MXPA00006493A - Method for producing 2,6-dmn from mixed dimethylnaphthalenes bycrystallization, adsorption and isomerization - Google Patents

Abstract

A method is disclosed to produce 2,6-dimethylnaphthalene (2,6-DMN), used for the production of polyethylene naphthalate, at high purity and high yield from a mixture of dimethylnaphthalene isomers without limitation to the specific isomers present in the feed by a series of fractionation, crystallization and adsorption steps.

Description

METHOD FOR PRODUCING 2, 6-DIMETHYLNAFTALENE FROM MIXED DIMETHYLNAPHALENES BY MEANS OF CRYSTALIZATION, ADSORTION AND ISOMERIZATION FIELD OF THE INVENTION The invention relates to a process for the separation of 2,6-DMN from other isomers of DMN, and the conversion of isomers that are not 2,6-DMN into the desired product 2,6-DMN .

BACKGROUND OF THE INVENTION 2,6-DMN is an intermediate produced during the manufacture of 2,6-naphthalene dicarboxylic acid (2,6-NDA) and 2,6-naphthalene dicarboxylate (2,6-NDC). 2,6-NDA and 2,6-NDC are monomers which, when combined with ethylene glycol, react to produce polyethylene naphthalate (PEN), a polyester with unique and advantageous commercial applications in films, fibers and packaging.

The isomers of dimethylnaphthalene are difficult to separate from one another by distillation, because their boiling points are very similar. There is the technology to recover 2,6-DMN by crystallization, or by adsorption, or by adsorption followed by REF.121244 crystallization. It is difficult to separate 2,6-DMN from 2,7-DMN by crystallization alone because they form a eutectic. It is expensive to recover 2,6-DMN from DMN mixed by adsorption alone because there are no known materials that selectively adsorb 2,6-DMN. In previous technology, when the adsorption and crystallization steps are combined, the adsorption step is always used to remove most of the undesirable DMN isomers. In addition, the adsorption step is often followed by a crystallization step to obtain the desired purity of the product.

A further complication in the commercial production of 2,6-DMN is the difficulty in converting DMN isomers other than 2,6-DMN into the desired 2,6-DMN isomer. It is well known that during the isomerization of DMN, it is easy to move methyl groups in a naphthalene ring when migrating from an alpha position (ie, 1, 4, 5 or 8) to a beta position (ie, 2, 3, 6 or 7) or vi ce versa, but it is difficult when methyl groups have to be rearranged from one beta position to another. The DMN isomers have been classified into groups called "triads", in which isomerization is carried out rapidly. These triads are (1) 1,5-DMN, 1,6-DMN, and 2,6-DMN; (2) 1,7-DMN, 1,8-DMN, and 2,7-DMN; and (3) 1,3-DMN, 1,4-DMN, and 2,3-DMN. The tenth isomer, 1,2-DMN, consists of two methyl groups in adjacent alpha and beta positions, and does not fall into one of the triads mentioned above.

Producers have developed methods to make commercial quantities of 2,6-DMN by avoiding co-producing the 2,7-DMN isomer, due to the difficulty of recovering 2,6-DMN in high yield in the presence of 2,7-DMN. In addition, producers have tried to avoid producing isomers outside the 2,6-triad due to the difficulty of isomerization through triads. Isomers that can not be converted to 2,6-DMN represent a loss of performance and inefficient use of raw materials. Additionally, adsorption is not practical when the concentration of 2,6-DMN in the feed stream is low due to that there are unknown materials that will adsorb 2,6-DMN preferentially over the other isomers. These limitations often necessitate the use of expensive raw materials and controlled organic synthesis reactions that can produce only isomers in the 2,6-triad, such as alkylation of butadiene and ortho-xylene, and methylation of methylnaphthalene.

The technologies that refer to the purification of 2,6-DMN from mixtures of DMN isomer by means of crystallization, adsorption and distillation are known as technologies that are related to the isomerization of non-2,6-DMN to 2 , 6-DMN.

The separation of DMN isomers by crystallization is relatively complete if the composition of the feed is very high in the 2,6-DMN isomer, or if a low yield is acceptable, or if the feed to be crystallized consists of isomers within of a triad. If the concentration of 2,6-DMN is well above the eutectic composition, crystallization alone can produce pure 2,6-DMN in high yields. If the concentration of 2,6-DMN is slightly above the eutectic composition, low yield of high purity DMN can be obtained. If the mixture consists of isomers within the triad of 2,6-DMN, the unrecovered material, a mixture of 1,5-DMN, 1,6-DMN and 2,6-DMN, can be easily isomerized to produce a mixture with 2,6-DMN above the eutectic composition. The crystallization alone becomes insufficient to purify mixed DMN to produce 2,6-DMN when both the 2,6-DMN isomer and the 2,7-DMN are present because they form a eutectic.

