DE2357872C3 - Mixing process for the separation and recovery of 2,6-dimethylnaphthalene from dimethylnaphthalenes - Google Patents

Description

'Il

uikl

CH ₃

CH ₃

(H)

contain, characterized in that one

a) the dimethylnaphthalene mixture in a manner known per se to form a dimethyltetralin mixture partially hydrogenated,

b) before or after the isomerization of this dimethyltetralin mixture to be carried out in a manner known per se the partially hydrogenated dimethyltetralins, which differ from the formula I derive from the partially hydrogenated dimethyltetralines, which go back to the formula II, separates,

c) the dimethyltetralins, which are derived from the formula I, in a known manner to give dimethylnaphthalenes dehydrated,

d) 2,6-dimethylnaphthalene from the obtained Separates dehydration products in the usual way and wins and the remaining Dimethylnaphthalenes returned to the partial hydrogenation stage (a).

The invention relates to a process for the separation and recovery of 2,6-dimethylnaphthalene from dimethylnaphthalene mixtures of the general formulas

(D

VXX

CH ₃

(II)

according to the preceding claim.

Ten isomers of dimethylnaphthalenes, which will be abbreviated to DMN below, are known, and ίο type 11

CH ₃

In Table I are examples of these isomers of Types 1 and II as well as their boiling points listed according to the Beilstein manual:

Table I.

²⁰ type I.

2,6-DVfN 262 "C

2,7 DMN 263 C

1,8 DMN 270 C

1.7-DMN 263 C

1,6 DMN 263 C

[, 5-DMN 265 C

Type II

[, 2-DMN 266 C

1,3-DMN 263 C

I.4-DMN 268 C

2.3 DMN 265 C

These DMN connections are known to be accordingly their shift series isomerized according to the following formulas I to 3:

(1) 2,6 DMN: £ 1,6 DMN ^ 1,5 DMN
(2) 2,7 DMN: £ 1,7 DMN ^ 1,8 DMN
(3) 2,3-DMN ^ - 1,3-DMN ^ 1,4-DMN

It is also known that 1,2-DMN is not isomerized to the other DMN isomers.

The DMN commonly present is a mixture of isomers of types 1 and II above as it is produced, for example, in the petrochemical industry. Of these isomers it can 2,6-DMN can easily be converted to naphthalene-2,6-dicarboxylic acid by oxidation. The received Dicarboxylic acid is a raw material for the production of polyesters used in the field of synthetic Fibers or films are useful. As a result, 2,6-DMN is of technical interest.

However, as can be seen from Table I above, it is extremely difficult to identify the isomers of Type I. to which 2,6-DMN belongs, of the type II isomers effectively and by simple procedures to be separated, since the former and latter isomers with their boiling points are very close to one another.

Furthermore, for example, the amount of in

2,6-DMN contained at most in the DMN mixtures produced in the petrochemical industry about 15 percent by weight, and to obtain 2,6-DMN in larger amounts, this is usually the case DMN mixture subjected to an isomerization reaction.

As in the shift series of formulas 1 to 3 As can be seen, the material can be 2,6-DMN. there only 1,5-DMN and 1,5-DMN isomerized to 2,6-DMN are prepared from the starting DMN mixture in an amount of at most about 25 percent by weight even if the 2,6-DMN is separated from the isomerization reaction product and the Residue is returned to the isomerization reaction system.

However, if the reaction is continued with recycling,!, 2-DMM will separate. the 2,7 DMN shift system isomers and the 2.3-DMN shift system isomers within the reaction system and prevent the isomerization reaction from proceeding smoothly. It's also difficult to find 1,6 DMN and to separate 1,5-DMN from these undesired deposited isomers. For this Reason it is practically impossible to carry out the above reaction simultaneously with a return of the Run residue in the circuit.

The object of the invention is therefore to create an improved method according to which 2,6-DMN separated from a DMN mixture in high yields and by means of a very simple separation process and can be won.

