Packed Bed Reactor

Yeast Infection Free Forever

Natural Treatments to get rid of Candida

Get Instant Access

Propane*

Butane*

Pentane

*, SCFs used in biocatalysis.

applying SCFs and then to any scaling-processes is the fact that the high-pressure equipment needed is quite costly.

Enzymes are not soluble in SCFs, and several free or immobilized enzymes (lipases, trypsin, chymotrypsin, penicillin acylase, and cholesterol oxidase) are used to catalyze chemical transformations (e.g., esterification, hydrolysis, alco-holysis) in SCFs (3-14). As in the case of nonaqueous solvents, the role of water in enzyme-catalyzed reactions in SCFs can be analyzed by the same rules as for organic solvents. Although, water is needed to maintain the active conformation of the enzyme, it can also act as a solvent for polar substances, if hydrolytic processes occur, and/or be consumed or produced in situ in the system, if esterification occurs. The solubility of water in SCFs is low (e.g., 0.31% v/v in scCO2 at 50°C and 345 bar). If the water content increases during an enzymatic synthetic reaction (e.g., esterification), dehydrating agents (e.g., molecular sieves) may be used to prevent decay in the synthetic activity. The actual amount of water needed is specific to each solvent-substrate-enzyme system and must be maintained at constant level throughout the process (3). In this context, the support used to immobilize the enzymes and the hydrophobicity of the SCF also need to be considered. As an example, Kamat et al. (10) pointed to the increased activity that could be obtained for the lipase-catalyzed alcoholysis of methyl methacrylate by increasing the hydrophobicity of the SCF in the same conditions (45°C and 110 bar): SF6 > propane > ethane > ethylene > CHF3 > CO2. In the case of scCO2, it has also been observed how its logP parameter changed from 0.9 to 2.0, which involved an increase in solvent hydrophobicity, as a consequence of increasing the pressure from 30 to 118 bar at 50°C (14). In all cases, the increase in SCF hydrophobicity produced a reduction in water solubility. However, one limitation of scCO2 is the fact that it preferentially dissolves hydrophobic compounds, although strategies— involving complexation with phenylboronic acid (9) or the addition of surfactants (4)—can be developed to dissolve hydrophilic materials in this SCF.

Furthermore, the poor stability exhibited by free or immobilized enzymes in SCFs is probably the main drawback of these solvents in industrial biocatalytic processes (4). In the case of scCO2, several adverse effects on enzyme activity and stability have been described (13). These effects have been attributed to local changes in the pH of the hydration layer (8,10), or by conformational changes produced during the pressurization/depressurization steps (12,15), as well as by the ability of CO2 to form carbamates with free amine groups on the protein surface, resulting in changes in the secondary structure (11,16). Recently, a new procedure for immobilizing enzymes by sol-gel entrapment in silica-aerogels has been described, whereby enzyme molecules are included within a rigid glass framework, and this has a clearly stabilizing effect against enzyme deactivation by scCO2 (17). However, the best results have been obtained using ionic liquids (ILs; see Chapter 23). The excellent ability of these neoteric solvents to overstabilize enzymes (e.g., free CALB, Novozymes®, among others) has also been observed for an scCO2 reaction medium, even under extremely harsh conditions (e.g., 150°C and 100 bar) (18-21). ILs have been shown to act as suitable media and liquidsupports for immobilizing enzymes molecules, providing an adequate microenvironment for many enzyme-catalyzed chemical transformations in nonaqueous conditions. Additionally, the exceptional ability of scCO2 to extract a wide variety of hydrophobic compounds from certain ILs has been clearly demonstrated because, although scCO2 is highly soluble in the IL phase, the same IL is not very soluble in the scCO2 phase (22). Thus, biphasic biocatalytic processes (e.g., ester synthesis, the kinetic resolution of sec-alcohols) in IL/scCO2 systems have provided excellent results, where a homogeneous enzyme solution is immobilized in the liquid phase, and substrate and products reside largely in the supercritical phase (18-24; see Fig. 2). This strategy, whereby the mass-transfer between both IL and scCO2 phases need to be optimized (23), constitutes an interesting way for designing integral green synthetic chemical bioprocess that provide pure products.

