Process and apparatus

Abstract

A process for the removal of a particulate catalyst from a packed catalyst bed within a process channel of a reactor, the process comprising directing at least one gas stream into open proximal ends of an array of process channels in order to create a pressure differential between neighbouring process channels, the pressure differential creating temporary deformation of the process channel walls such that at least some of the particulate catalyst is dislodged from the packed catalyst bed. Preferably the pressure differential is create by providing a gas stream into a first process channel at a rate and / or orientation different from that provided into a neighbouring process channel. Preferably the temporary deformation comprises oscillations and / or vibrations of the process channel wall.

Description

The present invention concerns a process for the removal of spent catalyst from a reactor. The invention is particularly but not exclusively concerned with a process for the removal of spent Fischer-Tropsch catalyst from process channels of a Fischer-Tropsch reactor. The Fischer-Tropsch process is widely used to generate fuels from carbon monoxide and hydrogen and can be represented by the equation: (2n + 1)H2 + nCO —> CnH2n+2 + nH2O This reaction is highly exothermic and is catalysed by a Fischer-Tropsch catalyst, typically a cobalt or iron based catalyst, under conditions of elevated temperature (typically at least 180°C, e.g. 200°C or above) and pressure (e.g. at least 10 bar). A product mixture is obtained, and n typically encompasses a range from 1 to about 90. It is desirable to maximise the conversion of carbon monoxide. Preferably at least about 70% w / w of the product mixture is distributed between n=10 and n=30. The hydrogen and carbon monoxide feedstock is normally synthesis gas. During the Fischer-Tropsch reaction, the catalyst is gradually degraded, decreasing its effectiveness and requiring a gradual increase in temperature to maintain acceptable carbon monoxide conversion. This is described in Steynberg et al “Fischer-Tropsch catalyst deactivation in commercial microchannel reactor operation” Catalysis Today 299 (2018) pp10-13. For a period of time it is possible to regenerate the catalyst periodically, which can be done in situ by for example subjecting the catalyst to de-waxing, oxidation and reduction processes, for example as described in WO2020249529. However, there comes a point in the lifetime of the catalyst at which the accumulation of non-regenerable poisons such as sulfur and other non-regenerable deactivation mechanisms such as sintering cause the catalyst to become unviable. At this point the catalyst must be discharged from the reactor and replaced with fresh catalyst. Removing spent catalyst from an operated pressure vessel is known in the art. US3916960 describes a catalyst unloader apparatus and method for unloading flowable particle catalyst from reactor tubes. The unloader apparatus forms a reference pressure area in a head adjacent an open end of the reactor tubes to provide a pressure differential for flowing the catalyst from the tubes to the head. It is also known from US2009252658 to remove spent catalyst from a Fischer-Tropsch reactor by placing an ultrasound-producing head in sonic contact with the channels and applying ultrasonic energy to the channels. However this method also has certain practical disadvantages. In particular, existing ultrasonic equipment and techniques have been found to remove spent catalyst too slowly and / or incompletely, particularly when trying to remove spent catalyst that is tightly held in small cavities. WO2021207622 describes the removal of spent catalyst from process channels by passing a high velocity air stream from an air knife. The air knife directs a high velocity stream via a continuous slot to deliver a uniform air curtain into the process channels. The simultaneous use of multiple slots is also suggested. However this method also creates practical disadvantages. For example, the pressure distribution provided by the continuous air slot creates pressure fluctuations that are not controlled. Such behaviour reduces the method’s efficacy. None of the above arrangements provide a sufficiently rapid, efficient removal capability for spent catalyst from a process channel, in particular when catalyst is packed within a tight cavity. Therefore, there remains a need for an improved process for the removal of catalyst located in packed bed which is efficient effective, and easy to employ. Accordingly, in one aspect, the present invention provides a process for the removal of a particulate catalyst from a packed catalyst bed within a process channel of a reactor, the process comprising: directing at least one gas stream into open proximal ends of an array of process channels effective to create a pressure differential between neighbouring process channels, the pressure differential creating temporary deformation of the process channel walls such that at least some of the particulate catalyst is dislodged from the catalyst bed. The skilled person would understand that the term “array” means that a multiplicity of process channels are present i.e., at least two process channels are present. The pressure differential may be created by ensuring that the gas stream influx into one process channel is provided at a rate and / or orientation different from that or those of the simultaneous gas stream influx into a neighboring process channel. This may be achieved for example by the provision of discrete and / or rotating gas streams juxtaposed or otherwise adapted differently at any given moment with respect the to process channel and its neighbour. The “proximal end” of the process channel is to be understood as the end at which the gas stream is directed into and is the open end of the cavity defined by the process channel walls. It is to be understood that process channels are arranged in such a way that they comprise an open proximal end and that the open proximal end is to be taken as the open end of the cavity of a process channel. The “distal end” is the opposite end, which optionally may be blocked by airtight sealing. The inventors have found that the process according to the present invention provides effective catalyst discharge from cavities in process channels, in particular tight cavities. Various methods of the art use a high-pressure gas stream to remove catalyst from tight cavities which, in turn, makes the discharge process less reliable and efficient. Such high pressures are not required for the process according to the present invention. Therefore, the process according to the present invention provides a more-effective and controlled process to remove catalyst particles. The inventors have found that the process according to the present invention can induce pressure differentials between neighbouring process channel cavities in a controlled and purposefully ordered manner, in contrast to conventional methods in the art. Additionally, it has been found that a gas stream, for example a high velocity air jet, provides high frequency oscillations when it is discharged from a smaller opening into a larger area. These oscillations may impinge onto a set of process channel cavities filled or partially filled with catalyst particles. These oscillations may be described as naturally occurring oscillations. The oscillations provided by the air jet, or subsequent vibrations from the process channel wall, have been found to induce pressure fluctuations within the process channel cavities. The inventors have additionally found that the channel cavity oscillation can be further controlled by adding targeted structural rigidity to specific regions of the array of process channels. Structural rigidity can be added to the susceptible channels in a variety of manners, including but not limited to, blocking some channels so that they remain full of catalyst while other process channels are discharged, inserting a structurally rigid tool into channels that are more susceptible to movement, and creating thicker, more rigid geometry in some channels. Therefore, the process according to the invention may further comprise adding a structural rigid means to at least one process channel in the array of process channels. The insertion of the structural rigid means may be temporary (i.e., reversible) such that the structural rigid means may be added to at least one process channel in the array of process channels whilst particulate catalyst and / or other particulate material is dislodged from the catalyst bed. The structural rigid means may be added to control the order and effectiveness at which the particulate catalyst is removed from the packed catalyst bed. The structural rigid means may be positioned inside at least one process channel or on top of at least one process channel (i.e., covering an open proximal end) or on the outside of the process channel, or a combination thereof (i.e., on top and on the outside of the process channel). After the desired particulate catalyst has been dislodged, the structural rigid means may be removed. Therefore, the inventors have beneficially found that the removal of particulate catalyst can be controlled without any significant reconstruction required. The structural rigid means may block the open proximal end of at least one process channel in the array of process channels. The inventors have advantageously found that this arrangement controls the dislodgment of particulate catalyst from other process channels whilst the blocked process channel remains full of catalyst. This determines the facilitation in the order of which spent catalyst is removed from