Accepted Manuscript Title: Feasibility of using waste polystyrene as a membrane material for gas separation Author: Guo-Liang Zhuang Hui-Hsin Tseng Ming-Yen Wey PII: DOI: Reference:
S0263-8762(16)30038-7 http://dx.doi.org/doi:10.1016/j.cherd.2016.03.033 CHERD 2245
To appear in: Received date: Revised date: Accepted date:
23-12-2015 17-3-2016 30-3-2016
Please cite this article as: Zhuang, G.-L., Tseng, H.-H., Wey, M.-Y.,Feasibility of using waste polystyrene as a membrane material for gas separation, Chemical Engineering Research and Design (2016), http://dx.doi.org/10.1016/j.cherd.2016.03.033 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
Highlights
2
Waste polystyrene was successfully converted into useful gas–separation
3
membrane. Waste PS–derived membranes can be applied to O2/N2 and CO2/N2 separation.
5
Waste PS–derived membranes showed a competitive separation performance.
6
The butadiene rubber-contained PS was helpful to restrain the plasticization.
us
cr
ip t
4
7
Ac ce
pt
ed
M
an
8
1
Page 1 of 56
1 2
Feasibility of using waste polystyrene as a membrane material
3
for gas separation
4 5
Guo-Liang Zhuang, Hui-Hsin Tseng, Ming-Yen Wey
7
ip t
6 Graphical abstract
cr
8
W-Expandable polystyrene (EPS)
W-High-impact polystyrene (HIPS)
W-High-impact polystyrene (HIPS)
10 11 12 13 14
Ac ce
9
pt
ed
M
an
us
W-Oriented polystyrene (OPS)
15
2
Page 2 of 56
1
Feasibility of using waste polystyrene as a membrane material for gas separation
2 Guo-Liang Zhuang 1, Hui-Hsin Tseng 2, 3,*, Ming-Yen Wey 1,*
3 4 1
Taichung 402, Taiwan, ROC 2
cr
School of Occupational Safety and Health, Chung Shan Medical University, Taichung 402, Taiwan, ROC 3
Department of Occupational Medicine, Chung Shan Medical University Hospital, Taichung 402, Taiwan, ROC
an
11
Ac ce
pt
ed
M
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
ip t
Department of Environmental Engineering, National Chung Hsing University,
us
5 6 7 8 9 10
*Corresponding author at: National Chung Hsing University, Department of Environmental Engineering, 250 Kuo Kuang Rd., Taichung 402, Taiwan, ROC. Tel.: +886-4-22840441 ext. 533; fax: +886-4-22862587. E-mail address:
[email protected] (M.-Y. Wey). School of Occupational Safety and Health, Chung Shan Medical University, Taichung 402, Taiwan, ROC. Tel.: +886 4 2473 0022 ext. 12118. Fax: +886 4 2324 8194. E-mail address:
[email protected] (H.H. Tseng)
3
Page 3 of 56
1 2
Abstract
An alternate reuse route for recycling plastic solid waste (PSW) was successfully
4
developed in this study. Polystyrene (PS) waste was directly re-used as a material for
5
gas-separation membranes using a solution-casting method. The waste materials
6
comprise three types: (1) Oriented polystyrene (OPS), (2) expandable polystyrene
7
(EPS), and (3) high-impact polystyrene (HIPS); these were investigated through
8
proximate analysis, Fourier transform infrared spectroscopy, scanning electron
9
microscopy, and thermogravimetric analysis. The waste materials have the same
10
composite and thermal properties as the raw materials except for waste EPS, which
11
contains a partially broken molecular chain. Thus, besides the waste EPS, the waste
12
PS–derived membranes were homogenous and symmetrical. The gas permeation
13
performances of the membranes were measured using the time-lag method at different
14
operating pressures. The results showed that the performances of the waste PS– and
15
raw PS–derived membranes are similar. Meanwhile, a HIPS membrane containing
16
butadiene rubber exhibited high CO2 plasticization resistance at high pressure with a
17
CO2 permeability of 67 Barrer and CO2/N2 selectivity of 10–11 at an operating
Ac ce
pt
ed
M
an
us
cr
ip t
3
Abbreviations: PSW: plastic solid waste; PS: polystyrene; EPS: expandable polystyrene; HIPS:
high-impact polystyrene; MSW: municipal solid waste; GPPS: general purpose polystyrene; OPS: oriented polystyrene; W: waste; R: raw; rea: reagent-grade; TGA: thermal gravimetric analysis; FT-IR: Fourier transform infrared spectroscopy; SEM: scanning electron microscopy; PB: polybutadiene; GPC: gel permeation chromatography. 4
Page 4 of 56
1
pressure of 5 atm. Therefore, the novel reuse route of PS waste is feasible as an
2
economically and environmentally friendly method for disposing PSW.
