NL2001313C2 - Use of a Li-faujasite for the separation of olefin / paraffin mixtures, a Li-faujasite and a process for the separation of olefin / paraffin mixtures. - Google Patents

Description

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Use of a Li-faujasite for the separation of olefin / paraffin mixtures, a Li-faujasite and a process for the separation of olefin / paraffin mixtures

The present invention relates to the use of Li-faujasite for separating mixtures comprising olefins and paraffins. The invention also relates to a Li-faujasite for such an application. Furthermore, the present invention relates to a process for separating mixtures of olefin and paraffin, in particular with the same carbon number, generally referred to as CxH2x / CxH2x + 2.

It is known in the art to separate mixtures comprising olefins and paraffins, in particular those with the same carbon number. Mixtures of particular interest are C 2 H 4 / C 2 H 6, C 3 H 6 / C 3 H 8, C 4 H 8 / C 4 H 10. However, other mixtures, where x = 5.6 or even more, are also important in this technique.

A commonly used method for separating such mixtures is distillation. A distillation column that can be used by such a separation method requires a large number of distillation trays, for x = 2 or 3 at least about 100.

Other methods for separating mixtures as mentioned above make use of pressure swing adsorption, temperature swing adsorption or simulated moving beds. These are technologies used to separate some gas species from a mixture of pressurized gases, in accordance with the molecular characteristics of the species and the specific affinity for an adsorbent material. They usually operate under mild temperature conditions (generally from room temperature to 150 ° C) and therefore differ from cryogenic gas separation distillation techniques. Special adsorbent materials (e.g., zeolites and the like) are used and one of the target gas species is either preferably adsorbed (adsorptive or equilibrium separation), or is strongly impeded to diffuse into the material (kinetic separation). Such methods are currently used for air separation (separation of oxygen and nitrogen).

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There are hundreds of different adsorbent materials that can be used in adsorptive processes. For example, the potassium or barium forms of X and Y-type faujasite are used in the separation of xylene isomers. Li-faujasite has also been used for air separation.

It is an object of the present invention to provide an improved process for separating olefin / paraffin mixtures.

It is a further object of the present invention to provide an adsorbent for use in a process for separating olefins / paraffins blends.

A further object of the invention is to provide a process for separating mixtures of olefins and paraffins.

In accordance with the present invention, a Li-faujasite is used to separate mixtures of olefins / paraffins. More specifically, the present invention relates to the use of Li-faujasite for the separation of CxH2x / CxH2X + 2. Li-faujasite is a highly preferred material because this adsorbent material has a much better selectivity to olefins relative to paraffins. This will become clear from the experiments to be described below.

It is a special advantage that the present adsorbent material, Li-faujasite, has a greater affinity to olefins and at the same time that the desorption of a significant amount of the adsorbed species can be performed at a relatively mild vacuum (e.g. 10 kPa ).

The present invention preferably relates to the use as mentioned above, wherein the mixtures are comprised of any of the group of ethylene / ethane, propylene / propane, butylene / butane, i.e. where x = 2, 3 or 4.

Furthermore, it has been shown that isomers, for example isobutane / isobutylene, can also be well separated, in accordance with the present invention.

In accordance with a further embodiment, the present invention relates to Li-faujasite, both of the X type and of the Y type, for use in accordance with the present invention, as described above.

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3, wherein the Li-faujasite is obtained by ion exchange of faujasite with any other cation or by direct synthesis. Na-faujasite, or sodium faujasite, is commercially available and generally known and sold under the designation 13X. Li-faujasite can be directly synthesized or obtained by ion exchange of the commercial sodium faujasite or any other cationic faujasite with a solution of a lithium salt (e.g., LiCl). It is particularly preferred that at least 50%, preferably at least 70%, more preferably at least 80%, most preferably at least 90% of the sodium is exchanged with lithium.

It is advantageous that the production of the Li-faujasite by ion exchange of sodium-faujasite is relatively easy. The method for producing the lithium form is also relatively inexpensive.