the backed catalyst bed. The structural rigid means may comprise means to increase the thickness of at least one of the process channel walls in the array of process channels or means to alter the geometry of the process channel. Therefore, the structural rigid means may be configured to increase the thickness and / or alter the geometry of the at least one process channel in the array of process channels. This is particularly used for process channels that may be more susceptible to movement. Accordingly, in some embodiments at least one process channel in the array of process channels may comprise a structural rigid means. Typically the particulate catalyst being removed in the process of the present invention is a spent catalyst. Alternatively, the particulate catalyst being removed from the reactor may be a fresh catalyst. The skilled person would understand that the particulate catalyst being removed from the reactor may comprise at least some spent catalyst and / or some particulate and / or inert material, or combinations thereof. The process channels may for example be in the form of a waveform corrugation situated within the process layers of a reactor which effectively divides the process layers into linear arrays of process channels. The process channels may therefore comprise a convex side and a concave side. In some embodiments, the process channels may be microchannels. The array of process channels may be a linear array. Alternatively, the array of process channels may be a non-linear array, for example, a triangular or square pitch pattern, a staggered pitch pattern, a V-shaped pattern or in a monolith. The use of at least one gas stream, most preferably discrete gas streams, has been found to be advantageous compared to alternative arrangements in the art, for example arrangements that supply a gas stream via a continuous opening or slot, due to an increase in the control of the pressure that is applied to the process channel walls. Embodiments of the art that use an air knife arrangement with a continuous slot cannot sufficiently control pressure fluctuations that occur, thereby decreasing the process efficacy, in particular when there is a high flow rate. The at least one gas streams of the invention create a pressure differential between neighbouring process channels. The inventors have advantageously found that the controlled orientation and flow rate of at least one gas stream, for example discrete gas streams, provides the necessary ordered pressure oscillations required to create temporary deformation of the process channel walls to facilitate catalyst removal. Therefore, the method according to the present invention is more effective at removing spent catalyst and / or fresh catalyst and / or inert material and reduces the likelihood of undesired pressure fluctuations applied elsewhere within the reactor. Furthermore modulating the gas stream, for example as a result of pulsing, can achieve a wide range of frequencies and pressure differentials between neighbouring process channel cavities, therefore the pressure can easily be controlled and modified depending on the catalyst required to be removed. The process channel walls of the present invention have the ability to temporarily deform, thereby aiding the removal of the catalyst from the process channel. In particular, the process channel walls have a degree of flexibility that can create the necessary movement and vibrations between the process channel walls and / or the catalyst particles to promote dislodgement. While temporary deformation is important to facilitate the removal of catalyst, particularly when the catalyst is packed inside tight, small cavities, the process channel wall should return to its original position and maintain its original strength after dislodgement occurs. The term “temporary deformation” is to be understood such that any stress or movement that the cavity or channel wall experiences is highly reversible. Therefore, the cavity or channel walls will return to their original position and maintain their necessary design strength. The inventors have advantageously found that the creation of a pressure differential between neighbouring process channels, in combination with temporary deformation of the process channel walls, improves catalyst discharge, in particular catalyst discharge efficiency from narrow cavities. The process channel walls may experience a varying degree of deformation dependent on the depth of the channel and the order, flow rate, and / or orientation of at least one gas stream. For example, the process channel wall closest to the process channel cavity opening may experience a higher degree of fluctuation compared to the process channel wall situated towards the opposite end of the cavity opening. Without wishing to be bound by theory, it is believed that the pressure differential created between neighbouring process channels encourage movement of the process channel wall (ie. temporary deformation) which is effective to dislodge catalyst efficiently. The temporary deformation of the process channel walls may comprise oscillations and / or vibrations of the process channel wall. This is advantageous because the oscillations and / or vibrations of the process channel wall has been found to result in varying forces being applied onto neighbouring process channel walls to facilitate catalyst removal, whilst also controlling the pressure differential. The inventors have surprisingly found that the process according to the present invention can effectively dislodge catalyst through the temporary deformation of process channel walls as a result of the differential pressure created across neighbouring cavities. Accordingly, extremely high air flow, for example supersonic air flow, is not necessary in the process according to the present invention. This is advantageous because the gas stream pressure may be controlled in a manner which creates a more ordered and effective means of dislodging catalyst, thereby reducing the likelihood of undesired pressure fluctuations elsewhere in the reactor. It is thought that the mechanism of spent catalyst dislodgement is at least partially concerned with the disruption, as a result of process channel wall movement, of the attractive forces between the particles and process channel wall. It is thought that the rapidly varying loads of pressure created by the process according to the present invention induces different pressure loads between the process channel cavity walls, in addition to applying stress and fatigue on the particle-particle (catalyst) and particle-to-cavity wall associations. “Associations” in this respect are to be interpreted as attractive forces of a physical or chemicophysical nature. Therefore, the inventors have advantageously found that the arrangement of the present invention has the ability to handle the stress and fatigue on the particle-particle and particle-to-cavity wall associations to aid in the dislodgement of catalyst from the process channel wall, in addition to the temporary deformation of the cavity walls such that the original position and strength is substantially returned after dislodgement (i.e., any loss is negligible), without damaging the cavity wall. Preferably, the stresses in the process channel wall remain below the fatigue limit of the process channel material. The present invention provides controlled pressure differentials acting along neighbouring channels. This feature facilitates rapid and effective catalyst removal. The pressure differential may be created by oscillatory fluctuations provided by the gas stream and / or repeating forces (ie. a pulsating source of gas stream). The pressure differential may generate process channel wall vibrations that create varying shear forces between the particulate catalyst and channel wall. The inventors have found that this arrangement further aids in the dislodging of catalyst due to the wall vibrations creating arrangements with larger openings to facilitate the removal of catalyst from tight spaces. The inventors have advantageously found that shear forces applied during the movement of the channel walls is sufficient to break catalyst particle-to-particle and particle-to-channel wall associations, thereby facilitating removal of spent catalyst. The shear forces may be created from oscillatory vibrations of pressure differentials that, in turn, generate wall vibrations and movement. The oscillatory vibrations of the channel walls as a result of the pressure differentials and / or repeating forces has been found to deliver time varying shear forces between the catalyst particulates and channel wall which aide it in catalyst discharge. The catalyst bed may reduce the pressure of the gas stream, therefore it has been found that applying oscillatory and / or repeating forces improves catalyst discharge from the process channel. Catalyst closest to the pressure loading at the proximal end of the process channel (ie. closest to the cavity opening) is removed more easily. After this catalyst has been removed, oscillating and / or repeating forces accommodate for further propagation of the pressure forces into the narrow cavities of the process channels, which in turn, discharges any remaining catalyst. This may be repeated until all, or substantially all, of the spent catalyst has been removed. It will be appreciated by the skilled person that the differential pressure and frequency required to discharge the catalyst is dependent on the catalyst used, the cavity / channel wall thickness and the process wall material. The process channel walls may be thin walls. By the term “thin” we preferentially mean that the process channel wall has a thickness