3
Keywords: plastic waste; reuse; polystyrene; gas-separation membrane
5
ip t
4 1. Introduction
cr
6
Plastic polymer–based products have become an integral and important part of
8
our lives. Synthetic polymers include polystyrene (PS), polyethylene, polypropylene,
9
and polyethylene (Siddique et al., 2008). Over the past years, growing production has
10
increased the amount of plastic solid waste (PSW). Recently, there was a global
11
production of 1.3 billion tons/year of municipal solid waste (MSW) (Hoornweg and
12
Bhada-Tata, 2012), and PSW comprises about 8%–13% in developing and emerging
13
countries (Périou, 2012). For example, PSW comprises 32.5 million tons (about
14
12.8% by weight) in the US (United States Environmental Protection Agency, 2015)
15
and 0.2 million tons (about 17% by weight) in Taiwan (Environmental Protection
16
Administration Taiwan, 2014; Kuo et al., 2011) of the total MSW. The plastic waste
17
has accumulated over the years, resulting in serious environmental problems due to
18
the low density and long life of PSW.
Ac ce
pt
ed
M
an
us
7
19
Numerous waste treatment and management methods have been developed and
20
applied for PSW disposal. According to the waste hierarchy (Gharfalkar et al., 2015), 5
Page 5 of 56
the recycling and reuse are a top priority because it is both economically and
2
environmentally friendly (Al-Salem et al., 2009). This measure involves partial or full
3
reuse of the waste for the same or other purposes by remanufacturing; this reduces the
4
cost and conserves the non-renewable resource. However, to generate a high-value
5
recycled product with equivalent properties to the original is the main challenge for
6
the recycle and reuse of waste material (Hopewell et al., 2009).
us
cr
ip t
1
Plastic polymers have gained much attention as attractive materials for
8
gas-separation membranes over the last thirty years. They are beneficial because they
9
facilitate industrial processes, such as carbon capture from natural gas, oxygen
10
enrichment from air, and hydrogen purification (Abedini and Nezhadmoghadam,
11
2010). Moreover, polymer membranes are generally easy to prepare using
12
solution-casting methods (Michael, 1996; Murali et al., 2013). Solution-casting
13
involves dissolution of a polymer in a good solvent to form a casting solution,
14
followed by evaporation of the solvent to obtain a dense homogeneous membrane
15
(Ismail et al., 2015).
M
ed
pt
Ac ce
16
an
7
Various materials, including organic polymer and inorganic substances, are used
17
to fabricate gas separation membranes. According to Baker and Low (2014), a
18
material must exhibit industrial-scale process ability and possess thin and large
19
effective membrane area to satisfy the requirement of a promising membrane material. 6
Page 6 of 56
Polymer is the preferred precursor of gas separation membranes. For example, PS is a
2
classic glass polymer membrane material and has been applied in several cases (Table
3
1). Puleo et al. (1989) investigated the gas transport properties of a series of
4
polystyrenes with different substituents including –H, methyl, halogen atoms (i.e., F,
5
Cl, and Br), butyl, and hydroxyl in the para-position of benzene for O2/N2 and
6
CO2/CH4 separation. Kim et al. (1997) reported blending PS with poly(phenylene
7
oxide): Increased amounts of PS led to enhanced density of the membrane and
8
enhanced O2/N2 selectivity (from 4 to 6). PS can also be used as a mixed-matrix
9
polymer with materials, such as fullerenes (Polotskaya et al., 2002), metals (Kim et al.,
10
2004), multi-walled carbon nanotubes (Kumar et al., 2012; Wu et al., 2014), and
11
ZIF-8 (Chi et al., 2015) for gas separation. Thus, PS polymers are suitable for gas
12
separation membranes for O2/N2 and CO2/N2 separation and beneficial when
13
combined with additives to develop efficient mixed-matrix membranes.
