METHOD FOR REDUCING POLLUTANT DISCHARGE IN PHENOL AND ACETONE PRODUCTION

Abstract

A method for reducing pollutant discharge in phenol acetone production, comprising at least one of the following steps: (A) collecting phenolic wastewater generated by a phenol-acetone plant, adjusting the pH value to acidic, and performing extraction and recovery on the phenols in wastewater using cumene as an extracting agent; (B) reducing the acetone content in the wastewater from a column bottom by means of optimizing the process of an acetone refining column; (C) treating the wastewater from the column bottom of the acetone refining column by using a permselective membrane, and recovering alkali; (D) neutralizing the wastewater obtained from step (C), mixing the neutralized wastewater with a condensation liquid at the top of a cumene oxidation column, and carrying out a detoxification treatment; (E) carrying out an oil separation treatment on total discharged wastewater from the phenol-acetone plant, and recovering organic matters comprising hydrocarbons; and (F) carrying out a biological treatment, a coagulation sedimentation treatment and a reinforced degradation treatment on the wastewater after undergoing the oil separation treatment. The method has at least one of characteristics of being capable of recovering resources, increasing product yield, reducing pollutant discharge, having low cost in wastewater treatment, and having stable quality for water output.

Claims

1. A method for reducing the pollutant discharge in the production of phenol and acetone, comprising the following steps: (A) collecting phenols containing wastewater produced by a phenol and acetone production plant, adjusting the pH to acidic, and performing extraction and recovery of the phenols in the wastewater by using cumene as an extracting agent; (B) reducing the content of acetone in the wastewater from column bottom by optimizing the process of acetone refining column; (C) treating the wastewater from the column bottom of the acetone refining column by using a permselective membrane, and recovering alkali; (D) neutralizing the wastewater obtained from step (C), then mixing the neutralized wastewater with overhead condensate of cumene oxidation column, and carrying out detoxification treatment; (E) carrying out oil separation treatment on the total discharged wastewater from the phenol and acetone production plant, and recovering organic matters including hydrocarbons; and (F) subjecting the wastewater, after undergoing the oil separation treatment, to at least one of the treatments selected from the group consisting of a biological treatment, a coagulation sedimentation treatment and a reinforced degradation treatment, wherein the detoxification treatment in step (D) comprises: mixing the wastewater treated in step (C) with the overhead condensate of the cumene oxidation column, controlling the pH of the wastewater ranging from 3 to 5 and the temperature being 20 to 60 C. adding 5-30 mg/L reductive catalyst, to reduce the toxicity of the wastewater against the activated sludge microorganisms, and reduce the inhibition rate of oxygen utilization of the activated sludge to less than 20%, and obtain a conversion rate of non-degradable organic matters in the wastewater from the column bottom of acetone refining column amounting to more than 70 wt %.

2. The method according to claim 1, wherein in step (A), adjusting the pH of the wastewater to acidic with a pH ranging from 4.5 to 5.5, extracting phenols from the wastewater by using cumene as an extracting agent with a volume ratio of cumene to wastewater ranging from 5:1 to 20:1, regenerating the cumene rich in phenols by using a 10 wt % to 20 wt % NaOH solution with the volume of the NaOH solution being 0.1 to 0.6 times of the wastewater and recycling the cumene after dephenolization as the extracting agent in the treatment of wastewater.

3. The method according to claim 1, wherein step (B) comprises at least one of the following means: (1) installing ringlike packing or structured packing in the liquid layer on the plates below the alkali liquor feed inlet of the acetone refining column; (2) separately controlling the acetone refining column and decreasing the column top pressure by 5 to 20 kPa; (3) reducing the overhead reflux for aldehyde removal by 10% to 50%; (4) increasing the stripping section below the overhead reflux plates for aldehyde removal by 1 to 2 theoretical plates; wherein after the treatment of step (B), the content of acetone in the wastewater is decreased to 0.01 wt % to 0.1 wt %.

4. The method according to claim 1, wherein in step (C), the treatment by permselective membrane includes cooling the wastewater of the column bottom of acetone refining column first, subjecting it to oil separation and activated carbon adsorption treatments, then circulating through a compartment formed by permselective membrane; and permselective membrane forms the same compartments on the other side for circulating deionized water; the NaOH in the wastewater passes through the permselective membrane and enters the deionized water side to achieve alkali recovery.

5. The method according to claim 4, wherein the permselective membrane is resistant to solvents of acetone and benzenes and enables selective permeation of NaOH.

6. (canceled)

7. The method according to claim 1, wherein the reductive catalyst is a divalent iron ion, a cobalt ion or a manganese ion.

8. The method according to claim 1, wherein in step (F), the biological treatment is an aerobic biological treatment, and the microorganism growth is a suspension growth or a suspension growth coexisted with an attachment growth; and the reinforced degradation treatment is performed by using ozone or H.sub.2O; as oxidants.

9. The method according to claim 8, wherein when ozone is used as an oxidant to perform the reinforced degradation treatment, the ozone column is filled with an aluminum-based or copper-based supported catalyst, the temperature is 20 to 40 C., the pH of the wastewater is 4 to 10, and ozone is added in an amount of 50 to 300 mg/L.

