New generation high performance composite hollow fiber membranes for low cost CO

(1)

14th International Conference on Greenhouse Gas Control Technologies, GHGT-14 21

^st

-25

^th

October 2018, Melbourne, Australia

New generation high performance composite hollow fiber membranes for low cost CO

2

capture

Hongyu Li

^1,2

*, Winny Fam

¹

, Putu Sutrisna

¹

, Jingwei Hou

¹

, Vicki Chen

^1,2

1UNESCO Centre for Membrane Science and Technology, School of Chemical Engineering, UNSW, Australia

2CO2CRC Limited

Abstract

Research and development of membrane materials could achieve high separation performance and provide an alternative technology for CO2 capture in natural gas sweetening, carbon capture from power plants and biogas applications. While syntheses of new materials are necessary, utilizing currently available commodity materials through incorporation of high performance novel materials for most efficient transport process could substantially improve the technology deployment process. This paper presents our recent development in this aspect through mixed matrix membranes using block copolymer material Pebax, incorporating metal organic frame nano-fillers such as ZIF-8 and UiO-66 and its derivatives for the development of mixed matrix membranes (MMMs) and strategically formed thin layers of these MMMs in composite hollow fibers membrane. Not only did those membranes achieve much higher CO2 permeance of more than 350 GPU, while maintaining or improving selectivity, the nano composite hollow fibers also demonstrated much improved performance sustainability such as improved plasticization resistance. On the other hand, composite hollow fibers developed with Pebax gelled ionic liquid membranes demonstrated even better separation performance with mixed gas feed containing water vapor and trace Nox, with promising application for flue gas carbon capture.

Keywords: CO2 capture, Composite membrane, Hollow fiber

1. Introduction

Research and development towards low cost CO2 capture with membrane technology depends strongly on the material design and process optimization. Development of membranes that possess not only high permeance of CO2

but also high selectivity over light gases such as N2 and CH4 could substantially reduce the capture cost. With lower cost of polymeric material and a relatively simpler production and modulation process, polymeric membranes could offer great opportunity for CO2 capture using membrane process compared to inorganic membranes. Apart from synthesising new materials with high separation performance, utilising commercially available commodity polymer through incorporation of novel materials such as metal organic frameworks (MOFs), graphene oxide (GO) and ionic liquids (ILs) into polymeric mixed matrix membranes achieves significantly higher separation performance and fabrication of thin film composite membranes, such that incorporating those novel material could substantially reduce the technology deployment time and cost.

Based on our previous studies in development of hollow fibre membranes for natural gas sweetening, and

composite hollow fibre membranes for flue gas CO2 capture [1-4], our current studies in developing new generation

* Corresponding author

E-mail address: [email protected]

(2)

minimising thickness of separation layer for high permeate flux. Commercially available block copolymer such as polyamide-polyethylene-oxide (PA-PEO), (commercial name Pebax®), with its strong affinity to CO2 and structural flexibility, make even distribution of inorganic filler in polymer matrix possible. Composite membranes that contain Metal Organic Frameworks (MOFs) with organic ligand and metal components in its structure, for example, Zeolitic Imidazolate Framework (ZIF) could substantially improve membrane stability and separation capability. In cases of graphene oxide (GO) nanosheets, the formation of aligned structure of GO inside polymer matrix ensures the importance of efficient gas transport.

Apart from that, development of composite hollow fiber membrane incorporating gelled ionic liquid (IL) into the selective layer to utilise the higher solubility of CO2 in ILs could also improve CO2 separation. Research is required in selection of compatible solvent and loading of ionic liquids in physical blending with block copolymers to

achieve optimal separation performance. Further improvements could be achieved through addition of nanofillers into gelled IL for IL-based mixed matrix membranes.

Following the development of new membranes, demonstration of their long-term separation performance in the context of industrial gas feed is vitally important for large scale deployment. For example, one of the main issues with long term performance of polymeric membrane for CO2 separation is the possibility of CO2 induced

plasticization of polymer material (particularly membranes made of glassy polymers) which could cause

deterioration of separation efficiency. In this aspect, testing of the promising membrane materials with gas mixture containing minor components commonly found in real gas feeds such as water vapor and trace components of nox and sox and for long test period are very important for demonstration of technology capability.