The feasibility of separation by adsorption of the DMN isomers has been demonstrated. However, no material that selectively adsorbs 2,6-DMN from a mixed DMN feed has been published. This limitation makes it costly to recover 2,6-DMN from DMN mixed by adsorption alone, because the adsorption equipment must be very large to remove all the different 2,6-DMN components from a feed stream containing small amounts of 2-DMN. , 6-DMN.

One technique to overcome the limitations of the purification of 2,6-DMN by crystallization or by absorption is to combine the two technologies. Such combination has always been done previously using the adsorption step as a step of. pretreatment of the feed before the crystallization step.

An alternative technique for breaking the eutectic 2, 6-DMN / 2, 7-DMN is to partially or completely saturate the naphthalene ring. The resulting decalins or tetralins do not form a eutectic to the same composition of dimethylnaphthalenes, whereby an increased amount of the 2,6- and 2,7- isomers can be recovered by alternatively hydrogenating and dehydrogenating the DMN feed.

It has been described that a mixture of non-eutectic DMN containing 2,6-DMN and 2,7-DMN together with smaller amounts of other hydrocarbons can be sublimated, such that the remaining solid is a mixture of 2,6-DMN and 2,7-DMN. However, no indication is given that sublimation can be used to purify a 2,6-DMN / 2, 7-DMN mixture that is in the form of a eutectic composition.

Previous isomerization technologies have been limited to intra-triad conversions, i.e., movement of methyl groups only between adjacent alpha and beta positions. Santilli and Chen, U.S. Patent Application. Serial No. 08 / 892,508, published July 14, 1997, which is incorporated herein by reference, discloses a method for isomerizing a feed of any composition of mixed dimethylnaphthalenes having a methyl group in each ring to a product that approximates a equilibrium mixture of mixed dimethylnaphthalenes having a methylene group in each ring (ie, the triads 2,6-DMN and 2,7-DMN). The method of the present invention incorporates this method of isomerization through the two triads.

Researchers have integrated separation and isomerization technologies in an attempt to improve the complete process of 2,6-DMN production. These various attempts to integrate the technologies have had limited success because several steps of the process suffer from such problems as low yields or the inability to isomerize between triads.

The technologies discussed above refer either generally or specifically to certain aspects of the presently claimed invention. These technologies are either not very effective or inexpensive to obtain substantially pure 2,6-DMN from feeds containing a variety of DMN isomers outside the 2,6- triad. What is needed is an economical method to produce high purity and high yield 2,6-DMN from a mixture of DMN isomers without being limited to the specific isomers present in the feed. A new method must convert different isomers of 2,6-DMN into the desired 2,6-DMN isomer to have an acceptable yield of 2,6-DMN from the power source. The present invention accomplishes these objectives.

BRIEF DESCRIPTION OF THE INVENTION An object of the present invention is to provide an economical method for separating 2,6-DMN from a mixture of DMN isomers in relatively high and stable yields. The method is highly efficient in its use of dimethylnaphthalene isomers, thus increasing the industrial significance of the process.

Another object of the present invention is to provide a method for purifying 2,6-DMN from a feed mixture of dimethylnaphthalene isomers and nearby boiling compounds, comprising the steps of crystallizing the mixture to precipitate a eutectic composition containing 2,6-dimethylnaphthalene and 2,7-dimethylnaphthalene; optionally dissolving the eutectic composition in a solvent; and recovering a composition of predominantly 2,6-dimethynaphthalene from the dissolved eutectic composition by absorption of the 2, 6-dimethylnaphthalenes in an absorption column. The crystallization achieves high recovery of 2,6-DMN independent of isomers present, while the adsorption step achieves high purity of 2,6-DMN independent of the isomers present.

Still another object of the invention is to fractionate the feed mixture of dimethylnaphthalene isomers and close boiling compounds before it purifies by crystallization and adsorption, to remove compounds that are either more volatile or less volatile than 2,6-DMN and 2,7-DMN. The fractionation step simplifies the downstream purification and reduces the downstream equipment size.

Yet another object of the invention is to recycle the DMN isomers, predominantly different isomers of 2,6-DMN, which either are retained in the mother liquor during the crystallization step or which are recovered in the extract stream during the step of adsorption to be isomerized in a mixture that closely approximates an equilibrium distribution of isomers of dimethylnaphthalene, which. they can be recycled to the p a s o f f a c c t i o n t i n t. The hydroisomerization / dehydrogenation is a highly efficient conversion and close to the balance of different isomers of 2,6-DMN in the desired 2,6-isomer.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a simplified process flow diagram of a preferred embodiment of the invention.

