The invention arose from considerations relating to the production of supercritical fluids and it is convenient to discus the invention in that context, but is not restricted to supercritical fluids.

It is sometimes desired to have a mixture of gases. This may be because it is desired to react the gases together, or with another substance. It may be because the gases are wanted for some other purpose. It is currently difficult to generate gas mixtures with a controlled composition and our invention is particularly useful in this respect.

Currently, supercritical fluid or dense phase gas formation is achieved by compressing a gas such as carbon dioxide (or a mixture of gases) to, near or above its critical pressure and heating to, near or above its critical temperature. This process requires the use of gas storage cylinders and equipment capable of withstanding high pressure. Also, the use of high- pressure pumps is required to achieve the supercritical state. Currently laboratory-scale supercritical fluids reactors are limited by the control of dosing of secondary gases into the supercritical fluid, and mass-flow control is difficult.

Supercritical fluids can be used as a medium for performing chemical reactions such as hydrogenation, acylation, alkylation, transesterification, etherification and cyclisation, or for use, for example in chromatography, extraction and impregnation. On a small scale, such as is currently used for laboratory screening, it is difficult both to meter the flow of gas and accurately to measure and maintain the composition of the fluid.

We have unexpectedly found that at least some of the foregoing disadvantages can be eliminated or reduced by producing supercritical fluids from liquid precursors instead of from gases. This invention circumvents problems by use of liquid precursor (s) to generate the dense phase gas mixture or supercritical fluid.

Accordingly, in one embodiment of the present invention we provide a method for the production of a supercritical fluid or dense phase gas in which at least one liquid precursor of said supercritical fluid or dense phase gas is chemically reacted, or is decomposed to form a gas.

The liquid precursor may be decomposed over a catalyst, or alternatively by means of energy input, for example, heat, light, sound, another energy source.

The gas or gas mixture produced may be conveyed to a reaction chamber or zone for the performance of chemical reactions. The gas or gas mixture may take part in the reactions or not.

We may also provide a supercritical fluid or dense phase gas made by the method described in the preceding paragraphs. We may also provide a reaction product of a chemical reaction that occurs in a supercritical fluid or dense phase gas produced by the method.

The liquid precursors are selected according to the chemical reaction and supercritical fluid desired. In principle, the precursor may be any substance that decomposes, can be decomposed or reacted to form a gas.

For example, the liquid precursor may be an organic acid, or a salt or an ester of an organic acid, for example formic acid. For performing hydrogenation reactions the precursors are preferably formic acid and ethyl formate. Alternatively, methyl formate, ethyl formate, propyl formate or dimethyl carbonate, or any mixture thereof, may be used to yield gas mixtures of methane and carbon dioxide, ethane and carbon dioxide, carbon monoxide and propane and water, methane and carbon dioxide respectively.

When the decomposition method involves a catalyst, the catalyst may comprise any catalytically-active species. The catalyst may comprise rhodium, iridium, palladium or platinum. The catalyst is preferably supported, in a finely-divided condition, on an inert support. Such an inert support may be silica, or alumina, or an alumosilicate.

Formic acid decomposes over a metal catalyst at elevated temperature to form carbon dioxide and hydrogen. Under the conditions of the decomposition in accordance with one aspect of the present invention, a single-phase gas mixture is obtained. The gas mixture in this case comprises carbon dioxide and hydrogen in a 1: 1 ratio. Variation of that ratio is impossible to achieve when the liquid precursor is formic acid alone and formation of a supercritical fluid is difficult. However, we have found that ethyl formate decomposes, under similar conditions, to form CO2 and ethane (C2H6). Ethane has a similar critical temperature to Cor.

Thus, when ethyl formate and formic acid are decomposed simultaneously, a gas mixture is formed (CO2 + H2 from the formic acid and CO2 and C2H6 from the ethyl formate) which has more easily accessible critical conditions and is more easily formed into a supercritical fluid.

The stoichiometry of said supercritical fluid, i. e. the ratio of CO2 and ethane to Hz, may be controlled by adjusting the rate at which the formic acid and the ethyl formate flow over the same catalyst bed.

