High-strength hollow fiber zeolite membrane and its preparation method

Abstract

The invention relates to a high-strength hollow fiber zeolite membrane and its preparation method, characterized in that the support of the high-strength zeolite membrane has a multi-channel hollow fiber configuration. The preparation method comprises first preparing a crystal seed solution, then immersing the dry support with the multi-channel hollow fiber configuration in the crystal seed solution, and extracting and drying the support to obtain a crystal-seeded support; and finally placing the crystal-seeded support in a zeolite membrane synthetic fluid, performing hydrothermal synthesis, and taking out, washing and drying the product to obtain the high-strength hollow fiber zeolite membrane. The multi-channel hollow fiber support can provide high mechanical property, which greatly reduces the depreciation rate of the hollow fiber zeolite membrane equipment during use. Meanwhile, the multi-channel hollow fiber zeolite membrane prepared by the Invention possesses high loading density of permeation flux and membrane module and can reduce the production cost and improve the separation efficiency significantly, and thus lays the foundation for promoting the industrial application of the hollow fiber zeolite membrane.

Claims

1. A method for preparing a high-strength hollow fiber zeolite membrane, the method comprising the following steps: (1) preparing a crystal seed solution: preparing a zeolite suspension liquid from zeolite crystal seed particles and water, wherein the mass fraction of the zeolite crystal seed particles in the zeolite suspension liquid is 0.5-5%, then adding sodium silicate in the zeolite suspension liquid and stirring to obtain a crystal seed solution; (2) crystal seed coating: obtaining a support having a multi-channel hollow fiber configuration, immersing said support in the crystal seed solution, extracting the support from the crystal seed solution, and drying the support to obtain a crystal-seeded support; and (3) synthesis of the high-strength hollow fiber zeolite membrane: placing the crystal-seeded support in a zeolite membrane synthetic fluid, performing hydrothermal synthesis on the crystal-seeded support to form a product, taking the product out of the zeolite membrane synthetic fluid, washing the product to pH=7-9, and drying the product to obtain the high-strength hollow fiber zeolite membrane.

2. A method according to claim 1, characterized in that the average particle diameter of the zeolite crystal seed particles is 50 nm-3 m; and the amount of the sodium silicate added in the zeolite suspension liquid is 0-25% of the mass fraction of the zeolite suspension liquid.

3. A method according to claim 1, characterized in that the multi-channel hollow fiber configuration in step (2) has 3-9 channels; an external diameter of the support is 2.0-4.0 mm, the diameter of each channel in the support is 0.6-1.2 mm, the support has an average pore diameter of 0.6-1.5 m, and the support has a porosity factor of 30-70%.

4. A method according to claim 1, characterized in that the material of the support of the high-strength zeolite membrane is one or more of aluminum oxide, titanium oxide, yttria-stabilized zirconia, or silicon oxide.

5. A method according to claim 1, characterized in that the zeolite crystal seed particles are one of the zeolites of NaA, T-type, MFI-type, or CHA-type.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is the support configuration of different multi-channel hollow fibers: wherein, (a) is four channels and (b) is seven channels;

(2) FIG. 2 is (a) surface microtopography and (b) fracture surface microtopography of four-channel hollow fiber NaA zeolite membrane in Embodiment 1;

(3) FIG. 3 is (a) surface microtopography and (b) fracture surface microtopography of seven-channel hollow fiber T-type zeolite membrane in Embodiment 5;

(4) FIG. 4 is (a) surface microtopography and (b) fracture surface microtopography of three-channel hollow fiber MFI zeolite membrane in Embodiment 7;

(5) FIG. 5 is the effect of operating temperature on the pervaporation property of the four-channel hollow fiber NaA zeolite membrane in Embodiment 2.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS OF THE INVENTION

Embodiment 1

(6) Four-channel Al.sub.2O.sub.3 hollow fiber is selected as the support (as shown in FIG. 1 (a)), of which porosity factor is 54%, average pore diameter 0.9 m, outer diameter 3.4 mm and channel diameter 0.9 mm. The breakage load of the four-channel hollow fiber with a span length of 4 cm is 17N in the three-point bending strength test of the support.

