Cyclical method of producing high-purity nitrogen and optionally a high-purity hydrocarbon from a feedstock containing nitrogen and a hydrocarbon

Abstract

The invention relates to a cyclical method for producing a nitrogen fraction, the purity of which is greater than or equal to 95 mol %, and a hydrocarbon-enriched fraction from a filler containing nitrogen and a hydrocarbon, said method using a specific class of porous hybrid solids as an adsorbent in a pressure-swing adsorption (PSA) process. The invention also relates to equipment for implementing said method.

Claims

1. A cyclical process for the production of a nitrogen fraction with a purity ≧95 mol %, on the one hand, and of a fraction enriched in hydrocarbon, on the other hand, from a feedstock comprising nitrogen and a hydrocarbon, each cycle comprising the following stages: i) bringing said feedstock into contact with an adsorbent bed provided with a feed end and with a production end and containing a solid adsorbent chosen from porous hybrid solids, said contacting operation being carried out under a pressure P.sub.1≧0.1 MPa and a temperature T.sub.1≧0° C.; ii) recovering, at the production end of the adsorbent bed, a first nitrogen fraction with a purity ≧95 mol % (2); iii) depressurizing the adsorbent bed cocurrentwise down to a pressure P.sub.2<P.sub.1 where P.sub.2≧0.1 MPa, so as to recover, at the production end of the adsorbent bed, a second fraction of nitrogen with a purity ≧95 mol %; iv) depressurizing the adsorbent bed countercurrentwise down to a pressure P.sub.3<P.sub.2 where 0.006 MPa≦P.sub.3≦0.05 MPa, so as to desorb the hydrocarbons from the bed and to recover, at the feed end of the adsorbent bed, a first fraction enriched in hydrocarbon v) purging the adsorbent bed countercurrentwise using the nitrogen fraction with a purity ≧95 mol % under the pressure P.sub.3, so as to recover, at the feed end of the adsorbent bed, a second fraction enriched in hydrocarbon; vi) repressurizing the adsorbent bed countercurrentwise using the nitrogen with a purity ≧95 mol % or with the feedstock up to the pressure P.sub.1; in which said adsorbent has a dynamic capacity with regard to the hydrocarbon of at least 3 mmol/g between 0.25 MPa and 0.05 MPa at 50° C. and a dynamic capacity with regard to the nitrogen of less than or equal to 0.50 mmol/g between 0.25 MPa and 0.05 MPa at 50° C., wherein the hydrocarbon is propylene and the solid adsorbent is MIL 100 (Fe).

2. The process as claimed in claim 1, wherein stage i) of bringing the feedstock into contact with the adsorbent bed is carried out at a pressure P.sub.1 of between 0.1 MPa and 1 MPa and at a temperature of between 0° C. and 100° C.

3. The process as claimed in claim 1, wherein the cocurrentwise depressurization stage iii) is carried out at a pressure P.sub.2 of between 0.2 MPa and 0.1 MPa.

4. The process as claimed in claim 1, wherein the depressurization stage iv) is carried out under vacuum.

5. The process as claimed in claim 1, wherein the depressurization stage iv) is carried out at a pressure P.sub.3 of between 0.01 MPa and 0.05 MPa.

6. The process as claimed in claim 1, wherein, before carrying out the depressurization stage iv), a portion of the fraction enriched in hydrocarbon is recycled in the adsorbent bed via the feed end, so as to saturate the bed with hydrocarbon and to recover, on conclusion of stage iv), a fraction enriched in hydrocarbon with a purity ≧90 mol %.

7. The process as claimed in claim 6, wherein the depressurization stage iv) is carried out under a pressure P.sub.3 of between 0.006 MPa and 0.05 MPa.

8. The process as claimed in claim 1, wherein the degree of recovery of nitrogen with a purity ≧95 mol % is greater than or equal to 80%.

9. The process as claimed in claim 6, wherein the degree of recovery of hydrocarbon with a purity ≧90 mol % is greater than or equal to 80%.

10. The process as claimed in claim 1, wherein the feedstock comprises at least 30 mol % of nitrogen and at most 70 mol % of hydrocarbon.

11. The process as claimed in claim 1, wherein the feedstock originates from a plant for the production of polypropylene.

12. A process for the production of polypropylene by polymerization of propylene optionally comprising a propane fraction, in which the polypropylene resulting from the polymerization stage is separated from the propylene and propane which have not reacted during the polymerization using a gas/solid separator into which a nitrogen charge is introduced in order to purify the polypropylene, which results in the formation of a nitrogen/propylene/propane mixture, said process being characterized in that said nitrogen/propylene/propane mixture is recovered and the stages as defined in claim 1 are carried out in order to produce, on the one hand, a nitrogen fraction with a purity ≧95 mol % and, on the other hand, a fraction enriched in propylene and propane.

