Catalytic activity of metal impregnated catalysts for degradation of waste polystyrene

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JIEC-1785; No. of Pages 8 Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx

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Catalytic activity of metal impregnated catalysts for degradation of waste polystyrene Jasmin Shah *, Muhammad Rasul Jan, Adnan Institute of Chemical Sciences, University of Peshawar, Khyber Pakhtunkhwa, Pakistan

A R T I C L E I N F O

Article history: Received 5 June 2013 Accepted 10 December 2013 Available online xxx Keywords: Alumina Impregnated catalyst Catalytic degradation Styrene monomer

A B S T R A C T

Waste disposal by degradation to selective and desirable products is the major challenge of our modern society. The current study presents cheap, easily achievable, and novel impregnated catalysts on alumina (Al2O3) support for the degradation of waste polystyrene (WPS) into value added products like toluene, ethylbenzene, styrene monomer, and dimer etc. Al2O3 impregnated catalysts were characterized by SEM, XRD, and N2 adsorption/desorption and their catalytic activities were investigated in the degradation of WPS. The WPS degradation experiments were carried out in a batch reactor at 450 8C. The yield of liquid and styrene monomer was creased with metal impregnated catalysts as compared to nonimpregnated alumina and thermal degradation. Higher yield of liquid and styrene monomer was obtained with 20% Zn–Al2O3 catalyst, 91.54 and 62.88 wt.%, respectively. Impregnation substantially changed the acidity and catalytic properties of alumina in WPS degradation and carbanion may lead to high yield of styrene monomer. The impregnated catalysts performance in terms of high yield of styrene monomer is Zn– Al2O3 > Cu–Al2O3 > Mg–Al2O3 = Al–Al2O3 > Fe–Al2O3 > Al2O3 > thermal. ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

1. Introduction High potential and unique properties make plastics the most desirable material which increases its demand day by day, on the other hand its increasing discarded waste is also creating serious environmental problems [1–3]. Polystyrene (PS) is one of the large demanding plastic due to its unique physiochemical properties, which constitute 10 wt.% of the total plastic waste. They are used as packing material of fragile materials, as insulating material in buildings, and air-conditions etc. [4–6]. Many researchers are working to control and reduce the increase of plastic wastes in different ways including landfill, incineration, and recycling. Plastics are non-biodegradable and due to their bulk shape they cause depletion of landfill [5,7–9]. Incineration of plastics is also prohibited due to production of toxic gases that are more dangerous for environment and health [7,10,11]. Modern world consider tertiary or chemical recycling one of the best way to decrease plastic wastes and produce valuable hydrocarbons [12]. For recycling, thermo-catalytic degradation is preferred on thermal degradation due to its high energy requirements and time consumption [13–15]. For degradation of PS the effect of brominated retardant and in the presence of antimony oxide for

* Corresponding author. Tel.: +92 91 9216652; fax: +92 91 9216652. E-mail address: [email protected] (J. Shah).

synergistic effect on thermal degradation has been studied [16– 19]. A number of heterogeneous acidic and basic catalysts have been reported in the literature, acidic group of catalysts include zeolites, FCC, MCM-41, and some Lewis acids [20,21] while basic catalysts are mostly metal oxides [22]. These methods are costly due to high temperature and time requirements, and low selectivity of products. Therefore, for high catalytic activity and selectivity of the products are now a days modified, impregnated or promoted catalysts are used [6,23,24] where negligible work is available on impregnated catalysts for the degradation of PS. Impregnation is the loading of metal active center on porous support where wet impregnation is the most employed technique for the preparation of impregnated catalysts [25,26]. Selection of proper metal active center and a support affect the catalyst performance [27,28]. Commonly used supports are alumina [29– 37], silica [38–41] titania [42–45], and charcoal [46,47] etc. Alumina is used commonly as supporting material due to its large surface area, well-defined pore size, stability within a wide temperature range and they are capable to disperse and stabilize the active phases effectively [29,48,49]. In the present paper a series of impregnated catalysts were prepared over Al2O3 with Mg, Zn, Al, Cu, and Fe as the active metal centers. The aim was to evaluate the performance of metal impregnated alumina for the catalytic degradation of WPS and to compare its results with nonimpregnated alumina catalytic and thermal degradation. The emphasis of the study is placed on the improvement in the yield of liquids as well as yield of styrene

1226-086X/$ – see front matter ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2013.12.055

