after the reaction are shown in Table 16.

(49) TABLE-US-00016 TABLE 16 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 20000 10000 0 0 Product 4000 1900 700 8600

COMPARATIVE EXAMPLE 4

(50) In this comparative example, 300 mL of caustic containing mercaptan sodium and sodium sulfide was added to a 500 mL glass flask, and air was introduced through an air duct at the bottom of the flask. Under an air flow rate of 15 L/h, the reaction was carried out for 1 h at a temperature of 50° C. and a stirring speed of 300 rpm, with a sulfonated cobalt phthalocyanine catalyst having a concentration of 10 mg/kg. The operation was performed under atmospheric pressure. The caustic compositions before and after the reaction are shown in Table 17.

(51) TABLE-US-00017 TABLE 17 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 100 50 0 0 Product 26 13 10 55

COMPARATIVE EXAMPLE 5

(52) This comparative example was carried out in the same manner as in Example 1, except that the sulfonated cobalt phthalocyanine catalyst was not included. The liquefied petroleum gas sweetening caustic containing both mercaptan sodium and sodium sulfide was heat exchanged to a temperature of 55° C. and pumped into the liquid inlet of a Higee reactor using wire mesh packing. The liquid was sheared and divided into tiny liquid membranes, filaments and droplets by a high-speed rotating rotor, providing a large specific surface area for interphase mass transfer and a rapidly renewing interphase surface. Air was metered through a flow meter and entered from the gas inlet, and the gas and liquid were mixed in the rotor of the Higee reactor where an intense gas-liquid mass transfer process took place. Since the necessary oxidation catalyst was not included, neither mercaptan sodium nor sodium sulfide in the caustic could undergo an oxidation reaction. The regenerated caustic and the oxidized off-gas were discharged at the liquid outlet and gas outlet of the Higee reactor, respectively. The unregenerated caustic was sent to a waste water treatment unit after being diluted at a large ratio. Here, in the Higee reactor, the gas-liquid ratio was 300:1 (v/v), the rotational speed applied was 1100 rpm, and the operating pressure was 0.15 MPa. The caustic compositions before and after the reaction are shown in Table 18.

(53) TABLE-US-00018 TABLE 18 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 20000 10000 0 0 Product 20000 10000 0 0

COMPARATIVE EXAMPLE 6

(54) In this comparative example, the gas-liquid ratio was 80:1 (v/v) in the Higee reactor. Under the condition of a sulfonated cobalt phthalocyanine catalyst having a concentration of 8 mg/kg, the rotational speed applied was 300 rpm, and the operating pressure was 0.1 MPa. The liquefied petroleum gas sweetening caustic containing both mercaptan sodium and sodium sulfide was heat exchanged to a temperature of 20° C. and pumped into the liquid inlet of a Higee reactor using wire mesh packing. The liquid was sheared and divided into tiny liquid membranes, filaments and droplets by a high-speed rotating rotor, providing a large specific surface area for interphase mass transfer and a rapidly renewing interphase surface. Air was metered through a flow meter and entered the gas inlet, and the gas and liquid were mixed in the rotor of the Higee reactor where an intense gas-liquid mass transfer process took place. Due to the small gas-liquid ratio, the oxidation reaction of mercaptan sodium and sodium sulfide was not complete, and sodium sulfide was not completely converted into sulfide and sodium hydroxide. Also, the separation process of the generated disulfide and polysulfide from the caustic was not complete, and thus a complete regeneration of the liquefied petroleum gas sweetening caustic was not achieved. The partially regenerated caustic and the oxidized off-gas containing disulfide and polysulfide were discharged at the liquid outlet and gas outlet of the Higee reactor, respectively. The partially regenerated caustic was diluted and sent to a waste water treatment unit, and the oxidized off-gas containing disulfide and polysulfide was sent to an off-gas treatment unit. The caustic compositions before and after the reaction are shown in Table 19.