The method according to the invention may preferably consist of: 1) a pressure swing adsorption method ("PSA"), 2) a temperature swing adsorption method ("TSA"), 3) a vacuum swing adsorption method ("VSA") or 4) a displacement method , either carried out in a gas phase or in a liquid phase. Such a displacement method may advantageously comprise the following steps: a) a step of contacting a mixture to be separated with a bed of the adsorbent material in accordance with the present invention to thereby adsorb the olefin (i.e., the most preferred compound adsorbed) from the mixture, b) preferably performing a step of contacting the bed of the adsorbent material with a stream of a desorbent material, c) a step of rinsing the bed of the adsorbent material with a stream of a mixture containing the desorbent material and products of the mixture that are less selectively adsorbed, d) a step of rinsing the bed of adsorbent material by means of a stream containing desorbent material and the olefin. Such a method is known, inter alia, from French patent application FR 2903981.

Yet another embodiment relates to a process for separating mixtures of olefin and paraffin, in particular mixtures of CxH2x / CxH2x + 2, where x 40 stands for 2, 3, 4, 5, 6 or even more, and which can be gaseous or liquid, wherein the steps as indicated in claim 7 are carried out. The compounds leaving the adsorption vessel in steps 2 and 3 can be collected for further reuse after they have optionally been separated. The compound leaving the adsorption vessel in step 4 comprises the olefin that was adsorbed to the adsorbent with the most selectivity and which is the target compound. In accordance with a general method, highly dependent on the adsorbent material used and the compound to be adsorbed, the pressure can be varied between about 10 atm. in the first step, about 5 atm. in the second and third step, up to about 0.1-2 atm. in the fourth step. In practice, however, these values can be varied widely and more steps can be used. Some embodiments may even combine some of the aforementioned steps.

More details regarding the separation are mentioned below in the examples.

The present invention furthermore preferably relates to such a method wherein the method is carried out in the gas phase.

However, it is also preferred to carry out the process in the liquid phase. The paraffin / olefin mixture can be in the liquid phase as such, but can also be dissolved in a solvent. Desorption of the adsorbent component can be achieved by a pressure reduction, a temperature increase or by the use of another displacing component. Further details and advantages of the present invention will become apparent from the claims and the description described above and given below.

The invention will now be described by way of examples.

The sorption of propylene and propane was determined in accordance with first experiments.

Example 1: Ion exchange of a commercial 13X 35 zeolite 100 grams of commercial 13X pellets (Sigma Aldrich,

Product number 334359) are subjected to ion exchange 3 times at a temperature of 25 ° C for 24 hours with a fresh solution of 1M LiCl (1 liter of fresh solution each time).

The analysis (ICP-OES) of the obtained sample after ion exchange showed a percentage of ion exchange of 80%.

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Example 2: Adsorption isotherms

A micromeritics ASAP 2010 gas adsorption analyzer (the stainless steel version) was used to measure the adsorption isotherms of propane, and propylene on LiX and NaX, in the pressure range of 0.002 to 120 kPa. The instrument is equipped with a turbo-molecular vacuum pump and three different pressure transducers (0.13, 1.33 and 133 kPa) to improve sensitivity in the different pressure ranges. The static-volumetric technique was used to determine the volume of gas that was adsorbed at different partial pressures: in adsorption a pressure decrease was seen in the gas phase which is a direct measure of the adsorbed amount.

The results of this experiment are shown in Figure 1, where a comparison between the adsorption isotherms for propane and propylene of NaX and LiX at 45 ° C is shown (on a sample obtained by a procedure similar to that which is described in example 1). It is clear from this figure that the amount of propylene adsorbed is much higher than the amount of propane when using Li-faujasite, compared to an embodiment using sodium faujasite.

Furthermore, when lithium faujasite is used, the adsorption isotherm for propane decreases much more with decreasing pressure than for propylene compared to sodium faujasite.

This means that lithium faujasite exhibits greater sensitivity to propylene relative to propane at higher partial pressure while, at a lower partial pressure, that is, to desorb propane, the sensitivity is lower. The difference between sensitivity to propane and propylene is greater for lithium faujasite than for sodium faujasite.

Example 3: Breakthrough Setup and Experiment Hereafter the efficiency of lithium faujasite is measured by using a mixture of propylene and propane.

