JPH0774172B2 - Method for separating 2,6-dimethylnaphthalene - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a mixture containing 2,6-dimethylnaphthalene.
The present invention relates to a method for separating 2,6-dimethylnaphthalene with high purity (98% by weight or more) (hereinafter dimethylnaphthalene is abbreviated as DMN).

Prior art 2,6-DMN is oxidized to 2,6-naphthalenedicarboxylic acid, which is industrially important as a raw material for polyesters, plasticizers, films and the like. 2,6-DMN is contained in various fractions of petroleum or coal tar as a mixture with other DMN isomers.

Several methods have been proposed in the past for separating 2,6-DMN from such a fraction.

For example, the DMN fraction extracted and concentrated from a petroleum or coal tar-based raw material by an appropriate method (for example, a fractional distillation method) is cooled,
It has been proposed to obtain a solid containing 2,6- and 2,7-DMN, and recrystallize or partially melt the solid to separate 2,6-DMN. However, DMNs form eutectic mixtures. For example, 2,6-body and 2,7-body have 41.5: 58.5,
The 2,6-form and the 2.3-form form a binary eutectic mixture in a molar ratio of 47.5: 52.5. Therefore, the separation yield of pure 2,6-DMN by the conventional crystallization method is theoretically determined by the initial raw material composition, and a high yield cannot be expected.

For example, the boiling point 250 to 270 ° C. fraction obtained from the catalytic cracking of petroleum contains 2,6-DMN8 to 13% and 2,7-DMN8 to 13%, so it is cooled, solidified, recrystallized or When separated and purified by partial melting, the recovery rate of 2,6-DMN is about 30% at maximum.

It is possible to raise the composition of 2,6-DMN in the raw material to about 30% by precision fractionation, but the ratio of 2,6-DMN and 2,7-DMN cannot be changed significantly. Therefore, the yield of pure 2,6-DMN does not improve.

Problems to be Solved by the Invention As described above, various fractions of petroleum or coal tar-based fractions contain equal amounts of 2,6-DMN and 2,7-DMN.
It contains many components such as DMN isomers.

The boiling points of 2,6-DMN and 2,7-DMN are very close to each other, and there is a possibility of forming a eutectic mixture and a solid solution.

Further, in the separation of 2,6-DMN, there are problems such as a decrease in the recovery rate of 2,6-DMN, the purity of 2,6-DMN is extremely unlikely to increase, and the separation and purification cost become extremely high. Atsuta

Therefore, for example, when 2,6-DMN is oxidized to be used as a 2,6-naphthalenedicarboxylic acid, thermal properties are deteriorated due to inclusion of a carboxylic acid derived from an isomer other than 2,6-DMN. . Also, the separation of naphthalenedicarboxylic acid is even more difficult.

MEANS FOR SOLVING THE PROBLEMS The present invention relates to 2,6-
A mixture containing at least 50% by weight of the component obtained by pre-concentrating dimethylnaphthalene, and a mixture containing other dimethylnaphthalene isomers, the temperature of the mixture was adjusted in advance to 60 to 90 ° C., and a slurry containing the crystal was obtained. Then, this is sealed in a pressure vessel and adiabatically pressurized to a pressure of 500 to 2500 kgf / cm ² ,
2,6-Dimethylnaphthalene is solidified into a solid-liquid coexisting state, and then the liquid is discharged from the solid-liquid coexisting system under pressure, and the solid remaining in the container is squeezed to residual liquid between solid particles. The present invention relates to a method for separating 2,6-dimethylnaphthalene, characterized in that 2,6-dimethylnaphthalene having a purity of 98% by weight or more is obtained by discharging the solid particles and integrating the solid particles.

Pressure Crystallization Pressure crystallization is a method for separating and purifying substances (Japanese Patent Publication No. 56-4128).
No. 2) is adopted.

The outline of this method is as follows.

This method pressurizes a mixed liquid containing two or more substances,
This is a method in which a specific substance in the mixture is solidified by the action of pressure and separated from the rest of the liquid. That is, a mixed liquid containing two or more kinds of substances is enclosed in a pressure vessel, and the specific substance is solidified by the action of pressure to make a solid-liquid coexisting state. Discharging the liquid from the coexisting system while maintaining a higher pressure than
Then, it is a method for separating and purifying a substance in which the solids remaining in the container are squeezed to discharge the residual liquid between the solid particles and integrate the solid particles.

