GB2475401A

GB2475401A - Agitated cell reactors

Info

Publication number: GB2475401A
Application number: GB1018978A
Authority: GB
Inventors: Robert Ashe
Original assignee: Ashe Morris Ltd
Current assignee: Ashe Morris Ltd
Priority date: 2009-11-11
Filing date: 2010-11-10
Publication date: 2011-05-18
Anticipated expiration: 2030-11-10
Also published as: GB2475401B; GB201018978D0; GB0919702D0

Abstract

Agitated cell reactors comprise a series of interconnected cells in a block provided with agitators which can activate materials within the cells by agitation of the system. The agitators can vary in size, and various types of agitator and designs of the block and the materials for which they may be made are described. The reactor can have a series of cells interconnected by inter cell conduits, and may be provided with means within the cells for agitation of the process material within the cells, wherein the agitation is provided by agitator elements within the cells without any physical connection across the walls of the cells, and an injection nozzle or sampling outlet may be provided to at least one cell. Alternatively the agitator elements may be of a different density from the process fluid, are not connected to a mechanical drive mechanism and the agitator may comprise a basket which holds a catalyst.

Description

IMPROVED AGITATED CELL REACTOR

PCT Publication Number WO 2008/06819 describes agitated cell reactors (hereafter known as ACR), comprising cells linked by inter-stage channels. The present invention provides an improved version of such reactors.

The ACR described herein is a multi cell flow system which uses shaft-less dynamic mixing. It can be used for continuous chemical and physical reactions, continuous mixing, continuous co-current extraction, continuous counter current extraction, continuous bio reactions, continuous polymerisation and any other unit operation where good mixing combined with good plug flow is required under continuous flow conditions.

The ACR provides one or more of the following significant features: 1. The reaction cells can be located within a single block of material 2. Agitation is generated by agitator elements within the cells. Typically these are loose and are made to move by shaking the cell or by magnetic action.

3. The size of the cell volumes may be controlled by varying the volume of the agitator or insert which allows the same cell system to be used for activities of different volumes.

4. Side connectors can be provided to selected cells for the introduction or sampling of materials in the selected cells.

The invention is illustrated by reference to the accompanying Figures.

Figure 1 shows an unassembled ACR block with 10 reaction cells with the agitator elements removed.

The number and size of reaction cells can be varied however in this example, 10 reaction cells of the same size are used. A loose agitator can be placed within each cell element which will move when the cell block is shaken to generate the desired activity such as mixing. The agitator elements maybe of different sizes which allow the user to S...

vary volumes within the cells without changing the size of the cells. One benefit is that this allows the user to employ small reactor volumes where the reaction is fast and big reactor volumes where the reaction is slow. The benefits of this are that hot spots can be controlled and plug flow of the medium can be optimised according to reaction rate.

The size of the inter-stage channels can be varied (smaller channels are used for long * 35 reaction times) so that good plug flow and low pressure drop can be maintained irrespective of reaction time. The cells may be of any size typically from less than 1 * millilitre to more than 100 litres.

The cells may be separate or in a single agitator block. The agitator block may be made of any suitable material. Preferred materials include Polytetrafluroethylene (PTFE), glass filled PTFE, glass lined steel, ceramic, hastelloy and stainless steel. A variety of other metals, plastics or composite materials can be used. Plastic materials are good for s low pressure applications and metals, ceramics and glass are good for high pressure applications.

Figure 2 shows an assembled ACR reactor block This shows the reactor block of Figure 1 provided with agitator elements. Optional sight glasses are provided on the front. The back plate can serve as a heater or cooler for controlling the temperature of the reaction cells.

Figure 3 shows an exploded diagram of a reactor block From bottom to top this comprises 1. Back flange for clamping the reactor together.