Ac ce
pt
ed
M
an
us
cr
ip t
1
7
Page 7 of 56
ip t cr
Type
Material a
Bulk polymer membrane
Polystyrene
us
Table 1 Types and applications of polystyrene polymer on gas separation membrane
Applications
O2/N2 and CO2/CH4
References (Puleo et al., 1989)
O2/N2 separation
(Murphy et al., 2013)
CO2 and O2 permeation
(Prodpran et al., 2002)
CO2/CH4 separation
(Maeda and Paul, 1984)
O2/N2 separation
(Kim et al., 1997)
O2/N2 separation
(Lee et al., 1990)
PS-co-SiPS
O2, N2, CO2
(Nagasaki et al., 1996)
PS-g-POSS
O2/N2 separation
(R´ıos-Dominguez et al., 2006)
PS-co-PEO
O2/N2 separation
(Minelli et al., 2013)
PS-co-PEO
CO2/N2 separation
Fullerene(C60)/PS
O2/N2 separation
(Wang et al., 2014) (Polotskaya et al., 2002)
Silver/PS
Natural gas separation
(Kim et al., 2004)
MWCNTs/PS
H2/CO2 separation
(Kumar et al., 2012)
MWCNTs/PS
O2/N2 separation
(Wu et al., 2014)
an
1
Polystyrene Blend membrane
PS/PPO
Ac c
Mixed matrix membrane
PS-co-PU
ep te
Copolymer membrane
d
PS/PPO
M
Polystyrene
2 3 4
ZIF-8/SEBS CO2/N2 and CO2/CH4 separation (Chi et al., 2015) : PPO, poly(phenylene oxide); PU, polyurethane; Si-PS, organosilicon-containing polystyrenes; SEBS, polystyrene-b-poly(ethylene-ran-butylene)-b-polystyrene; POSS, polyhedral oligomeric silsesquioxane; PEO, polyethylene oxide; MWCNTs, multi-walled carbon nanotubes. a
8
Page 8 of 56
The gas permeation performance of a membrane can also be affected by the
2
operating pressure, especially of a glassy polymer membrane. Puleo et al. (1989)
3
reported that the CO2 permeability of a PS membrane decreased with increased
4
feeding pressure because of plasticization; that is, the PS membrane performance is
5
dependent on the operating pressure despite the suitability of PS for gas-separation
6
membrane fabrication.
us
cr
ip t
1
In this study, methods for the reuse of waste PS to form gas-separation
8
membranes were proposed and evaluated. According to the ASTM international
9
standard (D7611/D7611M, 2014), the recycling number of waste PS is “six”. In
10
general, PS products can be divided into two categories (as shown in Fig. 1): (1)
11
General purpose polystyrene (GPPS), which is synthesized from styrene monomers,
12
and (2) high impact polystyrene (HIPS), which involves grafting or co-polymerizing
13
butadiene into a PS chain, thereby improving the impact resistance and
14
machinability (Katz and Mileski, 1988; Troughton, 2009). In addition, GPPS can be
15
processed into commercial polymers (i.e., pre-consumer products) including
16
oriented polystyrene (OPS) and expandable polystyrene (EPS) via different
17
production processes: OPS is produced by stretching and extrusion, which results in
18
high visibility and stiffness (Nielsen and Buchdahl, 1950), while EPS is expanded
19
by loading it with a blowing agent and used for many applications due to the
Ac ce
pt
ed
M
an
7
9
Page 9 of 56
resultant specific properties, such as its light weight and rigidity (The BPF
2
Expanded Polystyrene Group, 2015). However, the composition and properties of
3
the different kinds of waste PS material could impact the performances of
4
waste-derived products. Thus, waste PS including OPS, EPS, and HIPS were used as
5
materials in this study.
