DE1418959A1 - Method and apparatus for producing p-xylene - Google Patents

Description

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Disclosure documents ^ö - ^ö —-— ^ö -

1418359

Applicant; i'irma MAKHZsm SEK.IYU iiABUöEIKI KAIöHA Minamiku, Osakashi, Japan 3, Uagahoribashisuji 1-chome

"Process and device for the production of p ~ xylene"

The invention relates to a method and an IT mold

for the large-scale production of p-xylene. with a degree of purity over $ 95 and in high yield from a hydrocarbon mix. which is a substantial amount of one in the main Xylene mixture consisting of p-xylene, m-xylene, o-xylene and ethylbenzene contains, and in particular a method for crystallizing p-xylene by cooling in a crystallizer of special construction and subsequent deposition of the p-xylene from the xylene mixture,.

It is already well known that p-xylene by cooling the xylene mixture can be obtained in a cooler, wherein the 'p-xylene crystallizes out and then from the xylene mixture is deposited. However, in order to have such a pure p-xylene in To be able to produce high yields at low material and labor costs, of course, various devices are required. In particular - and this is the most important problem - the large p-xylo! Crystals must be in a crystallization stage are formed.

Documents νΛ7 | ΐΛ ** Ντ. 80 980 5/0742 BAD original

The crystallization can, by dividing the process into two stages are illustrated: the formation of a crystalline. · sation nucleus and the growth of the nucleus to form a crystal. So that a ' Solute crystallized from a solvent, must the solution in a solubility beyond saturation, are in a supersaturated state. There is no doubt that the saturation solubility is always influenced by its environment, however, nucleation is reduced when the solution is in the supersaturated solubility state, while, if the kernels are already present in the system, the supersaturation is almost entirely consumed in the growth of the kernels will.

Therefore, in the manufacture of p-xylene, if the Crystallization by cooling should take place a longer time Time required for gradual cool down during the one Maintain as steady a state of saturation as possible and it is better to keep the fluid in a less supersaturated state. These conditions are necessary to achieve larger crystals «

For this purpose, various methods have so far been used Preparation of p-xylene from the xylene mixture with an or several stages of crystallization and separation have been proposed and used. When performing these procedures, however, using a crystal display * - Apparatus such as a horizontal twin-tube cooler with a scraper, a jacket cooler for generating low temperatures and the like a completely satisfactory one Result cannot be achieved.

BAD ORiGlNAL 809805/0742

_ 3 -

As a result of various attempts it has now become proven that in the process with two crystallization units Filtration levels are given particularly large crystals can be denied if a number is chalked up one after the other Crystallization vessels of special design among selected ones Conditions are used, with p-xylene being of a high degree of purity and in greater yield than the previous methods is effectively deposited.

The invention provides a process for the industrial production of para-xylene with purity holism una in high yield from a ivohlenwasserstoffgeusisch, the composite substantial Mt.-n.ge a hauptsäenlich m- from _P-1 * XyIuI Xylul, o-xylene una iithylbenzol Contains crude xylene, where in the first .. η üiufe the p-xylene h us dym crude mixture crystallizes out and separated from this and in the second citufe melted the p-xylene, then recrystallized and deposited again Wiret, which is characterized by the fact that in each Second stage, K-crystallization vessels connected in series with an internal cylinder, a scraper attached to a scraper slowly rotating in a G-vessel, as well as a stirrer arranged on the lower part of the gas vessel and a cooling jacket are used, whereby the liquid in each The vessel is inevitably brought into circulation at one revolution of the agitator and the inner cylinder gradually sinks in each vessel, w ^ rrt-na a . & $ £ ■. initen aes heat bertraf'ungsgrad uufch ^ brehaben German right inside α · β.ί? G-ei'äe. es alt α en.-j, b. _: tr ei brazen 've.-hinuert ,. aie. Temperatur ί rn-er in each u-tz'ä3iT gleiolisir'sciig;: e; i; .lt-n unu _c : l? ichseiti .... .ie ri.?;·. "■!. Linger ζ .-. Lt ~ '-r jas ho * ■, 1.?. · -;: _{; t} ; eac ;;:> } -H ^: ic. , Ir-r-

809805/0742. _BA D ORIGINAL

will hold so that the Bohgemiseh gradually cools down and large p-xylene crystals arise, which stand out from let the mother liquor separate.

