DE19546070A1 - Process for purifying wastewater from 1,2-dichloroethane production - Google Patents

Abstract

The invention relates to a process for the purification of effluent obtained, in the reaction zone, during preparation of 1,2-dichloroethane by oxychlorination, extracted from the reactor with the gaseous stream of crude 1,2-dichloroethane, copper-bearing catalyst waste and other impurities, and subsequently condensed. Said process is characterised in that the condensed effluent separated from 1,2-dichloroethane and charged with the precipitated catalyst waste and other impurities is first treated in a first stage with caustic soda at temperatures of 70-100 DEG C while being mixed intimately.

Description

The invention relates to a process for the purification of wastewater, which in the production of 1,2-dichloroethane obtained by the oxychlorination process in the reaction zone and with the crude 1,2-dichloroethane gas stream and copper-containing catalyst attrition and others ren impurities discharged from the reactor and then condensed.

The industrial production of 1,2-dichloroethane takes place both by reaction of Ethylene and chlorine (direct chlorination) as well as by reaction of ethylene, chlorine water substance and oxygen (oxychlorination).

In the oxychlorination is in the reaction of a copper-containing catalyst in addition 1,2-dichloroethane also formed water. In the vast majority of Produktionsanla is used as the catalyst, a fluidized bed catalyst consisting of copper chloride, different promoters and alumina as a carrier material. As oxidation Medium air, pure oxygen or oxygen-enriched air is used.

In DE-A-40 33 048 a process for the preparation of 1,2-dichloroethane by Oxychlorination of ethylene, hydrogen chloride and oxygen at temperatures of 200 to 250 ° C and pressures of 2 to 5 bar in the presence of a copper (II) chloride on Alu miniumoxid as a carrier existing catalyst in a fluidized by recycle gas Fluidized bed described as a reaction zone. The reaction gases are pressurized in three Cooled condensation stages. In the first condensation stage, together with the Condensed 1,2-dichloroethane and water also deposited the catalyst and discharged with the water.  

DE-A-43 03 086 describes a process for the preparation of 1,2-dichloroethane, in by treating the reaction gases in a washing zone already very pure 1,2-dichloroethane is produced, which without complicated distillation for the preparation of Vinyl chloride can be used. The catalyst content obtained in this process The effluent is stripped to remove chlorinated hydrocarbons from the sewer Process drained.

Finally, DE-A-41 32 030 describes a method for dry removal of the Catalyst attrition from the crude 1,2-dichloroethane gas stream after exiting the reac by means of a dust separator or electrostatic precipitator, whereby after stripping a waste water from the Process is drained, which contains almost no heavy metals and inorganic sludge contains more.

A disadvantage of the above-described prior art, however, is that the sewage in general with environmentally relevant substances, in particular with dioxins or Furans is charged. Also other in the production of 1,2-dichloro-ethane Ver Impurities, especially heavy metals, are often not enough from the wastewater away.

The invention is therefore based on the object to provide a method, not only the catalyst abrasion and the heavy metals, but also at the same time the dioxins and furans resulting from the oxychlorination reaction from the wastewater be removed, so that a purified wastewater discharged from the reaction process can be added and the separated dioxins and furans a separate disposal can be led.

This object is achieved by a method of the type described above, characterized characterized in that the separated from the 1,2-dichloroethane, condensed wastewater, which with the precipitated catalyst abrasion and the other impurities initially in a first stage with caustic soda at temperatures of 70-100 ° C. treated with intensive mixing.  

The method according to the invention is optionally further characterized in that

• a) the other impurities are dioxins, furans, chlorinated hydrocarbons Fe and heavy metals, in particular dissolved copper and dissolved iron is;
• b) Wastewater from other stages of the first stage 1,2-dichloroethane production inflicts;
• c) the discharged from the reactor fine-grained, alumina and copper-containing Ka talysatorabrieb to aluminum hydroxide or copper hydroxide and / or to aluminum or Kupferoxidhydraten is converted;
• d) the treated wastewater with the converted catalyst abrasion of a Sedi mentation stage as a second stage for the removal of dioxins and / or furans feeds;
• e) a flocculant is added;
• f) adding the flocculant already in the condensation of the waste water;
• g) a filter aid is added;
• h) the overflow from the sedimentation stage to remove dissolved 1,2-dichloroethane is added to a stripper;
• i) passing the flow of the stripper through a filter in a sewer;
• j) withdrawing the collected after sedimentation catalyst slurry and with Steamed to remove residual 1,2-dichloroethane;
• k) returning the removed 1,2-dichloroethane to the manufacturing process;  
• l) filtering the treated catalyst slurry, feeding the first stage filtrate and supplying the catalyst slurry to an underground landfill or incineration;
• m) the catalyst sludge collected after sedimentation directly from a Ver incineration feeds.

