Ammonium Sulphate Production on Industrial Scale

Abstract

The invention provides a process for the production of crystalline ammonium sulfate, wherein the process comprises performing a Beckmann rearrangement reaction, neutralizing the Beckmann rearrangement reaction mixture, separating a first aqueous ammonium sulfate phase and an aqueous ε-caprolactam phase, charging the first ammonium sulfate phase to a first evaporative type crystallization section wherein crystalline ammonium sulfate is obtained, discharging from the first evaporative type crystallization section mother liquor enriched in organic components, extracting the aqueous ε-caprolactam phase to obtain an extracted ε-caprolactam phase and a second aqueous ammonium sulfate phase, discharging the mother liquor that is discharged from the first evaporative type crystallization section and/or the second aqueous ammonium sulfate phase to a second evaporative type crystallization section wherein evaporative type crystallization is performed so that a three-phase system occurs. At least a liquid oily phase is recovered from the three-phase system. The invention further provides a plant suitable to carry out the process of the invention, crystalline ammonium sulfate and a liquid oily phase obtained by the process of the invention.

Claims

1. A process for the production of crystalline ammonium sulfate in an industrial scale plant, wherein the plant comprises a Beckmann rearrangement reaction section, a neutralization section, a first liquid-liquid separation section, a first and a second extraction section, a first solvent recovery section, a first and a second evaporative type crystallization section, and a first liquid-solid separation section; wherein the method comprises the steps of: a) charging components (i) sulfuric acid and/or oleum; and (ii) cyclohexanone oxime to the Beckmann rearrangement reaction section and reacting the same to form a mixture comprising ε-caprolactam; b) discharging the resulting mixture comprising ε-caprolactam from the Beckmann rearrangement reaction section to the neutralization section; c) adding ammonia and water to the mixture comprising ε-caprolactam in the neutralization section, whereby a neutralized Beckmann rearrangement mixture is obtained that comprises a first aqueous ammonium sulfate phase and an aqueous ε-caprolactam phase, both of which comprise organic components as impurities; d) separating the first aqueous ammonium sulfate phase and the aqueous ε-caprolactam phase obtained in the neutralization section in the first liquid-liquid separation section; e) treating the first aqueous ammonium sulfate phase obtained in step d) by e.1) extracting the first aqueous ammonium sulfate phase with a first organic solvent in the first extraction section, whereby a phase comprising first organic solvent and ε-caprolactam, and an extracted first aqueous ammonium sulfate phase are obtained; e.2) charging the extracted first aqueous ammonium sulfate phase to the first solvent recovery section, wherein first organic solvent is recovered and a recovered first aqueous ammonium sulfate phase is obtained; e.3) charging the recovered first aqueous ammonium sulfate phase to the first evaporative type crystallization section and performing evaporative type crystallization therein to obtain crystalline ammonium sulfate and mother liquor in the first evaporative type crystallization section, wherein the mother liquor is an aqueous ammonium sulfate phase enriched in organic components compared to the recovered first aqueous ammonium sulfate phase entering the first evaporative type crystallization section; e.4) discharging mother liquor from the first evaporative type crystallization section; and e.5) discharging a slurry comprising crystalline ammonium sulfate from the first evaporative type crystallization section and charging it to the first liquid-solid separation section to recover crystalline ammonium sulfate; f) treating the aqueous ε-caprolactam phase obtained in step d) by f.1) extracting the aqueous ε-caprolactam phase in the second extraction section with a second organic solvent, whereby a phase comprising second organic solvent and ε-caprolactam, and a second aqueous ammonium sulfate phase comprising organic components are obtained; wherein the mother liquor that is discharged from the first evaporative type crystallization section in step e.4); and/or (ii) the second aqueous ammonium sulfate phase comprising organic components that is obtained in step f.1) are/is charged to the second evaporative type crystallization section, wherein evaporative type crystallization is performed so that a three-phase system occurs, which comprises the following phases: (1) a liquid oily phase comprising organic components; (2) a crystalline ammonium sulfate phase; and (3) a liquid aqueous ammonium sulfate comprising phase; (iii) recovering at least the liquid oily phase from said three-phase system.

2. A process according to claim 1, wherein the liquid oily phase comprises between 0.5 and 25 wt. % of ε-caprolactam; comprises 1 to 30 wt. % of ammonium sulfate; and has an organic components content from 500 to 2000 gram COD/kg of the liquid oily phase.

3. A process according to claim 1, wherein the liquid oily phase is used as fuel in an incineration device.

4. A process according to claim 1, wherein the second organic solvent is recovered from the second aqueous ammonium sulfate phase comprising organic components that is obtained in step f.1) prior to charging the resulting second aqueous phase comprising organic components to the second evaporative type crystallization section.

5. A process according to claim 4, wherein water is removed from the second aqueous ammonium sulfate phase comprising organic components prior to charging the resulting concentrated second aqueous ammonium sulfate phase to the second evaporative type crystallization section.

6. A process according to claim 1, wherein the recovery of crystalline ammonium sulfate from the first evaporative type crystallization section in step e.5) comprises the steps of e.5.1) discharging from the first evaporative type crystallization section a slurry comprising crystalline ammonium sulfate and charging said slurry to the first liquid-solid separation section; and e.5.2) discharging crystalline ammonium sulfate from the first liquid-solid separation section and charging the crystalline ammonium sulfate to a first drying section, wherein dried crystalline ammonium sulfate is obtained.