of less than about 1 cm, less than about 0.8 cm or less than about 0.7 cm. Thin wall dimensions of the process channels according to the present invention may be taken to be the distance between any two contact points on the process channel wall / thickness (d / t) on the wall being greater than 20 in any geometry dimension. The inventors have found that process channels with a thin wall facilitate the removal of catalyst. The gas stream may be generated by a high velocity jet. The use of a high velocity jet has advantageously been found to promote pressure differentials, such that the high velocity jet may experience naturally occurring oscillations as it discharges into a larger volume between the jet and the process channel cavity. The oscillations create high frequency pressure variations within the cavity containing catalyst particulates. The resulting pressure forces acting on the cavity walls and particles within the cavity may fluctuate with time and create cyclic loads. By using a high velocity jet, rapidly varying pressure can be applied to catalyst particles inside a cavity. The gas stream may be pulsed or continuous. Preferably, the gas stream is pulsed. Preferably the gas stream is air but any other suitable gas may be used, preferably inert. The process of the present invention may include a gas delivery device. The gas delivery device may be static or may be moveable, for example the gas delivery device may rotate about an axis. The gas delivery device may comprise a gas distribution manifold that delivers a gas stream. The gas distribution manifold may be movable and / or rotate about an axis. The terms gas delivery device and gas distribution manifold are to be construed to mean a device that is configured to provide gas and therefore in some embodiments such terms may be considered to be interchangeable. The use of such terms to describe an embodiment should not be taken as limiting. The gas stream may be provided by means of a rotating continuous slot nozzle, stationary or translating nozzle, or flow distribution screen. The gas stream may comprise multiple gas streams provided by means of a multiplicity of rotating continuous slot nozzles, stationary or translating nozzles, or flow distribution screens. The discrete gas stream may be generated by a flow distribution screen or a nozzle comprising a plurality of perforations. The gas stream may be directed at about 90 degrees (ie. perpendicular) to the perforations depth or perforations in the flow distribution screen. The inventors have found that in some embodiments deviating from 90 degrees can lead to process channel wall damage due to a lateral force on the wall at high flow rates. However, in some embodiments it may be preferable to direct the gas stream at an angle at lower flow rates. The inventors have found that the use of a flow distribution screen or nozzle comprising a plurality of perforations provides means that control the pressure differential between neighbouring process channels, thereby creating an environment with varying pressure such that removal of spent catalyst is stimulated in an ordered fashion that promotes more effective removal of the spent catalyst. In one embodiment, the discrete gas stream is generated by a flow distribution screen. The use of a flow distribution screen has been found to provide discrete gas streams, for example discrete air jets, that create the necessary differential pressure between neighbouring process channels. The flow distribution screen may comprise a plurality of perforations or openings. It will be understood by the skilled person that the term perforations and openings are interchangeable in this context. The thickness of the flow distribution screen can be varied dependent on the desired flow rate and pressure differential between neighbouring process channels. The thickness of the flow distribution screen may be between about 0.1 cm and 2.0 cm, preferably between about 0.2 mm and 1.5 mm, most preferably between about 0.3 cm and 1.3 cm. Controlling the thickness of the flow distribution advantageously has the potential to obtain a controlled steady pressure distribution, thereby reducing the likelihood of undesired pressure fluctuations. The number of perforations on the flow distribution screen may be varied depending on the catalyst being dislodged. The positioning of the perforations in the flow distribution screen may be varied. For example, the perforations in the flow distribution screen may extend over two or more, preferably 10 or more, more preferably 20 or more, most preferably all the process channel openings of a layer of process channels. The perforations of the flow distribution screen may extend over at least 70%, at least 80%, at least 90%, most preferably 100%, of the process channel openings on a layer of process channels. The perforations in the flow distribution screen may be positioned such that the discrete gas stream passes through a corresponding perforation in the flow distribution screen. The perforations in the flow distribution screen may be at least partially aligned with the gas stream and the process channel cavity opening. In some embodiments, the flow distribution screen may be moveable such that the perforations in the flow distribution screen are not aligned with the gas stream and process channel cavity opening. The number of perforations may not be the same as the number of process channels. Accordingly, in this embodiment, there may be process channels without a corresponding perforation directly in line with an air jet. The plurality of perforations may have a width approximately equal or smaller than the width of the process channel opening. The size of the perforations may be the same. The size of the perforations may be different. The size of the perforations may comprise at least two different sizes or at least three different sizes. The perforations may be equidistant from one another along the length of the flow distribution screen or may be arranged with repeating patterns of perforation clusters. The positioning of the perforations in the flow distribution screen have been found to allow for variable pressure to reach the process channels open end. This feature has also been found to allow the gas stream speed and pressure within the cavity to be easily tuned to achieve process wall movement or vibrations without damaging the wall. The inventors have found that the use of a flow distribution screen controls the gas stream speed and pressure within the process channel cavity to achieve temporary deformation, for example process channel wall movement and vibration, without damage. This is in contrast to arrangements in the art, for example, that include one continuous opening. Therefore, the arrangements according to the present invention are more cost-effective, efficient and reliable than alternative arrangements in the art. The gas stream upstream of the flow distribution screen may be pulsed. Pulsation of the gas stream has been found to achieve fast, repeated pressure differentials such that forces on the process walls are controlled over a wide range of frequencies. The pulsed gas stream may be applied up against the flow distribution screen. This arrangement has been found to avoid any pressure drop between the gas stream and flow distribution screen, thereby providing a more efficient process. The flow distribution screen may be fixed during operation. The flow distribution screen may be shifted during operation i.e., the flow distribution screen may be movable. For example, the flow distribution screen may be moveable in a forwards and backwards direction in the horizontal plane. Accordingly, in one arrangement the plurality of perforations may align with the gas stream provided by a gas distribution manifold, thereby delivering discrete air jets to the process channel opening. In another embodiment, i.e., when the flow distribution screen is moved, the plurality of perforations may be moved such that the perforations are located on a solid portion of the gas distribution manifold. Therefore, in some embodiments the plurality of perforations are not aligned with the gas stream and / or process channel cavity opening. In this arrangement, the gas flow through the plurality of perforations is interrupted. The inventors have found that the oscillatory motion of the perforated screen induces time-varying pressure differentials on the cavities holding the catalyst. Without wishing to be bound by theory, it is believed that the fluctuations in pressure differentials induces vibrations of the process channel wall, thereby aiding catalyst discharge from tight cavities. The use of a movable flow distribution screen has been found to generate pressure fluctuation by means of a set of discrete gas jets impinging on the proximal end of cavities holding catalysts. In particular, this arrangement has been found to be beneficial for dislodging catalyst from tight cavities with no, or minimal damage, to the process channel walls. Furthermore, this movable feature facilitates changes in flow distribution between channels. In particular, for areas where the catalyst removal is particularly difficult, movement of the flow distribution screen has been found to be beneficial. The flow distribution screen may be placed on top of a gas distribution manifold comprising a narrow slot. The presence of the flow distribution screen comprising a plurality of perforations ensures the generation of discrete air jets. After at least some of the catalyst has been dislodged, the catalyst may be removed from the top of the flow distribution screen. Advantageously, the pressure differentials created by the use of a flow distribution screen