Method to Prepare Lab-Sized Hollow Fiber Modules for Gas

Article pubs.acs.org/IECR

Method to Prepare Lab-Sized Hollow Fiber Modules for Gas Separation Testing Tom-Gøran Skog, Stine Johansen, and May-Britt Hag̈ g* Department of Chemical Engineering, NTNU, Sem Sælandsvei 4, NO-7491 Trondheim, Norway ABSTRACT: The objective in this work was to verify an in-house developed hollow fiber potting procedure for the making of lab modules. The method is a 3-step vertical molding procedure that protects the fiber ends during the fabrication, and which enables hard potting materials to be used for the application of the module at high pressures. (1) The hollow fiber ends are protected with a biopolymeric gel in a mold. (2) A potting material is injected above the gel and solidifies in the voids between the hollow fibers. (3) The gel is removed so the free fibers can easily be cut open. The assembled lab-sized modules were packed with prepared Polysulfone (PSf) hollow fibers (5% and 20% packing densities). The fibers were made by dry−wet spinning from a PSf/NMP/water system and spinning variables adjusted to produce support fibers for coating. The modules were pressurized with N2 up to 10 bar and found to be leak-free. The CO2 permeance at 2, 4, and 6 bar at room temperature was measured to be 44.2 ± 0.3 m3(STP)/(m2·bar·h) for the 5% packing density module and 216.6 ± 0.009 m3(STP)/(m2·bar·h) for the 20% packing density module. The CO2/N2 gas selectivity was 0.79 ± 0.03, which indicated Knudsen diffusion for these support fibers. A multivariate analysis revealed that gelatin was a better protecting gel than calciumcross-linked sodium alginate. However, the module fabrication had to be done at 2 °C to prevent the gel from melting due to the reaction heat produced from the potting material. About 97 ± 2% of the hollow fibers were preserved by this method. the oil industry (the Norwegian petroleum standard).10 Hence, for natural gas conditions (>40 bar pressure and temperature >50 °C), the module should be designed to withstand in the range of 120 bar and 150 °C. This will require a very strong, temperature resistant, and chemical inert potting material. The potting material must be carefully chosen, because in a real natural gas stream, it may be affected by other wellstream components such as water, acid gases, higher hydrocarbons, and glycols. Thus, it is necessary to use durable potting materials in these module fabrications. This leads to the core of the problem. From our experience on this topic, the hard potting materials (epoxy materials), which will be required for a safe operation at high pressures, will most likely damage the hollow fibers in the cutting process. The cutting process is here referred to as the process where the hollow fibers are sliced open with a knife subsequently of the potting procedures. This work addresses this challenge and presents an innovative method on how the fibers may be protected from damage in the cutting process. The developed molding method will, in short, protect the fiber ends from the potting material by using a biopolymeric gel. When the potting material is cured, the gel is removed and the free fiber ends can be cut open without damage. Gelatin and cross-linked sodium alginate were tested as protective gels. Gelatin comes from hydrolyzed collagen, which is a group of proteins that forms a thermoresponsive gel. The kinetics and the gel temperature depend on the type of gelatin, the conditioning, the molecular weight, and the molecular weight

1. INTRODUCTION Polymeric membranes for acid gas removal have been implemented in the offshore natural gas industry for many years; however, their part of the market is still fairly modest. It is believed that the offshore acid gas removal with polymeric membranes has a huge potential and it is expected that its marked share may increase to 20% in the near future.1 In the vast list of available polymeric materials are the polyimides and cellulose-based polymers the most common membrane materials, in the form of either hollow fibers or spiral wound membranes. The composite membranes may become competitive for natural gas application due to the introduction of polymeric coatings with a high CO2 permselectivity. The composite membranes have a thin layer of such a coating on a strong and porous fiber support.1,2 The implementation and the scaling up of such membrane systems for natural gas at realistic high pressure conditions begin with a suitable hollow fiber potting procedure. When the module fabrication is solved, there are many other challenges like the fiber adhesion, the fiber vibrations, the Joule−Thomson effect,3 the feed gas flow distributions,4 the chemical resistivity, the thermal durability, and the pressure resistance. It will be important to address all of these challenges to achieve future success with hollow fiber membranes for commercial high-pressure natural gas separation. The main topic of the current investigation is the hollow fiber potting procedure. A lot is known about the module designs and the operation in general.5,6 There is, however, not so much on the topic of the module fabrication; only one method was published.7 Some fragmented information may be found in patents.8,9 The module must be gastight. It must be applicable at realistic natural gas pressure as mentioned in the previous section. That means, however, that the equipment should be designed with a safety factor of 3 to be qualified for © 2014 American Chemical Society