7. A process according to claim 1, wherein the plant comprises a second liquid-liquid separation section and a second liquid-solid separation section and wherein the recovery of at least the liquid oily phase in step (iii) comprises the steps of (iii.1) discharging from the second evaporative type crystallization section a mixture comprising liquid oily phase and liquid aqueous ammonium sulfate comprising phase and charging the same to the second liquid-liquid separation section, where the two phases are separated; (iii.2) recovering the separated liquid oily phase and the separated liquid aqueous ammonium sulfate comprising phase from the second liquid-liquid separation section; and (iii.3) discharging from the second evaporative type crystallization section a slurry comprising crystalline ammonium sulfate and charging the same to the second liquid-solid separation section from which crystalline ammonium sulfate and a liquid aqueous ammonium sulfate phase are separately recovered.

8. A process according to claim 7, wherein the liquid aqueous ammonium sulfate comprising phase recovered from the second liquid-liquid separation section in step (iii.2) and/or the liquid aqueous ammonium sulfate phase recovered from the second liquid-solid separation section in step (iii.3) is/are charged to the second evaporative type crystallization section.

9. A process according to claim 7, wherein the crystalline ammonium sulfate that is discharged from the second liquid-solid separation section in step (iii.3) is washed with an aqueous solution.

10. A process according to claim 1, wherein the crystalline ammonium sulfate that is obtained from the second evaporative type crystallization section in step (i) is subsequently charged to a dissolving section, where the crystalline ammonium sulfate is dissolved in water, whereby an aqueous ammonium sulfate comprising phase is obtained that is charged to the first evaporative type crystallization section.

11. A process according to claim 1, wherein the weight ratio of the liquid oily phase to the liquid aqueous ammonium sulfate comprising phase of the mixture comprising the liquid oily phase and the liquid aqueous ammonium sulfate comprising phase that is discharged from the second evaporative type crystallization section and charged to the second liquid-liquid separation section in step (iii.1) is less than 1.

12. A process according to claim 1, wherein the first organic solvent used in the first extraction section and the second organic solvent used in the second extraction section are independently selected from the group consisting of benzene, toluene, trichloroethylene, alcohols, and mixtures thereof.

13. An industrial scale plant that comprises at least a Beckmann rearrangement reaction section, a neutralization section, a first liquid-liquid separation section, a first and a second extraction section, a first solvent recovery section, a first and a second evaporative type crystallization section, and a first liquid-solid separation section, wherein the plant is configured for carrying out a process as defined in claim 1.

14. (canceled)

15. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0164] In the following, the invention will be described with reference to the Figures, which depict certain embodiments of the invention. The invention, however, is as defined in the claims and as generally described herein. It should not be limited to the embodiments shown for illustrative purposes in the Figures below.

[0165] FIG. 1 describes the three alternative modes of the process of the invention. FIG. 1A describes an alternative mode of the process of the invention in which a second evaporative type crystallization section is fed only with mother liquor produced in a first evaporative type crystallization section. FIG. 1B describes an alternative mode of the process of the invention in which a second evaporative type crystallization section is fed only with a second aqueous ammonium sulfate phase generated by extracting an aqueous ε-caprolactam phase of a neutralized Beckmann rearrangement mixture. FIG. 1C describes an alternative mode of the process of the invention in which a second evaporative type crystallization section is fed with both mother liquor produced in a first evaporative type crystallization section and a second aqueous ammonium sulfate phase generated by extracting an aqueous ε-caprolactam phase of a neutralized Beckmann rearrangement mixture.

[0166] FIG. 2 describes an embodiment of the present invention, wherein two feeds comprising ammonium sulfate and organic components are fed to a second evaporative type crystallization section: On the one hand, mother liquor produced in a first evaporative type crystallization section is charged to the second evaporative type crystallization section. On the other hand, a second aqueous ammonium sulfate phase generated by extracting an aqueous ε-caprolactam phase of a neutralized Beckmann rearrangement mixture is charged to the second evaporative type crystallization section. In the second evaporative type crystallization section evaporative type crystallization is performed so that a three-phase system arises comprising a liquid oily phase, a crystalline ammonium sulfate phase and a liquid aqueous ammonium sulfate comprising phase. The liquid oily phase and the crystalline ammonium sulfate are recovered in the process.

[0167] FIG. 3 describes another embodiment of the present invention, wherein two feeds comprising ammonium sulfate and organic components are fed to a second evaporative type crystallization section: On the one hand, mother liquor produced in a first evaporative type crystallization section is charged to the second evaporative type crystallization section. On the other hand, a second aqueous ammonium sulfate phase generated by extracting an aqueous ε-caprolactam phase of a neutralized Beckmann rearrangement mixture is charged to the second evaporative type crystallization section. Prior to charging the second aqueous ammonium sulfate phase to the second evaporative type crystallization section said phase is concentrated in a pre-concentration section. In the second evaporative type crystallization section evaporative type crystallization is performed so that a three-phase system arises comprising a liquid oily phase, a crystalline ammonium sulfate phase and a liquid aqueous ammonium sulfate comprising phase. All three phases are further treated. The crystalline ammonium sulfate is dissolved in a dissolution section. The liquid oily phase is recovered in the process.

