Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
  • C07C29/74—Separation; Purification; Use of additives, e.g. for stabilisation
  • C07C29/76—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment
  • C07C29/80—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment by distillation

Definitions

• the invention relates to a process for the preparation of 1, 6-hexanediol, wherein a hexanediol having a nitrogen content of less than 5 ppm is obtained, 1, 6-hexanediol with a nitrogen content fraction of less 5 ppm and the use of this 1, 6-hexanediol for the production of polymers.
• 1, 6-hexanediol which has no catalytic amounts of amines for the production of polyurethanes, since these catalytic amounts of amines lead to significant by-products that impede the conversion to polyurethane.
• 6-hexanediol is based on the corresponding cyclo-C6 alkanes, alcohols, ketones and / or mixtures of these compounds which are oxidized either in the presence of nitric acid and / or an oxidation with subsequent water extraction of the organic Substance be subjected to.
• adipic acid-containing streams are produced, the z. B. obtained from cyclohexanol and / or cyclohexanone by oxidation with nitric acid.
• Adipic acid-containing streams are understood as meaning those which may contain adipic acid itself but also adipic acid in the form of their esters.
• oxidation both the adipic acid obtained by the oxidation and the mixture remaining after extensive separation of the adipic acid, which contains adipic acid, glutaric acid and succinic acid, can be used.
• adipic acid or adipic acid-containing streams may also be mentioned, which may also be mixed with the abovementioned streams, for example those which are obtained by oxidation of cyclohexane to cyclohexanol / cyclohexanone mixtures and subsequent water extraction of the organic stream.
• the above-mentioned streams contain impurities which are formed in the case of the oxidation of cyclohexanol / cyclohexanone by the oxidation with nitric acid and contain nitrogen. Also in the water extracts after the oxidation of cyclohexane with air, nitrogen components are found as undesirable secondary components.
• nitrogen compounds which may be present, for example, as a nitro group, amides or ammonium ion, are capable of forming amines during the hydrogenation of adipic acid-containing streams, which may also be esterified.
• nitro compounds can be directly hydrogenated to amines and / or amides.
• Ammonium ions can aminate alcohols formed during hydrogenation.
• Amines are basic components and as such are undesirable in 1,6-hexanediol since they have undesirable properties in the applications.
• these amines can be catalytically active in the production of polyurethanes, so that process control for producing a product with precisely defined properties is difficult, if not impossible. It can happen that entire production batches have to be disposed of. In principle, this also applies to the production of polyesters or polyester alcohols, which in turn are then further reacted with isocyanates to form urethanes.
• One way of determining whether undesirable N-containing compounds in the form of basic amines are present in 1,6-hexanediol is the determination of the so-called CPR value (controlled polymerization rate).
• the content of basic amine is coupled with the CPR value as follows and can be determined as explained for the example of 1,6-hexanediol:
• 1, 6-hexanediol are dissolved in 100 ml of a solution of potassium hydroxide in methanol (0.001 mol / l) and stirred for 15 min.
• this solution is titrated potentiometrically with 0.01 N hydrochloric acid to the end point using a Titroprozessor 682.TM. From Metrohm, Herison, Switzerland.
• the Titroprozessor 682 is equipped with two pH electrodes, a glass electrode (3 M KCl, Metrohm 6.0133.100) and a
• a CPR of 10 i. a net hydrochloric acid consumption of 1 g of 0.01 molar HCL about 5 ppm N in 1, 6 hexanediol.
• Such a CPR value of 10, i. an N content of 5 ppm already represents an undesirably high level and can already cause considerable side reactions in subsequent polyurethane reactions.
• the object of the present invention is therefore to provide a process which makes it possible to produce 1, 6-hexanediol which has a CPR value of less than 10, without increased overhead and costs with additional solvents and / or acidic and / or or to have to apply basic ion exchangers.
• step III collecting a 1, 6-hexanediol having a nitrogen content of less than 5 ppm, wherein before and / or during the distillation in step II more than 500 ppm of carboxylic acids and / or esters are contained, which has a higher boiling point than 1 , 6-hexanediol and are at temperatures of> 100 ° C for at least 5 minutes in contact with the 1, 6-hexanediol.