(55) TABLE-US-00019 TABLE 19 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 20000 10000 0 0 Product 13000 2900 2374 6679

COMPARATIVE EXAMPLE 7

(56) This comparative example was carried out in the same manner as in Example 1, except that the caustic to be treated was different. Under the condition of a sulfonated cobalt phthalocyanine catalyst having a concentration of 300 mg/kg, the liquefied petroleum gas sweetening caustic containing only mercaptan sodium was heat exchanged to a temperature of 55° C. and pumped into the liquid inlet of a Higee reactor using wire mesh packing. The liquid was sheared and divided into tiny liquid membranes, filaments and droplets by a high-speed rotating rotor, providing a large specific surface area for interphase mass transfer and a rapidly renewing interphase surface. Air was metered through a flow meter and entered the gas inlet, and the gas and liquid were mixed in the rotor of the Higee reactor where an intense gas-liquid mass transfer process took place and an oxidation reaction of sodium sulfide was accomplished. The caustic and oxidized off-gas having undergone the non-hazardous treatment process were discharged at the liquid outlet and gas outlet of the Higee reactor, respectively. The caustic was sent to a waste water treatment unit, and the oxidized off-gas was sent to an off-gas treatment unit. Here in the Higee reactor, the gas-liquid ratio was 300:1 (v/v), the rotational speed was 1100 rpm, and the operating pressure was 0.15 MPa. The caustic compositions before and after the reaction are shown in Table 20.

(57) TABLE-US-00020 TABLE 20 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 0 10000 0 0 Product 0 1460 0 8540

COMPARATIVE EXAMPLE 8

(58) This comparative example was carried out in the same manner as in Example 2, except that the type of Higee reactor and the gas-liquid ratio were different. Under the condition of a dinuclear cobalt phthalocyanine sulfonate catalyst having a concentration of 100 mg/kg, the liquefied petroleum gas sweetening caustic containing both mercaptan sodium and sodium sulfide was heat exchanged to a temperature of 45° C. and pumped into the liquid inlet of a Higee reactor using foam metal bulk particle packing with a diameter of 5 mm. Because the liquid could not be well sheared and divided by the bulk particle packing, the increase in surface area for interphase mass transfer and the interphase surface renewal rate was limited. A flow of oxygen-rich gas (having an oxygen content of 35%) was metered through a flow meter and entered the gas inlet, and the gas and liquid were mixed in the rotor of the Higee reactor where an intense gas-liquid mass transfer process took place. Because the increase in specific surface area for interphase mass transfer and the interphase surface renewal rate were limited, the mass transfer process of oxygen to the liquid phase could not meet the requirement for a complete regeneration of the caustic. As a result, the oxidation reaction of mercaptan sodium and sodium sulfide and the separation process of the formed disulfide and polysulfide from the caustic were incomplete, resulting in an inadequate regeneration of liquefied petroleum gas sweetening caustic. The partially regenerated caustic and the oxidized off-gas containing disulfide and polysulfide were discharged through the liquid outlet and gas outlet of the Higee reactor, respectively. The partially regenerated caustic was diluted and sent to a waste water treatment unit, and the oxidized off-gas containing disulfide and polysulfide was sent to an off-gas treatment unit. Here in the Higee reactor, the gas-liquid ratio was 80:1 (v/v), the rotational speed was 900 rpm, and the operating pressure was 0.6 MPa. The caustic compositions before and after the reaction are shown in Table 21.

(59) TABLE-US-00021 TABLE 21 Content (in terms Mercaptan Sodium Sodium of elemental sodium sulfide Sulfides thiosulfate sulfur) mg/kg NaSR Na.sub.2S R.sub.1S.sub.mR.sub.2 Na.sub.2S.sub.2O.sub.3 Feed 10000 3000 0 0 Product 6300 1560 561 979

(60) By comparing the above Examples and Comparative Examples, it can be seen that the regeneration method of liquefied petroleum gas sweetening caustic of the present invention has a simple procedure, and is capable of regenerating mercaptan sodium and sodium sulfide in a caustic to sodium hydroxide, disulfide, and polysulfide, where the disulfide and polysulfide in the caustic is eliminated to a content of less than 5 mg/kg.

(61) The above descriptions are only specific embodiments of the present invention, the scope of protection of the present invention is not limited thereto. Various changes or substitutions apparent to those skilled in the art within the scope of the present disclosure are intended to be encompassed within the protection scope of the invention.