[0168] FIG. 4 describes an embodiment of the present invention, wherein a cyclohexanone oxime is subjected to a Beckmann rearrangement reaction in the presence of oleum so that ε-caprolactam is produced. The Beckmann rearrangement reaction mixture comprising ε-caprolactam is neutralized. The neutralized Beckmann rearrangement mixture comprises two phases, a fist aqueous ammonium sulfate phase and an ε-caprolactam phase. Both phases of the neutralized Beckmann rearrangement mixture are further processed. In the further course of the process two aqueous ammonium sulfate phases comprising organic components are treated: On the one hand, a first aqueous ammonium sulfate phase directly obtained from the neutralized Beckmann rearrangement mixture is treated. On the other hand, a second aqueous ammonium sulfate phase is treated which is obtained by extracting an aqueous ε-caprolactam phase of a neutralized Beckmann rearrangement mixture.

DESCRIPTION OF THE DRAWINGS

[0169] FIG. 1 indicates the alternative modes of the process of the invention.

[0170] In FIG. 1A, a first aqueous ammonium sulfate phase [α] obtained from a neutralized Beckmann rearrangement mixture is processed and used for evaporative type crystallization in a first evaporative type crystallization section [l]. During evaporative type crystallization crystalline ammonium sulfate [γ] and mother liquor is obtained. The crystalline ammonium sulfate [γ] is recovered. The mother liquor is an aqueous ammonium sulfate phase enriched in organic components compared to the processed first aqueous ammonium sulfate phase entering the first evaporative type crystallization section [l]. A fraction of the mother liquor is discharged from the first evaporative type crystallization section [l] to the second evaporative type crystallization section [a]. A second aqueous ammonium sulfate phase [β] generated by extracting an aqueous ε-caprolactam phase obtained from a neutralized Beckmann rearrangement mixture is not charged to the second evaporative type crystallization section [a]. In the second evaporative type crystallization section evaporative crystallization is performed so that a three-phase system arises. Said three-phase system comprises a liquid oily phase, a crystalline ammonium sulfate phase and a liquid aqueous ammonium sulfate comprising phase. At least the liquid oily phase [δ] is recovered.

[0171] In FIG. 1B, a first aqueous ammonium sulfate phase [α] obtained from a neutralized Beckmann rearrangement mixture is processed and used for evaporative type crystallization in a first evaporative type crystallization section [l]. During evaporative type crystallization crystalline ammonium sulfate [γ] and mother liquor is obtained. Optionally, a fraction of the mother liquor is discharged from the first evaporative type crystallization section [l] to outside the process (not shown). The crystalline ammonium sulfate [γ] is recovered. A second aqueous ammonium sulfate phase [β] generated by extracting an aqueous ε-caprolactam phase obtained from a neutralized Beckmann rearrangement mixture is charged to a second evaporative type crystallization section [a]. In the second evaporative type crystallization section evaporative crystallization is performed so that a three-phase system arises. Said three-phase system comprises a liquid oily phase, a crystalline ammonium sulfate phase and a liquid aqueous ammonium sulfate comprising phase. At least the liquid oily phase [δ] is recovered.

[0172] FIG. 1C combines the alternative modes of the process of the invention described in FIG. 1A and FIG. 1B. In FIG. 1C a fraction of the mother liquor in the first evaporative type crystallization section [l] is charged to the second evaporative type crystallization section [a]. In addition, the second aqueous ammonium sulfate phase [β] is charged to a second evaporative type crystallization section [a].

[0173] In FIG. 2, the following two different ammonium sulfate comprising feeds [101] and [102] are charged to one or more evaporative type crystallizers in evaporative crystallization section [a] (e.g., Oslo (fluidized bed) crystallizers, draft tube baffle (DTB) crystallizers, forced circulation crystallizers): Mother liquor enriched in organic components [101], which was purged from an ammonium sulfate crystallization section, and a second aqueous ammonium sulfate phase comprising organic components, which was obtained as effluent from an extraction of a crude aqueous ε-caprolactam phase with an organic solvent. Optionally, prior to being charged to one or more evaporative type crystallizers in evaporative crystallization section [a], the second aqueous ammonium sulfate phase [102] comprising organic components is charged to a solvent recovery section, in which solvent is recovered (not shown). Optionally, prior to being charged to one or more evaporative type crystallizers in evaporative crystallization section [a], the second aqueous ammonium sulfate phase [102] comprising organic components is charged to a pre-concentration section, in which mainly water is removed, e.g., via evaporation and/or membrane filtration (not shown).

[0174] The water evaporated in the one or more evaporative type crystallizers in evaporative crystallization section [a] is condensed and discharged as condensate [103]. Generally, the condensate [103] is disposed of as waste and is treated in a waste water treatment system (not shown). Optionally, condensate [103] is re-used, optionally after purification treatment (e.g., adsorption treatment by activated carbon), for the Beckmann rearrangement reaction (not shown).