The above phenomenon will be explained based on the thermodynamic consideration of the solution. The impurity concentration in the residual liquid is X ₂ (molar concentration), the treatment temperature is T (absolute temperature), and the equilibrium pressure between the solution and the crystal is P.
₁ (Kg / cm ² ), solid-liquid transformation pressure of pure substance is P ₀ (Kg / cm ² ), P
_If the difference between ₁ and P ₀ is ΔP (Kg / cm ² ), the following relationship holds when X ₂ is relatively small.

R is a gas constant and ΔV is a volume change (generally negative except for a water-water system) associated with solidification per mole.

Next, a statistical average contact pressure of the crystal agglomerates surface Ps, solid-liquid equilibrium pressure P ₀ + △ P in the impurity concentration X ₂ of residual liquid, when the discharge pressure of the residual liquid and P _L, P ₀ <P _The most effective case is that _L <P ₀ + P <Ps. The closer the P _L is to P ₀ + ΔP, the greater the amount recovered as a solid, but the less the purification effect.
Conversely P _L is the recovery effect as a solid the closer to P ₀ becomes slightly lower, purification effect is large. By obtaining P _L close to P ₀ from P ₀ + ΔP according to the concentration of the residual liquid and its discharge amount, only a relatively small amount of the residual liquid is separated to obtain a larger amount of higher-purity solid. be able to.

This will be explained with reference to FIG. 1. Generally, the slope dP ₀ / dT of the solid-liquid equilibrium line of a substance is larger than zero as shown in the figure. When a pure substance, that is, a substance having an impurity concentration X ₂ = 0, has a solid-liquid equilibrium at a pressure P _{0 at} a temperature T, and an impurity concentration X ₂ , the solid-liquid equilibrium pressure becomes P ₀ + ΔP. When the discharge pressure is P _L , the solid in the vicinity of the liquid having the impurity concentration of X ₂ melts, and the solid-liquid equilibrium can be maintained at P _L , resulting in a higher purity. At this time, the statistical average value Ps of the contact pressure of the crystal agglomerates is much higher than these values, and accordingly, the crystal agglomerates are squeezed and the intergranular residual liquid is in a so-called "squeeze" state. .

In the figure, 'If lowered to, P' by connexion temperature for dissolution of some crystals with the setting of the discharge pressure P _L is T may be adjusted discharge pressure defined anew P _{0 0,} also again It may be understood as a variable that returns to its original value as the temperature recovers.

Next, the present invention will be described with reference to the drawings.

FIG. 2 is a schematic view showing an example of an apparatus for carrying out the method of the present invention. In the figure, a pressure vessel 1 is provided with a lower lid 2 below, and a piston 5 is provided so as to move up and down in the vessel 1 by the operation of a hydraulic unit 3. The piston 5 and the lower lid 2 are Therefore, the crystallization chamber 4 is formed in the pressure vessel 1. The crystallization chamber 4 and the drainage tank 6 are
It is connected by the arrangement 9 via the pressure reducing mechanism 10 and the on-off valve 11. Further, the crystallization chamber 4 and the preliminary crystallization can 7 are connected by a pipe 13 via a raw material supply pump 8 and an opening / closing valve 12.

In this apparatus, the raw material is supplied from the raw material tank 14 to the preliminary crystallization can 7 where it is cooled and crystallized to generate a seed crystal for pressure crystallization. This is because when pressure crystallization is performed with a liquid that does not contain seed crystals, high pressure is required for initial crystal formation, and ultrafine crystals are generated due to crystal formation under excessive saturation due to rapid pressurization. Is generated, which may make solid-liquid separation difficult. When it is supplied in the slurry state containing the seed crystal, the crystal growth starts with the pressurization without the occurrence of such supersaturation phenomenon.

Next, the raw material is injected into the crystallization chamber 4 from the pipe 13 through the valve 12. When the crystallization chamber 4 is filled with the raw material, the liquid begins to flow out through the overflow pipe 15 having an opening at the tip of the piston, so this is detected, valves 12 and 16 are closed, and pressurization by the piston 5 is started. To do. When the raw material liquid is pressurized, the crystallization of the specific substance in the raw material proceeds, and the inside of the crystallization chamber 4 becomes a solid-liquid coexisting state under high pressure. The solid formed at this time is generally an extremely high-purity substance. Although the temperature in the crystallization chamber 4 rises due to the latent heat of solidification generated with the progress of solidification, the pressure crystallization method generally does not perform cooling to prevent this temperature rise, and adiabatically applies the temperature. The method of pressing is adopted. The reached temperature after pressurization, that is, the solid-liquid separation start temperature affects the purity and yield of the product. Therefore, this is adjusted by the liquid supply temperature in consideration of the specific heat of the raw material mixture, latent heat of solidification and the like.