Received: Revised: Accepted: Published: 9841

December 5, 2013 April 6, 2014 April 9, 2014 April 9, 2014 dx.doi.org/10.1021/ie4041059 | Ind. Eng. Chem. Res. 2014, 53, 9841−9848

Industrial & Engineering Chemistry Research

Article

push the potting material outward and in between the fiber voids.7 This procedure may be difficult for larger modules and one may risk fiber end damages.9 A vertical molding process is simple to control and was thus chosen as a suitable method here. The mold was a 5 cm long and 2.54 cm wide stainless steel (316) pipe on a plate. A 0.5 cm hole was machined in the pipe wall to fit in a mixing tube. The inner side of the mold was covered completely with a Teflon lining. This prevents the potting material from adhering to the mold and can thus easily be removed. It is important that the mold is aligned correctly to the module or else the potting material may leak out. 2.3. Module Design. The module design is shown in Figure 1. The port connectors for potting are colored with yellow for simple visualization. The tube ends were polished with sandpaper and washed with ethanol. This was done to remove scratches, which may result in a potential leak during gas permeation experiments. The connections were tightened to the tube with a multihead hydraulic swaging unit from Swagelok. The expensive parts here are the connections. The connections that are in contact with the potting material must be replaced for each experiment. Thus, it was decided to inject the potting material into the port connectors, which are the cheapest replaceable parts here. The inside of the port connectors were blasted with sandpaper and washed with ethanol before the module assembly to increase the adhesion to the potting material. 2.4. Description of the Fabrication Process. A bundle of hollow fibers (40 or 130) was placed inside the module. A biopolymeric solution was injected into the mold using a syringe. It was allowed to solidify to a gel. Gelatin and sodium alginate were screened as a protective material. The action to initiate the gelling of the gelatin solution was done by cooling it below the gel temperature (25 °C, measured with a rheometer). There are several parameters that influence the gel temperature like the polymer concentration, the salt concentration, the molecular weight of the polymers, the polymer weight distribution, the polymer molecular composition, and the polymer physical structure. The solution concentration was studied closer as it affects the gel temperature, the solution viscosity, and the physical strength of the gel. The process of gelling gelatin has been described elsewhere.11 The solutions of sodium alginate gelled when mixed together with an amount of calcium chloride solution. The details of this gelling mechanism are explained by others.12 The viscosity of the polymeric solutions was measured with a rotational rheometer (MC100 Anton Paar, 21 °C in a bob-cup setup). The applied shear stress was varied between 1 and 1000 Pa. The results were fitted to the Ostwald model. The potting material was injected on top of the gel. It distributed in between the fibers and the port connector by gravity. The potting material here is a two-component epoxy, hence the curing initiated when equal amounts of the hardener and the resin were mixed in a mixing tube before being injected. The fixture time is temperature-dependent and it is approximately 15 min at room temperature.14 After the curing was completed, the potted module was removed from the mold. The mold was heated above 30 °C when the gelatin was used as the protecting gel. In this way, the gelatin melts and the module can be removed. A weak citric acid solution was applied to remove the cross-linked alginate gel. The free hollow fibers could then be cut open with a scalpel. An illustration of the procedure is shown in Figures 2 and 3. The procedure is here shown horizontal for practical reasons. It should be emphasized

distribution.11 Alginates may be extracted from marine brown algae. The alginates may be seen as linear random block copolymers with regional sequences of α-L-guluronate (Gblock), β-D-mannuronate (M-block), or with combinations like G−M blocks of different lengths. The alginate will gel in water when it is mixed with di- or trivalent cations, e.g., calcium ions (Ca2+). The guluronate can be physically cross-linked with the cations and thus form gels with different mechanical strength depending on the fraction of G-content.12 The method is verified by preparing a lab-sized hollow fiber module (2.54 cm in outer diameter and 40 cm long) with two different packing densities (5% and 20%). The modules were packed with polysulfone (PSf) hollow fibers spun in-house from a NMP/PSf/water system. The prepared modules were tested for gas pressure resistance up to 10 bar and the single gas permeation experiments (CO2 and N2) were performed at 2, 4, and 6 bar (g) at room temperature. A multivariate data analysis was done to find the best protective gel of the 226-bloom gelatin and the sodium alginate (M/G ratio = 10/60) by varying the solution concentration, the solution viscosity, the injection temperature, the curing conditions, and the gel removal conditions.