13. The process as claimed in claim 12, wherein a portion of the fraction enriched in propylene and propane is recycled in the adsorbent bed via the feed end, so as to saturate the bed with hydrocarbon and to recover, on conclusion of stage iv), a fraction enriched in propylene and propane with a purity ≧90 mol %.

14. An installation for the implementation of a process as claimed in claim 12, wherein said installation comprises: a polymerization reactor with an inlet which makes it possible to introduce propylene as reactant, said propylene comprising a propane fraction, as well as the other ingredients necessary for the polymerization; a gas/solid separator positioned at the outlet of the polymerization reactor which receives the solid polypropylene resulting from the polymerization reaction and also an unreacted propylene/propane mixture, said gas/solid separator additionally comprising: an inlet which makes it possible to introduce nitrogen intended to degas the solid polypropylene, an outlet (A) for the nitrogen/propylene/propane gas mixture; and an outlet (B) for recovering the solid polypropylene; at least one adsorbent column chosen from MIL 100 (Fe), said columns making it possible to receive the nitrogen/propylene/propane gas mixture so as to produce, on the one hand, a nitrogen with a purity ≧95 mol % and, on the other hand, a mixture enriched in propylene and propane.

15. The installation as claimed in claim 14, wherein said installation comprises a line which makes it possible to recycle the mixture enriched in propylene and propane in the adsorbent column, so as to saturate the bed with hydrocarbon and to recover a fraction of propylene and propane with a purity ≧90 mol %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 represents the adsorption isotherms for nitrogen on MIL-100(Fe) at different temperatures (50, 100 and 150° C.), up to 5 bar abs.

(2) FIG. 2 represents the comparison between the adsorption isotherms for nitrogen and propylene at 50° C. on MIL-100(Fe).

(3) FIG. 3 diagrammatically represents the stages of the cyclical process A) according to the invention.

(4) FIG. 4 diagrammatically represents the cyclical process A) for continuous operation with 4 columns.

(5) FIG. 5 diagrammatically represents the stages of the process B) according to the invention.

(6) FIG. 6 diagrammatically represents the cyclical process B) for continuous operation with 3 columns.

(7) FIG. 7 represents the adsorption capacity of MIL-100(Fe) (“C.sub.3H.sub.6 (mol/kg)”) as a function of the pressure (Pressure (bar abs.)) at 50° C. or at 70° C., either in the form of cylinders (batch 1) or in the form of beads (batch 2), under the conditions of Example 1 (simulation) or else under the conditions of Example 2 (pilot plant).

(8) FIG. 8 represents the comparison between the adsorption isotherms for nitrogen and propylene at 70° C. on MIL-125_NH.sub.2.

(9) FIG. 9 represents the comparison between the adsorption isotherms for nitrogen and propylene at 70° C. on UiO-66(Zr).

DETAILED DESCRIPTION OF THE DRAWINGS

(10) The examples which follow clarify the invention without limiting the scope thereof.

(11) In the examples which follow, all the pressures are expressed in bar abs. (bar absolute). 1 bar=0.1 MPa.

EXAMPLES: SEPARATION OF NITROGEN AND PROPYLENE USING MIL-100(Fe)

(12) MIL-100(Fe) is an iron(III) trimesate porous hybrid solid with a zeolite MTN topology synthesized at the Korea Research Institute of Chemical Technology (KRICT) (Yoon et al., 2010).

(13) Two batches were tested: batch 1: cylinders as described below, batch 2: beads as described below.

1) Example 1: Measurements of Equilibrium and Simulation

(14) FIG. 1 represents the adsorption isotherms for nitrogen on MIL-100(Fe) as characterized in Table 2 at different temperatures (50, 100 and 150° C.), up to 5 bar abs., measured in a Rubotherm magnetic suspension balance.

(15) FIG. 2 represents the comparison between the adsorption isotherms for nitrogen and propylene at 50° C. on MIL-100(Fe) as characterized in Table 2.

(16) It emerges from these isotherms that the propylene/nitrogen selectivity at 1 bar abs. and 50° C. is approximately 40.

(17) Two cyclical PSA processes were simulated: A) process for production of high-purity nitrogen from a nitrogen/propylene mixture, B) process for production of high-purity nitrogen, on the one hand, and of high-purity propylene, on the other hand, from a nitrogen/propylene mixture.

(18) The nitrogen/propylene mixture comprises 70 mol % of nitrogen and 30 mol % of propylene. It is introduced into the adsorbent bed under the following conditions: 70° C., 1 bar abs. and 4 SLPM, 10.7 mol/h. SLPM=Standard Liter Per Min (Standard: 70° F. and 14.696 psiA (21° C. and 1 Atm)).

