Continuous preparation of polyHIPE monoliths from ionomer-stabilized high internal phase emulsions (HIPEs) for efficient recovery of spilled oils

Accepted Manuscript Continuous preparation of polyHIPE monoliths from ionomer-stabilized high internal phase emulsions (HIPEs) for efficient recovery of spilled oils Tao Zhang, Qipeng Guo PII: DOI: Reference:

S1385-8947(16)31260-8 http://dx.doi.org/10.1016/j.cej.2016.09.024 CEJ 15734

To appear in:

Chemical Engineering Journal

Received Date: Revised Date: Accepted Date:

2 May 2016 1 September 2016 6 September 2016

Please cite this article as: T. Zhang, Q. Guo, Continuous preparation of polyHIPE monoliths from ionomer-stabilized high internal phase emulsions (HIPEs) for efficient recovery of spilled oils, Chemical Engineering Journal (2016), doi: http://dx.doi.org/10.1016/j.cej.2016.09.024

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Continuous preparation of polyHIPE monoliths from ionomer-stabilized high internal phase emulsions (HIPEs) for efficient recovery of spilled oils Tao Zhang, Qipeng Guo* Polymers Research Group, Institute for Frontier Materials, Deakin University, Locked Bag 20000, Geelong, Victoria 3220, Australia

* Corresponding Author E-mail: [email protected]; Fax: +61 3 5227 1103; Tel: +61 3 5227 2802

Abstract We present a facile and continuous approach to prepare polyHIPE monoliths for efficient reclamation of spilled oils. The polyHIPE monoliths were produced from a light induced polymerization of an ionomer, namely sulfonated polystyrene stabilized high internal phase emulsions (SPS-HIPEs). The SPS-HIPEs consisted of seawater as the dispersed aqueous phase and inexpensive monomers such as butyl acrylate and tetraethyl orthosilicate (TEOS) as the continuous phase. Sulfonated polystyrene was from used foams, realizing a sustainable transformation of waste polystyrene. PolyHIPE monoliths from SPS-HIPEs (SPS-polyHIPEs) reached a high gel fraction of 93 % with exposure to UV light for only 5 minutes, providing a possibility to produce them continuously. SPS-polyHIPEs are much greener in comparison to those from surfactant- or particles-stabilized HIPEs, and no purification is required prior to use. SPS-polyHIPE monoliths exhibit interconnected macro-porous structures, and the sizes of pores as well as pore throats can be controlled simply by the volume fraction of the dispersed phase. These monoliths are hydrophobic with a water contact angle over 140 o. 1

Excellent performances have been verified for oil spill reclamation, including high absorption capacity to a series of organic solvents or oils, high absorption rate of reaching saturated absorption in 3 to 5 minutes, a high recovery rate over 85% and a high reusability over 20 times. A continuous process has been illustrated using SPS-polyHIPEs as absorbents for oil spill recovery. Keywords: PolyHIPEs, iomomer, sulfonated polystyrene, waste polystyrene, oil spill recovery

2

1. Introduction Oil spills have attracted considerable attention, as they are one of the major issues in the current world and cause serious damages to environment, transportation and even our health [1]. Several kinds of technologies have been developed to remove the spilled oils [2]. They are bioremediation with microorganisms [3-4] or biological agents, in situ combust [5-6], chemical treatment with demulsifies [7] or dispersants [8-9] and mechanical treatment with oil-water gelators [10-13] or absorbents [14-19]. Among those technologies, mechanical treatment using absorbents is the most promising, since it can remove the pollutants and reclaim the spilled oils at the same time. Therefore, the manufacture and application of absorbent are important for efficient reclamation of spilled oils. A variety of absorbents have been investigated and fabricated for oil spill recovery [14-15, 20-23], and porous materials from emulsion templating (termed as polyHIPEs) have attracted considerable attention [16, 24], because they usually exhibit interconnected macro-porous structures which facilitate the absorption of viscous liquids such as crude oil [23, 25]. To produce polyHIPEs, stable HIPEs are required. HIPEs are traditionally stabilized by surfactants and particles. However, a careful choice of surfactant is required to avoid phase inversion of emulsions at a high volume fraction of internal phase [26] and a high concentration (up to 50% of the continuous phase) is usually needed [27-29]. Surfactants are usually removed once polyHIPEs are produced, and these used surfactant can be a new pollutant to environment. Although surfactant can be incorporated into polyHIPEs covalently, specific monomers and surfactant are needed [30]. Surface modified particle have also been reported to stabilize HIPEs and

