JPH0729951B2 - Method for separating 2,6-dimethylnaphthalene - Google Patents

Description

The present invention relates to a method for separating 2,6-dimethylnaphthalene from a feedstock containing a mixture of dimethylnaphthalene isomers. More specifically, the present invention uses a specific fixed adsorbent and a specific desorbent that selectively adsorbs and desorbs 2,6-dimethylnaphthalene, and 2,6-dimethylnaphthalene and at least one other species. For separating 2,6-dimethylnaphthalene from a feedstock feed stream containing a dimethylnaphthalene isomer and / or a hydrocarbon having a boiling range of 220 to 270 ° C and / or a derivative thereof Is.

[Conventional technology]

It is also recognized in the art that X- or Y-type zeolites containing certain cations at exchangeable cation sites can separate a particular dimethylnaphthalene from a mixture containing dimethylnaphthalene isomers. For example, U.S. Pat. No. 3,133,126 and U.S. Pat. No. 3,114,782 point out that X-type zeolites containing sodium or calcium at exchangeable cation sites are useful as selective adsorbents between dimethylnaphthalene isomers.

In Japanese Examined Patent Publication No. 52-945, Y type zeolite is used, and benzene, toluene and orthoxylene are used as desorbing agents.
Selectively 2,7 from 6 / 2,7-dimethylnaphthalene eutectic mixture
-It is stated that dimethylnaphthalene can be separated.

JP-B-49-27578 describes that Y-type zeolite can be used to separate 2,6-dimethylnaphthalene.
Furthermore, Dutch Patent 7307794, US Patent 3,772,399, US Patent 3,840,610, US Patent 3,895,080, US Patent 4,014,949.
In each of the above, it is described that Y-type zeolite is useful as an adsorbent in the separation of cyclic hydrocarbons.

[Problems to be solved by the invention]

However, US Patent 3,133,126 and US Patent 3,11
No. 4,782, when observing the adsorption selectivity between dimethylnaphthalene isomers, the adsorption selectivity of the dilute solution of the dimethylnaphthalene isomer mixture in the presence of paraffin, which does not actually strongly influence the adsorption, was determined by the static batch method. However, there is no description about the involvement of the desorbing agent, which is indispensable when actually operating industrially, for example, when performing continuous separation using a simulated moving bed or the like.

Regarding the industrially essential releasing agent, there is no description that the above-mentioned Japanese Patent Publication No. 49-27578, U.S. Patent 3,772,399, U.S. Patent 3,895,080, U.S. Patent 4,014,949, Dutch Patent 730779.
The same applies to 4. Generally, in an adsorption separation operation, an excellent adsorption separation system is that the adsorbent has a large separation coefficient and adsorption capacity when reaching an equilibrium state, no change in the substance to be separated, and further, It is required that the speed of adsorption and desorption of the substance to be separated be fast, and the desorbing agent has an intermediate level between the substance having the weakest adsorption force and the substance having the strongest adsorption force among the substances to be separated. Among the substances to be separated, a substance that promotes adsorption and desorption of a target substance is particularly required. If such requirements are not satisfied, problems such as increased tailing of the substance to be separated occur and the target substance cannot be efficiently separated.

[Means for solving problems]

We have found that dimethylnaphthalene isomer mixtures yield 2,6
-As a result of extensive studies on adsorption separation of dimethylnaphthalene, it is advantageous to use Y-type zeolite whose exchangeable cation site is ion-exchanged with lithium as an adsorbent and paraxylene as a desorbent. The present invention has been achieved by finding that naphthalene can be adsorbed and separated.

That is, the present invention, from the feedstock oil containing a mixture of dimethylnaphthalene isomers, in adsorbing and separating 2,6-dimethylnaphthalene, as the adsorbent, using a Y-type zeolite whose cation site is ion-exchanged with lithium, desorption This is a method for separating 2,6-dimethylnaphthalene using paraxylene as a releasing agent.

Hereinafter, the present invention will be described in more detail.

Many types of zeolite are known to be naturally produced and artificially synthesized. However, not all of these zeolites are effective as an adsorbent for separating 2,6-dimethylnaphthalene by the method of the present invention, and Y-type zeolite is used in the present invention. Y-type zeolite, which belongs to the faujasite-type zeolite, has 0.9 ± 0.2 Na ₂ O: Al ₂ O ₃ : 4.5 ± 1.5 SiO ₂ : YH ₂ O (where Y is zero or less than 0) The value can be expressed as the molar ratio of the oxide with respect to the sodium form. The sodium form of the Y-type zeolite is capable of ion-exchanging part or all of the sodium at its cation site with other cations according to known methods. Lithium is used as the exchange cation for the type zeolite.

