Method of and system for extracting dissolved substance from a liquid containing it by means of dense gas and porous membrane

The invention relates to a solute extraction method and a solute extraction system, in particular to an extraction using a hollow fibrous membrane module.

EP 0 547 575 discloses a gas separation membrane module comprising a hollow fiber bundle.

GB 2 268 096 discloses a method and apparatus for the continuous extraction of chemicals by passing a solute fluid on one side of a semipermeable membrane and by passing an extraction fluid on the other side thereof. The extraction fluid may be a gas or a compressed dense gas.

Another known solute extraction method is a conventional, equilibrium-based liquid-liquid extraction process using a contacting device, such as packing in an extraction column. Such an extraction method is known from US Pat. No. 3,477,856 (Schultz). This method consists in extracting a fragrance from a substance containing it with liquid carbon dioxide using an extraction column. In this typical system, the aqueous solution is introduced into the column upwards. At the same time, liquid CO2 enters the column downward. Due to the different densities, the aqueous solution moves downwards, while the liquid CO2 moves upwards in the column, liquid CO2 forming a solution with the organic solute. This liquid CO 2 odor phase then exits the extraction vessel from above, and the organic solute is then separated by the CO 2 evaporation.

One limitation of this traditional equilibrium-based extraction is that it is slurry-based and that solvents with different densities must be used depending on gravity. Another limitation of traditional liquid-liquid extraction is the possibility of forming stable emulsions, in which case no extraction will occur. In addition, the box

176 944 of the contact surface in the extraction apparatus can be reduced by channel formation. When two such phases are suspended from one another, they will tend to form and follow paths of least resistance inside the column. If the fillings are not tight, with the suspension of two phases, the mass extraction efficiency is low.

An improvement over the known liquid-liquid extractions is the use of microporous hollow fibrous membranes, which in the extraction apparatus are packed together inside the outer casing in the form of a bundle of fibers. One liquid is passed through the lumen in the hollow fiber and the other liquid is passed along the casing side of the fibers with the solute passing through the membrane. As membrane extraction is a non-dispersion operation, the system does not require a density difference between the phases. In addition, the possibility of emulsification is reduced as the membrane stabilizes the transition surface between the two phases. Seibert AF et al., "Hydraulics and Mass Transfer Efficiency of a Commercial-Scale Membrane Extractor", Separation Science and Technology, 28 (1-3), pp. 343-359 (1993).

Extraction using hollow fibrous membrane modules has had limited success. The mass transfer efficiency of these modules is lower than expected, mainly due to the phenomenon of significant fiber bypass on the sheath side, which involves a large proportion of the fibers located in the module on the sheath side. Consequently, only part of the total surface area of ​​the fibers is used, and therefore the entire module is relatively inefficient. This phenomenon may result in ineffectiveness of even 70 - 90% of the membrane surface area.

Some prior art solutions have attempted to reduce the bypass problem by creating a baffle within the module that forces the sheath-side fluid to better contact the membrane surface area. However, this technique does not solve the bypassing of the sheath side fibers and further increases the cost of production of the module. It is therefore desirable to provide a method and system for extracting a solute from a fluid using porous hollow fibrous membranes in which the bypassing of the sheath side fibers is reduced and the mass transfer efficiency is improved.

According to the invention, the method of extracting a dissolved substance consists in passing one of these fluids on one side of the membrane under pressure through a membrane which acts as a barrier between two fluids, at least one of which contains the dissolved substance to be extracted and the other is the extractant. and the other on the opposite side. Substantially the same pressure is maintained on both sides of the membrane, and extraction of the solute through the membrane is caused by the solute concentration gradient between the fluids.

The method is characterized in that prior to introducing the fluids into the membrane, which is porous and permeable to a solute, one of the fluids is converted into a fluid essentially forming a phase discrete with respect to the dense gas. The membrane is preferably dried with dense gas prior to applying fluid to the membrane.

