CA2303376A1 - Method for carrying out chemical reactions - Google Patents

Abstract

A method for effecting a chemical reaction between at least one component in a first fluid of one phase and at least one component in a second fluid of a different phase. The method comprises subjecting the two fluids to turbulent mixing, and allowing the selected components to react.

Description

Method for carryine out chemical reactions The present invention relates to a method for effecting a chemical reaction between components in two fluids. It is particularly concerned with a method in which the two fluids are of different phases.
Conventional. systems for effecting chemical reactions employ columns which may be packed columns, plate columns or bubble-cap columns, or columns with some other form of contact medium. In these systems, the gas and liquid streams flow countercurrently.
l0 These prior art systems suffer the disadvantage that in order to achieve a significant degree of gas/liquid contact, the columns have to be large and their operation is hampered by excessive foaming. In addition, any subsequent stripping section which might be required to remove the gas from solution must also be large, to handle the large volume of solvent or reagent used. Since the operation may well be carned out under high pressure and since the fluids involved may be highly corrosive, the capital costs of the large columns and subsequent stripping section are high. Furthermore, operating costs and maintenance costs are high. Finally, these systems tend to be inefficient.
It is an object of the present invention to provide a system for effecting a 2 o chemical reaction between components in two fluids of different phases, which does not suffer from the disadvantages of the prior art.
More generally, it is an object of the invention to provide a method of effecting a chemical reaction transfer between components in fluids of different phases with a high degree of efficiency and more economically than in existing 2 5 methods.
According to one aspect of the invention, there is provided a method of for effecting a chemical reaction between at least one component in a first fluid and at least one component in a second fluid of a different phase, the method comprising:
subjecting the two fluids to turbulent mixing, and allowing the selected components 3 0 to react.
In this application, fluids in different phases are any two fluids which are immiscible or are only partly miscible. Examples of such systems include gas/Iiquid, oil/water, fluidised solid/gas etc.
The invention also extends to the apparatus for carrying out this method.
The turbulent mixing is very intense and results in extremely efficient contact between the two fluids. The mixing regime is preferably turbulent shear layer mixing. The efficient mixing means that reaction can take place very rapidly and in a relatively small reactor volume compared to that required in conventional columns.
This in tum means that any liquid duty in the equipment is dramatically reduced resulting in a consequential reduction in the size of any downstream regeneration section. At the same time, the mixing system used is simple and inexpensive compared to prior art systems, leading to reduced costs. Finally, an efficiency of approaching 100% can be achieved for certain applications.
In addition, conventional methods often involve the evolution of heat which must then be removed from the system. While the method of the invention is capable of operation with a relatively low pressure drop across the mixing means, when greater pressure drop is employed, a cooling effect is achieved and this may render the need for additional cooling unnecessary.
The high mass and heat transfer coegicients of the method of the present invention make the system suitable for use in gas absorption processes. In particular, 2 0 the present invention has the advantage that any adiabatic expansion of a gas passing through a contactor reduces the contact temperature between a gas and a liquid, thereby increasing the quantity of gas which can be taken up by the liquid.
Additionally, in systems where the heat of condensation and heat of solution of a gas in a liquid is significant, and normally causes the liquid temperature to rise and thus 2 5 the absorption capacity of the liquid to fall, the adiabatic cooling can offset this undesirable effect.
The present method is also suitable for chemisorption reactions. In processes of adsorption with chemical reaction, the reactions are usually exothermic, and the heat of reaction causes the liquid temperature to rise. This reduces the adsorption 3 0 capacity of the liquid phase. Using the present method, the adiabatic cooling of the gas can offset the heating effect of the reaction, thereby maintaining the adsorption capacity of the liquid. Careful design of the apparatus may eliminate the need for external cooling which is required in many chemisorption processes.
The short contact time needed for reaction means that short contact lines can be achieved with high interphase transport fluxes. This property makes the apparatus of this invention suitable for treating heat sensitive or chemically unstable fluids or fluid mixtures.
Optionally a plurality of components are involved in the reaction. In one possible regime, the f rst fluid is a gas mixture and the second fluid is in the liquid phase. In another regime, the first fluid is a liquid mixture or a liquid solution and the second fluid in the liquid phase. In a third regime, the first fluid is a liquid mixture or a liquid solution and the second fluid is in the gas phase.
Preferably, the method is carried out as a continuous process with the two fluids flowing co-currently. The co-current flow eliminates any problems that might be associated with foaming and flooding, since separation can easily be effected downstream of the mixer.
The turbulent shear layer mixing may be achieved by any convenient means.
Preferably the mixing is conducted in a turbulent contactor including a first fluid inlet, a second fluid inlet, an outlet leading to a venturi passage, and a tube extending from the outlet back upstream, the tube being perforated and/or being spaced from 2 o the periphery of the outlet. Preferably, the tube is located in a vessel, the vessel including the first fluid inlet, the second fluid inlet and the outlet. In one arrangement, the first fluid is supplied to the tube, optionally directly, and the second fluid is supplied to the vessel, and so the first fluid draws the second fluid into the venturi and the two fluids are mixed. In another arrangement, the first fluid is 2 5 supplied to the vessel and the second fluid is supplied to the tube, optionally directly, whereby the first fluid is drawn into the venturi by the second fluid and the two fluids are mixed. In a further possible arrangement, one of the fluids is in the gas phase and one of the fluids is in the liquid phase, and both fluids are supplied to the vessel, the liquid being supplied to a level above the level of the outlet, whereby the gas is 3 0 forced out through the outlet via the tube, thereby drawing the liquid into the venturi so that the two phases are mixed.

