Polyurethane/polyvinylidene fluoride composite membrane for extracting organic sulfide from naphtha and preparation method therefor

Abstract

The present invention relates to the field of composite membrane and discloses a polyurethane/polyvinylidene fluoride composite membrane for extracting organic sulfide from naphtha. The polyurethane/polyvinylidene fluoride composite membrane includes an active layer and a support layer where the active layer is a polyurethane casting membrane and the support layer is a polyvinylidene fluoride membrane. The polyurethane/polyvinylidene fluoride composite membrane is prepared by coating the active layer onto the support layer. At the same time, a preparation method for the polyurethane/polyvinylidene fluoride composite membrane is disclosed. The present invention has the following beneficial effects: the polyurethane/polyvinylidene fluoride composite membrane prepared in the present invention may be used to extract organic sulfide in naphtha with high separation efficiency. Further, the composite membrane almost does not change the octane number and the like of the raw material oil, thereby improving the extraction rate of the organic sulfide.

Claims

1. A preparation method for a polyurethane/polyvinylidene fluoride composite membrane, comprising an active layer and a support layer, wherein the active layer is a polyurethane casting membrane, the support layer is a polyvinylidene fluoride membrane, and the polyurethane/polyvinylidene fluoride composite membrane is prepared by coating the active layer onto the support layer, and the active layer has a thickness of 20-30 μm and the support layer has a thickness of 110-120 μm, the preparation method comprising the following steps: (1) preparation of the support layer by a. adding polyvinylidene fluoride, polyethylene glycol, and N-Methyl pyrrolidone into a round-bottom flask at a first mass ratio, placing the round-bottom flask in a thermostatic water bath of 50-60° C. and holding for 12-24 hours until the added polyvinylidene fluoride, polyethylene glycol, and N-Methyl pyrrolidone are completely dissolved, and then performing filtration, degassing, film wiping and drying in sequence; b. placing the wiped film into de-ionized water and holding for 48-72 hours to remove N-Methyl pyrrolidone, and then placing into an air-blowing drying oven for drying with a temperature controlled to 50-60° C. to obtain the polyvinylidene fluoride membrane as the support layer; the first mass ratio of polyvinylidene fluoride, polyethylene glycol, and N-Methyl pyrrolidone is 1:0.1-0.2:5-8; a thickness of a knife is 100-200 μm when film wiping is performed on a non-woven fabric; (2) preparation of coating solution of the active layer by a. adding polyurethane, polyethylene glycol, and tetrahydrofuran into a round-bottom flask at a second mass ratio and waiting until the added polyurethane, polyethylene glycol, and tetrahydrofuran are completely dissolved so as to form a homogeneous casting solution; b. performing filtration for the homogeneous casting solution obtained at step a by using a stainless steel strainer with 300 meshes; c. standing the casting solution filtered at step b for 2-5 hours to remove bubbles so as to obtain the polyurethane casting solution as the active layer; (3) preparation of the composite membrane by a. coating, by the knife, the casting solution de-bubbled at step (2) onto the polyvinylidene fluoride membrane obtained at step (1), and then placing the polyvinylidene fluoride membrane into the air-blowing drying oven to remove tetrahydrofuran in the active layer so as to obtain the polyurethane/polyvinylidene fluoride composite membrane; at step (2), the second mass ratio of polyurethane, tetrahydrofuran and polyethylene glycol is 2:0.1-0.2:12, wherein an average molecular weight of polyethylene glycol at steps (2) is 200; at step (3), the thickness of the knife is 200-300 μm during film wiping, and the temperature of the air-blowing drying oven is controlled to 40-50° C. during drying.

2. The preparation method for the polyurethane/polyvinylidene fluoride composite membrane according to claim 1, wherein an average molecular weight of polyethylene glycol at step (1) is 200.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) The technical scheme of the embodiments of the present invention is described clearly and fully below. It is apparent that the embodiments described herein are merely some of the embodiments of the present invention rather than all the embodiments. All other embodiments obtained by those skilled in the art without paying creative work shall all fall within the scope of protection f the present invention.

Embodiment 1

(2) 1. 45.883 g of polyvinylidene fluoride, 7.058 g of polyethylene glycol and 300 g of N-Methyl pyrrolidone of which a mass ratio was 1:0.15:6.54 were added into a round-bottom flask and stirred for 12 h in a water bath of 50° C. until complete dissolution, and then filtration and de-bubbling were performed, a knife thickness of a film wiping machine was adjusted to 100 μm to perform film wiping on a non-woven fabric, the wiped film was then immersed into de-ionized water for 72 h, and then placed into a drying oven of 60° C. for drying so as to obtain a polyvinylidene fluoride membrane of 110-120 μm, i.e. a support layer.

(3) 2. 2 g of polyurethane, 0.1 g of polyethylene glycol and 12 g of tetrahydrofuran of which a mass ratio was 2:0.1:12 were added into a conical flask and dissolved at room temperature to obtain a casting solution;

(4) the prepared casting solution was filtered by a copper screen with 300 meshes and then stood for 2 h to remove bubbles so as to obtain a polyurethane casting solution as an active layer.

(5) 3. The knife thickness was adjusted to 300 μm, the casting solution obtained at step 2 was coated onto the polyvinylidene fluoride support layer obtained at step 1, and the obtained membrane was placed into an air-blowing drying oven of 40° C. to remove tetrahydrofuran so as to obtain a polyurethane/polyvinylidene fluoride composite membrane.

