Method of modifying an aluminosilicate by heating technique

Abstract

The present invention provides a method of modifying an aluminosilicate, using forced convective heating. The reaction conditions of this efficient method are mild, advantageously requiring less energy. The method yields a modified aluminosilicate having excellent textural and catalytic properties, to which the invention also relates, and which may beneficially be further transformed by impregnation with a metal.

Description

[0001] METHOD OF MODIFYING AN ALUMINOSILICATE BY HEATING TECHNIQUE

[0002] Field of the Invention

[0003] The present invention relates to a method of modifying an aluminosilicate, such as a zeolite, by forced convective heating. The method produces a modified aluminosilicate that is particularly suitable for use as a catalyst or an adsorbent surface, such as in a cracking process or in the treatment of exhaust gas.

[0004] Background

[0005] Solid catalysts such as aluminosilicates are used in heterogeneous catalysis, typically involving a cycle of molecular adsorption of a gas-phase reactant, followed by a reaction and then desorption, which occur at the catalyst surface.

[0006] Zeolites are crystalline aluminosilicates that possess well-defined porous systems of varying sizes and tuneable physicochemical properties. Due to these properties, zeolites are used extensively as solid catalysts in various refining and petrochemical industrial applications, such as cracking, alkylation of aromatics, reforming, dewaxing, isomerisation of xylenes, and the synthesis of various organic molecules.

[0007] Recently, attention has been devoted to the generation of zeolites with improved diffusional properties, either by the creation of wider porous structures or by decreasing the diffusional paths. This aids in reducing mass transfer constraints of reactants and products to and from the active centre, particularly when dealing with bulkier molecules. Additionally, it prevents undesired side reactions caused by the microporous channels of zeolite, which can lead to coking, catalyst deactivation and most significantly, the wastage of zeolite materials and energy. As a result, zeolites with such characteristics are appealing for many catalytic applications, e.g. Friedel-Crafts alkylation of arenes, cracking of plastics to liquid fuels, Fischer-Tropsch synthesis (FTS) process for the production of clean hydrocarbon fuels or chemicals from syngas, and direct oxidation of benzene to phenol.

[0008] Therefore, ongoing research and development efforts have been focused on improving the accessibility of the active sites within zeolite frameworks via the formation of ultra-large pore zeolites (ULP), zeolite nanocrystals with shorter diffusion paths and hierarchically modified zeolites with combined micro- and mesopores. However, the poor structural stability, loss of acidity and high synthesis cost of ULP zeolites have limited their practical applicability. Similarly, the synthesis of nanocrystal zeolites also faces many obstacles, since it involves the use of hazardous and costly templates, with serious implications to the environment [M. Usman Azam et al. (2023)]. On the other hand, hierarchical zeolites incorporate the benefits of multi-level porosity [S. Mitchell et al. (2015)]] that assist in the mobility of bulky molecules and decrease the probability for the catalyst to deactivate owing to the reduction of molecules retention time within the structure, while presenting comparable crystallinity and functionality to their parent counterparts [L. H. Chen et al. (2020)]. Hierarchical zeolites can be obtained either by bottom-up (soft or hard templating) or top-down methodologies (i.e. desilication or dealumination). Among all, the top-down technique based on the dealumination of zeolite is affordable and considered as a promising approach with practical applications [LH. Chen et al. (2020); P. Peng et al. (2020)]. It consists of a post-synthesis procedure, utilising organic or inorganic acids or through hydrothermal treatment with water vapour (steaming), where mesoporosity is generated by the elimination of aluminium, either framework and / or extra-framework species, from the zeolite [Z. Zhu et al. (2021 )].

[0009] Despite the significant advantages towards the affordability and formation of mesoporosity, removal of framework and / or extra-framework aluminium may be accompanied by a significant loss in the number of Bnansted and Lewis acid sites if dealumination conditions are not tightly controlled, which for some catalytic applications is not advantageous. Moreover, conventional dealumination methods, such as steaming or acid leaching, limit the sustainable properties of the resulting dealuminated zeolites, because steaming at high temperatures is generally an energy-intensive and time-consuming process (e.g. up to 500-600 °C for 5-6 hours), while acid leaching (e.g. using HCI and / or HNO3) significantly produces aqueous acidic wastes [S. Abdulridha et al. (2021 )].

[0010] Moreover, despite the harsh operating conditions, the steaming process may undergo channelling, which results in insufficient dealumination by just removing extra-framework aluminium species due to the formation of dense layers or surface blockage. This may also lead to limited access to active sites (i.e. strong acidic sites) and reduced catalytic performance.

[0011] Microwave-assisted methods to produce hierarchical Y zeolites have been investigated, but these require the addition of chelates to achieve the dealumination [S. Abdulridha et al. (2021 )].

[0012] Thus, it is desirable to optimise these methods to strike a balance between degree of dealumination and acidity with retained crystallinity, while ideally using chemistry that is more environmentally friendly.