The device for carrying out the inventive Procedure is characterized by the combination of at least three crystallization vessels in the first stage of the Crystallization process, each of which has an inner cylinder, one moving at slow speed in the (Jefäss scraper attached to the rotating shaft, one on the bottom part of the vessel arranged Kührwerfc, a cooling jacket and has a separator, wherein in the second stage of the crystallization process at least one crystallization- vessel of the same construction as the vessels in the first - crystallization stage and another separator provided oil,

According to the invention, large p-xylene crystals can be crystallized from the xylene mixture of low p-xylene concentration in the first stage, so that crystals of a high degree of purity and in high yield can be obtained in an effective manner The highly concentrated p-xylene thus formed can be purified by effective crystallization, as a result of which a p-xylene of a very high degree of purity is obtained.

A preferred embodiment of the erfindmigsgemässen Crystallization vessel is described below with reference to the drawings.

Show it: - '

Fig. 1 is a longitudinal section through a crystallization vessel and

2 shows a schematic flow diagram of the overall crystallization system,

In Fig. 1 is a crystallization housing 1 with a Surrounding cooling jacket 11 through which a coolant can flow, so that the inside of the crystallization vessel is cooled. 12 is the inlet for the coolant, 13 the coolant outlet. The circuit runs between "the housing 1 of the crystallization vessel and the outside of an inner cylinder 2 as well as in the Inside the inner cylinder and takes place by rotating the inner cylinder 2 with its scrapers 3 at a slower rate Speed driving shaft 4 of a motor 5 and at the same time by rotation of a driven by a motor 14 Shaft 16, which in turn is an example of a rudder blade, preferably as a propeller blade -, on but best designed as a paddle stirrer 8 with appropriate speed drives. A horizontal rod 18 holds the inner cylinder 2 and the scrapers 3. The ethoxylene mixture, which is introduced through a feed line 9 and flows downward through the interior of the inner cylinder 2 inevitably circulated to the outside of the inner cylinder and conveyed to the upper part of the vessel. A The guide cylinder 6 carried by a holding plate 7 surrounds it

the agitator 8. A guide block 17 is attached to the bottom of the vessel. The circulation of the liquid is effectively promoted both by the guide cylinder 6 surrounding the agitator 8 and carried by the holding plate and by the guide block 17 attached to the bottom part of the vessel, but these components are not essential for the positive circulation per se. In order to obtain the best conditions for the formation of p-xylene nuclei,

* 809805 / Q742 bad original

the flow rate of the raw mixture at one through the Coolant-cooled crystal formation surface 15 between the housing 1 of the crystallization vessel and the inner cylinder 2 at Ο, 3 - 5 m / seo, preferably at 1 m / sec. kept, with a reduction in the heat transfer value by the means Rotation of the inner cylinder taking place scraping of the scrapers on the crystal formation surface 15 is prevented. The ones in the The upper part of the transported crystal nuclei in the supersaturated liquid are during its passage through the indoor rotating at a suitable low speed cylinder fully grown. The liquid with the crystals formed in this way is now through an outlet 10 drained from the vessel.

The practical method according to the invention the p-xylene crystallized using the crystallization vessel described above and removed from the xylene mixture is deposited is explained below.

The Rohxylolgemiseh to be used according to the invention can be prepared from by isomerization or hydrogenation processes Products are obtained, the general composition of the xylene mixture from the following Table 1 can be seen.

Table 1

(Μ p-xylene H up to 20 percent by weight -j

t>. m-xylene 32 to 50 "" ©

"^. o-xylene .14 to 25" O

£ J ethylbenzene 5 to 30 "'p

o other substances 0 to 10 "

- * <In the first stage of crystallization. and separation process ens the eohxylene mixture is first removed from the separator the filtrate coming through a heat exchanger is cooled

after which it continues to heat the drainage to that from the The same separator gives off the "i" filtrate coming »This is the xylene mixture cooled from room temperature to about -11 ° C and then into a pre-cooling vessel of exactly the same design as the crystallization vessel used in the crystallization stage introduced, where it is cooled to a temperature slightly higher than that at which the Crystals appear, for example at -30 to -55 ° C, whereupon it in the first stage in the crystallization vessel is promoted. The residence time in the pre-cooling vessel is one and a half to three and a half hours.

