METHOD OF FORMING A COATING

Abstract

A method comprises the following steps: a) Providing a body having an internal surface which defines an internal pathway within the body, the body having an inlet and an outlet both communicating with the internal pathway; b) Introducing a liquid solution into the internal pathway so as to fill at least a portion of the internal pathway with the liquid solution, the liquid solution comprising a solute capable of undergoing thermal decomposition; c) Heating the liquid solution while the liquid solution fills said at least a portion of the internal pathway to a sufficient temperature so that the solute undergoes thermal decomposition to form a decomposition product within said at least a portion of the internal pathway.

The heating step forms a coating comprising the decomposition product on at least a part of the internal surface that borders the internal pathway.

Claims

1. A method of forming a coating within an internal pathway, comprising: providing a body having an internal surface which defines an internal pathway within the body, the body having an inlet and an outlet both communicating with the internal pathway for passage of a fluid successively into the inlet then through the internal pathway and then out of the outlet; introducing a liquid solution into the internal pathway so as to fill at least a portion of the internal pathway with the liquid solution, the liquid solution comprising a solute capable of undergoing thermal decomposition, wherein said at least a portion of the internal pathway forms at least 50% of the length of the internal pathway; heating the liquid solution while the liquid solution fills said at least a portion of the internal pathway to a sufficient temperature so that the solute undergoes thermal decomposition to form a decomposition product within said at least a portion of the internal pathway; the heating forming a coating comprising the decomposition product on at least a part of the internal surface wherein said at least a part of the internal surface borders the internal pathway.

2. The method according to claim 1, wherein the internal pathway is a channel which has first and second openings at the inlet and outlet respectively and which is fully enclosed by the internal surface between the first and second openings.

3-8. (canceled)

9. The method according to claim 1, wherein the internal pathway is elongate having a length extending between the inlet and the outlet, wherein said at least a portion of the internal pathway that is filled with the liquid solution is filled with an elongate body of the liquid solution, the elongate body of liquid solution having first and second ends, wherein said heating is performed while one of the inlet and the outlet is closed and the other one of the inlet and the outlet is open, the first end of the elongate body of the liquid solution lying closer than the second end to the open one of the inlet and outlet along the length of the internal pathway and the second end of the elongate body of the liquid solution lying closer than the first end to the closed one of the inlet and outlet along the length of the internal pathway, wherein said heating comprises applying heat progressively to successive regions of the elongate body of the liquid solution starting at the first end of the elongate body of the liquid solution and moving towards the second end of the elongate body of the liquid solution, whereby to reduce or prevent expulsion of liquid solution from the liquid pathway.

10. The method according to claim 9, wherein the body is a tube with the inlet at one end of the tube and the outlet at the other end of the tube, wherein said heat is applied by a heat source, and wherein the tube and the heat source are moved relative to one another to cause said progressive application of heat.

11. The method according to claim 10, wherein the heat source is annular and extends around the circumference of the tube and said heat is applied simultaneously all around the circumference of the tube.

12-14. (canceled)

15. A method of forming a coating within a porous body, comprising: providing a porous body having an internal surface which defines a plurality of interconnected internal spaces within the porous body; introducing a liquid solution into the internal spaces so as to fill the internal spaces with the liquid solution, the liquid solution comprising a solute capable of undergoing thermal decomposition; heating the liquid solution while the liquid solution fills the internal spaces to a sufficient temperature so that the solute undergoes thermal decomposition to form a decomposition product within the internal spaces; the heating forming a coating comprising the decomposition product on at least a part of the internal surface.

16. The method according to any preceding claim 1, wherein the decomposition product is a porous solid.

17-20. (canceled)

21. The method according to claim 16, wherein the coating comprises the porous solid decomposition product and a catalyst supported by the porous solid decomposition product, wherein the catalyst comprises metal particles, the metal particles being entrapped within the porous solid decomposition product.

22. The method according to claim 1 wherein the solute comprises a metallic cation, and wherein the decomposition product is a metal oxide.

23. The method according to claim 22, wherein the metallic cation is selected from the group consisting of: titanium, zinc, aluminium, magnesium, calcium, scandium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, gallium, germanium, strontium, yttrium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, tellurium, barium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, thallium, lead, bismuth, zirconium, and lanthanum or actinium group metals.

24. (canceled)

25. The method according to claim 22, wherein the solute comprises an anion or a ligand, and wherein the anion or the ligand is selected from the group consisting of: nitrate, acetate, acetyl acetonate, nitrite, chloride, citrate, ammonia, carbonyl, cyclopentadienyl and its derivatives, and anions of organic acids including amino acids.

26-29. (canceled)

30. The method according to claim 22, wherein the liquid solution comprises a further solute comprising a further solute metallic cation, the further solute metallic cation being selected from the group consisting of: platinum, palladium, rhodium, osmium, iridium, ruthenium, copper, silver, cobalt, iron, nickel or gold, and wherein said method comprises converting the further solute to form metal particles.