3

they are known as Pickering HIPEs [31-32], but the corresponding polyHIPEs usually have closed-cell structures [32]. Moreover, the toxicity of these nanoparticles are still in dispute [33-34]. Recently, various amphiphilic soft particles and block copolymers have been developed to stabilize HIPEs [35-38]. It has demonstrated that block copolymer (as HIPE stabilizer) is not removed during the purifying process as the entanglement of block copolymer in the polyHIPEs prevents leaching of the HIPE stabilizer [38]. We focus on the preparation of HIPEs and their applications in petroleum fields [20-21, 39-42]. An ionomer, sulfonated polystyrene has been reported previously as an efficient HIPE stabilizer [41]. Herein, we report a continuous approach to prepare polyHIPEs for oil spill recovery. The polyHIPEs (SPS-polyHIPEs) was prepared by light induced polymerization of sulfonated polystyrene stabilized HIPEs (SPS-HIPEs). The sulfonated polystyrene was obtained by sulfonation of waste polystyrene, realizing a transition from trash into treasure. SPS-polyHIPEs can be produced in a few minutes, providing a possibility to manufacture them continuously. The as-prepared SPS-polyHIPE monoliths are hydrophobic with controlled morphology, and they exhibit high absorption rate, recovery rate, high reusability and recycle. Therefore, this paper shows an environment-friendly and efficient approach to prepare and apply SPS-polyHIPE monoliths for oil spill reclamation.

2. Experimental section 2.1. Chemicals and reagents Waste polystyrene foams were collected from packing materials of vacuum cleaner (Homemake®). Ethylene glycol dimethacrylate, tetraethyl orthosilicate (TEOS) and 2-

4

Hydroxy-2-methylpropiophenone (Darocur 1173) were used as received. Butyl acrylate was purified by passing a neutral aluminium oxide column before use. All the chemicals mentioned above were purchased from Sigma-Aldrich. Seawater was collected from Anglesea, Australia. The other reagents and solvents were analytical grade and used directly. 2.2. Sample preparation Preparation of sulfonated polystyrene (SPS). SPS was obtained by the modification of waste polystyrene foams via sulfonation. The collected waste polystyrene foams were washed with water to remove dust, and they were cut into small pieces after drying at 50 oC for 3 hours. The sulfonation of polystyrene was according to the method reported in our previous paper [41]. The sulfonation degree of the as-prepared SPS was determined to be 9.8 mol % by a titration method. Preparation of SPS-polyHIPEs monoliths. SPS-polyHIPE monoliths were prepared by light induced polymerization of SPS-HIPEs. SPS-HIPEs were obtained by mixing SPS solution (25 w/v % in THF), ethylene glycol dimethacrylate, photoinitiator (Darocur 1173), butyl acrylate, TEOS and seawater for about 10 minutes with a mixer (IKA, RW16 basic). The seawater was also replaced by aqueous solutions with different pH values and salt concentrations to make a comparison. All the results are almost same and thus we will not describe them separately. The as-prepared HIPEs were transferred into transparent dishes for polymerization and the thickness of HIPEs are controlled to be less than 2 cm. SPSPolyHIPE monoliths were obtained by exposing the as-prepared SPS-HIPEs in a standard UV curing chamber (Electro-Lite ELC-500) for 5 minutes. The aqueous phase was removed by squeezing the as-obtained polyHIPEs before drying under sunlight. 2.3. Characterization