It is important in this example that the precursors are not pre-mixed before they enter the reaction chamber, to prevent undesirable hydrolysis reactions.

This method may be used such that the reactions may be carried out, in dense phase gases or supercritical fluids for example, hydrogenation reactions, Friedel-Crafts acylation and alkylation reactions, transesterification, etherification, hydrogenolysis, deprotection and cyclisation reactions, depending upon the composition of the supercritical fluid formed by the chosen precursor (s) and on the catalyst employed.

According to another aspect the invention comprises a method of producing a multi-component gas mixture having a first gas component and a second gas component comprising the steps of storing a precursor to the first gas component in liquid form and turning the precursor into said first gas component by chemical reaction or decomposition, preferably upon demand, and/or preferably in site at or near to a gas mixing chamber at which said first gas component encounters a second gas component.

By"at or near"to the gas mixing, or gas receiving, chamber we mean near enough to greatly reduce the volume of the components of the gas mixture present at a given time when compared with the situation where the components are held outside of the mixing chamber in storage cylinders or tanks. Preferably we react or decompose the precursor into gaseous form upon demand:-i. e. when it is desired to produce the gas.

This avoids the need to store gas for a long time prior to using the gas.

The gas receiving chamber may be a zone or region of a pipe, or it may be an enlarged chamber, of greater cross-sectional area than that of a first and/or second precursor delivery conduit. Delivery conduits may deliver liquid components to the chamber where the liquid components gasify, or they may deliver gaseous first and/or second components to the chamber.

There may be 2,3,4,5, or more components.

The reaction may occur with the gas components in a gaseous or fluid state. Alternatively the gas mixture may be in a supercritical fluid, or dense phase gas, state.

Preferred embodiments of the invention will now be illustrated, merely by way of example, but should not be taken as limiting on the scope of this method to one skilled in the art, in the following description and with reference to the accompanying drawings, of which:- Figure 1 shows a flow diagram of a reactor for the production and subsequent use of supercritical fluids according to the present invention; Figures 2A to 2C show modifications of feeds of precursor liquids;

Figure 3 shows a modified plant similar to that of Figure 1; Figure 4 shows a computer-controlled micro-reactor plant; and Figure 5a-5c shows different gas generator and chemical reactor configurations.

Referring to Figure 1, the reactor comprises two reservoirs, 1 and 5, for the liquid precursors and a reservoir 9, for a substrate. High-pressure pumps 2,6 and 10 are each provided with a non-return valve 3,7 and 11 respectively and a pressure monitor, 4,8 and 12 respectively, in order to charge the reactor with the precursors and the substrate. Two heated catalytic chambers 15 and 19 are provided, each having a temperature monitoring apparatus 16 and 20 respectively.

Introduction of the liquid precursors prior to exposure to the catalyst is achieved in a first cruciform pipework intersection, shown schematically at 13. Mixing of the precursors before introduction to the catalyst bed is avoided by use of internal pipework. The temperature of the input of the precursors is monitored by temperature monitor 14. The inlet pipework of one precursor may direct the one precursor away from an introduced stream of a second precursor.

Mixing of the substrate with the products emerging from catalyst chamber 1 is achieved in a second cruciform pipework intersection, shown schematically at 17. The temperature of the substrate input is monitored by temperature monitor 18.

The product output from catalyst chamber enters a T-shaped pipework intersection 21, where its temperature is monitored by temperature monitor 22. The output product can be tapped off at sample collector 25.

A back pressure regulator 24 is fitted between the tap 23 and sample collector 25, in order to maintain a constant pressure within the reactor.

Chamber 15 is a gas-production chamber, and chamber 19 is a chemical reactor chamber in which the gases react with the substrate.

Of course, in other arrangements only one chamber may be necessary, but a plurality of chambers allows different conditions to exist in the different chambers. There may be more than one reaction chamber. The gas mixture produced may not take part in the reaction-for example it may be a supercritical fluid or dense phase gas solvent in which reactions of other chemicals occurs.