[0013] The present invention has been devised in light of the above considerations.

[0014] Summary of the Invention

[0015] A first aspect of the invention is a method of modifying an aluminosilicate, the method comprising heating the aluminosilicate to produce a modified aluminosilicate, wherein the heating comprises forced convective heating for 0.5 to 5 hours at a temperature of at least 100 °C.

[0016] As is known in the art, an aluminosilicate is a material containing anionic Si-O-AI linkages. Thus, the aluminosilicate comprises at least silicon (Si), aluminium (Al) and oxygen (O). The aluminosilicate may be described as a solid catalyst. Suitably, the aluminosilicate is a crystalline aluminosilicate.

[0017] Forced convective heating refers to a type of heat transfer in which a fluid (e.g. a gas) is made to flow over a solid surface by an external source, such as a fan or pump. The force of the external source is applied to the fluid and increases the fluid’s flow rate. This type of heat transfer is different from natural convection, which occurs due to density differences in the fluid caused by temperature variations. Forced convection is typically more efficient than natural convection, because it allows for greater fluid flow and heat transfer control.

[0018] Suitably, the aluminosilicate is modified to impart a hierarchical structure. Unlike known techniques to achieve this, which require the use of strong acids or high-temperature steaming or the inclusion of additives, convective heating improves the process by circulating hot saturated air at a milder temperature and for a shorter run time, thus requiring less energy. While known techniques require large amounts of energy to heat essentially the whole of a vessel containing a solid catalyst sample, convective heating forces the hot air directly and uniformly over the solid catalyst, intensifying the process and beneficially providing a milder and more efficient way of modifying the solid catalyst in a controlled manner. The resultant modified aluminosilicate catalyst may have superior textural and catalytic properties, as described herein, with preserved structure crystallinity.

[0019] In some embodiments, heating the aluminosilicate causes dealumination of the aluminosilicate. By “dealumination”, it is meant that the aluminosilicate is chemically and structurally modified to remove from the framework a portion of the aluminium species that the aluminosilicate comprises, thus resulting in a modified aluminosilicate that has a hierarchical structure and typically modified catalytic properties. The removed aluminium may remain on the structure of the modified aluminosilicate, as so-called extraframework aluminium. Suitably, the hierarchical structure comprises micropores (pores having a diameter of less than 2 nm) and mesopores (pores having a diameter of from 2 to 50 nm).

[0020] In some embodiments, the aluminosilicate is a zeolite.

[0021] In some embodiments, the zeolite is selected from a faujasite, beta zeolite, ZSM-5 zeolite or HZSM-5 zeolite.

[0022] In some embodiments, the zeolite is a faujasite.

[0023] In some embodiments, the zeolite is faujasite type Y.

[0024] In some embodiments, the zeolite (such as faujasite, e.g. faujasite type Y) is a hydrogen form of zeolite.

[0025] The “Si / AI ratio” is a term of art used to describe the proportion of silicon species (i.e. atoms or ions) to aluminium species in a solid structure. This ratio is generally expressed as a single number, signifying the number of silicon species relative to a single aluminium species (e.g. if the proportion of Si species to Al species is 80:20, the “Si / AI ratio” is expressed as 4). Generally, the Si / AI ratio refers to the solid structure as a whole, considering all Si and Al atoms present, including framework and extra-framework positions (this may be alternatively denoted as the “global Si / AI ratio”). A “framework Si / AI ratio” may also be expressed, referring to the Si / AI ratio in the crystalline framework of the solid structure (e.g. of an aluminosilicate or a modified aluminosilicate).

[0026] In some embodiments, the aluminosilicate comprises silicon and aluminium in an Si / AI ratio or a framework Si / AI ratio of at least 1 , or at least 2, or at least 5, or at least 10, or at least 15, or at least 20, or at least 25, or at least 30, or at least 40, or at least 50. In some embodiment, the aluminosilicate comprises silicon and aluminium in an Si / AI ratio or a framework Si / AI ratio of at most 80, or at most 70, or at most 60, or at most 50, or at most 40, or at most 30, or at most 25, or at most 20, or at most 15, or at most 10.

[0027] In some embodiments, the aluminosilicate comprises silicon and aluminium in an Si / AI ratio or a framework Si / AI ratio of between 1 and 80. In some embodiments, the aluminosilicate comprises silicon and aluminium in an Si / AI ratio or a framework Si / AI ratio of between 50 and 80. In some embodiments, the aluminosilicate comprises silicon and aluminium in an Si / AI ratio or a framework Si / AI ratio of between 2 and 50. In some embodiments, the aluminosilicate comprises silicon and aluminium in an Si / AI ratio or a framework Si / AI ratio of between 2 and 40. In some embodiments, the aluminosilicate comprises silicon and aluminium in an Si / AI ratio or a framework Si / AI ratio of between 15 and 40. In some embodiments, the aluminosilicate comprises silicon and aluminium in an Si / AI ratio or a framework Si / AI ratio of between 2 and 10.