Figure 2 is a graphical representation of the amounts of various isomers of DMN in an effluent against time.

Figure 3 is a graphical representation of a solvent crystallization experiment.

Figure 4 is a graphical representation of the amounts of 2,6-DMN versus 2,7-DMN in an effluent against time.

DETAILED DESCRIPTION OF THE INVENTION A continuous process for the recovery and purification of 2,6-DMN from a hydrocarbon feed has been developed. It contains mixed dimethylnaphthalene isomers. The process of this invention is comprised of the steps of fractionation, crystallization, adsorption and εomerization. A simplified process flow diagram of a preferred embodiment of this process is shown in Figure 1.

The feed for the new process is a hydrocarbon mixture containing isomers of dimethylnaphthalene (DMN). The concentration of DMN in the feed is preferably greater than 5% p, more preferably greater than 50% p., And more preferably greater than 80% p. Potential sources of hydrocarbon feeds are oil refinery streams, coal tar liquid, or the reaction products of a synthetic chemical processing route. Examples of oil refinery streams include, but are not limited to, high-boiling aromatic fractions produced in petroleum naphtha reformation to produce high-octane gasoline; aromatic fractions produced by the thermofractionation of catalytically reformed gasoline; aromatic fractions produced by the thermally reformed catalytic thermofraction of naphtha; aromatic concentrates obtained from catalytic gas oil produced in catalytic or petroleum thermofraction; and crude oil units. The mixed DMN could be produced from the chemical synthesis route such as, but not limited to, dehydrocyclization of pentyl toluene made from alkylation of pentenes and toluene, dehydrocyclization of pentenyl toluene made from alkenylation of ortho-xylene and butadiene, or methylation of methylnaphthalene. In a preferred embodiment, the fresh feed is combined with recirculating streams of the isomerization step downstream of this process. Alternatively, the recirculation may be introduced downstream of the fractionation unit.

In a preferred embodiment, the feed is fractionated to obtain a heart cut that is rich in DMN isomers and which boils in the approximate range of 249-271 ° C (480-520 ° F), preferably in the range of 260- 265.5 ° C (500-510 ° F). The fractionation can be carried out by conventional distillation in one or more distillation columns. If a column is used, multiple feed and output currents are required. The preferred configuration is to use two columns. In the first column, the more volatile components that 2,6-DMN are distilled in the dome and can be recovered as valuable by-products, recirculated to previous steps of the DMN production process, or used as fuel. In the second column, the less volatile components than 2,6-DMN are collected in the bottom and can be recovered as valuable by-products, recirculated to previous steps of the DMN production process, or used as fuel. Fractionation may not be required before crystallization if the feed has a sufficiently high concentration of DMN, The fractionated DMNs may contain nearby boiling components such as, but not limited to, pentyltoluenes, pentenyl toluenes, methylnaphthalenes, ethylnaphthalenes, dimethylhydronaphthalenes, dimethyltetralins, di ethyldecalins, trimethylindanes, tri ethylnaphthalenes as well as other nearby boiling aromatics, and naphthenic compounds. It is desirable to minimize the concentration of components that would crystallize at a temperature above the crystallization temperature of 2,6-DMN, to minimize the simultaneous recovery of impurities with the desired 2,6-DMN product.

In a preferred embodiment, the fractional DMN mixture is cooled to precipitate 2,6-DMN and a eutectic composition of 2,6-DMN and 2,7-DMN. The final cooling temperature is dependent on the feed composition and on whether a solvent is added. For melt crystallization, the final cooling temperature is as high as 110 ° C (230 ° F) for a highly concentrated feed in 2,6-DMN, or as low as -16 ° C (3 ° F) for a feed diluted in 2,6-DMN. For the concentration range of interest, the final cooling temperature is in the range of 68 ° C to 27 ° C (155 ° F to 80 ° F). For crystallization with solvent, the cooling temperature could vary over a wide range, depending on the solvent and the concentration of the feed, but could be in the range of 110 ° C to -84 ° C (230 ° F to -120 ° F). ), preferably 26 ° C to 4 ° C (80 ° F to 40 ° F). The pressure can be from 0 to 3000 psi. An alternative to cooling is to precipitate 2,6-DMN and a eutectic by a combination of cooling plus pressurization of the system at between 7,000-20,000 psi. Crystallization could also be induced by removing solvent by evaporation or adding agents that reduce the solubility of DMN in solution.