Next, when the pressure is increased to a predetermined pressure and a predetermined solid-liquid ratio is reached, the valve 11 is opened while the pressure acting on the piston 5 from the hydraulic unit 3 is maintained and the pressure in the crystallization chamber 4 is maintained.
The liquid in the crystallization chamber is discharged to the drain tank 6 via the pressure reducing mechanism 10. Further, when the piston continues to descend while the pressure applied to the piston 5 is maintained, the crystal grain group in the crystallization chamber 4 is pressed and compressed, and the residual liquid between the crystal grains undergoes a so-called "squeeze action". And is discharged to the drainage tank 6.

When the piston 5 further descends, the crystal grain group is formed into one huge lump along the shape of the crystallization chamber 4. In this way, when the liquid is almost completely separated from the solid, the liquid phase pressure of the crystal grain boundary in the crystallization chamber 4 communicating with the drainage tank 6 gradually decreases, so that the crystal particles The surface is partially melted, a so-called "perspiration cleansing" is carried out and the solid product is purified. When the pressure of the waste liquid discharged from the crystallization chamber is reduced to a predetermined pressure, the piston 5 is stopped from descending, the piston is started to rise, and the high-pressure container 1 is also raised. It is taken out of the container 1 while being placed on the lower lid 2. This is taken out by a product take-out device (not shown), the high-pressure container 1 is lowered and attached to the lower lid 2, and then the process returns to the raw material injection step,
The same process is repeated. Prior to the injection of the raw material, the residual liquid in the overflow pipe 15 is purged with a gas such as nitrogen gas which is inactive with respect to the product, and is prepared for full liquid detection at the time of injection in the next step. .

Adjustment of Raw Material In order to perform pressure crystallization of the present invention, 2,6-dimethylnaphthalene as a raw material is at least 50% by weight or more, preferably
Mixtures with other dimethylnaphthalene isomers containing more than 70% by weight are used.

The reason is that the content of 2,6-dimethylnaphthalene in the raw material is 5
Below 0% by weight, the recovery of 2,6-dimethylnaphthalene is poor. Further, the purity of 2,6-dimethylnaphthalene cannot be 98% by weight or more.

As a raw material for pressure crystallization, 2,6-dimethylnaphthalene is at least 50% by weight or more, preferably 70% by weight or more.

In order to produce a dimethylnaphthalene isomer containing at least 50% by weight of 2,6-dimethylnaphthalene, which is a raw material used in the method of the present invention, for example, U.S. Pat.
Method described in No. 1 (cooling crystallization method), JP-B-47-44729
The method described in Japanese Patent Publication (complexing method) and the method described in Japanese Patent Publication No. 49-27578 (zeolite method) can be used alone or in combination.

Typical methods are the following two methods.

As a starting material, a fraction of catalytically cracked petroleum having a boiling point of 250 to 270 ° C., preferably 257 to 265 ° C. is used [hereinafter (A)
]].

In the first method, (A) is treated according to the cooling crystallization method (hereinafter referred to as the B method) at a cooling crystallization temperature of -15 to 5 ° C.

In the second method, (A) is used in accordance with the zeolite method (hereinafter referred to as C method) using Na—Y zeolite at a temperature of 80 to 100 ° C. and SV of 1 g /
After treatment under the condition of g / hr, further treatment is carried out at a cooling crystallization temperature of -35 to -10 ° C according to the cooling crystallization method (hereinafter referred to as D method).

Cooling Crystallization Method (Method B) The cooling crystallization method will be outlined below. In a method for separating 2,6-dimethylnaphthalene by crystallizing 2,6-dimethylnaphthalene from a raw material containing 2,6-dimethylnaphthalene and 2,7-dimethylnaphthalene at a cooling crystallization temperature of -15 to 5 ° C According to the concentration of 2,6-dimethylnaphthalene in the raw material and the difference in concentration between 2,6-dimethylnaphthalene and 2,7-dimethylnaphthalene, the desired purity of 2,6-dimethylnaphthalene can be obtained from FIG. This is a method of obtaining a temperature, crystallizing at this temperature, maintaining at this temperature for 2 to 7 hours to complete the crystallization, and then separating the liquid while maintaining this temperature.

