LAYERED DOUBLE HYDROXIDES
20190152794 ยท 2019-05-23
Assignee
Inventors
Cpc classification
C01P2002/77
CHEMISTRY; METALLURGY
C01G53/006
CHEMISTRY; METALLURGY
C01P2002/22
CHEMISTRY; METALLURGY
C01P2004/20
CHEMISTRY; METALLURGY
C01F7/784
CHEMISTRY; METALLURGY
C01P2002/72
CHEMISTRY; METALLURGY
C01G3/006
CHEMISTRY; METALLURGY
C01G9/006
CHEMISTRY; METALLURGY
International classification
Abstract
Layered double hydroxides (LDHs) are disclosed, as well as methods by which they may be manufactured. The LDHs are subjected to a solvent treatment step during manufacture, which confers high surface area and pore volume properties to the LDHs. The particular solvents used in the preparation of the LDHs renders allows for an overall more efficient and environmentally-friendly manufacturing process.
Claims
1. A process for preparing a layered-double hydroxide of formula (I) shown below:
[M.sup.z+.sub.1xM.sup.y+.sub.x(OH).sub.2].sup.a.sup.
[M.sup.z+.sub.1xM.sup.y+.sub.x(OH).sub.2].sup.a.sup.
2. The process of claim 1, further comprising a step d) of isolating the layered double hydroxide resulting from step c).
3. The process of claim 1, wherein the AIM-solvent is selected from the group consisting of m-cresol, o-cresol, p-cresol, n-butanol, sec-butanol, n-pentanol, n-hexanol, cyclohexanol, diethyl ether, diisopropyl ether, di-n-butyl ether, methyl tert-butyl ether (MTBE), tert-amyl methyl ether, cyclopentyl methyl ether, anisole, butyl carbitol acetate, cyclohexanone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methyl isoamyl ketone, methyl n-amyl ketone, isophorone, isobutyraldehyde, furfural, methyl formate, methyl acetate, isopropyl acetate, n-propyl acetate, isobutyl acetate, n-butyl acetate, n-amyl acetate, n-hexyl acetate, methyl amyl acetate, methoxypropyl acetate, 2-ethoxyethyl acetate, 2-butoxyethyl acetate, n-butyl propionate, n-pentyl propionate, triethylamine, 2-nitropropane, aniline, N,N-dimethylaniline, nitromethane, and a mixture of two or more thereof.
4. (canceled)
5. (canceled)
6. The process of claim 1, wherein when z is 2, M is Mg, Zn, Fe, Ca, Sn, Ni, Cu, Co, Mn or Cd or a mixture of two or more of these, or when z is 1, M is Li.
7. The process of claim 1, wherein when y is 3, M is Al, Ga, Y, In, Fe, Co, Ni, Mn, Cr, Ti, V, La or a mixture thereof, or when y is 4, M is Sn, Ti or Zr or a mixture thereof.
8. (canceled)
9. (canceled)
10. The process of claim 1, wherein X is an anion selected from at least one of halide, inorganic oxyanion, or an organic anion (e.g. an anionic surfactant, an anionic chromophore or an anionic UV absorber).
11. (canceled)
12. The process of claim 1, wherein in step a), the precipitate is formed by contacting aqueous solutions containing cations of the metals M and M, and the anion X.sup.n, in the presence of a base.
13. (canceled)
14. (canceled)
15. (canceled)
16. The process of claim 1, wherein after step a) and prior to step b), the water-washed, wet precipitate of formula (II) is washed with an AIM-solvent.
17. (canceled)
18. (canceled)
19. (canceled)
20. (canceled)
21. The process of claims 2, further comprising the step e) of contacting the isolated layered double hydroxide with an AIM-solvent, optionally wherein step e) comprises the steps of: i. dispersing the isolated layered double hydroxide in an AIM-solvent to form a slurry; ii. maintaining the slurry for a period of 0.5 to 72 hours; iii. isolating the layered double hydroxide resulting from step ii; and iv. optionally repeating steps i. to iii. a further 1-10 times (e.g., once or twice).
22. (canceled)
23. A layered double hydroxide of formula (I) obtainable, obtained or directly obtained by the process of any proceeding claim.
24. A layered double hydroxide of formula (I) shown below:
[M.sup.z+.sub.1xM.sup.y+.sub.x(OH).sub.2].sup.a.sup.
25. The layered double hydroxide of claim 24, wherein M is Al.
26. The layered double hydroxide of claim 24, wherein the layered double hydroxide of formula (I) is a Zn/Al, Mg/Al, Ca/Al, Ni/Al or Cu/Al layered double hydroxide.
27. The layered double hydroxide of claim 24, wherein X is carbonate, bicarbonate, hydrogenphosphate, dihydrogenphosphate, nitrite, borate, nitrate, sulphate or phosphate or a mixture of two or more thereof.
28. (canceled)
29. The layered double hydroxide of claim 24, wherein the AIM-solvent is selected from the group consisting of m-cresol, o-cresol, p-cresol, n-butanol, sec-butanol, n-pentanol, n-hexanol, cyclohexanol, diethyl ether, diisopropyl ether, di-n-butyl ether, methyl tert-butyl ether (MTBE), tert-amyl methyl ether, cyclopentyl methyl ether, anisole, butyl carbitol acetate, cyclohexanone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methyl isoamyl ketone, methyl n-amyl ketone, isophorone, isobutyraldehyde, furfural, methyl formate, methyl acetate, isopropyl acetate, n-propyl acetate, isobutyl acetate, n-butyl acetate, n-amyl acetate, n-hexyl acetate, methyl amyl acetate, methoxypropyl acetate, 2-ethoxyethyl acetate, 2-butoxyethyl acetate, n-butyl propionate, n-pentyl propionate, triethylamine, 2-nitropropane, aniline, N,N-dimethylaniline, nitromethane, and a mixture of two or more thereof.
30. (canceled)
31. The layered double hydroxide of claim 24, wherein 0<b5.
32. The layered double hydroxide of claim 24, wherein 0<c1.
33. The layered double hydroxide of claim 24, wherein the layered double hydroxide has a BET surface area of at least 180 m.sup.2/g.
34. The layered double hydroxide of claim 23, wherein the layered double hydroxide has a BET pore volume of at least 0.5 cm.sup.3/g.
35. The layered double hydroxide of claim 23, wherein the layered double hydroxide has a loose bulk density of less than 0.5 g/mL.
Description
DETAILED DESCRIPTION OF THE INVENTION
Processes of the Invention
[0038] As described hereinbefore, the present invention provides a process for preparing a layered-double hydroxide of formula (I) shown below:
[M.sup.z+.sub.1xM.sup.y+.sub.x(OH).sub.2].sup.a.sup.
[0039] wherein [0040] M is a charged metal cation; [0041] M is a charged metal cation different from M; [0042] z is 1 or 2; [0043] y is 3 or 4; [0044] 0<x<0.9; [0045] 0<b10; [0046] 0<c10; [0047] X is an anion; [0048] n is the charge on anion X; [0049] a is equal to z(1x)+xy2; and [0050] AIM-solvent denotes a solvent selected from the group consisting of m-cresol, o-cresol, p-cresol, n-butanol, sec-butanol, n-pentanol, n-hexanol, cyclohexanol, diethyl ether, diisopropyl ether, di-n-butyl ether, methyl tert-butyl ether (MTBE), tert-amyl methyl ether, cyclopentyl methyl ether, anisole, butyl carbitol acetate, cyclohexanone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methyl isoamyl ketone, methyl n-amyl ketone, isophorone, isobutyraldehyde, furfural, methyl formate, methyl acetate, isopropyl acetate, n-propyl acetate, isobutyl acetate, n-butyl acetate, n-amyl acetate, n-hexyl acetate, methyl amyl acetate, methoxypropyl acetate, 2-ethoxyethyl acetate, 2-butoxyethyl acetate, n-butyl propionate, n-pentyl propionate, triethylamine, 2-nitropropane, aniline, N,N-dimethylaniline, nitromethane, 2-pentanone, 3-methyl-2-butanone, 3-pentanone, 2,4-dimethyl-3-pentanone, 4-heptanone, 5-nonanone, and a mixture of two or more thereof;
said process comprising the steps of; [0051] a) providing a water-washed, wet precipitate of formula (II) shown below, said precipitate having been formed by contacting aqueous solutions containing cations of the metals M and M, and the anion X.sup.n, and then ageing the reaction mixture:
[M.sup.z+.sub.1xM.sup.y+.sub.x(OH).sub.2].sup.a.sup.