The crystallization could be carried out in batches or continuously. It could be carried out in a container or more than one physically separate series container. The preferred configuration depends on the relative concentrations of 2,6-DMN and other compounds that would co-precipitate, especially 2,7-DMN. If the crystallization is carried out in a vessel, the maximum recovery of 2,6-DMN is obtained by cooling the fractionated DMN mixture to the eutectic composition of 2,6-DMN / 2, 7-DMN until it has precipitated all the 2,6-DMN. If multiple crystallizers are used in series, 2,6-DMN partially precipitates from the mother liquor in the first crystallizer, separates from the supernatant, and the supernatant is then transferred to one or more vessels downstream for additional recovery of 2,6-DMN. . Throughout the entire process, the 2,6-DMN and eutectic crystals of 2,6-DMN / 2,7-DMN are collected together. At the time that the different isomers of 2,6-DMN do not co-precipitate in one of the crystallizers and there is a sufficiently high concentration of 2,6-DMN which is higher than the eutectic composition, it may be advantageous to collect and recover 2. , 6-DMN essentially pure before reaching the eutectic point.

The simplest crystallization technique is melt crystallization, provided the composition of 2,6-DMN plus 2,7-DMN in the feed mixture of the DMN is at least 20% by weight, preferably at least 50% by weight. p., and more preferably at least 90% p. Fusion crystallization can be carried out in either a static or a dynamic design. The mixture of DMN isomers is introduced into the crystallizer and the contents are cooled with a non-contact heat transfer medium. The desired crystals are formed and adhere to the heat transfer surface. When essentially all the 2,6-DMN has solidified, the cooling is stopped and the remaining liquid content is drained from the crystallizer. The heat transfer medium is then heated slightly to melt the solids from the heat transfer surface. The initial melt will contain a higher concentration of impurities than the mass of product, so it can be collected separately and sent with the other DMN isomers to the hydroisomerization / dehydrogenation unit, to increase the purity of the solution of 2-6. DMN / 2, 7-DMN that goes to the adsorption step. The mixture of 2,6-DMN and liquid 2,7-DMN is sent directly to the adsorption step.

As an alternative, solvent crystallization can be used to "separate the authentic 2,6-DMN / 2,7-DMN, and would be the preferred crystallization method for feeds with low concentrations of 2,6-DMN plus 2,7- DMN A solvent such as a low boiling hydrocarbon such as toluene, xylene, octane or heptane, or an alcohol such as methanol, ethanol or isopropanol, or other kinds of solvents such as ethers, or a low molecular weight carboxylic acid such as acetic acid, or a combination of solvents Light aromatic hydrocarbons are the preferred solvents with toluene and meta-xylene most preferred No solvent can be added to increase precipitation since these could impact the purity of the final product, if they can not be separated properly in the adsorption step In a solvent crystallization process, the 2,6-DMN and 2,7-DMN crystals are mechanically separated from the solution using, for example, example, filters or centrifuges, and already melted or re-dissolved before it is sent to the adsorption step. The supernatant mixture will contain all DMN isomers, including trace amounts of 2,6-DMN as well as nearby boiling compounds, and is sent to the hydroisomerization / dehydrogenation unit for further processing.

The crystals produced in a solvent crystallization process are optionally washed with another agent, such as methanol to remove the mother liquor retained between the particles and contaminants that could adhere to the surface of the particles. The crystals are separated once more mechanically from the washing solution using, for example, filters or centrifuges. The washing agent is cooled near the crystallization temperature to minimize that the DMN is dissolved in the washing solvent. After washing, the crystals could optionally be dried with moderate heating to remove the remaining washing agent and to partially sublimate the DMN isomers other than 2,6-DMN. An acceptable alternative for washing solvents is to partially melt the DMN crystals to remove impurities from the liquid that are made in a washing column.

The final purification step is the separation by adsorption of 2,7-DMN of 2,6-DMN. The adsorption could be developed either by a bed unit of an oscillation or, more preferably, a bed unit moving simulated countercurrently. For an oscillating bed unit, one bed operates in adsorption mode while another operates in regeneration mode. The adsorbent material selectively adsorbs 2,7-DMN from the feed stream, leaving essentially pure 2,6-DMN in the effluent. When unacceptable amounts of 2,7-DMN appear in the effluent, the operating bed is considered to have reached the useful limit of its ability to remove 2,7-DMN and is removed from service. The other bed is placed in line while the first bed is regenerated and the cycle repeats itself. Multiple beds can be staggered in adsorption mode and regeneration mode to optimize capital and operating costs. The adsorption and regeneration can be carried out batchwise or continuously. For a bed unit moving countercurrently simulated, the feed of 2,6-DMN / 2,7-DMN and a suitable desorbent are introduced to the fixed-bed adsorption column at two different places. Two streams of product are drawn from two different places along the column: an extract containing desorbent with 2,7-DMN and other impurities that were present in the feed, and a raffinate containing desorbent and 2,6-DMN essentially pure. The DMNs are recovered from their effluent streams from the respective adsorber by distillation. The desorbent is returned to the adsorber, 2,7-DMN is combined with the supernatant of the crystallizer and sent to the hydroisomerization / dehydrogenation unit, and 2,6-DMN is collected as the desired product.