[0028] In some embodiments, the framework Si / AI ratio of the modified aluminosilicate is greater than the framework Si / AI ratio of the aluminosilicate (i.e. the aluminosilicate before modification).

[0029] In some embodiments, the framework Si / AI ratio of the modified aluminosilicate is at least 1 .05 times greater, or at least 1.20 times greater, or at least 1.50 times greater than the framework Si / AI ratio of the aluminosilicate before modification.

[0030] In some embodiments, the framework Si / AI ratio of the modified aluminosilicate is at least 2, or at least 4, or at least 10, or at least 20, or at least 30, or at least 40, or at least 50, or at least 60, or at least 80, or at least 100.

[0031] In some embodiments, the framework Si / AI ratio of the modified aluminosilicate is at least 20.

[0032] In some embodiments, the framework Si / AI ratio of the modified aluminosilicate is at least 30.

[0033] In some embodiment, the framework Si / AI ratio of the modified aluminosilicate is at most 160, or at most 140, or at most 120, or at most 100, or at most 80, or at most 60, or at most 50, or at most 40, or at most 30, or at most 20.

[0034] In some embodiments, the external surface area (Sext) of the modified aluminosilicate is greater than the Sext of the aluminosilicate before modification.

[0035] In some embodiments, the micropore volume (Vmicro) and / or the mesopore volume (Vmeso) in the modified aluminosilicate is greater than in the aluminosilicate before modification.

[0036] In some embodiments, the micropore volume (Vmicro) in the modified aluminosilicate is greater than in the aluminosilicate before modification.

[0037] In some embodiments, the mesopore volume (Vmeso) in the modified aluminosilicate is greater than in the aluminosilicate before modification.

[0038] In some embodiments, the micropore volume (Vmicro) and the mesopore volume (Vmeso) in the modified aluminosilicate are greater than in the aluminosilicate before modification. The micropore volume and / or mesopore volume affect the activity and performance of the modified aluminosilicate, and so these volumes may be approximately tailored depending on the intended end use of the modified aluminosilicate.

[0039] In some embodiments, the Vmicro in the modified aluminosilicate is at least 0.230 cm3g-1. In some embodiments, the Vmicro in the modified aluminosilicate is at least 0.240 cm3g-1. In some embodiments, the Vmicro in the modified aluminosilicate is at least 0.244 cm3g-1.

[0040] In some embodiments, the Vmicro in the modified aluminosilicate is at most 0.300 cm3g-1. In some embodiments, the Vmicro in the modified aluminosilicate is at most 0.280 cm3g-1. In some embodiments, the Vmicro in the modified aluminosilicate is at most 0.260 cm3g-1.

[0041] In some embodiments, the Vmicro in the modified aluminosilicate is from 0.240 to 0.260 cm3g-1.

[0042] In some embodiments, the Vmeso in the modified aluminosilicate is at least 0.240 cm3g-1. In some embodiments, the Vmeso in the modified aluminosilicate is at least 0.250 cm3g-1. In some embodiments, the Vmeso in the modified aluminosilicate is at least 0.260 cm3g-1.

[0043] In some embodiments, the Vmeso in the modified aluminosilicate is at most 0.320 cm3g-1. In some embodiments, the Vmeso in the modified aluminosilicate is at most 0.300 cm3g-1. In some embodiments, the Vmeso in the modified aluminosilicate is at most 0.280 cm3g-1.

[0044] In some embodiments, the Vmeso in the modified aluminosilicate is from 0.250 to 0.280 cm3g-1.

[0045] In some embodiments, the Vmicro in the modified aluminosilicate is from 0.240 to 0.260 cm3g-1and the Vmeso in the modified aluminosilicate is from 0.250 to 0.280 cm3g-1.

[0046] Suitably, the forced convective heating comprises or consists essentially of forced convective steaming. That is to say, in some embodiments, a fluid that takes part in the forced convective heating comprises or consists essentially of steam.

[0047] In some embodiments, the forced convective heating is conducted in a fan-assisted heater or fan- assisted oven, which may be a so-called “air fryer”.

[0048] In some embodiments, the forced convective heating is carried out for at least 0.5 hours, or at least 1 hour, or at least 1.5 hours, or at least 2 hours.

[0049] In some embodiments, the forced convective heating is carried out for at most 5 hours, or at most 4 hours, or at most 3 hours, or at most 2.5 hours, or at most 2 hours, or at most 1.5 hours.

[0050] In some embodiments, the forced convective heating is carried out for 0.5 to 5 hours, or 0.5 to 4 hours, or 0.5 to 3 hours, or 0.5 to 2.5 hours, or 0.5 to 2 hours, or 0.5 to 1.5 hours, or 1 to 5 hours, or 1 to 4 hours, or 1 to 3 hours, or 1 to 2.5 hours, or 1 to 2 hours, or 1 to 1.5 hours, or 1.5 to 5 hours, or 1.5 to 4 hours, or 1.5 to 3 hours, or 1.5 to 2.5 hours, or 1.5 to 2 hours, or 2 to 5 hours, or 2 to 4 hours, or 2 to 3 hours, or 2 to 2.5 hours.