The process according to the invention for the separation and recovery of 2,6-dimethylnaphthalene from dimethylnaphthalene mixtures, which dimethylnaphthalenes of the general formulas

H ₁ C

i °

(D

CH,

, '. VX v / \ x

(H)

CH,

40

contained, is characterized in that one

a) the dimethylnaphthalene mixture (DMT) in a manner known per se to form a dimethyltetralin mixture (DMT) partially hydrogenated,

b) before or after the isomerization of this dimethyltetralin mixture to be carried out in a manner known per se the partially hydrogenated dimethyltetralins, which are derived from the formula I, from the partially hydrogenated dimethyltetralins, which go back to the formula II, separates,

c) the dimethyltetralins, which are derived from the formula I, in a known manner to give dimethylnaphthalenes dehydrated,

d) 2,6-dimethylnaphthalene from the dehydrogenation products obtained separated off and recovered in the usual way and the remaining dimethylnaphthalenes are recycled to the partial hydrogenation stage (a).

60

It has been found that when the process of the invention is carried out, 2,6-DMN in high yields can be obtained which achieve twice the yields previously available and often be more than 60 percent by weight of the starting DMN mixture.

In the process according to the invention, the above DMN mixture partially forming

a DMT mixture is hydrogenated and the resulting DMT mixture is isomes no need for the separation and removal of DMN of formula II, which is disadvantageous Influences on the isomerization reaction of DMN mixtures exerts, but it can cause the above reaction without any adverse effects be carried out. Even the presence of alkylbenzenes in the DMN mixture does not lead to any Trouble. In addition, since the DMN mixture is converted into the DMT mixture and then is isomerized, not only the isomers of the above shift series 1, but also the isomers of shift series 2 are isomerized to isomers of series 1.

As a result, the 2,6-DMN material can be obtained in high yields by the process of the present invention using any DMN mixtures as starting material which contain at least one DMN isomer from the group of 1,6-DMN, 1,5-DMN, 2,7-DMN, 1,7-DMN and 1,8-DMN will. The starting DMN mixture is usually from the dry distillation of Coal obtained oil and the oil obtained from the catalytic reforming of heavy naphtha or from the catalytic cracking of heavy oil. If the aromatics from such oils are extracted and distilled off, contains the fraction of the remaining hydrocarbon mixture with a boiling range of 260 to 270 C mainly the DMN mixture in addition to about 10 to 40% alkylbenzenes. It is very difficult to obtain the aromatic hydrocarbon mixture containing DMN in dimethylnaphthalenes and alkylbenzenes due to their almost identical boiling points to be separated by distillation. In the above-mentioned method according to the invention, a such a dimethylnaphthalene mixture containing alkylbenzenes is used directly as a raw material will.

In the process of the invention, the first step is the partial hydrogenation of the DM N-containing aromatic hydrocarbon mixture or a DMN mixture, which the materials

-CH,

CH ₃

CH,

(H)

contains, for example, the de; 2,6-DMN from the hydrocarbon mixture holding residue. A far greater difference arises in the boiling point between that of the part show hydrogenation of DMN of type I DMT (1) obtained from the partial hydrogenation voi Type II DMN obtained DMT (II) as this is the case between Type I DMN and DMN from Type II. That is, DMT (I) boils at about 230 bi: 240C. while DMT (II) at about 252-254 = C boils.

Due to the difference of slightly more than 12 ^° C. in the boiling points, the separation of the two materials is possible on the basis of a simple distillation. Since the alkylbenzenes present in the starting DMN mixture are not hydrogenated, they do not give rise to any change in their boiling points and it is therefore easy to separate the mixture into DMT (I) and DMT (M).

It is preferred that the partial hydrogenation be carried out to such an extent that only one the kernels of

is hydrogenated and only the core of the compounds which is not substituted _{by the group CH 3}

CH,

CH ₃

is hydrogenated. The partial hydrogenation can be carried out using known hydrogenation catalysts will. Specific examples of such catalysts are nickel (Raney nickel or stabilized Nickel), platinum, palladium, rhodium, copper chrome, iridium or ruthenium. It is cheap to buy a nickel, Palladium or copper chromium catalyst for the purpose of preventing the formation of dimethyldecalines and increasing the yields of DMT to apply. The partial hydrogenation reaction can be either batchwise as well as within a continuous flow system.