Suitable adsorbents include crystalline aluminosilicates, L-zeolites, X-zeolites, Y-zeolites, And Ofretite, and Ambersorb®563 (a carbonaceous adsorbent). The preferred adsorbents are Y-zeolites exchanged with Group I and / or Group II metals. { i.e., Na, K, Ca, Ba, etc.) with the most preferred Group I metal, which is potassium. Suitable desorbents include, but are not limited to, light aromatic hydrocarbons such as toluene, para-xylene, ethylbenzene, and para-diethylbenzene. Preferred desorbents are aromatic hydrocarbons and the most preferred is para-xylene. The desorbent could be a compound with a higher boiling point than dimethylnaphthalene.

Preferred operating conditions for the adsorption process require dissolution of the DMN feed mixture in a solvent. The DMN could dissolve at any concentration, but the preferred concentration range is 5% to 60% DMN. The solvent could be any liquid that can dissolve DMN and at the same time increase the adsorption selectivity. Suitable solvents are light aromatic hydrocarbons, or aliphatic hydrocarbons with carbon numbers of 5 to 20, with octane or heptane being the preferred solvents. Operating temperatures can be in the range of 26 ° C to 104 ° C (80 ° F to 220 ° F), depending on the concentration, with a preferred temperature of '60 ° C to 82 ° C (140 ° F to 180 ° F). The operating pressure may vary but is set high enough to maintain the solvent and the DMN feed in a liquid state through the column. The flow rate could vary but the preferred condition is with a liquid hourly space velocity (LHSV) of 0.1 to 10 hr "1.

The adsorbent should be carefully dried to the appropriate water content to maximize the separation factor between 2,6-DMN and 2,7-DMN. Y-zeolite is a low silica zeolite and, as such, rapidly adsorbs moisture from the air. If the water content in the adsorbent is too high, the adsorbed water will reduce the accessibility of the adsorbate molecules to the high surface area of the zeolite. However, if the water content is too low, the adsorption selectivity of 2,6-DMN and 2,7-DMN decreases.

The feed to the two-step hydroisomerization / dehydrogenation unit consists of depleted DMN-depleted 2,6-DMN as well as nearby boiling components. In a preferred embodiment, the source of these DMNs is the supernatant of the crystallizer and adsorber extract that was previously described, in addition, any feed that is substantially depleted in 2,6-DMN, such as petroleum refinery streams, tar liquids of coal, or rion products of a synthetic chemical processing route can be used exclusively or as a co-feed with the supernatant and extract.

The hydroisomerization / dehydrogenation is carried out as described in U.S. Patent Application. Serial No. 08 / 892,508 (Santillini and Chen), published on July 14, 1997, which is incorporated herein by reference. The aromatic rings of the DMN molecules in the feed are first partially or completely saturated to form dimethyltetralins (DMT) and dimethyldecalins (DMD) with a double functional metal-acid catalyst (eg, sulfur PdS / Boron-Beta with Al, sulfide PtS / Boron-Beta with Al, sulfur PdS / Y-zeolite, or non-sulfur PD / Boron-Beta with AL). Migration of the methyl group occurs rapidly under the rion conditions to produce a distribution of DMT and DMD with a methyl group in ring. The isomerized structures are essentially converted to an equilibrium distribution of DMN by passing a second catalyst in a subsequent dehydrogenation ror. The second catalyst is a reforming catalyst that suppresses transalkylation, dealkylation, and catalytic thermofraction rions (e.g., Pt / Re / Al203 sulfide, Pt / Na-ZSM-5 sulfide, or PtS / Cs / Boro-SSZ-42). In a preferred embodiment, the yield of partially saturated species (DMT) of the hydroisomerization reaction should be at least 5 weight percent. In a more preferred embodiment, the yield of partially saturated species (DMT) must be at least 10 weight percent. The space velocity per hour by weight (WHSV) can vary from approximately 0.1 to 100 hr "1, the pressure can vary from 0 to 3000 psi, the molar ratio of hydrogen / hydrocarbon can vary from <0.1 to 100, and the reactor temperature can vary from about 149 ° C to 538 ° C (300 ° F to 1000 ° F). Approximately 50% conversion of 2,7-DMN to the 2,6-dimethylnaphthalenes triad can be obtained with little or no formation of methylnaphthalenes, 1,2-DMN, 1,3-DMN, 1,4-DMN, 2, 3-DMN or trimethylnaphthalenes with this two-step process, by optimizing the process conditions. In all embodiments of the hydroisomerization / dehydrogenation process, the feed of dimethylnaphthalenes can flow over the catalyst together with hydrogen gas or the reaction can be carried out batchwise.

