WO2009104960A1

WO2009104960A1 - Use of a li-faujasite for separation of olefin/paraffin mixtures

Info

Publication number: WO2009104960A1
Application number: PCT/NL2009/050071
Authority: WO
Inventors: Jorge Gascon; Frederik Kapteijn
Original assignee: Technische Universiteit Delft
Current assignee: Technische Universiteit Delft
Priority date: 2008-02-22
Filing date: 2009-02-18
Publication date: 2009-08-27
Anticipated expiration: 2010-08-22
Also published as: NL2001313C2

Abstract

The present invention relates to separation of olefin/paraffin mixtures. The invention especially relates to the use of a Li-Faujasite, wherein the mixtures are comprised of any of the groups of C_xH_2x/C_xH_2x+2, wherein x = 2, 3 or 4, in particular a mixture of ethylene/ethane, propylene/propane, or butylene/butane. The invention further relates to the use of such a Li- Faujasite, wherein said Li-Faujasite is obtained by ion exchange of a Faujasite containing another cation. The invention also relates to such use for separating mixtures of olefin and paraffin, especially having the same carbon number, in particular a mixture of C₂H₄/C₂H₆, C₃H₆/C₃H₈, or C₄H₈/C₄H₁₀.

Description

Use of a Li-Faujasite for separation of olefin/paraffin mixtures

The present invention relates to the use of Li- Faujasite for separation of mixtures comprised of olefin and paraffin. Furthermore, the present invention relates to such use for separating mixtures of olefin and paraffin, especially having the same carbon number, generally- identified aS CχH₂χ/C_XH2_X+2 •

It is known in the art to separate mixtures comprised of olefins and paraffins, especially having the same carbon number. Mixtures that are of particular importance are mixtures of C₂H₄ZC₂H₆, C₃H₆Zc₃H₈, or C₄H₈ZC₄H₁₀.

A generally applied method for separating such mixtures is distillation. A distillation column to be applied for such separation process, requires a large number of distillation trays, for x=2 or 3 at least about 100. Other methods of separating mixtures as mentioned above, apply pressure swing adsorption, temperature swing adsorption or simulating moving beds. These are technologies used to separate some gas species from a mixture of gases under pressure according to the species' molecular characteristics and specific affinity for an adsorbent material . They usually operate at mild temperature conditions (generally from room temperature to 150 ⁰C) and hence differ from cryogenic distillation techniques of gas separation. Special adsorptive materials (for example zeolites and the like) are used and one of the target gas species is either preferentially adsorbed (adsorptive or equilibrium separation) , or is strongly hindered to diffuse into the material (kinetic separation) . Such methods are currently applied for air separation (separating oxygen and nitrogen) . There are hundreds of different adsorbents that can be used in adsorptive methods. For example, the potassium or barium forms of X and Y-type Faujasite are used in the separation of xylenes isomers. Lithium Faujasite has also already been used for air separation. The present invention aims at providing an improved use of Li-Faujasite for separating olefin/paraffin mixtures. The present invention further aims at providing an adsorbent for use in a method for separating mixtures of olefins/paraffins . The invention further aims at providing such use for separating a mixture of olefin and paraffin.

According to the present invention, a Li-Faujasite is used for separating mixtures of olefins/paraffins. More in particular, the invention relates to the use of Li-Faujasite for separating C_xH₂χ/C_xH₂χ₊₂, wherein x=2 , 3 or 4 , in particular wherein the mixture is comprised of any of the groups of C₂H₄/C₂H₆, C₃H₆/C₃H₈, C₄H₈Zc₄Hi₀ and wherein said Li-Faujasite is comprised of LiX Faujasite or LiY Faujasite. Hence, the present invention relates to the use of Li-Faujasite for seperating C₂H₄ from C₂H₆, or seperating C₃H₆ from C₃H₈, or seperating C₄H₈ from C₄Hi₀. In that respect, Li-Faujasite is a very favourable material, since this adsorbent has a much better selectivity to olefins than to paraffins. This will become clear from the experiments indicated hereafter. It is a special advantage that the present adsorbent, lithium Faujasite, shows a larger affinity towards olefins and, at the same time, that the desorption of a significant amount of the adsorbed species can be performed at relatively mild vacuum (for example 10 kPa) . The present invention relates to the use as mentioned above, wherein the mixture is comprised of any of the group of ethylene/ethane, propylene/propane, or butylene/butane, i.e. wherein x = 2, 3 or 4.

It has furthermore been shown that also isomers, for example isobutane/isobutylene can be separated well, according to the present invention.