31. (canceled)

32. The method according to claim 30, wherein after said conversion the metal particles are entrapped within the decomposition product of the said solute.

33-34. (canceled)

35. The method according to claim 1, wherein the solute comprises a metallic cation, wherein the metallic cation is selected from the group consisting of: platinum, palladium, rhodium, osmium, iridium, ruthenium, silver, rhenium, mercury or gold, and wherein said decomposition product is metal in non-compound form.

36-37. (canceled)

38. The method according to claims 16, wherein the coating consists substantially of said porous solid decomposition product, and wherein the method comprises the further step, performed subsequently to the formation of said coating, of providing metal particles within pores of said porous solid decomposition product.

39-41. (canceled)

42. The method according to claim 15, wherein the decomposition product is a porous solid.

43. The method according to claim 42, wherein the coating comprises the porous solid decomposition product and a catalyst supported by the porous solid decomposition product, wherein the catalyst comprises metal particles, the metal particles being entrapped within the porous solid decomposition product.

44. The method according to claim 15, wherein the solute comprises a metallic cation, and wherein the decomposition product is a metal oxide.

45. The method according to claim 44, wherein the liquid solution comprises a further solute comprising a further solute metallic cation, the further solute metallic cation being selected from the group consisting of: platinum, palladium, rhodium, osmium, iridium, ruthenium, copper, silver, cobalt, iron, nickel or gold, and wherein said method comprises converting the further solute to form metal particles.

46. The method according to claim 45, wherein after said conversion the metal particles are entrapped within the decomposition product of the said solute.

Description

[0052] The following is a more detailed description of embodiments of the invention, by way of example, with reference to the appended drawings, in which:

[0053] FIG. 1 is a schematic representation of a heating apparatus for applying heat progressively along a capillary tube;

[0054] FIG. 2 is a cross-sectional scanning electron microscope image showing a porous coating on an internal surface of a capillary tube;

[0055] FIG. 3 is a graphical representation of a coating thickness distribution along the axis of the capillary tube shown in FIG. 2; and

[0056] FIG. 4 is a graphical representation of a pore diameter distribution of the porous coating shown in FIG. 2.

[0057] Referring to FIG. 1, the heating apparatus comprises an annular heating element 10, a stepper motor 11, and a pair or rollers 12, 13. The rollers 12, 13 are mounted on the stepper motor 11 and spaced from one another so that a capillary tube 14 can be placed between the rollers 12, 13 and gripped by the rollers 12, 13. The rollers 12, 13 are driven by the stepper motor 11 so that the rollers 12, 13 can displace the capillary tube 14, when so gripped, in an upward direction as shown in FIG. 1.

[0058] The annular heating element 10 has an internal opening 15 having a diameter large enough to receive the capillary tube 14 so that the heating element 10 lies close to the external surface of the capillary tube 14. The rollers 12, 13 and the heating element 10 are positioned so that the capillary tube 14 is received in the opening 15 of the heating element 10 while the capillary tube is gripped by the rollers 12, 13. As shown in FIG. 1, the heating element 10 extends around the external circumference of the capillary tube 14. The heating element 10 is capable of applying heat to the capillary tube 14 all around the circumference of the capillary tube 14.

EXAMPLE 1

[0059] The following is an example of the use of the method to form a coating on the internal surface of a capillary tube. The heating apparatus shown in FIG. 1 is used to perform the heating step of the method.

[0060] A fused silica capillary tube (10 m long, 0.53 mm i.d.) was filled with a liquid solution of zinc (II) nitrate hexahydrate (6.0 g, Sigma-Aldrich, 98%), palladium (II) acetate (0.130 g, Sigma-Aldrich, 98%), Pluronic F127 (0.4 g, Sigma-Aldrich) in methanol (15 mL, Fischer Scientific, 99.9%).

[0061] The capillary tube 14 was then closed at one end with a shut off valve (not shown) and the other end was left open. The capillary tube 14 was placed between the rollers 12, 13 of the heating apparatus shown in FIG. 1 with the open end of the capillary tube 14 located upwards and with the open end lying within the internal opening 15 of the annular heating element 10. The temperature of the annular heating element was set to 300 C.

[0062] The capillary tube 14 was then moved upwardly through the internal opening 15 of the heating element 10 at a constant displacement speed of 3 mm s.sup.1. During this process, the volume of the liquid solution located within the annular heating element 10 at any point in time was heated and formed a coating on the internal surface of the capillary tube 14. The methanol solvent within the heated volume evaporated and was expelled as a gas from the open end of the tube. As the capillary tube was displaced upwardly, the application of heat moved along the capillary tube 14 progressively towards the lower closed end of the capillary tube 14 so that the formation of the coating and the evaporation of the methanol solvent also progressed towards the lower closed end of the capillary tube 14.