[0175] The concentration of organic components and the concentration of ammonium sulfate in the one or more evaporative type crystallizers in evaporative crystallization section [a] are so high that a three-phase system occurs: a liquid oily phase with a high organic components content, a liquid aqueous ammonium sulfate comprising phase and a crystalline ammonium sulfate phase.

[0176] A mixture [104] comprising liquid oily phase and liquid aqueous ammonium sulfate comprising phase is discharged from the one or more evaporative type crystallizers in evaporative crystallization section [a] and charged to a liquid-liquid separation section [b]. This mixture might also contain small amounts of the crystalline ammonium sulfate phase. A liquid-liquid separation section [b] consists of one or more separation vessels, in which, for example, a liquid oily phase with a high organic components content separates off as top layer and a liquid aqueous ammonium sulfate comprising phase (and optionally a crystalline ammonium sulfate phase) as bottom layer.

[0177] The liquid oily phase [106] is recovered from the liquid-liquid separation section [b]. Optionally, this liquid oily phase [106] is charged to an incinerator (not shown). It can also be stored and/or used or sold as fuel. Optionally, part of the heat that is produced by burning the liquid oily phase in the incinerator is used to generate steam (not shown).

[0178] A liquid aqueous ammonium sulfate phase [105] (and optionally an ammonium sulfate crystals comprising solid phase), is/(are) also discharged from the liquid-liquid separation section [b] and charged to the one or more evaporative type crystallizers in evaporative crystallization section [a].

[0179] An ammonium sulfate containing slurry [108] comprising liquid aqueous ammonium sulfate comprising phase and ammonium sulfate crystals is discharged from the one or more evaporative type crystallizers of evaporative type crystallization section [a] and charged to one or more liquid-solid separation devices in liquid-solid separation section [c] (e.g., (continuous) filters, centrifuges, decanters, elutriation columns, salt legs, hydrocyclones or combination thereof). In the liquid-solid separation section [c] wet ammonium sulfate crystals [110] are separated off from the liquid aqueous ammonium sulfate comprising phase. Optionally, this is followed by a washing step of the wet ammonium sulfate crystals, whereby the wet ammonium sulfate crystals are washed (preferably with water or an aqueous ammonium sulfate phase) in order to reduce the organic components content (adhering to the surface) of the wet ammonium sulfate crystals (not shown). The remainder, an aqueous ammonium sulfate phase or a diluted ammonium sulfate slurry [109] is charged back to the one or more evaporative type crystallizers [a].

[0180] The wet ammonium sulfate crystals [110] are dried in one or more drying devices in drying section [d] (e.g., fluidized bed dryers), whereby water vapor [120] and dried ammonium sulfate crystals [121] are obtained and separately discharged. Optionally, the dried ammonium sulfate crystals [121] are sieved, coated and/or blended with other compounds (not shown).

[0181] In FIG. 3, an aqueous ammonium sulfate phase [201] comprising organic components which was obtained as effluent by extracting a crude aqueous ε-caprolactam phase with an organic solvent is charged to pre-concentration section [f], in which mainly water is removed. Preferably, the pre-concentration section [f] comprises reverse osmosis membranes and/or one or more evaporators, e.g., falling film type, natural circulation type, forced circulation type, rising film type, climbing-film plate type, or combinations thereof. Optionally, prior to being charged to a pre-concentration section [f], the aqueous ammonium sulfate phase [201] comprising organic components is charged to a solvent recovery section, in which solvent is recovered (not shown). Water is separated off in the pre-concentration section [f] and is discharged as water flow [202]. Generally, the water flow [202] is disposed of as waste and is treated in a waste water treatment system (not shown). Optionally, water flow [202] is re-used, optionally after purification treatment (e.g., adsorption treatment by activated carbon), for the Beckmann rearrangement reaction (not shown). Optionally, in case water flow [202] is in the vapor phase (e.g., as a result of evaporation) then the heat of condensation might be recovered (not shown).

[0182] Pre-concentrated effluent [203] is discharged from the pre-concentration section [f] and is charged to one or more evaporative type crystallizers in an ammonium sulfate crystallization section [a] (e.g., Oslo (fluidized bed) crystallizers, draft tube baffle (DTB) crystallizers, forced circulation crystallizers). Optionally, for pH-adjustment, (aqueous) ammonia is charged to pre-concentrated effluent [203] prior to the charging to one or more evaporative type crystallizers in the ammonium sulfate crystallization section [a] (not shown). In addition, an aqueous ammonium sulfate phase comprising organic components which was purged from another ammonium sulfate crystallization section [204] is charged to one or more evaporative type crystallizers in the ammonium sulfate crystallization section [a].

[0183] Water which is evaporated in the one or more evaporative type crystallizers in the ammonium sulfate crystallization section [a] is condensed and discharged as condensate [205]. Generally, the condensate [205] is disposed of as waste and is treated in a waste water treatment system (not shown). Optionally, condensate [205] is re-used, optionally after purification treatment (e.g., adsorption treatment by activated carbon), in the process for the production of ammonium sulfate and ε-caprolactam based on cyclohexanone oxime that is produced from cyclohexanone (not shown).

[0184] The concentration of organic components and the concentration of ammonium sulfate in the one or more evaporative type crystallizers in ammonium sulfate crystallization section [a] are so high that a three-phase system occurs: a liquid oily phase with a high organic components content, a liquid aqueous ammonium sulfate comprising phase and a crystalline ammonium sulfate phase.