In a preferred embodiment of the invention, the dense gas and the fluid are passed countercurrently on opposite sides of the membrane, and the fluid used is fruit juice, fruit puree, vegetable juice, vegetable puree, oil-in-water emulsion, living cell broth or fermenter enzyme broth, or a second dense gas. having a density of at least about 0.5 g / cm 2³.

The passage of fluids through the membrane is preferably carried out at a temperature of -10 ° C to 200 ° C and a pressure of 2x10⁵ Pa up to 7x10⁷ Bye.

In a preferred embodiment of the process of the invention, carbon dioxide is used as a dense gas and the gas and the fluid are passed in opposite directions on opposite sides of the membrane, at least one of these media containing a dissolved flavor that is extracted and the other of them is the extractant.

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The dense gas used is preferably methane, ethane, propane, butane, isobutane, ethene, propene, fluorinated hydrocarbon, tetrafluoromethane, chlorodifluoromethane, carbon dioxide, carbon dinitoxide, sulfur hexafluoride, ammonia or methyl chloride, partially fluorinated as the fluorinated hydrocarbon. methane, ethane or propane.

According to the invention, the pressure module uses a membrane made of polypropylene, polyethylene, polytetrafluoroethylene, polyvinylidene difluoride, nylon, polysulfonate, polycarbonate, polyester, cellulose acetate, cellulose nitrate, cellulose or acrylic.

According to the invention, the solute extraction system comprises a pressurized module with fluid inlet and outlet openings and a diaphragm constituting a fluid barrier, two fluid sources connected to the module on opposite sides of the diaphragm, and a separator for the extracted substance, and is characterized in that the first fluid source is it is situated in the pressure vessel and the second fluid source is a dense gas source connected to the pressure module by a control unit, combining a pump and pressure, temperature and flow controls, while the diaphragm is porous and permeable to solute.

In the system according to the invention, the fluid inlet and outlet openings located in the pressure module are connected to one of the two sides of the diaphragm: the lumen or the skirt, while the dense gas inlet and outlet openings are connected to the other two sides of the diaphragm. Preferably, the fluid inlet and dense gas outlet openings are located on the opposite side of the module to the fluid outlet and dense gas inlet openings, and the pressurized reservoir is located in front of the module and includes a membrane, which is particularly a floating diaphragm.

In a preferred embodiment of the system according to the invention, the control unit is connected via the dense gas inlet valve to the pressurized reservoir, which in turn is connected via the fluid inlet valve to the fluid pump and comprises dense gas and fluid flow meters and a solute quantity meter, particularly preferably in the form of a sensor. light absorption. The system preferably includes a fluid return line connected to the fluid source and, optionally, a dense gas return line connected to the dense gas source.

The porous membrane in the system according to the invention is preferably a hollow fibrous membrane and particularly preferably has pores with a diameter of 0.001 µm to 1 µm, in particular with a diameter of 0.1 µm to 0.2 µm, and its thickness is in the order of 0.005-3 mm, especially of the order of 0.2 - 0.6 mm. The pores of the membrane are substantially the same size throughout its thickness.

According to the invention, dense gas and fluid are passed on opposite sides of the diaphragm, and even more preferably dense gas and fluid are passed in countercurrent on opposite sides of the diaphragm. Although the static system quickly reaches equilibrium, the passage of fluid and dense gas maintains the concentration gradient over time, and the countercurrent flow increases this gradient.

The gas gestures may be selected from a number of different gases, with carbon dioxide being particularly preferred. In addition to being inexpensive and readily available, carbon dioxide is non-toxic, non-flammable, relatively inert, and leaves no residue in the product to be extracted. Partially fluorinated methanes, ethanes, and propanes are also preferably used as dense gases, such as fluoromethane, trifluoromethane, tetrafluoroethane (generally known as HFC-134a), 1,1,1,2,3,3,3-hepafluoropropane (generally known as P227) , HFC-143a and HFC-125, and mixtures thereof.

The dissolved substance to be extracted can be any dissolved substance having some solubility in both the liquid and dense gas, and is often a smell, taste, pharmaceutical or chelated metal.

The range of temperature and pressure in which the method is carried out makes it applicable in all aqueous biological systems, both analytical and industrial.

