Patent Application
20190152794
The present invention relates to layered double hydroxides and their methods of manufacture. More particularly, the present invention relates to layered double hydroxides having high surface area and their methods of manufacture.
Layered double hydroxides (LDHs) are a class of compounds which comprise two metal cations and have a layered structure. A review of LDHs is provided in Structure and Bonding; Vol 119, 2005 Layered Double Hydroxides ed. X Duan and D. G. Evans. The hydrotalcites, perhaps the most well-known examples of LDHs, have been studied for many years. LDHs can intercalate anions between the layers of the structure. WO 99/24139 discloses the use of LDHs to separate anions including aromatic and aliphatic anions.
Owing to the relatively high surface charge and hydrophilic properties of LDHs, the particles or crystallites of conventionally synthesised LDHs are generally highly aggregated. The result of this is that, when produced, LDHs aggregate to form “stone-like”, non-porous bodies with large particle sizes of up to several hundred microns and low specific surface area of generally 5 to 15 m2/g (as disclosed for example in Wang et al Catal. Today 2011, 164, 198). Reports by e.g. Adachi-Pagano et al (Chem. Commun. 2000, 91) of relatively high surface area LDHs have specific surface areas no higher than 5 to 120 m2/g.
In certain applications (for example adsorbents or catalyst supports), it would be advantageous to provide LDHs with higher surface areas than those discussed above. Relatively high surface areas would lead to a greater number of active sites and facilitate mass transport from the surface to bulk.
WO2014/051530 and WO2015/144778 disclose processes of preparing higher surface area LDHs involving a post-production step of treating the LDH with a solvent that is miscible with water.
In spite of recent advances, there remains a need for optimized methods of manufacturing high surface area LDHs, as well as high surface area LDHs resulting from such methods.
The present invention was devised with the foregoing in mind.
According to a first aspect of the present invention there is provided a process for preparing a layered-double hydroxide of formula (I) shown below:
[Mz+1−xM′y+x(OH)2]a
wherein
[Mz+1−xM′y+x(OH)2]a
According to a further aspect of the present invention, there is provided a layered double hydroxide of formula (I) obtainable, obtained or directly obtained by a process defined herein.
According to a further aspects of the present invention, there is provided a layered double hydroxide of formula (I) shown below:
[Mz+1−xM′y+x(OH)2]a
wherein
As described hereinbefore, the present invention provides a process for preparing a layered-double hydroxide of formula (I) shown below:
[Mz+1−xM′y+x(OH)2]a
wherein
[Mz+1−xM′y+x(OH)2]a
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Organic solvents that are highly miscible with water (e.g. acetone and ethanol) are not used in the process of the invention.
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).
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.
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.
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.
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.
In an embodiment, b has a value according to the expression 0<b≤7.5. Suitably, b has a value according to the expression 0<b≤5. More suitably, b has a value according to the expression 0<b≤3. Most suitably, b has a value according to the expression 0<b≤1.5.
In an embodiment, c has a value according to the expression 0<c≤7.5. Suitably, c has a value according to the expression 0<c≤5. More suitably, c has a value according to the expression 0<c≤1. More suitably, c has a value according to the expression 0<c≤0.5. Most suitably, c has a value according to the expression 0<c≤0.35. The lower limit for c may be, for example, 0.001.
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.
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′mOn(OH)p−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.
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.
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.
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).
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:
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 Xn−, in the presence of a base being a source of OH− (e.g. NaOH, NH4OH, or a precursor for OH−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.
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.
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.
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.
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.
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.
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.
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.
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.
In step c), the slurry produced in step b) is maintained for a period of time. Suitably, the slurry is stirred during step c).
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.
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:
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).
Hence, step e) may comprise performing additional dispersion-maintaining-isolation cycles in order to remove residual water from the layered double hydroxide.
According to a further aspect of the invention, there is provided a process for preparing a layered-double hydroxide of formula (I) shown below:
[Mz+1−xM′y+x(OH)2]a
wherein
[Mz+1−xM′y+x(OH)2]a
It will be appreciated that M, M′, z, y, x, a, b, c and X can have any of those definitions appearing hereinbefore.
The AIM solvent may have any suitable hydrogen bond donor and/or acceptor groups. Hydrogen bond donor groups include R—OH, R—NH2, R2NH, whereas hydrogen bond acceptor groups include ROR, R2C═O RNO2, R2NO, R3N, ROH, RCF3, 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.
As described hereinbefore, the present invention also provides a layered double hydroxide of formula (I) shown below:
[Mz+1−xM′y+x(OH)2]a
wherein
The present invention also provides a layered double hydroxide of formula (I) obtainable, obtained or directly obtained by a process defined herein.
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.
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.
For the avoidance of doubt, the LDHs of the invention contain only those components (ions, anions, solvents, etc) recited in formula (I).
In an embodiment, b has a value according to the expression 0<b≤7.5. Suitably, b has a value according to the expression 0<b≤5. More suitably, b has a value according to the expression 0<b3. Most suitably, b has a value according to the expression 0<b≤1.5.
In an embodiment, c has a value according to the expression 0<c≤7.5. Suitably, c has a value according to the expression 0<c≤5. More suitably, c has a value according to the expression 0<c≤1. More suitably, c has a value according to the expression 0<c≤0.5. Most suitably, c has a value according to the expression 0<c≤0.35. The lower limit for c may be, for example, 0.001.
