Anti-coking nanomaterial based on stainless steel surface, and preparation method therefor

Abstract

An anti-coking nanomaterial based on a stainless steel surface. In percentage by weight, the nanomaterial comprises: 0 to 3% of carbon, 23% to 38% of oxygen, 38% to 53% of chromium, 10% to 35% of ferrum, 0 to 2% of molybdenum, 0 to 4% of nickel, 3.5 to 5% of silicon, 0 to 1% of calcium, and the balance of impurity elements. Also disclosed are a preparation method for the anti-coking nanomaterial, the anti-coking nanomaterial that is based on a stainless steel surface and that is prepared by using the preparation method, and a stainless steel substrate comprising the anti-coking nanocrystalline material.

Claims

1. A method for preparing an anti-coking nanocrystalline material characterized in that the method comprises the following steps: (1) chemically degreasing and etching with alkali a stainless steel surface using a sodium hydroxide solution and a solution containing an alkali etching additive, followed by washing with water; (2) oxidizing the stainless steel surface treated in the step (1) by an oxidizing solution, followed by washing with water; (3) immersing the stainless steel surface treated in the step (2) as a cathode in an electrolyte to electrolyze, followed by washing with water; and (4) placing the stainless steel surface treated in the step (3) at a temperature of 50-60° C. and a humidity of 60-70%, and then placing at a temperature of 35-40° C. and a humidity of 40-50% for hardening.

2. The method according to claim 1, characterized in that, in the step (1), a temperature of the sodium hydroxide solution and the solution containing the alkali etching additive is 80-85° C.; a concentration of the sodium hydroxide solution is 6.5-8 wt. %; a concentration of the solution containing the alkali etching additive is 0.3-0.5 wt. %; the alkali etching additive is an alkali etching additive to chemically etch with alkali; the chemically degreasing and etching with alkali is carried out for 10-15 minutes; and the washing with water is performed by using water with a temperature of 80-85° C., and a time for the washing is 3-5 minutes.

3. The method according to claim 1, characterized in that, in the step (2), preferably, the oxidizing solution contains 200-300 g/L of CrO.sub.3; a temperature of the oxidizing solution is 75-90° C.; a pH of the oxidizing solution is adjusted to 0.4-1.5 by adding a H.sub.2SO.sub.4 solution into the oxidizing solution; a concentration of the H.sub.2SO.sub.4 solution is 98 wt. %; a time for oxidizing is 15-35 minutes; and the washing with water after oxidizing in the step (2) is performed cyclically by using water at 25-40° C. for 3-5 minutes; and a pH of the water is >3.

4. The method according to claim 1, characterized in that, in the step (3), the electrolyte contains 100-150 g/L of CrO.sub.3, 80-100 g/L of Na.sub.2SiO.sub.3, 15-20 g/L of nano silicon nitride, and 3-5 g/L of nano silicon carbide; a temperature of the electrolyte is 40-52° C.; a pH of the electrolyte is adjusted to 0.5-1.5 by adding a H.sub.2SO.sub.4 solution into the electrolyte; and a concentration of the H.sub.2SO.sub.4 solution is 98 wt. %; a current for electrolyzing is carried out in the following manner: an initial current intensity is 40-42 A/m.sup.2, and then the current intensity is gradually reduced to 4_A/m.sup.2 according to a formula i=3+30/t, wherein i is current intensity in A/m.sup.2 and t is time in minutes; a time for electrolyzing is 25-55 minutes; and the washing with water is performed cyclically by using water at 25-40° C. for 3-5 minutes; and a pH of the water is >3.

5. The method according to claim 1, characterized in that, in the step (4), the placing of the stainless steel surface treated in the step (3) at a temperature of 50-60° C. and a humidity of 60-70% is performed for 3-3.5 hours; and the placing at a temperature of 35-40° C. and a humidity of 40-50% for hardening is performed for 48-72 hours.