2. EXPERIMENTAL SECTION 2.1. Chemicals and Materials for Module Making. The 226-bloom gelatin (Mw = 265 525 g/mol was measured with SEC-Mals) was provided by DGF Stoess. Sodium alginate (M/ G ratio = 10/60 and Mw = 150.00) was provided by FMC biopolymers. Both the biopolymers were used as received. The module housing (2.54 cm in outer diameter and 40 cm long) was made of stainless steel (316) and was purchased from EA Smith. The Swagelok connections were purchased from Svafas. The two-component epoxy Hysol 9455 from Loctite was tested as the potting material. Its properties are given in Table 1.13 Table 1. Loctite Hysol 945513 property

Hysol 9455

fixture time [min, 22 °C] viscosity [RVT, 25 °C, mPas] thermal expansion coeff. [K−1] tensile strength [N/mm2] 98% RH [40 °C, % in initial strength, 500 h] adhesion to stainless steel [N/mm2]

15 1200−4500 191 × 10−6 1.3 20 9

The PSf hollow fibers applied in this work were spun with a dry−wet spinning technique. Details about hollow fiber spinning in general and specifically PSf may be found elsewhere.14−17 The hollow fiber properties are listed in Table 2. 2.2. Mold Design. The module potting process may be done with a vertical or a centrifugal potting process. The centrifugal potting process use the centrifugal acceleration to Table 2. Hollow Fiber Properties material outer diameter [mm] wall thickness [mm] BET specific surface area [m2/g] P/l [m3(STP)/(m2·bar·h)] CO2 αCO2/N2

PSf 0.457 0.157 135.3 0.066 0.78

± ± ± ± ±

0.008 0.006 5 0.03 0.01 9842

dx.doi.org/10.1021/ie4041059 | Ind. Eng. Chem. Res. 2014, 53, 9841−9848


Article

Figure 1. Hollow fiber module design.

about chemometrics and multivariate data analysis may be found elsewhere.18 The analysis was performed using the software Unscrambler 10.1 from CAMO. Gelatin and sodium alginate were screened as a protective material with a fractional factorial design. The analysis was performed with five variables and three responses. Each variable had two values, which were defined to be “high” or “low”. A fractional factorial design with 25−3 was established. There were eight experiments using the values listed in Table 3. The gels were considered as a success if the module were leak-free in pressure tests up to 10 bar (g) with N2. Figure 2. Step 1: the injection of a biopolymeric solution.

Table 3. Experimental Values variable

high value

low value

PCA name

type of gel material gelatin sodium alginate concentration [g/100 g H2O] C = 10 C=1 curing mechanism gelatin: cooling [°C] 40 sodium alginate: CaCl2 [g/100 g sol] C = 70 injection temperature [°C] 40 viscosity [mPas] gelatin 49.6 sodium alginate 12.1 gel removal gelatin: heating [°C] 40 sodium alginate: citric acid [M] 1 response success gel removal time [min] set time [min] gelatin sodium alginate

Figure 3. Step 2: the potting material being injected over the gel.

that the lumen side was not sealed before the injection of the potting material. The high surface tension of the aqueous gel solutions to the hydrophobic polysulfone hollow fibers and the narrow pore sizes would probably then have prevented inflow of gel solution. Additionally, the gelling time was low and the diffusion of gel would have been restricted. 2.5. Chemometrics. Multivariate data analysis was used to find a suitable protective material. The analysis of the screening experiments was performed with a principal component analysis (PCA). The data was preprocessed by centering and normalized with its standard deviation. The number of PC’s in the final model was determined by the analyst and the explained variance was optimized by removing outliers and insignificant variables. The model quality was found from comparing the calibration and verification line in the explained variance plot. The PCA was performed with the nonlinear iterative partial least squares (NIPALS) algorithm and the model was validated by cross-validation. More information

collagen alginate C C=5 C=3 30 C = 0.30 30

temp_inj. viscosity

25.5 4.3 30 0.05 success t1 t2

2.8. Investigation of Preserved Hollow Fibers. The potted hollow fiber ends and the free hollow fiber ends were both cut open by hand with a scalpel. After this, the numbers of the open and the undamaged hollow fibers were counted using a microscope. The numbers of hollow fibers were known beforehand, thus the fractions of preserved hollow fibers could be calculated. An optical microscope MZ95 from Leica was used here. The pictures were analyzed in the LAS v3.7 software 2.9. Gas Permeation Characterization. The gas permeation properties were characterized with the single gases N2 and CO2 at 2, 4, and 6 bar (g) feed pressure and at low vacuum (10−5 bar) on the permeate side of the module. The module 9843



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Figure 4. PCA score plot illustrating the clustering of objects based on the type of material.