2. Heat transfer gasket with flow channel cut to direct flow across the cells 3. Heat transfer plate 4. Process side heat transfer gasket 5. Reactor block 6. Process side gasket 7. Front flange (with sight glasses) for clamping the reactor together Figure 4 shows the agitator platform The reactor block is mounted on a shaft inside the box of the platform. The shaft oscillates preferably backwards and forwards to perform the desired activity such as mixing. The box provides containment for spillages or leaks. Three switches are shown.

One is for starting the agitation. A second switch allows the reactor to be rotated through degrees for drain down. The shaft may also be turned to other orientations between O and 180 degrees for controlling the flow of the medium particularly multi phase 30 mixtures. The position of the outlet within the cell has an influence on how quickly a light or a heavy phase component exits each reaction cell. Orientating the reactor in different positions allows this to be controlled. The agitation platform also has a speed control switch. This allows the frequency of oscillation to be regulated. Flexible tubes are used for heat transfer fluid and process connections. This allows the reactor to oscillate and/or turn with the tube connections in place. A temperature sensor can be fitted to the outside of the reaction cell which can observe the cell temperature through the glass.

Figure 5 is a schematic illustration of the operation of the plafform shown in Figure 4 The feed from the bottles of feed material are pumped into the bottom of the reactor with the product leaving the top of the reactor and collecting in a third bottle.

Figure 6 shows the reactor with side connections.

Side connections allow samples to be taken or reactants/materials such as chemicals to be added at different points within the reactor. The advantage with side connections is that they give access to individual cells without affecting the use of sight glasses.

Temperature sensors can also be added via the side connections. Figure 6 also shows a temperature element fixed to the front of the reactor. The temperature element is an NIR device with push fit' connection.

Figure 7 shows an injection nozzle An injection nozzle can be fitted to any reaction cell. It can have its own entry to the cell or it can be inserted in place of the glass window. The injection nozzle can be designed like a shower rose' with a large number of small holes. This improves the overall mixing characteristics when adding chemicals. Single point injection and sampling can also be used. Such an injection nozzle is an embodiment of the present invention.

Figure 8 shows a plain agitator This is a loose agitator which generates mixing when the reactor block is shaken. The volume and/or diameter of the agitator can be varied in order to control the volume of the cell. In this embodiment two soft rings are fitted around the agitator. The rings prevent the agitator body from hitting the walls of the cell. The rings may also be elastic which improves the recoil of the agitator. Such an agitator is an embodiment of the present invention and as discussed the size of the agitator can be varied accordingly to the volume required for the particular activity to be performed in the cell.

* 30 Figure 9 shows a variation of the agitator which can operate as a high shear mixer High shear mixer uses multiple smaller mixing elements. These elements may be fins, holes, wires or plates. The mixing element may be concentric or acentric (as shown).

The advantage with acentric systems is that they improve macro mixing within the cell. *u * * S S * **

* 35 Figure 10 shows a ceramic high shear mixer Ceramic mixers have the benefit that they have high chemical resistance and can be made in complex shapes.

Figure 11 shows a basket element The basket element fulfils two functions. Firstly it is used for performing the desired function such as mixing as with other agitators. Secondly it allows solids to be held in the cells such as catalysts for example polymerisation, hydrogenation or oxidation catalysts, feed solids, carbon granules etc. Such a basked element is an embodiment of the present invention.

Figure 12 shows a double action mixer The double action mixer has low density at one end and high density at the other. The difference in density can be achieved by using construction materials of several densities and or having one end hollow. The double action mixer achieves mixing with less overall movement.

Figure 13 shows a block for multiphase mixtures The ability to control the flow rate of multiple phase mixtures is important for maintaining the right process conditions. The multiphase block is preferably designed so that the inter cell channels are in a single straight line. When the reactor block is rotated, the orientation of the inter cell channel can be changed so that the inter cell channel lies in the lower half, the upper half or at the midpoint of the cell. Under these conditions, the transfer characteristics between the cells can be modified. By altering the orientation of the block, a bias can be imposed with favours a light phase, a heavy phase or allows equal flow of light and heavy phases.