Examples Examples 1 and 2 below illustrate the use of supercritical fluids according to the present invention in the hydrogenation of trans-cinnamaldehyde and the effect of changing the flow rates of the precursors (formic acid and ethyl formate) on the yield of the desired product (hydrocinnamaldehyde) and on the amount of by-product (3-phenyl-1-propenol).

Example 1: Hydrogenation of trans-cinnamaldehyde The equipment was set up as shown in Figure 1. The catalyst chamber 1 (15) was charged with Deloxan AP II (Pt) 5% and maintained at a temperature of 400°C (16). Catalyst chamber 2 (19) was charged with Deloxan AP II (Pd) 5% and maintained at a temperature of 180°C (20).

Formic acid and ethyl formate (precursor materials) were each charged to separate pumps (2 and 6) and entered catalyst chamber 1 (15) at flow rates of 0.2 and 0.2 ml/min respectively. The pressure of the reactor was maintained at 200 bar by means of back pressure regulator (24). At this

temperature and pressure a supercritical liquid or dense phase fluid is formed (carbon dioxide, hydrogen, and ethane). Trans-cinnamaldehyde was charged to the substrate pump (10) from the reservoir. This was pumped into catalyst chamber 2 (19) at a flow rate of 0.05 ml/min. A solution containing the product was collected from the exit of the back pressure regulator (24) in an ice-cooled vial (25). Analysis of the solution by gas chromatography and'H NMR spectroscopy showed that the product was hydrocinnamaldehyde and that the yield was 65%. Gas chromatography and NMR analysis identified a yield of 30% of a second product, 3-phenyl-1-propenol.

Example 2 : Hydrogenation of trans-cinnamaldehyde The equipment was set up as shown in Figure 1. The catalyst chamber 1 (15) was charged with Deloxan AP II (Pt) 5% and maintained at a temperature of 400°C (16). Catalyst chamber 2 (19) was charged with Deloxan AP II (Pd) 5% and maintained at a temperature of 180°C (20).

Formic acid and ethyl formate were each charged to separate pumps (2 and 6) and entered catalyst chamber 1 (15) at flow rates of 0.1 and 0.4 ml/min respectively. The pressure of the reactor was maintained at 200 bar by means of a back pressure regulator (24). Trans-cinnamaldehyde was charged to the substrate pump (10). This was pumped into catalyst chamber 2 (19) at a flow rate of 0.05 ml/min. A solution containing the product was collected from the exit of the back pressure regulator (24) in an ice cooled vial (25). Analysis of the solution by gas chromatography and 1H NMR spectroscopy showed that the product was hydrocinnamaldehyde and that the yield was 90%. Gas Chromatography and NMR analysis identified a yield of only 5% of a second product, 3- phenyl-1-propenol. Thus, changing the precursor flow-rates resulted in significant improvement in the yield of the desired product.

Example 3: Production of cyclohexane without ethyl formate The equipment was set up as in Figure 1. The catalyst chamber 1 (15) was charged with Deloxan AP II (Pt) 5% and maintained at a temperature of 400C (16). Catalyst chamber 2 (19) was charged with Deloxan AP II (Pd) 5% and maintained at a temperature of 80°C (20). Formic acid was charged to pump (2) and entered catalyst chamber 1 (15) at a flow rate of 0.2 ml/min. The pressure of the reactor was maintained at 80 bar by means of a back pressure regulator (24). Cyclohexene was charged to the substrate pump (10). This was pumped into catalyst chamber 2 (19) at a flow rate of 0.5 ml/min. A solution containing the product was collected from the exit of the back pressure regulator (24) in an ice cooled vial (25). Analysis of the solution by gas chromatography and'H NMR spectroscopy showed that the product was cyclohexane and that the yield was 100%.