• the mixture to be distilled from step I of the process according to the invention in addition to 1,6-hexanediol also contains carboxylic acids and / or esters which have a higher boiling point than 1, 6-hexanediol itself.
• step I contains, in addition to the 1,6-hexanediol, already carboxylic acids and / or esters which form esters with higher boiling point with 1,6-hexanediol or else before and / or during the distillation in step II, the mixture of step I either carboxylic acids and / or esters having a higher boiling point than 1,6-hexanediol (high boilers) may be added or added to carboxylic acids and / or esters, which are part of the 1, 6-hexanediols are reacted to give esters which have a higher boiling point than 1,6-hexanediol after the reaction.
• This contact time must be at least 5 minutes during the distillation at a temperature range of> 100 ° C.
• a contact time of> 10 minutes is preferred, a contact time of> 15 minutes is particularly preferred.
• Contact time is the time in which the 1,6-hexanediol is in contact with the high-boiling and / or higher-boiling esters within the column in the liquid or gaseous state.
• the contact space in which the 1, 6-hexanediol must be in contact with the high boiler and / or the higher-boiling esters, the entire column and the associated piping and possibly the evaporator.
• the contact space thus comprises the packing within the column, the collectors and distributors, as well as the associated piping, the column bottom and an optionally connected evaporator and the pipeline to this.
• the temperature during the contact time should be> 100 ° C., preferably at least 120 ° C., particularly preferably at least 140 ° C.
• the carboxylic acids and / or esters which are optionally added to the mixture from step I before the distillation after step II are selected from the group of adipic acid, adipic acid esters, 6-hydroxycaproic acid, 6-hydroxycaproic acid esters.
• the amount of carboxylic acids and / or esters which are reacted with the 1,6-hexanediol to give the higher-boiling esters and also the amount of high-boiling esters added and the amount of mixtures of high-boiling and carboxylic acids and / or esters added to the 1, 6-hexanediol are reacted to the higher-boiling esters, are in the range> 500 ppm, preferably the amount is in the range of> 1000 ppm, more preferably> 1500 ppm, based on the amount of 1,6-hexanediol to be distilled.
• the pressures during the distillation are preferably between 5 and 3000 mbar absolute.
• other compounds may optionally be distilled off beforehand. These are, in particular, those compounds which have a boiling point which is lower by at least 50 ° C. than the 1,6-hexanediol itself and are referred to as low boilers.
• the low-boiling components are preferably selected from the group consisting of methanol, water, dimethyl ether, 1-hexanol and 1-methoxy-6-hydroxyhexane.
• the separation of the low boilers can be carried out in a separate column which is upstream of the distillation after step II.
• the pressure for example, if methanol and / or water to be separated, between 200 and 3000 mbar absolute, if 1,6-hexanediol should be separated from high boilers and / or the higher boiling esters, so is the Pressure during this distillation between 5, preferably 10 and 500 mbar absolute, preferably between 20 and 300 mbar absolute, more preferably between 30 and 200 mbar absolute.
• distillations can be carried out as a batch process or continuously, but the continuous operation is preferred, especially if the 1,6-hexanediol is to be produced in industrial quantities.
• adipic acid either by oxidation of cyclohexanol and / or cyclohexanone by means of nitric acid, by oxidation of cyclohexane to cyclohexanol / cyclohexanone mixtures and subsequent water extraction of the organic material stream or was prepared by oxidation of cyclohexane with air and subsequent water extraction.
• the adipic acid contained in these solutions is selected from the group consisting of methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, pentanols, hexanols, 2-ethylhexanol, 2-propylheptanol, 1, 5-pentanediol, 1, 6-hexanediol, tridecanol, pentadecanol or mixtures of the alcohols, preferably methanol, ethanol, propanol, n-butanol and 1, 6-hexanediol esterified. Particularly preferred are methanol and 1,6-hexanediol for esterification.
• the subsequent hydrogenation can take place in the gas phase or in the liquid phase.
• methanol is preferred as the alcohol for esterification.
• the alcohol is used at least equimolar to the carboxyl groups of adipic acid and optionally other carboxyl groups present other acids. However, a molar excess of alcohol per carboxyl group of at least 2 is preferred.
• the esterification can take place without added catalyst, but preference is given to using a catalyst, at least after an acid conversion of 50% by weight.
• a catalyst at least after an acid conversion of 50% by weight.