Figure 5. PCA correlation loading plot illustrating the influence of the variables on the successful formation of continuous gels.

gas leak experiments were tested up to 10 bar. The packing density was the total fiber cross section area to the inner cross section module area, see eq 1. It was indicated that the industrial packing densities are in the range of 45−60%.8 However, for the purpose of demonstrating the method, it was decided to make modules with packing densities 5% and 20%.

PD =

A fibers A module

The permeation measurements were performed according to the constant volume method.19 The pressure transducers were a MKS instrument type 629 (0−100 mbar) on the permeate side and an IMT Industrie (0−4 bar) on the feed side. The setup was evacuated 24 h before each gas measurement to remove atmospheric or adsorbed test gases. Leak tests were performed after each test series. The permeation values were calculated from eq 2. P is the permeability [m3 (STP)·m/(m2· bar·s)], l is the membrane thickness [m], V is the volume of the permeate tank [m3], A is the membrane area [m2], T and T0 are

(1) 9844



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Figure 6. Explained variance plot illustrating the amount of explained variance of the training data as a function of the number of principal components in the PCA model.

the experimental temperature and the standard condition temperature, dp is the pressure difference across the membrane, p0 is the standard pressure [bar] and dp/dt is the change in the permeate pressure with time [bar/s]. The ideal selectivity is shown in eq 3. P 1 VT0 dppermeate = · · l A Tp0 Δp dt

(2)

αideal = Pi /Pj

(3)

3. RESULTS AND DISCUSSION 3.1. Screening of a Protective Material. We present here the results from the screening experiments. The objective was to find a suitable protective material. The results are presented in the score, the correlation loading, and the explained variance plots, see Figure 4−6. The absolute values may be found in the Appendix. Two principal components explain 76% of the variance in the data set. The first component (PC1) describes the experiments were the protective material formed a continuous plug in between the fiber and the mold (success). The second component (PC2) describes the sample characteristics that affect the preparation and removal of the gels, i.e., the settle and melt time. As can be seen from the score plot, the gelatin gels are correlated to successful protection and the alginate failed. Experiments marked as “collagen” in the score plot are positively correlated to “success” in the loading plot. All gelatin solutions (5% and 10%) formed a continuous and solid plug in all of the experiments. Figure 7 shows a successful gelatin protective gel. Alginate, on the other hand, was not found to be suitable from these experiments. The mixing of the alginate and the cross-linker solution may not have been complete before the potting material was injected, i.e., the time interval between the alginate injection and the potting material injection may have been too short. The concentration of cross-

Figure 7. Fiber bundle with and without protective gelatin.

linkers was adjusted so that the alginate solution would immediately gel when mixed together. Thus, it may be that only the upper layer of the alginate solution in the mold gelled while the lower parts were still fluid. It was thus suggested that the cracks/holes in the cured potting material were created when the liquid alginate solution and the remaining cross-linker solution were displaced by the heavier potting material. For the experiments where the gelatin concentrations were 10 wt %, the set times were lower and the melt time were longer. The solution temperatures under the injection did not affect the successful plug formation, which is probably because the solution viscosities were low and thus the solutions were able to flow in between the fibers. The validation of this analysis is shown as the red line in Figure 6. The two lines should lie as close as possible for a good model. It was decided that the experiences made from the screening phase was sufficient to choose gelatin as protective material. The protective gel after the potting formation is 9845



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shown in Figure 7. The left picture shows before and the right shows how the free fibers look like after gel removal. 3.2. Gas Pressure Resistance. The modules with gelatin as protective gels were pressure tested for leaks up to 10 bar N2. The result is shown in Table 4. Table 4. Pressure Test of Modules Made with Different Potting Temperatures exp. no.

curing temperature (oC)

dp/dt [mbar/s]

1 2

20 2

70 ± 5 0.00005 ± 0.00001

The first results showed that the modules were leaking. It can be seen from experiment 1 that the pressure drop was approximate 70 mbar/s. This was a disappointing result. An inspection of the potting in the optical microscope revealed that big voids had evolved. This potting is shown in Figure 8.