Example 4: Production of tetrahydrofuran without formic acid (etherification) The equipment was set up as in Figure 1 and maintained. The catalyst chamber 1 (15) was charged with Deloxan AP II (Pt) 5% and maintained at a temperature of 400C (16). Catalyst chamber 2 (19) was charged with Amberlyst-15 and maintained at a temperature of 180C (20). Ethyl formate was charged to pump (6) and entered catalyst chamber 1 (15) at a flow rate of 0.4 ml/min. The pressure of the reactor was maintained at 200 bar by means of a back pressure regulator (24). 1,4-butanediol was charged to the substrate pump (10). This was pumped into chamber 2 (19) at a flow rate of 0.5 ml/min. A solution containing the product was collected from the exit of the back pressure regulator (24) in an ice cooled vial (25). Analysis of the solution by gas chromatography and

HNMR spectroscopy showed that the product was tetrahydrofuran (THF) and that the yield was 100% (see Table 1).

Example 5: Attempted Production of hydrocinnamaldehyde at 120 bar The equipment was set up as in Figure 1. The catalyst chamber 1 (15) was charged with Deloxan AP II (Pt) 5% and maintained at a temperature of 400°C (16). Catalyst chamber 2 (19) was charged with Deloxan AP II (Pd) 5% and maintained at a temperature of 100°C (20). Formic acid was charged to pump (2) and entered catalyst chamber 1 (15) at a flow rate of 0.4 ml/min. The pressure of the reactor was maintained at 120 bar by means of a back pressure regulator (24). Trans-cinnamaldehyde was charged to the substrate pump (10). This was pumped into catalyst chamber 2 (19) at a flow rate of 0.05 ml/min. A solution was collected from the exit of the back pressure regulator (24) in an ice-cooled vial (25). Analysis of the solution by gas chromatography and NMR spectroscopy showed that no reaction had occurred.

Example 6: Production of hydrocinnamaldehyde at 150 bar The equipment was set up as in Figure 1. The catalyst chamber 1 (15) was charged with Deloxan AP II (Pt) 5% and maintained at a temperature of 400°C (16). Catalyst chamber 2 (19) was charged with Deloxan AP II (Pd) 5% and maintained at a temperature of 100°C (20). Formic acid was charged to pump (2) and allowed to enter catalyst chamber 1 (15) at flow rate of 0.4 ml/min. The pressure of the reactor was maintained at 150 bar by means of a back pressure regulator (24). Trans-cinnamaldehyde was charged to the substrate pump (10). This was pumped into catalyst chamber 2 (19) at a flow rate of 0.05 ml/min. A solution containing the product was collected from the exit of the back pressure regulator (24) in an ice-cooled vial (25). Analysis of the solution by gas chromatography

and NMR spectroscopy showed that the product was hydrocinnamaldehyde and that the yield was 38%.

Example 7 : Production of 1,3,5,-trimethyl, 4-isopropylbenzene The equipment was set up as in Figure 1. The catalyst chamber 1 (15) was charged with Deloxan AP II (Pt) 5% and held at a temperature of 400C (16). Catalyst chamber 2 (19) was charged with Nafion SAC-13 and held at a temperature of 200C (20). Ethyl Formate was charged to pump (2) and allowed to enter catalyst chamber 1 (15) at a flow rate of 0.4 mL/min. The pressure of the cell was maintained at 100 bar by means of a backpressure regulator (24). 1,3,5-trimethylbezene was charged to the substrate pump (10). This was pumped into chamber 2 (19) at a flow rate of 0.05 mL/min. A solution containing the product was collected from the exit of the backpressure regulator (24) in an ice cooled vial (25). Analysis of the solution by gas chromatography and 1H NMR spectroscopy showed that a reaction had occurred; 1,3,5- trimethyl, 4-isopropylbenzene was identified as the only product, with a conversion of 45%.

Example 8: Production of 3 methyl, 4-isopropylphenol The equipment was set up as in Figure 1. The catalyst chamber 1 (15) was charged with Deloxan AP II (Pt) 5% and held at a temperature of 400C (16). Catalyst chamber 2 (19) was charged with Nafion SAC-13 and held at a temperature of 200C (20). Ethyl formate was charged to pump (2) and allowed to enter catalyst chamber 1 (15) at flow rate of 0.4 mL/min. The pressure of the cell was maintained at 300 bar by means of a back pressure regulator (24). M-cresol was charged to the substrate pump (10). This was pumped into chamber 2 (19) at a flow rate of 0.01 mL/min. A solution containing the product was collected from the exit of

the back pressure regulator (24) in an ice cooled vial (25). Analysis of the solution by gas chromatography and IH NMR spectroscopy showed that the product was 3-methyl, 4-isopropyphenol as the only product and the yield was 30%.

