Patent Application
20070265466
The present invention relates to a process for the coupled production of isocyanate(s) and chlorine comprising the following steps:
The nitration of each individual aromatic compound in step a) is conducted in mutually independent reactors which are not connected to one another. The nitration is conducted in the presence of sulfuric acid. The concentration of the sulfuric acid is dependent upon the compound to be nitrated and the nitration level. Concentrations of from 65.0 to 98.0 percent by mass of sulfuric acid, based on the total mass of sulfuric acid plus water, are generally used to catalyze the nitration reaction. Upon completion of the nitration, the sulfuric acid is diluted and has a concentration that, depending on the amount of sulfuric acid used and the number of nitration stages, is 0.5 to 25 percentage points less concentrated than the initial concentration of the sulfuric acid used.
The process of the present invention is advantageous if the chlorine gas is produced in step f) by any of the following processes: NaCl electrolysis; HCl electrolysis by the membrane or diaphragm method; HCl electrolysis in electrolytic cells with an oxygen depletion cathode; and/or catalytic HCl oxidation with oxygen.
The process of the present invention is particularly advantageous when the nitration product(s) produced in step a) are nitrobenzene, dinitrobenzene, nitrochlorobenzene, nitrochlorotoluene, nitrotoluene and/or dinitrotoluene.
The process of the present invention is advantageous if the dilute sulfuric acid obtained by step g) is freed from residual chlorine and/or HCl down to a residual concentration of <1000 ppm Cl before being combined with other sulfuric acid in the sulfuric acid concentration plant.
The process of the present invention is particularly advantageous if the dilute sulfuric acid obtained by step g) is freed from residual chlorine and/or HCl down to a residual concentration of <10 ppm Cl before combination with other sulfuric acid in the sulfuric acid concentration plant.
The process of the present invention is advantageous if, before being returned to step 1) of the process according to the invention, either the dilute sulfuric acid obtainable from step a) or the concentrated sulfuric acid obtained by step k) is freed from impurities using: inorganic nitrogen compounds such as nitrosyl sulfuric acid down to a residual concentration of <0.3 wt. %; or using highly volatile organic compounds such as dinitrotoluene, nitrobenzene, dinitrobenzene, nitrophenols, nitrocresols, nitrobenzyl alcohols, nitrobenzaldehydes down to a residual concentration of <50 ppm; or using low-volatility organic compounds such as hydroxynitrobenzoic acid, nitrobenzoic acids or aliphatic carboxylic acids down to a residual concentration of <500 ppm; or using volatile sulfur compounds such as SO2 down to a residual concentration of <30 ppm.
The process of the present invention is advantageous if toluene is used in step a) and after dinitration in step a) to produce dinitrotoluene using sulfuric acid with a concentration of 86.0 to 96.0 percent by mass of sulfuric acid (based on the total mass of sulfuric acid plus water) in the first nitration stage, which in the course of the second nitration stage is diluted to a concentration of from 80.0 to 85.9 percent by mass of sulfuric acid (based on the total mass of sulfuric acid plus water), the dinitrotoluene is then reacted in accordance with step c1) with hydrogen to form toluene diamine (TDA) which is then reacted with phosgene according to step d) to form toluene diisocyanate (TDI).
The sulfuric acid obtained from the second nitration stage having a concentration of from 80.0 to 85.9 percent by mass of sulfuric acid (based on the total mass of sulfuric acid plus water) is preferably returned once more to the first nitration stage of the process according to step a) and then diluted to a concentration of from 70.0 to 79.9 percent by mass of sulfuric acid (based on the total mass of sulfuric acid plus water) and this sulfuric acid is then fed to the sulfuric acid concentration plant in accordance with step b).
The process of the present invention is also advantageous if benzene is nitrated in step a) and after mononitration in step a) to obtain nitrobenzene using sulfuric acid with a concentration of from 69.5 to 72.5 percent by mass of sulfuric acid (based on the total mass of sulfuric acid plus water) which in the course of nitration is diluted to a concentration of 66.5 to 69.4 percent by mass of sulfuric acid (based on the total mass of sulfuric acid plus water), the nitrobenzene is then reacted with hydrogen to form aniline, which in turn is reacted with formaldehyde in the presence of an acid catalyst to form diamines and polyamines of the diphenylmethane series, which in turn are then reacted with phosgene to form the corresponding di- and polyisocyanates of the diphenylmethane series.
For the chlorine production element of the process according to the invention, any of the chlorine production processes known to the person skilled in the art can be used. Examples of known processes for the production of chlorine include: NaCl electrolysis; conversion of HCl to chlorine by electrolysis of aqueous HCl with diaphragms or membranes as the separating medium between the anode and cathode compartment; conversion of HCl to chlorine by electrolysis of aqueous HCl in the presence of oxygen in electrolytic cells with an oxygen depletion cathode (ODC); and conversion of HCl gas to chlorine by gas-phase oxidation of HCl with oxygen at elevated temperatures on a catalyst.