In an embodiment, the LDH has a BET surface area of at least 70 m2/g. Suitably, the LDH has a BET surface area of at least 180 m2/g. More suitably, the LDH has a BET surface area of at least 240 m2/g. Even more suitably, the LDH has a BET surface area of at least 275 m2/g. Most suitably, the LDH has a BET surface area of at least 300 m2/g. The high surface area of the LDHs makes them particularly attractive candidates for use as sorbents or support materials in catalytic applications.
In an embodiment, the layered double hydroxide has a BET pore volume of at least 0.5 cm3/g. Suitably, the layered double hydroxide has a BET pore volume of at least 0.75 cm3/g. More suitably, the layered double hydroxide has a BET pore volume of at least 0.9 cm3/g. The pore volume properties of the LDHs make them particularly attractive candidates for use in sorption technologies.
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 (V0) and after 1000 taps (Vt). The loose bulk and tap densities were calculated by: Loose bulk density=m/V0; Tap density=m/Vt. 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.
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.
According to a further aspect of the invention, there is provided a layered double hydroxide of formula (I) shown below:
[Mz+1−xM′y+x(OH)2]a
wherein
It will be appreciated that M, M′, z, y, x, a, b, c and X can have any of those definitions appearing hereinbefore.
The AIM-solvent may have any suitable hydrogen bond donor and/or acceptor groups. Hydrogen bond donor groups include R—OH, R—NH2, R2NH whereas hydrogen bond acceptor groups include ROR, R2C═O RNO2, R2NO, R3N, ROH, RCF3, where R represents a hydrocarbyl group of the AIM solvent.
Examples of the invention will now be described, for the purpose of illustration only, with reference to the accompanying figures, in which:
X-ray diffraction (XRD) patterns were recorded on a PANalytical X′Pert Pro instrument in reflection mode with Cu Ka radiation. The accelerating voltage was set at 40 kV with 40 mA current (λ=1.542°) at 0.01° s−1 from 1° to 70° with a slit size of ¼ degree.
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.
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.
Brunauer-Emmett-Teller (BET) specific surface areas were measured from the N2 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.
Brunauer-Emmett-Teller (BET) pore size distributions and pore volumes were calculated from the desorption isotherm.
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 H2O and AMO solvent content of the materials. Small variations in the H2O and acetone content was observed on repeat measurements.
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 (V0) and after 1000 taps (Vt). The loose bulk and tap densities were calculated by: Loose bulk density=m/V0; Tap density=m/Vt.
An aqueous solution (50 mL) of 0.80 M Mg(NO3)2.6H2O and 0.20 M of Al(NO3)3.9H2O was added drop-wise into a 50 mL of 0.5 M Na2CO3 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.
The various LDHs of the invention are identified in Tables 1-6 and
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.
The various comparator LDHs of the invention are identified in
Conventional LDH (“c-LDH”)
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(NO3)2.6H2O and 0.20 M of Al(NO3)3.9H2O was added drop-wise into a 50 mL of 0.5 M Na2CO3 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.).
The conventional LDH is denoted “water” in Tables 2-6 and
Table 1 below and
The various traces presented in
Table 2 below and
Having regard to Table 2 and
The mass loss data provided in Table 2 and
Table 4 below shows BET surface area properties for a variety of LDHs of the invention, as well as those for conventional LDH.
Table 5 below shows BET pore volume properties for a variety of LDHs of the invention, as well as those for conventional LDH.
Table 6 below provides density properties for a variety of LDHs of the invention, as well as those for conventional LDH.
LDHs of the invention (“AIM-LDHs”)
An aqueous solution (50 mL) of 0.80 M Mg(NO3)2.6H2O and 0.20 M of Al(NO3)3.9H2O was added drop-wise into a 50 mL of 0.5 M Na2CO3 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.
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.
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”)
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(NO3)2.6H2O and 0.20 M of Al(NO3)3.9H2O was added drop-wise into a 50 mL of 0.5 M Na2CO3 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.).
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:
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.
Table 8 below shows the water and solvent content of the various LDHs prepared in Example 6, as determined by elemental analysis.
Table 9 below shows cell data for various LDHs prepared in Example 6.
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.
For the ether AIM solvents having the general structure R1—O—R2, AIM-LDHs were prepared (according to the general protocol of Example 5) using the following solvents:
Table 10 below shows the water and solvent content of these ether AIM-LDHs, as determined by elemental analysis.
For the ketone AIM solvents having the general structure R1—C(O)—R2, AIM-LDHs were prepared (according to the general protocol of Example 5) using the following solvents:
Table 11 below shows the water and solvent content of these ketone AIM-LDHs, as determined by elemental analysis.
In the ether solvent series, it was found that the LDHs can totally be dispersed in most ether solvents.
In the ketone solvent series, it was found that the LDHs can totally be dispersed in the ketone solvents.
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.
Using the general protocol outlined in Example 5, a series of AIM-LDHs were prepared (AIM solvents—diisopropyl 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.
Table 12 below shows the water and solvent content of the AIM-LDHs used in this study, as determined by elemental analysis.
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.
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.
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.
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.
It will be appreciated that recycled AMO-solvent contains a quantity of water. Due to its miscibility with water, the AMO-solvent cannot—unlike AIM-solvents—be 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.
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.
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 solvents—1-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.
Table 14 below shows the water and solvent content of the AIM-LDHs used in this study, as determined by elemental analysis.
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:
An aqueous solution (100 mL) of 0.40 M Mg(NO3)2.6H2O, 0.10 M of Al(NO3)3.9H2O, 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.
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.
The XRD patterns shown in
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.
Table 15 below shows the water and solvent content of the comparative LDHs used in this study, as determined by elemental analysis.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1610663.5 | Jun 2016 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2017/051471 | 5/25/2017 | WO | 00 |