The solute extraction system may additionally comprise means for passing the dense gas and fluid on opposite sides of the membrane as also means for equalizing substantially the pressure of the dense gas and fluid before they enter the module. If desired, the pressure equalization means may include a means of preventing

176 944 substantially extracting the solute within the pressure equalization means prior to extraction in the pressure module. In addition, the system may include means for monitoring the dense gas, fluid, and the amount of solute transferred, as well as means for returning the gas and fluid to the dense gas and fluid sources after the solute is extracted.

A porous diaphragm, preferably a hollow fibrous diaphragm or a bundle of hollow fibrous membranes, allows a large contact surface area in the pressure module. If desired, other types of membranes can be used, such as, for example, a flat membrane configured in a spiral wound membrane module or a plate frame, which can be made of many different materials.

The pores are preferably substantially the same size throughout its thickness so that the surface defects of the membrane in the form of microscopic holes have a minimal effect on its performance. The pore diameter range of 0.1-0.2 µm provides the best balance of flow parameters in combination with a symmetrical pore structure. The thickness of the membrane is preferably on the order of about 0.005 mm to about 3 mm, more preferably 0.2 - 0.6 mm. These ranges provide an increasingly better balance of membrane strength and integrity combined with desired flow characteristics.

One of the advantages of the method and system of the invention is the improved mass transfer efficiency due to the reduced bypassing of the fibers on the sheath side. Unlike traditional liquids, dense gases tend to have lower viscosities and higher diffusion coefficients. These properties allow the dense gas to better decompose and penetrate the fiber surface in the module, thereby achieving better conveying efficiency.

A further advantage is the unexpected ability of the dense gas to dry the porous membrane prior to fluid introduction, thereby minimizing the membrane's post-fluid wetting potential and improving bulk transfer efficiency.

Another advantage is that the dense gas can be passed through the module at a faster speed than traditional liquid solvents. Flow rate is an important factor for conveying efficiency, but flow rate with conventional fluid is limited due to deleterious frictional forces and increased fiber bypass on the sheath side. Since the dense gas causes less friction in the module, it can be passed at a higher speed, resulting in improved conveying efficiency.

A further advantage of the method and system of the invention is the ability of a dense gas to occupy the pores of the membrane during extraction, thereby reducing the thickness of the boundary layer where extraction takes place, and improving the mass transfer efficiency.

Yet another advantage is that the dense gas does not wet the pores of the membrane with fluid when fluid is introduced into the module. Thereby, the fluid on the side of the diaphragm opposite to the dense gas can be passed through the module at a higher speed without displacing the dense gas from the pores, thereby improving the bulk transfer efficiency.

The subject matter of the invention is shown in the embodiments in the drawings, in which Fig. 1 shows schematically a system for extracting a dissolved substance, where the dense gas flow is indicated by black arrows and the fluid flow is indicated by white arrows, Fig. 2 shows a pressure module with a hollow porous fibrous membrane, partially sectioned, Fig. 3 - a second embodiment system schematically where the black arrows represent dense gas flow and white arrows represent fluid flow and Figure 4 is a schematic representation of the experimental setup, dense gas flow also being indicated by black arrows and fluid flow white.

Figure 1 shows a solute extraction system shown at 10. The system 10 includes a dense gas source 12 and a fluid source 14 for supplying dense gas and fluid to the pressure module 16 where solute extraction takes place. The system 10 also includes a U-shaped tube separator 18 attached

176 944 functionally to the pressure module 16 to recover the extracted solute in the extractant.

The dense gas source 12 includes a gas reservoir 20 and a flow control assembly 22. The gas tank 20 is a standard gas tank, such as a tank filled with CO2 at a pressure of 70,000 Pa (1000 psi). The flow control assembly 22 is a composite pump connection with pressure, temperature and flow controls adapted to convert the gas to a dense gas having a density of at least about 0.5 g / cm 2.³ and to provide a coarse control of the dense gas flow to the rest of system 10.

