Liquid phase separation of second-generation sugars by adsorption on FAU zeolite having a Si/Al atomic ratio of less than 1.5

Abstract

The invention relates to a process for the liquid-phase separation of xylose from a mixture of C5 and C6 sugars comprising at least xylose and glucose, by adsorption of xylose on a zeolitic adsorbent based on FAU-type zeolite crystals having an Si/Al atomic ratio of less than or equal to 1.5 comprising barium, wherein: said mixture is brought into contact with said adsorbent, by liquid chromatography, to obtain a glucose-enriched liquid phase and a xylose-enriched adsorbed phase; on the one hand, said glucose-enriched liquid phase is recovered and said phase adsorbed on said adsorbent is desorbed by means of a desorption solvent in order to recover the xylose on the other hand.

Claims

1. A process for the liquid-phase separation of xylose from a mixture of C5 and C6 sugars comprising at least xylose and glucose, by adsorption of xylose on a zeolitic adsorbent based on FAU-type zeolite crystals having an Si/Al atomic ratio of less than or equal to 1.5 comprising barium, wherein: said mixture is brought into contact with said adsorbent, by liquid chromatography, to obtain a glucose-enriched liquid phase and a xylose-enriched adsorbed phase; on the one hand, said glucose-enriched liquid phase is recovered and said phase adsorbed on said adsorbent is desorbed by means of a desorption solvent in order to recover the xylose on the other hand.

2. The process as claimed in claim 1, wherein said adsorbent comprises zeolite crystals having a diameter of less than or equal to 2 μm.

3. The process as claimed in claim 1, wherein said FAU-type zeolite has an Si/Al atomic ratio such that (1.00±0.05)≤Si/Al≤1.5.

4. The process as claimed in claim 1, wherein the content of barium oxide BaO in said adsorbent is such that the Ba.sup.2+ exchange rate is greater than 70%.

5. The process as claimed in claim 1, wherein said adsorbent comprises potassium and the content of potassium oxide K.sub.2O is such that the K.sup.+ exchange rate is less than 30%.

6. The process as claimed in claim 1, wherein said adsorbent comprises strontium and the content of strontium oxide SrO is such that the Sr.sup.2+ exchange rate is less than 25%.

7. The process as claimed in claim 1, wherein said adsorbent has a total content of oxides of alkali metal or alkaline-earth metal ions other than barium, potassium and sodium, such that the exchange rate of all of said ions relative to all of the alkali metal or alkaline-earth metal ions, is less than 30%.

8. The process as claimed in claim 1, wherein the separation by adsorption is carried out in a simulated moving bed: the glucose-enriched liquid phase is removed from contact with the adsorbent thus forming a raffinate stream, and the xylose-enriched phase adsorbed on said adsorbent is desorbed under the action of a desorption solvent, and removed from contact with the adsorbent then forming an extract stream.

9. The process as claimed in claim 1, wherein the desorption solvent is water.

10. The process as claimed in claim 8, wherein the separation by adsorption is carried out in an industrial adsorption unit of simulated countercurrent type with the following operating conditions: number of beds: 6 to 30 at least 4 operating zones, each located between a feed point and a withdrawal point, a temperature of from 20° C. to 100° C., preferably from 20° C. to 60° C., very preferably from 20° C. to 40° C.; pressure of between atmospheric pressure and 0.5 MPa.

11. The process as claimed in claim 1, wherein said adsorbent is in the form of an agglomerate comprising a binder and the number-average diameter of the agglomerates is from 0.4 to 2 mm.

12. The process as claimed in claim 1, wherein said adsorbent comprises zeolite crystals having a diameter of less than or equal to 1.7 μm.

13. The process as claimed in claim 1, wherein said FAU-type zeolite has an Si/Al atomic ratio such that (1.00±0.05)≤Si/Al≤1.3.

14. The process as claimed in claim 1, wherein the content of barium oxide BaO in said adsorbent is such that the Ba.sup.2+ exchange rate is greater than 90%.

15. The process as claimed in claim 1, wherein said adsorbent comprises potassium and the content of potassium oxide K.sub.2O is such that the K.sup.+ exchange rate is between 0.1% and 5%.

16. The process as claimed in claim 1, wherein said adsorbent comprises strontium and the content of strontium oxide SrO is such that the Sr.sup.2+ exchange rate is between 0.1% and 5%.

17. The process as claimed in claim 1, wherein said adsorbent has a total content of oxides of alkali metal or alkaline-earth metal ions other than barium, potassium and sodium, such that the exchange rate of all of said ions relative to all of the alkali metal or alkaline-earth metal ions, is between 0% and 5%.

18. The process as claimed in claim 1, wherein said adsorbent is in the form of an agglomerate comprising a binder and the number-average diameter of the agglomerates is between 0.4 and 0.8 mm.