Figure 14 shows a block for counter current flow The multiphase block is mounted in the vertical position. When light and heavy phases are in the reactor together, the light phase tends to flow upwards and the heavy phase goes downwards. Each cell in counter current block has two inlets and two outlets. The I...

two phases are mixed as they enter each cell from the side. The light phase goes to the top of the cell and flows into the side of the cell above. The heavy phase goes to the *:** bottom of the cell and flows into the side of the cell below. The light phase is introduced to the bottom of the system. Typically this is added on the second from bottom cell. The bottom cell is used for separating the heavy phase. The heavy phase is introduced to the top of the system. Typically this is added on the second from top cell. The top cell is used for separating the light phase. The counter current block is suitable for extraction such as solvent extraction as well as for reactions and is a further embodiment of the invention.

Materials of construction The reactor block is fabricated in a variety of materials to suit the application. Pure Polyvinylidene Fluoride (PVDF), FIFE or glass filled PTFE is used for a wide range of corrosive and non corrosive process materials. Other plastics or composites can also be used. For higher pressures and temperatures, metal reactor blocks can be used such as stainless steel. For more corrosive fluids, other metals such as hastelloy, nickel, titanium, tantalum and other exotic alloys can be used.

The agitators can be fabricated in a variety of materials. For successful operation, they need to have a density which is different from the density of the process material. Light materials like light weight or porous plastics are suitable as well as heavy materials like heavy plastics or metals. Agitator materials can include PTFE, polypropylene, PVDF and other plastics. Glass and ceramics can also be used and these have the advantage of higher density than plastics. Metals such as stainless steel, exotic alloys and titanium can be used. Heavier metals such as tantalum, tungsten or precious metals can also be used. High differences in density between the process fluid and the agitator, allow more energy to be put into the process fluid.

Any gaskets that are used can be made with metal, natural or synthetic rubber, PTFE, porous PTFE or other plastics.

Reactant and Materials addition Where reactants and/or materials such as chemicals are added as solids it is often better to use pulsed or intermittent flow. This may be achieved by having a valve which opens intermittently. The valve can be located upstream or downstream of the ACR.

The ACR uses dynamic mixing and therefore has generally very low pressure drops.

This makes addition control of reactants much easier to handle. In many cases addition * 30 control can be achieved by gravity transfer as the pressure drop is often only a few inches (based on water). Controlling product transfer can be achieved by weight difference. In this case the feed tank or discharge tank is preferably mounted on weigh cells. ** . * * * * U.

** 35 Design of the heat transfer plate The heat transfer plate on the back of the system is used to control the temperature in the process cells. In some cases the heat transfer plate can serve all the cells or it may split up into 2 or more zones so that different levels of heating and cooling can be applied to different cells or different groups of cells. In some cases, each cell may have its own heat transfer plate or jacket. Such a heat transfer plate is a further embodiment of the invention.

Multiple systems The system described so far consists of a single series of reaction stages. The system of the present invention can also be designed as a multiple system whereby the system consists of 2 or more channets each made up of 2 or more cells. A flow system of this type could be made up of 2 separate channels, 3 separate channels 5 separate channels or 10 separate channels or more than 10 separate channels. This would allow multiple flow streams to be run in parallel. Multiple systems can be split into two groups with opposing oscillating actions. This will reduce the tendency of the system to move and vibrate. Such a multiple system is a further embodiment of the present invention.

Split Cells Each cell can be split into two shorter sections such as cylinders by a barrier such as membrane or filter. On one side of the barrier, a particular material such as catalyst powder or other material may be retained. The produced fluid can then flow from one side of the cell to the other side of the next cell. One or both sides of the barrier may have agitating elements.

Removable cells Cells can be designed so that they can be removed or their contents removed and added in service. This arrangement can be used for such applications as catalyst systems where the catalyst needs to be replaced at intervals. Alternatively this could be used for other purposes such as powder dissolution. *SS * *

The benefits of Agitated cell reactors S.....