[0054] Through extensive studies, the inventors have now found that prior art techniques previously used to prepare high surface area LDHs can be markedly improved upon. In particular, the inventors have discovered that a novel post-preparation step of treating a pre-prepared LDH with a solvent having particular properties not only results in the formation of a high surface area LDH, but also considerably optimises the manufacturing process as a whole.
[0055] Compared to those prior art techniques that call for the use of an aqueous miscible solvent in a post-preparation treatment step, the inventors have now discovered have now identified numerous advantages associated with using solvents having radically different properties. In particular, the inventors have identified that both the hydrogen-bonding characteristics of a given solvent and its immiscibility with water collectively contribute to the formation of high surface area LDHs in the processes in the invention. Without wishing to be bound by theory, the inventors have hypothesised that by treating pre-prepared LDH with an organic solvent having hydrogen bonding characteristics (e.g. as donor or acceptor), residual water present between the layers of the LDH or on its surface can be efficiently removed. The removal of this residual water greatly reduces the extent to which individual LDH particulates or crystallites aggregate through hydrogen-bonding of residual water present on their surfaces, thereby resulting in a finer, free-flowing LDH powder having high surface area. In addition, the use of an aqueous immiscible solvent in the post-production treatment step greatly enhances the efficiency of the manufacturing process as a whole. In particular, when compared with aqueous miscible solvents whose separation from water requires energy-intensive distillation techniques, using an aqueous immiscible solvent in the post-production treatment step allows the solvent to be easily separated from the displaced residual water at the end of the treatment step (e.g. by simple partitioning), meaning that the solvent can be readily recycled for use in further sequential post-treatment steps of the same LDH, or in the post-treatment of a new batch of precipitated LDH. Hence, the use of an aqueous immiscible solvent allows for an overall more efficient and environmentally-friendly method of manufacturing high surface area LDHs.
[0056] In an embodiment, the AIM-solvent is selected from the group consisting of m-cresol, o-cresol, p-cresol, n-butanol, sec-butanol, n-pentanol, n-hexanol, cyclohexanol, diethyl ether, diisopropyl ether, di-n-butyl ether, methyl tert-butyl ether (MTBE), tert-amyl methyl ether, cyclopentyl methyl ether, anisole, butyl carbitol acetate, cyclohexanone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methyl isoamyl ketone, methyl n-amyl ketone, isophorone, isobutyraldehyde, furfural, methyl formate, methyl acetate, isopropyl acetate, n-propyl acetate, isobutyl acetate, n-butyl acetate, n-amyl acetate, n-hexyl acetate, methyl amyl acetate, methoxypropyl acetate, 2-ethoxyethyl acetate, 2-butoxyethyl acetate, n-butyl propionate, n-pentyl propionate, triethylamine, 2-nitropropane, aniline, N,N-dimethylaniline, nitromethane, and a mixture of two or more thereof.
[0057] In an embodiment, the AIM-solvent is selected from the group consisting of n-butanol, sec-butanol, n-pentanol, n-hexanol, cyclohexanol, diethyl ether, diisopropyl ether, di-n-butyl ether, methyl tert-butyl ether (MTBE), tert-amyl methyl ether, cyclopentyl methyl ether, cyclohexanone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methyl isoamyl ketone, methyl n-amyl ketone, furfural, methyl formate, methyl acetate, isopropyl acetate, n-propyl acetate, isobutyl acetate, n-butyl acetate, n-amyl acetate, n-hexyl acetate, methyl amyl acetate, methoxypropyl acetate, 2-ethoxyethyl acetate, 1-hexanol, triethylamine, nitromethane, and a mixture of two or more thereof.
[0058] In an embodiment, the AIM-solvent is selected from the group consisting of n-butanol, sec-butanol, n-pentanol, n-hexanol, cyclohexanol, diethyl ether, diisopropyl ether, di-n-butyl ether, methyl tert-butyl ether (MTBE), tert-amyl methyl ether, cyclopentyl methyl ether, cyclohexanone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methyl isoamyl ketone, methyl n-amyl ketone, furfural, methyl formate, methyl acetate, isopropyl acetate, n-propyl acetate, isobutyl acetate, n-butyl acetate, n-amyl acetate, n-hexyl acetate, methyl amyl acetate, methoxypropyl acetate, 2-ethoxyethyl acetate, nitromethane, and a mixture of two or more thereof.
[0059] In an embodiment, the AIM-solvent is selected from the group consisting of diethyl ether, diisopropyl ether, di-n-butyl ether, cyclohexanone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methyl acetate, isopropyl acetate, n-propyl acetate, isobutyl acetate, 1-hexanol, triethylamine, nitromethane, and a mixture of two or more thereof.
[0060] In an embodiment, the AIM-solvent is selected from the group consisting of diethyl ether, diisopropyl ether, di-n-butyl ether, cyclohexanone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methyl acetate, isopropyl acetate, n-propyl acetate, isobutyl acetate, and a mixture of two or more thereof.
[0061] In an embodiment, the AIM-solvent is selected from the group consisting of m-cresol, o-cresol, p-cresol, n-butanol, n-pentanol, n-hexanol, cyclohexanol, diethyl ether, diisopropyl ether, di-n-butyl ether, methyl tert-butyl ether (MTBE), tert-amyl methyl ether, cyclopentyl methyl ether, anisole, butyl carbitol acetate, cyclohexanone, methyl isobutyl ketone (MIBK), methyl isoamyl ketone, methyl n-amyl ketone, isophorone, furfural, isopropyl acetate, n-propyl acetate, isobutyl acetate, n-butyl acetate, n-amyl acetate, n-hexyl acetate, methyl amyl acetate, 2-butoxyethyl acetate, n-butyl propionate, n-pentyl propionate, 2-nitropropane, aniline, N,N-dimethylaniline, and a mixture of two or more thereof.
[0062] In an embodiment, the AIM-solvent is selected from the group consisting of diethyl ether, diisopropyl ether, di-n-butyl ether, cyclohexanone, methyl isobutyl ketone (MIBK), isopropyl acetate, n-propyl acetate, isobutyl acetate, and a mixture of two or more thereof.
[0063] In an embodiment, the AIM-solvent is selected from the group consisting of diethyl ether, diisopropyl ether, di-n-butyl ether, 1-butanol, 1-hexanol, methyl ethyl ketone, methyl tert-butyl ether, tert-amyl methyl ether, cyclopentyl methyl ether, anisole, 2-petanone, 3-methyl-2-butanone, 4-methyl-2-pentanone, 3-pentanone, 2,4-dimethyl-3-pentanone, 4-heptanone, 5-nonanone, and a mixture of two or more thereof.
[0064] In an embodiment, the AIM-solvent is selected from the group consisting of diethyl ether, diisopropyl ether, di-n-butyl ether, 1-hexanol, methyl ethyl ketone, methyl tert-butyl ether, tert-amyl methyl ether, cyclopentyl methyl ether, anisole, 4-methyl-2-pentanone, and a mixture of two or more thereof.
[0065] Organic solvents that are highly miscible with water (e.g. acetone and ethanol) are not used in the process of the invention.
[0066] The high surface area LDHs of the invention may be prepared, supplied and used as dispersions in the slurry formed in step b) and maintained in step c). Alternatively, in another embodiment, the process further comprises a step d) of isolating the layered double hydroxide resulting from step c).
[0067] When the process includes a step d) of isolating the layered double hydroxide resulting from step c), the layered double hydroxide may be isolated by a variety of means, including filtering, filter pressing, spray drying, cycloning and centrifuging. The isolated layered double hydroxide may then be dried to give a free-flowing powder. The drying may be performed under ambient conditions, in a vacuum, or by heating to a temperature below 60 C. (e.g. 20 to 60 C.). Suitably, in step d), the layered double hydroxide resulting from step c) is isolated and then heated to a temperature of 10-40 C. in a vacuum until a constant mass is reached.