Several types of enzymatic reactor, including stirred-tank (8-15,17), continuous packed bed (6,18-21,23,24), or membrane (25-27) reactors have been applied in SCFs, where they can be used with either free or immobilized enzymes, with and without ILs. The design of SCF bioreactors is another key feature, where masstransfer limitations, environmental conditions (pressure and temperature), and products can easily be recovered. As example, Marty et al. (6) developed a recycling packed bed enzyme-reactor at pilot scale for Lipozyme®-catalyzed ethyloleate synthesis by esterification from oleic acid and ethanol in scCO2. The proposed system was coupled with a series of four high-pressure separator vessels, in which a pressure cascade was brought about by back-pressure valves, allowing continuous recovery of the liquid product from the bottom of each separator and then the recycling of unreacted substrates. Furthermore, membrane reactors represent an attempt to integrate catalytic conversion, product separation and/or concentration, and catalyst recovery in a single operation. Thus, Lozano et al. (27) reported how enzymatic dynamic membranes, formed by depositing water-soluble polymers (e.g., gelatin or polyethyleneimine) on a ceramic porous support, exhibited excellent properties for continuous synthetic processes in scCO2, including a high degree of operational stability which favored reuse.

Polyethyleneimine

Fig. 2. High-pressure stirred tank reactor for enzyme-catalyzed transformations in scCO2. V1 to V3, needle valves; V4, safety valve; HPP, high pressure pump.

Fig. 2. High-pressure stirred tank reactor for enzyme-catalyzed transformations in scCO2. V1 to V3, needle valves; V4, safety valve; HPP, high pressure pump.

2. Materials

2.1. High-Pressure Stirred-Tank Reactor (see Fig. 2)

1. Liquid carbon dioxide tank (grade 4, 99.99 % minimum purity, water content lower than 10 ppm; see Notes 1-3).

2. Cooler.

3. High-pressure pump (HPP; Dosapro-Milton-Roy model Milroyal B).

4. Heater.

5. High-pressure stirred-tank reactor (Paar [www.paarinst.com], model 4560, 300 mL overall volume) equipped with needle valves and pressure, temperature, and stir rate controls.

6. High-performance liquid chromatography (HPLC) pump (Shimadzu Biotech, model LC-10AT, www.shimadzu.com).

7. Thermostated restrictor, calibrated at 1.5 mL/min overall flow (Teledyne Isco, Lincoln, NB; see Note 4).

2.2. High-Pressure Packed-Bed Reactor (see Fig. 3)

1. Liquid carbon dioxide tank (grade 4, 99.99 % minimum purity, water content lower than 10 ppm) pressurized at 100 bar (see Notes 1-3 and 5).

2. Supercritical fluid extractor (Teledyne Isco, model SFX 220), equipped with a syringe pump (model 100DX, 100 mL overall volume), needle valves, and devices for controlling pressure, temperature, and flow rate.

3. HPLC pump (Shimadzu, model LC-10AT).

4. Thermostated restrictor, calibrated at 1.5 mL/min overall flow (Teledyne Isco) (see Note 4).

Recirculated Packed Bed Reactor Lipase
Fig. 3. Packed-bed reactor for continuous enzyme-catalyzed transformations in scCO2, including the scheme of the biphasic nature of biotransformations in enzyme-IL-scCO2 systems.

2.3. Cross-Flow Membrane Reactor for Enzyme Immobilization (see Fig. 4)

1. a-Alumina microporous tubular membrane (130-mm length, 7-mm i.d., 0.2-|im pore size, 28.6-cm2 effective surface; Exekia, Bazet, France, www.exekia.com).

2. Aqueous solution of gelatin (5 mg/mL) containing 5 mg/mL polyethyleneimine (2 L).

3. Cross-flow filtration system for tubular ceramic membranes equipped with high-flow membrane pump (Hydra-Cell, model G037X, Wanner Engineering, Minneapolis, MN), needle valves and pressure gages (see Note 6).