The fluid source 14 is contained within a pressurized reservoir 24 having a sealed opening (not shown). Reservoir 24 may be opened to add additional fluid and / or solute. In this embodiment, the pressurized vessel 24 also serves as a means for equalizing the substantially pressures of the dense gas and fluid, and since the vessel 24 is located upstream of the module 16, the dense gas and fluid will have substantially the same pressure as when passing through the module 16. The pressure vessel 24 comprises moreover, a floating diaphragm 26 sandwiched between the fluid and the dense gas. The diaphragm 26 has a diameter close to the internal diameter of the vessel 24 and substantially prevents the extraction of the solute in the pressurized vessel 24. Since the solute is soluble in both the liquid and dense gas, some extraction may occur across the interface of two phases in the pressurized vessel 24 prior to extraction within the module 16. For this reason, a floating membrane 26 is used to substantially eliminate the occurrence of extraction in the tank 24.

The pressure module 16 is shown in greater detail in Fig. 2. The module 16, shown in simplified form, comprises a bundle 30 of three porous, hollow, fibrous membranes 28 extending longitudinally in the module 16. In industrial implementations, however, the bundle 30 would include a plurality of membranes 28. Each. the hollow fibrous diaphragm 28 ends in an attachment member 31 at opposite ends of the module 16. The bundle 30 is surrounded by a shield 32, with each fastening member 31 sealed at one end of the shield 32. The enclosure 32 is further enclosed in housing 34 using Buna N O-rings 56 to secure the shield 32 within the housing 34.

Housing 34 is typically made of stainless steel, and other metals or materials capable of operating at system pressures may be used as desired. The diaphragm 28, closing members 31 and sheath 32 are typically made of polypropylene, but may be made of any of a variety of other materials, such as, e.g. , cellulose or acrylic.

The material of the membrane can be selected depending on whether hydrophobicity or hydrophilicity is desired. For example, if an aqueous fluid is passed through module 16, then a hydrophobic membrane 28 may be desired. The hydrophobic membrane 28 will repel this aqueous fluid from the membrane pores, allowing the fluid to pass through module 16 at a higher speed without displacing the dense gas from the pores. Alternatively, if an oil or other hydrophobic fluid is used, then the hydrophyte membrane 28 is desirable for the same reason. In both cases, mass transfer efficiency is improved.

Module 16 has a fluid inlet port 36 and a fluid outlet port 38 operatively connected to module 16 such that fluid passes through module 16 on the lumen side 44 of porous hollow fibrous membranes 28. Module 16 also has dense gas inlet port 40 and dense gas outlet port 42. functionally connected to the shell side 46 membranes 28. In this way, extraction takes place through the porous hollow fibrous membranes 28 with a concentration gradient, the dissolved substance passing from the fluid on the lumen side 4-4 through the membranes 28 into the dense gas on the casing side 46. If desired, dense gas feed line 48 and conduit 50 fluid supply, as well as dense gas and fluid discharge lines 52,54 may be connected to module 16 such that

176 944 that the fluid flows through the module 16 on the casing side 46, while the dense gas flows on the lumen side 44.

U-tube separator 18 is connected to dense gas discharge port 42 via dense gas discharge line 52. When the dense solute laden gas passes through the separator 18, the gas expands and the extracted solute is recovered in the separator 18. If desired, the system can be configured such that the solute is extracted from the dense gas into the fluid. In such a case, the product recovery unit would be connected to the fluid outlet port 38 via the fluid discharge conduit 54 so that the dissolved substance could be recovered from the fluid using any of the many known separation techniques such as distillation etc.

The extraction system shown in Fig. 1 also includes other components. A fluid pump 70 is located on the fluid supply line 50 and serves to actively pass the fluid through the pressure module 16. In addition, the pump 70 can be set to various capacities, which allows the user to control the fresh fluid flow rate through the module 16. The system 10 includes several flow control devices. fluid and dense gas before and after module 16. The dense gas inlet valve 72 controls flow of dense gas to the dense gas supply line 48, and the inlet fluid valve 74 located at the bottom of pressure vessel 24 controls fluid flow from the fluid source 14. The flow of dense gas through system 10 is also controlled by a dense gas flow control valve 76 located along dense gas discharge conduit 52 between the dense gas outlet opening 42 and the U-tube separator 18.