has been found to be effective in the removal of catalyst whilst maintaining the structural integrity of the process channel wall. Additionally, the design and application of the screen is simple and can be easily modified and maintained, thereby providing a cost-effective solution. Due to the pressure differential created by the discrete gas stream passing through the flow distribution screen, unnecessarily high air speeds, for example supersonic air speed, is not required to achieve dislodgement of the catalyst. Therefore, lower volumetric flow rates can be used compared to alternative methods in the art, thereby reducing the likelihood of damage to the process channel walls. In some embodiments, the discrete gas stream is generated by a nozzle comprising a plurality of perforations. The use of a nozzle comprising a plurality of perforations has been found to generate sufficient discrete gas streams, for example discrete air jets, that create the necessary differential pressure along neighbouring process channels. This arrangement has advantageously been found to operate under unstable environments which may be controlled by the geometry and positioning of the perforations, in addition to the distance between the perforations and the process channel cavity. The process according to the invention may use a nozzle of any suitable shape. In some embodiments, the shape of the nozzle may provide a gas stream in one dimension. In some embodiments, the shape of the nozzle may provide gas streams in two dimensions. For example, the nozzle may be V-shaped. The plurality of perforations may all be the same shape. The plurality of perforations may comprise different shapes. The perforations may comprise at least two different shapes, or at least three different shapes. Non-limiting examples of suitable shaped perforations have been found to include rectangular slots, cylindrical perforations, diamond shaped holes, oval shaped holes and serrated slots. In some embodiments, the perforation may be a continuous slot. The size of the perforations may all be the same. The size of the perforations may comprise different sizes. The perforations may comprise at least two different sizes, or at least three different sizes. The perforations may be equidistant from one another or may be arranged with repeating patterns of perforation clusters. The perforations may be positioned in a singular line across the width of the nozzle. The perforations may be arranged along the nozzle in a linear pattern, a V-shaped pattern, a stepped pattern, a triangular pitch pattern, a square pitch pattern or a staggered pitch pattern or other patterns favoring the presence of pressure differentials. The inventors have identified that different perforation arrangements in the present invention have the ability to induce pressure differentials with different magnitudes and fluctuations favorable for catalyst discharge from tight cavities, The perforations may be positioned in multiple lines across the width of the nozzle. For example, the perforations may be positioned on at least two lines, or at least three lines across the width of the nozzle. In embodiments with multiple lines of perforations across the width of the nozzle, the perforations may be arranged in a pattern. Non-limiting examples of suitable patterns include rectangular patterns, circular patterns and triangular patterns. The presence of perforations across multiple lines has advantageously been found to control the pressure distribution between neighboring process channel cavities across several cavity openings. This is in contrast to arrangements of the art that utilise a single continuous slot opening. Without wishing to be bound by theory, in embodiments where there is more than one line of perforations across the width of the nozzle, and the nozzle is not stationary, it is believed that as the nozzle is swept across an array of process channel cavities, the channels will experience multiple pressure variations such that each process channel will experience both high and low side pressure variations. For example in embodiments where the multiple line arrangement is a double line arrangement, every other process channel in the process channel layer that was previously more closed will become more open when the next wave of air is received. The nozzle may remain stationary throughout the process according to the present invention. In such arrangement, the air jets will impinge on a specific location. Alternatively, the nozzle may move over an array of process channel cavities throughout the process according to the present invention. Accordingly, in some embodiments, the nozzle may sweep over the process channels. Preferably, the nozzle (and consequently the gas stream) is moved transversely over the process channels. This feature facilitates rapid and effective catalyst removal. The distance between the nozzle and the open end of the process channels may remain constant as the nozzle sweeps over it. In some embodiments, the distance between the nozzle and the open end of the process channels may vary as the nozzle is swept over. This has beneficially been found to better control the pressure differential over specific regions of the reactor. Accordingly, the distance between the nozzle and the proximal ends of the process channels may vary as the nozzle moves transversely over the array of process channels. Furthermore, it has been found that in this embodiment, as the nozzle sweeps across multiple process channel cavities, a wide range of pressure fluctuations are generated within the cavities at varying frequencies. The varying frequency ranges has been found to be a result of the nozzles displacement velocity, the perforations positioning across the width of the nozzle and the naturally occurring oscillations from the air jet. In some embodiments, the nozzle may move towards and away from the open end of the process channel cavity. This has been found to regulate the pressure differential. The process of the present invention may include a rotating gas delivery device or rotating gas distribution manifold. The rotating gas delivery device may comprise a nozzle rotated about an axis whilst directing at least one gas streams into open proximal ends of an array of process channels. The rotating gas delivery device may comprise a gas distribution manifold. The at least one gas stream may comprise a plurality of discrete gas streams. The rotating gas delivery device may comprise a nozzle comprising at least one array of perforations, at least one rotating coupling and optionally, hollow gas delivering supports. For example, a gas stream may be delivered to the process by a rotating gas delivery device rotating along its longitudinal or transverse axis. The rotating gas delivery device has been found to facilitate the creation of a pressure differential between neighbouring process channels and oscillations on catalyst containing cavities, thereby facilitates the removal of catalyst. For example, the nozzle may rotate and undergo a rotating motion along its longitudinal axis. In some embodiments, the nozzle may be stationary (i.e., not sweep across the process channels) and rotate about its longitudinal axis. In other embodiments, the nozzle may sweep across the process channels whilst rotating about its longitudinal axis. The inventors have advantageously found that the rotating motion, in combination with the linear displacement of the nozzle, creates oscillatory and varying gas delivery to the catalyst containing cavities such that temporary deformation of the process channel walls is achieved (i.e., wall vibration), which in turn, improves catalyst discharge. The rotation of the nozzle may be controlled by air flow out of the nozzle. Alternatively, or additionally, rotation of the nozzle may be controlled by an electric motor. The nozzle may comprise multiple arrays of perforations. For example, there process may comprise a nozzle comprising at least two, at least three or at least four arrays comprising a plurality of perforations. The number of arrays present has been found to influence the rotation speed of the nozzle. The nozzle may be held between hollow gas delivering supports. The gas delivering supports may be configured to distribute gas within the nozzle which, in turn, delivers gas to the array(s) comprising a plurality of perforations. The presence of a plurality of perforations has been found to generate sufficient discrete gas streams, for example discrete air jets, that create the necessary differential pressure between neighbouring process channels. The gas delivering supports may comprise rotating couplings therebetween. The rotating couplings aid the rotation of the nozzle. The rotating couplings may be configured to allow gas to pass through. The arrangement may further include means to regulate and / or redirect the flow of air from the perforations. For example, the means may include baffles or an enclosure. The inventors have found that the inclusion of means to redirect the flow of air from the perforations helps to prevent pressure fluctuations on undesired regions of the reactor. Alternatively, the rotation of the nozzle may occur around an axis parallel to the gas flow direction i.e., along its transverse axis. In this embodiment, there may be a rotating coupling to rotate the nozzle. The rotation of the nozzle may therefore occur around the axis of the rotating coupling. In this embodiment, a gas stream enters the nozzle through the rotating coupling and exits through the perforations in the nozzle. In some embodiments, the nozzle may be stationary (i.e., not sweep) and rotate. In other embodiments, the nozzle may sweep across the