The conditions for the partial hydrogenation reaction vary depending on the catalyst used and are generally chosen ^{within a range of a temperature of 100 to 300 °} C. and a hydrogen pressure of 1 to 250 kg / cm ^2. The preferred conditions vary slightly according to the kind of the catalyst. For example, in the case of using a nickel catalyst, the initial ^{hydrogen pressure is in the range from 5 to 50 kg / cm 2} at a reaction ^{temperature of 150 °} C., the DMT in a yield of 99% using hydrogen into that for the conversion of DMN can be produced in DMT stoichiometrically required amounts. DMT can generally be produced in yields of greater than 98% by adjusting the reaction temperature to 200 ° C., using hydrogen in the above amounts and at a reaction pressure of 2 to 10 kg / cm ² . In the case of using a copper bromine catalyst, it is preferable to carry out the partial hydration reaction at 2Q to 250 ° C. and a pressure of 20 to 2QGkTgASn ^2. Although this catalyst has poor activity, it has "superior selectivity;" therefore there is no carrioning of dimetiryl decalms.

Beiör ⁱ erfindungsgenläBeo method includes the feOöierisiernng the ^ obtained DMT mixture diejÄliÄ m-eniHiag and recovery of DMT (I) or aa is vöroer. For this purpose, the catalyst used in the partial hydrogenation reaction is separated off and removed before the isomerization.

The isomerization reaction of the DMT mixture or the separated DMT (I), in presence of a solid catalyst at 150 to 450 "C. Preferably at 200 to 40O ⁰ C, are carried out. It is advantageous if the liquid hourly space velocity between 0.1 and 10 V / V / hour, preferably between 0.2 to 3 VV / hour. The isoneration reaction can be carried out under atmospheric pressure, reduced pressure or increased pressure. A carrier gas, for example inert gases such as hydrogen or nitrogen, can be used in the reaction. or lower hydrocarbons such as methane, ethane or propane, aromatic hydrocarbons such as benzene, toluene, xylene or mixtures thereof can be used. Examples of solid acidic catalysts that can be used in the isomerization reaction are catalysts of the zeolite type, for example silica-alumina, Silica-magnesia, alumina-boron oxide, Y-type zeolites or mordenite catalysts Ators can be subjected to calcination prior to use or placed on a suitable support.

The isomerization reaction is a process in which the concentration of each of the isomers, namely 2,6-isomer. 1.6-isomer, 2.6-isomer, 2.7-isomer, 1,7-isomer and 1,8-isomer within the system led close to the thermodynamic equilibrium concentration at the reaction temperature will.

Therefore it is possible to convert practically all isomers into 2,6-DMN materials, when DMT (I) dehydrates again to DMN, the 2,6-DMN is extracted therefrom and the residue is returned.

In the process of the invention, the DMT (I) can easily be separated from DMT (II) by conventional distillation measures separated and recovered. The distillation can be carried out under atmospheric pressure or reduced Printing can be carried out. When distilled at atmospheric pressure, a DMT fraction becomes with a boiling range of 230 to 240C, at which a methyl group is attached to each of the rings and from which 2,6-DMN can be prepared; a fraction with a boiling range from 252 to 254 ° C contains DMT in which two methyl groups are bonded to the same ring and a fraction with a boiling range of 260 to 270 ° C is the alkylbenzenes.

In the process according to the invention, the DMT (I) obtained in this way is dehydrated into the original form of DMN of type I, which contains the 2,6-DMN. The dehydrogenation reaction can be carried out using a dehydrogenation catalyst such as platinum, palladium, nickel, aluminum oxide-chromium, or aluminum oxide-molybdenum oxide. It is preferred that the dehydris rank 6c is carried out under an increased hydrogen pressure in order to avoid demethylation as a side reaction ¹ SSX and to increase the yields; lfeefr 'the hydrogen draft is supposed to carry less than. AJunü ^ iwnoad <fcomori 6s. hardly causes any Enönerhyliemng and possible, the dehydrogenation reaction in the water stream at atmospheric pressure. '* *

The dehydrogenation reaction will be feet 250 to 45 ° £

361S

Ό I O I

accomplished. The preferred reaction temperatures are 250 to 350 ^° C. for a platinum or palladium catalyst, since this has a high activity, and 350 to 450 ° C. for an aluminum oxide-chromium oxide catalyst.