One suitable contactor is a mixer supplied by Framo Engineering A/S and is described in EP-B-379319. Alternatively, the contactor may be an ejector. such as a jet pump.
It will be appreciated that the invention is broadly applicable to any chemical reactions between components in two different fluid phases and is particularly applicable to any application where the reaction kinetics are rapid.
The following are possible areas of application of this method although this list is not to be regarded as exhaustive. (i) The refining of fuel gas and feedstock gas purification using various solvents for the contaminating gases (including H,S, HCI, l0 RHS, COS, S02). (ii) The stabilisation of petroleum oils and/or distillates by the removal of dissolved gas from the oils andlor distillates, and controlling the vapour pressure by depressurising the liquid across the contactor and recycling the gas phase, or by using an inert carrier gas (e.g. N~, steam). (iii) The removal of dissolved hydrocarbon gases or acid gases and odorous components from refining waste water.
(iv) Oxygenation/aeration of refinery waste water in aerobic biochemical treatment processes. (v) Absorption recovery of components from "waste" gases, both reaction and combustion gases. (vi) Gas-liquid reactions where the products) is/are a liquid, where the gas absorbs into the liquid phase and then undergoes a chemical reaction.
(vii) Gas liquid reactions where the gas phase is recycled and part is vented to control 2 o the concentration of inert components which may reduce the reaction conversion, or of components which may poison the catalyst(s).
Thus, the invention therefore also extends to a method for effecting a chemical reaction between two or more components in different fluid phases which comprises: forming a homogeneous mixture of the fluid phases, the homogeneous 2 5 mixture being formed by subjecting the fluid phases to turbulent mixing conditions, preferably turbulent shear layer mixing conditions, separating a first fluid phase and a second fluid phase; and optionally treating the relevant phases) to remove the reaction product(s).
The fluid mixture may be a mixture of gases or may be in the liquid phase.
3 o The components to be reacted may be a finely divided solid disperse phase, a dissolved solid, a liquid or a gas.