4. 2% Glutaraldehyde solution ( w/v) in 50 mL of 0.1 M carbonate buffer, pH 9.2.

6. Candida antarctica lipase B (CALB, cat. no. 525L, Novozymes, Krogshoejvej, Denmark) solution (15 mg protein/mL) 0.1 Mphosphate buffer, pH 7.8.

2.4. High-Pressure Membrane Reactor With Recirculation (see Fig. 5)

1. Liquid carbon dioxide tank (grade 4, 99.99 % minimum purity, water content lower than 10 ppm; see Notes 1-3).

2. Cooler.

3. High-pressure pump (Model Milroyal B, Dosapro, Milton-Roy).

4. Heater.

Recirculated Packed Bed Reactor Lipase
Fig. 4. High-pressure membrane reactor with recirculation for enzyme-catalyzed transformations in scCO2. Vj, V2, V3, V5 and V6, needle valves; V4, safety valve; HPP, High pressure pump; RP, recirculation pump.

5. High-pressure recirculation membrane reactor, constructed in stainless-steel (internal volume 125 mL), equipped with needle valves, pressure and flow controls, recirculation pump (model 219 Micropump) and mass-flowmeter (Rheonik, Munich, Germany, www.rheonik.com) and placed in thermostated room (see Note 7).

6. HPLC pump (model LC-6A, Shimadzu).

7. Thermostated restrictor, calibrated at 1.5 mL/min overall flow rate (Teledyne Isco; see Note 4).

8. Ceramic membrane containing immobilized CALB.

3. Methods

3.1. Novozymes®-Catalyzed Butyl Butyrate Synthesis in ScCO2 Using a

Stirred-Tank Reactor (27)

1. Switch on the cooler (0°C), the heater (40°C) and the thermostated restrictor (50°C) of the system for 30 min in advance.

2. Place 50 mg Novozymes 435 (a commercial immobilized CALB preparation) in the reactor tank and carefully close the system (see Note 8).

3. Open valve V2 and closed valves V1 and V3, and then open the CO2 tank to fill the reactor to the same pressure as the bottle (see Fig. 2).

4. Switch on HPP to fill the reactor with pressurized CO2 until reach a pressure of 100 bar is reached in the reactor. Then, close valve V2 and quickly stop the HPP (see Notes 9-11).

5. Switch on the mechanic stirrer at 150 rpm.

Cross Flow Filtration
Fig. 5. Cross-flow filtration system for tubular ceramic membranes. (1) feed tank, (2) membrane pump, (3) safety valve, (4) membrane carter, (5) needle valve.

6. To start the reaction, open valve V1 and introduce 2 mL of an equimolar solution of pure substrates (4.54 M vinyl butyrate and 1-butanol, respectively) at 2 mL/ min flow rate by using the HPLC pump (for exactly 1 min). Then, stop the pump and immediately close the valve V1 (see Chapter 23).

7. To follow the reaction, aliquots could be taken from the reaction mixture at appropriate intervals of time. Carefully open valve V3 and bubble the reaction mixture into a controlled amount of hexane (e.g., 2 mL) placed on an ice-bath for exactly 3 min. Then, close the valve V3. Full reaction occurs at 3 h, giving a 99.5% synthetic product yield (see Note 12).

8. If necessary, pump additional CO2 into the reactor to reach and/or maintain desired pressure (e.g., 100 bar; see Note 8).

9. Mix 500 |L of hexane extract with 500 |L of 10 mMpropyl acetate (internal standard) solution in hexane, and chromatographically analyzes 1 |L of the resulting solution.