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monomer. In addition, the prepared catalysts were characterized using N2Ads/des, scanning electron microscopy (SEM), and X-ray diffractometry (XRD). 2. Experimental 2.1. Materials Alumina (Al2O3), MgCl26H2O, ZnCl2, and FeCl36H2O was purchased from (Merck, Darmstadt Germany). AlCl36H2O and CuCl22H2O was obtained from BDH Laboratory Supplies, Poole, England. Waste expanded polystyrene (WPS) with average molecular weight (Mw) 200,000 g/mol was used for degradation reaction, the samples were meshed and heated at 150 8C in order to contract and exhaust any present gases. 2.2. Catalyst preparation Al2O3 was loaded with 5, 10, 15, 20, and 25% of each metal (i.e., Mg, Zn, Al, Cu, and Fe) with wet impregnation technique. The precursor metal of each active center metal solution was added to the slurry of Al2O3 support and stirred the mixture at 60 8C for 1 h followed by drying in oven at 110 8C for 6 h. The sample was calcined at 300 8C for 4 h and then meshed (<445 mm). 2.3. Apparatus and procedure The degradation experiments were conducted in a Pyrex glass reactor with internal diameter 7 cm and height 22 cm, and indigenously designed heating assembly coupled with thermocouple. WPS in a mixture with appropriate amount of impregnated catalysts was degraded collecting the liquid products after condensation. Liquid was the major product of the degradation reaction in all cases, besides these gases and residue were also the products of the degradation reaction. The yield of these were measured and expressed in terms of wt.% of WPS sample degraded. 2.4. Catalyst characterization The BET surface area of supporting material Al2O3 and all impregnated catalysts were determined using Surface Area Analyzer NOVA2200e Quantachrome, USA by N2 adsorption and desorption at 77.4 K. The surface morphology and particle size of Al2O3 support in comparison with impregnated catalysts prepares were determined using scanning electron microscope (SEM) JSM5910, JEOL, Japan. The composition of the impregnated products was confirmed with the help of X-ray diffraction patterns using JDX-3532 JEOL (Japan) diffractometer, the radiation used at room temperature were Cu Ka radiation. The parameters used for the recording of diffractogram of the samples are range: 2u, angles: 108–808 at 40 KV, and 30 mA. 2.5. GC-MS analysis The liquid products from thermo-catalytic degradation of WPS were analyzed by GC-MS (Shimadzu QP2010 Plus) with DB-5MS (from J&W Scientific) fused silica capillary column having dimensions 30 m  0.25 mm ID, 0.25 mm film thickness. The stationary phase was 95% dimethylpolysiloxane and 5%

polyphenyl. Helium (1.5 ml/min flow rate) was used as a carrier gas. The split ratio was 30:1 with injection temperature 300 8C and injection volume 1 mL. The oven temperature scheme was initially oven was heated at 35 8C for 5 min then raised to 100 8C with 5 8C/ min rate and held for 1 min. Then the temperature was raised to 150 8C with 10 8C/min rate and held for 10 min, again the temperature was raised to 290 8C at 2.5 8C/min rate and held for 10 min. The temperature of ion source was 280 8C and the interface temperature was 290 8C. The ion mass spectra were used for the characterization of compounds in comparison with spectral libraries. 3. Results and discussions 3.1. Catalyst characterization BET surface area of the supports and catalysts used were determined and the results are given in Table 1. The results show that the surface area of Al2O3 catalyst increased with metal impregnation. SEM analyses were performed in order to study the morphology of the catalysts samples with maximum catalytic activities and its comparison with the support used for impregnation. Fig. 1(a) shows the morphology of Al2O3 support, the micrograph of the sample depicts oval discs like particles, the particle are with smooth evident edges looks like flattened beans having a relative size of 2–3 mm. Fig. 1(b) presents the morphology of 15% Mg–Al2O3 catalyst. The SEM photograph of 15% Mg–Al2O3 clearly show change in the morphology of support, the catalyst having large particle size with rough surface, large cracks, and pores opening paths to the active metal centers (i.e., Mg) through micro pores. Where in case of 20% Zn–Al2O3 shown in Fig. 1(c), the micrograph shows slabs of the catalyst with varying shape and size range from 1 mm to 6 mm. 20% Al–Al2O3 is shown in Fig. 1(d) exhibiting rough surface with evident macro and micro cracks, the micro cracks formed are due to accumulation of nano-crystalline structures with crystal size 300–500 nm. On the other hand Fig. 1(e) represents 20% Cu–Al2O3 showing irregular shape with rough surface. The particles are bright clear with white shape confirming the presence of Cu loadings. The catalyst has particle size 2–5 mm in separated aggregation throughout the micrograph with adequate dispersion of Cu metal on Al2O3 aggregation providing more reaction site for the degradation reaction. The last micrograph in Fig. 1(f) represents 5% Fe–Al2O3 catalyst with large particles, each particle is 5–13 mm in size with dense black structure and evident emerging bodies. Al2O3 support and its supported catalysts were analyzed using XRD. The diffractogram of Fig. 2(a) shows Al2O3 support according to ICDD Card No. 46212 and 520803, Fig. 2(b) corresponds to 15% Mg–Al2O3 revealing MgAl2O4 (spinel mineral) according to ICDD Card No. 211152 along with some residues gmelinite-Na, KCrF4, chlorocalcite, and KCaAl2F9 (elpasolite). Fig. 2(c) shows 20% Zn– Al2O3, the diffractogram indicates Al2O3, and zinc aluminum oxide (Zn3Al94O144) according to ICDD Card No. 461212 and ICDD Card No. 231490 along with secondary phases ZnCl2 and AlCl3. 20% Al– Al2O3 is shown in Fig. 2(d) which show according to ICDD Card No. 441473 and 270009 chloraluminite (AlCl36H2O) and aluminum chloride hydroxide hydrate (Al10Cl3(OH)2713H2O), respectively. Where Fig. 2(e) corresponds to 20% Cu-Al2O3 revealing the pattern