• These may be, for example, sulfuric acid or sulfonic acids, but also acidic solids such as ion exchangers, usually based on sulfonic acid.
• the resulting water of reaction is preferably separated during the esterification, for example by distillation. It also alcohol is carried. Therefore, it is preferable to separately distill the alcohol-water mixture and to recycle the alcohol.
• the dialkyl adipate may already be usable for the hydrogenation, but it may also be that alcohol and water must still be separated or the dialkyl adipate must be purified by distillation in order to separate from incompletely reacted acid, which is either disposed of , or preferably, optionally with the elimination of a small percentage, to avoid accumulation, of undesirable components, is returned to the esterification.
• the optionally purified dialkyl adipate is then hydrogenated. This can be done in the liquid phase or gas phase preferably on Cu-containing catalysts.
• pressures of 100 to 330 bar are preferably used in absolute terms; 150 to 270 bar overpressure are preferred; in the gas phase, 5 to 100 bar overpressure is expedient; 20 to 70 bar are particularly preferred.
• the hydrogenation in the hydrogenation also contains carboxyl groups, preferably esters.
• carboxyl groups preferably esters.
• esters may be, for example, adipic acid dimethyl ester, methyl 6-hydroxycaproate, adipic acid 1,6-hexanediol methyl ester, adipic di-1,6-hexanediol ester and / or 1,6-hydroxcaproic acid 1,6-hexanediol ester.
• These corresponding higher-boiling esters are selected from the group of adipic acid 1,6-hexanediol methyl ester, adipic di-1,6-hexanediol ester and / or 6-hydroxcaproic acid 1,6-hexanediol ester.
• the content of these high-boiling esters, based on the content of 1,6-hexanediol, is at least 500 ppm, preferably> 1000 ppm, more preferably> 1500 ppm.
• the reaction of dimethyl adipate and methyl 6-hydroxycaproate with 1,6-hexanediol can be carried out either purely thermally or by the presence of catalytically active compounds, such as acids or bases.
• the methanol has already been removed by distillation at least 50% prior to this contact time. This is preferably combined with the methanol removal step upstream of the actual distillation after step II.
• the mixture which comprises 1,6-hexanediol, the high-boiling point, higher-boiling ester and optionally light-safe is fractionated by distillation.
• a first distillation unit e.g. a continuously operated column
• compounds having a lower boiling point than 1,6-hexanediol, e.g. the low boilers such as methanol separated by distillation.
• By-products such as e.g. Water and dimethyl ether are produced together with the methanol.
• the energy is preferably introduced via the bottom of the column, for example via a bottom circulation.
• the temperature of the sump should be at least 100 ° C.
• the inlet temperature is also advantageous to keep the inlet temperature to the column above 20 ° C, for example, at the level at which the hydrogenation are incurred, so that their thermal energy can be shared in the column.
• the average residence time of 1,6-hexanediol together with the abovementioned high boilers and higher-boiling esters is at least 5 minutes in this column at temperatures of at least 100 ° C.
• This 1, 6-hexanediol-containing stream is advantageously processed in a further column to 1, 6-hexanediol with a nitrogen content of less than 5 ppm.
• a dividing wall column or a column with a side draw in which low boilers such as e.g.
• 1-hexanol, 1-methoxy-6-hydroxy-hexane is distilled off together with as little as 1, 6-hexanediol over the top, high boilers and / or higher-boiling esters, which also contain as little as possible 1, 6-hexanediol withdrawn and over sidestream , liquid or gaseous withdrawing 1, 6-hexanediol with a nitrogen content of less than 5 ppm.
• this 1,6-hexanediol contains less than 3 ppm of nitrogen.
• This column is operated at bottom temperatures above 100 ° C and average residence times of over 5 minutes. The nitrogen-containing components are discharged at least 50% with the high-boiling bottom stream.
• adipic acid itself.
• a hydrogenation catalyst are then, for example, Co, Re and Ru-containing catalysts.
• the conversion of carboxylic acids and / or esters should not be complete, so that the proportion of carboxylic acids and / or esters in the hydrogenation is preferably above 500 ppm, more preferably above 1000 ppm.
• the 1,6-hexanediol thus prepared which has a nitrogen (N) content of less than 5 ppm, can be used in any preparation process for the preparation of polymers in which diols are used. Since the 1, 6-hexanediol has only an N content of less than 5 ppm, thereby polymers are available without problems.