The invention also extends to the apparatus for canrying out this method.
According to a more specific aspect of the invention, there is provided a method for effecting a chemical reaction between two or more components in different fluid phases which comprises: supplying the fluids to a mixer or turbulent 5 contactor; subjecting the fluids to turbulent shear layer mixing in the contactor to form a homogeneous mixture; allowing the selected components to react;
optionally cooling the homogeneous mixture; separating the cooled homogeneous mixture into separate phases; treating the separated phases to remove the reaction product{s); and, if appropriate, recycling either of the fluid phases containing unreacted reactants.
The separation of the homogeneous mixture into separate phases may take place in any suitable separator. For example, a gas-Liquid mixture may be separated in a hydrocyclone. Preferably any cooling and/or heating of either the reagents or products is achieved, at least in part, by mutual heat exchange.
Preferably, in instances where the first fluid is a gas mixture at a low pressure, and the second fluid is a liquid, the liquid is pumped to the contactor and thereby draws the gas mixture with it through the contactor. Preferably, when the first fluid is a gas mixture at a high pressure, and the second fluid is a liquid, the gas is conveyed to the contactor at a high pressure and thereby draws the liquid with it through the contactor.
2 0 The invention also extends to apparatus for carrying out such a method.
Preferably, the contactor is a turbulent contactor as described above, or alternatively an ejector or a jet pump.
The invention rnay be considered to extend to the use of a turbulent contactor to effect a chemical reaction between at Least one component in a first fluid phase and 2 5 at least one component in a second fluid of a different phase.
The preferred features of any'of the various aspects of the invention described above may be equally applicable to the other aspects of the invention.
The reaction systems described are single operations, however it will be appreciated that mufti-reactions may be performed. These may be carried out 3 0 simultaneously or sequentially and may also be carried out in series or in parallel.
The present invention is applicable in wide variety of applications. For example it can be used in petroleum and gas production in a number of ways -sweetening, removal of CO,, removal of NOX gases, stabilisation of liquid feedstocks and products, waste water treatment, in deodorising, removal of acid gas, removal of NH3 etc. It can also be used in wastewater treatment, in particular denitrification of wastewater and run off water from landfills. In petrochemical and fine chemicals manufacture, the contactor may be used on vent lines to recover reactants from vent gas or as a tail gas scrubber to recover products or remove toxic/noxious compounds.
In gas phase chemical reactions, the contactor may be used to selectively recover reaction products from reactor discharge gases. In the food and consumer products 1 o industries, the contactor may be used to prepare emulsions, the device affording a method of control of emulsion form by pressure control in phase continuity drop size distribution. As stated previously, this list is not to be regarded as exhaustive, but merely illustrative of the scope of use of the method of this invention.
The invention may be put into practice in various ways and two specific embodiments will be described by way of example to illustrate the invention with reference to the accompanying drawings, in which:
Figure 1 is a flow diagram of the process for use when the first fluid is a gas under low pressure;
Figure 2 is a flow diagram of the process for use when the first fluid is a gas 2 0 under high pressure;
Figure 3a is a view of a turbulent contactor suitable for use in the method of this invention;
Figure 3b is a view of a contactor similar to that in Figure 3a, but with the tube connected to a fluid inlet;
2 5 Figure 4a is a variant of the contactor shown in Figure 3a;
Figure 4b is a view of a contactor similar to that in Figure 4a, but with the tube connected to a fluid inlet;
Figure 5 is a view of a contactor similar to that shown in figure 3a but with the perforated tube arranged so that all the fluid which passes through the outlet does 3 0 so by way of the tube;
Figure 6 is a variant of the contactor shown in figure 5; and Figure 7 is a view of a jet pump which can be used as ari alternative to the contactor.
In one embodiment of the invention, a continuous process operation for a chemical reaction between a component in a gas phase and a second component in a liquid phase is shown in figure 1. A liquid stream 1 including the second selected component is conducted by a pump 2 to a contactor 3 (though this could be an ejector) capable of inducing turbulent mixing. A gas stream 4, including the first selected component is drawn into the contactor 3 by the low pressure generated in the venturi by the liquid stream after it has passed through the pump (stream la).
This arrangement provides an automatic means of self regulation as the gas mixture to liquid ratio can be maintained for varying flow rates. At the outlet of the contactor 3 the liquid and the gas stream are in the form of a homogeneous mixture (stream 5) and the chemical reaction between the selected components may occur very rapidly.
The mixed two phase stream 5 may then be conveyed to a cooler 6 and on into a hydrocyclone 7 or other suitable separator device. A gas stream 8, which may or may not contain a reaction product, may be taken off and the liquid stream 9, which may or may not contain a reaction product, may pass on to a regeneration system. The reaction products) will be separated from the appropriate streams) by any suitable means, and any unreacted reagents may be recycled for reuse. For 2 o example if the reaction product is a liquid, this may be separated from the unreacted liquid phase by means of heating (10) and then condensing of the product stream (11) in a condenser (not shown). Alternatively, if the reaction product is a solid, the product may be removed by filtration.
It will be clear to a person skilled in the art that the cooler 6 and the heater 10 2 5 if they are present may be combined to form a heat exchange unit.
An alternative system for a chemical reaction between two or more components, one or more in a high-pressure gas stream, and the rest in a liquid stream, is shown in figure 2. A high-pressure gas stream 20 containing a first selected component is conveyed to a contactor 21 similar to that shown in figure 3a.
The high 3 o pressure of the gas draws a controlled amount of the liquid stream from the recycle stream 22 and from a reservoir 23 into the contactor 21.