6. The method according to claim 4, characterized in that, the electrolyzing is carried out for 10-25 minutes at an initial current intensity of 40-42 A/m.sup.2, and then electrolyzing at a current intensity gradually reduced to 4 A/m.sup.2 according to the formula i=3+30/t during 14-18 minutes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, in which:

(2) FIG. 1 is an element distribution diagram of surface of an anti-coking nanomaterial based on a 304 substrate;

(3) FIG. 2 is an element SEM crystal diagram of surface of an anti-coking nanomaterial based on a 304 substrate;

(4) FIG. 3 is a trend chart of material composition layer of the nanocrystalline material according to the present invention analyzed by X-ray photoelectron spectroscopy;

(5) FIG. 4 shows the thickness of the coke layer when a 316L stainless steel substrate packing sheet is placed at minus three lines of a vacuum tower for 3 years and 5 months;

(6) FIG. 5 shows the thickness of the coke layer when a 316L stainless steel substrate packing sheet treated by the nanocrystalline material according to the present invention is placed at minus three lines of a vacuum tower for 3 years and 5 months;

(7) FIG. 6 shows the thickness of the coke layer when a 317L stainless steel substrate packing sheet is placed in the washing section of a vacuum tower for 3 years and 5 months;

(8) FIG. 7 shows the thickness of the coke layer when a 317L stainless steel substrate packing sheet treated by the nanocrystalline material according to the present invention is placed in the washing section of a vacuum tower for 3 years and 5 months;

(9) FIG. 8 is a current-time profile according to the formula i=40-2.33t (wherein, i is current intensity, t is dense duration time (min)) after electrolyzing for 15 min;

(10) FIG. 9 is a current-time profile after electrolyzing for 15 min, wherein at 0-5 min, the current is 40 A/m.sup.2; at 5-10 min, the current is 20 A/m.sup.2; at 10-15 min, the current is 15 A/m.sup.2;

(11) FIG. 10 is a current-time profile according to the formula i=30+30/t (wherein, i is current intensity, t is dense duration time (min)) after electrolyzing for 15 min.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(12) Further described the present invention in detail in conjunction with specific embodiments below, the examples are given only for illustrating the present invention and are not intended to limit the scope of the invention.

(13) The experimental methods in the following examples are conventional methods unless otherwise specified. The raw materials, reagent materials, etc., in the following examples are commercially available products unless otherwise specified.

Example 1 Diesel Cracking Coking Test

(14) A cracking furnace tube, which used the anti-coking nanomaterial based on a 317L stainless steel substrate according to the present invention (diesel was used (the distillation range was 186-316.2° C.)) and a untreated cracking furnace tube, which used an ordinary 317L stainless steel substrate, were tested by a Chinese Sinopec Research Institute, the result was shown as Table 5.

(15) TABLE-US-00005 TABLE 5 Parameters for cracking and scorching during the testing process Furnace types Laboratory Test Device Across-over temperature 560° C. Cracking temperature 790° C. Residence time 0.33 S Water/oil ratio (weight) 1 Export pressure MPa (Pressure gauge) normal Feeding amount 150 g/h Cracking time 2 h Scorching temperature 790° C.

(16) After being tested, the coking amount on the surface of the untreated cracking furnace tube, which used the ordinary 317L stainless steel substrate, was 1.5464 g, the coking amount on the surface of the first cracking furnace tube, which uses the anti-coking nanomaterial based on the 317L stainless steel substrate according to the present invention, was 1.0487 g, the coking amount relatively reduced by 32%, the coking amount on the surface of the second cracking furnace tube, which used the anti-coking nanomaterial based on the 317L stainless steel substrate according to the present invention, was 1.0049 g, the coking amount relatively reduced by 35° %, this results show that the anti-coking nanomaterial according to the present invention has obvious anti-coking effect.