• the 1,6-hexanediol according to the invention is preferably used for the preparation of polyurethanes and polyesters.
• 1,6-hexanediol for the polyurethanes is reacted with diisocyanates such as hexamethylene diisocyanate, toluene-2,4-diisocyanate, diphenylmethane diisocyanate, isophorane diisocyanate and 4,4'-diisocyanatodicyclohexylmethane.
• diisocyanates such as hexamethylene diisocyanate, toluene-2,4-diisocyanate, diphenylmethane diisocyanate, isophorane diisocyanate and 4,4'-diisocyanatodicyclohexylmethane.
• the 1,6-hexanediol according to the invention is used in the presence of dicarboxylic acids such as succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, dodecanedioic acid, terephthalic acid, isophthalic acid and phthalic acid.
• dicarboxylic acids such as succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, dodecanedioic acid, terephthalic acid, isophthalic acid and phthalic acid.
• Adipic acid obtainable as product of the oxidation of cyclohexanol / cyclohexanone with nitric acid, containing 4 ppm of nitrogen, is esterified by means of an acidic ion exchanger as catalyst (Amberlie IR 120) and methanol to dimethyl adipate. After complete esterification and separation of ion exchanger and excess methanol, the ester is distilled (18 mbar, boiling point 1 15 ° C) and obtained with a purity of 99.98%. The nitrogen (N) content in the ester was 4 ppm.
• the adipic acid dimethyl ester is hydrogenated in the gas phase at 60 bar and 195-210 ° C. on a copper-containing catalyst.
• the catalyst loading is 0.15 kg Esterfeed / liter of catalyst per hour.
• the reactor is a shaft reactor, which is preceded by an evaporator, in which the feed stream is evaporated at about 195 ° C by means of a hydrogen gas stream.
• the hydrogen gas stream is composed of fresh gas (4.5 mol / mol of adipic acid dimethyl ester) and a circulating gas stream (about 80 mol of hydrogen / mol of feed stream).
• the gaseous mixture is cooled and withdrawn liquid products.
• the gaseous discharge is recycled by means of a circulation gas compressor. A small part of the gas stream is used as waste Gas discharged.
• the adipic acid dimethyl ester conversion is about 99.9%. Some methanol was lost through the exhaust gas flow.
• the collected discharges (about 30% by weight of methanol, about 68% by weight of 1,6-hexanediol, about 0.5% by weight of 6-hydroxycaproic acid methyl ester and 0.06% by weight of 6-hydroxycaproic acid hexanediol ester, about 0.3% by weight of hexanol, 0.1% by weight of dimethyl adipate, the remainder each below 0.1% by weight) have an N content of 5 ppm and are worked up by distillation. In this case, predominantly methanol is first removed at bottom temperatures of up to 140 ° C. and pressures of 1013 mbar absolute to 100 mbar within one hour.
• the remaining bottoms (about 0.08% by weight of adipic acid 1,6-hexanediol methyl ester, 0.02% by weight of adipic di-1,6-hexanediol ester, 0.3% by weight of 6-hydroxycaproic acid-1 , 6-hexanediol) is fractionally distilled within two hours in a distillation column (1 m packed column, reflux ratio 5, no access of air) at 100 mbar and bottom temperatures of about 185 ° C fractionated.
• 1,6-hexanediol is obtained in a distillation yield of about 90% with a purity of 99.9% and an N content of 1 ppm.
• the N content in the remaining sump is 15 ppm.
• Example 1 is repeated, with the difference that in the hydrogenation additionally a second reactor is installed, which corresponds in size and content of the first and flows through the first reactor. Accordingly, the catalyst load decreases to 0.75.
• the conversion of dimethyl adipate was virtually complete, in addition to methanol and hexanediol were 6-hydroxycaproic acid ester in the form of methyl and Hexandiolester in amounts below 0.03 wt .-%, about 0.6 wt .-% hexanol, the balance in each case less than 0.05% by weight.
• the discharge again has an N content of 5 ppm. It is further processed as in Example 1 1, 6-hexanediol. The resulting 1, 6-hexanediol had an N content of 5 ppm, the bottom product of 7 ppm.

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