The isomerization can also be carried out at the same time as the dehydrogenation. This method is particularly effective if 1,5- and 1,6-isomers are contained in the starting DMN mixture in large amounts, and the 2,6-isomer contained is further processed by the isomerization in the case of conversion to the DMT- Mixture increased. The dehydroisomerization is carried out in the presence of a solid acidic catalyst, for example silica-alumina. In this case, side reactions may occur as a demethylation _5, when the activity of the solid acid catalyst is too strong.

In the process according to the invention, the 2,6-DM N is separated off from the dehydrogenation product obtained and recovered; the remaining Type I dimethylnaphthalenes are recycled to the hydrogenation stage. Embodiments for Separation and recovery of 2,6-DMN from the dehydrogenation product are as follows:

a) The 2,6-DMN is precipitated from the above dehydrogenation product by cooling, the molar ratio of 2,6-DMN to 2,7-DMN in the dehydrogenation product being at least 0.725. For this reason, this method can only be used for DMN mixtures in which this ratio is at least 0.725, preferably at least 0.8. _T. ,.

b) A complex of 2,6-DMN and m-nitrobenzenic acid is formed by bringing the DMN mixture into contact with the m-nitrobenzoic acid. The formation of the complex takes place even at room temperature and it is also possible to use the complex precipitate as crystals when immersed in m-nitrobenzoic acid is dissolved at elevated temperature and then cooled. The separation of 2,6-DMN from the complex is carried out by various methods, for example, by blowing steam, Heating or blowing an inert gas, or with heating or dissolution of m-nitrobenzoic acid

in an alkaline aqueous solution. Furthermore, the 2,6-DMN from the complex by washing the Complex separated at elevated temperatures with a hydrocarbon, for example heptane will. Solvents hardly dissolve the m-nitrobenzoic acid, but dissolve the DMN well.

The 2,6-DMN finally obtained in this way can, if desired, be further purified, for example by recrystallization in the melt or in solvents such as methanol.

The remaining BMN mixture obtained after the separation of 2,6-DMN is recycled to the partial hydrogenation stage.

Desirable impurities then become impurities that would inhibit the recycle step, e.g. that Sr used the separation m-nitrobenzoic acid, eritieftrt- ·; The typical execution form of the present Veiidirens is given in the flow chart of Fig. 1 or j Ia F i g. 1 denotes the Besögsziffeiv1 the partial hydration stage, wpaö the DMN-

88% inagewaatielt w "L The e *" * "" *? **** ^ © «anisole * fwird the tsomeriäerungsswiez clotted and isomerized m. Then the isomerization product in the distillation stage 3 in dimethyltetralins (I) is dimethyltetralins ( II) and alkylbenzenes separated.

The function of the dimethyltetralins (l) then becomes DMN in dehydrogenation stage 4 dehydrated and this DMN is conveyed to the 2,6-DMN separation stage S, where the 2,6-DMN is obtained will. The remaining DMN is returned to process 1. A fresh addition to the Raw material can be done before level 1 or 5.

F i g. 2 is similar to FIG. 1, only is the order of isomerization stage 2 and distillation stage 3 vice versa. The amount of to the isomerization stage The DMT supplied is lower as a result.

The raw material can be fed in before stage 1 or before stage 5. However, it is preferred to choose the former feed mode if the 2,6-DMN content in the raw material is low and Separation is not worthwhile, and to choose the latter form of supply if the salary is large and that 2,6-DMN can be effectively separated.