[0068] In an embodiment, when z is 2, M is Mg, Zn, Fe, Ca, Sn, Ni, Cu, Co, Mn or Cd or a mixture of two or more of these, or when z is 1, M is Li. Suitably, z is 2 and M is Ca, Mg, Zn or Fe. More suitably, z is 2 and M is Ca, Mg or Zn.
[0069] In an embodiment, when y is 3, M is Al, Ga, Y, In, Fe, Co, Ni, Mn, Cr, Ti, V, La or a mixture thereof, or when y is 4, M is Sn, Ti or Zr or a mixture thereof. Suitably, y is 3. More suitably, y is 3 and M is Al.
[0070] In an embodiment, x has a value according to the expression 0.18<x<0.9. Suitably, x has a value according to the expression 0.18<x<0.5. More suitably, x has a value according to the expression 0.18<x<0.4.
[0071] In an embodiment, b has a value according to the expression 0<b7.5. Suitably, b has a value according to the expression 0<b5. More suitably, b has a value according to the expression 0<b3. Most suitably, b has a value according to the expression 0<b1.5.
[0072] In an embodiment, c has a value according to the expression 0<c7.5. Suitably, c has a value according to the expression 0<c5. More suitably, c has a value according to the expression 0<c1. More suitably, c has a value according to the expression 0<c0.5. Most suitably, c has a value according to the expression 0<c0.35. The lower limit for c may be, for example, 0.001.
[0073] In an embodiment, the layered double hydroxide of formula (I) is a Zn/Al, Mg/Al, Ca/Al, Ni/Al or Cu/Al layered double hydroxide.
[0074] The anion X in the LDH may be any appropriate organic or inorganic anion, for example halide (e.g., chloride), inorganic oxyanions (e.g. X.sub.mO.sub.n(OH).sub.p.sup.q; m=1-5; n=2-10; p=0-4, q=1-5; X=B, C, N, S, P: e.g. carbonate, bicarbonate, hydrogenphosphate, dihydrogenphosphate, nitrite, borate, nitrate, phosphate, sulphate), anionic surfactants (such as sodium dodecyl sulfate, fatty acid salts or sodium stearate), anionic chromophores, and/or anionic UV absorbers, for example 4-hydroxy-3-10 methoxybenzoic acid, 2-hydroxy-4 methoxybenzophenone-5-sulfonic acid (HMBA), 4-hydroxy-3-methoxy-cinnamic acid, p-aminobenzoic acid and/or urocanic acid. In an embodiment, the anion X is an inorganic oxyanion selected from carbonate, bicarbonate, hydrogenphosphate, dihydrogenphosphate, nitrite, borate, nitrate, sulphate or phosphate or a mixture of two or more thereof. More suitably, the anion X is an inorganic oxyanion selected from carbonate, bicarbonate, nitrate or nitrite. Most suitably, the anion X is carbonate.
[0075] In a particularly suitable embodiment, M is Ca, Mg, Zn or Fe, M is Al, and X is carbonate, bicarbonate, nitrate or nitrite. Suitably, M is Ca, Mg or Zn, M is Al, and X is carbonate, bicarbonate, nitrate or nitrite. More suitably, M is Ca, Mg or Zn, M is Al, and X is carbonate.
[0076] The term water-washed wet precipitate of formula (II) used in step a) will be understood to define a material having a composition defined by formula (II) which has been precipitated out of a solution of reactants and has subsequently been washed with water and then dried and/or filtered to the point that it is still damp. The wet precipitate may have a moisture content of 30 to 50% relative to the total weight of the wet precipitate.
[0077] In an embodiment, the water-washed wet precipitate of formula (II) is a wet cake. The term wet cake will be familiar to one of ordinary skill in the art. For example, the wet cake may be the product obtained by washing the precipitate of formula (II) with water, and then filtering off a portion of the residual water (e.g. under reduced pressure) to leave a damp solid (e.g. of moisture content 30 to 50% relative to the total weight of the solid).
[0078] It will be understood that the water-washed wet precipitate of step a) may be pre-formed. Alternatively, the water-washed wet precipitate of step a) may be prepared as part of step a), in which case step a) comprises the following steps: [0079] (i) precipitating a layered double hydroxide having the formula (II) from an aqueous solution containing cations of the metals M and M, and the anion X.sup.n; [0080] (ii) ageing the layered double hydroxide precipitate obtained in step (i) in the reaction mixture of step (i); [0081] (iii) collecting the aged precipitate resulting from step (ii), then washing it with water; and [0082] (iv) drying and/or filtering the washed precipitate to the point that it is still damp.
[0083] In an embodiment, in step a)(i), the precipitate is formed by contacting aqueous solutions containing cations of the metals M and M, and the anion X.sup.n, in the presence of a base being a source of OH.sup. (e.g. NaOH, NH.sub.4OH, or a precursor for OH.sup.formation). Suitably the base is NaOH. In an embodiment, the quantity of base used is sufficient to control the pH of the solution at 6.5-13. Suitably, the quantity of base used is sufficient to control the pH of the solution at 7.5-13. More suitably, the quantity of base used is sufficient to control the pH of the solution at 9-11.
[0084] In an embodiment, in step a)(ii), the layered double hydroxide precipitate obtained in step (i) is aged in the reaction mixture of step (i) for a period of 5 minutes to 72 hours at a temperature of 1-100 C.
[0085] Suitably, in step a)(ii), the layered double hydroxide precipitate obtained in step (i) is aged in the reaction mixture of step (i) for a period of 1 to 72 hours. More suitably, in step a)(ii), the layered double hydroxide precipitate obtained in step (i) is aged in the reaction mixture of step (i) for a period of 5 to 48 hours. Most suitably, in step a)(ii), the layered double hydroxide precipitate obtained in step (i) is aged in the reaction mixture of step (i) for a period of 12 to 36 hours.
[0086] Suitably, in step a)(ii), the layered double hydroxide precipitate obtained in step (i) is aged in the reaction mixture of step (i) at a temperature of 10-60 C. More suitably, in step a)(ii), the layered double hydroxide precipitate obtained in step (i) is aged in the reaction mixture of step (i) at a temperature of 10-40 C.
[0087] In an embodiment, in step a)(iii), the aged precipitate resulting from step (ii) is collected, then washed with water (e.g. using a Buchner apparatus under ambient conditions) until the filtrate has a pH in the range of 6.5-7.5.
[0088] In an embodiment, in step a)(iv), the washed precipitate is subjected to drying and/or filtration under reduced pressure at a temperature of 10-35 C. (e.g. using a Buchner apparatus under ambient conditions) to yield a wet cake of precipitate. Optionally, after step a)iv), the wet cake is taken up in an excess of water and step a)iv) is then repeated.
[0089] In an embodiment, the water-washed wet precipitate of step a) may be the product of a urea hydrothermal LDH preparation process. Urea hydrothermal processes are well-documented in the art, and give rise to well-crystallised, large platelet-like (as opposed to rosette/flower-type) LDHs.
[0090] In step b), the water-washed wet precipitate of formula (II) resulting from step a) is dispersed in an AIM-solvent as defined herein to produce a slurry. Optionally, prior to step b), the water-washed wet precipitate of formula (II) resulting from step a) is first washed (e.g. using Buchner apparatus under ambient conditions) with at least one AIM-solvent as defined herein.
[0091] In an embodiment, the slurry produced in step b) and then maintained in step c) contains 1-100 g of water-washed wet precipitate per 1 L of AIM-solvent. Suitably, the slurry produced in step b) and maintained in step c) contains 1-75 g of water-washed wet precipitate per 1 L of AIM-solvent. More suitably, the slurry produced in step b) and maintained in step c) contains 1-50 g of water-washed wet precipitate per 1 L of AIM-solvent. Most suitably, the slurry produced in step b) and maintained in step c) contains 1-30 g of water-washed wet precipitate per 1 L of AIM-solvent.
[0092] In step c), the slurry produced in step b) is maintained for a period of time. Suitably, the slurry is stirred during step c).
