DE1568172C - Process for separating one or more hydrocarbons from mixtures of alkyl aromatic and / or alkenyl aromatic hydrocarbons - Google Patents

Description

The invention relates to a process for separating off alkylaromatic and / or alkenylaromatic ones Components made from hydrocarbon mixtures.

A11 cock and Siegel (JACS, 1964, vol. 86, p. 5140) found that the compound tris- (o-phenylenedioxy) -cyclotriphosphazene, hereinafter referred to as TPNT, forms molecular inclusion compounds with certain organic liquids. The preferred inclusion of a component of the liquid mixtures heptene-cyclohexane, hexane-benzene, hexane-cyclohexane and carbon tetrachloride-benzene is also mentioned. It can be seen that each of these mixtures contains a cyclic and a non-cyclic component which differ in their molecular structure.

It has now been found that preferred absorption of one or more components from mixtures of Hydrocarbons from the group of alkyl aromatic hydrocarbons with 8 or 9 carbon atoms and the alkenyl aromatic hydrocarbons with 8 or 9 carbon atoms from the liquid or vapor phase takes place on phosphonitrile compounds of the type mentioned below.

Separations can thereby be achieved of components of mixtures containing any or all xylene isomers and ethylbenzene, or mixtures containing any or all C ₈ alkyl aromatic isomers, or mixtures containing any or all C ₉ alkenyl aromatic isomers including their various geometric ones Isomers and optionally styrene, or mixtures containing any or all of the C ₈ alkyl aromatic hydrocarbons and any or all of the C ₉ alkyl aromatic hydrocarbons, or mixtures containing styrene and any or all of the C ₈ alkyl aromatic isomers, or mixtures containing styrene and any or all of the C ₉ alkyl aromatic isomers, or mixtures containing any or all of the C ₈ alkyl aromatic isomers and any or all of the C ₉ alkenyl aromatic isomers, including their various geometric isomers, or mixtures of any or all of the C ₉ alkyl aromatic en isomers and any or all of the C ₉ alkenyl aromatic isomers including their various geometric isomers.

In general, aromatic hydrocarbons have the structure

y - R ₁ and / or

where R _{1 is} a methyl, ethyl or vinyl radical and R is a methyl, ethyl, n-propyl, isopropyl or vinyl radical, preferably _{absorbed before other C 8} and C ₉ alkyl and / or alkenyl aromatic hydrocarbons. For example, p-xylene is absorbed preferentially over m-xylene, p-ethyltoluene preferentially over m-ethyltoluene, n-propylbenzene preferentially over mesitylene, ethylbenzene preferentially over m-xylene and styrene preferentially over o-xylene. It is also generally stated that aromatic isomers of the structure

be absorbed. For example, p-xylene is preferentially absorbed over isopropylbenzene.

The invention therefore relates to a process for separating off one or more hydrocarbons from mixtures of alkyl aromatic and / or alkenyl aromatic hydrocarbons with 8 or 9 carbon atoms, which is characterized by that the liquid, preferably vaporous mixture of hydrocarbons with a cyclotriphosphazene compound the general ring structure

ao preferably with tris (o-phenylenedioxy) cyclotriphosphazene brings into contact and from the inclusion compounds formed the hydrocarbon components wins in a known manner by desorption.

It is believed that in the presence of hydrocarbon molecules that create the PNT structure the complex forms (guest molecules), the phosphonitrile compound (host compound) a structure with periodically recurring cavities in which the guest molecules are trapped will. For example, in the case of TPNT, it is assumed that regular channels with hexagonal Cross-section can be formed in the presence of the guest molecules. The forces that the guest molecules retained in the channels are weak, so the guest molecules are easily removed from the complex can be. It is believed that the TPNT crystal lattice upon removal of the guest molecules ruptures and forms again in the presence of additional guest molecules.

Molecular shape is an important factor in determining the extent of absorption, i.e. H. the Ease with which a guest molecule is incorporated into the PNT structure. One aspect of the molecular shape is the cross-section, which is important but not the only criterion for absorption. For example TPNT was found to absorb p-xylene preferentially over ethylbenzbl, although the cross-sections these compounds are very similar. Another one

Example is the preferred * absorption of p-ethyltoluene over isopropylbenzene by TPNT.