Figure 2A shows two precursor liquids 50 and 52 being metered and provided by precursor supply control meters 54 and 56 and shows the two liquids mixing before non-return valve 58. This may be permissible if the two liquids do not react together, or if they do react together but the reaction products are indeed what is wanted for introduction to the reaction chamber.

Figure 2B shows two liquids 50'and 52'mixing after passing through respective non-return valves 58'and 60. This prevents any contamination of the liquids 50'and 52'in liquid reservoirs 62 and 64.

Figure 2C schematically shows a precursor liquid 70 in a precursor liquid reservoir 72, where the liquid 70 is made of two different liquid substances, schematically shown as 74 and 76. The liquids 74 and 76 may be miscible or immiscible.

Figure 3 shows a micro-production facility similar to that of Figure 1, except that it has a gas liquid chromatograph (GLC) 80 which takes an on-line sample of what is being produced and analyses it. An infrared spectrometer 82 is also shown taking an on-line sample for on-line analysis.

The GLC and/or IR spectrometer could be at a different place in the production line, and/or samples from more than one place in the reaction sequences could be analysed.

Figure 4 shows a micro-reactor plant 90 having a reaction chamber 92, precursor liquids 94,96,98 held in reservoirs 95,97 and 99, metering pumps 100,102,104, pressure sensors 106,108,110, precursor inflow lines 112,114,116 leading to chamber 92, a pressure sensor 118 in chamber 92, a temperature controller 120 to control the temperature in chamber 92, a temperature sensor 122 in chamber 92, a back pressure regulator/pressure controller 124 controlling the pressure in chamber 92, a product collection reservoir 126, a gas/liquid chromatograph 128, an infrared spectrometer 130, and a microprocessor controller 132.

The controller 132 receives sensor signals from the sensors and output control signals to the pumps 100,102,104, the temperature controller 120, the pressure regulator 124, and the IR and GLC 128 and 130. The IR and GLC also provide information/analysis signals to the processor 132. The total volume of the chamber 92 and pipe work from reservoirs 92,96,98 to the chamber 92 is about 5ml.

The processor 132 can be programmed by a user to pump a known and carefully controlled amount of precursors 94,96 and 98 (sometimes different amounts of each, sometimes the amounts may be the same) to the chamber 92 where the liquid precursors become gaseous. In many examples the pressure and temperature in chamber 92 is such that gaseous precursor materials, or their reaction products, become supercritical fluids. Chemical reaction occurs in the chamber 92, the course of the reactions occurring in chamber 92 being controlled by the temperature, pressure, and amounts of precursor allowed into the chamber. The reaction products are analysed in an on-line process, which may be continuous, by IR and/or GLC. The processor 132 can control conditions responsive to the feedback it receives from the sensors.

The processor 132 may be programmable by a user to produce different, selectable, reaction products, possibly from the same starting precursors, or possibly using different precursor substances.

By using small pilot, or laboratory, scale equipment for supercritical fluid reactions, but starting with relatively cheap or common starting materials (e. g. simple, small, organic molecules) has the advantage that if a reaction product of interest is made, it is relatively simple to produce the same reaction product from the same or similar starting precursors in a larger production facility. This approach contrasts with traditional laboratory synthesis of new substances, which typically uses complex and expensive starting materials to prove that a particular substance can be synthesised. Industrial chemists usually have to redesign the synthetic pathway typically using cheaper starting materials to make the large scale synthesis economically viable. In this new approach the laboratory synthesis chemist uses the same starting materials that are commonly available to the industrial chemist.

In some embodiments we may make the gases from liquid precursors, and mix them and/or react them with each other, and possibly with another substance, in a chamber.