The crystallization used in the first stage vessels are made up of at least three vessels of the above The special construction described, the xylene mixture being pumped into each vessel and it is cooled in the last vessel to a temperature which is slightly higher than that at which p-xylene finally closes forms eutectic products with m-xylene or o-xylene, wherein this temperature varies between -60 and -85 ° C depending on the composition of the xylene mixture. In this

the temperature difference between the one to be introduced into the vessel and the one already in the vessel. Liquid in each vessel kept at less than 10 ° C and the xylene mixture newly introduced into the vessel by rotating the agitator, scraper and inner cylinder for a very short time with the one in the vessel liquid intimately mixed «The capacity each keg is sized so that the liquid for

809805/074?

can stay in it for at least an hour, while the number of jars is chosen so that the temperature difference between the one to be added and the one that is already in the container Liquid can be kept within 10 ° C? this can reduce the oversaturation of the Always bring the liquid to the minimum that prevents the formation of new crystallization nuclei.

Those in the first stage of the crystallization process The crystals produced have a flat, platelet shape, with the distribution curve of the crystal sizes at its maximum reached at 100 x 400 x 50yu. The crystals thus formed are separated from the mother liquor by means of a separator. A yield can be achieved here through the formation of large crystals of over $ 95 for a ~ m cake with a purity of over $ 85 can be achieved. The yield in the separator is affected the final yield, and the higher the degree of purity of the p-xylene contained in the cake, the more the solidification load reduced.

The second stage consists of recrystallization and redeposition of what was obtained in the first stage p-xylene cake.

In the deposition process in the first stage, it is very difficult to remove the liquid from the crystals due to the very low temperature and the very high viscosity of the liquid. Moreover, since the concentration of p-xylene in the p-Xylolkuchen in the remaining mother liquor is very low, it is difficult Xylul-p of high Hein recognition alone in the first stage TUs Kristallisäti y..r

ft η ί> * ■ * ~ * "· - ■ * ■

and to win the deposition process. Hence, in the second Stage using vessels of the same construction like the vessels used in the first stage, a recrystalline. sation made, and between that obtained in the first stage Cake melted again and then recrystallized at a temperature of about 5 to -25 ° C in Crystallization vessels of exactly the same type as used in the first stage are introduced.

To this end, the amount of that contained in the final crystal pulp To determine solid matter, something is now done by the separator in the second stage filtered mother liquor with appropriate mixed with the crystal pulp. The crystallization vessels, at least two of the same construction and application as those used in the first stage.

Those obtained in the second stage of the crystallization process Crystals have a flat platelet shape and the maximum value lies in the distribution curve of the crystal sizes at 300 x 1000 x 100 / u. The crystals thus formed will be separated again by the separator.

The degree of purity of the cake is a function here the deposition temperature, however, if the other conditions which remain happy, the purity of the final The larger the crystals, the higher the p-xylene. After this process according to the invention, if the deposition temperature in the second stage of the deposition process is above -20 C, p-xylene with a degree of purity exceeding 95 / '* be won.

BATH ORIGINAL

8.0.980 5/0

example

782 parts by weight of the crude xylene feed mixture 19 with the in the following Table 2 composition are given with 84 parts by weight of the centrifuge through a pipe 70 coming Mitrats mixed, whereby the xylene mixture is given the composition given in Table 3.

Table 2

p-xylene 18.7 percent by weight

m-xylene 42.1 «

o-xylene 18.7 "

Ethylbenzene 18.7

other fabrics 1.8 "

Table 3

p-xylene 23.8 percent by weight

m-xylene ■ \ 39.6 "

o-xylene x 17.5 "

Ethylbenzene 17.5 "other substances 1.6"

This xylene mixture is pumped by a pump 20 and transfers the heat to a heat exchanger 21 to the S SA in the first stage through a conduit 47 of the centrifuge coming, ffiltrat from, cooled to about 5 ° C and then through a conduit 22 where it A drying apparatus 23 is conveyed, whereupon, after dewatering, it continues to give V / poor to a Viärmeaustauscher 24 and thereby cooled down to about -11 ° C and then through a pipe 25 to one of the same construction as was used in the first stage Crystallization vessels having pre-cooling vessel 26 is conveyed and is cooled here to a temperature that is slightly higher than aie.