The preferred compound with the PNT structure is tris- (o-phenylenedioxy) -cyclotriphosphazene, TPNT, which has the following formula:

CH ₃
preferred over those of the structure

R-

wherein R and R _{1 have} the meaning mentioned, Further compounds with PNT structure, the

3 4

Inclusion complexes of the type described form the absorbent is used as a fixed bed,

are trimereso-phenylenediamino-phosphonitrile although this is not essential. The PNT connection

and trimeric 2,3-naphthyldioxyphosphonitrile. can with hydrocarbon in an amount up to

_{TPNT itself can form a comtrid chloride trimer (PNC1 2} ) ₃ prepared with catechin 5 plex by reacting the phosphoni- about 10 percent by weight of its weight. It was found that it was growing. The phosphonitride chloride trimer can be produced most economically, at the saturation capacity or together with other phosphonitrile derivatives due to their proximity, and only to remove part of the decomposition of ammonium chloride with phosphorus-sorbed molecules in each cycle, pentachloride. TPNT is a white solid that is fed to the absorbent bed and has a melting point of 244 to 245 ° C. The material can be diluted or undiluted. When

The compound with PNT structure can be worked granulated in the vapor phase, can be an inert one used in free form or on an inert carrier gas such as nitrogen. One Carrier are applied. As a carrier are suitable rinsing stage can optionally between absorption and For example, ground chamotte, diatomaceous earth, desorption can be switched on. For this rinse Silica gel, alumina or porous glass. An inert gas or an inert liquid can be advantageous be to silanize the carrier. The used or rinsing is done by lowering the pressure Bonding with the PNT structure can also be made as thinner up to a suitable value. on Film on a sheet-like base or in this way is absorbed on the surface and fibrous base can be applied. Unsorbed material was removed. The rinse stage can found that the connection to the PNT structure 20, for example, can be omitted when the volume from a solution in an organic solvent of the reactor in which the desorption takes place, so by stirring and heating with the carrier material large and the amount of material produced by the rinsing can be removed under reflux under nitrogen, cooling, filtration, is so low that the relative and drying under reduced pressure applied concentration of this material can be neglected can be. By the applicant, TPNT was set to 25 can. When using the pressure reduction method In this way from a solution in xylene to silanized it is essential that the, upon absorption, rinse Diatomaceous earth of a particle size of 0.15 bis and desorption pressures applied in this 0.18 mm applied. Furthermore, the TPNT order was lowered, but it is not necessary from 5 to 30 percent by weight on ground agile, that these pressures have a certain value Chamotte have a particle size of 1.4 to 2.06 mm and are uniform. The flush and the achieved by the chamotte with a solution of desorption can expediently as a continuous 6 parts by weight in 100 parts by volume xylene soaked, process by gradually lowering the pressure by the Solvent evaporated and the process carried out until.

repeated to achieve the required load.

would. 35 combination of absorption, rinsing and desorption

The carrier material must be chosen so that operations are applied. An example of one among other things the pressure drop in the reactor, which the combination process would be a vapor phase PNT material contains, low and the filling with absorption with subsequent rinsing with a PNT material per unit volume of the reactor is highly inert gas and final desorption by pressure, however, care must be taken that the 40 lowering. When using a diluted use-speed, with the the PNT material with the materials can flush by reducing the Hydrocarbon material comes into equilibrium, concentration of the feed is made is not too low. will. By using an inert gas

The absorbate can be released from the PNT material through thin feedstock in a vapor phase displacement with a different absorbate or by 45 it is possible to reduce the pressure in each phase of the Elution with an inert gas or an inert liquid process above the vapor pressure of the carbon or by lowering the ambient pressure, d. H. Hydrogen components of the feed in the Lowering the vapor pressure of the absorbed material to maintain operating temperature. When the pressure is over (according to the so-called "pressure change process") the vapor pressure of the hydrocarbon when removed will. Desorption can also be increased by using an undiluted feedstock, Increase in temperature can be made. liquefaction takes place, which can be undesirable. Which method is chosen depends on a number of factors; to use sequential absorption beds in the preferred vapor phase the desorption process is carried out by lowering the pressure and the outlet flow of one bed is preferred, and a particularly suitable means of enrichment with one or more components Achieving this pressure reduction is the condensation of the feed to this bed in one of the desorbed material. To introduce a process for generating another bed.