cr
ip t
1
No
Yes
High impact polystyrene (HIPS)
M
6 7
Expandable polystyrene (EPS)
Adding butadiene
an
Polystyrene
General purpose polystyrene (GPPS)
us
Oriented polystyrene (OPS)
Fig. 1. Terms of polystyrene (PS) product. In this work, we focused on preparing PS polymer membranes derived from
9
different PS wastes (i.e., post-consumer products) using a simple solution-casting
10
method to provide an innovative solution for the reuse of PS waste. The waste
11
materials were characterized by thermal gravimetric analysis (TGA) and Fourier
12
transform infrared spectroscopy (FT-IR). The effects of the properties of the waste
13
materials on the gas permeation of the waste PS–derived membrane for H2, CO2, O2,
14
N2 and CH4 at different operating pressures were determined. The results contribute
15
to the investigations of possible reuse of waste PS materials as raw membrane
16
materials for gas separation.
17
Ac ce
pt
ed
8
10
Page 10 of 56
1
2. Material and methods
2 3
2.1. Materials
ip t
4
Waste PS-derived membranes were prepared using four waste PS containers
6
obtained from local markets. The characteristics of various PS materials are
7
tabulated in Table 2. The waste PS containers can be divided into two type: (1)
8
GPPS, which is pure PS polymer and comprises (a) W-OPS and (b) W-EPS, and (2)
9
HIPS, which is a copolymer and comprises (c) W-HIPSa and (d) W-HIPSb. The
10
waste underwent pretreatment involving crushing, washing, and drying before use. It
11
was then cut into small plastic flakes (5–10 mm), cleaned via ultra-sonication in
12
deionized water and ethanol, and dried at 75 °C in an oven overnight. To determine
13
the difference between the raw and waste materials, raw plastic (denoted as R-GPPS
14
and R-HIPS) and reagent-grade plastic (denoted as rea-GPPS and rea-HIPS) were
15
obtained from a local market and Sigma-Aldrich Co., respectively, for comparison.
us
an
M
ed
pt
Ac ce
16
cr
5
11
Page 11 of 56
ip t cr
Table 2
2
Characteristics of reagent grade, raw, and waste GPPS and HIPS used in the experimental study. R-GPPS
W-OPS
424.13
409.44
-
-
Material Appearance
W-HIPSa
W-HIPSb
402.76
438.69
427.56
417.31
327.34/431.96
-
4.0
3.7
2.9
4.0
-
Ac c
(wt%)*
408.90
R-HIPS
ep te
(°C)* Theoretical CPB
rea-HIPS
M
temperature, Td
W-EPS
an
Decomposition
rea-GPPS
d
Polymer
us
1
3
*: Decomposition temperature (Td) and theoretical concentration (CPB) of PB in the PS materials measured by TGA and FT-IR analyses,
4
respectively.
12
Page 12 of 56
1
2.2. Preparation of waste PS–derived membranes
2 Polymer membranes were prepared using the solution-casting method. The
4
polymer dope solution was 15–24 wt% in toluene solvent and was stirred overnight
5
prior to use. The resultant solutions were cast onto glass slides using a 350 μm
6
casting knife at ambient temperature. The polymer membranes were left in the air
7
for a few seconds and then kept overnight in an oven at 75 °C to evaporate the
8
solvent. The membranes were then placed in a water bath at 25 °C, washed with
9
deionized water, and dried in a vacuum oven at 75 °C overnight.