The system 10 includes several devices for monitoring the flow of fluid and dense gas. The sample fluid valve 78 and the dense gas sample valve 80 allow the user to selectively bypass module 16 by passing the fluid and / or dense gas through the rest of the system 10 without extracting a solute. To measure the flow rate of fluid and dense gas through system 10, system 10 includes a fluid flow meter 82 and a dense gas flow meter 86. System 10 also includes a fluid counter 84 and a dense gas counter 88 for measuring the total volumes of fluid and dense gas passing through system 10.

The extraction of the dissolved substance is measured using a light absorption detector 90. The detector 90 is connected to dense gas and fluid discharge lines 52, 54 through a multi-position valve 96 allowing the user to selectively pass a dense gas or fluid sample through detector 90. In addition, a carrier fluid pump 94 pumps a carrier fluid through carrier fluid line 92 and a multi-position valve 96 to the detector. detector 90. A carrier fluid must be used as needed to dilute the dense gas or fluid measured by detector 90, and should be a carrier fluid that does not absorb ultraviolet radiation and is capable of dissolving solvents in both fluid and dense gas form. For example, methanol is a suitable carrier fluid when water and dense CO2 are used.

The non-sampled fluid to the light absorption detector 90 flows through the multi-position valve 96 into the fluid return line 98 and flows back to the pressurized reservoir 24. Meanwhile, the non-sampled dense gas is discharged into the atmosphere at ambient pressure after passing through the dense gas volume expansion unit 100 attached to dense gas discharge line 52. System 10 may be arranged to return gas from dense gas discharge line 52 back to flow control assembly 22 to re-pressurize and recycle via a gas return line (not shown) if desired.

In addition, system 10 has a pressure holding line 102 connected to the dense gas supply line 48 and the fluid discharge line 54. This line 102 has a one-way check valve 104 and provides a supplementary element for maintaining pressure in system 10. The one-way check valve 106 in the discharge line 54 also helps to stabilize the pressure. In addition, a mass flow sensor 112 and a heat exchanger 110 are included along the fluid supply conduit 50 to module 16.

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In operation, the fluid containing the dissolved substance to be extracted is placed in the pressurized reservoir 24, and then the reservoir is sealed. The hollow fibrous membranes 28 are dried and system 10 is pressurized by slowly opening the dense gas inlet valve 72 with the dense gas flow control valve 76 closed during this startup. After this pressurizing step, a dense gas at a selected process pressure is contained on both the lumen side 44 and the shell side 46 of the hollow fiber module 16. This dense gas also fills the headspace of the pressurized vessel 24, thereby equalizing the pressures of dense gas and fluid within system 10.

Fluid is then pumped into the module 16 by opening the fluid inlet valve 74 and selecting the desired stroke setting of the pump 70. At the same time, the dense gas flow control valve 76 is opened to provide the desired dense gas flow rate shown in dense gas flow meter 86.

At this point, fluid passes through module 16 on one side of porous hollow fibrous diaphragm 28 and dense gas is passed countercurrently through module 16 on the other side of diaphragm 28. Preferably, fluid passes through a lumen steep 44, while dense gas passes on casing side 46. However, this can be reversed by swapping the lead-in and out-flow lines. Inside the module 16, the extraction of the solute is driven by the concentration gradient. Since the pressurized vessel 24 has substantially equalized the pressures between the dense gas and the fluid, the pressure differential across the membranes 28 is minimal.