The method of the invention is explained in more detail below with reference to the drawings (Figures 1 and 2 Fig..):
Via line 1 and preheater 2 , a hydrogen chloride stream is fed to the fluidized-bed reactor 7 . At the same time, oxygen is passed via line 3 and preheater 4 into the reactor 7 after mixing with the hydrogen chloride stream. Via line 5 and preheater 6 , ethylene is introduced into the reactor 7 . The reaction of the aforementioned feed gases to the reaction gas takes place in the reactor 7 on a fluidized bed catalyst which consists of copper chloride and aluminum oxide.

The oxychlorination reaction is exothermic, the temperature is controlled by a hot water circulated at about 210 to 230 ° C. The pressure in the entire system is thereby 3 to 6 bar.

About one or depending on the design of the system and three cyclones, the reaction gas passes via line 8 in the first condensation stage 9 , where it is cooled with water of reaction from separation tank 12 via pump 17 and line 18 to about 95 ° C. In this case, unused hydrogen chloride dissolves, the largest amount of water of reaction condensed Siert, and at the same time is located in the reaction gas catalyst abrasion niederge beat or washed out. Via line 10 and cooler 11 (2nd condensation stage), the gas is cooled to about 35 ° C. 1,2-dichloroethane and residual water condense and are separated in the separation vessel 12 as a two-phase mixture.

The uncondensed gas components are cooled in cooler 13 (3rd condensation stage) to a temperature between 5 and 18 ° C. In the separator 14 is collected nachkonden siertes 1.2 dichloroethane and returned to the separation vessel 12 . The remaining gas is after discharge of small gaseous by-products, for example, carbon monoxide and carbon dioxide, via line 19 as exhaust gas and Lei device 20 , compressor 21 , line 22 , preheater 23 and line 24 as recycle gas to Reak tor 7 returned.

From the separation vessel 12 Rohdichlorethan is pumped via line 15 and pump 16 for destilla tive workup stage, while the water phase is recycled to the condensation stage 9 . The resulting at the bottom of the first condensation stage 9 reaction water in which the catalyst abrasion is suspended, but in which dioxins and furans and a small amount of 1,2-dichloroethane are dissolved, is first introduced via line 26 for further purification in the treatment tank 27th deducted. In this Behäl ter to which contaminated water from the entire vinyl chloride production plant can be supplied via line 30 , takes place with intensive mixing of the addition of small amounts of flocculant via line 29 and sodium hydroxide via line 28th

Here, the discharged from the reactor fine-grained, alumina and copper containing catalyst abrasion to aluminum hydroxide or copper hydroxide and / or alumi converted nium- or Kupferoxidhydraten.

By means of the pump 32 , the catalyst-containing suspension is pumped via line 33 and with the addition of further flocculant via line 34 into the thickener 35 (Sedi mentationsstufe). At the bottom of the thickener 35 then collects the entire catalyst in the form of flakes, while at the upper overflow the clarified solids-free reaction water flows through line 36 for the removal by distillation of small amounts of 1,2- dichloroethane in the stripper 37 . Via line 38 and heat exchanger 39 then a gerei tended wastewater flows into the sewer of the system.

The catalyst collected at the bottom of the thickener 35 is discontinuously discharged via line 41 into the collecting tank 42 and treated there via line 43 with steam at about 100-110 ° C to remove in particular 1,2-dichloroethane. While the resulting 1,2-dichloroethane / water mixture is fed via line 44 with a similar mixture from the stripper 37 via line 40 to the separation vessel 12 , it follows the deduction of the liberated from 1,2-dichloro catalyst sludge by means of pump 45 via line 46th for water removal in a filter press 47 . In this case anfal loin filtrate is returned by means of the pump 48 via line 31 back into the container 27 , while the dehydrated, but impurities containing catalyst sludge from the filter press an underground storage or incineration plant is supplied.