[0093] In an embodiment, in step c), the slurry is maintained for a period of 0.5 to 96 hours. Suitably, in step c), the slurry is maintained for a period of 0.5 to 72 hours. More suitably, in step c), the slurry is maintained for a period of 0.5 to 48 hours. Even more suitably, in step c), the slurry is maintained for a period of 0.5 to 24 hours. Yet more suitably, in step c), the slurry is maintained for a period of 0.5 to 10 hours. Most suitably, in step c), the slurry is maintained for a period of 1 to 8 hours.
[0094] In an embodiment, the process further comprises a step e) of contacting the layered double hydroxide isolated in step d) with at least one AIM-solvent as defined herein. In certain embodiments, it may be advantageous to perform one or more additional AIM-solvent treatment steps on the precipitate isolated in step d). In an embodiment, in step e), the isolated layered double hydroxide is washed with at least one AIM solvent (e.g. using Buchner apparatus). Alternatively, step e) comprises the steps of:
[0095] i. dispersing the isolated layered double hydroxide in an AIM-solvent to form a slurry;
[0096] ii. maintaining the slurry for a period of 0.5 to 72 hours;
[0097] iii. isolating the layered double hydroxide resulting from step ii; and
[0098] iv. optionally repeating steps i. to iii. a further 1-10 times (e.g. once or twice).
Hence, step e) may comprise performing additional dispersion-maintaining-isolation cycles in order to remove residual water from the layered double hydroxide.
[0099] According to a further aspect of the invention, there is provided a process for preparing a layered-double hydroxide of formula (I) shown below:
[M.sup.z+.sub.1xM.sup.y+.sub.x(OH).sub.2].sup.a.sup.
[0100] wherein [0101] M is a charged metal cation; [0102] M is a charged metal cation different from M; [0103] z is 1 or 2; [0104] y is 3 or 4; [0105] 0<x<0.9; [0106] 0<b10; [0107] 0<c10; [0108] X is an anion; [0109] n is the charge on anion X; [0110] a is equal to z(1x)+xy2; and [0111] AIM-solvent denotes a solvent having a water solubility of 80 g/L under ambient conditions and having one or more hydrogen bond donor and/or acceptor groups;
said process comprising the steps of; [0112] a) providing a water-washed, wet precipitate of formula (II) shown below, said precipitate having been formed by contacting aqueous solutions containing cations of the metals M and M, and the anion X.sup.n, and then ageing the reaction mixture:
[M.sup.z+.sub.1xM.sup.y+.sub.x(OH).sub.2].sup.a.sup.
[0115] It will be appreciated that M, M, z, y, x, a, b, c and X can have any of those definitions appearing hereinbefore.
[0116] The AIM solvent may have any suitable hydrogen bond donor and/or acceptor groups. Hydrogen bond donor groups include ROH, RNH.sub.2, R.sub.2NH, whereas hydrogen bond acceptor groups include ROR, R.sub.2CO RNO.sub.2, R.sub.2NO, R.sub.3N, ROH, RCF.sub.3, where R represents a hydrocarbyl group of the AIM solvent. It will be understood that ambient conditions refers to a temperature of 10-40 C. and atmospheric pressure.
LDHs of the Invention
[0117] As described hereinbefore, the present invention also provides a layered double hydroxide of formula (I) shown below:
[M.sup.z+.sub.1xM.sup.y+.sub.x(OH).sub.2].sup.a.sup.
[0118] wherein [0119] M is a charged metal cation [0120] M is a charged metal cation different from M [0121] z is 1 or 2 [0122] y is 3 or 4 [0123] 0<x<0.9 [0124] 0<b10 [0125] 0<c10 [0126] X is an anion [0127] n is the charge on anion X [0128] a is equal to z(1x)+xy2; and [0129] AIM-solvent denotes solvent selected from the group consisting of m-cresol, o-cresol, p-cresol, n-butanol, sec-butanol, n-pentanol, n-hexanol, cyclohexanol, diethyl ether, diisopropyl ether, di-n-butyl ether, methyl tert-butyl ether (MTBE), tert-amyl methyl ether, cyclopentyl methyl ether, anisole, butyl carbitol acetate, cyclohexanone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methyl isoamyl ketone, methyl n-amyl ketone, isophorone, isobutyraldehyde, furfural, methyl formate, methyl acetate, isopropyl acetate, n-propyl acetate, isobutyl acetate, n-butyl acetate, n-amyl acetate, n-hexyl acetate, methyl amyl acetate, methoxypropyl acetate, 2-ethoxyethyl acetate, 2-butoxyethyl acetate, n-butyl propionate, n-pentyl propionate, triethylamine, 2-nitropropane, aniline, N,N-dimethylaniline, nitromethane, 2-pentanone, 3-methyl-2-butanone, 3-pentanone, 2,4-dimethyl-3-pentanone, 4-heptanone, 5-nonanone, and a mixture of two or more thereof.
[0130] The present invention also provides a layered double hydroxide of formula (I) obtainable, obtained or directly obtained by a process defined herein.
[0131] The LDHs of the invention present numerous advantages over those currently available. Perhaps most notably, the LDHs of the invention have particularly high surface areas and pore volumes, making them attractive candidates for use in a variety of catalytic applications and sorption processes. By virtue of the AIM-solvent treatment to which they are subjected, the LDHs of the invention may be referred to here as AIM-LDHs.
[0132] For the LDHs of the invention, M, M, z, y, a, b, c, X, n and the AIM solvent may have any of those definitions appearing hereinbefore.
[0133] For the avoidance of doubt, the LDHs of the invention contain only those components (ions, anions, solvents, etc) recited in formula (I).
[0134] In an embodiment, b has a value according to the expression 0<b7.5. Suitably, b has a value according to the expression 0<b5. More suitably, b has a value according to the expression 0<b3. Most suitably, b has a value according to the expression 0<b1.5.
[0135] In an embodiment, c has a value according to the expression 0<c7.5. Suitably, c has a value according to the expression 0<c5. More suitably, c has a value according to the expression 0<c1. More suitably, c has a value according to the expression 0<c0.5. Most suitably, c has a value according to the expression 0<c0.35. The lower limit for c may be, for example, 0.001.
[0136] In an embodiment, the LDH has a BET surface area of at least 70 m.sup.2/g. Suitably, the LDH has a BET surface area of at least 180 m.sup.2/g. More suitably, the LDH has a BET surface area of at least 240 m.sup.2/g. Even more suitably, the LDH has a BET surface area of at least 275 m.sup.2/g. Most suitably, the LDH has a BET surface area of at least 300 m.sup.2/g. The high surface area of the LDHs makes them particularly attractive candidates for use as sorbents or support materials in catalytic applications.
[0137] In an embodiment, the layered double hydroxide has a BET pore volume of at least 0.5 cm.sup.3/g. Suitably, the layered double hydroxide has a BET pore volume of at least 0.75 cm.sup.3/g. More suitably, the layered double hydroxide has a BET pore volume of at least 0.9 cm.sup.3/g. The pore volume properties of the LDHs make them particularly attractive candidates for use in sorption technologies.
[0138] In an embodiment, the layered double hydroxide has a loose bulk density of less than 0.5 g/mL. Suitably, the layered double hydroxide has a loose bulk density of less than 0.35 g/mL. More suitably, the layered double hydroxide has a loose bulk density of less than 0.25 g/mL. In another embodiment, the layered double hydroxide has a tap density of less than 0.5 g/mL. Tap densities are calculated by standard testing method (ASTM D7481-09) using a graduated cylinder. The powder was filled into a cylinder and a precise weight of sample (m) was measured. The volume was measured before (V.sub.0) and after 1000 taps (V.sub.t). The loose bulk and tap densities were calculated by: Loose bulk density=m/V0; Tap density=m/V.sub.t. Suitably, the layered double hydroxide has a tap density of less than 0.4 g/mL. More suitably, the layered double hydroxide has a tap density of less than 0.35 g/mL. The density properties of the LDHs make them particularly attractive candidates for use in sorption technologies.
[0139] The LDHs of the invention are suitably provided in a dry, particulate form. Alternatively, the LDHs of the invention may be provided as a dispersion or slurry in an AIM-solvent.