The DMN produced in the hydroisomerization / dehydrogenation unit is recirculated and recovered as product, and the different isomers of 2,6-DMN are recirculated until extinction. In a preferred embodiment, the mixed DMN product of the hydrolyzing / dehydrogenation unit, referred to earlier as isomerized, is recirculated and combined with the fresh hydrocarbon feed to the fractionation unit to remove the light and heavy contaminants. Alternatively, the contaminants in the isomerization could be removed in a separate and distinct distillation unit, and recovered as by-products or fuel. For example, MN and TMN could be transalkylated to produce DMN and increase the total throughput of this process. In yet another embodiment, in the absence of light and heavy contaminants, the isomerized can be combined with DMN distilled from the fractionating column as feed to the crystallization unit.

EXAMPLES Example 1 The following example illustrates that a complex mixture of DMN isomers can be separated by dissolving it in a solvent, and passing the solution through a column of adsorbent, furthermore, this example also illustrates that the isomers of 2,6-DMN and 2,7-DMN are well separated from each other in this way. This example also illustrates that other isomers, such as 1,6-DMN, 1,5-DMN and 1,7-DMN elute earlier than 2,7-DMN and about 2,6-DMN. Therefore, using an adsorption purification process to recover 2,6-DMN when the feed contains 1,6-DMN, 1,5-DMN and 1,7-DMN isomers, as in the prior art, has an efficiency reduced and therefore it is more expensive to operate. The adsorption process becomes much more efficient when a previous step is used to remove or reduce the amount of different isomers of 2,6-DMN and 2,7-DMN.

A mixture of DMN isomers having the composition of 8.93% of 1,7-DMN; 1.88% of 1,5-DMN; 8.94% of 1,6-DMN; 31.05% of 2,7-DMN; and 49.20% of 2,6-DMN was dissolved in meta-xylene and passed through a potassium exchange column of Y (K-Y) adsorbent zeolite. The weight of the adsorbent was 2.12 grams and the space velocity per hour of the liquid (LHSV) of the column was 1.2 hr "1. In a 40 to 50 minute interval, the DMN in the effluent was approximately 100. % of 2,6-DMN, and at 50 minutes of running time the concentration ratio of the effluent to feed concentration, Cef / C0, was approximately 0.2.In the interval between 50 and 60 minutes, the DMN in the effluent was of approximately 91.2% of 2,6-DMN, and at 60 minutes of running time, the Cßf / Ca was approximately 0.75 In the interval between 60 and 70 minutes, the DMN in the effluent was approximately 81.5% of 2 , 6-DMN, and at 70 minutes of running time, the Cßf / CQ was approximately 0.975.In the interval between 70 and 80 minutes, the DMN in the effluent was approximately 74.5% of 2,6-DMN; the 80 minutes of running time, the Cef / C0, was approximately 1.05, a more complete graphic representation of the amount It is of the several isomers of DMN in the effluent against time shown in Figure 2.

Example 2 The following example illustrates the use of a coarse crystallization step to reduce the level of isomers nc-2, 6/2, 7.

A mixture of isomers of 6.3 grams of 1,6-DMN, 5.7 grams of 1,7-DMN, 1.8 grams of 1,5-DMN, 6.3 grams of 2,7-DMN and 6.3 grams of 2,6-DMN dissolved in 15 grams of toluene, then cooled in a stirred vessel at 0 ° C (32 ° F). The solution was filtered and a precipitate recovered. The precipitate was rinsed with cold methanol, and then dried at room temperature under vacuum overnight. The product was found to be 90% 2,6-DMN, 6% 2,7-DMN and 3% other DMN isomers.

Example 3 This example illustrates the total separation process to produce pure 2,6-DMN from a reformed oil feed.