5

Gel fraction Measurement. The as-prepared SPS-polyHIPE monoliths were extracted with THF at its boiling temperature for 24 h before they were evaporated in fume hood. The residual monoliths were dried under vacuum for 24h at room temperature prior to weight measurement. Gel fractions were calculated by dividing the theoretical weight with the actual weight. Contact angle measurements. Contact angle measurements of SPS-polyHIPE monoliths were performed on a KSV CAM 101 contact angle instrument at room temperature. Distilled water was used for all the measurement and an average value was reported based on 5 measurements. Small-angle X-ray scattering (SAXS). SAXS experiments were carried out on the small/wide-angle X-ray scattering beam-line. SPS solutions and SPS-polyHIPEs were put into 1.0 mm quartz capillaries and a multiwall plate, respectively. Scanning electron microscopy (SEM). Surface morphologies of SPS-polyHIPEs were conducted on a Zeiss Supra 55VP at an acceleration voltage of 5.0 kV. The surfaces were coated with a thin gold layer prior to observation. Evaluation of recovery of model spilled oils using SPS-polyHIPEs To evaluate the properties of these SPS-polyHIPE monoliths for recovery of spilled oils, various oils were used. The properties were evaluated by the absorption rate, oil absorption capacity and recovery rate. Absorption rate. The absorption rates of these SPS-polyHIPEs were studied with toluene and gasoline. Typically, about 0.3g of monolith (m0) was put into toluene or gasoline, and monitored the weights of the monolith (mt) with time. Each sample was measured three

6

times and the average weight gained of the SPS-polyHIPE monolith at time t was defined as (mt-m0). Oil absorption capacity. Oil absorption capacity measurements were carried out according to our previous methods. In brief, 15 mL of oil was mixed with 20 mL of water in 50 ml of beaker, and then about 0.3 g of SPS-polyHIPE monolith was put into the beaker. After oil absorption reached their equilibrium, the monolith was picked up with a tweezer. It was weighed after removal of surface oil with a filter paper. Absorption capacity was calculated as follows: absorption capacity =


 



, where  and  stands for the weights

of SPS-polyHIPE monolith before and after oil absorption. Recovery rate. These SPS-polyHIPE monoliths can be reused by simple squeezing, and the absorbed oil or organic solvent was recovered from these SPS-polyHIPEs. The recovery rate was calculated as



where  is the weight of the recovered organic solvents or

(  )

oil from SPS-polyHIPEs,  the weight of SPS-polyHIPEs at the saturated state and m0 represents the initial weight of SPS-polyHIPEs.

3. Results and Discussion 3.1. SPS-polyHIPEs from SPS-stabilized HIPEs SPS with a sulfonation degree of 9.8 mol% was obtained by the sulfonation of used polystyrene foams. Polystyrene foams are commonly used as packing material and thermal insulation material, and used polystyrene foams are usually deposed into landfill because polystyrene is completed decomposed into toxic gases instead of carbonization at moderate temperature. As an amphiphilic macromolecule, SPS was has reported as an efficient water-in-oil HIPE stabilizer.[41] Here, a low concentration

7

(0.5 w/v % with regards to the continuous phase) of SPS is enough to stabilize HIPEs, and the HIPEs show the same phase inversion as reported previously.[41] The concentration is much lower than the conventional HIPE stabilizers. For conventional surfactants, which are usually required 5-50% of the continuous phase. Inorganic particles as HIPE stabilizer are usually required to be in nano-scale.[32] Recent reported stabilizers such as microgels, organogels and structured polymers either require high concentration or are difficult to be prepared [36, 40, 43]. Thus, it is safe to conclude that SPS is of economic efficiency as a stabilizer to prepare SPS-polyHIPEs. This becomes vital important once polyHIPEs are designed for reclamation of spilled oils. Therefore, a trash to treasure transformation has been realized by sulfonation of waste polystyrene foams into SPS to stabilize HIPEs. It is interesting to see that SPS shows a very high efficiency in stabilizing HIPEs, and the high efficiency can be explained in terms of the formation of HIPEs and the stability of HIPEs. For the preparation of HIPEs, SPS was dissolved into THF to form a homogenous solution. No peak can be observed from the SAXS profile of the SPS solution (Fig. S1), demonstrating that no microphase phase separation took place in the solution. This can be accounted for by the fact that that THF is a good solvent for polystyrene segments of SPS and can efficiently destroy the hydrogen bonds between –SO3H groups [44-45]. When butyl acrylate and ethylene glycol dimethacrylate were added to the THF solution, -SO3H groups can form hydrogen bonds with themselves or –COO- groups [46] due to the dilution of THF. With the addition of the aqueous phase into the organic phase, SPS may be absorbed on to the interface of the organic phase and the aqueous phase because of the hydrophobicity of –SO3H groups. This has been observed with a gentle shake of the organic phase and the aqueous phase (see Fig. S2). It means that the SPS works like a surfactant to reduce the interfacial tension and to stabilize HIPEs. SPS serving as surfactant to stabilize HIPEs was further 8