Example 2: Anti-Coking Test in Packed Vacuum Tower

(17) A branch company of China Petroleum & Chemical Corporation designed high-sulfur and high-acid crude oil as the crude oil in an atmospheric and vacuum distillation device of a crude oil deterioration reconstruction project. (1) An untreated packing sheet based on a 316L stainless steel substrate and a packing sheet using the anti-coking nanomaterial based on a 316L stainless steel substrate according to the present invention as the surface layer were placed at the bottom of the third section of a packed vacuum tower. Specific temperature was shown as Table 6:

(18) TABLE-US-00006 TABLE 6 Temperature of packing sheets to be tested Minus three lines Sulfur Acid Carbon residue temperature(° C.) content value content 213~331.2 0.77 m % 1.06 2.26%

(19) After being operated for 3 years and 5 months, the above-mentioned packing sheets were subjected to metallographic preparation to observe the thickness of the coking layer. The result was shown as follows:

(20) The thickness of the coking layer of the untreated packing sheet based on the ordinary 316L stainless steel substrate was shown in FIG. 5, the thickness of the coking layer of the packing sheet using the anti-coking nanomaterial based on the 316L stainless steel substrate according to the present invention was shown in FIG. 6. When comparing the two packing sheets, it can be seen that the thickness of the coking layer in FIG. 5 was 6.39 μm, while the thickness of the coking layer in FIG. 6 (the packing sheet using the anti-coking nanomaterial based on the 316L stainless steel substrate according to the present invention as the nano surface layer) was 2.55 μm, the coking amount relatively reduced by 60.1%. (2) An untreated packing sheet based on a 317L stainless steel substrate and a packing sheet using the anti-coking nanomaterial based on a 317L stainless steel substrate according to the present invention as the surface layer were placed at the bottom of the fourth section of a packed vacuum tower. Specific temperature was shown as Table 7:

(21) TABLE-US-00007 TABLE 7 Temperature of packing sheets to be tested Minus four lines Sulfur Acid Carbon residue temperature(° C.) content value content 329-388 0.77 m % 1.06 11.4%

(22) After being operated for 3 years and 5 months, the above-mentioned packing sheets were subjected to metallographic preparation to observe the thickness of the coking layer. The result was shown as follows:

(23) The thickness of the coking layer of the untreated packing sheet based on the ordinary 317L stainless steel substrate was shown in FIG. 7, the thickness of the coking layer of the packing sheet using the anti-coking nanomaterial based on the 317L stainless steel substrate according to the present invention was shown in FIG. 8. When comparing the two packing sheets, it can be seen that the thickness of the coking layer in FIG. 7 was 12.22 μm, while the thickness of the coking layer in FIG. 8 (the packing sheet using the anti-coking nanomaterial based on the 317L stainless steel substrate according to the present invention as the nano surface layer) was 5.61 μm, the coking amount relatively reduced by 54.1%.

Example 3: Silicon Content Test of the Anti-Coking Nanomaterial of the Present Invention

(24) The inventors have found that the content of silicon has a decisive influence on the anti-coking effect of the stainless steel surface, the more the content of silicon on the stainless steel surface was, the better the anti-coking effect was. The silicon content was determined by controlling the concentration of Na.sub.2SiO.sub.3 and nano silicon nitride. The 304 stainless steel substrate material was taken as an example, the results were shown in Tables 7 and 8.

(25) TABLE-US-00008 TABLE 7 Silicon content of the anti-coking nanomaterial Concentration Na.sub.2SiO.sub.3g/L 0 20 40 60 80 100 120 130 150 Maximum Si content 0.31 1.18 1.45 2.22 2.87 2.93 2.53 2.50 2.42

(26) It can be seen from Table 7 that the content of silicon in the anti-coking nanomaterial was relatively high when the concentration of Na.sub.2SiO.sub.3 was 80-100 g/L.

(27) TABLE-US-00009 TABLE 8 Silicon content of the anti-coking nanomaterial Concentration Nano silicon nitride g/L 0 5 10 15 20 25 30 40 Maximum Si content 2.91 3.52 4.07 4.55 4.88 5.06 5.18 5.22

(28) It can be seen from Table 8, nano silicon nitride has certain influence on the silicon content of the anti-coking nanomaterial, however, too much silicon nitride will increase the roughness of the anti-coking nanomaterial, decrease the adhesion of the anti-coking nanomaterial layer in fluid environments, and this will be unfavorable for anti-coking property. Therefore, the best range of the silicon nitride of the present invention is 15-20 g/L.

