Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/02—Treatment of water, waste water, or sewage by heating
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/26—Treatment of water, waste water, or sewage by extraction

Definitions

• the invention relates to a process for the treatment of wastewater from the nitration.
• nitrobenzene NB
• dinitrobenzene DNB
• MNT and DNT mono- and dinitrotoluene
• NNB nitrochlorobenzene
• Nitroxylol in small amounts and mono-, di- and tri nitrophenols, mono-, di- and Trinitrokresole and mono-, di- and Trinitroxylenole and other hydroxyl and nitro containing compounds, hereinafter also referred to as nitrophenols formed. These must be removed from the nitroaromatics prior to their further use.
• aromatic nitro compounds which do not contain a hydroxyl group in the molecule are also referred to below as nitro bodies or neutral nitro bodies.
• the nitrophenols are completely removed from the crude nitroaromatic mixture after removal of the nitrating acid by selective washing with sodium hydroxide solution, an aqueous bicarbonate solution or an aqueous ammonia solution.
• the resulting aqueous solution always contains nitro bodies in addition to the nitrated phenols. This aqueous solution must be treated in order to then be able to supply it to the water treatment.
• nitrophenols, nitro cresols, nitroxylenols and especially their salts are intensely colored and highly toxic to the environment.
• the trinitrophenols, and especially their salts are explosives in higher concentrations or as pure substances and must be removed from them before discharge of the waste water and destroyed in such a way that they pose no danger to the environment and their explosive properties.
• the aim of the invention was therefore to find a method for removing or destroying the mono-, di- and trinitrophenols, which avoid an additional use of acids and bases and salification on the technically necessary level.
• EP 0 005 203 describes a process in which the sodium salts of mono-, di- and trinitrophenols, mono-, di- and trinitrocresols and mono-, di- and tri- nitro Nitroxylenole be successfully decomposed in the waste liquors from the nitration process of the corresponding aromatics with exclusion of oxygen by heating under pressure to temperatures of 150 to 500 0 C, so that a deposition of dirt and cracking products on the heat exchanger and reactor walls is avoided.
• the disadvantage of this method is that the degradation of the nitro bodies is not complete when radical scavengers such as oxygen are present, and that in addition to carbon dioxide and carboxylic acids and dicarboxylic acids such as oxalic, succinic and / or benzoic arise, which are difficult to biodegrade.
• radical scavengers such as oxygen
• carboxylic acids and dicarboxylic acids such as oxalic, succinic and / or benzoic
• EP 0 503 387 a process for the degradation of mono-, di- and trinitrophenols in waste water from plants for the production of nitrobenzene by treatment with nitric acid, for example with a concentration of 1, 5% of nitric acid, under pressure of 40-250 bar described and 180-350 0 C.
• EP 0 953 546 describes a process for the degradation of neutral aromatic nitro compounds, such as nitrobenzene, mononitrotoluene and dinitrotoluene, dissolved in wastewaters from nitration plants, in the presence of mono-, di- and trinitrophenols.
• the effluents are adjusted to a pH of 7-14 and are heated to temperatures of 150-350 0 C under a pressure of 10-300 bar.
• Both the neutral nitro bodies which do not carry an OH group and the nitrophenols are degraded to less than 1 ppm under the conditions described after one hour of reaction time.
• thermolysis in the presence of nitric acid is that standard stainless steels such as 1.4571 can be used for the required apparatus and no expensive special materials are required.
• a further advantage of the process described in EP 0 953 546 is that the effluents from the nitration fed into the thermolysis no longer have to be pretreated and the inhibition of the decomposition of the nitrophenols by oxygen is suppressed.
• EP 1 132 347 describes a process in which after removal of the water-vapor-volatile neutral nitro bodies from the wash liquor of the alkaline washing stage by distillation, this wash liquor undergoes a thermal degradation treatment in the supercritical region or in the subcritical region for water at temperatures and pressures at which the nitrophenols are decomposed.
• nitrobenzene in an alkaline wastewater of about 3000 ppm after distilling off about 80% of the water from the alkaline wastewater only to about 360 ppm.
• a nitrophenol-containing alkaline wastewater containing this content of nitrobenzene is not suitable for a thermolysis at temperatures between 280 and 350 0 C and pressures between 80 and 120 bar.
• EP 1 593 654 a process is described in which in an alkaline wastewater from the production of nitrobenzene after a pre-separation before feeding this alkaline waste water into a thermal treatment at 275 ° C and 110 bar the still dissolved in this wastewater nitrobenzene by stripping with Steam is removed to a level of less than 2 ppm.
• thermolysis of an alkaline wash water from the wash of a crude nitroaromatic mixture so that the deposition of pyrolysis products is avoided, that no additional new waste streams arise that require additional treatment no additional aids such as oxidants are needed and the energy required and the investment costs can be minimized by dispensing with the use of expensive special materials in the thermolysis.
• the neutral nitro bodies which are at the same time also a valuable product, should be separated from the alkaline washing water so that they are available as a product and can be recycled to the nitration.