process channels whilst rotating along its transverse axis. The rotating motion of a gas source has been found to deliver oscillatory pressure fluctuation to neighbouring process channels via gas jets impinging on to the proximal ends of the cavities containing catalyst thereby improving catalyst discharge, in particular catalyst discharge efficiency from narrow cavities. The rotation of the nozzle may be controlled by air flow exiting the nozzle. Alternatively, or additionally, the rotation of the nozzle may be controlled by an external source, for example an electric motor. The nozzle may comprise multiple arrays of perforations. For example, there may be a nozzle comprising at least two, at least three or at least four arrays comprising a plurality of perforations. The number of arrays present may influence the rotation speed of the nozzle and / or the discrete air jets created. The process for the removal of a particulate catalyst from a packed catalyst bed within a process channel of a reactor may comprise a linear array of the rotating nozzles. For process may comprise at least two, or at least three rotating nozzles in a linear array. The process channels may comprise a convex side and a concave side. The process channels may be in a waveform structure. In some embodiments, the process channels have a convex and a concave side and the plurality of perforations located on the nozzle sweep over the process channels to discharge any catalyst. This arrangement has been found to be particularly advantageous in removing catalyst from the process channels with more precision and efficiency. Without wishing to be bound by theory, it is believed that the desired air flow of the gas stream is obtained as a result of the gas stream starting and ending on the convex side of a process channel as the nozzles are swept over a layer of process channels. This arrangement results in a preferable order of discharge to improve discharge effectiveness. This has particularly found to be the case when the nozzles are V-shaped and moved over the length of the process channels. A variety of different catalysts may be removed from an array of process channels. The array of process channels may be a linear array. Alternatively, the array of process channels may be a non-linear array, for example, a triangular or square pitch pattern, a staggered pitch pattern, a V-shaped pattern or in a monolith. In some embodiments the catalyst is a Fischer-Tropsch catalyst. The Fischer-Tropsch catalyst may be in any suitable form, for example fixed bed of particulate solids. The Fischer-Tropsch catalyst may optionally comprise cobalt or iron and a support. The catalyst may optionally have a cobalt or an iron loading in the range from about 10 to about 60% by weight, or from about 15 to about 60% by weight, or from about 20 to about 60% by weight, or from about 25 to about 60% by weight, or from about 30 to about 60% by weight, or from about 32 to about 60% by weight, or from about 35 to about 60% by weight, or from about 38 to about 60% by weight, or from about 40 to about 60% by weight, or from about 40 to about 55% by weight, or from about 40 to about 50% by weight of cobalt. The Fischer-Tropsch catalyst may optionally further comprise a noble metal. The noble metal may for example be one or more of Pd, Pt, Rh, Ru, Re, Ir, Au, Ag and Os. The noble metal may be one or more of Pt, Ru and Re. The noble metal may be Ru. As an alternative, or in addition, the noble metal may be Pt. The Fischer-Tropsch catalyst may optionally comprise from about 0.01 to about 30% in total of noble metal(s) (based on the total weight of all noble metals present as a percentage of the total weight of the catalyst precursor or activated catalyst), or optionally from about 0.05 to about 20% in total of noble metal(s), or optionally from about 0.1 to about 5% in total of noble metal(s), or optionally about 0.2% in total of noble metal(s). The Fischer-Tropsch catalyst may optionally include one or more other metal-based components as promoters or modifiers. These metal-based components may optionally also be present in the catalyst precursor and / or activated catalyst as carbides, oxides or elemental metals. A suitable metal for the one or more other metal-based components may for example be one or more of Zr, Ti, V, Cr, Mn, Ni, Cu, Zn, Nb, Mo, Tc, Cd, Hf, Ta, W, Re, Hg, Tl and the 4f-block lanthanides. Suitable 4f-block lanthanides may be La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and / or Lu. The metal for the one or more other metal-based components may for example be one or more of Zn, Cu, Mn, Mo and W. The metal for the one or more other metal-based components may for example be one or more of Re and Pt. The catalyst may optionally comprise from about 0.01 to about 10% in total of other metal(s) (based on the total weight of all the other metals as a percentage of the total weight of the catalyst precursor or activated catalyst), or optionally from about 0.1 to about 5% in total of other metals, or optionally about 3% in total of other metals. The Fischer-Tropsch catalyst may optionally be derived from a catalyst precursor which may be activated to produce the Fischer-Tropsch catalyst, for instance by heating the catalyst precursor in hydrogen and / or a hydrocarbon gas (e.g., methane), or in a hydrogen and / or hydrocarbon gas diluted with another gas, such as nitrogen and / or methane, to convert at least some of the carbides or oxides to elemental metal. In the active catalyst, the cobalt may optionally be at least partially in the form of its carbide or oxide. The Fischer-Tropsch catalyst may optionally include a catalyst support. The support may optionally comprise a refractory metal oxide, carbide, carbon, nitride, or mixture of two or more thereof. The support may optionally comprise alumina, zirconia, silica, titania, or a mixture of two or more thereof. The surface of the support may optionally be modified by treating it with silica, titania, zirconia, magnesia, chromia, alumina, or a mixture of two or more thereof. The material used for the support and the material used for modifying the support may be different. The support may optionally comprise silica and the surface of the silica may optionally be treated with an oxide refractory solid oxide such as titania for example. The material used to modify the support may be used to increase the stability (e.g. by decreasing deactivation) of the supported catalyst. The catalyst support may optionally comprise up to about 30% by weight of the oxide (e.g., silica, titania, magnesia, chromia, alumina, zirconia or a mixture of two or more thereof) used to modify the surface of the support, or from about 1% to about 30% by weight, or from about 5% to about 30% by weight, or from about 5% to about 25% by weight, or from about 10% to about 20% by weight, or from about 12% to about 18% by weight, for example. The catalyst support may optionally be in the form of a structured shape, pellets or a powder. The catalyst support may optionally be in the form of particulate solids. While not wishing to be bound by theory, it is believed that the surface treatment provided for herein helps keep the Co from sintering during operation of the Fischer-Tropsch process. The deactivation rate of the Fischer-Tropsch catalyst may optionally be such that it can be used in a Fischer-Tropsch synthesis for more than about 300 hours, or more than about 3,000 hours, or more than about 12,000 hours, or more than about 15,000 hours, all before a catalyst rejuvenation or regeneration is required. The Fischer-Tropsch catalyst may optionally be used for an extended period (e.g. >300 hours) with a deactivation rate of less than about 1.4% per day, or less than about 1.2% per day, or between about 0.1% and about 1% per day, or between about 0.03% and about 0.15% per day. The Fischer-Tropsch catalyst may have any size and geometric configuration that fits within the process channels. The catalyst may optionally be in the form of particulate solids (e.g., pellets, powder, fibers, and the like) having a median particle diameter of from about 1 to about 1000 pm (microns), or from about 10 to about 750 pm, or from about 25 to about 500 pm. The median particle diameter may optionally be in the range from 50 to about 500 pm or from about 100 to about 500 pm, or from about 125 to about 400 pm, or from about 170 to about 300 pm. In one embodiment, the catalyst may be in the form of a fixed bed of particulate solids. In some embodiments, the process channels may be microchannels. The microchannels may be defined by a corrugated sheet located between facing walls of the adjacent cooling panels, for example as disclosed in US10159954B2, the contents of which are hereby incorporated by reference. The corrugated sheets may be fabricated from a heat conducting material, typically copper, and shaped to form multiple vertical reactor channels. The walls of the cooling panels may be parallel stainless-steel plates. The parallel plates are usually internally cooled by a coolant fluid. In operation, the reactor channels may be filled with a particulate catalyst material. Also provided in accordance with the invention is a multi-channel reactor vessel comprising at least one array of process channels, the reactor comprising associated apparatus for removing spent catalyst from the process channels, the associated apparatus comprising means for directing at least one gas stream into open proximal ends of the linear array of process channels effective to create a pressure differential between neighbouring process channels in order to create temporary deformation of the process channel walls. The array of process channels may be a linear