10. Analysis of samples can be carried out using a gass chromatography (GC) semicapillary Nukol column (15 m x 0.53 mm x 0.5 |m; Supelco, Bellefonte, PA, www.sigmaaldrich.com) and a flame ionization detector. Chromatographic conditions are as follows: carrier gas (N2) at 8 kPa (20 mL/min total flow); temperature programme: 45°C, 4 min, 8°C/min, 133°C; split ratio, 5:1; detector, 220°C. Retention times of peaks are as follows: propyl acetate, 3.2 min; vinyl butyrate, 4.3 min; 1-butanol, 6.6 min; butyl butyrate, 7.7 min and butyric acid, 13.5 min.

3.2. Free CALB-Emim NTf2-Catalyzed Kinetic Resolution of rac-1-Phenylethanol in ScCO2 Using a Continuous Packed-Bed Reactor (17)

1. Into a test tube containing 2 mL of emim+ NTf2-, add 65 |L of 0.9% (w/v) CALB solution (cat. no. 525L, Novozymes) and shake the mixture mechanically at room temperature until a clear solution is obtained (see Chapter 23).

2. Fill a Teledyne Isco 220 SFX cartridge (10-mL total volume) with glass-wool (2 g). Then, add the enzyme-emim+ NTf2- solution to wet the glass-wool, and finally place the cartridge in the high pressure extraction apparatus.

3. Open CO2 tank to fill the syringe pump at the desired pressure (e.g., 100 bar) (see Fig. 3).

4. Program the Teledyne Isco system as a dynamic extraction process at constant pressure (100 bar) and temperature (40°C).

5. Simultaneously switch on both the Teledyne Isco system and the HPLC pump to start the process by introduction of an equimolar solution of pure substrates (4.28 M vinyl propionate and rac-1-phenylethanol, respectively) at 0.01 mL/min flow rate (42.8 |imol/min mass-flow for each substrate; see Fig. 7 for reaction mechanism).

6. The system automatically opens the exit valve, continuously bubbling the reaction mixture through a calibrated heated restrictor (1 mL/min, 60°C) in a controlled amount of hexane (e.g., 2 mL) previously placed on an ice-bath. To follow the reaction kinetic, substitute the hexane every 30 min for analysis (see Note 13).

7. Mix 500 ||L of hexane extract with 50 |L of 100 mMbutyl butyrate (internal standard) solution in hexane, and chromatographically analyze 1 ||L of the resulting solution.

8. Analysis of samples can be carried out by using a GC beta-DEX-120 capillary column (30 m x 0.25 mm x 0.25 |im, Supelco) and a flame ionization detector. Chromatographic conditions are as follows: carrier gas (He) at 1 MPa (205 mL/ min total flow); temperature program: 60°C, 10°C/min, 130°C; split ratio, 100:1; detector, 300°C. Retention times of peaks are as follows: vinyl propionate, 3.2 min; propionic acid, 6.5 min; butyl butyrate, 7.3 min; ^-1-phenylethanol, 15.4 min; 5-1-phenylethanol, 16.0 min; ^-1-phenylethyl propionate, 19.3 min.

3.3. Immobilization of CALB on Ceramic Tubular Membranes (see Fig. 6 and ref. 25)

1. Place the a-alumina membrane in the carter (see Fig. 4), and then pump pure water at 20 L/min flow rate and room temperature to hydrate and wash the membrane.

2. Slightly close the recirculation needle valve to reach a backpressure of 2 bar in the system, allowing hydration of the pores.

3. Place the gelatin/polyethyleneimine solution in the feed tank and pump at 20 L/ min flow rate and room temperature. The polymer film at the inner surface of the membrane is formed by cross-flow filtration of this solution at 2 bar backpressure for 60 min. The resulting filtrate solution is re-added to the feed tank during the process (see Fig. 6).

4. Open the system and carefully remove the ceramic membrane.

5. Fill the ceramic membrane with the glutaraldehyde solution and allow to react for 30 min at room temperature to activate the free amino groups.

6. Wash the membrane with water to remove the excess of glutaraldehyde.

7. Fill the activated ceramic membrane with 15 mg/mL CALB solution (Novozymes 525L) in 0.1 M phosphate buffer, pH 7.8, and keep overnight at 8°C.