[0051] In some embodiments, the forced convective heating is carried out for 0.5 to 5 hours.

[0052] In some embodiments, the forced convective heating is carried out for 0.5 to 2.5 hours. In some embodiments, the forced convective heating is carried out for 0.5 to 1.5 hours.

[0053] In some embodiments, the forced convective heating is carried out at a temperature of at least 100 °C, or at least 125 °C, or at least 150 °C, or at least 175 °C, or at least 200 °C.

[0054] In some embodiments, the forced convective heating is carried out at a temperature of at most 300 °C, or at most 275 °C, or at most 250 °C, or at most 225 °C, or at most 200 °C, or at most 175 °C, or at most 150 °C.

[0055] In some embodiments, the forced convective heating is carried out at a temperature of between 100 °C and 250 °C.

[0056] In some embodiments, the forced convective heating is carried out at a temperature of between 150 °C and 250 °C.

[0057] In some embodiments, the forced convective heating is carried out at a temperature of between 100 °C and 200 °C.

[0058] Varying the temperature and / or the time generally affects the extent of modification of the aluminosilicate. For example, where heating the aluminosilicate causes dealumination of the aluminosilicate, higher temperatures and longer times generally result in greater dealumination of the aluminosilicate. In order to achieve a particular degree of dealumination, the parameters of temperature and time are essentially inversely proportional to each other - that is to say, if the temperature is increased then the time may be decreased to achieve a particular degree of dealumination (and vice versa). Meanwhile, a greater degree of dealumination may be achieved by increasing the temperature while keeping the time constant, or by increasing the time while keeping the temperature constant.

[0059] The temperature and / or the time may be selected according to several factors, including the Si / AI ratio of the aluminosilicate. For instance, an aluminosilicate having a relatively high Si / AI ratio may require forced convective heating at a higher temperature and / or for a greater amount of time, because such aluminosilicates are generally more difficult to dealuminate (due to the lower Al content). Conversely, an aluminosilicate having a relatively low Si / AI ratio may undergo forced convective heating at a lower temperature and / or for a lower amount of time, because such aluminosilicates are generally easier to dealuminate (due to the greater Al content).

[0060] For example, an aluminosilicate having an Si / AI ratio of at most 20 may undergo forced convective heating at a temperature of at most 200 °C (such as at most 175 °C or at most 150 °C) and / or for a time of at most 1.5 hours. Meanwhile, an aluminosilicate having an Si / AI ratio of at least 50 may undergo forced convective heating at a temperature of at least 200 °C (such as at most 300 °C or at most 275 °C) and / or for a time of at least 1.5 hours (such as at most 5 hours, or at most 3 hours).

[0061] The heating by forced convective heating is a step of the method of the invention.

[0062] In some embodiments, the method comprises one step of heating the aluminosilicate by forced convective heating. In other embodiments, the method comprises two or more steps (such as two, three or four) of heating the aluminosilicate by forced convective heating. These multiple steps effectively represent multiple cycles of modification (e.g. dealumination). The multiple steps may be carried out at the same temperature and / or time, or at different temperatures and / or times. Multiple steps may be preferred for aluminosilicates having a relatively high Si / AI ratio (e.g. at least 50).

[0063] The method may further comprise a step of impregnating the modified aluminosilicate with a metal to produce a metal-impregnated modified aluminosilicate.

[0064] Such impregnation may improve the overall activity of the catalyst. For example, a metal-impregnated modified aluminosilicate may beneficially be multifunctional. The added metal may result in a catalyst having multiple active sites. For instance, the metal-impregnated modified aluminosilicate may be bifunctional and have two active sites, such as one for cracking and one for hydrogenation / dehydrogenation.

[0065] In some embodiments, the step of impregnating the modified aluminosilicate with the metal comprises adding to the modified aluminosilicate an aqueous solution comprising the metal, optionally followed by drying, optionally followed by calcining.

[0066] In some embodiments, the step of impregnating the modified aluminosilicate with the metal comprises adding to the modified aluminosilicate an aqueous solution comprising the metal, and then drying and calcining.

[0067] In some embodiments, the metal-impregnated modified aluminosilicate comprises at least 1 wt%, or at least 2 wt%, or at least 3 wt%, or at least 4 wt%, or at least 5 wt% of the metal.

[0068] In some embodiments, the metal-impregnated modified aluminosilicate comprises at most 20 wt%, or at most 18 wt%, or at most 16 wt%, or at most 14 wt%, or at most 12 wt%, or at most 10 wt%, or at most 8 wt% of the metal.

[0069] In some embodiments, the metal-impregnated modified aluminosilicate comprises from 2 to 10 wt% of the metal.

