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WO1997038770A1 - Suppression du dinitrotoluene contenu dans l'eau de process - Google Patents

Suppression du dinitrotoluene contenu dans l'eau de process Download PDF

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Publication number
WO1997038770A1
WO1997038770A1 PCT/US1997/005796 US9705796W WO9738770A1 WO 1997038770 A1 WO1997038770 A1 WO 1997038770A1 US 9705796 W US9705796 W US 9705796W WO 9738770 A1 WO9738770 A1 WO 9738770A1
Authority
WO
WIPO (PCT)
Prior art keywords
water
nitric acid
βaid
dinitrotoluene
concentration
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US1997/005796
Other languages
English (en)
Inventor
Allen B. Quakenbush
Majid N. Keyvani
Michael C. Fullington
James L. Meyer
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Lyondell Chemical Technology LP
Original Assignee
Arco Chemical Technology LP
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US08/827,326 external-priority patent/US5763696A/en
Application filed by Arco Chemical Technology LP filed Critical Arco Chemical Technology LP
Priority to AU24468/97A priority Critical patent/AU2446897A/en
Publication of WO1997038770A1 publication Critical patent/WO1997038770A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/34—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping with one or more auxiliary substances

Definitions

  • This invention relates generally to the production of dinitrotoluene. More particularly, the invention relates to an improved distillation process for removing dinitrotoluene impurity from process effluent water.
  • Dinitrotoluene is a versatile and valuable chemical intermediate which is widely used in the production of toluene diisocyanate. However, if it i ⁇ allowed to flow uncontrolled in the environment, for example if present as an impurity in a stream or pond, it may pose a potential pollution problem and a hazard to aquatic life.
  • DNT is produced by a process involving the nitration of toluene first to mononitrotoluene and then to DNT. Historically, the nitration reaction has been carried out commercially using a mixed acid system, namely, nitric acid and sulfuric acid.
  • the nitration reaction results in the generation of a substantial amount of water, i.e., water produced as a by-product of the nitration reaction, water contained in the nitric acid feed stock and water used throughout the production process for various utility functions. All this water, which is often referred to as the "process _ _
  • effluent water or simply "process water” is collected and ultimately discharged as a process effluent stream.
  • process water must be treated to remove objectionable impurities and thereby meet environmentally acceptable standards or permitted discharge requirements.
  • distillation is often considered to be the most efficient and cost-effective purification operation.
  • DNT process effluent water contains dissolved DNT in concentrations which, although relatively low, could pose a pollution or environmental problem. Accordingly, this invention is directed to a relatively simple and economically attractive improvement for solving this problem. And in a broader sense, the invention provides an improved process for substantially reducing the DNT concentration in any aqueous medium or stream containing DNT as an impurity.
  • a process has been found for substantially reducing the concentration of DNT ⁇ .n water containing such DNT as an impurity, which comprises distilling off the water in the presence of nitric acid. Further according to the invention, an improved distillation process is provided whereby process effluent water generated in the production of DNT can be separated in suitable condition for biological treatment and proper disposal.
  • the present invention relates to a process for reducing the concentration of dinitrotoluene in water containing said dinitrotoluene as an impurity, which process comprises distilling the water in the presence of nitric acid.
  • the present invention relates to a process for reducing the concentration of dinitrotoluene in water in a composition containing said dinitrotoluene and said water which comprises distilling at least a portion of said water in said composition in the presence of nitric acid to provide vaporized water containing a reduced concentration of said dinitrotoluene.
  • the present invention relates to a process for reducing the concentration of dinitrotoluene from a composition containing said dinitrotoluene and said water which comprises:
  • the invention is based on two discoveries relating to the separation and removal of process water which is generated during the production of DNT.
  • the first discovery is that when contained in water in low concentrations, DNT has a volatility which i ⁇ close to, and in the case of the 2,6- isomer, higher than, the volatility of water.
  • the second discovery is that the volatility of DNT, when contained in water in low concentrations, can be reduced by the addition of nitric acid.
  • this discovery not only provides the means for separating and removing process water which is substantially free of DNT, but also enables the achievement of this objective in a simple and cost efficient way.
  • the need for elaborate purification equipment is eliminated and the nitric acid employed in carrying out the distillation is the very acid used in the nitration reaction. As such it is easily and conveniently recycled to the nitration reactor either directly or after undergoing concentration, if necessary.
  • the process of the invention can be advantageously used tp treat any aqueous medium or stream containing dinitrotoluene in a concentration which cannot be readily removed by phase separation.
  • dinitrotoluene has limited solubility in water. That i ⁇ to say, it ordinarily will dissolve in water but only up to a limited concentration level.
  • This concentration level limit technically known or referred to as the saturation point, varies depending on the DNT isomer mix and also depending on temperature and other phy ⁇ ical or chemical conditions. For example, while under normal conditions the saturation point may range up to about 1,200 parts per million by weight (ppm) , if a substantial amount of nitric acid i ⁇ pre ⁇ ent, it would raise the ⁇ aturation point dramatically.