array. Alternatively, the array of process channels may be a non-linear array, for example, a triangular or square pitch pattern, a staggered pitch pattern, a V-shaped pattern or in a monolith. The associated apparatus may be adapted to operate the process disclosed herein. Also provided in accordance with the invention is the aforesaid associated apparatus. The invention also concerns the use of the aforesaid apparatus to remove spent catalyst from a multi-channel reactor. The invention will now be more particularly described with reference to the following figures, in which: Figure 1 illustrates a diagrammatic view of a reactor and flow distribution screen in accordance with the present invention; Figure 2a illustrates a perspective diagrammatic view of a gas delivery device comprising a flow distribution screen in accordance with the present invention; Figure 2b illustrates a plan view of the embodiment of Figure 2a in an arrangement where gas air jets are delivered; Figure 2c illustrates a plan view of the embodiment of Figure 2a in an arrangement where gas flow is interrupted; Figure 3a illustrates a perspective diagrammatic view of a perforated air nozzle in accordance with an embodiment of the present invention; Figure 3b illustrates a magnified view of a section of perforated slots as shown in Figure 3a; Figure 3c illustrates a top view of Figure 3a; Figure 4a illustrates a perspective diagrammatic view of a perforated air nozzle in accordance with an alternative embodiment of the present invention; Figure 4b illustrates a top view of Figure 4a; Figure 5 illustrates a diagrammatic view of a process channel layer and air nozzle in accordance with an alternative embodiment of the present invention; Figure 6 illustrates a sequence of velocity magnitude contour plots of an embodiment as shown in Figures 3a to 3c; Figure 7 illustrates a plot showing pressure fluctuations within a process channel cavity according to an embodiment of the invention; Figure 8 illustrates a plot showing cavity wall deformation of the arrangement shown in Figure 4a as a function of time; Figure 9a illustrates a perspective view of a rotating gas delivery device in accordance with the present invention; Figure 9b illustrates a part-cutaway view of the embodiment shown in Figure 9a; Figure 9c illustrates a perspective view of a nozzle according to an embodiment of the present invention; Figure 9d illustrates a side cut-away view of a gas delivering device (bottom) shown in Figures 9a and 9b and catalyst holding device (top); Figure 9e illustrates a side cut-away view of a gas delivering device shown in Figures 9d comprising an enclosure; Figure 10a illustrates a diagrammatic view of an alternative rotating gas delivery device in accordance with the present invention; Figure 10b illustrates a plan view of the rotating gas delivery of Figure 10a in use; Figure 10c illustrates a plan view of more than one rotating gas delivery of Figure 10a in use; Figure 1 illustrates a schematic view of an arrangement according to the present invention showing a layer of process channels 10. A layer of process channels may, for example, comprise hundreds of individual process channels 11. The process channels 11 have thin walls 12 that are approximately 0.006 inches (0.01524 cm) thick that define the process channels 11 and a cavity opening 11a. The process channels 11 of this exemplified embodiment are in a waveform structure. The catalyst is not shown in the figure, however, in practice each process channel will be packed, at least partially, with a catalyst. A flow distribution screen is shown in this embodiment, with the flow distribution screen comprising a plurality of perforations 13. The flow distribution screen sits on top of a gas distribution manifold (shown in Figure 2a). In operation, the flow distribution screen helps to generate a pressure differential between neighbouring process channels 11. The flow distribution screen is fixed in place approximately 0.5 inches (1.27 cm) away from the cavity opening 11a. The cavity opening faces the ground such that, during operation, discharged catalyst falls freely as a result of gravity. As shown by Figure 1, the flow distribution screen can have variable openings of different shapes and sizes that selectively distribute the gas stream such that a differential pressure is achieved. The gas stream (not shown), is supplied at approximately 90 degrees to the flow distribution screen. The gas stream passes through each perforation 13 to create discrete high velocity air jets that generate a pressure differential along adjacent cavities 11a. The high velocity jet experiences naturally occurring oscillations as it discharges into the larger volume between the air jet and the process channel cavity. The oscillations create high frequency pressure variations within the cavity containing catalyst particulates. The pressure forces acting on the cavity walls and particles within the cavity fluctuate with time and create cyclic loads. The varying loads induce different pressure loads between the cavity walls, as well as stress and fatigue on the particle-to-particle and particle-to-cavity wall associations. Additionally, the differential pressure loads on each cavity wall generate differential movement of the walls. The varying differential movement of the cavity walls generates a wider opening to aide in catalyst discharge within the vessel. In some embodiments, the pressure differentials are of oscillatory nature and generate wall vibrations and movement, which in turn deliver time varying shear forces between the catalyst granules and the cavity walls. The cavity wall stress and movement facilitates dislodging of the catalyst. Therefore, at least some of the catalyst is dislodged and falls freely as result of gravity to create room between the cavity and the gas stream to easily blow any remaining dislodged catalyst away to avoid the flow distribution screen from clogging. In some embodiments, the flow distribution screen is shifted during operation and moves across an array of process channel cavities (shown in Figures 2a to 2c). In some embodiments, the gas stream is pulsed to create fast, repeated pressure differentials and subsequent forces on the process channel walls. Either during or after each cycle, the catalyst is removed from the top of the screen. The cycle is repeated until the catalyst is adequately dislodged and removed. After spent catalyst is removed it can be replaced with fresh catalyst. Referring to Figure 2a, an arrangement according to the present invention is shown wherein a gas delivery device 20 comprises a flow distribution screen 21 on top of a gas distribution manifold 22. The flow distribution screen 21 is provided with a plurality of discrete perforations 23 across its length. In the exemplified embodiment, the perforations 23 are circular in shape and are of equal size and are equidistant. In operation, the flow distribution screen is moveable in a forwards and backwards direction in the horizontal plane, as shown by arrow 24. The flow distribution screen 21 sits on top of a gas distribution manifold 22 which comprises a narrow slot (not shown). Gas enters the device 25 and flows through the discrete perforations 23 in the flow distribution screen 21 to deliver multiple discrete air jets 26 towards the cavities open end (not shown). The gas stream 25 is supplied at approximately 90 degrees to the flow distribution screen 21. The gas stream passes through each perforation 23 to create discrete high velocity air jets that generate a pressure differential along adjacent cavities (not shown). When the perforations 23 are aligned with the slot 27 of the gas distribution manifold (as shown in Figure 2b) multiple discrete air jets are delivered to the cavities open end. When the flow distribution screen 21 is moved along the horizontal plane 24, the perforations 23 are no longer aligned with the slot 27 of the gas distribution manifold and instead the perforations 23 are located on top of a solid region of the gas distribution manifold (as shown in Figure 2c). In this arrangement of Figure 2c, the gas flow through the perforations 23 is temporarily interrupted. In operation, the arrangement may therefore alternate between that shown in Figures 2b and 2c. The oscillatory motion of the perforated flow distribution screen 21 induces time-varying pressure differentials on the cavities holding the catalyst (not shown). The cavity wall stress and movement facilitates dislodging of the catalyst. After spent (or fresh) catalyst is removed from the cavity, it can be replaced with fresh catalyst. Referring to Figure 3a, an arrangement according to the present invention is shown wherein a gas delivery device 30 comprises a gas distribution manifold 31 and a nozzle 32 is provided with multiple perforations 33 across its length. In this particular embodiment, the perforations 33 are rectangular slots and are arranged in a singular line across the nozzle width. In this embodiment, the distance between the perforations is equidistant (as shown more clearly in Figure 2b). The distance between the perforations 34 in this embodiment is approximately 0.184 inches (0.4674 cm), the width of the slot 35 is approximately 0.184 inches (0.4674 cm) and the slot gap 26 is approximately 0.015 inches (0.0381 cm). The dimensions of the slot width and slot separation can be altered to create different pressure forces. In operation, the discrete perforations 33 deliver multiple discrete air jets 37 towards the cavities open end (not shown) that create pressure differentials across adjacent process channels (as shown more clearly in Figure 2c). The high velocity air jets experience naturally