As shown in Fig. 1, dense gas laden with the dissolved substance passes through the dense gas outlet opening 42 into the dense gas outflow conduit 52. The dense gas continues to flow through the multi-position valve 96 and the dense gas flow control valve 76 to the U-tube separator 18 where dissolved material is recovered from the gas and gas is released to the atmosphere. Meanwhile, the fluid devoid of the solute passes through the fluid outlet port 38 into the fluid discharge conduit 54 and further through the fluid sampling valve 78 and the multi-position valve 96. The fluid. it then flows back to the pressurized reservoir 24 via fluid return line 98. The user may also measure solute extraction by passing a dense gas or fluid sample through the light absorption detector 90. If desired, the system can be configured such that the dissolved substance is extracted from the dense gas into the fluid. In such a case, a product recovery unit such as a distillation chamber or the like is positioned along the fluid discharge conduit 54 so that the dissolved substance can be recovered from the fluid.

another preferred embodiment of the principles of the invention is shown generally in Fig. 3. This embodiment is a continuous system in which dense gas is returned to the system after passing through the module. This alternative embodiment is similar in principle to the arrangement of Fig. 1 with slight differences. The main difference is the addition of a gas return line 126 that guides gas from the dissolved substance recovery 120 back to the gas flow control 22 where the gas is converted to a dense gas for further use in the system. Furthermore, the fluid source 14 is separate from the pressure equalization element. The fluid source 14 has a sealable fill opening (not shown) and is connected to a fluid flow rate control 118 that causes the fluid to pressurize. The pressurized fluid and dense gas pass from the respective flow rate control assemblies 118, 22 to the fluid supply line 50 and the dense gas supply line 48, where their pressures are substantially equalized by a pressure equalization chamber 122 connected to the two supply lines. The chamber 122 has a floating diaphragm 26 similar to the diaphragm of Fig. 1. Unlike the arrangement 10 shown in Fig. 1, however, this embodiment does not have a fluid pump 70. In addition, the fluid flow control valve 124 enables the user to control the fluid flow rate from the fluid discharge conduit 54 to the extracted fluid conduit 98 and to the extracted fluid manifold 128.

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If desired, this embodiment can also include various control and monitoring devices discussed above.

Example. This example illustrates the extraction of caffeine from water using dense CO2 as the extractant according to the method and system of the invention. The extraction system used in this example is shown in Figure 4, and is a simplified version of that shown in Figure 1 and discussed above.

The extraction was performed using a standard CO2 gas tank 20 at a pressure of 70,000 Pa (1000 psi) and a pressure tank 24 with a capacity of 300 cm. Pump 70 was a variable stroke LDC type displacement pump with a sapphire plunger with a 7.5 cm flow rate.⁵/ min. at 100% stroke setting. The material used for the vessel 24 was # 316 stainless steel and the tubing connecting the various components was 1/8 inch (3.2 mm) stainless steel.

The pressure module 16 used in this example was made of polypropylene and stainless steel. Polypropylene was used for the porous hollow fibrous membranes 28, the skirt 32, and the attachment members 31. The housing surrounding the shield was made of 25 mm (1 inch) stainless steel No. 316 tubing with a wall thickness of 2.8 mm (0.109 inch) and the shield was secured inside the housing by Buna N O-rings 56.

The polypropylene sheath 32 was 41 cm (16 inches) in length and had an outer diameter

18-20 mm (0.7 / 8 inch). The module comprised three porous hollow fibrous membranes 28, each membrane measuring 41 cm (16 inches) in length. In addition, each membrane had an inner diameter of 0.6 mm, an outer diameter of 1.0 mm, a pore size of 0.2 mm, and a porosity of 75%. The total area formed by the three membranes 28 was 40 cm². The holding volume of the module was 0.33 ml for the liquid and 5.1 ml for the dense CO2. The flow meter 86 was a rotary flow meter and the meter 88 was a conventional flow meter / dry test meter.

The layout used in this example also included some additional elements. The dense gas supply line 48 had a humidifier 134 for saturating the incoming dense gas with water. This humidifier 134 was a 100 cm cylinder³ filled with 3 mm glass beads and 15 cm3 of water. The dense gas discharge conduit 52 included a heated expansion valve 130 which heated the dense gas prior to admitting it into the U-tube separator 18. The fluid discharge conduit 54 comprised a fluid sampling conduit 138 having a fluid sampling valve 136 that allowed the user to collect a fluid sample. after fluid has passed through module 16. Also, fluid return line 98 included a one-way check valve 132.