As mentioned above, can according to the invention Process which produces 2,6-DMN in high yields from 2,7-DMN, 1,7-DMN and 1,8-DMN will. Another advantage of the process of the invention is that alkylbenzenes with nearly the same boiling point as DMN can be easily separated from the DMN.

The following examples illustrate the process of the invention. Unless otherwise stated, all percentages are by weight.

example 1

The one obtained by separating 2,6-DMN from that in the petrochemical industry using m-nitrobenzoic acid-prepared DMN mixture obtained residue (2,6-DMN content 2.3%) was with Washed with alkali to completely remove the m-nitrobenzoic acid; then the residue was washed with water and dried and used as a starting oil.

The starting oil contained 25% alkylbenzenes and 18% DMN in which two methyl groups are the same Ring were bound. The remainder (57%) consisted of DMN, in which there was a methyl group on each Ring was bound.

a) Partial hydrogenation stage

500 g of the starting oil was placed in a 2 liter autoclave and 20 g of stabilized nickel was added. Subsequently, the hydrogenated oil partially by introducing the required amount of hydrogen into the autoclave while maintaining the hydrogen pressure at 10 to 40 kg / cm ² at 130 to 15O ⁰ C. After the catalyst had been separated off, the reaction product was analyzed. The dimethyldecalin content was 0.4% and the total content of dimethyltetralins and alkylbenzenes was 99.6%.

b'l isomerization stage

A stainless steel tube was used with IQGj one, from a mixture of 50% mordenite from Η-type loaded with 50% bentonite shaped catalyst, and 2 © 0gdes in the previous stage obtained partially hydrogenated Öjs were, with a Speed of 50 g / h at a temperature

609631/265

from 270 to 310 ° C for 4 hours for isomerization of the oil introduced.

Distillation of the product obtained gave HOg of a fraction with a boiling point of 235 up to 243 ° C.

c) dehydration stage

50 g of an alumina-chromium oxide catalyst (chromium oxide 25%) was placed in a stainless reaction tube introduced and reduced by passing hydrogen at 35O ° C for 20 hours. Then 110 g of the DMT mixture obtained in step b) above and having a boiling point were added from 235 to 243 ° C at a rate of 30g / hour. introduced at 380 ° C. Analysis of the obtained Product by gas chromatography showed that the concentration of 2,6-DMN to 17% had increased. The product obtained contained 4% of unreacted substances and methylnaphthalene.

d) the step of separating off 2,6-DMN

To 100 g of the above dehydrogenation product 50 g of m-nitrobenzoic acid was added and dissolved in the heat to form a complex. Subsequently the complex was precipitated by cooling and filtered off. The focus on 2,6-DMN in 70 g of the filtrate fell to 8%. The filtrate was used as the raw material for the partial hydrogenation step used after washing with alkali and dried.

The complex was dissolved in ether and after adding a 5% aqueous sodium hydroxide solution the solution was stirred well to decompose the complex. The m-nitrobenzoic acid was added to the aqueous solution Solution of sodium hydroxide and the 2,6-DMN went into the ethereal layer. After the evaporation of the The 2,6-DMN obtained was recrystallized from methanol using ether and gave 7.5 g of 2,6-DMN (purified Product.

Example 2

The partially hydrogenated obtained in step a) of Example 1 oil was isomerized with a silica-alumina catalyst (alumina 35%) at 320 to 35O ⁰ C and at a liquid hourly space velocity (V / V / hr.) Of 5. A fraction with a boiling range of 235 to 245 ° C obtained by distilling the product was used as a raw material for the dehydrogenation step.

The fraction was with a palladium (1%) - aluminum oxide catalyst at 300 ⁰ C and at a V / V / hour. dehydrated by 1. The 2,6-DMN content in the product was 20.3%, and 2,7-DMN it was 20.5%. After cooling the product to 35 ^° C., 6 g of crude 2,6-DMN with a purity of 80% were separated off % Chromium oxide with 1 Gewichlstcil of a silica-magnesium oxide catalyst with a content of 30% magnesium oxide was used. The concentration of 2,6-DMN in the dehydrogenation product obtained was 19% and was slightly higher than in Example 1.