This paper presents selected results of our recent research and development of high performance membranes, in particular, composite hollow fiber membranes in the context of CO2 capture in both natural sweetening and power plant flue gas applications. As part of the currently ongoing CO2CRC Otway Capture Project, our in-house developed hollow fiber membranes are being tested in Otway site with both mixed gas and well gas feed, some results will be shared in this paper.

2. Materials and methods 2.1 Materials

Based on its mechanical strength chemical stability, polyvinylidene fluoride (PVDF) hollow fiber membrane (provided by OriginWater Pure Tech Co. (China)) with pore size of 0.05μm, the outer and inner diameter 1.1 mm and 0.5 mm respectively was selected as substrate for the composite membrane.

Polyamide-polyethylene-oxide (PA-PEO), (commercial name Pebax®, chemical structure shown in Fig. 1 (a)), particularly Pebax® 1657 comprising 60 wt% PEO and 40 wt% PA6 was obtained in pellet form from Arkema, was used for mixed matrix membrane fabrication.

Poly(1-trimethylsilyl-1-propyne) (PTMSP, Gelest), chemical structure shown in Fig.1 (b) was used to prepare solution (hexane (Chem Supply)) as solvent) for coating of gutter layer and protective layer of the multi-layer composite membranes.

Zeolitic Imidazolate Framework-8 (ZIF-8) (chemical structure shown in Fig. 1 (c) was prepared in-house following the room temperature method [5] with Zinc nitrate hexahydrate and 2-methylimidazole supplied by Sigma-Aldrich, while methanol was used as the solvent.

University of Oslo-66 (UiO-66) particles (structure shown in Fig. 1 (d) were kindly provided by Dr. Deanna M.

D’Alessandro from University of Sydney.

(3)

GHGT-14 H. Li, W. Fam, P. Satrisna, J.Hou and V. Chen 3

(a) (b)

(d)

(c)

Fig. 1 Chemical structure of Pebax (a) and Poly(1-trimethylsilyl-1-propyne) (PTMSP) (b). Zeolitic Imidazolate Framework -8 (ZIF-8), The sphere represents the pore size within the structure that can be used to store gas. Zn metallic component in ZIF-8 structure is represented by blue tetrahedra, nitrogen by a green dot, and carbon by a black dot. (c), UIO-66 (d).

2.2 Fabrication of composite hollow fiber membranes

Composite hollow fiber membranes were fabricated using multi-layer dip coating technique with a semi-automatic dip coater. The dip-coating process involves

x wetting of substrate pores with water for avoidance of coating solution penetration into the substrate micropores;

x forming of gutter layer on substrate through dip coating of substrate with 2 wt% PTMSP solution, normally 4 coats were required for defect free gutter;

x coating of selective layer (3 wt% Pebax incorporating different loading of MOFs with respect to the polymer dry weight), well dispersion of nanoparticle in Pebax solution was very important. In preparation of gelled ionic liquid composite membrane, preparation of the mixed Pebax and ionic liquids with selected solvent and loading was important;

x coating of protective layer using either PTMST or Pebax solution

CH3

C C

Si

CH3

CH3 CH3

n

(4)

Fig. 2: schematic of dip coating process and structure of multi-layer composite hollow fiber.

2.3 Gas permeate tests and separation performance evaluation

Gas permeate tests were conducted with hollow fiber modules with 1-2 fibers potted inside a stainless-steel housing tube with outside-in configuration. In the permeate tests, the feed pressure was monitored using a pressure transducer connected to a desktop computer and the permeate flow rate was measured using a digital flowmeter.

Fig. 3 illustrates the gas permeate test rig with a photo of a hollow fiber membrane module inserted.

Fig. 3 gas permeate test rig and a photo of a hollow fiber membrane module with outside in transport of gas through hollow fiber.

(5)

Apart from permeation test to compare the CO2 permeation rate and CO2/N2, CO2/CH4 selectivity, the influence of feed pressure on the membrane permeation performance was evaluated by monitoring gas permeation at different feed pressure between 2 to 15 bars.