(19) The process A) comprises the 5 following stages: the nitrogen/propylene mixture is introduced at the feed end of the adsorbent bed, adsorption under a pressure of 2.5 bar abs., the high-purity nitrogen is recovered at the production end of the adsorbent bed, cocurrentwise depressurization under a pressure of 1 bar abs., in order to increase the degree of recovery of the nitrogen, countercurrentwise depressurization (blowdown) under a pressure of 0.4 bar abs., so as to recover a first fraction enriched in propylene, then a purge under a pressure of 0.4 bar abs. using a fraction of the high-purity nitrogen, in order to regenerate the adsorption bed and to recover a second fraction enriched in propylene, countercurrentwise repressurization of the adsorbent bed using a fraction of the high-purity nitrogen.

(20) The process B) comprises the same stages as the process A), with in addition a rinse stage which consists in recycling a portion of the fraction enriched in propylene obtained on conclusion of the stage of countercurrentwise depressurization in the adsorbent bed, so as to saturate the latter with propylene and to thus recover a fraction of high-purity propylene. The pressure in the countercurrentwise depressurization stage and in the rinse stage is 0.1 bar abs.

(21) FIG. 3 diagrammatically represents the stages of the process A).

(22) FIG. 4 diagrammatically represents the cyclical process A) for continuous operation with 4 columns.

(23) FIG. 5 diagrammatically represents the stages of the process B).

(24) FIG. 6 diagrammatically represents the cyclical process B) for continuous operation with 3 columns.

(25) The meanings of the expressions used in FIGS. 3, 4, 5 and 6 are shown in the following Table 1:

(26) TABLE-US-00001 TABLE 1 “Adsor.” Adsorption stage “CoDep” or “CocD” or “D” Cocurrentwise depressurization stage “Rinse” Recycling stage (rinse) “Blowdown” or “Blowd” or Countercurrentwise depressurization stage “B” (blowdown) “Purge” Countercurrentwise purge stage “Press.” or “P” Countercurrentwise repressurization stage “N.sub.2 product” High-purity nitrogen recovered “C.sub.3H.sub.6 product” High-purity propylene recovered “C.sub.3H.sub.6 waste” Unrecovered propylene fraction

(27) The mathematical model for carrying out the simulation is that described in Da Silva et al., 1999, Da Silva and Rodriges, 2001, and Ribeiro et al., 2008.

(28) The values of the transport parameters required by the model were calculated by employing the correlations normally used. The axial dispersion coefficients of the mass and of the heat, and also of the mass transfer and convection heat transfer coefficients, were estimated by using the Wakao and Funazkri correlations (Wakao and Funazkri, 1978; Yang, 1987; Da Silva 1999). The coefficient for heat transfer by convection between the gas and the wall of the column was calculated with the Wash and Froment correlation (Wash and Froment, 1972). The macropore diffusivity was calculated with the Bosanquet equation and the diffusivities were determined with the Chapman-Enskog equation (Bird et al., 2002). The general properties of the gases, such as the density, the viscosity and the molar specific heat, were obtained according to Bird et al., 2002. It was assumed that the molar specific heat of the adsorbed gas was equal to that of the gas phase (Sircar, 1985).

(29) The dimensions of the adsorbent bed and the properties of the adsorbent are shown in the following Table 2:

(30) TABLE-US-00002 TABLE 2 Length of the bed (m) 2 Diameter of the bed (m) 0.026 Porosity of the bed 0.41 Adsorbent MIL-100(Fe) Form of the adsorbent cylinders Radius of the cylinder (m) 1.5 × 10.sup.−3 Length of the cylinder (m) 3.85 × 10.sup.−3  Particle density (kg/m.sup.3) 888 Porosity of the cylinder 0.34 Crystal diameter 1.4 × 10.sup.−3

(31) The values of the transport parameters under the feed conditions are shown in the following Table 3:

(32) TABLE-US-00003 TABLE 3 Axial dispersion coefficient of the mass (m.sup.2/s) 5.5 × 10.sup.−4 Axial dispersion coefficient of the heat (W/m/K)  0.50 Mass transfer coefficient of the film (m/s) 2.3 × 10.sup.−2 Coefficient for transfer of heat of the film between 85 the gas and the particle (W/m.sup.2/K) Coefficient for transfer of heat of the film between 60 the gas and the wall (W/m.sup.2/K) Overall heat transfer coefficient (W/m.sup.2/K) 40 Macropore diffusivity (m.sup.2/s) C.sub.3H.sub.6: 3.04 × 10.sup.−6 N.sub.2: 3.07 × 10.sup.−3 Crystalline diffusivity (m.sup.2/s) C.sub.3H.sub.6: 1.18 × 10.sup.−10 N.sub.2: 1.13 × 10.sup.−9