At the outlet of the contactor 21 the two phases are in the form of a homogeneous mixture (stream 24) and the chemical reaction between the selected components takes place.
The two-phase mixture (stream 24} may pass through a cooler 25 to a 5 hydrocyclone unit 26 or other suitable separation device. The gas stream is taken off in stream 27 and the liquid stream 28 may pass to a regeneration system. Again the reaction products) may be solid, liquid or gas and will be separated from the appropriate stream using any suitable apparatus. As before, either or both of the gas and liquid streams containing unreacted reagents may be recycled. As before, a liquid 1 o product may be separated from the liquid stream 28 by means of heating 29 and then condensing the product stream 30.
As in the first embodiment, the heater 29 and the cooler 25 if present may be combined to form a heat exchange unit.
The contactor used in both the above embodiments may be that shown in 15 figure 3a. The turbulent contactor 100 comprises a vessel 101 having a first fluid inlet 102, a second fluid inlet 103 and an outlet 104 leading to a venturi passage 105.
There is a tube 106 (which may or may not be perforated) extending from the outlet 104 back into the vessel 101. The tube 106 may be open ended into the vessel 101 as shown in figure 3a, or it may be connected to the fluid inlet 103, as shown in figure 20 3b.
In a first arrangement, the first fluid (e.g. a gas mixture) is supplied to the vessel 101 and the second fluid (e.g. a liquid) is supplied to the tube 106 whereby the first fluid is drawn into the venturi by the second fluid and the two phases are mixed.
In a second arrangement, the second fluid (e.g. a liquid) is supplied to the 2 5 vessel 1 O1 and the first fluid (e.g. a gas mixture) is supplied to the tube 106, whereby the second fluid is drawn into the venturi by the first fluid and the two phases are mixed.
In a third arrangement, the second fluid (e.g. a liquid) and the first fluid (e.g. a gas mixture) are supplied to the vessel 101, the second fluid being supplied to a level 3 o above the Ievel of the outlet 104, whereby the first fluid is forced out through the outlet 104 via the tube 106, thereby drawing the second fluid into the venturi so that the two phases are mixed.
A fourth variant is shown in figure 4a. This embodiment is similar to that shown in figure 3a, but the contactor 110 is inverted and is suitable only for use with gas-liquid reactions. It comprises a vessel 111 with a liquid inlet 112, a gas inlet 113 and an outlet 114 leading to a venturi passage 115. There is a tube 116 (which may or may not be perforated) extending from the outlet 114 back into the vessel 111.
The tube 116 may be connected directly to the gas inlet 113.
In this embodiment the liquid is forced up the tube 116 and the gas is drawn into the venturi passage 115 by the liquid and the two phases are mixed. When the tube 116 is perforated, the gas may be drawn into the tube 116 through the perforations.
A fifth arrangement is shown in figure 4b. This embodiment is similar to that shown in figure 4a, but the first fluid inlet 113 is connected to the tube 116 and is not open ended as in figure 4a. The arrangement comprises a vessel 111 with a second fluid inlet 112, an outlet 114 leading to a venturi passage 115. The fluid inlets 112 and 113 may be fed by gas as well as liquid.
A further example of a contactor which may be used in both the above embodiments is that shown in figure 5. The turbulent contactor 200 comprises a vessel 201 having a first fluid inlet 202, a second fluid inlet 203 and an outlet 204 2 0 leading to a venturi passage 205. There is a perforated tube 206 extending from the outlet 204 back into the vessel 201. The perforated tube 206 is arranged such that there is no gap at the outlet 204 of the vessel 201 for the fluids to pass through. The result of this arrangement is that all the fluid exits the vessel 201 via the perforated tube 206.
In a first arrangement, the first fluid (e.g. a gas mixture) is supplied to the vessel 201 and the second fluid (e.g. a liquid) is supplied to the tube 206 whereby the first fluid is drawn into the venturi by the second fluid and the two phases are mixed.
In a second arrangement, the second fluid (e.g. a liquid) is supplied to the vessel 201 and the first fluid (e.g. a gas mixture) is supplied to the tube 206 whereby 3 0 the second fluid is drawn into the venturi by the first fluid and the two phases are mixed.