(7) Firstly, NaA zeolite crystal seed particles with an average particle diameter of 80 nm are fully dispersed in water to prepare the crystal seed suspension liquid with a mass fraction of 1%; then sodium silicate is added into the zeolite crystal seed suspension liquid, with an amount that is 5% of the mass fraction of the zeolite suspension liquid; then a dispersed crystal seed solution is obtained after full stirring. The dried support is immersed in the crystal seed solution to obtain an outer surface crystal-seeded four-channel hollow fiber support after extracting and drying (as shown in FIG. 2).

(8) The synthetic fluid of NaA zeolite membrane is prepared according to the mole ratio as Al.sub.2 O.sub.3:SiO.sub.2:Na.sub.2O:H.sub.2O=1:2:2:120; the crystal-seeded multi-channel hollow fiber support is added into the prepared synthetic fluid and washed with deionized water to PH=8 after crystallizing and cooling, and finally dried for standby application. The photographs of surface and fracture surface of the prepared zeolite membrane are shown in FIG. 3.

Embodiment 2

(9) Four-channel Al.sub.2O.sub.3 hollow fiber is selected as the support, of which the porosity factor is 50%, average pore diameter 1.2 m, outer diameter 3.0 mm and channel diameter 0.8 mm. The breakage load of the four-channel hollow fiber with a span length of 4 cm is 19N in the three-point bending strength test.

(10) Firstly, NaA zeolite crystal seed particles with an average particle diameter of 220 nm are fully dispersed in water to prepare a crystal seed suspension liquid with the mass fraction of 3%; then sodium silicate is added into the zeolite crystal seed suspension liquid, with an amount that is 10% of the mass fraction of the zeolite suspension liquid; then a dispersed crystal seed solution is obtained after full stirring. The dried support is immersed in the crystal seed solution to obtain an inner surface crystal-seeded four-channel hollow fiber support after extracting and drying.

(11) A synthetic fluid is prepared according to the mole ratio as Al.sub.2O.sub.3:SiO.sub.2:Na.sub.2O:H.sub.2 O=1:2:2:150; the preparation of the synthetic fluid of four-channel hollow fiber NaA inner membrane is the same as that in Embodiment 1.

Embodiment 3

(12) Four-channel Al.sub.2O.sub.3 hollow fiber is selected as the support (as shown in FIG. 1 (b)), of which porosity factor is 45%, average pore size 0.9 m, outer diameter 3.2 mm and channel diameter 0.8 mm. The breakage load of the four-channel hollow fiber with a span length of 4 cm is 21N in the three-point bending strength test.

(13) Firstly, NaA zeolite crystal seed particle with an average particle diameter of 2 m in water to prepare a crystal seed suspension liquid with a mass fraction of 5%; then sodium silicate is added into the zeolite crystal seed suspension liquid, with an amount that is 20% of the mass fraction of the zeolite suspension liquid; then a dispersed crystal seed solution is obtained after full stirring.

(14) The crystal seed coating is the same as that in Embodiment 1; a synthetic fluid is prepared according to the mole ratio as Al.sub.2O.sub.3:SiO.sub.2:Na.sub.2O:H.sub.2O=1:2:2:120; the synthesis of the NaA zeolite membrane is the same as that in Embodiment 1.

(15) For measurement of the pervaporation property of the multi-channel NaA zeolite membrane prepared by the Invention, the pervaporation property of the membrane is evaluated with penetration water flux (J) and separation factor ().