* 30 Flow reactors have an inherent cycle time advantage over batch reactors because filling, emptying, heat up, cool down etc operate in parallel with the reaction process. The other properties of flow reactors (plug flow, improved heat transfer and more efficient mixing) also translate into faster reaction times, more efficient use of catalyst, higher yields, better selectively, improved purity and lower use of solvents. The scale of these benefits ** 35 will vary according to the type of process being handled but commercial benefits variously include higher value products, reduced raw material costs, lower reprocessing and work up costs, improved safety and lower capital equipment charges. Many flow reactors rely on static mixing or diffusion for mixing. The benefits of multi stage dynamically mixed flow reactors over statically mixed reactors however are well recognised (mixing and plug flow are not constrained by residence time or reactor length). The advantages of the agitated cell reactor (ACR) of this invention over other multi stage reactors are as follows: I. On a like for like basis, the build cost of the ACR is substantially lower than that of other multistage dynamically mixed flow reactors. The reasons for this are that no baffles, rotating shafts, mechanical seals, magnetic couplings are required in the ACR.

2. The internal design of the ACR is simpler than that of other multistage dynamically mixed flow reactors. A simple internal design is important for preventing blockage and to enable cleaning.

3. The mixing performance of the ACR is superior to incumbent mechanically mixed systems by virtue of the transverse mixing technique. The option to rapidly reverse the direction of the agitator can create a high differential velocity (between the process fluid and the agitator). This type of mixing can also prevent centrifugal separation (caused by rotational mixing) when materials of different densities are present. This is important for effective mixing with multi phase mixtures particularly slurries.

4. The agitator sizes and types can be changed to optimise the reactor. This allows the user to vary the reactor volume or mixing characteristics without altering the reactor body.

The significance of the ACR design can be summarised by: good plug flow, improved mixing performance, lower build cost and the ability to handle multiphase mixtures. The commercial benefits are: Lower product development costs The raw materials consumed when studying flow reactions can be a significant cost I...

factor when developing new processes. The ACR can maintain good plug flow (by virtue * 30 of multiple stages), and good mixing (by virtue of dynamic mixing) at very low throughputs. It can also handle multi phase mixtures at low throughputs.

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The net fluid velocity in the ACR can be varied with minimal impact on plug flow or mixing. This allows the residence time to be changed without changing process variables or shutting down the reactor for reconfiguration.

The reactor can be adapted for a wide range of applications without altering the reactor body. The volume, residence time distribution and mixing characteristics can be altered by changing the agitators.

Lower equipment costs By using cells (rather than narrow channels) and dynamic mixing, the ACR has much lower pressure drop than reactors which rely on static mixing. This reduces the required capacity and the capital cost of the reactor feed pumps.

This reduced physical size (and in some cases, the operating pressure) of the ACR reactor reduces the capital cost. Whilst these benefits are common to other flow reactors, the ACR can deliver these performance benefits where reactions have very long reaction times and/or have multiple phases.

Polymerisation The quality and hence value of a polymer or copolymer product is related to uniform (and correct) polymer chain size. This in turn is related to good temperature control, good mixing and good time control of the reaction. The ACR of the present invention has been used for polymerisation reactions and proved effective due to: * Efficient mixing of reactants at comparatively low pressure drops (by virtue of dynamic mixing) * Good reaction time control by virtue of having a large number of reaction stages (10 stages on the one tested) * Good temperature control by virtue of having a large heat transfer surface to reaction mixture volume ratio a (when compared to batch reactors).

Continuous gas/liquid reactions (e.g. hydrogenation, oxidation) Equipment complexity and cost is a major consideration in gas/liquid reactions. There * are also practical problems of handling solid catalysts in flow systems. The ACR of this invention has proved very effective at handling gas liquid reactions for the following reasons: * In tests on the bio catalytic oxidation of amino acid using gaseous oxygen, the mixing performance of the ACR exceeded a 1/2 litre batch reactors operating at mixing speeds of 600 rpm. This means that the ACR can generate high : conversion rates in small reactor volumes. S.