Example 4: Electrolyzing Test

(29) The inventors have found that the change in current during electrolysis has a large influence on the smoothness of the anti-coking nanomaterial surface. Therefore, the inventors determined the change of the friction coefficient based on the change of the current intensity. The less the friction coefficient was, the better the anti-coking effect was, thus, the surface will be not easy to adhere dirt.

(30) As shown in FIGS. 9-11, X axis is time (min), Y axis is current intensity (A/m.sup.2);

(31) Scheme 1: In FIG. 9, the current intensity i=40-2.33t (i is current intensity, t is duration time);

(32) Scheme 2: In FIG. 10, the current intensity was 40 A/m.sup.2, which was kept for 0-5 min; the current intensity was 20 A/m.sup.2, which was kept for 5-10 min; the current intensity was 5 A/m.sup.2, which was kept for 10-15 min.

(33) Scheme 3 (the current was controlled according to the method of the present invention): In FIG. 11, the current intensity i=3-30/t (i is current intensity, t is duration time);

(34) The result was shown in Table 9:

(35) TABLE-US-00010 TABLE 9 friction coefficients of the anti-coking nanomaterial based on a 304 stainless steel substrate: Schemes Friction coefficient μ Scheme 1 0.095 Scheme 2 0.103 Scheme 3 0.086

(36) Conclusion: Different ways of changing the current lead to different atomic packing factor of stainless steel nano surfaces. It can be seen from this table, the less the friction coefficient μ was, the higher the atomic packing factor on the nanocrystalline surface was, the smoother the nano-surface film layer was, this will result in good adhesion effect of the scaling layer.

Example 5: Preparation of the Nanocrystalline Material Based on a Stainless Steel Surface (304 Substrate) According to the Present Invention

(37) (1) Sodium hydroxide solution with a concentration of 7% and a solution containing 0.5% of HDW-1050 alkali etching additive was used to chemically degrease and etch with alkali a stainless steel surface (a 304 substrate). The total amount of the entire solution was adequate to fully immerse the stainless steel surface. The temperature of the above solution was controlled at 80° C. The operation was performed for 15 min. After that, water with a temperature of 80° C. was used for washing for 3 min. (2) The composition of the used oxidizing solution contained 300 g/L of CrO.sub.3. At 78° C., H.sub.2SO.sub.4 solution with a concentration of 98% was used to adjust the pH value to 1.3, the time for oxidizing was 15 min, after that, water under normal temperature was used for washing for 3 min. (3) The composition of the used electrolytic solution contained 100 g/L of CrO.sub.3, 100 g/L of Na.sub.2SiO.sub.3, 18 g/L of nano silicon nitride, 3 g/L of nano silicon carbide. H.sub.2SO.sub.4 solution with a concentration of 98% was used to adjust the pH value to 1.3. The temperature was controlled at 40° C. The stainless steel piece (304 substrate) was used as cathode, on the basis of the surface area of the stainless steel, the electrolysis was performed for 10 min with a current intensity of 40 A/m.sup.2 firstly, and then for 15 min with a current intensity, which gradually reduced according to the formula i=3+30/t (i is current intensity, A/m.sup.2, t is duration time, min). After that, the electrolyte on the surface of the stainless steel piece was washed at room temperature. (4) The stainless steel piece (304 substrate) was placed in an environment with a temperature of 55° C. and a humidity of 60% to harden for 3 hours. After that, the film layer was placed at a temperature of 38° C. and a humidity of 45% to harden for 72 hours. Thus, an anti-coking nanomaterial based on the stainless steel surface (304 substrate) was obtained.

(38) The testing results of the anti-coking nanomaterial based on 304 stainless steel of the present invention were as follows: the nanocrystalline material contained 0.71/of carbon, 34.62% of oxygen, 42.81% of chromium, 13.11% of iron, 3.1% of nickel, 4.73% of silicon, 0.92% of calcium, and with the balance being remaining amount of impurity elements.