(16) $\begin{array}{cc}J=\frac{m}{A.Math.t}& \left(1\right)\\ =\frac{Y_2/Y_1}{X_2/X_1}& \left(2\right)\end{array}$

(17) In formula (1), m represents the mass of the water on permeation side, unit: Kg; A represents the available membrane area, unit: m.sup.2; t represents the penetration time, unit: h. In formula (2), Y.sub.1 represents the content of the water on permeation side; Y.sub.2 represents the content of the organics on permeation side; X.sub.1 represents the content of the water on raw material side and X.sub.2 represents the content of the organics on raw material side.

(18) The pervaporation property of the multi-channel NaA zeolite membrane is measured through pervaporation ethanol dehydration separation experiments. The feed liquid is stirred constantly under the effect of magnetic stirring apparatus for even temperature and density of the feed liquid. The single multi-channel hollow fiber is placed in the feed liquid tank, with one end sealed and the other end connected to the vacuum system. The pressure of the vacuum system is kept lower than 200 Pa and the permeation product is trapped by liquid nitrogen condensation. The pervaporation results of the multi-channel hollow fiber NaA zeolite membrane in Embodiments 1, 2 and 3 with regard to 90 wt. % ethanol/water system separation at 75 C. are listed in Table 1. The breakage loads of the supports in the aforesaid embodiments are more than 17N, the separation factors of the prepared NaA zeolite membrane are more than 10000 and meanwhile the permeation water fluxes are more than 8.0 kg.Math.m.sup.2.Math.h.sup.1. The results indicate that the NaA zeolite membrane of excellent property can be prepared with the four-channel hollow fiber supports with different property parameters.

(19) TABLE-US-00001 TABLE 1 Measurement Results of the Pervaporation Property in Each Embodiment Pervaporation property under the Breakage condition of 90 wt. % ethanol/water, 75 C. Embodiments load/N Water flux/kg .Math. m.sup.2 .Math. h.sup.1 Separation factor 1 17 12.8 >10000 2 19 9.9 >10000 3 21 8.0 >10000

(20) Note: breakage load means the force loaded when the hollow fiber with a span length of 4 cm breaks in the three-point bending strength test.

Embodiment 4

(21) The property of the four-channel hollow fiber support, the preparation of crystal seed solution and the crystal seed coating are the same as that in Embodiment 3; a synthetic fluid of NaA zeolite membrane is prepared according to the mole ratio as Al.sub.2 O.sub.3:SiO.sub.2:Na.sub.2O:H.sub.2O=1:4.5:48:950; the synthesis of the NaA zeolite membrane is the same as that in Embodiment 1.

Embodiment 5

(22) Seven-channel YSZ hollow fiber is selected, of which porosity factor is 65%, average pore diameter 1.4 m, outer diameter 3.8 mm and channel diameter 1.0 mm. The breakage load of the four-channel hollow fiber with a length of 4 cm is 22 N in the three-point bending strength test.

(23) Firstly, T-type zeolite crystal seed particles with an average particle diameter of 2 m are fully dispersed in water to prepare a crystal seed suspension liquid with a mass fraction of 5%; then a dispersed crystal seed solution is obtained after full stirring. The dried support is immersed in the crystal seed solution to obtain a crystal-seeded seven-channel hollow fiber support after extracting and drying. A synthetic fluid of T-type zeolite membrane is prepared according to the mole ratio as SiO.sub.2:Al.sub.2O.sub.3:Na.sub.2O:K.sub.2O:H.sub.2O=1:0.02:0.4:0.2:25; the outer surface crystal-seeded multi-channel hollow fiber support is added into the prepared synthetic fluid and washed with deionized water to PH=7 after crystallizing and cooling, and finally dried to obtain T-type zeolite membrane. For its SEM photograph, please refer to FIGS. 3(a) and 3(b).

Embodiment 6

(24) The property of the seven-channel hollow fiber support, the preparation of crystal seed solution and the crystal seed coating are the same as that in Embodiment 5; a synthetic fluid of the T-type zeolite membrane is prepared according to the mole ratio as SiO.sub.2:Al.sub.2O.sub.3:Na.sub.2O:K.sub.2O:H.sub.2O=1:0.05:0.2:0.04:13; the synthesis of the T-type zeolite membrane is the same as that in Embodiment 5.