809805/0742

in which the p-xylene crystals appear, for example on -35, C by doing this in the first stage through a pipe 46 The filtrate coming from the centrifuge is passed through a jacket 27 and then in turn to each crystallization vessel first stage is promoted.

A coolant such as methanol or pentane flows through the Pipeline 46 to the jacket of each crystallizer the first stage. The xylene mixture pumped out of the precooling vessel 26 by means of a pump 28 is conveyed by a Pipeline 29 to the first vessel 30 of the first crystallization stage conveyed where it is to about -40 ° C, and then in turn in a second vessel 31 to about -45 C, in one third vessel 32 to about -51 ° C, in a fourth vessel 33 to about -60 ° C, in a fifth vessel 34 to about -72 ° C is cooled. The total residence time for the liquid in the first. The crystallization stage is 18 to 20 hours. The pulp containing about 20 $ p-xylene crystals is then removed from a pump 36 from the sixth vessel of the first crystallization stage pumped out and conveyed via a pipe 37 to a bread roll container 38, from where part of the porridge is fed back through a pipe 39 for the purpose of renewed circulation into the first crystallization vessel 35. Of the Slurry is now from the Sauimel tank 58 through a pipeline 40 conveyed to a centrifuge 41 - in which the temperature rises. the degree borrowed is held as in a sixth vessel 35 and where by centrifugation in 184 parts of p-xylene cake with a purity of about $ 90 and 682 parts of mother liquor filtered is «The mother liquor is through a pipe 42 to

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~ 12 -

1418969

conveyed to a ZwiecJi ^ ngefäsa 43, from which it is pumped out by a pump 44 and passed on through pipes 45, 46, 47, whereupon it is conveyed back through a pipe 48 into the storage tank after heat has been given off to the feed mixture. On the other hand, 184 parts of p-xylene cake separated in this way are conveyed through a pipeline 49 to the Sehmel vessel 50, which is provided with a propeller agitator 51, and after heating in this vessel to about 15 ° C., a pump 52 transports it to a storage tank 53. Then the p-xylene liquid with a degree of purity of about 9Qfo is pumped out by a pump 54 and mixed with parts of the filtrate coming through a pipeline 69 from the centrifuge of the second stage, whereupon it passes through a pipeline 55 to the first vessel 56 of the second crystallization column and by a pump 58 to the second vessel 59 is fefeförflert. The coolant, for example methanol or pentane, runs through the pipe 77 to the jackets 57 of the crystallization vessels of the second stage, the temperature in the first vessel being kept at 1.5 ° G and in the second vessel at around 0 ° C. The total residence time for the liquid in the vessels of the second crystallization stage is about 6 to 10 hours. 499 parts of the pulp containing about 20 $ p-xylene crystals are now pumped out of the crystallization vessel 59 by means of a pump 60 and through a pipe 61 into a collecting container

62 conveyed, from where a feil of the pulp through a pipeline

63 for the purpose of renewed circulation in the crystallization vessel 59 transported back and the greater part of the belt _ by a

• Pipeline 64 is conveyed into a centrifuge 65 in which äie The same temperature prevails as in the crystallization vessel 59 and where the pulp is centrifuged into 100 parts of p-xylene crystals with a purity of about $ 98.5 and 399 parts of mother liquor is shared. Hachdem the mother liquor through a pipe 66 - Has been conveyed into an intermediate tank 67, it is pumped out by means of a pump 68 and 315 parts of the mother liquor are conveyed through the pipeline 69 to the second stage, while the remaining 84 parts are conveyed through the pipeline 70 Will and mix with the mixed food supply 19. The p-xylene crystals having a purity of about $ 98.5 are now through a pipe 71 to a Melting vessel 72 conveyed, in which the melting temperature is kept at about 25 ° 0, whereupon the molten p-xylene through a pipeline 73 is fed to a pump 74, which the p-xylene liquid through conduit 75 to the reservoirs promoted for the final product.