In separating 2,6-dimethylnaphthalene by the method of the present invention, a feed stream of a feed oil containing a mixture of dimethylnaphthalene isomers is applied to a chromatographic column with a Y-type zeolite having lithium at a cation site as a single bed. Using a continuous separation technique such as an elution chromatographic method or a simulated moving bed method in which the packed material is brought into contact with and subsequently a desorbent substance for selectively desorbing 2,6-dimethylnaphthalene on this bed is passed. You can Zeolite as an adsorbent is not limited to powder form, may be formed into pellets, extruded products, granules, etc. In that case, silica, alumina, clay or the like is used as a binder, but any binder material is used. It can also be used. When packed in a column, the shape of the zeolite may be spherical, crushed, or the like, but when the average particle diameter of the zeolite is d and the inner diameter of the packed column is D, the ratio thereof is Those having a size such that D / d is 15 or more, preferably 20 or more are preferable.

The selection of a desorbing agent is important for efficient adsorption separation of 2,6-dimethylnaphthalene. That is, the desorbing agent is capable of selectively and easily desorbing 2,6-dimethylnaphthalene from the lithium-exchanged Y-type zeolite separately from the other feed oil components, and then further distilling or other methods. Therefore, it must be easily removable from 2,6-dimethylnaphthalene. For that purpose, a desorbing agent having an adsorbing power to the zeolite between the 2,6-dimethylnaphthalene present in the feedstock containing a mixture of dimethylnaphthalene isomers and the component having the strongest adsorbing power is preferable. In the present invention, the desorption agent used for desorption of 2,6-dimethylnaphthalene is paraxylene.

It is also possible to use a mixture of para-xylene and an inert diluent as the desorbing agent, examples of diluents being saturated chain or cyclic hydrocarbons which are liquid at the operating temperature.

The feedstock oil containing the dimethylnaphthalene isomer mixture that is the raw material in the method of the present invention, as the dimethylnaphthalene content, 2,6-dimethylnaphthalene, 2,7-dimethylnaphthalene, 2,3-dimethylnaphthalene, 1,2- 2,6 of dimethylnaphthalene, 1,3-dimethylnaphthalene, 1,4-dimethylnaphthalene, 1,5-dimethylnaphthalene, 1,6-dimethylnaphthalene, 1,7-dimethylnaphthalene, 1,8-dimethylnaphthalene -Containing one or more dimethylnaphthalene isomers of dimethylnaphthalene and other dimethylnaphthalene, and further a hydrocarbon compound having a boiling range of 220 to 270 ° C, for example, α-methylnaphthalene, β-methylnaphthalene, α -Ethylnaphthalene, β-ethylnaphthalene, biphenyl, alkane, cycloalkane, alkene, cycloalkene, etc. Is shall.

The method of the present invention can be carried out in either the gas phase or the liquid phase, but the liquid phase is preferred. The operating conditions when the substance to be separated and the desorbent are brought into contact with the zeolite adsorbent, the physical properties of the substance to be separated and the desorbent, such as melting point, boiling point, viscosity, etc. must be appropriately selected in consideration of the liquid. In order to maintain the phase state, a temperature in the range of 0 to 300 ° C. and a pressure in the range of about atmospheric pressure are preferable. More preferably, it is selected from a temperature range of 60 to 200 ° C. and a pressure in the range of approximately atmospheric pressure to 20 atmospheres. Generally, as an index showing the separating ability of the adsorbent, the separation coefficient K defined as the ratio of the same two components of the adsorbed phase to the ratio of the two components of the unadsorbed phase in the adsorption equilibrium state between specific two components in the raw material feed. To use. That is, when the volume% of the unadsorbed phase of the components A and B is X _A and X _B , and the volume% of the adsorbed phase is Y _A and Y _B , respectively, The separation coefficient ▲ K ^A _B ▼ of the components A and B defined by Here, the adsorption equilibrium state is a state in which no net mass transfer occurs between the non-adsorption phase and the adsorption phase. If B a component having a strong adsorption force, the weak component of the suction force was set to A, ▲ K ^B _A ▼
The larger the value of, the better the separability of the adsorbent. In other words, when the value of K ^B _A of the two components A and B is close to 1.0, the adsorbent does not preferentially adsorb the component B with respect to the component A, and the two components are almost equal to each other. Adsorbed. Further, ▲ K ^B _A ▼ value that is greater than 1.0 means that the component B is preferentially adsorbed as compared to component A. For raw material feeds containing a mixture of dimethylnaphthalene isomers, dynamic test equipment was used to measure the adsorbent properties of adsorption capacity, selectivity and desorption rate using various adsorbents and desorbents. To do. This device
It is a stainless steel column with an inner diameter of 8 mm and a length of 1 m, and has a jacket for heat retention on the outside. At the inlet of the column, a distributor for liquid dispersion is provided to prevent uneven flow. Using this device, a pulse test is performed according to the general procedure described below to measure data such as selectivity for various adsorbent / desorbent systems. The adsorbent is packed in a column, and conditioning is performed through a desorbent. Then, the raw material containing the dimethylnaphthalene isomer mixture was injected in a pulse for several minutes, and after a predetermined amount was introduced into the column, the flow was changed to the desorbing agent flow again, and the desorption was carried out within the flow range in which the plug flow was maintained and the reverse mixing diffusion did not occur. The agent is flowed and the raw material feed is developed in the column. A sampling port is provided at the column outlet, and a fixed amount of the effluent is periodically sampled from this, and analyzed by a gas chromatograph to quantify each component in the fraction. When the concentration of each component is spelled with respect to the corresponding outflow time, the envelope of the peak corresponding to each component can be obtained.