Ten experimental cycles were performed using the system shown in Figure 4. Each cycle was run at a specified pressure and temperature for a set time with a specified CO2 flow rate and aqueous solution (caffeine in water) flow rate as listed in Table 1. For each cycle, 150 g of a 1% caffeine solution in distilled water was sealed in a pressure vessel

24. With the expansion valve 130 in the off position, the entire system was pressurized by slowly opening the dense gas inlet valve 72. After pressurizing the system, both sides 44, 46 of the lumen and skirt of module 16 contained dense CO2 at the experimental pressure. This dense CO2 also filled the headspace of the pressurized reservoir 24 substantially equalizing the pressures of the dense CO2 and the aqueous solution.

At time zero, the fluid pump 70 was started at a 30% or 100% stroke setting, giving 2.25 or 7.5 cm3 / min, respectively, as shown in Table 1. Simultaneously, the heated expansion valve 130 was opened to provide the selected CO2 flow rate. , shown in flow meter 86. At the end of the selected extraction time (given in Table 1) the flow of the dense gas and fluid was stopped. The total amount of CO2 used was shown on the counter 88 in liters at one atmosphere and at ambient temperature. This volume has been converted into grams of CO2 for the presentation in Table 1.

In all experimental cycles, the temperature was at ambient temperature and therefore CO2 was sub-quoted. However, at the pressures of 98, 210, and 280 kPa (1400, 3000, and 4000 psi) used, CO2 had a density of about 0.8, 0.9, and 0.95 g / cm3, respectively.

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In experimental runs 8, 9, and 10, dense CO2 was saturated with 0.1-0.2% H2O as it passed through the humidifier 134.

The material recovered in the U-tube separator 18 was a concentrated solution of caffeine in water. The separator 18 was rinsed with acetone and combined with an acetone residue rinse in the heated depressurized valve 130. Evaporation in the pan resulted in a weighted amount of 0.1 mg crystalline caffeine, and the amount of caffeine recovered from each experimental cycle is given in Table 1.

Table 1

<td colspan="2"></td><td colspan="9">Experimental data</td>

<td>No.</td><td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td><td> 6</td><td> 7</td><td> 8</td><td> 9</td><td> 10</td>

<td>Pressure kPa (psi)</td><td> 98</td><td> 210</td><td> 210</td><td> 98</td><td> 98</td><td> 280</td><td> 210</td><td> 210</td><td> 210</td><td> 210</td>

<td></td><td> (1400)</td><td> (3000)</td><td> (3000)</td><td> (1400)</td><td> (1400)</td><td> (4000)</td><td> (3000)</td><td> (3000)</td><td> (3000)</td><td> (3000)</td>

<td>Temperature ° C</td><td> 25</td><td> 23-24</td><td> 24</td><td> 24-25</td><td> 24</td><td> 23</td><td> 23</td><td> 24</td><td> 24</td><td> 24</td>

<td>Co2g flow rate</td><td> 258</td><td> 263</td><td> 263</td><td> 261</td><td> 263</td><td> 263</td><td> 263</td><td> 185*</td><td> 261*</td><td> 261*</td>

<td>Time, min</td><td> 30</td><td> 31</td><td> 29</td><td> 28</td><td> 15</td><td> 30</td><td> 30</td><td> 19</td><td> 23</td><td> 28</td>

<td>Flow rate H.₂Oh cm³/ min</td><td> 2,25</td><td> 2,25</td><td> 7,5</td><td> 7,5</td><td> 7,5</td><td> 7,5</td><td> 2,25</td><td> 0</td><td> 2,25</td><td> 2,25</td>

<td>Caffeine recovered from CO2, mg</td><td> 53,2</td><td> 30,0</td><td> 24,3</td><td> 24,5</td><td> 14,6</td><td> 9,1</td><td> 21,3</td><td> 5,7</td><td> 24,1</td><td> 27,3</td>

* CO2 saturated with 0.1-0.2% H2O