  • the process of the invention can be used to reduce the level of DNT pre ⁇ ent in any concentration, and any i ⁇ omer mix, in water.
  • impurity a ⁇ used herein with reference to the presence of DNT in the process water, i ⁇ intended to mean and include any concentration which will re ⁇ ult in ⁇ ome DNT being dissolved in the water.
  • the 2,4- i ⁇ omer differe from the 2,6- i ⁇ omer in that it ⁇ volatility (when pre ⁇ ent in relatively low concentrations in water) remains above, although quite clo ⁇ e to, the volatility of water.
  • the proces ⁇ of the invention i ⁇ especially adapted for distilling water containing DNT a ⁇ an impurity in a concentration up to about the ⁇ aturation point.
  • a critical parameter in practicing the distillation proce ⁇ of the invention i ⁇ to effect thi ⁇ operation in the pre ⁇ ence of nitric acid has been developed to ⁇ ugge ⁇ t that an alternative source of nitrate ions, other than nitric acid, may also be effective.
  • nitric acid in any suitable concentration i ⁇ added to the water before or during the distillation operation. It ha ⁇ been found, moreover, that there i ⁇ an inverse relationship between the concentration of nitric acid pre ⁇ ent and the concentration of DNT in the overhead water. That is to say, within certain limits, the greater the concentration of nitric acid in the water being distilled, the lower the concentration of DNT in that water after distillation.
  • any concentration of acid may be used, it i ⁇ preferable to employ such amounts of nitric acid as to provide an acid concentration in the water of at least about 10 percent by weight and more preferably from about 15 to about the azeotropic concentration of nitric acid in water, i.e., normally about 70 percent by weight.
  • the most preferred acid concentration range is from about 25 to about 60 percent by weight.
  • the necessary amount of acid which is calculated to provide the desired concentration i ⁇ simply added to the water either before commencement of the distillation operation or shortly thereafter.
  • the desired acid concentration is achieved by both including some acid in the water entering the column and injecting more acid into the column at a point above the water level as mentioned above.
  • the distillation can be carried out using any suitable or conventional apparatus or equipment ranging from a simple fla ⁇ h still to a fractional distillation column, which can be single-stage or multi-stage, with trays, packing or other mass _ _
  • Multi-stage distillation is preferred, particularly when the objective is to achieve a reduction of DNT concentration to less than about 100 ppm.
  • DNT concentrations of below about 60 ppm by weight, and even below about 50 ppm (e.g., between 25 and 45 ppm) are achieved using multi-stage distillation.
  • the di ⁇ tillation i ⁇ performed at any ⁇ uitable temperature.
  • the actual boiling temperature of water will depend on the concentration of the nitric acid therein, and it is also governed by, and i ⁇ a function of, the di ⁇ tillation pressure. As for the latter, it may range from a ⁇ low a ⁇ about 25 mm. of mercury to about 40 p ⁇ ia, with a preferred range of from about 150 mm. of mercury to about 25 p ⁇ ia.
  • the proce ⁇ of the invention may be carried out batch-wi ⁇ e or a ⁇ a continuou ⁇ operation, the latter being preferred.
  • the di ⁇ tillation can proceed, if de ⁇ ired, until azeotropic conditions are attained, i.e., until sufficient water ha ⁇ been evaporated ⁇ o that the concentration of the acid in the remaining water reaches or approaches the azeotropic concentration.
  • the distillation i ⁇ stopped and the purified overhead water i ⁇ taken out for further processing or biotreatment, as required, before it i ⁇ properly di ⁇ charged.
  • the water to be distilled is continuously fed to the di ⁇ tillation column at a rate which approximately equals the combined rate of bottoms and overheads coming out of the column.
  • the water entering the column may already contain the de ⁇ ired concentration of nitric acid in it, or, alternatively, the acid may be injected into the column a ⁇ a separate stream.
  • i ⁇ preferred, i ⁇ to provide for the pre ⁇ ence of nitric acid in two ways by (a) adding some acid to the water entering the di ⁇ tillation column (for example ⁇ uch a ⁇ to provide an acid concentration from about 5 to about 25 percent by weight) , and (b) injecting further amounts of acid into the column, preferably at a point where it will come in contact with the rising vapor.
  • the di ⁇ tillation column bottoms (whether resulting from a batch or continuous operation) , containing higher concentrations of both nitric acid and DNT, can be recycled as such to the toluene nitration reactor or, depending on the desired acid concentration in the recycle stream nd/or in the reactor, the bottoms may first be concentrated before being recycled to the reactor.
  • the following examples are provided merely to illu ⁇ trate the invention. All part ⁇ and percentage ⁇ are by weight unless otherwise specified. r
  • a water stream containing 2,6-DNT in a concentration of 0.0099 mole percent (based on the combined moles of water and DNT) is fed continuou ⁇ ly to a ⁇ imple, flash still, with nitric acid being continuously _ _
  • the overhead ⁇ tream contained 0.0083 mole percent of 2,6-DNT; wherea ⁇ , the bottom ⁇ ⁇ tream contained 0.0102 mole percent.
  • the ⁇ ame run wa ⁇ repeated, but this time no nitric acid wa ⁇ used.
  • the overhead stream contained 0.0119 mole percent of 2,6-DNT, while the bottoms contained 0.0079 mole percent.
  • a distillation column is used consi ⁇ ting of a lower section housing a boiling still and an upper section containing a series of distillation trays for enhanced vapor-liquid contact.
  • an aqueous solution containing 5,000 ppm of DNT and 14% nitric acid is fed to the column at the rate of 4.5 grams per minute.
  • Example 2 the identical procedure of Example 2 is followed, except that in addition to the 14% acid concentration in the water, more acid is added. Specifically, a 70% solution of nitric acid i ⁇ injected at the rate of 3.5 grams per minute, this acid solution entering the column at the top of the trayed section, thereby coming in contact with the rising vapors. The overhead stream is found to contain only 40 ppm of DNT.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