The performance of an adsorbent is generally determined by a capacity index which is an index of adsorption capacity, a known reference point, a separation coefficient ▲ K ^A _B ▼ representing the sensitivity of separation of two components A and B, and a target substance to be desorbed. The rate of desorption by the desorbing agent can be evaluated. The volume index is measured by the distance between the center of the peak envelope of the selectively adsorbed component. This is represented by the volume of desorbent pumped by the pump during the time period. The known reference point is determined using the volume of this desorbent. The void volume between the adsorbent particles in the column, that is, the volume in which the tracer components that do not participate in adsorption flow, is used to measure the adsorbent physical properties such as the adsorbent true density and pore volume, and the packing density when packed in the column. You can always know. The known reference point is defined as the time taken by dividing this void volume by the desorbent volume. Separation factor ▲ K ^A _B ▼ is component A
It can also be expressed by the ratio K _A / K _B of the capacity index K _A of the component B and the capacity index K _B of the component B. Therefore, in the present invention, the separation coefficient ▲ K ⁱ _{2,6 of the} other component i with respect to 2,6-dimethylnaphthalene.
The value of ▼ is related by the ratio of the distance between the center of the peak envelope of component i and the reference point to the distance between the center of the peak envelope of 2,6-dimethylnaphthalene and the reference point. According to the method of the present invention, the separation coefficient ▲ K ⁱ _2,6 ▼ of other dimethylnaphthalene isomers with respect to 2,6-dimethylnaphthalene is larger than 1, and it is clear that 2,6-dimethylnaphthalene can be selectively separated. is there.

〔Example〕

Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention.

Example 1 Granules of Y-type zeolite having a lithium cation site (particle size distribution of 250 to 420 μm) were packed in a stainless steel column with an inner diameter of 8 mm and a length of 1 m and a jacket for heat insulation. At the inlet of the column, a distributor for liquid dispersion was attached so that uneven flow did not occur. The column temperature was maintained at 100 ° C., and paraxylene as a desorbent was fed from one end of the column at a rate of 5 ml / min, and the column was filled with the desorbent to perform a conditioning operation. Then, after feeding the raw material containing the dimethylnaphthalene isomer mixture to the top of the column as a 3 ml pulse, switching to the desorbent flow again and 0.4 ml / min.
The desorbent was fed in at a ratio of, and the raw material feed was developed in the column. The outlet flow is sampled at regular intervals with the time point when the development with the desorbent is started as 0, and the components contained in each fraction are quantified using a gas chromatograph,
The change in the concentration of the raw material components in the outlet flow with the elapse of the outflow time was measured. The peak envelope is obtained by dot stapling the analytical values of each fraction of the effluent. The obtained results are shown in FIG. 1 and Table 1.

Comparative Example 1 Similar to Example 1, a granular Y-type zeolite having a cation site exchangeable with the adsorbent replaced with lithium (particle size distribution 250 to 420 μm) was used. The same procedure as in Example 1 was carried out except that orthoxylene was used as the releasing agent. The obtained results are shown in FIG.

Compared to Example 1, the elution time of dimethylnaphthalene isomers other than 2,6-dimethylnaphthalene was closer to the elution time of 2,6-dimethylnaphthalene, which is a separation target substance, and 2,6- It can be seen that the separation from dimethylnaphthalene is not good.

Comparative Example 2 Y-type zeolite granules having a replaceable cation site replaced with sodium (particle size distribution 250 to 420 μm) were packed in the same stainless steel column with a jacket as in Example 1 as an adsorbent, and the same as in Example 1 below. The dimethylnaphthalene isomer mixture was separated. Table 1 shows the separation factors of other dimethylnaphthalene isomers relative to 2,6-dimethylnaphthalene.

[Effect of the Invention] According to the present invention, 2,6-dimethylnaphthalene can be efficiently and selectively separated from a stock oil containing a dimethylnaphthalene isomer mixture.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and FIG. 2 are diagrams showing the results of Example 1 and Comparative Example 1, respectively. In the figure, the horizontal axis is the outflow time (minutes), and the vertical axis is the weight percentage of the components contained in the fraction sampled at regular intervals.

Claims (1)

[Claims] 1. When adsorbing and separating 2,6-dimethylnaphthalene from a feedstock containing a mixture of dimethylnaphthalene isomers, a Y-type zeolite whose cation site is ion-exchanged with lithium is used as an adsorbent. A method for separating 2,6-dimethylnaphthalene, which comprises using paraxylene as an agent.