The cooling crystallization temperature is obtained from FIG.

The concentration and recovery rate of 2,6-dimethylnaphthalene (referred to as 2,6-DMN) when the pressure crystallization method of the present invention (hereinafter referred to as E method) and the above-mentioned various methods (BCD method) were combined were determined as follows. The results are shown in Table 1.

In the pressure crystallization method, as described above, it is preferable to supply the raw material in a slurry state. Therefore, in the present raw material system, this is cooled to about 50 to 90 ° C. in advance to 5-25%.
It is preferable to prepare a slurry of a certain degree.

Further, this raw material supply temperature is closely related to the purity and yield of the product, and when the liquid is supplied at 50 ° C or lower, the purity is lowered due to insufficient perspiration cleaning and insufficient squeezing during depressurization. On the other hand, the supply temperature is 90
When the temperature is higher than 0 ° C, the purity is improved, but the yield is decreased, which is not economical.

[Examples] The present invention is described below with reference to Examples and Reference Examples, but the present invention is not limited thereto.

(Example-1) A raw material mixture (D) mainly consisting of a DMN isomer mixture containing 2,6-DMN at 71.6% and the other at 2,7-DMN at 15% was adjusted to a temperature of 83 ° C. To prepare a slurry containing 2,6-DMN crystals, which was supplied to the high-pressure container of the piston / cylinder structure shown in FIG.
As a result of the oil pressure acting on the piston, the pressure is 1500 kgf /
Adiabatic pressure was applied to cm ² (case E-1) and 2000 kgf / cm ² (case E-2). Subsequently, the liquid phase in the high-pressure container was discharged while the oil pressure acting on the piston was maintained, and the crystals were squeezed by the piston until the liquid phase pressure dropped to 200 kgf / cm ² .

The feed temperature of the raw material and the pressure for pressure crystallization were determined from Fig. 5 (solid-liquid equilibrium diagram of 2,6-DMN under pressure), latent heat of fusion of 2,6-DMN, specific heat of raw material mixture, etc. .

The purity and yield of the product 2,6-DMN obtained in each case of E-1 and E-2 are shown in Table 2.

(Example-2) The raw material mixture (6) containing 2,6-DMN at 61.3% and 2,7-DMN at 9.8% was mainly mixed with the raw material mixture (D), and the temperature was adjusted to 73 ° C. Pressure crystallization was performed in two cases under the same conditions as in Example 1 except that the pressure crystallization was performed in a high-pressure vessel. The purity and yield of the product obtained as a result of the third
Shown in the table.

(Example-3) A raw material mixture (D) consisting mainly of a DMN isomer mixture containing 68% 2,6-DMN and 9% 2,7-DMN.
Was subjected to pressure crystallization in two cases under the same conditions as in Example-1 except that the temperature was adjusted to 79 ° C and the temperature was supplied to the high-pressure vessel. The purity and yield of the resulting product are shown in Table 4.

In the above example, the pressure at which the pressing is completed is 500 kgf / c.
Although it is m ² , this can be appropriately changed, and if this end pressure is high, the yield will be increased, but the purity will be decreased. Therefore, this end pressure is set to the optimum condition under the condition that a high yield can be obtained within the range where the required purity can be achieved.

Reference Example 1 50 mmHg of petroleum catalytic cracking oil (FCC method) as a starting material,
Precision distillation was performed with 40 theoretical plates, a reflux ratio of 30: 1 and a boiling point of 253-265 ° C.

The obtained fraction (A) 9 was converted into Na-Y zeolite (Al / Si0.65
.About.0.2, water content 12%), adsorption and separation at 100.degree. C. and SV 1 g / g / hr were carried out to obtain a 2,6-DMN-enriched fraction (C).

The obtained fraction (C) was cooled at −30 ° C., crystallized at this temperature to complete crystallization, and then the liquid was separated while maintaining this temperature to give 2,6-DMN (D). Got

The purity and recovery rate of the obtained 2,6-DMN (D) are shown in Table 5.