Gas permeation test with gas mixture including CO2/CH4 (20/80, v/v) gas mixture, CO2/N2. For composite hollow fibers with IL in selective layer, humidified gas mixture was also applied as feed to evaluate the separation performance.

2.4 Characterization of membrane properties

Various analytical techniques were applied to characterize physical, thermal and chemical characteristics of nano particles as well as the composite membranes. Those analysis were vital for confirmation of chemical, thermal and physical characteristics of membranes to achieve desired CO2 separation process. Detailed characterization technique and results can be found in our resent publications [5-8].

3. Results and discussion

3.1 Composite hollow fiber membranes incorporating nano-particles in selective layer

Compared to the composite hollow fiber membranes with different loading of ZIF-8 nano-particles in the selective layers, the CO2 permeance increased for more than 200% (Fig. 4 (a) and improved CO2/CH4 selectivity (Fig. 4(c)) with the increase of nanofiller loading. Incorporation of nano-particles in the mix matrix membrane also substantially improved membrane plasticization resistance, with much stable CO2 permeance in pressurization and depressurization process (much smaller difference between the solid and the dashed lines) as shown in Fig 4. Strong interaction between the ZIF-8 and glassy PA section of the block copolymer Pebax lead to improved compaction resistance of membrane matrix and swelling resistance of polymer chain in the PA section thus improving membrane plasticization resistance, and better sustainable performance of the membrane.

Fig. 4 Gas separation performance of composite hollow fiber membrane with Pebax incorporating different loading of ZIF-8 in mixed matrix membrane as selective layer (a) CO2 permeance, (b) CH4 permeance and (c) CO2/CH4 gas ideal selectivity (Solid line: pressurization; dash line:

depressurization).

When nano-particles of UiO-66 with and UiO-66 two other functional group were incorporated into the Pebax selective layer of the composite hollow fiber membrane, a much higher loading (up to 80wt%) of nano-particle could be incorporated into the selective layer. As shown in Fig. 5 (a), CO2 permeance was substantially improved (from 200 GPU to more than 300 GPU) with UiO-66-(COOH)2. At the same time, the CO2/N2 and CO2/CH4 selectivity was substantially improved, particularly at 50% loading for CO2/N2 as shown in Fig. 5 (b).

(6)

(a) (b) (c)

Fig. 5 Gas separation performance of UiO-66/Pebax-1657 based composite membranes at different particle loading: (a) CO2 permeance, (b) CO2/N2 gas selectivity and (c) CO2/CH4 gas selectivity (solid line represents pure gas and dash line represents mixed gas)

The presence of amine groups on the organic ligands improved the selective CO2 uptake for UiO-66-NH2, leading to higher CO2 solubility within the thin selective layer. The presence of amine groups also rigidified the Pebax polymer chains via the formation of hydrogen bonds that led to reduced passage of the bulkier gas molecules (e.g. N2 and CH4), thus higher selectivity. For the UiO-66-(COOH)2 nanofillers, the carboxylate groups can form hydrogen bond with PA sections of Pebax polymers and improve the gas selectivity. For both functionalized MOFs, the highest selectivities were obtained at 50 wt%, suggesting the good compatibility between nanofillers and the polymeric matrix.

3.2 Composite hollow fiber membrane with gelled IL

The composite hollow fiber with gelled IL in the selective layer not only improved CO2 permeance compared with the composite hollow fiber membrane without IL, unlike commonly observed permeance reduction with gas feed containing water vapor, the presence of water vapor enhances CO2 permeation by 30% for wet CO2/N2 feed at 80 wt % IL loading and only slightly increased the permeation of the other gas components. As a result, the gas pair selectivity with wet feeds are maintained or improved in case of CO2/N2 selectivity for composite hollow fiber containing Pebax/IL40 gel membranes as shown in Fig. 6 (c). The enhancement of CO2 permeance in the presence of water vapor traces can be attributed to swelling effect that increases gas diffusivity and preferential interaction of PEO segments and IL with CO2 over the other gas components.

(7)

Fig. 6 Comparison of gas permeations of TFC Pebax®1657/[emim][BF4] gel membranes with dry (solid line) and humidified (dashed line) mixed-gas mixtures of (a) CO2/N2 (20:80) with 0.96% NOx (b) CO2/CH4 (20:80) and (c) comparison of the gas pair selectivities.