verified by the fact that no microphase separation was revealed by the SAXS profile of polyHIPE (see Fig. S3) and the formation of polyHIPEs with interconnected structures (see SEM images in Fig. 2). Most polyHIPEs with interconnected pores are formed from surfactant stabilized HIPEs, although some have been reported from Pickering emulsions recently. The high efficiency can be attributed to the high molecular weight which hinders the motions at the interface. This result is agreeable to the fact that all the efficient HIPEs stabilizers are high-molecular-weight molecules [36, 39, 47]. Once HIPEs are formed, SPS stabilized HIPEs are always stabile due to their high viscosity. It is well-known that the stability of emulsions consists of the stability of droplets and the stability of dispersion [48]. To maintain the stability of droplets, it is required to prevent the occurrence of coalescence and coarsening. SPS stabilized HIPEs showed a high viscosity with a flow-free behavior, and as a result, Brownian motions as well as the collision of the droplets in the dispersed phase are hindered, resulting in the suppression of coalescence. The immiscibility of the internal phase and the continuous phase serves as a barrier to the diffusion of the aqueous phase and thus prevents coarsening [49]. Therefore, the HIPEs possess high droplet stability. Due to the repulsion between droplets, HIPEs usually have a high stability of dispersion. In all, SPS can stabilize HIPEs at a low concentration and they are quiet stable once formed. A typical formulation of SPS-stabilized HIPEs (SPS-HIPEs) for the preparation of SPS-polyHIPEs is shown in Table 1. All the chemicals used are commercially available, which provides possibility for large scale production. Butyl acrylate was chosen as the monomer, because its polymer, poly(butyl acrylate) has a low Tg. As a result, butyl acrylate based polyHIPEs may be soft and thus squeezed to remove the absorbed oils or organic liquids. TEOS may increase the hydrophobicity of polyHIPEs and help the stability of pores in the butyl acrylate based polyHIPEs during drying 9

process. It is worth mentioning that seawater can be used directly as the dispersed aqueous phase. Seawater in oceans has an average salinity of about 3.5% (35 g L-1, or 0.599 M), and salt concentration is much higher than the critical value (about 0.15M) that we reported previously for the preparation of water-in-oil HIPEs [41]. In experiments, we successfully used seawater (from Angle Sea, Australia) to prepare SPS-HIPEs and subsequently these SPS-HIPEs were polymerized into SPS-polyHIPEs. The use of seawater directly may reduce the producing cost of polyHIPEs, and make it possible to produce polyHIPEs close to the oil spill, reducing the transportation cost of polyHIPEs.

Table 1 A typical formulation of SPS-HIPEs for the preparation of SPS-polyHIPEs.

Continuous

Components

Amounts

Butyl acrylate

10% of the total volume

organic phase

Dispersed

(v/v) Ethylene glycol dimethacrylate

2.5% of the monomer (v/v)

TEOS

2.5% of the monomer (v/v)

25 % of SPS solution in THF (w/v)

2% of the monomer (v/v)

Darocur 1173

2.5% of the monomer (v/v)

Seawater

89% of the total volume

aqueous phase

In the few existing examples of the preparation of polyHIPEs, the continuous manufacture of polyHIPEs was impossible due to their long polymerization and purification times. However, this aspect should be addressed to prepare a large scale of 10

polyHIPEs for oil spill recovery. We therefore designed the polymerization of SPSHIPEs under UV light, and the reaction was triggered with a commercial available photoinitiator. The polymerization of SPS-HIPEs can be realized in a short time, and this was verified by a high transition of SPS-HIPEs into SPS-polyHIPEs (gel fraction of 93%) after exposure of UV light only for 5 minutes. It noted that the high transition applied only to thin samples ( lower than 2 cm), a thick sample leads to a polymerized shell with original SPS-HIPEs. This can be explained by the great difference in refractive index between the continuous phase and the dispersed phase avoids the light transmittance and subsequently initiation of polymerization [42]. The polymerization time is as short as a few minutes and thus guarantees the continuous production of SPS-polyHIPEs. A scheme (Scheme1) is shown to demonstrate the real scenario of the continuous manufacture of SPS-polyHIPEs.