The adsorption of binary (50:50) mixtures of propylene / propane in helium (used as a balance, the total 40 consisting of helium: propylene: propane in a ratio 6 of 50:25:25 vol%) was assessed to a sample obtained by a procedure similar to that described in Example 1 by means of a breakthrough and desorption experiment in a breakthrough arrangement. Each experiment was performed at least twice to check the reproducibility. For these experiments, the starting pressure of the column was packed with the Li-faujasite set at 108 kPa. After each desorption example, the packed column was rinsed with helium in an amount of 125 ml min -1 (SATP) for 6 hours at the measurement temperature. An increase in temperature after these 6 hours did not lead to a desorption of additional adsorbed hydrocarbons, confirming that all gases from the column are desorbed at that time.

The total analysis time of each breakthrough experiment was approximately 1 hour. Because the breakthrough of both components occurred much earlier, this implies a balance time of at least 1/2 hour. The desorption of the packed column was carried out isothermally with a helium rinse of 20 ml min -1 (SATP) and analyzed for 4 hours.

In the breakthrough arrangement, the CompactGC (Interscence) is used to determine a mole fraction of the two components at the outlet of the column. The GC is equipped with three parallel 8 meter long Rt-QPlot capillary columns (diameter 0.32 mm) and each column has its own flame ionization detector (Flame Ionization Detector, FID). Each time the GC is started, 45 samples can be analyzed consecutively, after which it takes 1-1½ minutes to determine the detection of the last sample, to store the results and to trigger the EXCHrom Elite software attack (trigger). zero chromatogram. With this configuration and a continuous injection of gas samples into the GC columns, it is possible to analyze the composition of the mixture every 8 seconds.

From the results as shown in Figure 2, it is clear that when the reactor is flushed, propane is first released, and that propylene presses out a significant amount of the previously adsorbed propane. A very steep increase in propylene to t / tO = 1.5 and the very steep decrease in propane at the same time is an indication of the excellent utility of lithium faujasite for the present separation. Characteristic of the experiment as shown in Figure 2 is that the breakthrough experiment of propylene / propane was carried out over a sample of lithium faujaite at a temperature of 50 ° C. FC3h8 = FC3h6 = 2 mln / min; FHe = 4 mln / min; MLix FA0 (dry) = 0.50 g.

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Claims (10)

Use of Li-faujasite for adsorption-based separation of mixtures of CxH2X / CxH2X + 2, where x = 2, 3, 4, 5, 6 or more. The use according to claim 1, wherein the Li faujasite comprises LiX faujasite or LiY faujasite. Use according to claim 1 or 2, wherein the mixtures each comprise from the groups of C 2 H 4 / C 2 H 6, C 3 H 6 / C 3 H 8, C 4 H 8 / C 4 H 10. Li-faujasite for an application according to claims 1 to 3, wherein the Li-faujasite is obtained by ion exchange of a faujasite containing another cation, exchanging at least 50%, preferably at least 70% , more preferably at least 80%, most preferably at least 90% of the other cation by Li. 5. Process for separating olefin and paraffin mixtures, in particular with the same number of carbon atoms, for example mixtures of C2H4 / C2H6, C3H6 / C3H8, Ο4Η8 / θ4Η10, C5H10 / C5H12, C6H12 / C6H14, wherein the method is a comprises of: 1) a pressure swing adsorption method, 2) a temperature swing adsorption method, or 3) a displacement method, either carried out in a gas phase or in a liquid phase. 6. Method according to claim 5, wherein the method comprises a moving method that is performed in a simulated moving bed. Pressure swing adsorption method for separating mixtures of olefin and paraffin, in particular with the same number of carbon atoms, e.g. feeding the mixture in a adsorption vessel containing a Li-faujasite sorbent material according to claim 3 in a first step, in order to obtain a first pressure, - reducing the pressure in the vessel in a second step in order to obtain a second one, relatively lower pressure, - adding an olefin on a first side of the vessel in a third step and opening the vessel on a second opposite side, such that the supplied olefin comes into contact with the sorbent material, for removing the paraffin from the vessel on the first side, and - rinsing the vessel in a fourth step, optionally with an inert compound, for removing and collecting the olefin. The method according to claim 6 or 7, wherein the method is carried out in the gas phase. The method according to claim 6 or 7, wherein the method is carried out in the liquid phase. The method according to claim 9, wherein the paraffin and olefins are dissolved in a solvent. 2. n1 111