[0185] A mixture comprising mainly liquid oily phase with a high organic components content and liquid aqueous ammonium sulfate comprising phase [206] is discharged from the one or more evaporative type crystallizers in ammonium sulfate crystallization section [a] and charged to a liquid-liquid separation section [b]. This mixture might also contain small amounts of crystalline ammonium sulfate phase. A liquid-liquid separation section [b] consists of one or more separation vessels, in which liquid oily phase with a high organic components content separates off as top layer and liquid aqueous ammonium sulfate comprising phase as bottom layer. Optionally, the bottom layer also contains a low fraction (<4 wt. %) of crystalline ammonium sulfate phase.

[0186] The top layer is recovered from the liquid-liquid separation section [b] as liquid oily phase [208]. Optionally, this liquid oily phase [208] is charged to an incinerator (located on-site or optionally not on-site) (not shown). Optionally, part of the heat that is produced by burning the liquid oily phase in the incinerator is used to generate steam (not shown).

[0187] The bottom layer, a liquid aqueous ammonium sulfate comprising phase (that optionally contains crystalline ammonium sulfate phase), is discharged from the liquid-liquid separation section [b] as aqueous phase [207] and is charged to the one or more evaporative type crystallizers in ammonium sulfate crystallization section [a].

[0188] Ammonium sulfate containing slurry [209] is discharged from the one or more evaporative type crystallizers of the ammonium sulfate crystallization section [a] and is charged to one or more liquid-solid separation devices in liquid-solid separation section [c] (e.g., (continuous) filters, centrifuges, decanters, elutriation columns, salt legs, hydrocyclones or combination thereof). In the liquid-solid separation section [c] wet ammonium sulfate crystals [211] are separated off. Optionally, a washing step of the wet ammonium sulfate crystals is included, whereby the wet ammonium sulfate crystals are washed (preferably with water or an aqueous ammonium sulfate phase) in order to reduce the organic components content (adhering to the surface) of the wet ammonium sulfate crystals (not shown).

[0189] The remainder, a liquid aqueous ammonium sulfate comprising phase or a diluted ammonium sulfate slurry [210] is charged back to the one or more evaporative type crystallizers in ammonium sulfate crystallization section [a].

[0190] The wet ammonium sulfate crystals [211] and a water comprising phase [212] are charged to an ammonium sulfate dissolution section [e]. Preferably, the water comprising phase [212] comprises more than 90 wt. % water. Optionally, the water comprising phase [212] comprises ammonium sulfate. Generally, the ammonium sulfate dissolution section [e] consists of one or more vessels which contain a mixing compartment and an overflow compartment. An aqueous flow of ammonium sulfate [213] is discharged from the ammonium sulfate dissolution section [e]. Preferably, the aqueous flow of ammonium sulfate [213] is an aqueous phase that contains about 40 wt. % ammonium sulfate and does not contain any solid ammonium sulfate crystals. Preferably, the aqueous flow of ammonium sulfate [213] is charged as feed to an ammonium sulfate crystallization section, in which crystalline ammonium sulfate, aqueous condensate and a purge are produced.

[0191] In FIG. 4, cyclohexanone oxime [1] and oleum [2] are charged to a Beckmann rearrangement section [A]. The cyclohexanone oxime might be produced by various technologies. One option is the HPO® technology, in which cyclohexanone oxime is formed by reacting hydroxylamine obtained by hydrogenation of nitrate and cyclohexanone. Another option to produce cyclohexanone oxime is the ammoximation technology, in which cyclohexanone oxime is formed by reacting ammonia, hydrogen peroxide and cyclohexanone. A further option to produce cyclohexanone oxime is the Raschig technology in which cyclohexanone oxime is formed by reacting hydroxylamine obtained by the reduction of nitrite and cyclohexanone.

[0192] The Beckmann rearrangement mixture [3] and an aqueous ammonia phase [4] are added to a neutralization section [B] so that a neutralized Beckmann rearrangement mixture [5] is produced. Alternatively, the aqueous ammonia phase [4] is replaced by separate additions of water and gaseous ammonia (not shown). A neutralized mixture containing an aqueous ammonium sulfate phase and an aqueous crude ε-caprolactam phase are obtained in the neutralization section [B]. The aqueous ammonium sulfate phase comprises ε-caprolactam and organic components as impurities. The aqueous crude ε-caprolactam phase comprises ammonium sulfate and organic components as impurities.

[0193] The neutralized mixture [5] is charged to a liquid-liquid separation section [C], in which the aqueous ammonium sulfate phase and the aqueous crude ε-caprolactam phase are separated from each other by phase separation. The aqueous crude ε-caprolactam phase [6] and the aqueous ammonium sulfate phase [7] leave the liquid-liquid separation section [C].

[0194] The aqueous ammonium sulfate phase [7] is charged to an extraction section [F], in which a solvent [8] is added to recover dissolved ε-caprolactam. Various solvents can be used, e.g., benzene, toluene, trichloroethylene, and alcohols, inter alia 1-octanol and 2-ethylhexanol and mixtures of alcohols. Extraction section [F] might comprise one or more extraction units, e.g., (counter-current) extraction columns and mixer-settlers. A mixture comprising ε-caprolactam and solvent [9] leaves the extraction section [F].