[0140] According to a further aspect of the invention, there is provided a layered double hydroxide of formula (I) shown below:
[M.sup.z+.sub.1xM.sup.y+.sub.x(OH).sub.2].sup.a.sup.
[0141] wherein [0142] M is a charged metal cation [0143] M is a charged metal cation different from M [0144] z is 1 or 2 [0145] y is 3 or 4 [0146] 0<x<0.9 [0147] 0<b10 [0148] 0<c10 [0149] X is an anion [0150] n is the charge on anion X [0151] a is equal to z(1x)+xy2; and [0152] AIM-solvent denotes a solvent having a water solubility of 80 g/L under ambient conditions and having one or more hydrogen bond donor and/or acceptor groups.
[0153] It will be appreciated that M, M, z, y, x, a, b, c and X can have any of those definitions appearing hereinbefore.
[0154] The AIM-solvent may have any suitable hydrogen bond donor and/or acceptor groups. Hydrogen bond donor groups include ROH, RNH.sub.2, R.sub.2NH whereas hydrogen bond acceptor groups include ROR, R.sub.2CO RNO.sub.2, R.sub.2NO, R.sub.3N, ROH, RCF.sub.3, where R represents a hydrocarbyl group of the AIM solvent.
EXAMPLES
[0155] Examples of the invention will now be described, for the purpose of illustration only, with reference to the accompanying figures, in which:
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Materials and Methods
[0190] X-ray diffraction (XRD) patterns were recorded on a PANalytical XPert Pro instrument in reflection mode with Cu Ka radiation. The accelerating voltage was set at 40 kV with 40 mA current (=1.542) at 0.01 s.sup.1 from 1 to 70 with a slit size of degree.
[0191] Transmission electron microscopy (TEM) analysis was performed on JEOL 2100 microscope with an accelerating voltage of 400 kV. Samples were dispersed in ethanol with sonication and then cast onto copper TEM grids coated with lacey carbon film.
[0192] Scanning electron microscopy (SEM) analyses were performed on a JEOL JSM 6100 scanning microscope with an accelerating voltage of 20 kV. Powder samples were spread on carbon tape adhered to an SEM stage. Before observation, the samples were sputter coated with a thick Platinum layer to prevent charging and to improve the image quality.
[0193] Brunauer-Emmett-Teller (BET) specific surface areas were measured from the N.sub.2 adsorption and desorption isotherms at 77 K collected from a Quantachrome Autosorb-6B surface area and pore size analyser. Before each measurement, LDH samples were first degassed overnight at 110 C.
[0194] Brunauer-Emmett-Teller (BET) pore size distributions and pore volumes were calculated from the desorption isotherm.
[0195] Thermal gravimetric analyses (TGA) were carried out using a Perkin Elmer TGA7 Thermogravametric Analyser. Approximately 10 mg of sample was heated in a platinum pan in the furnace. Initially the temperature was held at 30 C. for 5 minutes and then was increased to 800 C. at a rate of 5 C. per minute. The sample was held at 800 C. for five minutes. These data were used to determine both the thermal stability and the H.sub.2O and AMO solvent content of the materials. Small variations in the H.sub.2O and acetone content was observed on repeat measurements.
[0196] The loose bulk and tap densities were measured by standard testing method (ASTM D7481-09) using a graduated cylinder. The powder was filled into a cylinder and a precise weight of sample (m) was measured. The volume was measured before (V.sub.0) and after 1000 taps (V.sub.t). The loose bulk and tap densities were calculated by: Loose bulk density=m/V0; Tap density=m/V.sub.t.
Part A
Example 1Synthesis of LDHs
LDHs of the Invention (AIM-LDHs)
[0197] An aqueous solution (50 mL) of 0.80 M Mg(NO.sub.3).sub.2.6H.sub.2O and 0.20 M of Al(NO.sub.3).sub.3.9H.sub.2O was added drop-wise into a 50 mL of 0.5 M Na.sub.2CO.sub.3 solution with stirring and the pH was controlled at 10 using 4.0 M NaOH solution. After stirring at room temperature for 24 hours, the product was filtered and washed with DI water until the pH was close to 7. Then the wet cake was re-dispersed in 100 mL of DI water. The 25 mL of dispersion was filtered to remove water. The wet cake was rinsed with 500 mL of an AIM-solvent then re-dispersed and stirred in 300 mL of this solvent at room temperature for 4 hours. The AIM-solvent was removed by filtration and the obtained LDHs was further rinsed by 200 mL of this solvent. The product was dried in the vacuum oven overnight. The AIM-solvents used were; diethyl ether, 1-butanol, 1-hexanol, methyl ethyl ketone (MEK), methyl tert-butyl ether (MTBE), nitromethane and triethylamine.
[0198] The various LDHs of the invention are identified in Tables 1-6 and
Comparator LDHs
[0199] Various comparator LDHs were prepared by an identical synthesis to that described in respect of the LDHs of the invention, except that the an aqueous immiscible non-hydrogen-bonding solvent (i.e. no hydrogen bond donor or acceptor groups) was used instead of the AIM-solvent. The aqueous immiscible non-hydrogen-bonding solvents used were toluene, hexane and chloroform.
[0200] The various comparator LDHs of the invention are identified in
Conventional LDH (c-LDH)
[0201] Another comparator LDH was prepared according to a conventional synthesis employing simple water-washing, and without any post-synthesis solvent treatment step. The conventional LDH was prepared by the following protocol: an aqueous solution (50 mL) of 0.80 M Mg(NO.sub.3).sub.2.6H.sub.2O and 0.20 M of Al(NO.sub.3).sub.3.9H.sub.2O was added drop-wise into a 50 mL of 0.5 M Na.sub.2CO.sub.3 solution with stirring and the pH was controlled at 10 using 4.0 M NaOH solution. After stirring at room temperature for 24 hours, the product was filtered and washed with DI water until the pH was close to 7. (The product was filtered to remove water and dried in vacuum oven overnight.).
[0202] The conventional LDH is denoted water in Tables 2-6 and
Example 2Characterisation of LDHs
XRD
[0203]
[0204] Table 1 below and
TABLE-US-00001 TABLE 1 XRD data for diethyl ether-treated LDHs of the invention Mean crystallite Rinsing d-spacing domain lengths Unit cell No. volume d003 d110 D003 D110 parameter of Solvent (mL) () () () () a c layers Diethyl 100 mL 7.73 1.52 59.5 92.8 3.05 23.18 8 ether 300 mL 7.68 1.52 64.7 87.7 3.05 23.05 8 500 mL 7.69 1.52 54.0 83.7 3.05 23.08 7 1000 mL 7.73 1.52 60.4 92.9 3.05 23.19 8
[0205] The various traces presented in
TGA
[0206] Table 2 below and
TABLE-US-00002 TABLE 2 Thermal properties of conventional LDH and LDHs of the invention Change Change Washing T.sub.0 w.r.t water T.sub.1 w.r.t water solvent ( C.) ( C.) ( C.) ( C.) Water 110 179 1-Hexanol 103 7 171 9 Diethyl ether 102 163 16
[0207] Having regard to Table 2 and
[0208] The mass loss data provided in Table 2 and
TABLE-US-00003 TABLE 3 Compositional data for conventional LDH and LDHs of the invention Washing solvent b c Formula of LDH Water 0.63 0.00 Mg.sub.0.8Al.sub.0.2(OH).sub.2](CO.sub.3).sub.0.10.63H.sub.2O 1-Hexanol 0.63 0.06 Mg.sub.0.8Al.sub.0.2(OH).sub.2](CO.sub.3).sub.0.10.63H.sub.2O0.06(1-hexanol) Diethyl ether 0.54 0.08 Mg.sub.0.8Al.sub.0.2(OH).sub.2](CO.sub.3).sub.0.10.54H.sub.2O0.08(diethyl ether)
Example 3Surface Area and Pore Volume Studies
[0209] Table 4 below shows BET surface area properties for a variety of LDHs of the invention, as well as those for conventional LDH.