8Q9805 / 0742

Claims (1)

Claims 1. Process for the large-scale production of p-xylene with a high degree of purity and in high yield from a hydrocarbon mixture, that is a substantial amount of one mainly composed of p-xylene, m-xylene, o-xylene and ethylbenzene Contains Eohxylolgemisehes, wherein in the first stage the p-xylene crystallizes out of the Eoh mixture and separated from it and in the second stage the p-xyiol is melted, then recrystallized and is deposited again, characterized in that in each stage connected in series Crystallization vessels with an inner cylinder, scrapers attached to a slowly rotating shaft in a vessel, as well as one arranged on the lower part of the vessel A stirrer and a cooling jacket connected can be used, wherein the liquid in each vessel by the turn of the agitator and the inner cylinder inevitably circulated and the temperature in each vessel gradually drops, while the degree of heat transfer is reduced by scraping prevents the inside of the vessel with the scrapers, the temperature in each vessel is also kept constant and at the same time the correct residence time for the Eohmixture in each vessel is observed, so that the Eoh mixture gradually is cooled and large p-xylene crystals are formed, ' 'which can be separated from the mother liquor. # 2 The method according to claim 1, characterized in that the first stage ia three to eight, and in the second Stage- SAD ORIGiJMAL one to one animal continuously arranged crystallization vessels be used. 3i method according to claims 1 and 2, characterized in that that the crystallization vessels in the first and second stage a guide cylinder bypassing an agitator and a guide bloom attached to the bottom part of the vessel exhibit. 4. The method according to claims 1 to 3, characterized in that that the temperature in each vessel is gradually increased the subsequent cooling in each vessel gradually falls to -60 to -85 ° C in the last vessel and at the same time the residence time for the liquid in each vessel is kept free for more than an hour so that the Rohgrlolseaiech cools down gradually and gradually, so that groan · p »xylalkristalle can arise, whereupon the p-xylolkuohen <mn Her mother liquor aegeBchiede *, again to the liquid Jor »melted and the p-xylene liquid thus formed closed promoted and promoted the second stage criatalization there it is cooled again to 5 to -25 ° C, whereby p-xylene crystal arise, which then, separated from the mother liquor will. 5. The method according to claim 4, characterized in that in the crystallization process in the first stage of Temperature difference between the liquid to be introduced into the vessel and the liquid already contained in the vessel in each ' Vessel kept at 10 ° C and carried to each vessel Liquid within a very short period of time by turning the agitator, the inner cylinder and the scraper with the in 809005/0742 sad original the liquid already in the vessel is intimately mixed will. 6. The method according to claims 1 to 5, characterized in that in the crystallization process of the first stage crystals of the order of about 100 x 400 x 50 / u and in the crystallization process of the second stage those in the order of about 300 x 1000 x 100 Ai be won. 7. The method according to claims 1 to 6, characterized in that that the Bohxylolmixture dehydrates and initially in a pre-cooling vessel of the same construction as the one First stage crystallization vessels to one temperature The temperature is slightly higher than the temperature at which the p-xylene crystals are formed, which leads to the crystallization vessel the first stage is promoted. 8 »Device for the large-scale production of. p-xylene with a high degree of unity and in high yield when carrying out the process according to claims 1 to 7, characterized by the combination of at least three Jiristallisierungsgefässen in the first stage of the crystallization process, each of which has an inner cylinder (2), one at a slow speed in the vessel rotating shaft (4) attached scrapers (3), an agitator (8) arranged on a boa part of the vessel, a cooling jacket (11) and a separator ruf weir.-1, whereby in the second stage of the crystallization process at least? a crystallization vessel ^BATH ■ - 17 - ■■ .-. of the same construction as the G-vessels in the first one Crystallization stage and another separator are provided. 9. Device according to claim 8, characterized in that the crystallization vessels an agitator (8) have umgebenden'Mhrungs cylinder (6) and a rn, a lower part aes G-eiässes arranged guide block (17) in the first and second stage. 10. Device according to claim η 8 and 9y characterized in that effective heat exchangers and pre-cooling vessels from the prior to the first stage of the crystallization process Same construction as that of the crystallization vessels are. 11. Crystallization vessel for use in the process according to claims 1 to 7, characterized by a Inner cylinder (2), attached to a scraper (3) which is rotating at slow speed in the G-e-drum (4), an agitator (8) attached to the bottom part of the G-vessel and a coat (11). . 12. Crystallization vessel for use in the process according to patent claims 1 to 7, characterized by a guide cylinder (6) surrounding the agitator (8) and a on the lower part of the vessel arranged guide block (17). BATH ORIGINAL 809805/0742