supply of the necessary vacuum for the desorption In the following tables 1 to 3 are the ranges by direct condensation of what is called by the absorption, from which the reaction conditions for the middle layer draining product in a circle- 60 different procedures can be selected is in British Patent 1110 494 NEN, namely for a through-described in the liquid phase, guided process in which the desorption with a process in which the said desorption inert liquid is carried out for a in the Methods are applied, are expediently vapor phase carried out process with desorption carried out periodically, d. H. on a cycle 65 through an inert gas and through one in the vapor phase Complex formation and the extraction of the complex-led process with desorption by pressure-bound persons Materials follows another. It became kung. It can be seen that in the areas for found that good results are obtained when individual stages use a dilute

5 6

or undiluted feed and the application of its decomposition temperature, use or

The use or non-use of a rinse stage takes into account the non-use of a carrier and the type of

are sighted. Carrier material.

The following dimensions or conditions are: The following are the preferred ranges of the

Common to all three types of process: 5 conditions for a vapor phase process named,

. at the TPNT for the separation of the components

Ratio of bed length to bed length of a mixture of C 1 -C alkyl aromatic isomers

™ ^ser _t ³ n; cu · ^{1 S} "4 is used. In Table 4 are the conditions

Particle diameter 0.15 to 4.7 mm _{for the process> with the inert gas for ώβ} desorption

temperature 15 to 25U C _{10 is used; and Ta b} le 5 the conditions for

^{a process} > ^{in which the} desorption is carried out by reducing the pressure in Table 1 is specified. In the

Inlet pressure 0.7 to 350 kg / cm ² Table 4 named ranges for the ratio of

Process stage bed length to diameter, particle size, temperature

Absorption 0.1 to 10 V / V / hour *) 15 and duration of the process steps also apply to

inert liquid Table 5.

(up to 50 V / V / hour) Table 4

Flushing " _r . ..,. ",

(optional) inert liquid bed length ratio

(up to 50 V / V / hour) ₂ o ™ bed diameter ... 20: 1 to 4: 1

Desorption inert liquid, particle size 0 15 to 4 7 mm

(up to 50 V / V / hour) Temperature ™ ίϊ? * ™ £? ,

2 £ _xX pressure 0.7 to 35 kg / cm ²

Absorption 10 seconds to 60 minutes process stage _e , _TnT , _et . , u

Rinsing 10 seconds to 60 minutes 25 absorption 0.2 to 5 V / V / hour (related to

Desorption 10 seconds to 5 hours ^ ^^ Α ^ ¹¹ ^

* Room flow velocity related to the liquid state ht 1 C}

Table 2 irrigation

Pressure 0.7 to 70 kg / cm ² 30 (optional) inert gas (up to 500 V / V / hour,

Process stage calculated as gas)

Absorption 0.1 to 10 V / V / hour Desorption inert gas (up to 500 V / V / hour,

(based on the liquid state) _. calculated as gas)

+ Inert gas (up to 1000 V / V / ^time , ui * ™ · ♦

Hours, calculated as gas) 35 absorption 30 seconds to 15 minutes

Flush Flush 30 seconds to 15 minutes

(optional) inert gas (up to 1000 V / V / desorption 120 seconds to 150 minutes

Hours, calculated as gas) Table 5

Desorption inert gas (up to 1000 V / V / pressure

_Time ^hours -> calculated as gas) 40 absorption 0.7 to 35 kg / cm ²

Absorption 10 seconds to 60 minutes fwaSise) 0.07 to 1.4 kg / cm *

Flushing. JO seconds to 60 minutes desorption 0.007 to 0.35 kg / cm ²

Desorption 10 seconds to 5 hours process stage

Table 3 ⁴⁵ Absorption 0.2 to 5 V / V / hr. (based

Process stage to liquid state) + inert absorption 0.1 to 10 V / V / hour, related to gas (up to 500 V / V / hour,