Table 1 Surface area analysis for Mg, Zn, Al, Cu, and Fe impregnated Al2O3 catalysts. Catalysts 2

BET surface area (m /g)

Al2O3

15% Mg–Al2O3

20% Zn–Al2O3

20% Al–Al2O3

20% Cu–Al2O3

05% Fe–Al2O3

68.31

72.62

77.38

70.16

73.99

109.12

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Fig. 1. SEM micrograph of (a) Al2O3 support, (b) 15% Mg–Al2O3, (c) 20% Zn–Al2O3, (d) 20% Al–Al2O3, (e) 20% Cu–Al2O3, and (f) 05% Mg–Al2O3.

for CuAl2O4 with ICDD Card No. 330448 and Al2O3 with ICDD Card Nos. 110661, 11243, and 160394 along with Cu(ClO4)2 and Al2.892Cu6.1808 with ICDD Cards No. 320448 and 190010, respectively. The Fig. 2(f) represent 05% Fe–Al2O3, there is no pattern for this catalyst suggest that the catalysts is amorphous.

degradation temperature [24,50,53]. However, most degradation work of WPS has been conducted with constant temperature [10,23]. In order to study the effect of degradation temperature WPS samples were degraded with varying degradation temperature range from 250 to 500 8C using Al2O3 as catalyst, the degradation time was 60 min and polymer to catalyst ratio was

3.2. Catalyst degradation activity The WPS samples prepared were subject to degradation in mixture with the impregnated catalyst on Al2O3. The catalysts activities were determined in terms of maximum liquid products yield (activity) and selectivity of the yielding components. For the activity of WPS degradation different parameters were optimized i.e., temperature, time, and polymer to catalyst ratio. In order to check the activity only is because pre-experimental data and literature where low molecular weight products like benzene, toluene, ethylbenzene, and styrene increase with the ramp of temperature [24,50] which decreased beyond 500 8C [8] with exception where different additives or solvent have been used. [51,52]. 3.2.1. Effect of temperature The degradation of WPS has been reported with various degradation temperatures in literature with different nature of products. Low degradation temperature yield high molecular weight aromatic hydrocarbons or simply cause depolymerization process where high degradation temperature degrade WPS molecules yielding low molecular weight aromatic hydrocarbons with high activity and acceptable selectivity as compared to low

Fig. 2. XRD diffractogram of (a) Al2O3 support, (b) 15% Cu–Al2O3, (b) 20% Mg–Al2O3, (c) 20% Zn–Al2O3, (d) 20% Al–Al2O3, and (e) 05% Cu–Al2O3.

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Liquid Yield (%)

90.00 88.00 86.00 84.00 82.00 80.00 30 Fig. 3. Effect of degradation temperature using Al2O3 support as catalyst (reaction conditions; heating time 30 min, polymer to catalyst ratio 1:0.2).

60

90 120 Time (min)

150

180

Fig. 4. Effect of heating time using Al2O3 support as catalyst (reaction conditions; temperature 450 8C, polymer to catalyst ratio 1:0.2).

1:0.2 (Fig. 3). The degradation of WPS was initially slow and at higher temperatures the yield of liquid products increased linearly with the increase of temperature. The liquid products was 80.20  1.91 wt.% with 450 8C with 100% total percent conversion. The yield of liquid products does not affected with the increase of temperature above 450 8C.