The reformed oil from a chemical synthesis was purified to produce pure 2,6-DMN. The reformed had the composition shown below in Table A: Table A The first purification step was to distill a heart cut between 260 ° C and 271 ° C (500 ° F and 520 ° F). The composition of the resulting distillate is given below in Table B. 38 grams of distillate were diluted with 38 grams of toluene and cooled from 27 ° C to -20.5 ° C (80 ° F to -5 ° F) at a rate of 0.17 ° C / min (0.3 ° F / min) in a stirred crystallizer in a batch. The relative concentration of several DMN isomers in solution during this process is shown in Figure 3. In Figure 2, it can be seen that the concentration of 2,6-DMN was reduced as the temperature dropped below -1 ° C ( 30 ° F). At temperatures below -20.5 ° C (-5 ° F), the concentration of 2,7-DMN also drops. However, the other isomers present were substantially remanent in the solution. For the. both these isomers were separated from the 2,6-DMN and 2,7-DMN phase. The solid precipitate formed was collected and separated from the volume of the adhesion fluid. The composition of the resulting precipitate is then given in Table B.

The precipitate was dissolved in m-xylene and fed to a column of adsorbent with K-Y zeolite. The effluent was recovered and dried. The product was essentially pure 2,6-DMN.

Table B Example 4 This example illustrates the use of ordinary crystallization followed by adsorption when the feed has a high proportion of 2,6-DMN. 83. 5 grams of a mixture of DMN and meta-xylene (with the composition shown in Table C) was charged into a 250 ml agitation vessel with a glass jacket. A cooler was passed through the jacket to cool the solution from 24 ° C to 7 ° C (75 ° F to 45 ° F) at a rate of 1 ° C (1.8 ° F) every 7 minutes. The solids precipitated and the resulting crystals were filtered through an 8 micron filter paper, and recovered. The crystals were washed with a small amount of methanol and dried in vacuo. The purified crystals weighed 1.25 grams and the composition of the solids analyzed is shown in Table C. The recovery of 2,6-DMN in this crystallization example was calculated to be 16.4%.

Table C The recovered crystals were dissolved in meta-xylene to give a 5% solution of DMN. The above solution was pumped through a stainless steel column (width 0.95 cm, 3/8", length 30.48 cm, 12") packed with 5.7 grams of K-Y powdered zeolite. The concentration of DMN isomers in the effluent was measured over time and is shown in Figure 4. The solution was recovered for 105 minutes, during which time the interference of 2,6-DMN was detected. The recovered effluent was dried and the product was pure 2,6-DMN.

Example 5 This example illustrates the additional purification that can be obtained by means of a partial sublimation process that occurs during drying.

A sample of 2,6-DMN containing other DMN isomers was rinsed with cold methanol. The mixture moistened with methanol was analyzed and found to have the reported composition, in a solvent-free base, in Table D. The wetted solid was dried at room temperature overnight under vacuum. The resulting composition is also reported in Table D.

Table D Example 6 This example illustrates the additional purification that can be obtained by means of a partial sublimation process, which occurs during a drying step.

A sample of 2,6-DMN containing isomers of 2,7-DMN was rinsed with cold acetone. The mixture moistened with acetone was analyzed and found to have the reported composition, in a solvent-free base, in Table E. The wetted solid was dried at room temperature overnight under vacuum. The resulting composition is also reported in Table E.

Table E Although a few embodiments of the invention have been described in detail before, it will be apparent to those skilled in the art that various modifications and alterations can be made to the particular embodiments shown, without departing materially from the new indications and advantages of the invention. Therefore, it will be understood that such modifications and alterations are included within the spirit and scope of the invention as defined by the following claims.

Side note: Ambersorb® is a registered trademark of Rohm & Haas Company.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (36)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A method for purifying 2,6-dimethylnaphthalene from a feed mixture of dimethylnaphthalene isomers and nearby boiling compounds, characterized in that it comprises the steps of: (a) crystallizing the mixture to precipitate from a supernatant a precipitate containing 2,6- dimethylnaphthalene and 2,7-dimethylnaphthalene; (b) dissolving the precipitate in a solvent; and (c) passing the dissolved precipitate through an adsorbent to recover an effluent containing 2,6-dimethylnaphthalene.

2. The method according to claim 1, characterized in that the method further comprises, before step (a), a fractionation step to remove more volatile and less volatile compounds than 2,6-dimethylnaphthalene and 2,7-dimethylnaphthalene.

The method according to claim 2, characterized in that the method further comprises isomerizing the dimethylnaphthalene isomers other than 2,6-dimethylnaphthalene which are retained in the supernatant of step (a) or adsorbed in the adsorbent of step (c) for converting the isomers to a mixture consisting essentially of an equilibrium mixture of dimethylnaphthalene isomers.

4. The method according to claim 3, characterized in that the equilibrium mixture of isomers of dimethylnaphthalene is recirculated to the fractionation step.

5. The method according to claim 3, characterized in that the equilibrium mixture of isomers of dimethylnaphthalene is recirculated to the crystallization step.