on liquid state + inert- calculated as gas)

gas (up to 1000 V / V / hour, _5o when using an undiluted feedstock

~ T calculated as gas) _{] is the upper limit of the} pressure in Table 4

Tl. · «-Π. · ™, 1» and in Table 5 at about 10.5 atmospheres, as this

Absorption 0.7 to 70 kg / cm ² Vapor pressure of the feed material in the decomposition

bpulung "" ",. _,, "Temperature of TPNT is. The above mentioned

(optional) ⁰ A ¹ Ju- ⁷ n ^, 55 pressure limits apply only when a dilute

Desorption 0.007-0.7 kg / cm ^{2 of} feed is used.

.,. ., _Λ r,,,,. s _n χ , · For a procedure carried out periodically

Absorption should be JO seconds to 60 minutes _{using a number of} fixed beds

Flush 10 seconds to 60 minutes _{the operating times for} absorption, flushing and

^Desor P ^{TLON 10} seconds to 5 hours _{6o desorption in} simple ratios to one another

In Tables 2 and 3 the room air flow is shown in order to facilitate the switchover,

rate of feed to the liquid from a mixture containing the C ₈ -alkylarpmatic

state related, although the use in the steam contains isomers, p-xylene and ethylbenzene

phase is fed. The actual values that are preferentially absorbed before o-xylene and m-xylene. That is

can be selected from the above ranges, 65 is the selectivity of TPNT with regard to absorption

depend, among other things, on the type of use of p-xylene and ethylbenzene, but differ

materials, the purity of the product or the products, these two isomers are more strongly absorbed than

and the type of PNT material used, for example o- and m-xylene. Just with one cycle of PNT

Absorption and desorption are obtained fractions that contain one or more components of a hydrocarbon mixture are enriched, and with further cycles become practically pure Components formed. The more a given component absorbs, the longer the desorption time is. So it is possible in one cycle from a mixture of 25 percent by weight p-xylene, 25 percent by weight Ethylbenzene and 50 percent by weight m-xylene to produce a concentrate that except m-xylene only Contains 4 percent by weight of other ingredients, with a relatively long desorption time applied is to xylene and ethylbenzene imported from the previous cycle, which are more firmly held and would otherwise contaminate the m-xylene front. As an alternative, a Cycle a fraction containing only 3 percent by weight of m-xylene can be obtained from the same mixture, while the remainder of the fraction consists of p-xylene and ethylbenzene. In this case, the desorption time be relatively short.

B e i s ρ i e 1 1

In one process for separating m-xylene from p-xylene, a vaporous mixture of these two isomers was passed into a fixed bed reactor (30 x 3 cm internal diameter, capacity 212 ml) which contained 43 g of TPNT, the same amount by weight of silanized diatomaceous earth Particle size of 0.15 to 0.177 mm was applied. During this sorption stage, the p-xylene was preferentially absorbed and an outlet stream enriched with m-xylene was obtained. The unsorbed hydrocarbon was then purged from the reactor with nitrogen and additional nitrogen was passed through the reactor to complete the cycle to desorb the sorbed p-xylene. All gases and vapors fed to the reactor were preheated. The bed temperature was kept at 155 ° C. The procedure was performed intermittently, with one cycle of sorption, flushing and desorption being followed by the next cycle. The gases and vapors emerging from the reactor were introduced through appropriate valves into coolers, where the enriched p- and m-xylene fractions were recovered. With those indicated in Table 6, the process amounts 84gewichtsprozentiges 10.5 ml m-xylene and 8.6 ml of 97 ° showed / ₀ sodium p-xylene from a 45 ml of equal parts by volume of the two isomers existing mixture during the course of ten in each case at the same Pressure (normal pressure) performed cycles.