3.2.3. Effect of polymer to catalyst ratio The selection and characteristics of catalysts are responsible for the activity and selectivity of liquid products yield. Catalysts also alter products in the degradation of WPS reported in the literature [54,55] and there are also some reports for the effect of polymer to catalyst ratio [50,56]. The degradation of WPS was optimized for the effect of polymer to catalyst ratio using Al2O3 support as catalyst using 450 8C degradation temperature and 60 min heating time (Fig. 5). The WSP was degraded with Al2O3 from 1:0.1 to 1:0.5 polymer to catalyst ratio. The yield of liquid products was small with 1:0.1 polymer to catalyst ratio as compared to the yield of 1:0.2 polymer to catalyst ratio. The yield of liquid products decreased with the increase of catalyst because the bulk of catalysts provided more surface area in turn providing more reaction sites for degradation reaction ultimately leading to the formation of more gaseous products and decreases the yield of liquid products. The maximum liquid products were 87.00  0.80 wt.% obtained with 1:0.2 polymer to catalyst ratio with 100% total conversion. The degradation of WPS was proceeded with prepared metal impregnated catalysts over Al2O3 support for catalytic activities, the percentage of each active center loading (i.e., Mg, Zn, Al, Cu, and

Fig. 5. Effect of catalyst to polymer ratio using Al2O3 support as catalysts (reaction conditions; temperature 450 8C, heating time 60 min).

Fe) on Al2O3 were optimized for the formation of maximum liquid products (Fig. 6). The percentage of Mg, Zn, Al, Cu, and Fe precursor metals loading on Al2O3 was optimized from 5 to 25% with respect to support weight. Use of metals as catalyst has brought revolutionary change in industrial productions [57] the use of metal not only catalyze the products but also act as synergist in degradation processes [4,58]. In all impregnated catalysts main product was liquid. The degradation of WSP for maximum liquid products increased with the increase of each precursor metal loading on Al2O3 except Fe–Al2O3 where the liquid products decreased with the increase of percentage of Fe loading on Al2O3. The yield of liquid products were increased from 5% Mg–Al2O3 to Mg-Al₂O₃

Zn-Al₂O₃

Al-Al₂O₃

Cu-Al₂O₃

Fe-Al₂O₃

100.00

Liquid yield (% )

3.2.2. Effect of time The increase in degradation temperature up to certain limit not only increases activity and selectivity of products but also decreasing the reaction time which in turns decreases the cost of the degradation reaction. However, reaction time does affect the yield of liquid products. In the literature most of the degradation carried out with constant reaction time and no effect has been recorded for degradation reaction time [22,23]. The effect of time was optimized for maximum liquid products yield for the degradation of WSP from 30 to 150 min at optimized temperature (450 8C) and 1:0.2 polymer to catalyst ratio (Fig. 4). The yield of liquid product was small as compared to 60 min heating time where the liquids yield showed the same behavior above 60 min heating time with the decrease of liquid products. This decrease of liquid product is the consequence of high residence time of the product in reactor causing further cracking of the products to low molecular weight hydrocarbons. The maximum yield of liquid products was obtained with 60 min heating time, the yield of liquid was 87.00  0.80 wt.% with 100% total conversion.

60.00

20.00

Al₂O₃ -20 .00

5

10

15

20

25

Percentage (% ) of the impregnated metal

Fig. 6. Effect of impregnated metals (i.e., Mg, Zn, Al, Cu, and Fe) percentage on Al2O3 for the degradation of PS (Reaction conditions: temperature 450 8C, heating time 60 min and polymer to catalyst ratio 1:0.2).

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Table 2 Comparison of reaction condition and yield of products using thermal degradation, degradation with Al2O3 support as catalyst and Al2O3 impregnated catalyst.