Particularly preferred is the production of chlorine by reaction of HCl gas by gas-phase oxidation with oxygen at temperatures in the range from 180° C. to 500° C. in a Deacon process or in a process derived from the Deacon process (as described, for example, in EP-743277-B1; DE 19734412-A1; DE 19748299-A1; DE 10242400; and DE 10244996) on a fixed catalyst containing at least one metal in elemental or bound form selected from Cu, Ru, Au, Rh, Pd, Pt, Os, Ir, Ag, Re, Ce, Bi, Ni, Co, Ga, Fe and Nd. The metals or metal compounds can be unsupported or be supported on, e.g., metal or semi-metal oxides such as aluminum oxides, silicon oxides, titanium oxides, zirconium oxides or tin oxides, on mixed metal oxides, on ceramic materials, on activated carbons, carbon blacks or carbon nanotubes, on metal or semi-metal carbides, on metal or semi-metal nitrides or on metal or semi-metal sulfides.
If catalytic gas-phase oxidation is used to react the hydrogen chloride formed in step e), the gaseous hydrogen chloride from the phosgenation process is generally transferred to the HCl oxidation process. Before gas-phase oxidation is performed with the hydrogen chloride gas, purification operations can optionally be carried out, for example to remove phosgene, residual solvent such as chlorobenzene or o-dichlorobenzene, chlorinated hydrocarbons, organic and inorganic sulfur or nitrogen compounds or carbon oxides such as CO or CO2. Possible separation or purification operations that can be used are, for example, adsorption, adsorption/desorption, freeze condensation, compression, pressure distillation or selective oxidation. The catalytic gas-phase oxidation and processing of the product gas stream can be performed in accordance with any of the techniques known to those skilled in the art. Examples of such techniques are described in EP-B1 743277; U.S. Pat. No. 6,852,667; DE-A 19734412; WO 2005014470; DE-A 10244996; US-A 200411411; and EP-B 767138.
The nitration process of step a) can be used to produce a wide array of nitro aromatics, particularly those selected from the group of nitrobenzene, dinitrobenzene, nitrochlorobenzene, nitrochlorotoluene, nitrotoluene and dinitrotoluene. All processes for sulfuric acid-catalyzed nitration known to the person skilled in the art, such as that described for example in EP-A 0708076, can be used.
The coupling of one or more different chlorine production processes to one or more nitro aromatic production processes or isocyanate production processes is also possible.
The acid can be concentrated by any of the common processes of the prior art for removing water from sulfuric acid. Examples of these include single-stage or multi-stage vacuum distillation or flash evaporation, heating with microwaves or electromembrane methods. The use of single- or multi-stage vacuum distillation and/or flash evaporation is particularly preferred, however.
In a particularly preferred embodiment of the process of the present invention, concentrated sulfuric acid in the concentration range from 90.0 to 98.0 percent by mass of sulfuric acid (based on the total mass of sulfuric acid plus water) is used to dry the chlorine gas and the dilute sulfuric acid having a concentration in the range from 70.0 to 90.0 percent by mass of sulfuric acid (based on the total mass of sulfuric acid plus water) generated from the chlorine gas drying is fed to a sulfuric acid concentration unit in a nitration plant (e.g., a plant for the dinitration of toluene). The amount of acid supplied to the nitration/acid concentration process corresponds to all or part of the sulfuric acid losses from the nitration/acid concentration process.
In an alternative mode of operation, the sulfuric acid from the chlorine drying process can also be introduced directly into one or more reaction stages of the nitration process and used as a catalyst for the nitration reaction, the dilute sulfuric acid that is formed then being supplied to an acid concentration stage. In this way, by combining the processes, disposal and associated neutralization with sodium hydroxide solution or special processing of the sulfuric acid from the chlorine gas drying process is avoided and the amount of fresh sulfuric acid purchased for the nitration process is minimized.
Impurities in the dilute sulfuric acid from the chlorine production process according to step g), such as residual chlorine, can optionally be separated off before introduction of the dilute sulfuric acid into the sulfuric acid concentration plant in a nitration plant or a nitration process, in order to prevent corrosion and chlorine contamination in the nitration process. This purification of the sulfuric acid can take place by a wide variety of methods, such as those described in DE-A 2 063 592 (adsorption on activated carbon) or Khorasani et al., Journal of Bangladesh Academy of Sciences, 1982, 6 (1-2), 205-207 (stripping with air). To avoid corrosion problems, resistant materials such as the special nickel alloys disclosed in JP 2006045610 can also be used in the sulfuric acid concentration plant. Removal of residual chlorine by stripping is preferred. Here the sulfuric acid is freed from residual chlorine and HCl so that a residual chlorine concentration in the range of <1000 ppm, preferably less than 100 ppm, most preferably less than 10 ppm, is obtained.