If necessary, a small amount of flocculant of the first stage of condensation can also be added via line 51 . It is also possible to continuously divert the at the bottom of the thickener 35 to concentrated suspension.

The content of dioxins and / or furans, which are usually present in polychlorinated form according to the NATO list in the following examples, in ng or μg TE / kg (or per liter) indicated. TE stands for Toxicity Equivalency. This data represents the sum of different dioxins / furans that are different toxic equivalences.

Example 1 (according to the invention)

5940 Nm³ / h of hydrogen chloride were heated via line 1 and preheater 2 to 140 ° C, 1575 Nm³ / h of oxygen were heated via line 3 and preheater 4 to 140 ° C and introduced together into the reactor 7 . 3000 Nm³ / h of ethylene were heated via line 5 and preheater 6 to 140 ° C and heated 10 000 Nm³ / h of recycle gas via line 24 and preheater 23 to 140 ° C and fed together to the reactor 7 . The temperature in the reactor was 220 ° C, the pressure 4 bar. In the reactor were 40 t fluidized bed Ka catalyst (alumina with a copper content of 4 wt .-%), the heat of reaction was removed via a hot water cycle with steam extraction.

The reaction gas passed through a cyclone after leaving the fluidized bed for the separation of cracked catalyst particles in the upper part of the reactor before it entered via line 8 at a temperature of 210 ° C in the first condensation stage 9 . In this stage, it was cooled with the water from separation tank 12 via line 18 to about 95 ° C and in the other two condensation stages 2 and 3 (cooler 11 and 13 ) to 6 ° C. While 12.9 t of 1,2-Rohdichlorethan were withdrawn from the separation tank 12 hourly for further work-up by distillation via line 15 and pump 16 , 2.7 t of water of reaction with 0.2 wt .-% 1 fell at the bottom of the first purification stage 9 every hour , 2-dichloroethane, 36 ng TE / kg and 1 kg of catalyst abrasion, which could not be separated by the reactor cyclones from the reaction gas, in the form of a wäßri conditions cloudy suspension.

From the remaining after the third condensation stage gas small amounts of gaseous by-products such as carbon monoxide and carbon dioxide were discharged via line 19 and fed to a combustion plant, while the rest of the gas was pressed as circulating gas via line 22 and 24 by means of compressor 21 back into the reactor 7 .

The incurred in the first purification stage 9 aqueous suspension flowed via line 26 into the treatment tank 27 , where it was mixed with intensive mixing with 300 kg / h 25 wt percent strength sodium hydroxide solution and 5 l / h flocculant solution. In this 5 m³ container, 0.5 t of water contaminated with chlorinated hydrocarbons from the distillative workup of the 1,2-crude dichloroethane was also passed via line 30 every hour. If appropriate, further, accumulating in the production plant and contaminated water can be supplied to the aforementioned container.

From the tank 27 , the mixture of water of reaction and other Waswas water was withdrawn with the converted to a slurry suspension catalyst by means of pump 32 and line 33 at the bottom, mixed via line 34 with 30 l / h further flocculation medium solution and in the upper part of the thickener 35 pumped. In this 17 m³ container, the catalyst settled in the form of large-volume flakes on the bottom, while at the upper outlet via line 36 about 3.5 t / h clear, alkaline water phase the stripper 37 for distillation treatment.

By means of steam introduced directly into the bottom part (pressure about 6 bar), 40 kg / h of 1,2-dichloroethane were recovered at the top of the column via line 40 and returned to the container 12 , while at the bottom via line 38 and condenser 39 approx 3.9 t of clear, alkaline wastewater was drained off.