Scheme 1 Schematic illustration of the preparation of SPS-polyHIPE monoliths.

11

After the polymerization, the water in SPS-polyHIPEs can be squeezed out directly. Drying polyHIPEs from butyl acrylate without TEOS usually leads to the collapse of pores, but no collapse was observed to polyHIPEs from butyl acrylate and TEOS. The stability of pores may be explained by the formation of interpenetrating networks [44]. Poly(butyl acrylate) has a low glass transition temperature of -55oC, and thus the-prepared SPS-polyHIPEs are still soft with a low modulus. The dispersed phase can be removed easily by simple squeezing without using expansive and complicated equipment. As the surfaces of the as-obtained SPS-polyHIPE monoliths are hydrophobic, most of the aqueous phase are removed by the squeeze process and the residue may be dried under the sun. The hydrophobicity of SPS-polyHIPE monoliths may result from the condensation of TEOS to form interpenetrating networks [50]. The surface modification could be finished in a short time, probably because the existence of –SO3H of serves as catalyst to the hydrolysis of TEOS. SPSpolyHIPEs can be used directly without further purification due to the entanglement of SPS and polymeric scaffold to avoid the removal of HIPE stabilizer. This is very different from polyHIPEs from surfactant stabilized HIPEs, where surfactants tend to be removed during purification process. The separated aqueous phase was successfully reused to prepare HIPEs for at least 4 times. The direct use of seawater, fast polymerization of HIPEs and easy purification of SPS-polyHIPEs allow the preparation of polyHIPE monoliths near the site of oil spills, and thus facilitate the reclamation of spilled oils on sea far from coast to reduce the high transport cost of absorbents. The formulation and process of SPSHIPEs are green and sustainable, and the manufacture of SPS-HIPE monoliths is economical efficient.

3.2. Surface property and morphology of SPS-polyHIPEs 12

Densities were calculated to be 0.16, 0.14 and 0.09 g cm-3 for SPS-polyHIPE monoliths from HIPEs containing 80%, 83% and 89% of the dispersed phase, respectively. These densities are consistent with the amount of the continuous phase in their corresponding SPS-HIPEs. The low density also shows the presence of large portion of voids in the monoliths.

Surface property. The surface property of these SPS-polyHIPE monoliths was checked with water contact angle, and the results showed that the contact angles of SPS-polyHIPEs to water were 140°, 145° and 148°, corresponding to 2.0, 2.5 and 3.0% of TEOS in the continuous phase, respectively. The addition of TEOS increases the hydrophobicity of polyHIPEs monoliths. All these SPS-polyHIPEs are highly hydrophobic and they also have good oleophilicity where oil droplets can be absorbed quickly. Therefore, the SPS-polyHIPEs exhibit high selectivity from oil to water, which will facilitate the absorption of oil from oil-water mixture. With the incorporation of TEOS in the continuous phase, SPS-polyHIPEs with interpenetrating networks were formed [50]. The mechanical properties of SPSpolyHIPE monoliths increased although we do not study it quantitatively here. Therefore, the content of TEOS in the continuous phase controls both the surface property and the mechanical properties of SPS-polyHIPE monoliths, which may facilitate the manufacture of SPS-polyHIPEs with tuneable properties for oil spill recovery. We used HIPEs with 2% of TEOS in their continuous phase to produce SPSpolyHIPEs for morphology and performance study.

Morphology. The morphology of SPS-polyHIPEs were studied by SEM. Typical pores (also termed voids or cells) from emulsion templating and a fully open macroporous scaffold can be observed. Open-cell polyHIPEs are usually obtained

13

from surfactant stabilized HIPEs although several examples of polyHIPEs with opencell structures have been fabricated from particles stabilized HIPEs [51-53]. The pores of polyHIPEs were formed from the dispersed droplets in their parent HIPEs. From the comparison of a typical confocal micrograph of parent HIPE and the corresponding SEM micrograph of corresponding SPS-polyHIPEs in Fig. 1, it can be seen that the sizes of the dispersed droplets and pores are similar, showing that the pore sizes were maintained during polymerization process.