• the object was inventively achieved in that the alkaline wastewater from the washing of a crude nitroaromatic mixture after nitration, which dissolved both the washed out highly nitrated phenols and the neutral nitro bodies such as NB, DNB, MNT, DNT, nitroxylols or nitrochlorobenzenes and / or micro - contains emulsion with the aromatics to be nitrated, such as benzene, toluene, xylene, and / or chlorobenzenes or in the case of multiply nitrated aromatics such as DNB or DNT optionally with a nitro group containing less nitroaromatic, such as in the case of DNT with MNT extracted, the alkaline wastewater after separation of the extractant by stripping, for example with steam, freed from the still dissolved in the waste water traces of the volatile extractant and the only still containing the highly nitrated phenols alkaline wash water is fed into a thermolysis, in
• the invention accordingly provides a process for working up wastewaters from the nitration of aromatic compounds to give mono-, di- and trinitric aromatics having a pH of 7-13 by heating the effluents to temperatures of 150 to 350 ° C C under a pressure of 10-300 bar, characterized in that prior to heating, the dissolved in these wastewater aromatic nitro compounds containing no hydroxyl group are removed by extraction from the effluents.
• the extractant together with the dissolved nitroaromatic is fed into the nitration.
• the water obtained during the stripping, still containing extractant, together with the extractant removed during the stripping is added back to the alkaline wash water prior to extraction.
• the alkaline wastewater obtained after washing the crude nitroaromatic mixture with a base contains up to 1.0% of nitroaromatic dissolved and / or suspended, up to 5000 ppm of nitrophenols , Picric acid, mono-, di- and Trinitrokresole, mono-, di- and Trinitroxylenole, Nitrobenzoe Text- ren and / or salt-forming degradation products from the oxidation of the nitro body in the course of nitration and has, depending on the base used, a pH -Value from 7-13.
• the pH of the water is adjusted to 7-12, preferably to 8.5-1. This ensures that only the neutral nitro bodies and not the nitrophenols or other weak acid decomposition products are extracted.
• the extraction of the alkaline wastewater with the extractant, in particular the aromatic to be nitrated, is carried out in one to four stages, preferably in two stages, and in particular in countercurrent.
• Mixers / settlers can be used as extractors. But also static mixers in conjunction with suitable separating apparatus or stirred multi-stage or pulsed packed and sieve tray columns or columns without energy input can be used to carry out the extraction.
• the extractant used in a preferred embodiment of the invention is in each case the aromatic to be nitrated. That is, in the nitration of benzene to NB or DNB is benzene, in the nitration of toluene to MNT or DNT is toluene, or in the case of multi-nitrated aromatics such as DNB or DNT, in addition to the non-nitrated aromatic, one nitro group less containing nitroaromatic, such as in the case of DNT the MNT, used.
• the extraction is preferably carried out in a temperature range of 20-80 0 C, more preferably at the temperature at which the washing of the crude Nitroaroma- is performed tengemisches with the base, to prevent deposition of neutral nitro body from the wash liquor, at the partial cooling ,
• the ratio extractant / wastewater should be chosen so that extraction of the neutral nitro bodies can be achieved up to the desired limit with the lowest possible number of extraction stages.
• the weight ratio of extractant used to aqueous phase can be varied in the range from 1.2: 1 to 0.04: 1, preferably from 0.6: 1 to 0.15: 1, wherein the amount of extractant used for a Ton of nitrated product should not exceed the required amount of aromatics.
• the extractant laden with extracted nitroaromat after phase separation can be recycled within each countercurrent stage and only that corresponding to the intended ratio of extractant / Wastewater freshly added extractant is discharged and returned to the nitration.
• the aqueous phase after extraction usually contains about 500-2000 ppm extractant.
• the extractant is removed by steam stripping from the extracted aqueous phase. The energy requirement for stripping the volatile extractants is substantially lower than that for stripping the nitro compounds made therefrom.
• the condensate extractant / water obtained in the steam stripping is preferably recycled to the waste water extraction.
• the liberated from the extractant alkaline wash water with a pH of 7-13, which contains substantially only the highly nitrated nitrophenols and other salt-forming degradation products from the nitration is fed batchwise or continuously in a thermolysis in which the nitrophenols at temperatures of 150 to 350 0 C, pressures of 10-300 bar and residence times 20-60 minutes, preferably at temperatures of 250-320 0 C and pressures of 80-120 bar are degraded.
• the effluent leaving the thermolysis reactor containing less than 10 ppm, preferably less than 2 ppm, of undecomposed nitrophenols is used to preheat the untreated sewage and subsequently to undergo a biological treatment prior to discharge to a receiving water.
• a waste water with a DNT content of less than 5 ppm, with 500 ppm nitrocresols, a COD of 4300 mgOVI and a pH value of 10.0 was obtained in a tubular reactor at 300 0 C, a pressure of 100 bar and a residence time of 30 minutes was treated.
• thermolysis resulted in a wastewater containing DNT less than 1 ppm, nitro cresols less than 1 ppm, nitrate 1400 ppm, nitrite 800 ppm, ammonia 210 ppm, a COD of 3500 mgOVI and a pH of 9.0.
• a separation of pyrolysis products in the reactor and in the heat exchangers could not be observed.

Applications Claiming Priority (2)

Publications (1)

Family

ID=39938136

Family Applications (1)

Country Status (1)

Cited By (12)

Citations (5)

• 2008
  • 2008-08-27 WO PCT/EP2008/061185 patent/WO2009027416A1/de active Application Filing

Patent Citations (5)

Non-Patent Citations (1)

Similar Documents

Legal Events