The analysis revealed levels of:

substance amounts 1,2-dichloroethane <0.5 mg / kg organic adsorbable hydrocarbon (AOX) <1.0 mg / kg copper 0.2 mg / kg solid fuel <1.0 mg / kg Dioxane / furan <0.1 ng TE / kg

Relative to the impurities accumulated in the water of reaction at the bottom of the 1st condensation stage 9 , separation rates of:

substance separation rate 1,2-dichloroethane | <99.9% copper <98.0% solid fuel <99.0% Dioxane / furan <99.0%

From the lower part of the thickener 35 every four weeks via line 41 a Sus pension with 670 kg flocky catalyst abrasion in the container 42 was drained, which then directly to remove residual amounts of 1,2- dichloroethane via line 43 with 300 kg / h blasenem Steam was treated for a period of 10 hours.

In this case, 20 kg of 1,2-dichloroethane were distilled off and recycled via line 44 to the container 12 , while the stripped catalyst slurry was pressed by means of pump 45 and line 46 in a membrane filter press 47 and dewatered there. The resulting filtrate was zurückgege ben by means of pump 48 via line 31 in the container 27 , while 1120 kg of moist catalyst sludge was discharged with a solids content of 60% from the press over 49 and bottled in barrels.

In the catalyst slurry, 58 μg TE / kg of dioxane / furan and less than 10 mg 1,2-dichloroethane / kg found.

The low content of 1,2-dichloroethane in the pressed catalyst slurry allowed to dispose of it in an underground landfill.

The added flocculant solution had a concentration of 0.1% active Flockungsmittelkomponente.

Example 2 (Comparative Example according to DE-A-40 33 048)

The prior art, as it results from DE-A-40 33 048, will be described with reference to the case of game 2 and the associated Fig. 1.

5910 Nm³ / h of hydrogen chloride were heated via line 1 and preheater 2 to 140 ° C, 1581 Nm³ / h of oxygen were heated via line 3 and preheater 4 to 140 ° C and introduced together into the reactor 7 . 3000 Nm³ / h of ethylene were heated via line 5 and preheater 6 to 140 ° C and heated 10 000 Nm³ / h of recycle gas via line 24 and preheater 23 to 140 ° C and fed together to the reactor 7 . In the reactor be found 40 t of fluidized bed catalyst (alumina with a Cu content of 4 wt .-%), the heat of reaction was removed via a hot water circuit under Dampfgewin tion. The temperature in the reactor was 218 ° C, the pressure 4 bar.

The reaction gas passed through a cyclone after leaving the fluidized bed for the separation of cracked catalyst particles in the upper part of the reactor before it entered via line 8 at a temperature of 210 ° C in the first condensation stage 9 . In this stage, it was cooled with the water from separation tank 12 via line 18 to about 95 ° C and in the other two condensation stages 2 and 3 (cooler 11 and 13 ) to 6 ° C.

While 12.9 t of 1,2-Rohdichlorethan was withdrawn from the separation tank 12 every hour for further de stillative workup via line 15 and pump 16 , fell at the bottom of the first purification stage 9 every hour 2.7 t acidic water of reaction with 0.2% 1, 2-dichloroethane, 30 ng TE / kg and 0.95 kg of catalyst abrasion, which could not be separated by the reac torzyklon from the reaction gas in the form of an aqueous cloudy suspension.

From the remaining after the third condensation stage gas small amounts of gaseous by-products such as carbon monoxide and carbon dioxide were discharged via line 19 and fed to a combustion plant, while the rest of the gas was pressed as circulating gas via line 22 and 24 by means of compressor 21 back into the reactor 7 .

The incurred in the first purification stage 9 aqueous suspension flowed via line 26 to the stripping column 28 , where it was mixed before entering the column to neutralize over schüssigem hydrogen chloride via line 27 with 205 kg / h 25 wt .-% sodium hydroxide solution. By means of steam injected directly into the bottom part (pressure about 6 bar), 5.5 kg / h of 1,2-dichloroethane were recovered at the top of the column via line 31 and recycled to the container 12 , while at the bottom via condenser 29 and line 30 2.9 t with catalyst and wastewater contaminated with dioxanes / furans.

The analysis revealed levels of:

substance amounts 1,2-dichloroethane 1 mg / kg organic adsorbable hydrocarbon (AOX) 5 mg / kg copper 11 mg / kg solid fuel 300 mg / kg Dioxane / furan 25 ng TE / kg

This contaminated with dissolved copper and dioxane / furans wastewater, in which the suspended and poorly filterable catalyst was, must be subjected to extensive treatments for further purification. In addition, in the course of the operating time, catalyst is deposited in the stripping column 28 , cooler 29 and line 28 , so that blockages and thus also operational interruptions occur.