Embodiment 2

(6) 1, 50.285 g of polyvinylidene fluoride, 5.145 g of polyethylene glycol and 300 g of N-Methyl pyrrolidone of which a mass ratio was 1:0.1:5.97 were added into a round-bottom flask and stirred for 12 h in a water bath of 50° C. until complete dissolution, and then filtration and de-bubbling were performed, a knife thickness of a film wiping machine was adjusted to 100 μm to perform film wiping on a non-woven fabric, the wiped film was then immersed into de-ionized water for 72 h, and then placed into a drying oven of 60° C. for drying so as to obtain a polyvinylidene fluoride membrane of 110-120 μm, i.e. a support layer.

(7) 2. 2 g of polyurethane, 0.15 g of polyethylene glycol and 12 g of tetrahydrofuran of which a mass ratio was 2:0.15:12 were added into a conical flask and dissolved at room temperature to obtain a casting solution;

(8) the prepared casting solution was filtered by a copper screen with 300 meshes and then stood for 2 h to remove bubbles so as to obtain a polyurethane casting solution as an active layer.

(9) 3. The knife thickness was adjusted to 250 μm, the casting solution obtained at step 2 was coated onto the polyvinylidene fluoride support layer obtained at step 1, and the obtained membrane was placed into an air-blowing drying oven of 40° C. to remove tetrahydrofuran so as to obtain a polyurethane/polyvinylidene fluoride composite membrane.

Embodiment 3

(10) 1. 47.241 g of polyvinylidene fluoride, 9.365 g of polyethylene glycol and 350 g of N-Methyl pyrrolidone of which a mass ratio was 1:0.2:7.41 were added into a round-bottom flask and stirred for 12 h in a water bath of 50° C. until complete dissolution, and then filtration and de-bubbling were performed, a knife thickness of a film wiping machine was adjusted to 100 μm to perform film wiping on a non-woven fabric, the wiped film was then immersed into de-ionized water for 72 h, and then placed into a drying oven of 60° C. for drying so as to obtain a polyvinylidene fluoride membrane of 110-120 μm, i.e. a support layer.

(11) 2. 2 g of polyurethane, 0.2 g of polyethylene glycol and 12 g of tetrahydrofuran of which a mass ratio was 2:0.2:12 were added into a conical flask and dissolved at room temperature to obtain a casting solution;

(12) the prepared casting solution was filtered by a copper screen with 300 meshes and then stood for 2 h to remove bubbles so as to obtain a polyurethane casting solution as an active layer.

(13) 3. The knife thickness was adjusted to 200 μm, the casting solution obtained at step 2 was coated onto the polyvinylidene fluoride support layer obtained at step 1, and the obtained membrane was placed into an air-blowing drying oven of 40° C. to remove tetrahydrofuran so as to obtain a polyurethane/polyvinylidene fluoride composite membrane.

(14) 1. Naphtha was Treated with the Polyurethane/Polyvinylidene Fluoride composite Membrane

(15) The polyurethane/polyvinylidene fluoride composite membranes prepared in the embodiments 1, 2 and 3 were used to perform an extraction test for organic sulfide in naphtha. The data of permeation flux and sulfur content in enriched liquid were obtained by treating different sulfur contents in naphtha using the three polyurethane/polyvinylidene fluoride composite membranes. The specific test results were shown in Table 1.

(16) TABLE-US-00001 TABLE 1 Sulfur content Feed Permeation Sulfur content in in naphtha flowrate flux enriched liquid Embodiment mg/L mL/min kg .Math. m.sup.−2 .Math. h.sup.−1 mg/L Embodiment 1 1300 90 1.25 4000 2300 90 1.27 6000 6200 90 1.00 18000 Embodiment 2 1300 100 1.29 3900 2300 100 1.36 6000 6200 100 1.25 18000 Embodiment 3 1300 110 1.32 4000 2300 110 1.34 5500 6200 110 1.30 17500

(17) The results show that under the test conditions, the permeation fluxes of the composite membranes prepared in the three embodiments can all reach 1-2 kg.Math.m.sup.−2.Math.h.sup.−1 or higher and the sulfur enrichment factors (sulfur content in enriched liquid/sulfur content in naphtha) are all around 3.00. Therefore, the membranes have good extraction effect on sulfide.

(18) 2. Life of the Polyurethane/Polyvinylidene Fluoride Composite Membrane

(19) Further, life test was performed for the polyurethane/polyvinylidene fluoride composite membranes prepared in the embodiments 1, 2 and 3. With the sulfur content in naphtha being 1300 mg/L and the feed flow rate being 90 mL/min, the test was run continuously for 100 h and then the test data obtained were shown in Table 2 below.

(20) TABLE-US-00002 TABLE 2 Permeation Sulfur Mean flux Mean flux enrichment enrichment Embodiment kg .Math. m.sup.−2 .Math. h.sup.−1 kg .Math. m.sup.−2 .Math. h.sup.−1 factor factor Embodiment 1 ≥1.00 1.03 ≥3.00 3.29 Embodiment 2 ≥1.00 1.12 ≥3.00 3.13 Embodiment 3 ≥1.00 1.15 ≥3.00 3.04

(21) The test results show that under the test conditions, the permeation fluxes are all at or above 1.00 kg.Math.m.sup.−2.Math.h.sup.−1, and the sulfur enrichment factors are all maintained at or above 3.00.

(22) In the present invention, a spacing of molecular chains of polyurethane can be increased by adding polyethylene glycol to polyurethane. Polyethylene glycol also has good affinity to organic sulfide. Fewer sulfur enrichment factors will be lost while the permeation flux is increased. Thus, a trade-off effect of the permeation flux and the enrichment factor that is encountered frequently at the time of modification of the pervaporation membrane can be avoided, thereby significantly improving the extraction rate of the sulfur-containing organic compound from naphtha.

(23) Of course, the foregoing descriptions are not limiting of the present invention and the present invention is not limited to the above embodiments. Any change, modification, addition or substitution made by those skilled in the art within the essence scope of the present invention shall all fall within the scope of protection of the present invention.