La présente invention concerne la réduction de la teneur de l'eau en impureté que constitue le dinitrotoluène, et ce par une distillation en présence d'acide nitrique. Le procédé choisi pour cette réduction consiste (a) à mettre la composition considérée en contact avec de l'acide nitrique pour réaliser une composition contenant de l'acide nitrique, (b) à distiller au moins une partie de l'eau considérée dans la composition contenant de l'acide nitrique pour obtenir une vapeur d'eau à moindre concentration en dinitrotoluène, et (c) à séparer la vapeur d'eau de la composition contenant de l'acide nitrique.
PCT/US1997/005796 1996-04-12 1997-04-07 Suppression du dinitrotoluene contenu dans l'eau de process Ceased WO1997038770A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU24468/97A AU2446897A (en) 1996-04-12 1997-04-07 Removal of dinitrotoluene from process water

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US1531496P 1996-04-12 1996-04-12
US60/015,314 1996-04-12
US08/827,326 1997-03-26
US08/827,326 US5763696A (en) 1997-03-26 1997-03-26 Removal of dinitrotoluene from process water

Publications (1)

Publication Number Publication Date
WO1997038770A1 true WO1997038770A1 (fr) 1997-10-23

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1997/005796 Ceased WO1997038770A1 (fr) 1996-04-12 1997-04-07 Suppression du dinitrotoluene contenu dans l'eau de process

Country Status (2)

Country Link
AU (1) AU2446897A (fr)
WO (1) WO1997038770A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7928270B2 (en) 2006-03-07 2011-04-19 Basf Aktiengesellschaft Process for distillatively removing dinitrotoluene from process wastewater from the preparation of dinitrotoluene by nitrating of toluene with nitrating acid

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3620928A (en) * 1970-07-13 1971-11-16 Badger Co Method of separating isomers of mononitrotoluene
US4236973A (en) * 1979-05-14 1980-12-02 The Dow Chemical Company Method of removing contaminants from water
US4261908A (en) * 1977-02-04 1981-04-14 Bayer Aktiengesellschaft Process for isolating aromatic dinitro compounds
US4344827A (en) * 1976-08-21 1982-08-17 Bayer Aktiengesellschaft Process for working up nitric acid
US5345012A (en) * 1993-03-22 1994-09-06 Bayer Aktiengesellschaft Process for the preparation of dinitrotoluene
US5354924A (en) * 1988-06-22 1994-10-11 Olin Corporation Process for the production of dinitrotoluene

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3620928A (en) * 1970-07-13 1971-11-16 Badger Co Method of separating isomers of mononitrotoluene
US4344827A (en) * 1976-08-21 1982-08-17 Bayer Aktiengesellschaft Process for working up nitric acid
US4261908A (en) * 1977-02-04 1981-04-14 Bayer Aktiengesellschaft Process for isolating aromatic dinitro compounds
US4236973A (en) * 1979-05-14 1980-12-02 The Dow Chemical Company Method of removing contaminants from water
US5354924A (en) * 1988-06-22 1994-10-11 Olin Corporation Process for the production of dinitrotoluene
US5345012A (en) * 1993-03-22 1994-09-06 Bayer Aktiengesellschaft Process for the preparation of dinitrotoluene

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7928270B2 (en) 2006-03-07 2011-04-19 Basf Aktiengesellschaft Process for distillatively removing dinitrotoluene from process wastewater from the preparation of dinitrotoluene by nitrating of toluene with nitrating acid

Also Published As

Publication number Publication date
AU2446897A (en) 1997-11-07

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