Enzymatic Reactor Tank Heater
Fig. 6. Schematic procedure for the preparation of dynamic membranes with immobilized enzymes.
Packed Bed Reactor Schematic
Fig. 7. Lipase-catalyzed kinetic resolution of rac-1-phenylethanol.

8. Collect the remaining enzyme solution and wash the enzymatic membrane twice with 0.1 M phosphate buffer, pH 7.8. All removed enzyme fractions can be used to quantify the immobilization yield (25).

9. Store the enzymatic membrane under dry conditions over P2O5 in a dessicator at 8°C.

3.4. Immobilized CALB-Catalyzed Butyl Butyrate Synthesis in ScCO2 Using a Membrane Reactor With Recirculation (27)

1. Switch on the cooler (0°C), the heater (40°C), room thermostat (40°C), and the thermostatic restrictor (50°C) of the system for 30 min in advance.

2. Place the enzymatic ceramic membrane in the carter (see Fig. 5) and carefully close the system.

3. Open valves V1 and V5 and close valves V2, V3 and V4, and then open the CO2 tank to fill the circuit to reach the pressure of the bottle (see Fig. 4).

4. Switch on HPP to fill the reactor with pressurized CO2 to reach a pressure of 90 bar in the reactor. Then, close valve Vj and quickly stop the HPP (see Notes 9-11).

5. Switch on the recirculation pump (RP) and flowmeter to control mass-flow.

6. To start the reaction, open valve V3 and introduce 2 mL of an equimolar solution of pure substrates (4.54 M vinyl butyrate and 1-butanol, respectively) at 2 mL/ min flow rate using the HPLC pump (for exactly 1 min). Then, stop the pump and immediately close valve V3 (see Chapter 23).

7. To follow the reaction, aliquots could be taken from the reaction mixture at appropriate intervals of time. Carefully open valve V5 and bubble the reaction mixture into a controlled amount of hexane (e.g., 2 mL) placed on an ice-bath, for exactly 3 min. Then, close the valve V5. Full reaction occurs at 4 h, giving a 99.5% synthetic product yield (see Note 14).

8. If necessary, pump additional CO2 into the reactor to reach and/or maintain the desired pressure (e.g., 100 bar) (see Note 8).

9. Mix 500 |L of hexane extract with 500 |L of 10 mMpropyl acetate (internal standard) solution in hexane, and chromatographically analyze 1 |L of the resulting solution.

10. The samples can be analyzed by a GC semicapillary Nukol column (15 m x 0.53 mm x 0.5 |im, Supelco) and a flame ionization detector. Chromatographic conditions are as follows: carrier gas (N2) at 8 kPa (20 mL/min total flow); temperature program: 45°C, 4 min, 8°C/min, 133°C; split ratio, 5:1; detector, 220°C. Retention times of peaks are as follows: propyl acetate, 3.2 min; vinyl butyrate, 4.3 min; 1-butanol, 6.6 min; butyl butyrate, 7.7 min and butyric acid, 13.5 min.

4. Notes

1. Purity of carbon dioxide should be as least grade 4 (99.99 %). Optionally, CO2 can be dried by placing in-line a special drying filter.

2. Carbon dioxide is an asphyxiating gas and the tank must be placed in a well-ventilated room

3. Carbon dioxide line should be is 1/4-stainless-steel tube.

4. A heater restrictor is necessary to prevent the exit-tube from freezing as samples are taken. For this, a 1/16 stainless-steel HPLC tube (1.5-m length) placed in a thermostatic bath can be used. A back-pressure regulator or two-series of needle valves must be placed to regulate the overall flow at the exit.

5. The CO2 tank pressure is 55 bar. Hyper-pressurized CO2 is obtained by capping the tank with helium until the desired pressure is reached; it is necessary to use a tank equipped with a siphon system to take CO2 from the bottom of the bottle. The use of this kind of CO2 tank is encouraged when high-pressure syringe pumps are used to reach supercritical conditions.