[0195] The obtained extracted aqueous ammonium sulfate phase [10] is charged to a solvent recovery section [G], in which the solvent is recovered from the extracted aqueous ammonium sulfate phase [10] and is discharged as recovered solvent [11]. Solvent recovery section [G] might comprise one or more distillation columns and/or one or more steam strippers.

[0196] The aqueous ammonium sulfate phase after solvent recovery [12] is pH-adjusted by addition of pH modifying agent [13] (preferably ammonia or sulfuric acid) in a pH-adjustment section [H], whereby a pH-adjusted aqueous ammonium sulfate phase [14] is obtained.

[0197] The pH-adjusted aqueous ammonium sulfate phase [14] is charged to one or more evaporative type crystallizers in evaporative type crystallization section [l] (e.g., an Oslo (fluidized bed) crystallizer, a draft tube baffle (DTB) crystallizer or a forced circulation crystallizer). Vapor recompression and/or multiple-effect evaporation might be applied in order to reduce energy consumption required for the evaporation of water in the ammonium sulfate crystallizer(s). Aqueous flow of ammonium sulfate [213] that is discharged from the ammonium sulfate dissolution section [e] is charged to one or more evaporative type crystallizers in evaporative type crystallization section [l]. The water evaporated in the one or more evaporative type crystallizers in evaporative type crystallization section [l] is condensed and discharged as condensate [15]. Optionally, condensate [15] is re-used, optionally after purification treatment (e.g., adsorption treatment by activated carbon), for the Beckmann rearrangement reaction (not shown). A purge [204] is discharged from one or more evaporative type crystallizers in the evaporative type crystallization section [l]. Purge [204] is mother liquor which is an aqueous ammonium sulfate phase with an increased organic components content compared to the organic components content of the charged pH-adjusted aqueous ammonium sulfate phase [14]. Purge [204] is charged to the second evaporative type crystallization section [a].

[0198] An ammonium sulfate containing slurry [16] is discharged from the one or more evaporative type crystallizers in evaporative type crystallization section [l] and is charged to one or more liquid-solid separation devices [J] (e.g., (continuous) filters, centrifuges, decanters, elutriation columns, salt legs, hydrocyclones or combination thereof), whereby wet ammonium sulfate crystals [18] are separated off. The remainder, an aqueous ammonium sulfate phase or a diluted ammonium sulfate slurry [17] is charged to the one or more evaporative type crystallizers in evaporative type crystallization section [l].

[0199] Optionally, a washing step of the wet ammonium sulfate crystals is included, whereby the wet ammonium sulfate crystals are washed (preferably with water or an aqueous ammonium sulfate phase) in order to reduce the content of organic components (adhering to the surface) of the wet ammonium sulfate crystals (not shown).

[0200] The wet ammonium sulfate crystals [18] are dried in one or more drying devices [K] (e.g., fluidized bed dryers), whereby water vapor [19] and dried ammonium sulfate crystals are discharged. Optionally, the dried ammonium sulfate crystals [20] are sieved, coated and/or blended with other compounds (not shown).

[0201] In extraction section [L], the aqueous crude ε-caprolactam [6] is extracted with a solvent [21], whereby an aqueous effluent [22] and a mixture comprising ε-caprolactam and solvent [25] are obtained. Various solvents can be used, e.g., benzene, toluene, trichloroethylene, and alcohols, inter alia 1-octanol and 2-ethylhexanol and mixtures thereof. Extraction section [L] might comprise one or more extraction units, e.g., (counter-current) extraction columns and mixer-settlers. The obtained aqueous effluent [22] is charged to a solvent recovery section [M].

[0202] In solvent recovery section [M] solvent is recovered from the aqueous effluent [22] and is discharged as recovered solvent [23]. Solvent recovery section [M] might comprise one or more distillation columns and/or one or more steam strippers. The resulting aqueous effluent after solvent recovery [201] is charged to a pre-concentration section [f], in which mainly water is removed. Preferably, the pre-concentration section [f] comprises reverse osmosis membranes and/or one or more evaporators, e.g., falling film type, natural circulation type, forced circulation type, rising film type, climbing-film plate type, or combinations thereof. Water is separated off in the pre-concentration section [f] and is discharged as water flow [202]. Generally, the water flow [202] is disposed of as waste and is treated in a waste water treatment system (not shown). Optionally, water flow [202] is re-used, optionally after purification treatment (e.g., adsorption treatment by activated carbon), for the Beckmann rearrangement reaction (not shown). Optionally, in case water flow [202] is in the vapor phase (e.g., as a result of evaporation) then the heat of condensation might be recovered (not shown).

[0203] The mixture comprising ε-caprolactam and solvent [24] that is discharged from extraction section [L] is further worked-up in an ε-caprolactam purification and concentration section [N], whereby recovered solvent [25] and purified ε-caprolactam [26] are obtained. In industrial practice, various embodiments of ε-caprolactam purification and concentration section [N] are realized. Generally, these embodiments might comprise of a combination of units for extraction, hydrogenation, ion exchange, crystallization, pH-adjustment and/or (vacuum) distillation.