[0070] In some embodiments, the metal-impregnated modified aluminosilicate comprises about 5 wt% of the metal.

[0071] Suitably, the metal is not aluminium.

[0072] In some embodiments, the metal is selected from nickel, palladium, platinum and ruthenium.

[0073] In some embodiments, the metal is nickel. Hence, in these embodiments, metal-impregnated modified aluminosilicate is a Ni-impregnated modified aluminosilicate. As described herein, it is found that nickel improves the overall activity of a zeolite catalyst, which consequently has two active sites: one active site for cracking originating from the modified zeolite structure, and another active site for (de)hydrogenation originating from the nickel. A second aspect of the invention provides a modified aluminosilicate produced by the method of the first aspect, or a metal-impregnated modified aluminosilicate produced by the method of the first aspect.

[0074] A third aspect of the invention provides use of the modified aluminosilicate or the metal-impregnated modified aluminosilicate of the second aspect as a catalyst or an adsorbent surface.

[0075] For example, the modified aluminosilicate or the metal-impregnated modified aluminosilicate may be used as a catalyst or an adsorbent surface in a cracking process (including a hydrocracking or fluid catalytic cracking process), in the treatment of exhaust gas, in the treatment of waste water, in molecular sieves, or in a chemical sensor. Furthermore, the modified aluminosilicate or the metal-impregnated modified aluminosilicate may be used in oil refineries, in biomedical applications, in cation exchange applications, as well as other adsorption and separation processes.

[0076] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided. Preferred features mentioned in relation to the first aspect of the invention may apply equally to the other aspects.

[0077] Summary of the Figures

[0078] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0079] Figure 1 depicts a scheme showing dealumination of zeolite through traditional steaming;

[0080] Figure 2 depicts a scheme showing dealumination of zeolite through forced convective heating;

[0081] Figure 3 depicts a graph showing product selectivity based on carbon number of n-heptane soluble liquid obtained by hydrocracking;

[0082] Figure 4 shows an impact assessment of different dealumination techniques on global warming (in graph (a)) and on freshwater aquatic ecotoxicity (in graph (b)).

[0083] Detailed Description of the Invention

[0084] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0085] In the following examples, faujasite (FAU) type Y zeolite is utilised as a benchmark catalyst because of its industrial application in petroleum refineries for fluid catalytic cracking (FCC) and hydrocracking. Dealumination

[0086] Dealumination of the type Y zeolite was carried out by forced convective steaming and compared to a conventional dealumination procedure.

[0087] The conventional dealumination of a parent type Y zeolite involved hierarchical modification through traditional steaming. Specifically, a commercial HY zeolite (hydrogen form, Si / AI —30, available from Alfa Aesar) was calcined at 500 °C for 4 hours in a tube furnace under a 100 mL / min continuous flow of compressed air saturated with water, as shown in the scheme depicted in Figure 1. The resultant (comparative) modified aluminosilicate solid catalyst is denoted as “DAHY-S”.

[0088] Meanwhile, in the forced convective steaming process, the commercial HY zeolite was added to a crucible and placed in a heater equipped with a convective fan, which generated saturated hot air under operation. The bottom side of the heater was charged with DI water (2 g / g catalyst) and the vessel was operated a 200 °C for 1 hour. The generation of steam at the high flow of air resulted in the controlled dealumination of the zeolite. A scheme of this process is shown in Figure 2. The resultant (inventive) modified aluminosilicate solid catalyst is denoted as “DAHY-CS”.

[0089] As shown in Table 1 below, for DAHY-S, despite the intense steaming of the zeolite starting material at higher temperatures and for a considerable amount of time, only a small quantity of EFAI (extraframework aluminium species) were eliminated from the structure. In contrast, for DAHY-CS, the forced convective steaming managed to remove aluminium from the framework, even at milder reaction conditions.

[0090] As a result, the forced convection technique appears to be more efficient in achieving similar or even superior textural properties (i.e. assuming the EFAI would have been removed), especially considering the elevated Si / AI ratio of the zeolite. This technique has the potential to achieve significant dealumination of zeolites with high Si / AI ratios without the use of harsh reaction conditions or solvent-based procedures. Furthermore, given the higher removal of aluminium from the framework, the convection sample is expected to have a smaller number of Bnansted acid sites but higher acidity strength.

[0091] Table 1 - Physicochemical properties of the zeolite samples Table 1 compares physicochemical properties of the HY aluminosilicate, the comparative modified aluminosilicate DAHY-S and the inventive modified aluminosilicate DAHY-CS.

[0092] Crystallinity is estimated from XRD data by comparison of the peaks area for 2 theta range from 5° to 30° of dealuminated zeolite samples to that of the parent zeolite. X-Ray diffraction (XRD) patterns of calcined samples were obtained from a PANalytical X'Pert X-ray Powder diffractometer (PIXcel 1 D detector) with Cu Ka radiation with a step size of 0.047s and operating at 40 kV and 40 mA. Based on the area under the peaks, the relative intensities of the powdered samples were compared to that of the parent HY zeolite. Additionally, NaCI was used as an internal standard to locate the exact diffraction positions, and Bragg’s Law was used to calculate the unit cell parameter (ao) of the pristine and various dealuminated HY zeolites.