10. The method according to claim 8, wherein when H.sub.2O.sub.2 is used as an oxidant to perform the reinforced degradation treatment, the catalyst is divalent iron ion, the pH of the wastewater is adjusted to 3 to 6, the divalent iron ion is added in an amount of 5 to 200 mg/L, and H.sub.2O.sub.2 is added in an amount of 100 to 330 mg/L.

Description

DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 shows the process for producing phenol and acetone based on traditional cumene method.

[0043] FIG. 2 shows an improved process for producing phenol and acetone based on traditional cumene method, according to the present application.

[0044] FIG. 3 shows a schematic diagram of an acetone refining column.

[0045] FIG. 4 shows a schematic diagram of a compartment formed by a permselective membrane (countercurrent operation).

[0046] FIG. 5 is a schematic diagram of the packing installed in the liquid layer on the plates of the acetone refining column.

DETAILED DESCRIPTION OF EMBODIMENTS

Example 1

[0047] Phenol and acetone were prepared by using the traditional cumene method (see FIG. 1). The COD of the total discharged wastewater was up to 4000-8000 mg/L.

[0048] The method according to the present application modified the traditional cumene method and the facilities thereof by at least one of the following means:

[0049] (1) A separate vacuum system was installed in the acetone refining column, which decreased the column top pressure by 15 kPa, A thin layer of structured packing was installed in the liquid layer on the plates below the alkali liquor feed inlet (see FIG. 3 and FIG. 5). The overhead refluxes to column top and for aldehyde removal were decreased by 25%. While ensuring the product quality of the side draw, the steam consumption of the column bottom of the acetone refining column was reduced by 20% and the content of acetone from the column bottom was reduced from 2200 mg/L to 520 mg/L.

[0050] (2) After collecting the phenol containing wastewater in the phenol containing wastewater tank, the pH was adjusted to 5 with sulfuric acid, cumene was used as an extracting agent and the flow was 20 times of the wastewater. In the extraction column, phenol in the wastewater was extracted. The obtained cumene rich in phenol was regenerated with a 15 wt % NaOH solution in amount of 0.5 times of the wastewater. After dephenolization and regeneration, the cumene was recycled as an extracting agent for extracting wastewater. Sodium phenolate solution obtained by regeneration was acidized by sulfuric acid. After passing a two-stage desalination separator, the organic phase containing phenols entered a neutralization section for recycling phenol and the aqueous phase was subjected to extraction treatment. The concentration of the phenol in the wastewater was decreased from 5000 mg/L to 50 mg/L.

[0051] (3) The wastewater of the column bottom of acetone refining column was cooled (via heat exchange) and subjected to oil separation treatment, then circulated through a compartment formed by a perfluorinated cation exchange membrane. The ion exchange membrane constituted the same compartment on the other side for circulating deionized water. NaOH in the wastewater passed through the ion exchange membrane and entered the deionized water side to achieve alkali recovery, see FIG. 4. By this step, the concentration of the alkali in the wastewater can be reduced from 2 mol/L, to 0.5 mol/L. The alkali solution recovered can be used for neutralizing acidic wastewater.

[0052] (4) After recovering alkali, the wastewater of the column bottom of the acetone refining column was neutralized, followed by mixing with an overhead condensate of a cumene oxidation column. 10 mg/L Mn.sup.2+ was added as a catalyst and the reaction was carried out at pH of 5, at a temperature of 30 C. for 10 min. The inhibition rate of the activated sludge OUR was reduced to less than 20%. The non-degradable organic matters in the wastewater of the column bottom of acetone refining column was removed by more than 70 wt/o.

[0053] (5) After being treated by all the above means (1)-(4), the total discharged wastewater of the plant was subjected to oil separation treatment. At this time, the COD of the treated wastewater was 1800 mg/L. Then the wastewater was subjected to aerobic activated sludge treatment, and the COD was removed by 88%. Aluminum sulfate and polyacrylamide (PAM) were used as coagulant and coagulant aid, respectively, for coagulation and sedimentation treatment. Ozone was then used as an oxidant for a reinforced degradation treatment. The ozone column was filled with a copper-based supported catalyst, wherein ozone was 200 mg/L in amount. The COD of the effluent treated was below 50 mg/L, and phenol and acetone were not detectable.

Example 2

[0054] The method according to the present application modified the traditional cumene method and the facilities thereof by at least one of the following means:

[0055] The modifications of (1) to (4) were the same as in Example 1.

[0056] (5) The total discharged wastewater of the plant was subjected to oil separation treatment. At this time, the COD of the treated wastewater was 1800 mg/L. Then the wastewater was subjected to aerobic biological fluidized bed treatment, and the COD was removed by 87%. Polyaluminium chloride (PAC) and PAM were used as coagulant and coagulant aid, respectively, for coagulation and sedimentation treatment. H.sub.2O.sub.2 was then used as an oxidant for a reinforced degradation treatment, wherein H.sub.2O.sub.2 was added in amount of 250 mg/L. Ferrous ions were used as the catalyst in amount of 50 mg/L. The COD of the effluent treated was below 50 mg/L, and phenol and acetone were not detectable.

[0057] The above embodiments are presented only for illustrating the preferred embodiments of the present application, which are not intended to limit the scope of the present application. Without departing from the spirit of the present application, those skilled in the art can make various modifications and improvements to the technical solutions of the present application, which should fall within the protection scope defined by the claims of the present application.