TABLE-US-00004 TABLE 4 BET surface area properties of LDHs Surface area (m.sup.2/g) Washing % Deaggregation solvent Value Change factor* Formula of LDH Water 9 Mg.sub.0.8Al.sub.0.2(OH).sub.2](CO.sub.3).sub.0.10.63H.sub.2O 1- 364 3944 40 Mg.sub.0.8Al.sub.0.2(OH).sub.2](CO.sub.3).sub.0.10.63H.sub.2O0.06(1- Hexanol hexanol) Diethyl 327 3533 36 Mg.sub.0.8Al.sub.0.2(OH).sub.2](CO.sub.3).sub.0.10.54H.sub.2O0.08(diethyl ether ether) Nitro 331 3578 37 methane Triethyl 363 3933 40 amine *Deaggregation factor = BET surface area/BET surface area of equivalent water-washed LDH.
[0210]
[0211]
[0212]
[0213] Table 5 below shows BET pore volume properties for a variety of LDHs of the invention, as well as those for conventional LDH.
TABLE-US-00005 TABLE 5 BET pore volume properties of LDHs Pore volume (cc/g) Washing % solvent Value Change Formula of LDHs Water 0.01 Mg.sub.0.8Al.sub.0.2(OH).sub.2](CO.sub.3).sub.0.10.63H.sub.2O 1-Hexanol 1.02 10100 Mg.sub.0.8Al.sub.0.2(OH).sub.2](CO.sub.3).sub.0.10.63H.sub.2O0.06(1-hexanol) Diethyl ether 1.02 10100 Mg.sub.0.8Al.sub.0.2(OH).sub.2](CO.sub.3).sub.0.10.54H.sub.2O0.08(diethyl ether) Nitromethane 1.33 13200 Triethylamine 1.1 10900
[0214]
Example 4Density Studies
[0215] Table 6 below provides density properties for a variety of LDHs of the invention, as well as those for conventional LDH.
TABLE-US-00006 TABLE 6 Density properties of LDHs Loose bulk Tap density density (g/ml) (g/ml) Washing % % solvent Value Change Value Change Formula of LDHs Water 1.07 1.21 Mg.sub.0.8Al.sub.0.2(OH).sub.2](CO.sub.3).sub.0.10.63H.sub.2O 1-Hexanol 0.15 86 0.23 81 Mg.sub.0.8Al.sub.0.2(OH).sub.2](CO.sub.3).sub.0.10.63H.sub.2O0.06(1-hexanol) Diethyl 0.12 88 0.2 83 Mg.sub.0.8Al.sub.0.2(OH).sub.2](CO.sub.3).sub.0.10.54H.sub.2O0.08(diethyl ether) ether Nitro 0.15 86 0.27 78 methane Triethyl 0.16 85 0.22 82 amine
[0216]
[0217]
Part B
Example 5Synthesis of LDHs
[0218] LDHs of the invention (AIM-LDHs)
[0219] An aqueous solution (50 mL) of 0.80 M Mg(NO.sub.3).sub.2.6H.sub.2O and 0.20 M of Al(NO.sub.3).sub.3.9H.sub.2O was added drop-wise into a 50 mL of 0.5 M Na.sub.2CO.sub.3 solution with stirring and the pH was controlled at 10 using 4.0 M NaOH solution. After stirring at room temperature for 24 hours, the product was filtered and washed with DI water until the pH was close to 7. Then the wet cake was re-dispersed in 100 mL of DI water. The 25 mL of dispersion was filtered to remove water. The wet cake was rinsed with 500 mL of an AIM-solvent then re-dispersed and stirred in 300 mL of this solvent at room temperature for 4 hours. The AIM-solvent was removed by filtration and the obtained LDHs was further rinsed by 200 mL of this solvent. The product was dried in the vacuum oven overnight. The AIM-solvents used were; diethyl ether, methyl ethyl ketone (MEK) (butanone), 1-hexanol, 1-butanol, nitromethane, trimethylamine, methyl tert-butyl ether (MTBE), tert-amyl methyl ether, cyclopentyl methyl ether, anisole, diisopropyl ether, di-n-butyl ether, 2-pentanone, 3-methyl-2-butanone, 4-methyl-2-pentanone, 3-pentanone, 2,4-dimethyl-3-pentanone, 4-heptanone and 5-nonanone.
Comparator LDHs (Aqueous Immiscible Weakly/Non-Hydrogen-Bonding Solvent)
[0220] Various comparator LDHs were prepared by an identical synthesis to that described in respect of the LDHs of the invention, except that the an aqueous immiscible weakly-hydrogen-bonding solvent was used instead of the AIM-solvent. The aqueous immiscible weakly-hydrogen-bonding solvents used were toluene, hexane, cyclohexane, dichloromethane and chloroform.
Comparator LDHs (Aqueous Miscible Hydrogen-Bonding Solvent)
[0221] Various comparator LDHs were prepared by an identical synthesis to that described in respect of the LDHs of the invention, except that an aqueous miscible hydrogen-bonding solvent was used instead of the AIM-solvent. The aqueous miscible hydrogen-bonding solvents (termed AMO solvents) used were acetone, ethanol, 1-methyl-2-pyrrolidone and isopropyl alcohol. Such comparator LDHs were termed AMO-LDHs.
Conventional LDH (c-LDH)
[0222] Another comparator LDH was prepared according to a conventional synthesis employing simple water-washing, and without any post-synthesis solvent treatment step. The conventional LDH was prepared by the following protocol: an aqueous solution (50 mL) of 0.80 M Mg(NO.sub.3).sub.2.6H.sub.2O and 0.20 M of Al(NO.sub.3).sub.3.9H.sub.2O was added drop-wise into a 50 mL of 0.5 M Na.sub.2CO.sub.3 solution with stirring and the pH was controlled at 10 using 4.0 M NaOH solution. After stirring at room temperature for 24 hours, the product was filtered and washed with DI water until the pH was close to 7. (The product was filtered to remove water and dried in vacuum oven overnight.).
[0223] Table 7 below shows the water and solvent content of various AIM-LDHs, comparator LDHs and conventional LDHs prepared according to the above-described protocols, as determined by elemental analysis:
TABLE-US-00007 TABLE 7 Elemental composition of various AIM-LDHs, comparator LDHs and conventional LDHs Washing solvent b c Formula of LDHs C-LDH Water 0.634 0.000 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.634H.sub.2O AMO Acetone 0.225 0.113 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.225H.sub.2O0.113(Acetone) solvents 1-Methyl-2- 0.512 0.092 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.512H.sub.2O0.092(1-Methyl-2-pyrrolidinone) pyrrolidinone Ethanol 0.245 0.215 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.245H.sub.2O0.215(Ethanol) Isopropyl 0.033 0.109 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.033H.sub.2O0.109(Isopropylalcohol) alcohol AIM 1-Butanol 0.041 0.099 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.041H.sub.2O0.099(1-Butanol) solvents 1-Hexanol 0.110 0.087 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.110H.sub.2O0.087(1-Hexanol) Diethyl ether 0.370 0.021 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.370H.sub.2O0.021(Diethyl ether) 2-Butanone 0.051 0.082 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.051H.sub.2O0.082(2-Butanone) Methyl tert- 0.247 0.040 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.247H.sub.2O0.040(Methyl tert-butyl ether) butyl ether Nitromethane 0.214 0.049 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.214H.sub.2O0.049(Nitromethane) Triethylamine 0.124 0.036 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.124H.sub.2O0.036(Triethylamine) Weak H- Toluene 0.402 0.001 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.402H.sub.2O0.001(Toluene) bonding Hexane 0.548 0.002 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.548H.sub.2O0.002(Hexane) solvents Chloroform 0.593 0.042 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.593H.sub.2O0.042(Chloroform)
Example 6Effect of Mg/Al Ratio
[0224] To investigate the effect of varying the Mg/Al cation ratio within the LDH, the general synthetic protocols outlined at Example 5 were adapted to prepare a series of AIM-LDHs (wherein the AIM solvent is diethyl ether), a series of AMO-LDHs (wherein the AMO solvent is acetone or ethanol) and a series of c-LDHs having Mg/Al cationic ratios of 2, 3 and 4.
[0225] Table 8 below shows the water and solvent content of the various LDHs prepared in Example 6, as determined by elemental analysis.