[0093] Si / AI ratio is calculated using Global Si / AI determined from elemental analysis (ICP-OES). Si / Ahv denotes the framework Si / AI ratio, calculated from the unit cell parameter using the Breck-Flanigen equation [see W. Lutz (2014)]. FAI and EFAI denote framework aluminium species and extra-framework aluminium species respectively.

[0094] Sext denotes external surface area. Vmicro and Vmeso denote micropore volume and mesopore volume respectively. The textural properties of the calcined zeolite samples were measured by IXL-physisorption in a Tristar-3000 apparatus (Micromeritics) at -196 °C. Before the adsorption, for the fresh catalyst, a calculated amount of sample was degassed at 350 °C for 6 h under N2. The spent catalysts were degassed at 120 °C for 2 h to avoid any removal of coke. The total pore volume (Vtotai) was estimated from the amount of N2 adsorbed at a relative pressure (P / Po) of 0.97, while the microporosity (Vmicro) and external surface area (Sext) were computed using the t-plot method. The difference between Vtotai and Vmicro was USed to calculate Vmeso.

[0095] Metal impregnation

[0096] Metal-impregnated modified aluminosilicates were prepared by incipient wetness impregnation using 5 wt% of nickel [see M. Usman Azam et al. (2023)]. A calculated volume of an aqueous solution of the metal precursor (nickel nitrate hexahydrate) was added dropwise to the dried HY zeolite support. The Ni- impregnated zeolite samples were calcined at 500 °C for 6 h under dry airflow of 60 ml min-1g-1after being dried at 100 °C for 12 h in an oven.

[0097] The Ni-loaded samples were denoted as “Ni-DAHY-S” (5% Ni-impregnated dealuminated Y zeolite through conventional steaming), and “Ni-DAHY-CS” (5% Ni impregnated dealuminated Y zeolite through forced convective steaming).

[0098] Both Ni-loaded dealuminated Y zeolites were compared for the hydrocracking of virgin high density polyethylene (HDPE) at different reaction temperatures (275-400 °C), 20 bar initial cold H2 pressure for 60 min residence time. As shown in Table 2 below, inventive Ni-DAHY-CS showed better conversion even at lower temperature (i.e. 275 °C) and achieved -99% cracking at 350 °C with better selectivity of lighter oils. On the other hand, comparative Ni-DAHY-S showed lower cracking ability at 275 °C and required a higher temperature (i.e. 375 °C) to crack HDPE with comparable overall product distribution. This shows the better cracking ability of Ni-DAHY-CS, which may be related to the higher acidity strength.

[0099] Table 2 - Performance comparison and product distribution of catalytic hydrocracking of HDPE, using different Ni-loaded dealuminated catalysts at different reaction temperatures

[0100] Moreover, Figure 3 shows the effect of reaction temperature on the product distribution of lighter oils. Specifically, the graph of Figure 3 depicts product selectivity based on carbon number of the n-heptane soluble liquids obtained by the hydrocracking of virgin HDPE in a 300 ml_ autoclave reactor, 20 bar initial cold H2 pressure, feed to catalyst ratio of 20:1 (by weight) for 60 min residence time at different reaction temperatures.

[0101] Both Ni-loaded dealuminated Y zeolite samples show good selectivity for gasoline range fuels (i.e. C5- C12) even at 325 °C. However, Ni-DAHY-CS has higher selectivity for lighter gasoline range products (i.e. Cs-Cs), whereas Ni-DAHY-S shows significant affinity towards diesel (C13-C18) and higher hydrocarbons (C19+), even at higher reaction temperatures. This could be due to the effective cracking ability of Ni-DAHY-CS, which is believed to be due to the higher acidity strength of the catalyst.

[0102] Similarly, calculations based on kinetic parameters were made, i.e. activation energy (EA) and frequency factor (A) at different reaction temperatures (i.e. 275 to 375 °C) and with distinct specific rate constant (k). In the case of Ni-DAHY-S, the obtained values of k were 4.10*10“3, 3.23*10“2, 5.21 *10“2, 7.68*10“2; whereas Ni-DAHY-CS showed specific rate constant values of 9.16*10-3, 4.89*10-2, 8.15*10-2, 1.04*10-1at different reaction temperatures. By simply plotting the graph between In k and 1 / T, and by using straight-line equation, Ni-DAHY-S shows an activation energy of 88 kJ / mol, whereas Ni-DAHY-CS requires an energy of 74 kJ / mol. This shows the surprising and beneficial cracking advantage of forced convective steamed dealuminated zeolite over traditional steamed zeolite.