occurring oscillations that cause pressure fluctuations within the cavities and time varying forces on the catalyst particles (not shown). In some embodiments, during operation the air nozzle 32 is stationary. In other embodiments, the nozzle 32 moves over an array of cavities. As the nozzle 32 moves across the array of cavities a wide range of pressure fluctuations are created within the cavities at varying frequencies. The high velocity jet experiences naturally occurring oscillations as it discharges into the larger volume between the air jet and the process channel cavity. The oscillations create high frequency pressure variations within the cavity containing catalyst particulates. The pressure forces acting on the cavity walls and particles within the cavity fluctuate with time and create cyclic loads. The varying loads induce different pressure loads between the cavity walls, as well as stress and fatigue on the particle-to-particle and particle-to-cavity wall associations. Additionally, the differential pressure loads on each cavity wall generate differential movement of the walls. The varying differential movement of the cavity walls generates a wider opening to aide in catalyst discharge within the vessel. In some embodiments, the pressure differentials are of oscillatory nature and generate wall vibrations and movement, which in turn deliver time varying shear forces between the catalyst granules and the cavity walls. The cavity wall stress and movement facilitates dislodging of the catalyst. The frequency range of the fluctuations is as a function of the nozzle’s displacement velocity, the positioning of perforations and the air jets naturally occurring oscillations. After spent catalyst is removed it can be replaced with fresh catalyst. Figure 4a and 4b show a multiple line arrangement of the embodiment shown in Figure 3a and 3b. The gas delivery device 40 comprises a gas distribution manifold 41 and a nozzle 42. The nozzle 42 comprises three parallel lines of perforations 43. The shape of the perforations 43 in this embodiment are cylindrical and staggered. The shape and size of the perforations alternate between a larger and smaller size across the nozzle. The resulting arrangement controls the pressure differential distribution between neighbouring cavities across numerous cavity openings. Referring to Figure 5, there is shown a process channel structure according to the present invention in the form of thin walls sandwiched between coolant plates 51, which define process channels on either side. The process channels 52 are arranged in a waveform structure and comprise a convex side and a concave side wall. For the sake of clarity, the catalyst is not shown, but in practice each channel will be packed with catalyst. In this embodiment, the nozzle 53 is a V-shape. The nozzle 53 delivers high velocity discrete air streams via a plurality of perforations (not shown) into the process channels 53 to discharge the packed catalyst within the process channels. The thick black arrows show the direction of the moving air nozzle, in combination with the dashed V-shaped nozzles illustrating the movement of the nozzle 53. During operation, the nozzle 53 moves transversely over the layer of the process channels. As the nozzle 53 moves transversely over the process channel, the catalyst is discharged from the packed catalyst bed. The nozzle 53 moves over the layer of the process channels creating the desired air flow pressure distribution within the cavities. The high velocity air stream experiences naturally occurring oscillations as it discharges into the larger volume between the air jet and the process channel cavity. The oscillations create high frequency pressure variations within the cavity containing catalyst particulates. The pressure forces acting on the cavity walls and particles within the cavity fluctuate with time and create cyclic loads. The varying loads induce different pressure loads between the cavity walls, as well as stress and fatigue on the particle-to-particle and particle-to-cavity wall associations. Additionally, the differential pressure loads on each cavity wall generate differential movement of the walls. The varying differential movement of the cavity walls generates a wider opening to aide in catalyst discharge within the vessel. The movement of the air nozzle 53 in the direction of the black arrows reduces the likelihood of undesired movement in the lateral direction (as shown by the grey arrow). Figure 6 shows a sequence of velocity contour plots on a plane perpendicular to the perforation’s depth when a perforated air nozzle is used (for example, as shown in Figure 3). The plots indicate the air jet variation as a function of time. The perforations 61 are equidistant with one another. In this embodiment, the nozzle is stationary. As can be seen by Figure 5, the air jet 62 oscillates at a specific, fast frequency. Figure 7 shows a plot indicating the pressure fluctuations within a cavity. As can be seen by Figure 7, the fluctuation in pressure varies depending on the depth of the cavity. For example, the depth at 1 inch (2.54 cm) within a cavity has greater fluctuation in pressure, compared to the depth at 10 inches (25.4 cm), which fluctuates to a significantly lower degree. This is as result of the air jet impinging on the cavity opening, therefore pressure is greatest towards the open end of the cavity (i.e. at the lowest depth). Figure 8 is a graph showing cavity wall deformation induced by an arrangement as shown in Figure 3, as a function of time. The vibration generated by an air nozzle on a cavity containing catalyst is shown, with the graph focusing on the deformation between channels 3 and 4 of a linear array of channels. As shown in Figure 8, pressure differential varies with depth. Additionally, the flat linear lines referring to 8.50 inches (21.59 cm), 8.62 inches (21.90 cm), 12.00 inches (30.48 cm) and 24.00 inches (60.96 cm) indicate that deformation of the cavity at this depth is not (or very minimally) changing with time. This is the case when the cavity is filled with catalyst. However, as catalyst is dislodged from the cavity according to the process of the present invention, the lines referring to 8.50 inches (21.59 cm) and 8.62 inches (21.90 cm), show fluctuation in deformation as a result of the air jet being able to further propagate into the process channel cavity. Turning to Figure 9a, there is shown a rotating gas distribution manifold 90 comprising a nozzle 91 comprising a plurality of perforations 92 across its length. In this particular embodiment, the perforations 92 are cylindrical in shape and are arranged in a singular line across the nozzle width. The nozzle 91 is held between two gas-delivering supports 93a which are hollow. As more clearly shown in Figure 9b, a rotating coupling 93b exists between the support 93a and the nozzle 91 to facilitate the rotating motion along the longitudinal axis. As shown in Figure 9c, in operation, the nozzle 91 of the gas distribution manifold 90 receives a gas stream 85 that enters through the hollow supports (not shown) and the rotating couplings (not shown). The gas is then distributed inside the nozzle 91 and flows into the multiple arrays of perforated cylindrical holes 92. The number of arrays comprising a plurality of perforations shown in this embodiment is 4, however it would be understood by the skilled person that different numbers of arrays can be implemented. The gas 94 then flows out of the holes 92 as discrete air jets. In the embodiment shown, the arrangement of the discrete air jets impose a rotating motion (shown by arrow 95) on the nozzle 91. The gas distribution manifold 90 and imposed rotating motion is more clearly shown in Figure 9d. In addition to the rotating motion of the device (arrow 95), in some embodiments the device sweeps across the cavities that contain catalyst 96. The sweeping motion is illustrated by arrow 97. In operation, the gas 94 is delivered to a packed bed 98a to vibrate walls 98b as a result of the combination of rotation motion and linear displacement create oscillatory and varying gas delivery. In some embodiments, additional baffles or enclosures 99 are introduced into the gas distribution manifold, as shown in Figure 9e. This redirects the flow of gas from the perforations. A catalyst discharge system may include an array (not shown) of any of the devices shown in Figures 9a to 9e. Turning to Figure 10a, there is shown a rotating gas delivery device 100 comprising a gas distribution manifold 101 where the rotation occurs around an axis parallel to the gas flow direction. The rotating gas delivery device 100 with a narrow slot 102 and a rotating coupling 103. The gas stream 104 enters the device through the rotating coupling 103 and exits it through the slot 102. The gas delivery device has a rotating motion 104 around the axis of the rotating coupling 103. In addition to the rotation, the device can sweep along direction 106 to operate over an array of tight cavities. The rotating motion of the device can be induced through external means such as motors or be imposed by the gas stream exiting the device. 5 Figure 10b shows the gas delivery device 100 in operation and how it acts on an array of cavities holding catalyst 107. The device 100 rotates and sweeps across 106 the array. Figure 10c shows how an array of can delivering devices 100 can be arranged to act on an array of cavities. Each device 100 has a rotation motion 105 and the array of devices 100 sweeps in a direction of arrow 106 across the array of cavities 107. The rotation and sweep across the 10 array induces pressure differentials and pressure variations on the cavities.