According to a further embodiment, the invention relates to Li-Faujasite, both of the X- and the Y-type, for use according to the present invention, as mentioned above, wherein said 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 sold/known as 13X. Lithium-Faujasite can be directly synthesised or obtained by ion exchange of the commercial sodium-Faujasite or any other cationic Faujasite with the solution of a lithium salt (for example LiCl) . It is especially preferred that at least 50%, preferably at least 70%, more preferably at least 80%, most preferably at least 90% of said sodium is exchanged by lithium.

It is advantageous that the production of the lithium-Faujasite by ion exchange of sodium-Faujasite is relatively easy. Also, the method for producing the lithium form is relatively cheap.

The use according to the invention may preferably be comprised of: 1) a pressure swing adsorption method (^ΛPSA'), 2) a temperature swing adsorption method (^lTSA')# 3) a vacuum swing adsorption method ('VSA') or 4) a displacing method, either performed in a gas phase or a liquid phase. Such displacing method can advantageously comprise the steps of: a) a step of contacting a mixture to be separated with a bed of the adsorbent according to the present invention so as to adsorb the olefin (i.e. the compound that is most preferentially adsorbed) from said mixture, b) preferentially a step of contacting the bed of adsorbent with a stream of a desorbent, c) a step of flushing the bed of adsorbent with a stream of a mixture containing said desorbent and products of the mixture that are least selectively adsorbed, d) a step of flushing of the bed of adsorbent by means of a flow containing desorbent and the olefin. Such method is among others known from the French patent application FR 2903981.

A still further embodiment relates to the use of Li- Faujasite for separating mixtures of olefin and paraffin, especially mixtures of C_xH_2x/C_xH_2x+2 , wherein x is 2, 3 or 4 , and that may be gaseous or liquid, wherein the steps, as indicated in claim 5, are performed. The compounds leaving the adsorbent vessel in step 2 and 3 may be collected for further reuse after optionally having been separated. The compound leaving the adsorbent vessel at step 4 is comprised of the olefin, that was adsorbed with most selectivity to the adsorbent and is the target compound. According to a general embodiment of the use according to the present invention, strongly dependent on the adsorbent used and the compound to be adsorbed, the pressure may be swung from about 10 atm. in the first step, about 5 atm. in the second and third step, to about 0.1 - 2 atm. in the fourth step. However, in practice these values may be varied widely and more steps can be applied. Some embodiments may even combine some of the above mentioned steps .

More particulars regarding this separation are mentioned hereafter in the examples. The present invention further preferably relates to such a use wherein the method is performed in the gas phase. However, it is also preferred to perform the method in the liquid phase. The paraffin/olefin mixture may be in the liquid phase as such, but may also be dissolved in a solvent. Desorption of the adsorbed component may be achieved by a pressure reduction, a temperature increase, or the use of another displacing component. Further particulars and advantages of the present invention become clear from the claims and the description as given above and hereafter.

The invention will now be described by means of examples .

According to first experiments, the sorption of propylene and propane was determined.

EXAMPLE 1: Ion exchange of a commercial Zeolite 13X

100 grams of commercial 13 X pellets (Sigma Aldrich, Product number 334359) are ion exchanged 3 times for 24 h at 25 ⁰C with a fresh solution IM of LiCl (1 liter of fresh solution each time) . The analysis (ICP-OMS) of the obtained sample after ion exchange revealed a percentage of ion exchange of an 80%.

EXAMPLE 2 : Adsorption isotherms

A Micromeritics ASAP 2010 gas adsorption analyser (stainless steel version) was used to measure the adsorption isotherms of propane, and propylene on LiX and NaX, in the pressure range from 0.002 to 120 kPa. The instrument is equipped with turbomolecular vacuum pumps and three different pressure transducers (0.13, 1.33 and 133 kPa) to enhance the sensitivity in the different pressure ranges. The static- volumetric technique was used to determine the volume of the gas adsorbed at different partial pressures: upon adsorption a pressure decrease was observed in the gas phase, which is a direct measure for the amount adsorbed.

The results of this experiment are shown in fig. 1, where a comparison between the adsorption isotherms for propane and propylene of NaX and LiX (on a sample obtained by a procedure similar to the one described in example 1) at 45⁰C has been shown. From this figure, it is clear that the amount of propylene adsorbed, is much higher than propane when using lithium-Faujasite, as compared when using sodium- Faujasite.

Furthermore, when using lithium-Faujasite, the adsorption isotherm for propane decreases much more with decreasing pressure than for propylene compared to sodium- Faujasite

This means that lithium-Faujasite shows a high sensitivity to propylene with respect to propane at higher partial pressure whereas, at lower partial pressure, i.e. for desorbing propane, said sensitivity is lower. The difference between sensitivity towards propane and propylene is higher for lithium-Faujasite than for sodium-Faujasite.