[0103] The hydrocracking experiments were performed in a 300 ml_ cylindrical Parr reactor (Series 4560 mini reactors). The feed of catalyst and virgin HDPE pellets (MW 155,000 g / mol, melting point 140 °C, density 0.95 g / cm3, obtained from Sigma-Aldrich) were completely dried in an oven at 100 °C for 2 h before being used in the reactor. Afterwards, a known quantity of feed (5 g) and catalyst (20:1, g / g) were introduced in a glass liner, and the reactor vessel was tightly closed. The reactor was purged with nitrogen (3 times) followed by hydrogen (3 times), and the system was checked for any leaks. A desired initial H2 pressure (10-30 bar) and a temperature setpoint (275, 325, 350, 375 and 400 °C) were given to the reactor. When the temperature reached 225 °C, the agitator was set at 500 rpm. This is to ensure that HDPE (melting point 140 °C) melts completely before being mixed with the catalyst. The reaction time was initiated when the temperature reached the desired setpoint. The reaction was run for 45 min and / or 1 h and then the agitation and heating were turned off. The reactor was placed in an ice bath for cooling down. After that, gaseous products were collected from the gas release valve, whereas liquids and solids were collected from the reaction vessel.

[0104] The liquid and solid reaction products were collected from the reactor using a solvent extraction approach. A known quantity of n-heptane was added to the reaction vessel containing the liquids and solids. The lighter liquid products, identified as "lighter oils", were extracted using n-heptane, and the “heavier oils” were dissolved in tetra hydrofuran (THF). The total fraction of lighter and heavier oils is categorised as liquids. Any remaining insoluble part was completely dried and referred to as solids.

[0105] The n-heptane fraction of oils was analysed by GC analysis using an Agilent DB-1 capillary column of 50 m length and a flame ionisation detector (FID). In detail, a known quantity of lighter oils was combined with a known quantity of n-heptane as an internal standard and analysed by gas chromatography. The chromatograph was calibrated using in-house prepared standards of hydrocarbons (C5-C20).

[0106] The overall conversion (C) of different products were calculated using the following equation:

[0107] The selectivity of the products was calculated using the following equation: Yi

[0108] % St = - x 100

[0109] C is the conversion, mHDPEis the mass of feed, S and Y correspond to the selectivity and y ield% of / thproduct respectively (i.e. , / represents the gaseous / oils or heavier oils). Table 3 - Inventory data for the modification of dealuminated Y zeolites

[0110] Moreover, the environment profiles of different modification methods for the dealuminated Y zeolite samples were studied using a simple life-cycle assessment, as per ISO standards and systems. The primary goal of this assessment is to determine the environmental impacts associated with the hierarchical modification of Y zeolites with a functional unit of 1 g of each catalyst. The inputs related to energy utilisation and different materials used calculated based on laboratory studies and the LCI (lifecycle inventory) data are shown in Table 3 above.

[0111] Overall, DAHY-CS shows the lowest environmental impact (0.56 kg CO2 eq. / FU) because of the minimum utilisation of resources (i.e. electricity), whereas DAHY-S shows an impact of 4.84 kg CO2 eq. / FU. This global warming GWPIOOa comparison is shown in graph (a) in Figure 4.

[0112] A similar trend was seen over freshwater aquatic ecotoxicity (FWAE), as shown in graph (b) in Figure 4. Namely, DAHY-CS shows a lower impact (i.e. 0.12 kg 1 ,4-DB eq.), while DAHY-S reveals a 34-fold higher impact (4.12 kg 1,4-DB eq.) due to significant utilisation of resources (i.e. electricity and water).

[0113] These results highlight the importance of the catalysts of the invention with regard to sustainability principles and minimising environmental impacts. As such, the potential of forced convective heating for the modification of aluminosilicate catalysts provides an opportunity to develop innovative processes for producing hierarchical modified aluminosilicate catalysts that are highly energy-efficient with the least environmental impacts and significant relevance on an industrial scale.

[0114] The catalysts are suitable for a range of adsorption and separation processes. The catalysts may be used in petroleum industries including in oil refineries, such as for cracking (e.g. hydrocracking or fluid catalytic cracking) of heavy hydrocarbons to produce valuable fuels and petrochemical feedstocks. In particular, plastics are difficult to recycle due to their bulky and complex chain molecular structure, but the catalysts of the invention can be used to crack long-chain polymers into value-added chemicals.

[0115] The catalysts may also be used in the automotive industry for catalytic exhaust gas treatment, as well as in fine chemicals and pharmaceuticals. Further and specific applications include use in the treatment of waste water (and other environmental remediation treatments to remove heavy metals, etc.), in molecular sieves, in cation exchange applications, in chemical sensors, and in biomedical applications.

[0116] The features disclosed in the foregoing description, or in the following claims, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0117] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0118] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0119] Any section headings used herein are for organisational purposes only and are not to be construed as limiting the subject matter described.

[0120] Throughout this specification, including the claims which follow, unless the context requires otherwise, the words “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0121] It must be noted that, as used in the specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about”, it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means, for example, + / - 10%.