Figure 9. Measured temperature profile inside the potting material in the curing process.

the majority of the hollow fibers from the embedded fiber ends were deformed from the cutting process, hence only 45 ± 25% of the fibers were preserved. Cutting the free fibers was much easier. The fraction of open fibers was here 96 ± 2%. The remaining fibers were found deformed inside the module, this probably happened when being inserted into the module. These were still embedded in the potting material. A gentle method to introduce the hollow fibers in to the module has been explained elsewhere. Adapting this will probably improve the potting method derived here.7 3.4. Gas Permeation Tests. Modules with two different packing densities were prepared according to the developed method. The permeance and the selectivity values may be found in Figures 12 and 13. The module with 20% packing density had 216 m3 (STP)/(m2·h·bar) in CO2 permeance and 0.82 in pure gas selectivity. The 5% module displayed 44.2 m3 (STP)/(m2·h·bar) in CO2 permeance and 0.76 in pure gas selectivity. This indicates Knudsen flow (0.79 in ideal selectivity) in both of the modules. This was not unexpected because the single hollow fibers spun with this solution formulation and spinning conditions will be used as support for a composite membrane like, e.g., the FSC membrane.2 However, the permeance differences between the modules were probably due to nonuniform hollow fibers. The hollow fibers were prepared continuously, hence the spinning times where long because the spin-rates were 4 m/min. This means that the concentration of solvent in the bath would be higher toward the end than in the beginning. This concentration was not measured. Hence it is believed that the different permeance properties came from different conditions in the coagulation baths and naturally affect the module with highest packing density the most. The modules contained about 52 and 260 m, respectively, with hollow fibers. The spin session for the 20% module lasted longer, thus it may be that the concentration of NMP became higher over time. It is known that the precipitation rate of polymeric solution may change when some solvent is added to the coagulation bath.6 The variation of the gas selectivity is within the range of viscous flow and most likely some of the fibers were more permeable than others. It was shown in the previous section that the potted modules had no gas leaks. Some of the spinning sessions lasted several hours to obtain sufficient amounts of fibers. During this time, the solvent may

Figure 8. Image shows a defect potting. The upper right corner shows the defect area.

This indicated that the potting procedure had a flaw. It is known that the potting material may produce heat in the curing process.8 Hence it was decided to measure the temperature profile inside 20 mL of the curing potting material with a handheld digital thermometer (Mettler-Toledo). The measurements were done immediately after the mixing of the resin and the hardener. This was done until a maximum temperature was found. Figure 9 shows the temperature profile. The curing makes the temperature increase to 60 °C during 4 min. The gelatin gel (10%) melts at 30 °C. This indicates that the gel melted before the potting material became hard. The density of the potting material is higher than Gelatin solution, thus it probably sank and created the voids in the same process. The curing rate was reduced by lowering the temperature to 2 °C. This solved the leaks as it may be seen in experiment 2 in Table 4. This indicates that the method may be adaptable to other potting materials which produce less heat, i.e., the curing may not need to take place in a cold room. 3.3. Preserved Hollow Fibers. The purpose of this potting procedure was to enable cutting of free hollow fibers. It is easier to cut free fibers than when they are embedded in the hard potting materials. Thus, this would preserve the hollow fibers. Figures 10 and 11 compare the hollow fibers after cutting the free and the embedded fibers. The right image indicates that 9846



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Figure 10. Cross section of the hollow fibers from the 5% packing density module after applying the new cutting process (left) and cross section of the embedded hollow fibers after cutting with the old potting method (right).

Figure 13. Gas selectivity as a function of module packing density. Figure 11. Average fraction of preserved hollow fibers for the 5% and 20% packing density modules.

fiber ends during the curing process of the potting material. Gelatin was found to be a suitable protective material when the method was performed at 2 °C. The gas pressure measurements indicated that the modules were leak free up to 10 bar. The permeance measurements indicated that the hollow fibers showed Knudsen diffusion.