EXAMPLE 3 : Breakthrough setup and experiment

Hereinafter, 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, wherein the total mixture consisted of Helium: Propylene: Propane of 50:25:25 vol.%) was investigated on a sample obtained by a procedure similar to the one claimed in example 1 via breakthrough and desorption experiments in a breakthrough setup. Each experiment was performed at least twice to check the reproducibility. For these experiments the exit pressure of the breakthrough column was set at 108 kPa. After each desorption experiment the breakthrough column was flushed for 6 hours with helium at 125 ml min^"1 (SATP) at the measurement temperature. A temperature increase after these 6 hours did not result in the desorption of additional adsorbed hydrocarbons, which confirms that all gases have desorbed from the column at that time.

The total analysis time of each breakthrough experiment was approximately 1 h. Since the breakthrough of both components occurred much earlier, this implies an equilibration time of at least ¹AIn.. The desorption of the breakthrough column was performed isothermally with a helium flush of 20 ml min^"1 (SATP) and was analyzed for 4 h. In the breakthrough setup the CompactGC (Interscience) is used to determine the mol fraction of both components at the exit of the breakthrough column. The GC is equipped with three parallel 8 meter Rt-QPlot capillary columns (diameter 0.32 mm) and each column is equipped with its own Flame Ionization Detector (FID) . Whenever the GC is triggered, 45 samples can be analyzed consecutively, after which 1-1¹A minute is required to allow the detection of the last sample, to save the results and to reset the trigger of the EZChrom Elite software for the next chromatogram. With this configuration and the continuous injection of gas samples in the GC columns, it is possible to analyse the mixture composition every 8 s .

From the results as shown in fig. 2, it is clear that, when flushing the reactor propane is released first, and that propylene pushes out an important amount of the previously adsorbed propane. A very steep increase of propylene after t/tθ = 1.5 and the very steep decrease of propane at the same time, is an indication of the excellent usability of lithium-Faujasite for the present separation. Characteristics of the experiment shown in fig. 2, is that the propylene/propane breakthrough experiment was performed over a sample of lithium-Faujasite at 5O⁰C. F_C3HS = Fc_3H6 = 2 mln/min: F_He = 4 mln/min; M_{Lix FAU} (dry) = 0.50 g.

Claims

1. Use of Li-Faujasite for adsorptive based separation of a mixture of CχH₂χ/CχH2χ₊2 , wherein x = 2, 3 or 4, in particular wherein the mixture is comprised of any of the groups of C₂H₄/C₂H₆, C₃H₆/C₃H_8/ C₄H₈Zc₄Hi₀ and wherein said Li- Faujasite is comprised of LiX Faujasite or LiY Faujasite.

2. Use of a Li-Faujasite according to claim 1, wherein said 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 said other cation by Li.

3. Use of a Li-Faujasite according to claim 1 for separating a mixture of olefin and paraffin, chosen from any mixture of C₂H₄/C₂H₆, C₃H₆/C₃H₈, and C₄H₈/C₄Hi₀, , wherein said method comprises one of: 1) a pressure swing adsorption method, 2) a temperature swing adsorption method, 3) a vacuum swing adsorption method (^λVSA^#) or 4) a displacing method, either performed in a gas phase or a liquid phase.

4. Use of a Li-Faujasite according to claim 3, wherein the method comprises a displacing method that is performed in a simulated moving bed.

5. Use of a Li-Faujasite according to claim 3 in a pressure swing adsorption method for separating mixtures of olefin and paraffin, chosen from any mixture of C₂H₄/C₂H₆, C₃H₆/C₃H₈, and C₄H₈/C₄H₁₀, wherein: - in a first step feeding said mixture into an adsorption vessel containing a Li-Faujasite sorbent as mentioned in claim 1, so as to obtain a first pressure,

- in a second step reducing pressure in said vessel so as to obtain a second, relatively lower pressure, - in a third step adding an olefin at a first side of the vessel and opening said vessel at a second, oppositely positioned side, such that said added olefin contacts the sorbent, for removing the paraffin from the vessel at said first side, and - in a fourth step, flushing the vessel, optionally with an inert compound, for removing and collecting the olefin .

6. Use of a Li-Faujasite in a method according to claim 4 or 5, wherein the method is performed in the gas phase.

7. Use of a Li-Faujasite in a method according to claim 4 or 5, wherein the method is performed in the liquid phase .

8. Use of a Li-Faujasite in a method according to claim 7, wherein the paraffins and olefins are dissolved in a solvent.