6. The method according to claim 2, characterized in that, after step (c), the method further comprises purifying the effluent by a method comprising: (a) cooling the effluent to produce the solid precipitate; (b) washing the solid precipitate; and (c) drying the washed precipitate under conditions that allow partial sublimation of different isomers of 2,6-dimethylnaphthalene from the precipitate.

7. The method of claim 1, characterized in that the feed mixture is prepared by a process comprising the steps of: (a) alkylating toluene with a C5 olefin or C5 olefins mixed in the presence of an alkali metal to form pentyltoluenes; and (b) dehydrocyclization of the pentyl toluenes with a catalyst containing a Group VIII metal or a mixture of Group VIII metals and a support material.

8. The method of claim 7, characterized in that the Group VIII metal is selected from the group consisting of Pt, Pd, Ni and Ir.

9. The method of claim 7, characterized in that the support material is alumina.

10. The method of claim 7, characterized in that the catalyst further contains a metal selected from the group consisting of Re, Ge and Sn.

11. The method of claim 1, characterized in that the feed mixture is prepared by a method comprising the steps of: (a) alkenylation of ortho-xylene with butadiene to form pentyl toluenes; and (b) dehydrocyclizing the pentyl toluenes in one or more steps to form a mixture of dimethylnaphthalene isomers.

12. The method of claim 1, characterized in that the feed mixture is prepared by means of a process comprising alkylating methylnaphthalene to form mixed dimethylnaphthalenes.

13. The method of claim 1, characterized in that the feed mixture is prepared by means of a process comprising the fractionation of mixed hydrocarbon streams resulting from oil refining.

14. The method of claim 1, characterized in that the feed mixture is prepared by means of a process comprising the fractionation of mixed hydrocarbon streams found in coal tar liquids.

15. The method of claim 1, characterized in that, in step (a), the mixture is cooled.

16. The method of claim 1, characterized in that, in step (a), the mixture is cooled in a solvent.

17. The method of claim 1, characterized in that, in step (a), the mixture is added to a solvent and the solvent is evaporated.

18. The method of claim 1, characterized in that step (a) is carried out in a container.

19. The method of claim 1, characterized in that step (a) is carried out by partially precipitating 2,6-MN and 2,7-DMN of the supernatant in a first container, and then transferring the supernatant to a second container to further precipitate 2,6-DMN and 2,7-DMN of the supernatant.

20. The method of claim 1, characterized in that it further comprises, before step (a), cooling the feed mixture just above the eutectic point 2, 6-DMN / 2, 7-DMN and recovering pure 2,6-DMN.

21. The method of claim 1, characterized in that step (c) uses two or more adsorption vessels operating as a bed unit moving simulated countercurrently.

22. The method of claim 1, characterized in that step (c) uses two or more adsorption vessels operating as an oscillating bed unit.

23. The method of claim 1, characterized in that the adsorbent comprises a material selected from the group consisting of crystalline aluminosilicates, L-zeolites, X-zeolites, Y-zeolites, and Ofretite, carbonaceous adsorbents and mixtures thereof.

24. The method of claim 23, characterized in that the adsorbent is exchanged with metals selected from the group consisting of Group I metals, Group II metals and mixtures thereof.

25. The method of claim 24, characterized in that the adsorbent is exchanged with a Group I metal.

26. The method of claim 25, characterized in that the adsorbent is exchanged with potassium.

27. The method of claim 1, characterized in that the solvent in step (b) is a light aromatic hydrocarbon.

28. The method of claim 1, characterized in that the solvent in step (b) is an aliphatic hydrocarbon having a carbon number of from 5 to 20.

29. The method of claim 28, characterized in that the solvent is heptane.

30. The method of claim 28, characterized in that the solvent is octane.

31. The method of claim 1, characterized in that the method further comprises regenerating the adsorbent of step (c) with a desorbent comprised of an organic solvent.

32. The method of claim 31, characterized in that the organic solvent is a light aromatic hydrocarbon selected from the group consisting of toluene, xylenes, ethylbenzene, and para-ethylbenzene.

33. The method of claim 32, characterized in that the organic solvent is para-xylene.

34. The method of claim 1, characterized in that the method further comprises, after step (c), the steps of: (a) hydroisomerizing with an acid catalyst the dimethylnaphthalene isomers other than 2,6-dimethylnaphthalene which are retained in the supernatant from step (a) or adsorbed on the adsorbent of step (c), to produce a mixture of dimethyldecalins and dimethyltetralins; and (b) dehydrogenating the mixture of dimethyldecalins and dimethyltetralins.

35. The method of claim 1, characterized in that the steps are practiced in a continuous manner.

36. The method of claim 1, characterized in that the steps are practiced in a batch manner.