TABLE-US-00008 TABLE 8 Elemental composition of AIM-LDHs, AMO-LDHs and c-LDHs having varying Mg/Al ratios LDH with Mg/Al ratio Solvents b c Formula of LDHs Mg/Al = 2 Water 0.415 0.000 [Mg.sub.0.67Al.sub.0.33(OH).sub.2(CO.sub.3).sub.0.125]0.415H.sub.2O Acetone 0.081 0.074 [Mg.sub.0.67Al.sub.0.33(OH).sub.2(CO.sub.3).sub.0.125]0.081 H.sub.2O0.074(Acetone) Diethyl ether 0.246 0.044 [Mg.sub.0.67Al.sub.0.33(OH).sub.2(CO.sub.3).sub.0.125]0.246H.sub.2O0.044(Diethyl ether) Mg/Al = 3 Water 0.461 0.000 [Mg.sub.0.75Al.sub.0.25(OH).sub.2(CO.sub.3).sub.0.125]0.461 H.sub.2O Acetone 0.248 0.067 [Mg.sub.0.75Al.sub.0.25(OH).sub.2(CO.sub.3).sub.0.125]0.248H.sub.2O0.067(Acetone) Ethanol 0.396 0.176 [Mg.sub.0.75Al.sub.0.25(OH).sub.2(CO.sub.3).sub.0.125]0.396H.sub.2O0.176(Ethanol) Diethyl ether 0.182 0.086 [Mg.sub.0.75Al.sub.0.25(OH).sub.2(CO.sub.3).sub.0.125]0.182H.sub.2O0.086(Diethyl ether) Mg/Al = 4 Water 0.634 0.000 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.634H.sub.2O Acetone 0.225 0.113 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.225H.sub.2O0.113(Acetone) Ethanol 0.245 0.215 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.245H.sub.2O0.215(Ethanol) Diethyl ether 0.370 0.021 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.370H.sub.2O0.021 (Diethyl ether)
[0226] Table 9 below shows cell data for various LDHs prepared in Example 6.
TABLE-US-00009 TABLE 9 Mean crystallite domain lengths and unit cell parameters of AIM-LDHs and c-LDHs with different ratios of Mg/Al Washing d003 D003 No. of d110 Mg/Al ratio solvent () () layers () a c 2 Water 7.52 147.5 20 1.48 2.96 22.56 Diethyl ether 7.63 33.7 4 1.52 3.03 22.89 3 Water 7.62 107.3 14 1.53 3.05 22.87 Diethyl ether 7.73 36.6 5 1.52 3.04 23.2 4 Water 7.53 262.8 35 1.52 3.05 22.58 Diethyl ether 7.75 40.8 5 1.53 3.05 23.25
[0227]
[0228]
Example 7Effect of Solvent Structure
[0229] The effect of AIM solvent structure on the properties of the AIM-LDH (BET surface area, density, pore volume and pore size distribution) was investigated. A series of ether solvents and ketone solvents were studied.
[0230] For the ether AIM solvents having the general structure R.sub.1OR.sub.2, AIM-LDHs were prepared (according to the general protocol of Example 5) using the following solvents:
##STR00001##
[0231] Table 10 below shows the water and solvent content of these ether AIM-LDHs, as determined by elemental analysis.
TABLE-US-00010 TABLE 10 Elemental composition of ether AIM-LDHs Ether solvents b c Formula of LDHs R1CH3 Diethyl ether 0.370 0.021 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.370H.sub.2O0.021(Diethyl ether) group Diisopropyl 0.525 0.012 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.525H.sub.2O0.012(Diisopropyl ether) ether Di-n-butyl 0.630 0.013 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.630H.sub.2O0.013(Di-n-butyl ether) ether R1R2 Methyl tert- 0.247 0.040 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.247H.sub.2O0.040(Methyl tert-butyl ether) butyl ether Tert-amyl 0.503 0.016 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.503H.sub.2O0.016(Tert-amyl methyl ether) methyl ether Cyclopentyl 0.490 0.011 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.490H.sub.2O0.011(Cyclopentyl methyl ether) methyl ether Anisole 0.506 0.007 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.506H.sub.2O0.007(Anisole)
[0232] For the ketone AIM solvents having the general structure R.sub.1C(O)R.sub.2, AIM-LDHs were prepared (according to the general protocol of Example 5) using the following solvents:
##STR00002##
[0233] Table 11 below shows the water and solvent content of these ketone AIM-LDHs, as determined by elemental analysis.
TABLE-US-00011 TABLE 11 Elemental composition of ketone AIM-LDHs Ketone solvents b c Formula of LDHs R1CH3 2-Butanone 0.051 0.082 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.051H.sub.2O0.082(2-Butanone) group 2-Pentanone 0.130 0.302 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.130H.sub.2O0.302(2-Pentanone) 3-Methyl-2- 0.431 0.136 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.431H.sub.2O0.136(3-Methyl-2-butanone) butanone 4-Methyl-2- 0.564 0.049 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.564H.sub.2O0.049(4-Methyl-2-pentanone) pentanone R1R2 3-Pentanone 0.062 0.181 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.062H.sub.2O0.181(3-Pentanone) Diisopropylketone 0.310 0.053 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.310H.sub.2O0.053(Diisopropylketone) 4-Heptanone 0.309 0.059 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.309H.sub.2O0.059(4-Heptanone)
[0234] In the ether solvent series, it was found that the LDHs can totally be dispersed in most ether solvents.
[0235]
[0236]
[0237] In the ketone solvent series, it was found that the LDHs can totally be dispersed in the ketone solvents.
[0238]
[0239]
Example 8Effect of Dispersion Time
[0240] The effect of AIM solvent dispersion time on the properties of the AIM-LDH (BET surface area, density, pore volume and pore size distribution) was investigated.
[0241] Using the general protocol outlined in Example 5, a series of AIM-LDHs were prepared (AIM solventsdiisopropyl ether, di-n-butyl ether, anisole and cyclopentyl methyl ether), in which the dispersion time of the LDH in the AIM solvent was varied between 4 and 24 hours.
[0242] Table 12 below shows the water and solvent content of the AIM-LDHs used in this study, as determined by elemental analysis.
TABLE-US-00012 TABLE 12 Elemental composition of AIM-LDHs AIM Dispersion solvents time b c Formula of LDHs Diisopropyl 4 h 0.525 0.012 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.525H.sub.2O0.012(Diisopropyl ether) ether 8 h 0.260 0.013 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.260H.sub.2O0.013(Diisopropyl ether) Di-n-butyl 4 h 0.630 0.013 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.630H.sub.2O0.013(Di-n-butyl ether) ether 8 h 0.387 0.009 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.387H.sub.2O0.009(Di-n-butyl ether) Cyclopentyl 4 h 0.490 0.011 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.490H.sub.2O0.011(Cyclopentyl methyl ether) methyl 24 h 0.328 0.056 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.328H.sub.2O0.056(Cyclopentyl methyl ether) ether Anisole 4 h 0.506 0.007 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.506H.sub.2O0.007(Anisole) 24 h 0.022 0.009 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.022H.sub.2O0.009(Anisole)
[0243]
[0244]
[0245]
Example 9Effect of Recycling Solvent
[0246] The benefits of using AIM solvents over AMO solvents were investigated by comparing the effect of using recycled solvents in the rinsing step of the LDH manufacturing process. In the protocol described in Example 5, the rinsing step uses the largest quantity of solvent. Hence, the ability to use recycled solvent in this step would be a key advantage.
[0247] An AIM-LDH was prepared (AIM-LDH1) according to the protocol described in Example 5, except that after filtering the 25 mL dispersion and then rinsing the wet cake LDH with 500 mL of hexanol, the filtrate (containing hexanol and water) was collected and water was removed therefrom with the aid of a separating funnel. The protocol described in Example 5 was then resumed to afford the finished AIM-LDH1. The recycled hexanol from the rinsing step of AIM-LDH1 was then used in the same rinsing step of a subsequent batch of AIM-LDH (AIM-LDH2), after which the filtrate was again collected and water was separated from hexanol. The protocol described in Example 5 was then resumed to afford the finished AIM-LDH2. The hexanol was recycled a total of 4 times, with the BET surface area and density for each resulting LDH (AIM-LDH1-5) being recorded.