[0204] Sections [a], [b], [c], and [e] in FIG. 4 and the various in- and outflows from these sections are as described for FIG. 3 above.

EXAMPLES

[0205] The following examples serve to explain the invention in more detail, in particular with regard to certain forms of the invention. The examples, however, are not intended to limit the present disclosure.

[0206] The COD contents mentioned in the following examples are determined in accordance with the dichromate method according to ASTM D 1252-95.

[0207] The Examples and the Comparative Examples were carried out in industrial -scale continuously operating plants with annual capacities above 200 kta ε-caprolactam, in which both ε-caprolactam and crystalline ammonium sulfate were produced.

Comparative Example 1

[0208] Comparative Example 1 is very similar to the embodiment of the invention depicted in FIG. 4. In the Comparative Example, however, the aqueous effluent after benzene recovery [201] was charged to a waste water treatment system. In addition, the purge [204] was charged to a waste water treatment system.

[0209] In a commercial caprolactam plant cyclohexanone oxime was produced according to the HPO® process from cyclohexanone. The cyclohexanone oxime [1] was converted into ε-caprolactam in a three-stage Beckmann rearrangement reaction section [A] with oleum [2]. The resulting Beckmann rearrangement mixture [3] (sulfate of ε-caprolactam in excess sulfuric acid) was then neutralized with aqueous ammonia [4] in a neutralization section [B], whereby a neutralized mixture of aqueous crude ε-caprolactam and an aqueous ammonium sulfate phase [5] were obtained. These two phases were separated in liquid-liquid separation section [C] into aqueous crude ε-caprolactam [6] and an aqueous ammonium sulfate phase [7].

[0210] The aqueous crude ε-caprolactam [6] was extracted with benzene [21] in a counter-current extraction column in extraction section [L], whereby a benzenic-ε-caprolactam mixture [24] and an aqueous effluent [22] were obtained. The benzenic-ε-caprolactam mixture [24] was further worked-up in ε-caprolactam purification and concentration section [N], whereby recovered benzene [25] and first grade ε-caprolactam [26] were obtained. The first grade ε-caprolactam [26] was sold as raw material for nylon-6 production. The aqueous effluent [22] was fed to a distillation column in benzene recovery section [M] from which benzene [23] was recovered as top product and an aqueous effluent after benzene recovery [201] was obtained as bottom product. The aqueous effluent after benzene recovery [201] consisted of ca. 4 wt. % ammonium sulfate, ca. 4 wt. % organic components and the remainder was mainly water. In Comparative Example 1, the aqueous effluent after benzene recovery [201] was charged to a waste water treatment system, in which most of the ammonium and organic components were removed.

[0211] The aqueous ammonium sulfate phase [7] was charged to the upper-part and benzene [8] was charged to the lower part of a counter-current extraction column in extraction section [F]. A benzenic-ε-caprolactam comprising mixture [9] and an extracted aqueous ammonium sulfate phase [10] were discharged from the extraction section [F]. The extracted aqueous ammonium sulfate phase [10] was fed to a distillation column in a benzene recovery section [G] from which benzene [11] was recovered as top product and an aqueous ammonium sulfate phase after benzene recovery [12] was obtained as bottom product. The aqueous ammonium sulfate phase after solvent recovery [12] was pH-adjusted to a pH value of about 5 (measured at a temperature of 25° C.) by addition of aqueous ammonia [13] in pH-adjustment section [H], whereby a pH-adjusted aqueous ammonium sulfate phase [14] was obtained.

[0212] This pH-adjusted aqueous ammonium sulfate phase [14] was charged to three Oslo type crystallizers with multi-effect evaporation in evaporative type crystallization section [l]. The water evaporated in evaporative type crystallization section [l] was condensed and discharged as condensate [15]. In Comparative Example 1, the purge [204] was discharged from evaporative type crystallization section [l]. The purge [204] was then charged to a waste water treatment system, in which most of the ammonium and organic components were removed. Purge [204] consisted of water, about 40 wt. % ammonium sulfate and organic impurities (about 40 gram COD/kg of the purge).

[0213] An ammonium sulfate containing slurry [16] was discharged from evaporative type crystallization section [l] and was charged to centrifuges in a liquid-solid separation section [J], in which, after washing with water, wet ammonium sulfate crystals [18] were separated off. The remainder, an ammonium sulfate phase with some fine ammonium sulfate crystals in it [17] was charged to the evaporative type crystallization section [l]. Finally, the wet ammonium sulfate crystals [18] were dried in a fluidized bed dryer in drying section [K], whereby water vapor [19] and dried ammonium sulfate crystals [20] were discharged. The dried ammonium sulfate crystals [20] were screened before being sold as high grade crystalline ammonium sulfate. The dried ammonium sulfate crystals [20] had a mean median diameter of almost 3 mm and the color was whitish.

Example 1

[0214] Example 1 describes an embodiment of the invention as depicted in FIG. 4.

[0215] The experiment described in Comparative Example 1 was repeated, with the difference that now the purge [204] and the aqueous effluent after benzene recovery [201] were not charged to a waste water treatment system, but were charged to an apparatus, that comprises a pre-concentration section [f], an ammonium sulfate crystallization section [a], a liquid-liquid separation section [b], a liquid-solid separation section [c], and an ammonium sulfate dissolution section [e]. From this apparatus an aqueous flow of ammonium sulfate phase [213] was charged to the first ammonium sulfate crystallization section [l]. From the liquid-liquid separation section [b] a liquid oily phase with a high content of organic components [208] was discharged and combusted in an incinerator.