(33) The energy consumption of the process was also calculated. An adiabatic compression was assumed and the following equation was used:

(34) $\mathrm{Power}=\frac{1}{\eta }\stackrel{.}{n}{R}_g{T}_1\frac{\gamma }{\gamma -1}\left({\left(\frac{P_2}{P_1}\right)}^{\frac{\gamma -1}{\gamma }}-1\right)$
in which:
η is the efficiency, {dot over (n)} is the molar flux, R.sub.g is the ideal gas constant, T.sub.1 is the feed temperature, P.sub.1 and P.sub.2 are respectively the inlet pressure and the outlet pressure and γ is the ratio of the heat capacity of the gas mixture at constant pressure to the heat capacity of the gas mixture at a constant volume (γ=Cp/Cv) (Mc Cabe et al., 1993; McAllister, 2009). For the compression of the feed feedstock from 1 bar abs. to 2.5 bar abs., an efficiency of 85% was set. In the case of vacuum pumps (required for the countercurrentwise depressurization and purge stages), an efficiency of 60% has been assumed.

(35) The performance of the PSA process was evaluated from the following parameters: purity of the product recovered, degree of recovery and productivity as defined by Rota and Wankat (Rota and Wankat et al.).

(36) 1.1. Recovery of the High-Purity Nitrogen (Process A):

(37) The purity of the nitrogen is defined in the following way:

(38) $\frac{n_{N_2}^S\left(\mathrm{Adsorption}\right)+n_{N_2}^S\left(\mathrm{Depressurization}\right)}{n_{\mathrm{Total}}^S\left(\mathrm{Adsorption}\right)+n_{\mathrm{Total}}^S\left(\mathrm{Depressurization}\right)}$
in which:
n.sub.N.sub.2.sup.S (Adsorption) represents the number of moles of nitrogen exiting in the gas phase during the adsorption stage,
n.sub.N.sub.2.sup.S (Depressurization) represents the number of moles of nitrogen exiting in the gas phase during the depressurization stage,
n.sub.Total.sup.S (Adsorption) represents the total number of moles exiting in the gas phase during the adsorption stage,
n.sub.Total.sup.S (Depressurization) represents the total number of moles exiting in the gas phase during the depressurization stage.
The degree of recovery of the nitrogen is defined in the following way:

(39) $\frac{\begin{array}{c}{n}_{N_2}^S\left(\mathrm{Adsorption}\right)+n_{N_2}^S\left(\mathrm{Depressurization}\right)-\\ n_{N_2}^E\left(\mathrm{Purge}\right)-n_{N_2}^E\left(\mathrm{Pressurization}\right)\end{array}}{n_{N_2}^E\left(\mathrm{Adsorption}\right)}$
in which:
n.sub.N.sub.2.sup.S (Adsorption) represents the number of moles of nitrogen exiting in the gas phase during the adsorption stage,
n.sub.N.sub.2.sup.S (Depressurization) represents the number of moles of nitrogen exiting in the gas phase during the depressurization stage,
n.sub.N.sub.2.sup.E (Purge) represents the number of moles of nitrogen entering the column during the purge stage,
n.sub.N.sub.2.sup.E (Pressurization) represents the number of moles of nitrogen entering the column during the repressurization stage,
n.sub.N.sub.2.sup.E (Adsorption) represents the number of moles of nitrogen entering with the feedstock during the adsorption stage.
The simulation results are shown in the following Table 4:

(40) TABLE-US-00004 TABLE 4 Duration of the stages (s) Countercurrentwise Cocurrentwise depressurization Adsorption depressurization (blowdown) Purge Repressurization 300 100 250 500 50 P (bar abs.) P (bar abs.) P (bar abs.) Feed T (° C.) 2.5 1.0 0.4 70 Adsorption flow rate (SLPM) Purge flow rate (SLPM) 4.0 0.24 Nitrogen recovered Degree of Productivity Fraction enriched in propylene Purity (%) recovery (%) (mol.sub.N2/kg.sub.ads/h) Purity (%) 99.9 81.5 2.74 67.3 Energy consumption 19.7 W (3.2 Wh/mol.sub.N2)
1.2. Recovery of the High-Purity Nitrogen, on the One Hand, and of the High-Purity Propylene, on the Other Hand (Process B):
The purity of the nitrogen is defined in the following way:

(41) $\frac{n_{N_2}^S\left(\mathrm{Adsorption}\right)+n_{N_2}^S\left(\mathrm{Depressurization}\right)+n_{N_2}^S\left(\mathrm{Rinse}\right)}{\begin{array}{c}{n}_{\mathrm{Total}}^S\left(\mathrm{Adsorption}\right)+\\ n_{\mathrm{Total}}^S\left(\mathrm{Depressurization}\right)+n_{\mathrm{Total}}^S\left(\mathrm{Rinse}\right)\end{array}}$
n.sub.N.sub.2.sup.S (Adsorption) represents the number of moles of nitrogen exiting in the gas phase during the adsorption stage,
n.sub.N.sub.2.sup.S (Depressurization) represents the number of moles of nitrogen exiting in the gas phase during the depressurization stage,
n.sub.N.sub.2.sup.S (Rinse) represents the number of moles of nitrogen exiting in the gas phase during the rinse stage,
n.sub.Total.sup.S (Adsorption) represents the total number of moles exiting in the gas phase during the adsorption stage,
n.sub.Total.sup.S (Depressurization) represents the total number of moles exiting in the gas phase during the depressurization stage,
n.sub.Total.sup.S (Rinse) represents the total number of moles exiting in the gas phase during the rinse stage.
The purity of the propylene is defined in the following way:

(42) $\frac{n_{C_3{H}_6}^S\left(\mathrm{Blowdown}\right)+n_{C_3{H}_6}^S\left(\mathrm{Purge}\right)}{n_{\mathrm{Total}}^S\left(\mathrm{Blowdown}\right)+n_{\mathrm{Total}}^S\left(\mathrm{Purge}\right)}$
in which:
n.sub.C.sub.3.sub.H.sub.6.sup.S (Blowdown) represents the number of moles of propylene exiting in the gas phase during the countercurrentwise depressurization stage,
n.sub.C.sub.3.sub.H.sub.6.sup.S (Purge) represents the number of moles of propylene exiting in the gas phase during the purge stage,
n.sub.Total.sup.S (Blowdown) represents the total number of moles exiting in the gas phase during the countercurrentwise depressurization stage,
n.sub.Total.sup.S (Purge) represents the total number of moles exiting in the gas phase during the purge stage.
The degree of recovery of the nitrogen is defined in the following way:

(43) $\frac{\begin{array}{c}{n}_{N_2}^S\left(\mathrm{Adsorption}\right)+n_{N_2}^S\left(\mathrm{Depressurization}\right)+\\ n_{N_2}^S\left(\mathrm{Rinse}\right)-n_{N_2}^E\left(\mathrm{Purge}\right)-n_{N_2}^E\left(\mathrm{Pressurization}\right)\end{array}}{n_{N_2}^E\left(\mathrm{Adsorption}\right)}$
which:
n.sub.N.sub.2.sup.S (Adsorption) represents the number of moles of nitrogen exiting in the gas phase during the adsorption stage,
n.sub.N.sub.2.sup.S (Depressurization) represents the number of moles of nitrogen exiting in the gas phase during the depressurization stage,
n.sub.N.sub.2.sup.S (Rinse) represents the number of moles of nitrogen exiting in the gas phase during the rinse stage,
n.sub.N.sub.2.sup.E (Purge) represents the number of moles of nitrogen entering the column during the purge stage,
n.sub.N.sub.2.sup.E (Pressurization) represents the number of moles of nitrogen entering the column during the repressurization stage,
n.sub.N.sub.2.sup.E (Adsorption) represents the number of moles of nitrogen entering with the feedstock during the adsorption stage.
The degree of recovery of the nitrogen is defined in the following way:

(44) $\frac{n_{C_3{H}_6}^S\left(\mathrm{Blowdown}\right)+n_{C_3{H}_6}^S\left(\mathrm{Purge}\right)-n_{C_3{H}_6}^E\left(\mathrm{Rinse}\right)}{n_{C_3{H}_6}^E\left(\mathrm{Adsorption}\right)}$
in which:
n.sub.C.sub.3.sub.H.sub.6.sup.S (Blowdown) represents the number of moles of propylene exiting in the gas phase during the countercurrentwise depressurization stage,
n.sub.C.sub.3.sub.H.sub.6.sup.S (Purge) represents the number of moles of propylene exiting in the gas phase during the purge stage,
n.sub.C.sub.3.sub.H.sub.6.sup.E (Rinse) represents the number of moles of propylene entering with the feedstock during the rinse stage,
n.sub.C.sub.3.sub.H.sub.6.sup.E (Adsorption) represents the number of moles of propylene entering with the feedstock during the adsorption stage.
The simulation results are shown in the following Table 5:

(45) TABLE-US-00005 TABLE 5 Duration of the stages (s) Countercurrentwise Cocurrentwise depressurization Adsorption depressurization Rinse (blowdown) Purge Repressurization 800 100 600 250 600 50 P (bar abs.) P (bar abs.) P (bar abs.) Feed T (° C.) 2.5 1.0 0.1 70 Adsorption flow rate (SLPM) Rinse flow rate (SLPM) Purge flow rate (SLPM) 4.0 1.3 0.17 Nitrogen recovered Propylene recovered Degree of Productivity Degree of Productivity Purity (%) recovery (%) (mol.sub.N2/kg.sub.ads/h) Purity (%) recovery (%) (mol.sub.N2/kg.sub.ads/h) 99.9 97.4 4.33 97.9 87.6 1.67 Energy consumption 36.6 W (5.0 Wh/mol.sub.N2, 13.0 Wh/mol.sub.C3H6)

2) Example 2: Experiment at the Pilot Scale

(46) The dynamic adsorption capacity (dynamic capacity) of the MIL-100(Fe) with respect to propylene was determined at 50° C. and 70° C.