[0248] A series of AMO-LDHs were prepared according to an analogous procedure to the one described above, except that the AMO-solvent (ethanol) was not separated from water as part of each solvent recycling step.
[0249] Table 13 below shows the water and solvent content of the AIM-LDHs and AMO-LDHs used in this study, as determined by elemental analysis.
TABLE-US-00013 TABLE 13 Elemental composition of AIM-LDHs and AMO-LDHs Solvent Washing recycle solvent time(s) b c Formula of LDHs Ethanol 0 0.245 0.215 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.245H.sub.2O0.215(Ethanol) (AMO) 1 0.018 0.268 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.018H.sub.2O0.268(Ethanol) 2 0.019 0.247 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.019H.sub.2O0.247(Ethanol) 3 0.045 0.215 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.045H.sub.2O0.215(Ethanol) 4 0.048 0.219 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.048H.sub.2O0.219(Ethanol) Hexanol 0 0.232 0.113 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.232H.sub.2O0.113(1-Hexanol) (AIM) 1 0.257 0.091 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.257H.sub.2O0.091(1-Hexanol) 2 0.260 0.146 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.260H.sub.2O0.146(1-Hexanol) 3 0.240 0.188 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.240H.sub.2O0.188(1-Hexanol) 4 0.172 0.225 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.172H.sub.2O0.225(1-Hexanol)
[0250]
[0251] It will be appreciated that recycled AMO-solvent contains a quantity of water. Due to its miscibility with water, the AMO-solvent cannotunlike AIM-solventsbe straightforwardly separated from water. Without wishing to be bound by theory, it is believed that the presence of water in the recycled AMO solvent causes re-adsorption of some water molecules to the surface of the LDH during the rinsing of subsequent LDH batches, which manifests itself as a lower LDH surface area. In contrast to this, the immiscibility of the AIM solvent with water allows water to be straightforwardly separated from the AIM-solvent, meaning that notably purer solvent can be used in subsequent rinsing steps, thereby reducing the risk of water being re-adsorbed onto the surface of the LDH, thus giving rise to substantially identical surface area values across the 5 AIM-LDH samples.
[0252] Given the high costs associated with rinsing LDHs with large quantities of solvent, the ability to recycle such solvents without deleterious effect to the LDH properties is significant.
Example 10Effect of Solvent Rinsing Volume
[0253] The effect of solvent rinsing volume on the composition of the AIM-LDH was studied. Following the general protocol outlined at Example 5, a variety of AIM-LDHs were prepared (AIM solvents1-butanol, 1-hexanol and diethyl ether) in which the wet cake was initially rinsed with either 500 mL of AIM solvent (as in Example 5) or 100 mL of AIM solvent.
[0254] Table 14 below shows the water and solvent content of the AIM-LDHs used in this study, as determined by elemental analysis.
TABLE-US-00014 TABLE 14 Elemental composition of AIM-LDHs Rinsing Solvent volume (mL) b c Formula of LDHs 1-Butanol 100 mL 0.220 0.118 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.220H.sub.2O0.118(1-Butanol) 500 mL 0.041 0.099 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.041H.sub.2O0.099(1-Butanol) 1-Hexanol 100 mL 0.176 0.075 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.176H.sub.2O0.075(1-Hexanol) 500 mL 0.110 0.087 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.110H.sub.2O0.087(1-Hexanol) Diethyl 100 mL 0.537 0.089 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.537H.sub.2O0.089(Diethylether) ether 500 mL 0.370 0.021 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.370H.sub.2O0.021(Diethylether)
Example 11Effect of Solvent Treatment on Platelet-Like LDHs
[0255] The effect of solvent treatment (AIM or AMO) on platelet-like LDHs was explored. Unlike the rosette-type LDHs (also termed flower LDHs) discussed in Examples 1-10, platelet-like LDH have a plate-like morphology, and are composed of fewer layers. The platelet-like LDHs were prepared as follows:
[0256] An aqueous solution (100 mL) of 0.40 M Mg(NO.sub.3).sub.2.6H.sub.2O, 0.10 M of Al(NO.sub.3).sub.3.9H.sub.2O, and 0.80 M urea was prepared. The mixed solution were transferred to a Teflon-lined autoclave and heated in an oven at the 100 C. for 24 hours. After the reactions were cooled to room temperature, the precipitate products were washed several times with deionised water by filtration until the pH was close to 7. Then the wet cake was re-dispersed in 100 mL of deionised water. The 25 mL of dispersion was filtered to remove water. The wet cake was rinsed with 500 mL of an AIM- or AMO-solvent then re-dispersed and stirred in 300 mL of this solvent at room temperature for 4 hours. The solvent was removed by filtration and the obtained LDHs was further rinsed by 200 mL of this solvent. The product was dried in the vacuum oven overnight. The solvents used were acetone, ethanol, 1-hexanol and diethyl ether.
[0257] A conventional platelet-like LDH (c-LDH) was also prepared according to the above described urea hydrothermal method, omitting the AIM- or AMO-solvent treatment step.
[0258] The XRD patterns shown in
[0259]
[0260]
[0261]
[0262]
Comparative Example 1Use of Weakly Hydrogen-Bonding Solvents
[0263] Comparative LDHs were prepared according to the general protocol outlined in Example 5 using weakly hydrogen bonding solvents (toluene, hexane, chloroform, cyclohexane and dichloromethane). For each solvent, a series of LDHs were prepared in which the dispersion time of the LDH in the solvent varied from 4 to 120 hours.
[0264] Table 15 below shows the water and solvent content of the comparative LDHs used in this study, as determined by elemental analysis.
TABLE-US-00015 TABLE 15 Elemental composition of comparative LDHs Weak H-bond Dispersion solvents time b c Formula of LDHs Toluene 4 h 0.402 0.001 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.402H.sub.2O0.001(Toluene) 24 h 0.532 0.004 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.532H.sub.2O0.004(Toluene) 48 h 0.630 0.001 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.630H.sub.2O0.001(Toluene) 72 h 0.486 0.005 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.486H.sub.2O0.005(Toluene) Hexane 4 h 0.548 0.002 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.548H.sub.2O0.002(Hexane) 24 h 0.596 0.006 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.596H.sub.2O0.006(Hexane) 48 h 0.518 0.003 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.518H.sub.2O0.0003(Hexane) 72 h 0.550 0.004 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.550H.sub.2O0.004(Hexane) 96 h 0.356 0.017 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.356H.sub.2O0.017(Hexane) 120 h 0.211 0.020 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.211H.sub.2O0.020(Hexane) Chloroform 4 h 0.593 0.042 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.593H.sub.2O0.042(Chloroform) 24 h 0.683 0.020 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.683H.sub.2O0.020(Chloroform) 48 h 0.649 0.022 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.649H.sub.2O0.022(Chloroform) 72 h 0.430 0.045 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.430H.sub.2O0.045(Chloroform) Cyclohexane 4 h 0.467 0.004 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.467H.sub.2O0.004(Cyclohexane) 24 h 0.473 0.004 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.473H.sub.2O0.004(Cyclohexane) 48 h 0.455 0.006 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.455H.sub.2O0.006(Cyclohexane) 72 h 0.632 0.007 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.632H.sub.2O0.007(Cyclohexane) 96 h 0.483 0.006 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.483H.sub.2O0.006(Cyclohexane) 120 h 0.498 0.004 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.498H.sub.2O0.004(Cyclohexane) Dichloro 4 h 0.616 0.014 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.616H.sub.2O0.014(Dichloromethane) methane 24 h 0.896 0.230 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.896H.sub.2O0.230(Dichloromethane) 48 h 0.732 0.015 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.732H.sub.2O0.015(Dichloromethane) 72 h 0.771 0.196 [Mg.sub.0.80Al.sub.0.20(OH).sub.2(CO.sub.3).sub.0.125]0.771H.sub.2O0.196(Dichloromethane)
[0265]
[0266] While specific embodiments of the invention have been described herein for the purpose of reference and illustration, various modifications will be apparent to a person skilled in the art without departing from the scope of the invention as defined by the appended claims.