[0216] The aqueous effluent after benzene recovery [201], that consisted of ca. 4 wt. % ammonium sulfate, ca. 4 wt. % organics and the remainder mainly being water, was charged to a steam-heated falling film evaporator in pre-concentration section [f], whereby a portion of the water was evaporated that was discharged as vapor [202].

[0217] The obtained pre-concentrated effluent [203] consisting of ca. 8 wt. % ammonium sulfate, ca. 8 wt. % organic components and the remainder mainly being water, was discharged from the falling film evaporator in pre-concentration section [f] and was charged to an Oslo crystallizer in ammonium sulfate crystallization section [a], preceded by charging aqueous ammonia for pH adjustment. In addition, purge [204] that was discharged from evaporative type crystallization section [l] was charged to the Oslo crystallizer in ammonium sulfate crystallization section [a]. Vapor [202] was fed to a heat exchanger of the Oslo crystallizer in ammonium sulfate crystallization section [a]. Water was evaporated in the Oslo crystallizer in ammonium sulfate crystallization section [a] and was condensed and discharged as condensate [205]. The temperature in Oslo crystallizer in ammonium sulfate crystallization section [a] was maintained at about 70° C. The concentration of organic components and the concentration of ammonium sulfate in the Oslo crystallizer in ammonium sulfate crystallization section [a] were so high that a three-phase system was formed: a liquid oily phase with a high content of organic components, a liquid aqueous ammonium sulfate comprising phase and a solid phase comprising ammonium sulfate crystals.

[0218] A mixture of mainly the liquid oily phase with a high content of organic components, and the liquid aqueous ammonium sulfate comprising phase [206] was discharged as a side-stream from the Oslo crystallizer in ammonium sulfate crystallization section [a] and charged to a separation vessel in liquid-liquid separation section [b]. This mixture did contain small amounts of the fine ammonium sulfate crystals. The weight to weight ratio of the liquid oily phase with a high content of organic components, and the liquid aqueous ammonium sulfate comprising phase in mixture [206] was on average about 1:8. In the separation vessel in liquid-liquid separation section [b] a phase separation was observed, whereby a liquid oily layer was on top. The average residence time in the separation vessel in liquid-liquid separation section [b] was about 1 hour. The top layer was discharged from the separation vessel in liquid-liquid separation section [b] as liquid oily phase with a high content of organic components [208]. A typical composition of this liquid oily phase [208] was: organic components content (expressed as COD): 1000 to 1500 gram/kg liquid oily phase; ε-caprolactam: 3 to 6 wt. %; ammonium sulfate: 12 to 20 wt. %; water 18 to 30 wt. %. The density (measured at a temperature of 25° C.) of this liquid oily phase [208] ranged from 1150 to 1220 kg/m.sup.3 liquid oily phase. The bottom layer, an aqueous ammonium sulfate comprising phase was discharged from the separation vessel in liquid-liquid separation section [b] as aqueous phase [207] and was charged to the Oslo crystallizer in ammonium sulfate crystallization section [a].

[0219] An ammonium sulfate containing slurry [209] was discharged from the Oslo crystallizer in ammonium sulfate crystallization section [a] and was charged to a continuous centrifuge in liquid-solid separation section [c], in which ammonium sulfate crystals were separated off. The ammonium sulfate crystals were washed with water before being discharged as washed wet ammonium sulfate crystals [211]. The remainder, an aqueous ammonium sulfate comprising phase or a diluted ammonium sulfate slurry [210] was recharged to the Oslo crystallizer in ammonium sulfate crystallization section [a].

[0220] The washed wet ammonium sulfate crystals [211] and water [212] were charged to a stirred vessel in ammonium sulfate dissolution section [e]. An aqueous flow of ammonium sulfate phase [213], that contained about 40 wt. % ammonium sulfate, was discharged from the stirred vessel in ammonium sulfate dissolution section [e]. The aqueous flow of ammonium sulfate phase [213] was charged as feed to evaporative type crystallization section [l].

[0221] The quality of both the first grade ε-caprolactam [28] and the dried ammonium sulfate crystals [21] produced in Example 1 were equal to those in Comparative Example 1.

[0222] However, in Example 1, the amount of dried ammonium sulfate crystals [21] per ton of produced ε-caprolactam was increased by about 3 wt. % compared to Comparative Example 1.

[0223] The comparison of the results of Example 1 to those of Comparative Example 1 show that the disposal of phases comprising aqueous ammonium sulfate and organic components can be avoided without negative effects on the quantity and quality of the obtained products ε-caprolactam and ammonium sulfate. Further, Example 1 shows that 3% more high grade crystalline ammonium sulfate is obtained. And in addition, a liquid oily phase is obtained that can be incinerated without addition of extra fuel. All these advantages allow the generation of more valuable products, lower costs related to disposal of by-products, and less impact on the environment. As an overall result, Example 1 reduced the overall carbon footprint of the process to produce polyamide 6 and its coproducts.