In another embodiment of the present invention, the dilute sulfuric acid from the chlorine gas drying from step g) and the dilute sulfuric acid from the nitration process of step b) are combined in a single sulfuric acid concentration plant and processed and part of the concentrated sulfuric acid is returned to the nitration process of step a) and part to the chlorine drying of step g) or to a further nitration plant producing a different aromatic nitro compound from the first nitration plant. This particular embodiment of the process allows, with a single sulfuric acid concentration plant, (i) chlorine to be dried, (ii) dinitrotoluene to be produced in the first nitration plant, and (iii) nitrobenzene to be produced in a second nitration plant, using the dilute sulfuric acid obtainable from the chlorine drying process, optionally before the concentration step k), as a catalyst in both nitrations. This process is advantageous if the amount of dilute sulfuric acid from the chlorine drying exceeds the sulfuric acid losses from one of the nitration processes. This in turn reduces the use of fresh sulfuric acid in the chlorine drying step g) by the recycled proportion.
Since different sulfuric acid concentrations may be required for catalysis of the nitration reaction and for chlorine drying, the sulfuric acid can be concentrated in several stages in order to provide the appropriate sulfuric acid concentration in the necessary amounts. Thus, for example, a sulfuric acid concentration of 86 to 91 percent by mass of sulfuric acid (based on the total mass of sulfuric acid plus water), as disclosed in EP-A 0903 336, may be needed for the nitration of toluene, whereas a higher concentration of 96.0 to 98.0 percent by mass of sulfuric acid (based on the total mass of sulfuric acid plus water) is advantageous for chlorine drying. In this case, the process according to the invention can be executed in such a way that the entire stream is concentrated in the sulfuric acid concentration plant to the concentration required for nitration and only the split stream required for chlorine drying is concentrated further in an additional distillation stage. In this way, the goal of a reduction in investment costs is also achieved.
Before sulfuric acid from a common acid concentration stage is returned to chlorine gas drying, purification steps can optionally be performed to remove any possibly disruptive components for the chlorine production process, such as organic nitro compounds, benzoic acids, nitrous gases or nitrosyl sulfuric acid. This can be done by means of adsorption or stripping methods.
The process according to the invention is particularly advantageous if toluene or benzene is used as the aromatic starting compound. Thus in the case of toluene, dinitrotoluene can be obtained after dinitration according to step a), which can then be reacted with hydrogen by any of the known processes in step c1) to form toluene diamine (TDA) and then reacted with phosgene by any of the known processes in step d) to form toluene diisocyanate (TDI).
In the case of dinitration to produce dinitrotoluene, in the second nitration stage, in which mononitrotoluene is nitrated further to form dinitrotoluene, a sulfuric acid concentration in the range from 86.0 to 96.0 percent by mass of sulfuric acid (based on the total mass of sulfuric acid plus water) is conventionally used before the addition of nitric acid. This sulfuric acid is then diluted with the water of reaction formed during nitration to a concentration of 80.0 to 85.9 percent by mass of sulfuric acid (based on the total mass of sulfuric acid plus water). The dilute sulfuric acid obtained from this second nitration stage with the concentration range from 80.0 to 85.9 percent by mass of sulfuric acid is then used as a feedstock sulfuric acid for the first nitration stage from toluene to mononitrotoluene, this sulfuric acid used being diluted in the course of this first nitration stage to a concentration of 70.0 to 79.9 percent by mass of sulfuric acid.
In the case of benzene, nitrobenzene is obtained by mononitration according to step a), the nitrobenzene is then reacted with hydrogen by any of the known processes to form aniline, which in turn is reacted with formaldehyde in the presence of an acid catalyst to form diamines and polyamines of the diphenylmethane series. The diamines and polyamines can then be reacted with phosgene by any of the known processes in step d) to form the corresponding di- and polyisocyanates of the diphenylmethane series.
In the nitration of benzene, before the addition of nitric acid, a sulfuric acid is used which has a concentration in the range from 69.5 to 72.5 percent by mass of sulfuric acid. On completion of nitration, the sulfuric acid obtained from this nitration has a concentration of 66.5 to 69.4 percent by mass of sulfuric acid.
Chlorine obtained by the process of the present invention can then be reacted with carbon monoxide by any of the known processes to form phosgene which can be used for the production of TDI or MDI from TDA or MDA, respectively. The hydrogen chloride produced during the phosgenation of TDA and MDA can then be reacted by any of the known processes to form chlorine.
Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102006022447.7 | May 2006 | DE | national |