Fig. 1. Typical (a) confocal micrograph of SPS-stabilized HIPE (83%) and (b) SEM micrograph of its corresponding SPS-polyHIPEs.

The average sizes of pores and pore throats (also termed as holes, interconnecting pores or windows) were calculated from the diameters of 50 pores and pore throats respectively through image analysis (Fig. 2). The average diameters of pores in SPS-polyHIPEs from corresponding HIPEs with 80%, 83% and 89% of the

14

dispersed phased are 82.3, 105.3 and 145.6 µm, respectively, and the corresponding average size of pore throats are 7.8, 10.2 and 13.5 µm. These results showed that the sizes of pores and pore throats of these SPS-polyHIPEs increase with the increase of dispersed phase in the parent HIPEs. It shows that the sizes of pores in SPSpolyHIPEs can be controlled by simple change of the volume fraction of the dispersed phase in their corresponding parent HIPEs. The large size of pores facilitates the absorption of liquids, especially for viscous liquids, and the pore throats on the wall guarantee transportation of liquids. Based on the structures of these SPS-polyHIPEs, it is expected that they can absorb oil quickly and easily.

(d)

Diameter / µm

100

10 Pore Pore throat

80%

83%

89%

Volume fraction of the dispersed phase

Fig. 2. SEM micrographs of SPS-polyHIPEs from HIPEs containing (a) 80%, (b) 83% and (c) 89% of dispersed phase, and (d) the sizes of pores and pore throats of SPSpolyHIPEs. 15

3.3. Evaluation of recovery of model spilled oils using SPS-polyHIPEs The performances of SPS-polyHIPE monoliths for reclamation of spilled oil were evaluated by absorption rate, absorption capacity, reusability and recycle. Oil-water mixture was used to model spilled oils, and a variety of fuels and solvents including gasoline, diesel, engine oil, xylene, toluene, dichloromethane and chloroform were used. The oil-water ratio, nature of the aqueous solution (basic, acidic, neutral, saturated NaCl and Na2SO4 solution), temperature (0 oC, 20 oC and 35 oC) as well as type of water (seawater from Anglesea and pure water) do not change oil absorption from oil-water mixture, demonstrated the robustness of these SPS-polyHIPE monoliths.

Absorption Capacity (g/g)

25 20 15 10 5

Gasoline Toluene

0 0

1

2

3

4

5

6

7

8

Time (min)

Fig. 3. Weight gains of SPS-polyHIPEs to toluene and gasoline versus time.

Absorption rate. The absorption rates of SPS-polyHIPEs for toluene and gasoline are shown in Fig. 3, and it can be seen that the saturated absorption of SPS-polyHIPE monoliths can be reached from 2 to 5 min. The fast absorption could be explained by existence of the interconnected structures (macro-size pore throats) in SPS-polyHIPE monoliths. It has been reported that the permeability is dependent on the size of pore 16

throats.[54] Here, oils can be absorbed so quickly by all SPS-polyHIPE monoliths that no difference could be observed with different sizes of pore throats.

Absorption capacity. To be an efficient absorbent, SPS-polyHIPEs should have a high absorption capacity to spilled oils. In experiments, a variety of organic solvents and oils have been used to mimic the spilled oils. It was observed that all SPSpolyHIPEs absorbed oils from oil-water mixtures and after absorption, these SPSpolyHIPEs still floated on water surface. Diesel could be absorbed completely with SPS-polyHIPEs and the resultant oil absorbed SPS-polyHIPEs was floating on the surface of water. The absorbed oil in these SPS-polyHIPEs can be squeezed out easily. This process showed that the spilled oil could be separated and reclaimed from water with SPS-polyHIPEs as sorbents. The other hydrophobic solvents can also be separated in a similar way to diesel.

Absorption Capacity (g/g)

40

75% 80% 85%

30

20

10

0

ne rm e ne ylene tha ofo olin lue X roe lor as To o h l G h C Dic

il l se eo gin D ie n E

Fig. 4. Absorption capacity of SPS-polyHIPEs to various organic solvents and oils.