Example 3 (Comparative Example according to DE-A-41 32 030)

The prior art according to DE-A-41 32 030 will first be described with reference to FIG. 3:
Via line 1 with preheater 2 , hydrogen chloride is fed to the reactor 7 . At the same time oxygen are passed via line 3 with preheater 4 and ethylene via line 5 with preheater 6 in the reactor 7 . In the reactor 7 is the catalyst. The crude 1,2-dichloroethane gas stream flows via cyclone 8 and line 25 into the dust separator 26 . The entrained catalyst particles fall from the cyclone 8 back into the reactor. 7 The catalyst abrasion is separated on the bag filter 27 and accumulates in the dust collector 26 . The bag filters 27 are periodically backwashed with recycle gas via the lines 43 and 44 and compressor 42 for cleaning.

The separated catalyst abrasion falls through the gas lock 28 and downpipe 29 in the desorber 30th The desorbed catalyst abrasion is discharged through the gas lock 31 and down pipe 32 . Via line 33 with heater 34 and line 35 , the gassing medium is blown into the desorber 30 . The gassing medium then flows ßend via line 36 into the dust collector 26th By means of the valves 37 , 38 and 39 , the gassing medium can be supplied to the desorber 30 in a heated or cold state.

The crude 1,2-dichloroethane gas stream, after passing through the dust collector 26 via line 40 of the condensation 9 , which acts as a first condensation zone, where it reacts with the reaction water from separation tank 12 via pump 17 and line 18 to about 90 ° C. is cooled. In this case, the unreacted hydrogen chloride dissolves in the water of reaction. Via line 41 , a portion of the reaction water is discharged, mixed with sodium hydroxide solution via line 42 and freed in the stripping column 43 by direct steam from 1,2-dichloroethane. The 1,2-dichloroethane-water mixture is returned to the process via line 46 , while the contaminated wastewater is discharged via cooler 44 and line 45 .

Via line 10 and cooler 11 , which acts as the second condensation zone, the 1,2-dichloroethane gas stream is cooled to about 40 ° C, condensed and separated in separation tank 12 in a 1,2-dichloroethane water phase. The liquid 1,2-dichloroethane phase is removed via line 15 and pump 16 for further purification; the gaseous Antei le be cooled to 5 to 18 ° C in the cooler 13 , which acts as a third condensation zone, and the condensate in the separator 14 in a liquid phase, which flows into the separation vessel 12 , and a gas phase separated. The gas phase is recycled via line 20 , compressor 21 , line 22 , preheater 23 and line 24 to the reactor 7 . Via line 19 , a partial gas stream is fed to a combustion.

For the comparative example 4900 Nm³ / h of hydrogen chloride were heated via line 1 and preheater 2 to 160 ° C, 1325 Nm³ / h of oxygen were heated via line 3 and preheater 4 to 140 ° C and introduced together into the reactor 7 . 2500 Nm³ / h of ethylene were heated via line 5 and preheater 6 to 160 ° C and heated 10 000 Nm³ / h of recycle gas via line 24 and preheater 23 to 160 ° C and fed together to the reactor 7 . The reactor contained 35 t of fluidized bed catalyst (Aluminiu oxide with a Cu content of 4 wt .-%), the heat of reaction was removed via a hot water circuit with steam extraction. The reaction gas flowed through after leaving the fluidized bed for the separation of entrained catalyst particles in obe ren part of the reactor, the cyclone 8 , before it was pressed via line 25 at a temperature of 210 ° C through the bag filter 27 . In the dust collector, 0.9 kg of catalyst abrasion accumulated every hour. After passing through the dust collector 26 , the reaction gas entered via line 40 in the first condensation stage 9 a. In this stage, it was cooled with the water from separation tank 12 via line 18 to about 95 ° C and in the two far ren condensation stages 2 and 3 (radiator 11 and 13 ) to 6 ° C.