[0122] References

[0123] A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of these references is incorporated herein.

[0124] M. Usman Azam et al., Hydrocracking of surgical face masks over Y Zeolites: Catalyst development, process design and life cycle assessment, Fuel, (2023), 349, 128704. https: / / doi.Org / 10.1016 / J. FUEL.2023.128704

[0125] S. Mitchell et al., Structural analysis of hierarchically organized zeolites, Nat. Commun. (2015), 6, 8633. https: / / doi.Org / 10.1038 / ncomms9633 L. H. Chen et al., Hierarchically structured zeolites: From design to application, Chem. Rev. (2020), 120, 11194. https: / / doi.org / 10.1021 / acs.chemrev.0c00016

[0126] P. Peng et al., Diffusion and catalyst efficiency in hierarchical zeolite catalysts, Natl. Sci. Rev. (2020), 7, 1726. https: / / doi.org / 10.1093 / nsr / nwaa184

[0127] Z. Zhu et al., Insight into tri-coordinated aluminum dependent catalytic properties of dealuminated Y zeolites in oxidative desulfurization, Appl Catal. B. (2021 ), 288, 120022. https: / / doi.Org / 10.1016 / J. APCATB.2021 .120022

[0128] S. Abdulridha et al., An efficient microwave-assisted chelation (MWAC) post-synthetic modification method to produce hierarchical Y zeolites, Microporous and Mesoporous Materials (2021), 311, 110715. https: / / doi.Org / 10.1016 / J.MICROMESO.2020.110715 W. Lutz, Zeolite Y: synthesis, modification, and properties - a case revisited, Adv. Mater. Sci. Eng. (2014), article ID 724248. https: / / doi.org / 10.1155 / 2014 / 724248

Claims

Claims:

1. A method of modifying an aluminosilicate, the method comprising heating the aluminosilicate to produce a modified aluminosilicate, wherein the heating comprises forced convective heating for 0.5 to 5 hours at a temperature of at least 100 °C.

2. The method of claim 1, wherein heating the aluminosilicate causes dealumination of the aluminosilicate.

3. The method of either claim 1 or claim 2, wherein the aluminosilicate is a crystalline aluminosilicate.

4. The method of claim 3, wherein the aluminosilicate is a zeolite.

5. The method of claim 4, wherein the zeolite is selected from a faujasite, beta zeolite, ZSM-5 zeolite or HZSM-5 zeolite.

6. The method of claim 5, wherein the zeolite is a faujasite.

7. The method of claim 6, wherein the zeolite is faujasite type Y.

8. The method of any one of claims 1 to 7, wherein the aluminosilicate comprises silicon and aluminium in an Si / Al ratio of between 15 and 40.

9. The method of any one of claims 1 to 8, wherein the framework Si / AI ratio of the modified aluminosilicate is greater than the framework Si / AI ratio of the aluminosilicate before modification.

10. The method of any one of claims 1 to 9, wherein the micropore volume (Vmicro) and / or the mesopore volume (Vmeso) in the modified aluminosilicate is greater than in the aluminosilicate before modification.

11. The method of any one of claims 1 to 10, wherein the micropore volume (Vmicro) in the modified aluminosilicate is from 0.240 to 0.260 cm3g-1.

12. The method of any one of claims 1 to 11 , wherein the mesopore volume (Vmeso) in the modified aluminosilicate is from 0.250 to 0.280 cm3g-1.

13. The method of any one of claims 1 to 12, wherein the forced convective heating comprises forced convective steaming.

14. The method of any one of claims 1 to 13, wherein the forced convective heating is carried out for 0.5 to 5 hours.

15. The method of any one of claims 1 to 14, wherein the forced convective heating is carried out at a temperature of between 100 °C and 250 °C.

16. The method of any one of claims 1 to 15, further comprising a step of impregnating the modified aluminosilicate with a metal to produce a metal-impregnated modified aluminosilicate.

17. The method of claim 16, wherein the step of impregnating the modified aluminosilicate with the metal comprises adding to the modified aluminosilicate an aqueous solution comprising the metal, and then drying and calcining.

18. The method of either claim 16 or claim 17, wherein the metal-impregnated modified aluminosilicate comprises from 2 to 10 wt% of the metal.

19. The method of any one of claims 16 to 18, wherein the metal is selected from nickel, palladium, platinum and ruthenium.

20. The method of claim 19, wherein the metal is nickel.

21. A modified aluminosilicate produced by the method of any one of claims 1 to 15.

22. A metal-impregnated modified aluminosilicate produced by the method of any one of claims 16 to 20.

23. Use of the modified aluminosilicate of claim 21 or the metal-impregnated modified aluminosilicate of claim 22 as a catalyst or an adsorbent surface, optionally in a cracking process, in the treatment of exhaust gas, in the treatment of waste water, in molecular sieves, or in a chemical sensor.

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