(47) Furthermore, adsorption/desorption cycles in VPSA (Vacuum Pressure Swing Adsorption) mode were carried out in order to experimentally confirm the simulation results described above.

(48) 2.1. Description of the Pilot Plant

(49) The pilot plant is composed of nitrogen and liquid propylene storage tanks, of a regulator which makes it possible to regulate the nitrogen flow rate, of a positive displacement pump intended for the liquid propylene and of an evaporator located over the mixture, upstream of the adsorption column. The adsorbent (MIL-100(Fe) as described below) bed is placed in the adsorption column with an internal diameter of 1″ and with a height of 2 m. This column is equipped with an external jacket in which a temperature-regulated heat-exchange fluid capable of operating between 20 and 200° C. circulates. Three thermocouples are placed at the bottom, at the middle and at the top of the column, at 0.1 m, 1 m and 1.80 m from the bottom of the adsorbent bed, at the center of the column.

(50) Pressure regulation at the column outlet makes it possible to control the pressure in the column. A vacuum pump is also connected to the column so as to be able to operate under vacuum during the regeneration of the adsorbent. An in-line infrared analyzer makes it possible to analyze the streams at the inlet and on the outlets of the column. Flowmeters are also present at the inlet and at the outlet of the adsorption column.

(51) During the adsorption stage, the liquid propylene is pumped using the positive displacement pump and mixed with the nitrogen. The gas/liquid mixture is then completely vaporized before entering the adsorption column in upward fashion. The stream is controlled using a regulator located on the pump and using a system for regulating the flow rate, and the pressure is controlled using a pressure-regulating loop located after the adsorption column.

(52) The desorption stage is carried out by decreasing the pressure by entrainment under vacuum, a small amount of nitrogen being introduced into the column.

(53) The MIL-100(Fe) tested is provided in the form of beads with a diameter of 2.5 mm and with a specific surface, measured according to the BET method, of greater than 2100 m.sup.2/g.

(54) The MIL-100(Fe) has to be activated before use: 3 hours at 150° C. under vacuum of nitrogen. On conclusion of the activation, the loss in weight is approximately 13%, with respect to the initial weight. After each test, the MIL-100(Fe) was reactivated under these conditions using a slight stream of nitrogen under vacuum (less than 3 mbar).

(55) 2.2. Operating Conditions

(56) Temperature: 20-200° C.

(57) Pressure: 0-80 bar

(58) TABLE-US-00006 TABLE 6 Pressure Minimum Normal range Maximum Adsorption   1 bar abs. 1-20 bar abs. 80 bar abs. Desorption 0.02 bar abs. 0.1 bar abs.  5 bar abs.
2.3. Sampling and Analysis

(59) The analysis of the various gas streams is carried out in line using three-way valves. These valves make possible the analysis of the mixture at the inlet of the column, of the mixture at the column outlet or of the mixture which passes through the vacuum pump. The analysis is carried out using an analyzer with a platinum-based infrared source (ABB).

(60) 2.4. Results

(61) 2.4.1 Determination of the Dynamic Capacity of the MIL-100(Fe) with Respect to Propylene at 50° C. And 70° C.

(62) The breakthrough curves and the temperature profiles with regard to MIL-100(Fe) for propylene (feed flow rate: 80 Sl/h±5%) at 50° C. and 1.25 bar abs. were determined. The operating conditions and the amount of propylene adsorbed at equilibrium are shown in Table 7. The dynamic capacity of the MIL-100(Fe) with respect to propylene at 50° C. and 1.25 bar abs. is 4.290 mol/kg.

(63) The breakthrough curves and the temperature profiles with regard to MIL-100(Fe) for propylene (feed flow rate: 80 Sl/h±5%) at 70° C. and 1.28 bar abs. and 2.4 bar abs. were determined. The operating conditions and the amount of propylene adsorbed are shown in Table 8. The dynamic adsorption capacity of the MIL-100(Fe) with respect to propylene at 70° C./1.28 bar abs. and 70° C./2.40 bar abs. is 3.862 mol/kg and 5.387 mol/kg respectively.