M
an
us
cr
ip t
3
12
2.3. Characterization of waste PS materials
pt
11
ed
10
The thermal decomposition temperature (Td) and proximate analysis of the
14
waste PS were determined using a thermal analyzer (TGA/differential scanning
15
calorimeter, Perkin Elmer, STA 6000) with a variety of heating procedures. The Td
16
was measured through purging and heating from 50 to 650 °C at a rate of 15 °C/min
17
under a N2 flow of 20 mL/min. The proximate analysis was carried out in the
18
following three stages (ASTM D5630-13, 2013; ASTM D1603-14,2012): The
19
samples were (i) heated from 50 to 105 °C at a rate of 10 °C/min and then held
Ac ce
13
13
Page 13 of 56
isothermally for 40 min under a N2 flow of 20 mL/min to remove any moisture, (ii)
2
heated to 900 °C at the same rate and then kept for 20 min to remove the volatile
3
matter (polymer content), and then (iii) swept with air at 20 mL/min and held
4
isothermally for 30 min to ensure removal of any fixed carbon. Finally, the ash
5
content was obtained by determining the residual weight. The chemical properties
6
and structures of the four kinds waste PS were determined by FT-IR (JASCO-4100
7
spectrophotometer). The weight- and number-average molecular weights (Mw and
8
Mn) were determined by gel permeation chromatography (Ultimate 3000 Quaternary
9
Analytical LC System). The morphologies of the waste PS–derived membranes were
10
observed by scanning electron microscopy (SEM; model JEOL JSM-6700F).
11
Surface morphologies and mechanical properties of the membranes were evaluated
12
using an atomic force microscope (AFM; BRUKER Dimension Icon). Samples were
13
sliced into 1 cm2. Surface roughness was determined in terms of mean surface
14
roughness (Ra). The mechanical properties evaluated included elastic modulus and
15
adhesion.
cr
us
an
M
ed
pt
Ac ce
16
ip t
1
17
14
Page 14 of 56
1
2.4. Gas permeation tests
2 3
Gas
permeation
properties
were
determined
using
the
constant-volume/variable-pressure method with a lab-made instrument for H2 (2.89
5
Å), CO2 (3.3 Å), O2 (3.46 Å), N2 (3.64 Å), and CH4 (3.8 Å). The membranes were
6
placed in a stainless steel cell, and both sides of the gas permeation instrument were
7
degassed under high vacuum at ambient temperature. The increase in permeate
8
pressure with time was measured using a Bourdon sensor pressure transmitter
9
(limited to 9 bar). The permeabilities of the gas pairs were measured at a range of
10
pressures including 1, 2, 3, 4, and 5 bar. The gas permeability (P) and ideal gas
11
selectivity (α) were calculated using the following equations (Ranjbaran et al., 2015;
12
Swaidan et al., 2013; Zhuang et al., 2014):
pt
ed
M
an
us
cr
ip t
4
14 15 16
Ac ce
13 P DS 1010
i/l
273.15 Vl dp 76 AT p0 dt
(1)
Pi , Pj
(2)
17 18
where P is the gas permeability (Barrer = 1 × 10−10 cm3 (STP) cm/cm2 s cm-Hg), D
19
is the diffusion coefficient (cm2/s) obtained from the time-lag (θ) as D = l2/6Vθ, S is 15
Page 15 of 56
the solubility coefficient (cm3 (STP)/cm3 cm-Hg), V is the downstream chamber
2
volume (cm3), l is the thickness of the membrane (cm), A is the effective area of the
3
membrane (cm2), T is the temperature (K), p0 is the feeding pressure (cm-Hg), dp/dt
4
is the steady-state downstream chamber pressure rise (cm-Hg/s), and αi/j is the ideal
5
gas selectivity of the membrane for gas i with respect to gas j.
cr us
6 7
3 Results and discussion
an
8 3.1. Analysis of PS wastes
M
9
pt
12
3.1.1. Proximate analysis
ed
10 11
ip t
1
The results of proximate analysis of different PS sources are given in Table 3,
14
the waste materials (W) contain 95%–99% and