In a third arrangement, the second fluid (e.g. a liquid) and the first fluid (e.g. a gas mixture) are supplied to the vessel 201, the second fluid being supplied to a level above the level of the outlet 204, whereby the first fluid is forced out through the outlet 204 via the tube 206, thereby drawing the second fluid into the venturi so that 5 the two phases are mixed.
A fourth variant is shown in figure 6. This embodiment is v similar to that shown in figure 5, but the contactor 210 is inverted. It comprises a vessel 211 with a liquid inlet 212, a gas inlet 213 and an outlet 214 leading to a venturi passage 215.
There is a perforated tube 216 extending from the outlet 214 back into the vessel 211.

10 As for the embodiment shown in figure 5, the perforated tube 216 is arranged such that there is no gap at the outlet 214 of the vessel 211 for the gas mixture to pass through. All the fluids must pass through the perforated tube 216 to the venturi passage 215.
In this embodiment the liquid is forced up the tube 216 and the gas is drawn into the venturi passage 215 by the liquid and the two phases are mixed. Since the tube 216 is perforated, the gas is drawn into the tube 216 through the perforations.
The contactors referred to in the above embodiments may be replaced by jet pump arrangements which are capable of inducing turbulent mixing. Figure 7 shows a jet pump 120 comprising a ~ first fluid inlet I2I for the high-pressure fluid and a 2 0 second fluid inlet 122 for the low-pressure fluid. The high-pressure fluid draws the low-pressure fluid along the length of the jet pump 120 to the outlet 123. The fluids are well mixed into a homogenised mixture in the region 124 at the outlet of the high-pressure inlet 121.

Claims (9)

Claims:

1. A method for effecting a chemical reaction between at least one component in a first fluid of one phase and at least one component in a second fluid of a different phase, the method being carried out as a continuous process with the two fluids flowing co-currently, the method comprising subjecting the two fluids to turbulent mixing, and allowing the selected components to react, the mixing being conducted in a turbulent contactor including a first fluid inlet, a second fluid inlet, an outlet leading to a venturi passage, and a tube extending from the outlet back upstream, the tube being perforated and/or being spaced from the periphery of the outlet.

2. A method as claimed in Claim 1, in which a plurality of components react together.

3. A method as claimed in Claim 1 or Claim 2, in which the first fluid is a gas mixture and the second fluid is in the liquid phase.

4. A method as claimed in Claim 1 or Claim 2, in which the first fluid is a liquid mixture or a liquid solution and the second fluid in the liquid phase.

5. A method as claimed in Claim 1 or Claim 2, in which the first fluid is a liquid mixture or a liquid solution and the second fluid is in the gas phase.

6. A method as claimed in Claim 1, in which the tube is located in a vessel, the vessel including the first fluid inlet, the second fluid inlet and the outlet.

7. A method as claimed in Claim 6, in which the first fluid is supplied to the tube and the second fluid is supplied to the vessel, and so the first fluid draws the second fluid into the venturi and the two fluids are mixed.

8. A method as claimed in Claim 6, in which the first fluid is supplied to the vessel and the second fluid is supplied to the tube, whereby the first fluid is drawn into the venturi by the second fluid and the two fluids are mixed.

9. A method as claimed in Claim 6, in which one of the fluids is in the gas phase and one of the fluids is in the liquid phase, and both fluids are supplied to the vessel, the liquid being supplied to a level above the level of the outlet, whereby the gas is ~
force out through the outlet via the tube, thereby drawing the liquid into the venturi so that the two phases are mixed.