Claims

1. A process for the removal of a particulate catalyst from a packed catalyst bed within a process channel of a reactor, the process comprising:directing at least one gas stream into open proximal ends of an array of process channels effective to create a pressure differential between neighbouring process channels, the pressure differential creating temporary deformation of the process channel walls such that at least some of the particulate catalyst is dislodged from the packed catalyst bed.

2. The process according to Claim 1 wherein the pressure differential is created by providing a gas stream influx into a first process channel at a rate and / or orientation different from that or those of the simultaneous gas stream influx into a neighbouring process channel.

3. The process according to Claim 2 wherein the pressure differential is created by the provision of discrete and / or rotating gas streams juxtaposed or otherwise adapted differently at any given moment with respect to the process channel and its neighbour.

4. The process according to Claims 1 to 3 wherein the process further comprises adding a structural rigid means to at least one process channel in the array of process channels.

5. The process according to Claim 4 wherein the structural rigid means blocks the open proximal end of at least one process channel in the array of process channels.

6. The process according to Claim 4 wherein the structural rigid means is configured to increase the thickness and / or alter the geometry of the at least one process channel in the array of process channels.

7. The process according to any one of Claims 1 to 6 wherein the temporary deformation of the process channel wall comprises oscillations and / or vibrations of the process channel wall.

8. The process according to any one of Claims 1 to 7 wherein the gas stream is pulsed.

9. The process according to any one of Claims 1 to 8 wherein the gas stream provides a high velocity air jet.

10. The process according to any one of Claims 1 to 8 wherein the gas stream comprises a plurality of discrete gas streams generated by a flow distribution screen or a nozzle comprising a plurality of perforations.

11. The process according to Claim 10 wherein the discrete gas streams are generated by a flow distribution screen.

12. The process according to Claim 11 wherein the flow distribution screen comprises a plurality of openings.

13. The process according to Claim 12 wherein the plurality of openings are positioned such that at least one discrete gas stream passes through an opening and an open proximal end of the process channel.

14. The process according to Claim 12 or Claim 13 wherein the plurality of openings include at least two different sizes.

15. The process according to Claim 10 wherein the discrete gas streams are generated by a nozzle comprising a plurality of perforations.

16. The process according to Claim 15 wherein the plurality of perforations are located across the width of the nozzle.

17. The process according to Claim 15 or Claim 16 wherein the perforations are positioned on a singular line.

18. The process according to Claim 15 or Claim 16 wherein the perforations are positioned over multiple lines.

19. The process according to any one of Claims 15 to 16 wherein the shape of the perforations is selected from rectangular slots, cylindrical perforations, diamond shaped holes, oval shaped holes and serrated slots.

20. The process according to Claim 18 or Claim 19 wherein the perforations are arranged in a linear pattern, a V-shaped pattern, a stepped pattern, a triangular pitch pattern, a square pitch pattern or a staggered pitch pattern.

21. The process according to any one of Claims 15 to 20 wherein the nozzle moves transversely over the array of process channels.

22. The process according Claim 21 wherein the distance between the nozzle and the proximal ends of the process channels varies as the nozzle moves transversely over the array of process channels.

23. The process according to any one of Claims 15 to 22 further comprising providing a rotating gas delivery device wherein the nozzle is rotated about an axis whilst directing at least one gas streams into open proximal ends of an array of process channels.

24. The process according to any one of Claims 1 to 9 wherein the gas stream is provided by means of a rotating continuous slot nozzle or flow distribution screen.

25. The process according to Claim 24 wherein the gas stream comprises multiple gas streams provided by means of a multiplicity of rotating continuous slot nozzles or flow distribution screens.

26. A multi-channel reactor vessel comprising at least one array of process channels, the reactor comprising associated apparatus for removing spent catalyst from the process channels, the associated apparatus comprising means for directing at least one gas stream into open proximal ends of the array of process channels effective to create a pressure differential between adjacent process channels in order to create temporary deformation of the process channel walls.

27. The multi-channel reactor according to claim 26 wherein the associated apparatus is adapted to operate the process of any one of claims 1 to 25.

28. The associated apparatus of claim 24 or claim 25.

29. Use of the aforesaid apparatus of claim 28 to remove spent catalyst from a multichannel reactor.33

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