(64) TABLE-US-00007 TABLE 7 Temperature 50° C. Adsorption pressure 1.25 (bar abs.) Adsorption temperature 323 (K) Average volumetric 80 flow at the inlet of the column (Sl .Math. hr) Propylene in the feed 100 feedstock (%) Molar flux at the inlet 9.92 × 10.sup.−4 of the column (mol .Math. s) Weight of adsorbent 0.331 in the bed (kg) Volume of the adsorbent 1.067 × 10.sup.−3 bed (m.sup.3) True density of the 888 adsorbent (kg/m.sup.3) Porosity of the bed (ε) 0.65 Diameter (m) 0.02606 Height of the bed (m) 2 Position of the sensors At the At the At the T bottom middle top h (m) 0.10 1.00 1.80 Adsorbed at equilibrium Amount of 1.418 propylene (mol) Dynamic capacity 4.290 (mol/kg)

(65) TABLE-US-00008 TABLE 8 Temperature 70° C. Adsorption pressure 1 1.28 (bar abs.) Adsorption pressure 2 2.40 (bar abs.) Adsorption temperature 343 (K) Average volumetric 81.3 flow at the inlet of the column (Sl .Math. hr) Propylene in the feed 100 feedstock (%) Molar flux at the inlet 1.01 × 10.sup.−3 of the column (mol .Math. s) Weight of adsorbent 0.331 in the bed (kg) Volume of the adsorbent 1.067 × 10.sup.−3 bed (m.sup.3) True density of the 888 adsorbent (kg/m.sup.3) Porosity of the bed (ε) 0.65 Diameter (m) 0.02606 Height of the bed (m) 2 Position of the sensors At the At the At the T bottom middle top h (m) 0.10 1.00 1.80 Equilibrium 1 Amount of 1.276 propylene adsorbed (mol) Dynamic capacity 3.862 (mol/kg) Equilibrium 2 Amount of 0.504 propylene adsorbed (mol) Dynamic capacity 5.387 (mol/kg)

(66) FIG. 7 represents the adsorption capacity of the MIL-100(Fe) (“C.sub.3H.sub.6 (mol/kg)”) as a function of the pressure (pressure (bar abs.)) at 50° C. or at 70° C., either in the form of cylinders (batch 1) or in the form of beads (batch 2), under the conditions of Example 1 (simulation) or else under the conditions of Example 2 (pilot plant).

(67) It can be seen in FIG. 7 that the adsorption capacity of the MIL-100(Fe) with respect to propylene under dynamic conditions (Ex. 2) is very similar to that determined under the static conditions (Ex. 1). The results are uniform.

(68) These results on a pilot plant validate the results obtained by simulation and show that porous hybrid solids, such as MIL-100(Fe), exhibit a dynamic adsorption capacity with respect to hydrocarbons, in particular propylene, which is sufficiently high (at least greater than 3 mmol/g) to make possible efficient separation of the nitrogen within pressure ranges appropriate for an industrial application.

(69) 2.4.2 Cycles in VPSA (Vacuum Pressure Swing Adsorption)

(70) Adsorption/desorption cycles in VPSA (Vacuum Pressure Swing Adsorption) mode were carried out in order to experimentally confirm the simulation results of example 1.

(71) Stages:

(72) adsorption (2.5 bar abs.), cocurrentwise depressurization (1.5 bar abs.), countercurrentwise depressurization (blowdown) (0.5 bar abs.), countercurrentwise purge using 100% pure nitrogen, repressurization using 100% pure nitrogen, the nitrogen is recovered on conclusion of the adsorption and cocurrentwise depressurization stages.
Operating Conditions: adsorption pressure: 2.5 bar abs. absorption temperature: 70° C. desorption pressure: 0.5 bar abs.
Composition of the feedstock at the inlet of the bed: 70 mol % propylene 30 mol % nitrogen
Amount of activated MIL-100(Fe) (beads): 330 g

(73) The results on a pilot plant in comparison with those obtained by simulation are shown in Table 9:

(74) TABLE-US-00009 TABLE 9 Unit Simulation Pilot plant Adsorption time s 1180 1180 Length of the bed m 1.99 1.99 Diameter of the bed m 0.026 0.026 Flow rate of the feedstock mol/h 2.68 2.68 Flow rate of the purge SLPM 0.13 0.13 MIL-100(Fe) MIL-100(Fe) Adsorbent cylinders beads Diameter of the adsorbent m 0.0015 0.0025 Weight of the adsorbent kg 0.560 0.330 Density of the adsorbent kg/m.sup.3 888 888 Porosity of the bed 0.41 0.65

(75) The purity of the nitrogen is defined according to the following formula:

(76) $\frac{n_{N2}^s\left(\mathrm{Adsorption}\right)+n_{N2}^s\left(\mathrm{depressurization}\right)}{n_{\mathrm{Total}}^s\left(\mathrm{Adsorption}\right)+n_{\mathrm{Total}}^s\left(\mathrm{depressurization}\right)}$
in which: n.sub.N2.sup.s (Adsorption) represents the number of moles of nitrogen exiting in the gas phase during the adsorption stage n.sub.N2.sup.s (depressurization) represents the number of moles of nitrogen exiting in the gas phase during the depressurization stage n.sub.Total.sup.s (adsorption) represents the total number of moles exiting in the gas phase during the adsorption stage n.sub.Total.sup.s (depressurization) represents the total number of moles exiting in the gas phase during the depressurization stage.

(77) The degree of recovery of the nitrogen is defined according to the following formula:

(78) $\frac{n_{N2}^s\left(\mathrm{Ads}\right)+n_{N2}^s\left(\mathrm{depressurization}\right)}{n_{N2}^e\left(\mathrm{Recomp}\right)+n_{N2}^e\left(\mathrm{Ads}\right)+n_{N2}^e\left(\mathrm{purge}\right)}$
in which: n.sub.N2.sup.s (Ads) represents the number of moles of nitrogen exiting in the gas phase during the adsorption stage n.sub.N2.sup.s (depressurization) represents the number of moles of nitrogen exiting in the gas phase during the depressurization stage n.sub.N2.sup.e (Recomp) represents the number of moles of nitrogen entering the column during the recompression stage n.sub.N2.sup.e (Ads) represents the number of moles of nitrogen entering with the feedstock during the adsorption stage n.sub.N2.sup.e (purge) represents the number of moles of nitrogen entering the column during the purge stage.

(79) These values are determined over a complete cycle after stabilization of the process.

(80) The purity of nitrogen recovered is 97.6 mol %.

(81) The degree of recovery of the nitrogen is 63.4%.

(82) These results show that porous hybrid solids, such as MIL-100(Fe), exhibit a dynamic adsorption capacity with respect to hydrocarbons, in particular propylene, which is high (at least greater than 3 mmol/g) over pressure ranges appropriate for an industrial application.

(83) Furthermore, these results show that porous hybrid solids, such as MIL-100(Fe), can be used to separate nitrogen from hydrocarbons in a very efficient way, that is to say with very high levels of purity (>95%) and degrees of recovery of greater than 80%, if, in addition, a stage of cocurrentwise depressurization after the adsorption stage and a countercurrentwise purge using high-purity nitrogen as described in example 1 are carried out.

3) Example 3: Measurements of Equilibrium on MIL-125(Ti)_NH2 or UiO-66(Zr)

(84) FIG. 8 represents the comparison between the adsorption isotherm for nitrogen and the adsorption isotherm (black points) and desorption isotherm (white points) for propylene at 70° C. over MIL-125(Ti)_NH.sub.2, the characteristics of which are shown in the following table 10.

(85) FIG. 9 represents the comparison between the adsorption isotherm for nitrogen and the adsorption isotherm (black points) and desorption isotherm (white points) for propylene at 70° C. over UiO-66(Zr).

(86) TABLE-US-00010 TABLE 10 MIL-125 (Ti)_NH.sub.2 UiO-66(Zr) Form of the adsorbent Powder Powder Porosity 0.59 cc/g 0.8 cc/g BET specific surface 1450 m.sup.2/g 1350 m.sup.2/g

(87) The sorption isotherms were measured using a device of IGA (Intelligent Gravimetric Analyzer, Hiden Analytical Ltd.) type with control of the pressure of the gas (0-5 bar) at 70° C. Before carrying out the adsorption measurements, the samples of adsorbent (30 mg) were dehydrated at 200° C. for 12 hours under vacuum (<10.sup.−5 torr).

(88) It emerges from these isotherms that the propylene/nitrogen selectivity at 1 bar abs. and 70° C. over MIL-125(Ti)_NH.sub.2 is 47.2.

(89) It emerges from these isotherms that the propylene/nitrogen selectivity at 1 bar abs. and 70° C. over UiO-66(Zr) is 33.4.

(90) The embodiments above are intended to be illustrative and not limiting. Additional embodiments may be within the claims. Although the present invention has been described with reference to particular embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

(91) Various modifications to the invention may be apparent to one of skill in the art upon reading this disclosure. For example, persons of ordinary skill in the relevant art will recognize that the various features described for the different embodiments of the invention can be suitably combined, un-combined, and re-combined with other features, alone, or in different combinations, within the spirit of the invention. Likewise, the various features described above should all be regarded as example embodiments, rather than limitations to the scope or spirit of the invention. Therefore, the above is not contemplated to limit the scope of the present invention.