Embodiment 7

(25) Three-channel TiO.sub.2 hollow fiber is selected, of which porosity factor is 30%, average pore diameter 0.6 m, outer diameter 2.4 mm and channel diameter 0.6 mm. The breakage load of the four-channel hollow fiber with a length of 4 cm in the three-point bending strength test of 4 cm is 26N.

(26) Firstly, MFI-type zeolite crystal seed particles with an average particle diameter of 50 nm are fully dispersed in water to prepare a crystal seed suspension liquid with a mass fraction of 1%; then a dispersed crystal seed solution is obtained after full stirring. The dried support is immersed in the crystal seed solution to obtain a crystal-seeded four-channel hollow fiber support after extracting and drying. A synthetic fluid of T-type zeolite membrane is prepared according to the tetrapropyl ammonium hydroxide:tetraethyl orthosilicate: 1:3.2:560 (mole ratio); the outer surface crystal-seeded multi-channel hollow fiber support is added into the prepared synthetic fluid, and washed with deionized water to PH=9 after crystallizing and cooling, and finally dried to obtain MFI membrane. For its SEM photograph, please refer to FIGS. 4(a) and 4(b).

Embodiment 8

(27) The property of the three-channel TiO.sub.2 hollow fiber support, the preparation of crystal seed solution and the crystal seed coating are the same as that in Embodiment 7; a synthetic fluid of MFI zeolite membrane is prepared according to the tetrapropyl ammonium hydroxide:tetraethyl orthosilicate: 1:5.2:1200 (mole ratio); the synthesis of the MFI zeolite membrane is the same as that in Embodiment 7.

Comparative Example 1

(28) The literature Journal of the American Chemical Society (2009, 131(20): 6910-6911) reported that the research group of Professor Wang Zhengbao of Zhejiang University adopts the combined method as dip coating-wipe coating of crystal seed coating to prepare NaA zeolite membrane on the single-channel aluminum oxide hollow fiber with a porosity factor of 50%; when separating 90 wt. % ethanol/water mixture at 75 C., the flux is 9.0 kg.Math.m.sup.2.Math.h.sup.1. In Embodiment 1 of the Invention, the permeation water flux of the NaA zeolite membrane prepared on the four-channel aluminum oxide hollow fiber with a porosity factor of 54% is up to 12.8 kg.Math.m.sup.2.Math.h.sup.1. It is thus clear that the permeation property of the NaA zeolite membrane prepared on the four-channel hollow fiber support is higher than that of the single-channel hollow fiber support.

Comparative Example 2

(29) Patent CN200910193335.9 reported the method for synthesizing the NaA zeolite membrane on -Al.sub.2O.sub.3 hollow fiber surface invented by Yuan Wenhui et al. However, when separating 90 wt. % ethanol/water at 60 C., the permeation flux of the single-channel aluminum oxide hollow fiber NaA zeolite membrane prepared by them is only 1.950.35 kg.Math.m.sup.2.Math.h.sup.1, while the permeation water of the four-channel aluminum oxide hollow fiber NaA zeolite membrane in Embodiment 2 of the Invention tested under the same condition is 6.2 kg.Math.m.sup.2.Math.h.sup.1 (refer to FIG. 5), which is 2-3 times of the former.

Comparative Example 3

(30) The literature Membrane Science and Technology (2011, 31(2):19-22) reported the NaA zeolite membrane prepared on the optimized single-channel aluminum oxide hollow fiber by us; the flux of which is up to 7.37 kg.Math.m.sup.2.Math.h.sup.1; the bending strength of the selected support is 142.7 Mpa and the breakage load of the four-channel hollow fiber with a span length of 4 cm is 6N in the three-point bending strength test. The breakage load of the four-channel aluminum oxide hollow fiber with a span length of 4 cm selected in Embodiment 3 of the Invention is 18N, which is 3 times of the former.