Description

EXAMPLES

[0088] Several types of adsorbents are prepared: zeolitic adsorbents based on X zeolite (A to G), zeolitic adsorbents based on Y zeolite (H, I), ion-exchange resins (J, K).

[0089] The characteristics of the adsorbents are as follows: [0090] A: Adsorbent based on X zeolite in sodium form having an Si/Al atomic ratio equal to 1.23, used in the form of a 0.6 mm diameter bead. [0091] B: Adsorbent based on X zeolite having an Si/Al atomic ratio equal to 1.23 exchanged with calcium ions such that the calcium exchange rate is 95%, used in the form of a 0.6 mm diameter bead. [0092] C: Adsorbent based on LSX zeolite having an Si/Al atomic ratio equal to 1.02 exchanged with barium ions such that the barium exchange rate is 98%, used in the form of a 0.6 mm diameter bead. [0093] D: Adsorbent based on X zeolite having an Si/Al atomic ratio equal to 1.23 exchanged with barium ions such that the barium exchange rate is 99%, used in the form of a 0.6 mm diameter bead. [0094] E: Adsorbent based on X zeolite having an Si/Al atomic ratio equal to 1.23 exchanged both with barium and potassium such that the barium exchange rate is 93% and the potassium exchange rate is 5%, used in the form of a 0.6 mm diameter bead. [0095] F: Adsorbent based on X zeolite having an Si/Al atomic ratio equal to 1.23 exchanged both with barium and strontium such that the barium exchange rate is 79% and the strontium exchange rate is 21%, used in the form of a 0.6 mm diameter bead. [0096] G: Adsorbent based on X zeolite having an Si/Al atomic ratio equal to 1.23 exchanged both with barium and potassium such that the barium exchange rate is 74% and the potassium exchange rate is 26%, used in the form of a 0.6 mm diameter bead. [0097] H: Adsorbent based on Y zeolite having an Si/Al atomic ratio equal to 2.74 exchanged with barium such that the barium exchange rate is 65%, the other cations present being sodium, used in the form of a 0.6 mm diameter bead. [0098] I: Adsorbent based on Y zeolite having an Si/Al atomic ratio equal to 2.74 exchanged both with barium and potassium such that the exchange rate for each of the cations is around 50%, used in the form of a 0.6 mm diameter bead. [0099] J: Ca.sup.2+ exchanged Dowex® 99 resin [0100] K: Dowex® 99 resin initially with calcium, exchanged with barium

[0101] A breakthrough test (frontal chromatography) is performed with the adsorbents A to K to evaluate their efficiency.

[0102] The procedure for obtaining the breakthrough curves is as follows: [0103] Filling a column of about 20 cm.sup.3 with the adsorbent and insertion in the test bench. [0104] Filling with the solvent (water) at ambient temperature. [0105] Gradual increase to the adsorption temperature (30° C.) under a stream of solvent with a flow rate of 0.5 cm.sup.3/min. [0106] Solvent/feedstock changeover to inject the feedstock with a flow rate of 0.5 cm.sup.3/min. [0107] Online Raman analysis of the effluent and optional collection for offline analysis by other techniques for analyzing sugars (HPLC, etc.).

[0108] The injection of the feedstock is maintained for a sufficient time for the composition of the effluent to correspond to the composition of the feedstock.

[0109] The pressure is sufficient for the feedstock to remain in liquid phase at the adsorption temperature (30° C.), i.e. 0.12 MPa.

[0110] The composition of the feedstock used for the tests is as follows: [0111] xylose: 0.145 g/g [0112] glucose: 0.145 g/g

[0113] The selectivity of the xylose (X) relative to the glucose (G) is calculated from the adsorbed mass quantities q.sub.X and q.sub.G of the two compounds (the latter being determined by material balance from the analysis of the breakthrough effluent) and of the composition of the feedstock (feedstock in which the mass fraction of the compounds is y.sub.X and y.sub.G):

[00001]$.Math.a_{X/G}=\frac{q_X{y}_G}{q_G{y}_X}.$

[0114] The breakthrough results are given in Table 1 below:

TABLE-US-00001 TABLE 1 Qads Xylose Qads Glucose Xylose/Glucose Adsorbent (g/g) (g/g) selectivity Comparative A 0.038 0.049 0.8 Comparative B 0.016 0.024 0.7 According to C 0.042 0.018 2.1 the invention According to D 0.063 0.021 2.9 the invention According to E 0.063 0.030 2.1 the invention According to F 0.051 0.032 1.6 the invention According to G 0.063 0.032 2.0 the invention Comparative H 0.031 0.068 0.5 Comparative I 0.023 0.033 0.7 Comparative J 0.034 0.032 1.1 Comparative K 0.040 0.038 1

[0115] The example shows that the zeolitic adsorbents in accordance with the invention have improved properties of selectivity of xylose relative to glucose compared to the adsorbents or resins known from the prior art.