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APPENDIX

Table 5. Data for the Principal Component Analysis

Figure 12. CO2 permeance as a function of module packing density.

become concentrated in the coagulation bath. This is probably the reason why the permeance values are different between the 5% and 20% modules, and the average fiber permeance for the modules are different as well.

material

C

temp_inj.

melt.temp

t1

t2

viscosity

success

collagen collagen collagen alginate alginate alginate alginate collagen

5 10 10 5 3 1 3 5

40 40 30 30 30 40 30 30

60 30 20 0 0 0 0 40

10 20 10 1000 1000 1000 1000 1000

1 5 7 3 3 1 3 3

1 5 7 3 3 1 3 3

1 1 1 0 0 0 0 1

■

4. CONCLUSION We have presented and verified a method to fabricate hollow fiber modules by protecting the fiber ends during the fabrication. This method may be useful when preparing hollow fiber modules for high pressure gas testing. The 3-step method was developed where the main point is to protect the hollow

AUTHOR INFORMATION

Corresponding Author

*M.-B. Hägg. Tel: +47 73594033. E-mail: may-britt.hagg@ ntnu.no. Notes

The authors declare no competing financial interest. 9847



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ACKNOWLEDGMENTS We acknowledge the discussions and molecular weight characterization of Gelatin from Magnus Hattrem. Professor Gudmund Skjåk-Bræk from the Department of Biotechnology for providing sodium alginate. We also thank Gas Technology Centre at NTNU-Sintef for financial support.

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REFERENCES

(1) Baker, R. W.; Lokhandwala, K. Natural Gas Processing with Membranes: An Overview. Ind. Eng. Chem. Res. 2008, 47 (7), 2109− 2121. (2) Sandru, M.; Kim, T.-J.; Hägg, M.-B. High molecular fixed-sitecarrier PVAm membrane for CO2 capture. Desalination 2009, 240 (1− 3), 298−300. (3) Rautenbach, R.; Dahm, W. Gas permeation  module design and arrangement. Chem. Eng. Processing: Process Intensif. 1987, 21 (3), 141−150. (4) Zheng, J.; Xu, Y.; Xu, Z. Flow distribution in a randomly packed hollow fiber membrane module. J. Membr. Sci. 2003, 211 (2), 263− 269. (5) Bruining, W. J. A general description of flows and pressures in hollow fiber membrane modules. Chem. Eng. Sci. 1989, 44 (6), 1441− 1447. (6) Mulder, M. Basic principles of membrane technology, Second ed.; Kluwer Academic Publishers: Dordrecht, The Netherlands, 1996. (7) Li, D.; Wang, R.; Chung, T.-S. Fabrication of lab-scale hollow fiber membrane modules with high packing density. Sep. Purif. Technol. 2004, 40 (1), 15−30. (8) Tada, Y.; Ebihara, Y.; Mizuno, T. Potting material, Hollow fiber module and process for producing the same. Patent EP 1992399 A1, February 5, 2009. (9) Masahiro yamasaki, T. A., Yoshihiro, M.,Tosikuni M. Cutting apparatus for potting material with hollow fibers embedded therein. Patent US 4271740 A, June 9, 1981. (10) Norwegian petroleum standard M-001, Rev. 4, November, 2002; Norwegian Technology Centre: Oslo, Norway, 2002. (11) Schrieber, R.; Gareis, H. Gelatine handbook; Wiley-VCH:Weinheim, Germany, 2007. (12) Draget, K. I.; Moe, S. T.; Skjak-Braek, G.; Smidsrod, O. Alginates. CRC Press-Taylor & Francis Group: Boca Raton, FL, 2006; pp 289−334. (13) Loctite Hysol 9455; Technical data sheet; Henkel: Tallaght business park, Ireland, July, 2003. (14) Clausi, D. T.; Koros, W. J. Formation of defect-free polyimide hollow fiber membranes for gas separations. J. Membr. Sci. 2000, 167 (1), 79−89. (15) Pesek, S. C.; Koros, W. J. Aqueous quenched asymmetric polysulfone hollow fibers prepared by dry/wet phase separation. J. Membr. Sci. 1994, 88 (1), 1−19. (16) McKelvey, S. A.; Clausi, D. T.; Koros, W. J. A guide to establishing hollow fiber macroscopic properties for membrane applications. J. Membr. Sci. 1997, 124 (2), 223−232. (17) Chong, K. L.; Peng, N.; Yin, H.; Lipscomb, G.G.; Chung, T. S. Food sustainability by designing and modelling a membrane controlled atmosphere storage system. J. Food Eng. 2013, 114, 361−37. (18) Esbensen, K. H. Multivariate data analysis in practice, Fifth ed.; CAMO software AS: Oslo, Normay, 2009. (19) Lindbråthen, A.; Hägg, M.-B. Membrane separation of chlorine gas. Chem. Eng. Processing: Process Intensif. 2009, 48 (1), 1−16.

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Method to Prepare Lab-Sized Hollow Fiber Modules for Gas

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