17

The absorption capacity of SPS-polyHIPEs to different organic solvents and oils was investigated. The capacity was calculated from the weights of oils or organic solvents in the SPS-polyHIPEs relative to the original weight of the corresponding SPS-polyHIPEs, and the results are shown in Fig. 4. These SPS-polyHIPEs showed high absorption capacity ranging from 11.2 to 37.5 g/g depending to SPS-polyHIPEs and oils. The absorption capacity is quiet high, and high capacity may be attributed to the porous characters and oleophilic properties of these SPS-polyHIPE monoliths. Moreover, it can be seen that the absorption capacity increases obviously with the increase of the volume fraction of the dispersed phase in their parent HIPEs, perhaps because these large pores contain more hydrophobic solvents and oils.

Reusability and Recovery rate. The reusability and recovery rate are important for absorbent materials to decrease the cost of spill recovery. The as-prepared SPSpolyHIPEs were studied repeatedly for spill recovery with absorption-squeezing outseparation process, and the results of reusability and recovery rate are shown in Fig. 5. It demonstrated that the absorption-recovery process of oil from oil-water mixture by SPS-polyHIPEs, and that these SPS-polyHIPEs can be used for many times. In experiments, 20 cycles have been performed to mimic the reclaim oil spills from oilwater mixtures. The toluene and diesel absorbed by these porous materials can be recovery with a recovery rate of 82- 89%.

18

40

0.8

Recovery Rate

20

0.4

10

0.2

0

0.0 0

5

10

15

15

0.6

Saturated Squeezed Recovery Rate

10

0.4

5 0.2

0

20

0.0 0

Numbers of Cycles

Recovery Rate

0.6

Saturated Squeezed

1.0

0.8

Recovery Rate

30

(b) 20

Absorption Capacity (g/g)

1.0

Absorption Capacity (g/g)

(a) 50

5

10

15

20

Numbers of Cycles

Fig. 5. Absorption capacities of SPS-polyHIPEs and spilled oil recovery with (a) chloroform and (b) diesel absorption–squeezing-out cycle number.

Scheme 2 Schematic illustration of reclamation of spiled oils with SPS-polyHIPEs.

To further enhance the efficiency of SPS-polyHIPE monoliths, we designed a continuous process for oil spill recovery. The process is schematically illustrated by Scheme 2. The SPS-polyHIPE monoliths are firstly packed into bunch, and bunches 19

are connected to form a cycle. Some bunches may absorb spilled oils from oil water mixture, and the absorbed bunches can be draw back into boat. Meanwhile, new bunches enter the oil water mixture, the absorbed oils are recovered by simple squeeze and then the polyHIPE monoliths are reused, realizing the continuous collection of oils from oil water mixture. Absorbents with both fast absorption and high absorption capacity are not common though many of them may show either of the advantages. Combining advantages of easy recovery, high recovery rate as well as the continuous process, the application of SPS-polyHIPEs for oil spill recovery is highly efficient.

4. Conclusions SPS-polyHIPEs

has

been

successfully

fabricated

from

light

induced

polymerization of SPS-stabilized HIPEs. The SPS was prepared from waste foams, realizing a sustainable method to deal with waste polystyrene. SPS-polyHIPEs with a high gel fraction of 93% can be obtained in 5 minutes, and they can be used directly without a purification process. These monoliths are hydrophobic with controllable interconnected microporous structures, which facilitate the reclamation of spilled oils. These monoliths showed high absorption capacity, and simple recovery for a series of organic solvents and oils from oil-water mixtures. The absorption capacity of these SPS-polyHIPEs varies from 10 to 38 times to different oils and organic solvents, and the absorbed oils can be recovered by squeezing out, with a high recovery rate above 85%. The SPS-polyHIPEs absorbed oils from oil-water mixtures in a few seconds, and they can be used over 20 times without clear deterioration in oil separation

20

performance. These SPS-polyHIPEs can be manufactured sustainably for efficient reclamation of oils from waste water and oil-water mixture.

Acknowledgements SAXS measurements were conducted on the SAXS/WAXS beam-line at the Australian Synchrotron, Victoria, Australia.

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Graphical abstract

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Research highlights

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HIPEs are stabilized by an ionomer from waste polystyrene foams.

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Hydrophobic polyHIPEs can be produced continuously and used directly.

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The as-prepared polyHIPEs are excellent candidates for oil spill recovery.

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Continuous collection of spilled oils with polyHIPEs has been demonstrated.

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