6. The cross-flow system will be constructed in 1/2-stainless-steel tube to support up 30 L/min recirculation flow without any backpressure in the system.

7. A safety valve must be included in the system, which is previously calibrated to the desired pressure (e.g., 100 bar).

8. Carefully close the reactor to avoid any loss of chemicals and/or CO2 when the system is pressurized.

9. The HPP can only pump liquids (e.g., CO2 at 0°C and 55 bar), but not gases.

10. To avoid a fall in the pressure close valve V2 before stopping the HPP pump.

11. If pressure exceeds desired limit, the safety valve V4 opens automatically to release the excess of CO2.

12. To avoid loss of immobilized enzyme and prevent the needle valves from becoming blocked by particulate solids, a frit stainless-steel filter must be placed at the beginning of tube for taking samples (inside the reactor).

13. The system reaches a stationary state for synthetic product at 120 min, giving a 60% enantioselective product yield.

14. Alternatively, the thermostated restrictor can be placed in valve V2 to take samples directly from the circuit.

Acknowledgments

Work partially supported by CICYT (Ref.: PPQ2002-03549) and SENECA

Foundation (Ref.: PB/75/FS/02) grants.

References

1. Oakes, R. S., Clifford A. A., and Rayner, C. M. (2001) The use of supercritical fluids in synthetic organic chemistry. J. Chem. Soc. Perkin Trans. 1, 917-941.

2. Street, W. B. (1983) Phase equilibria in fluid and solids mixtures at high pressures. In: Chemical Engineering at Supercritical Fluid Conditions (Paulatis et al., eds.) Ann Arbor Science, Ann Arbor, MI, pp. 3-30.

3. Mesiano, A. J., Beckman, E. J., and Russel. A. J. (1999) Supercritical biocatalysis. Chem. Rev. 99, 623-633.

4. Knez, Z. and Habulin, M. (2002) Compressed gases as alternative enzymatic-reaction solvents: a short review. J. Supercrit. Fluids. 23, 29-42.

5. Nakamura, K. (1990) Biochemical reactions in supercritical fluids. Trends Biotechnol. 8, 288-292.

6. Marty, A., Combes, D., and Condoret, J. S. (1994) Continuous reaction-separation process for enzymatic esterification in supercritical carbon dioxide. Biotechnol. Bioeng. 43, 497-504.

7. Beckmann, E. J. (2004) Supercritical and near-critical CO2 in green chemical synthesis and processing. J. Supercrit. Fluids. 28, 121-191.

8. Chulalaksananukul, W., Condoret, J. S., and Combes, D. (1993) Geranyl acetate synthesis by lipase catalyzed transesterification in supercritical carbon dioxide. Enzyme Microb. Technol. 15, 691-697.

9. Castillo, E., Marty, A., Combes, D., and Condoret, J. S. (1994). Polar substrates for enzymatic reactions in supercritical CO2: How to overcome the solubility limitation? Biotechnol. Lett. 16, 169-174.

10. Kamat, S., Barrera, J., Beckman, E. J., and Russell, A. J. (1992). Biocatalytic synthesis of acrylates in organic solvents and supercritical fluids: I. Optimization of enzyme environments. Biotechnol. Bioeng. 40, 158-166.

11. Kamat, S., Critchley, G., Beckman, E. J., and Russell, A. J. (1995) Biocatalytic synthesis of acrylates in organic solvents and supercritical fluids: III. Does carbon dioxide covalently modify enzymes? Biotechnol. Bioeng. 46, 610-620.

12. Almeida, M. C., Ruivo, R., Maia, C., Freire, L. Correa de Sampaio, T., and Barreiros S. (1998) Novozym 435 activity in compressed gases. Water activity and temperature effects. Enzyme Microb. Technol. 22, 494-499.

13. Habulin, M. and Knez, Z. (2001) Activity and stability of lipases from different sources in supercritical carbon dioxide and near-critical propane. J. Chem. Technol. Biotechnol. 76, 1260-1266.