Reference Example 2 Using the same starting material as in Reference Example 1, the obtained fraction (A)
Was cooled to -6 ° C and crystallized at this temperature to complete crystallization, and then the liquid was separated while maintaining the temperature at 2,6-D.
MN (D) was obtained.

The purity and recovery rate of the obtained 2,6-DMN (D) are shown in Table 6.

Reference Example 3 As a starting material, the same material as in Reference Example 1 was used. The concentration of 2,6-DMN in the raw material was 39 wt.%.

This was crystallized by a pressure crystallization method at a temperature of 75 ° C and a pressure of 2000 kgf / cm ² , and then the pressure was maintained at 100 kgf while maintaining this temperature.
/ cm ² and the liquid was separated.

The purity of the obtained 2,6-DMN was 84 wt.% And the recovery rate was 19%.

Effects of the Present Invention The following effects are obtained by the present invention.

1) Since the temperature is controlled instead of the temperature, the entire system can be controlled under uniform conditions, and the purity of the 2,6-DMN obtained can be increased, resulting in high recovery and high purification efficiency. To be

2) The residual mother liquor can be used repeatedly in the next step, so no problem occurs.

3) The equipment is compact and the purification cost is low.

4) Both batch and continuous operations are possible, and the desired time is short.

[Brief description of drawings]

FIG. 1 is a graph showing a solid-liquid equilibrium curve of a substance by temperature and pressure for explaining the pressure crystallization method, and FIG. 2 is a schematic explanatory view of an apparatus for carrying out the method of the present invention. Fig. 4 is a eutectic diagram with 2,6-DMN, Fig. 4 is a graph showing the relationship between temperature and the purity and recovery of 2,6-DMN, and Fig. 5 is 2,6 depending on temperature and pressure. -A graph showing a solid-liquid equilibrium curve of DMN. In FIG. 2, 1 ... Pressure vessel, 2 ... Lower lid, 3 ... Hydraulic unit, 4 ... Crystallizing chamber, 5 ... Piston, 6 ... Drainage tank, 7 ... Preliminary crystallization can, 8 ... Pump, 9, 13 ... Piping, 10 ... Pressure reducing mechanism, 11, 12, 16 ... Valve, 14 ... Raw material tank, 15 ... Overflow pipe.

Front page continuation (72) Inventor Hiroshi Takeshita 2-7-3 Marunouchi, Chiyoda-ku, Tokyo Within Showa Shell Sekiyu Co., Ltd. (72) Inventor Harumasa Tanabe 7-58 Kasumigaoka, Tarumi-ku, Kobe-shi, Hyogo ( 72) Inventor Masami Takao 5-7-11 Fukuda, Tarumi-ku, Kobe City, Hyogo Prefecture (72) Inventor Kazushi Hatakeyama 77-10 Nagata, Onoe Town, Kakogawa City, Hyogo Prefecture (56) Reference JP-A-61-157304 (JP) , A)

Claims (2)

[Claims] 1. At least 50 of 2,6-dimethylnaphthalene.
A mixture containing wt% and other dimethylnaphthalene isomers is injected into the high pressure vessel of the pressure crystallizer, and 500 to 2500 k
Pressurize to a pressure of gf / cm ² to increase the amount of crystals of 2,6-dimethylnaphthalene, form a solid-liquid coexisting state under high pressure, and then discharge the liquid phase component out of the container under pressure. Then, the solid phase fraction in the container is increased, and the pressure of the residual liquid phase is gradually decreased to partially dissolve the solid phase and purify the solid phase.
In the method for producing a crystal mass of 2,6-dimethylnaphthalene in a high-pressure container by applying a pressing force to the solid phase to discharge the residual liquid phase component, 2,6-dimethylnaphthalene and other dimethyl A mixture containing a naphthalene isomer was adjusted in temperature to 60 to 90 ° C. in advance to obtain a slurry state containing crystals of 2,6-dimethylnaphthalene, and this slurry was injected into the high pressure vessel of the pressure crystallizer. , Starting temperature 80
Purity 98 characterized by pressurizing adiabatically from ~ 105 ℃
A method for producing 2,6-dimethylnaphthalene in an amount of at least wt%. 2. The solid-liquid separation pressure is 10 in the pressure crystallization.
The method for producing 2,6-dimethylnaphthalene according to claim 1, which is from 00 to 2000 kgf / c ² .