3.3 On site tests at Otway Capture Test Facility

As part of CO2CRC Otway Capture Project, the hollow fiber membranes modules fabricated in-house (Fig. 7) with membrane areas of 40 cm² and 210 cm² have been tested with mixed gas feed on site of Otway Capture Test Facility. All selected modules have shown stable separation CO2 from CH4, (with CO2 concentration in the permeate above 97% with feed gas of 30/70 CO2/CH4. All modules were able to withstand temperature variation over 24 hour/day cycle with continuous operation without compromising separation efficiency. Lessons learnt in the initial campaigns of the project have been fed back to the modification of rig and operation procedures and the project in currently ongoing.

Fig 7: Modules prepared for Otway Capture Test Facility and a close-up of one end of the membrane module showing potting of hollow fiber inside the module for connection to the permeate line.

(8)

commitment in testing with industrial relevant gas feeds would contribute to relevant information for design and operation of membrane system for CO2 capture in large scale application.

Acknowledgement

The authors would like to thank CO2CRC and its partners and the Australian Government for funding this project.

We also acknowledge Dr. Deanna D.M’Alessandro and team in University of Sydney for their helps on preparation of UiO-66 particles.

References

[1] Dong, G., H. Li, and V. Chen, Plasticization mechanisms and effects of thermal annealing of Matrimid hollow fiber membranes for CO2 removal. J. Memb. Sci. 369 (2011) 206-220.

[2] T. Hu, G. Dong, H. Li, V. Chen, Effect of PEG and PEO−PDMS copolymer additives on the structure and performance of Matrimid® hollow fibers for CO2 separation, J. Memb. Sci. 468 (2014) 107–117.

[3] Y. Wang, H. Li, G. Dong, C. Scholes, V. Chen, Effect of Fabrication and Operation Conditions on CO2 Separation Performance of PEO-PA Block Copolymer Membranes, Ind. Eng. Chem. Res. 54 (2015) 7273–7283.

[4] Wang, Y., et al., Enhancing Membrane Permeability for CO2 Capture Through Blending Commodity Polymers with Selected PEO and PEO- PDMS Copolymers and Composite Hollow Fibres. Energy Procedia, 2014. 63: 202-209.

[5] Putu Doddy Sutrisna, Jingwei Hou, Hongyu Li, Yatao Zhang and Vicki Chen, Improved operational stability of Pebax-based gas separation membranes with ZIF-8: a comparative study of flat sheet and composite hollow fibre membranes, Journal of Membrane Science, 524, 266-279, 2017.

[6] P.D. Sutrisna, J. Hou, M.Y. Zulkifli, H. Li, Y. Zhang, W. Liang, D.M. D’Alessandro, V. Chen, Surface functionalized UiO-66/Pebax-based ultrathin composite hollow fiber gas separation membranes, J. Mater. Chem. A. 6 (2018) 918–931

[7] W. Fam, J. Mansouri, H. Li, and V. Chen, Improving CO2 separation performance of thin film composite hollow fiber with Pebax®1657/ionic liquid gel membranes, J. Memb. Sci. 537 (2017) 54–68.

[8] W. Fam, J. Mansouri, H. Li, J. Hou, and V. Chen, Gelled graphene oxide-ionic liquid composite membranes with enriched ionic liquid surfaced for improved CO2 separation, ACS Appl. Mater. Interfaces 10 (2018) 7389-7400.

(9)

(10)

1 of 10 3/21/2022, 3:19 PM

(11)

SSRN 14th Greenhouse Gas Control Technologies Conference Melbou... https://papers.ssrn.com/sol3/JELJOUR_Results.cfm?form_name=journ...

2 of 10 3/21/2022, 3:19 PM

(12)

3 of 10 3/21/2022, 3:19 PM

(13)

4 of 10 3/21/2022, 3:19 PM

(14)

5 of 10 3/21/2022, 3:19 PM

(15)

6 of 10 3/21/2022, 3:19 PM

(16)

7 of 10 3/21/2022, 3:19 PM

(17)

8 of 10 3/21/2022, 3:19 PM

(18)