The 2,6-DMN was obtained from the above dehydrogenation product separated according to the procedure of Example I.

Example 4

1000 parts of a DMN-mixture containing 12.3% 2,6-DMN, 14.2% 1,6-DMN, 1.0% 1,5-DMN and 12.3% 2,7-DMN cooled to H ⁰ C for the crystallization of the 2,6-DMN. The 2,6-DMN which had crystallized out was separated off and washed with petroleum ether and 40 parts of 2,6-DMN were obtained. The residue was partially hydrogenated according to the procedure given in Example 1 and the product isomerized and dehydrogenated. When the DMN product was cooled to TC , 35 parts of 2,6-DMN (87.5% of the 2,6-DMN initially obtained) were obtained.

Comparative example 1

The same residue as had been obtained in Example 4 by separating off the 40 parts of 2,6-DMN from 1000 parts of the DMN mixture was isomerized without partial hydrogenation. The product was ^{cooled to 90 °} C. and the crystals obtained were separated off, whereupon it was washed with petroleum ether and 21 parts of 2,6-DMN (corresponding to 52.5% of the 2,6-DMN initially obtained) were obtained.

The results obtained are summarized in Table 1. It follows from this that in the process without partial hydrogenation (comparative example) the ratio of 2,7-DMN to 2,6-DMN | ^r ° ß ^Wlrd ' ^{because the} isomerization of 2,7-DMN to 2,6-DMN does not take place to any noticeable extent, so that there is a lowering of the yield. "

table

Gehall l parts) in Isomerization product

2.6-DMN 2.7-DMN (parts)

Amount of ratio of the cooled second yield

2,6-DMN to the first crop

and separated 2.6 DMN

109
101

109
118

35
21

87.5 52.5

Example 3

In the same way as in Example 1, a reaction with a boiling range of 235 to 245 ° C, which dmdx ßestfllatiOH the partially hy- - ³ ^ ⁴ -! ÄBSgmgsöfes erbaSeTJ was, with a ^ff ^ «^^ mmlitiräo ^ -KiaMlysat <ir (alumini-

- 3961 Üef 3I0 * C uad one V /? / Hour. from 06

isotneesiett The isomerization product was at 38F © deifydMfeoewsfet, By acting as a catalyst

Example 4
Comparative example! >

Example 5 _f

The same residue as is hydrogenated in the example of the separation of 40 parts of 2,6-DMN "^ SSS *"*; ™ * te partial as in Ifeßlfl 1 and the eihal & L. ^ * Rad aer Sfufe ^ * © H Example 1 intt «Sflem

«^ ^ JaSöBum« teem Sed

250 ⁰ C weföhe dnBSh DsäÄtiöfi

J.1

Risierungsproduktcs had been obtained dehydrated to form the DMN mixture. By separating the crystals from the resulting mixture at 25 C and washing the same with Petroliither were 35 parts of 2,6 DMN made.

Comparative example 2

A Y-type Ca-substituted zeolite catalyst was used to isomerize 2,7-DMN to 2,6-DMN using the same residue as obtained in Example 5. used. The reaction was carried out at 400 "C. and at an hourly space velocity of 0.5. The product of the reaction was the DMN fraction 44 the lower-boiling fractions (naphthalene and methylnaphthalenes) and monocyclic aromatics 31,; and the higher-boiling fractions (mainly 1-methylnaphthalene ) 24.8%. the distillation of the P domestic product yielded 500 parts of a DMN fraction ι a boiling range of 250 to 270 ° C. Then wu the DMN fraction at 14 ⁰ C to deposit crystals ι cooled. the crystals obtained Wun with petroleum ether washed, and 15 parts of 2,6-DN were prepared, the yield corresponding to 37.5 percent by weight of the 2,6-DMN initially separated.

1 sheet of drawings

Claims (1)

Claim: these isomers can be divided into the following two types Process for the separation and recovery of type I 2,6-dimethylnaphthalene from mixtures of dimethylnaphthalene , soft dimethylnaphthalenes of the general formulas _{and (1}