[0063] The capillary tube 14 was then washed with methanol (100 L min.sup.1 for 60 min) and dried at 110 C.

[0064] After the washing step, the capillary tube 14 had a continuous coating which covered the entire internal surface of the capillary tube 14. The mass of the coating obtained was 6.5 mg m.sup.1 and the palladium loading was 3.4% by mass as a percentage of the total mass of the coating. The coating consisted of zinc oxide formed by thermal composition from the zinc nitrate together with palladium particles formed by thermal decomposition from the palladium acetate.

[0065] FIG. 2 shows a representative scanning electron microscopy (SEM) cross-sectional image of the capillary tube 14 with the coating consisting of plate-like crystallites of ZnO. As determined by X-ray diffraction (results not shown), the coating comprised hexagonal zincite crystallites 254 nm in diameter. Transmission electron microscopy showed the palladium nanoparticles to be 3-5 nm in diameter

[0066] Studies on the axial distribution of the coating thickness (see FIG. 3) showed that the coating was uniform with an average thickness of 3.6 m and standard deviation of 2.4 m. The maximum coating thickness observed was less than 10 m, so no narrow places in the capillary tube 14 were present where high pressure drop and pore diffusion limitations might otherwise have been expected. These data agree with very low pressure drop (of 0.2 bar) in the system when the coated capillary tube was used for a hydrogenation reaction as described below in Example 2.

[0067] Nitrogen physisorption studies (see FIG. 4) showed that the coating was mesoporous with an average BJH desorption pore diameter of 26 nm and BET specific surface area of 16 m.sup.2g.sup.1.

EXAMPLE 2

[0068] Solvent-free hydrogenation of 2-methyl-3-butyn-2-ol (MBY) was performed using the coated capillary tube 14 prepared in Example 1. Briefly, hydrogen and MBY from a mass-flow controller and a syringe pump, respectively, were combined in a T-joint and passed through the coated capillary tube 14 which was placed in a temperature-controlled water bath. The flow rate of hydrogen was constant, 19 mL min.sup.1 (STP), while the reaction temperature and the MBY flow rate were varied to optimise the 2-methyl-3-buten-2-ol (MBE) yield.

[0069] For every reaction temperature, MBE yield achieved a maximum at a certain MBY flow rate, where the product of MBY conversion and the MBE selectivity was the highest. At a lower MBY flow rate, the residence time increased leading to over-hydrogenation to 2-methyl-2-butanol (MBA); while at a higher MBY flow rate the decreased residence time lead to lower MBY conversion. The hydrogenation rate increased with temperature and resulted in the shift of the maximum MBE yield to higher flow rates. Regardless of the reaction temperature, the maximum MBE yield was above 95% and MBE selectivity was higher than 98% up to 90% MBY conversion. High selectivity of Pd/ZnO catalysts was caused by the in situ formation of an PdZn alloy resulting in the decreased adsorption of alkene species on the catalyst surface.

EXAMPLE 3

[0070] The following is an example of the use of the method to form a coating within a porous body.

[0071] First a porous body was prepared as follows. A stainless steel tube having an external diameter of 6.35 mm and an internal diameter of 4.2 mm was filled with porous cylinders formed from silicon carbide (SiC) foam. Each cylinder had an external diameter of slightly less that the internal diameter of the tube, so as to be a close fit within the tube, and a height of about 5 mm. In total, enough silicon carbide foam cylinders were used, end-to-end within the tube, to fill a 20 cm length of the stainless steel tube. In this way, a porous body comprising the stainless steel tube and the silicon carbide foam cylinders is formed. Each silicon carbide foam cylinder has an internal surface which forms a plurality of interconnecting internal spaces, and the interconnecting internal spaces form an internal pathway through the foam cylinder from one end the foam cylinder to the other end.

[0072] The porous body was then flushed by passing petroleum ether and acetone down the filled tube while subjecting the porous body to ultrasonic treatment. This flushing step serves to remove surface contaminants.

[0073] The tube was then filled with an aqueous solution of 5 wt% zinc nitrate hexahydrate and closed at one end with a valve. The aqueous solution filled the internal spaces of the silicon carbide foam cylinders.

[0074] The tube, filled with the zinc nitrate solution, was then displaced, open end first, at a rate of 0.1 mm/s, into a vertical tube furnace held at a temperature of 350 C. Once the tube had been introduced completely in the furnace it was left within the furnace for a further 30 minutes. The application of heat caused the zinc nitrate to undergo thermal decomposition to form a zinc oxide coating. The water was evaporated and expelled harmlessly from the open end of the tube as gas.

[0075] The porous body was then flushed with water to remove loosely bound material and dried at 120 C. in an oven for 2 hours.

[0076] After drying, the internal spaces of the silicon carbide foam cylinders were coated with zinc oxide. The mass of the coating obtained was 70 mg for the 20 cm length filled tube.