This method may also be conveniently used to convert Paraformaldahyde (CHO) n to CO + H2, (an industrially important gas mixture known as Syngas). The ratio of CO to H2 may be varied in Syngas for different purposes. Different customers want a different mix. In our method, the ratio of CO to H2 can be easily varied by judicious use and combination of two or more of the following reactions; (1) (CHO),- CO + H2

(2) HCOOH-HzO + CO.

(3) Indeed, any liquids + H2 (4) or liquids + CO which can be used to vary the amount of H2 versus CO in the resulting mixture of gases.

Thus, by varying the proportions of the liquid precursors (for example by changing their respective flow rates) we can vary the ratio of the resultant components within the gas mixture.

The reaction HCOOCzHg-)-COz + C2H6 is interesting because ethane has a relatively low critical point. We can use HCOOC2Hs specifically to create a supercritical ethane/carbon dioxide mixture. This mixture can be used as a vehicle for chemical reactions, or drying biological materials, to name but two uses.

Another useful reaction is: HCOOCH3 o CH4 + COz. We have made supercritical fluids using this. It will be appreciated that in the examples given in the Figures, the liquid precursors are delivered to the chamber 15 in liquid form and turn into gas in the chamber. They may then turn into a dense phase gas or supercritical fluid.

Figure 5A shows a chemical reactor 200 having a gas-production chamber 202 and a chemical reaction chamber 204. A liquid precursor 206 to a gas is introduced to the chamber 204 via port 208. A substance 210 is introduced to the chamber 202 via port 212. The gas produced from the precursor 206 and the substance 210 flow into the reaction chamber 204 where a chemical reaction takes place. The chamber 204 typically, but not always, has a catalyst 214 to facilitate the chemical reaction. A reaction product 216 leaves the chamber 204 via port 218.

The substance 210 may be a liquid precursor to a gas, or a gas itself, or a liquid, or a solid. The chemical reaction in chamber 204 preferably takes place in the supercritical fluid or dense phase gas state. The gas/substance mixture (or compound or mixture of compounds if they react) is preferably in the supercritical fluid or dense phase gas state in the chamber 202 and/or chamber 204. The liquid precursor 206 may be involved in the chemical reaction in the chamber 204, or it may not. The substance 210 may be involved in the chemical reaction or it may not (either of the gas from the precursor 206 or the substance may simply be a supercritical fluid/dense phase gas).

Figure 5B shows a reactor 220 that is similar to that of Figure 5A, except that no substance 210 is introduced. Similar components have been given similar reference numerals.

Figure 5C shows a variant on the chemical reactor arrangement. Reactor 230 has a first gas production chamber 202a and a second gas production chamber 202b. The chamber 202a receives liquid precursor 206". The chamber 202b receives a substance 210", which may be a gas, or a liquid precursor which experiences a chemical change to become a gas, or it may be a liquid which experiences a physical change to become a gas.

Gas from chambers 202a and 202b mix in pipework 232 and a chemical substrate 234 is introduced at or prior to a chemical reactor 204".

Figure 5D shows a variant discussed above where the substance 210"of Figure 5C is itself a liquid precursor, precursor 206 (b), and precursor 206"is also a liquid precursor (206a), both liquid precursors experiencing a chemical change to produce different gases or gas mixtures which are mixed prior to (or in some cases after) the introduction of a chemical substrate 234"'.

It will be appreciated that in preferred embodiments of the chemical reactors of Figures 5A to 5D the reactors comprise supercritical or dense phase fluid chemical reactors adapted to synthesise chemicals.

One way of looking at some embodiments of the invention is that we can provide supercritical fluids without gases as the starting point.

In summary, in one embodiment a gas or mixture of gases is produced by decomposition or chemical reaction of liquid precursor (s). The gas may be converted to a dense phase or supercritical fluid state which can be used as a medium for chemical reactions, chromatography, extraction or impregnation/modification of solid substrates. Changes in the gas composition may be made simply by modification of the metered flow rates or chemical composition of the liquid precursor (s).

The invention is performed, preferably, in a continuous flow reactor.