Table 6

Sorption

Input material ... p- and m-xylene (50 parts each)

Application amount .... 1.8 ml / min, (liquid) or

(0.51 V / V / hour, calculated as a liquid)

Diluent nitrogen at 495 ml / min. (14V / V / hour, calculated as

Gas)

Time 2.5 minutes

Flushing

Inert gas nitrogen

so flow rate .. 670 ml / min. (190 V / V / hour,

calculated as gas)

Time 1.25 minutes

Desorption

Inert gas nitrogen

Flow rate .. 670 ml / min. (190 V / V / hour,

calculated as gas) time 6 minutes

By extending the desorption time to about 1 hour, whereby the p-xylene content of the layer was reduced to a very low value, and by extending the sorption time to 6 minutes, it was possible to use m-xylene, the purity of which approached 100 ° / ₀ , during the sorption stage and p-xylene with a purity of 97% during desorption.

Example 2

Using a typical, commercially available xylene fraction in place of that in Example 1 Mixture of p- and m-xylene used as feed, but using the same Flow rates, which are given in Table 6, it was possible to produce a product during the desorption stage to win, which was significantly enriched in p-xylene. The composition of the feed and of the desorbate and the yield over ten cycles are given below:

Composition of the mission
Weight percent In 10 cycles
introduced
Use amount composition
of desorbate
Weight percent In the course of
10 cycles won
Desorbate m-xylene 51.2
p-xylene 22.8
o-xylene 7.3,
Ethylbenzene 16.6
Toluene 0.3
Paraffins u.
Naphthenes 1.8 45 ml m-xylene 4
p-xylene 66
Ethylbenzene 30 8.7 ml

. . 65 surface size of 1.41 to 2.38 mm was applied. The

Example 3 the same feedstock as in Example 1 was used

The reactor described in Example 1 was also used, but this time the pressure change

38 g of TPNT filled, which is applied to 67 g of a sub-method. The bed temperature was over

109 536/378

Claims (1)

9 ίο all ^ stages held at 165 ° C. The remaining separation of TPNT by gas-liquid chromato- Conditions are given in Table 7. "graphie analyzed, with the following combination _ ■: ■ «- ■ 'settlement was found:
Table 7 Absorption r isopropylbenzene 3.6 percent by weight Use and amount of m- and p-xylene (volumetric n-propylbenzene 44.0 percent by weight ratio 50:50), 1.8 ml / min. 1-methyl-4-ethylbenzene .. 42.1 percent by weight (liquid) or 0.51 V / V / hour _{This result shows> that the simply} substituted . . · -Calculated as gas) + N _{2 and the p} . _d i _su bstituierten C ₉ alkyl aromatics by ■ - (25 ml / mm or 7 V / V / h, _{Io TpNT} J ^ was _absorbed ⁹ _the /
calculated as gas) Pressure normal pressure · '■ ' Time 4 minutes. Claim:. Flushing (by pressure method to separate one or more Lowering) _mic1 , _9N 15 "hydrocarbons from mixtures of alkyl Final pressure 10 mm Hg (0.15 kg / cm ² ) aromatic and / or alkenyl aromatic hydrocarbons ^LQl \ ...... 2.5 minutes of hydrogen with 8 or 9 carbon atoms, Desorption characterized in that one (by lowering the pressure), ·, «" « _{,,, Ά} the liquid, preferably vaporous carbon ■; Final pressure --- ^ mm Hg (0.035 kg / cm ^) ₂₀ hydrogen mixture with a cyclotriphosphazene ^Time · · ■ · · · ·; " ^Mmuten connection of the general ring structure With these flow rates in one cycle \ / ■ 7.2 ml of one from equal parts of the space m- and ^ P ' p-xylene existing mixture is used, where // \ 1.15 ml of m-xylene of a purity of 85 ° / ₀ and 1.05 ml of 25 NN p-xylene having a purity of 90% was obtained. . 1 || . At game 4 / P P \ A mixture of equal parts of all 'N Cs-alkyl aromatic. Isomers was at room 30 temperature and normal pressure with linerless TPNT, preferably with tris- (o-phenylenedioxy) -cyclotri- mixed in such an amount that a liquid phosphazene brings into contact and out of the Excess was present: After leaving to stand, the inclusion compounds formed were the carbon the liquid filtered off and the TPNT dried. The hydrogen components are known per se absorbed hydrocarbons were recovered by desorption in an ab- 35 manner.