While from the separation vessel 12 hourly 10.7 t 1,2-Rohdichlorethan was withdrawn for further de stillative workup via line 15 and pump 16 , fell at the bottom of the first purification stage 9 every hour 2.3 t acidic water of reaction with 0.25% 1, 2-dichloroethane, 14 ng TE / kg, 0.2 mg copper / kg and less than 5 mg solid / kg. From the remaining after the third condensation stage gas small amounts of gaseous by-products such as carbon monoxide and carbon dioxide were discharged via line 19 and fed to a combustion plant, while the rest of the gas was pressed as circulating gas via line 22 and 24 by means of compressor 21 back into the reactor 7 .

The incurred in the first purification step 9 aqueous solution flowed via line 41 to the stripping 43 , where it was added before entry into the column to neutralize excess hydrogen chloride via line 42 with 165 kg / h 25 wt .-% sodium hydroxide solution. Using direct steam, 5.8 kg of 1,2-dichloroethane were recovered hourly at the top of the column via line 46 and returned to the process container 12 , while at the bottom via cooler 44 and line 45 2.5 t dioxane / furan-contaminated wastewater from was left.

The analysis yielded the following values:

substance amounts 1,2-dichloroethane 0.6 mg / kg organic adsorbable hydrocarbon (AOX) <5 mg / kg copper 0.2 mg / kg solid fuel <5 mg / kg Dioxane / furan 13 ng TE / kg

The polluted wastewater, whose content of dioxane / furan is more than a hundred times higher As in Example 1 according to the invention, requires further treatment before it enters the Duct network can be submitted.  

The catalyst discharged from the dust collector 26 and treated in the desorber 30 at a temperature of 180 ° C. and 5 m 3 / h of nitrogen over a period of 1.5 hours contained 10 mg / kg of 1,2-dichloroethane and 25.3 μg of TE / kg dioxane / furan.

He could then be fed to an underground landfill for disposal.

Claims (14)

1. A process for the purification of wastewater, which is obtained in the production of 1,2-dichloroethane by the oxychlorination in the reaction zone and with the crude 1,2-dichloroethane gas stream and copper-containing catalyst abrasion and other Verun cleanings discharged from the reactor and then condensed is characterized in that the separated from 1,2-dichloroethane, condensed wastewater, which is laden with the precipitated catalyst abrasion and the other Verunrei levels, first in a first stage with sodium hydroxide at temperatures of 70-100 ° C under intensive Blended. 2. The method according to claim 1, characterized in that it is in the other Ver impurities for dioxins, furans, chlorinated hydrocarbons and heavy metals, ins special dissolved copper and dissolved iron, is. 3. The method according to claim 2, characterized in that wastewater from others Steps of 1,2-Dichlorethanherstellung the first stage adds. 4. The method according to at least one of claims 1 to 3, characterized in that that discharged from the reactor fine-grained, alumina and copper-containing Catalyst abrasion to aluminum hydroxide or copper hydroxide and / or to aluminum um- or Kupferoxidhydraten is converted. 5. The method according to at least one of claims 1 to 4, characterized in that the treated wastewater with the converted catalyst abrasion of a Sedi mentation stage as a second stage for the removal of dioxins and / or furans feeds.   6. The method according to claim 5, characterized in that a flocculant supplied is set. 7. The method according to claim 6, characterized in that be the flocculant be already added during the condensation of the wastewater. 8. The method according to at least one of claims 5 to 7, characterized in that a filter aid is added. 9. The method according to at least one of claims 5 to 8, characterized in that the overflow from the sedimentation stage to remove dissolved 1,2-dichloroethane a stripper supplies. 10. The method according to claim 9, characterized in that the sequence of the strip pers via a filter into a sewer. 11. The method according to at least one of claims 1 to 10, characterized that deducting the collected after sedimentation catalyst slurry and treated with steam to remove residual 1,2-dichloroethane. 12. The method according to claim 11, characterized in that the remote 1,2-dichloroethane in the manufacturing process leads back. 13. The method according to claim 11 or 12, characterized in that treating the Filtered catalyst slurry, the filtrate fed the first stage and the cata- sludge from an underground landfill or incineration. 14. The method according to at least one of claims 1 to 10, characterized in that the catalyst sludge collected after sedimentation is added directly to a Ver incineration feeds.