* The ACR can carry a combination of solids, liquids and gases under well mixed plug flow conditions and there are many gas/liquid reactions use 3 phases (gas, liquid and solids).

Good mixing and good plug flow give faster reaction times. This contributes to improved yield and reduced equipment cost (through reduced size and/or reduced operating pressure).

Bio processes The ACR of this invention has demonstrated good handling characteristics for continuous reactions with live cells. This is combined with a high tolerance of slurries, a low propensity to foul and simple cleaning characteristics (by virtue of the cellular design).

Other reactions The ACR of this invention delivers a combination of good plug flow combined with good mixing for reactions which last from periods of a few seconds to reactions of many hours.

For mixing sensitive reactions with homogenous fluids, the ACR of this invention has achieved mixing efficiencies comparable to static mixers with the process fluid flowing at over 4 metres per second. With immiscible liquids the ACR of this invention has given comparable mixing performance to a I litre stirred vessel with an agitator speed of circa 400 rpm. These qualities combined with good slurry handling and simple internal geometry makes the ACR of this invention suitable for a wide range of reactions. Good mixing is required for optimum yield with competitive reactions. Plug flow is important for optimum yield and cycle time with order reactions (where n is greater than zero).

Plug flow is also important for maximising yield for reactions with unstable products. *S.I * * ****

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Claims

CLAIMS1. A system for treating a process fluid which flows continuously or intermittently through the system comprising two or more cells wherein said cells connected by S inter cell conduits through which the process fluid flows wherein mixing within the cells is generated by moving agitator elements within the cells which are of different density to the process fluid and which are not connected to a mechanical drive mechanism wherein an injection nozzle and/or a sampling outlet are provided to at least one cell.
2. A system according to Claim 1 which has 4 or more cells.
3. A system according to Claim I or Claim 2 wherein inserts are provided within one or more of the cells to provide the desired volumetric capacity of the cell.
4. A system according to Claim 3 wherein the inserts are agitator elements.
5. A reactor comprising a series of cells interconnected by inter cell conduits and provided with means within the cells for agitation of the process material within the cells wherein the agitation is provided by agitator elements within the cells without any physical connection across the walls of the cells wherein an injection nozzle and/or a sampling outlet are provided to at least one cell.
6. A reactor according to Claim 5 in which the cells are provided with a cooling/heating system in the form of a jacket.
7. A reactor according to Claim 5 or Claim 6 in which the volume of process fluid in the cells is varied by varying the size of the agitator elements.S*..IS.

* 30
8. A system for treating performing a catalytic reaction upon a process fluid which flows continuously or intermittently through the system comprising two or more cells wherein said cells connected by inter cell conduits through which the process fluid flows wherein mixing within the cells is generated by moving agitator *..: elements within the cells which are of different density to the process fluid and 35 which are not connected to a mechanical drive mechanism and wherein the agitator comprises a basket which holds a catalyst.
9. A system according to Claim 8 wherein inserts are provided within one or more of the cells to provide the desired volumetric capacity of the cell.
10. A system according to Claim 9 wherein the inserts are agitator elements.
11. A reactor comprising a series of cells interconnected by inter cell conduits and provided with means within the cells for agitation of the process material within the cells wherein the agitation is provided by agitator elements within the cells without any physical connection across the walls of the cells and the agitator elements comprise a basket which holds a catalyst for the reaction.
12. A reactor according to Claim 11 in which the cells are provided with a cooling/heating system in the form of a jacket.
13. A reactor according to Claim 11 or Claim 12 in which the volume of process fluid in the cells is varied by varying the size of the agitator elements. * S *5I* *5*55** * * * S..... * SS S..* * * I* S * . S * ** S. * * * . * S.