14. Nakaya, H., Miyawaki, O., and Nakamura, K. (2001) Determination of log P for pressurized carbon dioxide and its characterization as a medium for enzyme reaction. Enzyme Microb. Technol. 28, 176-182.

15. Lozano, P., Avellaneda, A. Pascual, R., and Iborra, J. L. (1996). Stability of immobilized a-chymotrypsin in supercritical carbon dioxide. Biotechnol. Lett. 18, 1345-1350.

16. Striolo, A., Favaro, A., Elvassore, N., Bertucco, A., and Di Notto, V. (2003). Evidence of conformational changes for protein films expossed to high-pressure CO2 by FT-IR spectroscopy. J. Supercrit. Fluids. 27, 283-295.

17. Lozano, P., de Diego, T., Carrié, D., Vaultier, M., and Iborra, J. L. (2002) Continuous green biocatalytic processes using ionic liquids and supercritical carbon dioxide. Chem. Commum. (Camb), Apr. 7 (7), 692,693.

18. Lozano, P., de Diego, T., Carrié, D., Vaultier, M., and Iborra, J. L. (2003) Lipase catalysis in ionic liquids and supercritical carbon dioxide at 150°C. Biotechnol. Prog. 19, 380-382.

19. Lozano, P., De Diego, T., Carrié, D., Vaultier, M., and Iborra, J. L. (2003) Enzymatic catalysis in ionic liquids and supercritical carbon dioxide. In: Ionic Liquids as Green Solvents: Progress and Prospects (Rogers, R. D. and Seddon K. R., eds.) ACS Symposium Series 856, Washington DC, pp. 239-250.

20. Dzyuba, S. V. and Bartsch, R. A. (2003). Recent advances in applications of room-temperature ionic liquids/supercritical CO2 systems. Angew. Chem. Int. Ed. 42, 148-150.

21. Blanchard, L. A., Gu, Z., and Brennecke, J. F. (2001) High-pressure phase behaviour of ionic liquids/CO2 systems. J. Phys. Chem. B. 105, 2437-2444.

22. Lozano, P. De Diego, T., Carrie, D., Vaultier, M., and Iborra. J. L. (2004) Synthesis of glycidyl esters catalyzed by lipases in ionic liquids and supercritical carbon dioxide. J. Molec. Catal. A. 214, 113-119.

23. Lozano, P., de Diego, T., Gmouh, S., Vaultier, M., and Iborra, J.L. (2004). Criteria to design green enzymatic processes in ionic liquid/supercritical carbon dioxide systems. Biotechnol. Prog. 20, 661-669.

24. Novak, Z., Habulin, M., Krmelj, V., and Knez, Z. (2003). Silica aerogels as supports for lipase catalyzed esterifications at sub- and supercritical conditions. J. Supercrit. Fluids. 27, 169-178.

25. Lozano, P., Pérez-Marín, A. B., De Diego, T., et al. (2002). Active membranes coated with immobilized Candida antarctica lipase B: preparation and application for continuous butyl butyrate synthesis in organic media. J. Membrane Sci. 201, 55-64.

26. Knez, Z., Habulin, M., and Primozic, M. (2003) Hydrolases in supercritical CO2 and their use in a high-pressure membrane reactor. Bioprocess Biosyst. Eng. 25, 279-284.

27. Lozano, P., Víllora, G., Gómez, G., et al. (2004) Membrane reactor with immobilized Candida antarctica lipase B for ester synthesis in supercritical carbon dioxide. J. Supercrit. Fluids. 29, 121-128.

Was this article helpful?

0 0
Natural Remedy For Yeast Infections

Natural Remedy For Yeast Infections

If you have ever had to put up with the misery of having a yeast infection, you will undoubtedly know just how much of a ‘bummer’ it is.

Get My Free Ebook


Responses

  • abdullah
    What valve for continuous stirred tank reactor?
    8 years ago
  • Neftalem
    How to fill a teledyne isco pump?
    8 years ago
  • Roxy Donaldson
    How immobilized enzymes work on packed bed reactor?
    1 year ago

Post a comment