Reaction conditions Temperature (8C) Time (min.) Pol. to Cat. ratio

Thermal

Al2O3

15% Mg–Al2O3

20% Zn–Al2O3

20% Al–Al2O3

20% Cu–Al2O3

05% Fe–Al2O3

500 150 –

450 60 1:0.2

450 30 1:0.3

450 120 1:0.3

500 60 1:0.2

450 30 1:0.3

450 30 1:0.2

Contents of products (wt.%) Liquid yield Gas yield Residue Total conversion

78.07 20.40 1.53 98.47

87.00 13.00 0.00 100.00

95.47 4.53 0.00 100.00

15% Mg–Al2O3 reaching a maximum of 95.47  0.12 wt.% with 100% total percent conversion and decrease in the yield of liquid products was observed with further increase in the percentage of Mg content above 15%. The trend of liquid products yield were somewhat identical for Zn–Al2O3, Al–Al2O3 and Cu–Al2O3 catalysts, in case of these catalysts the liquid products increased with the increase of precursor percentage on Al2O3 and the yield of liquid products reached to maximum with 20% and beyond this percentage the yield of liquids were almost constant. The liquid products were 90.20  0.35, 91.20  0.35, and 86.87  0.23 wt.% with 20% Zn– Al2O3, 20% Al–Al2O3, and 20% Cu–Al2O3, respectively. The total percent conversion was 100% for all three catalysts. The behavior of Fe impregnated catalyst was reverse, the liquid products decreased with the increase of Fe percentage on Al2O3 and maximum liquid products were obtained using 5% Fe–Al2O3 i.e., 89.27  0.31 wt.% with total percent conversion 94.27%. The maximum yield of liquid products was 95.47  0.12 wt.% with 100% total conversion obtained with 15% Mg–Al2O3 thus, revealing an efficient catalyst for the maximum liquid products from WPS degradation Table 2. The yield of liquids, gases, and residue were compared with that of thermal degradation of WPS without using any catalyst; the maximum liquid products were 78.07  0.64 wt.% obtained with 500 8C and 150 min heating time. 3.3. Composition of liquid products The liquid products of the degradation reactions using thermal degradation and Al2O3 impregnated catalysts were characterizes

90.20 9.70 0.00 100.00

91.20 8.70 0.00 100.00

86.87 13.00 0.00 100.00

89.27 5.00 5.73 94.27

by GC–MS. The yield of products is expressed in term of wt.% of WPS used for the degradation. Table 3 shows the comparison of thermal degradation, Al2O3 catalyst and its impregnated catalysts i.e., 15% Mg–Al2O3, 20% Zn–Al2O3, 20% Al–Al2O3, 20% Cu–Al2O3, and 5% Fe–Al2O3. The chromatograms are shown in Figs. 7–9. Table 3 reveals that degradation of WPS with thermal or thermo-catalytic degradation gave off maximum 12 products in major except 5% Fe– Al2O3 where the major products of analysis were 15. High surface area with disclosed and adequate active centers with good SEM and XRD confirmation reveal the high dispersion and action of active centers as well as supporting materials on the degradation of WPS. Moreover, the impregnation of Lewis acids over acidic supports bears both Brønsted and Lewis reaction sites [59] acting as super acids [60,61]. Lewis acid catalysts are reported to detach a hydride anion from the benzylic position in PS reported by Karmore et al. [21] with b-scission of the polymer [55]. The minimum numbers of products with major selectivity were obtained with 20% Zn–Al2O3 and 20% Cu–Al2O3, most of the products obtained with these catalysts were low molecular weight aromatic hydrocarbons with potential value. Like other degradation experiments reported in literature [4,55] styrene monomer was the major product of thermal degradation as well as thermocatalytic degradations, maximum styrene was 62.88 and 60.48 wt.% with 20% Zn–Al2O3 and 20% Cu–Al2O3, respectively. Impregnated catalysts except 05% Fe–Al2O3 yielded selective liquid products that were mostly low molecular weight hydrocarbons and the yield of high molecular weight hydrocarbons were almost negligible. The impregnated catalysts showed excellent catalytic

Table 3 List of products formed by WPS degradation using thermal degradation, Al2O3 as catalyst and metal impregnated catalysts on Al2O3. Products

Benzene Toluene 3-Hexen-2-one 2-Pentanone, 4-hydroxy-4-methyl Ethylbenzene 5-Hexene-2-one Styrene a-Methylstyrene Indene Benzene,1,10 -(1,1,2,2-tetramethyl-1,2-ethanediyl)bis Naphthalene Benzene, 1,10 -(1,2-ethanediyl)bis Benzene, 1,10 -(1-methyl-1,2-ethanediyl)bis Benzene, 1,10 -(1,3-propanediyl)bis Benzene, 3-butynyl Benzene, (1-methyl-3-butenyl) 2-Phenylnaphthalene 1,2-Propanediol, 3-benzyloxy-1,2-diacetyl Other hydrocarbons Residue + gases

Percent composition Thermal

Al2O3

15(%) Mg–Al2O3

20(%) Zn–Al2O3

20(%) Al–Al2O3

20(%) Cu–Al2O3

05(%) Fe–Al2O3

0.04 2.06 0.00 0.00 0.85 0.00 39.31 1.33 0.00 0.00 0.00 0.13 0.04 1.97 17.56 1.16 0.06 10.10 3.44 21.93

0.00 2.58 0.00 0.00 1.40 0.00 45.65 1.11 0.00 0.00 0.04 0.94 0.47 0.98 14.29 0.72 0.45 13.75 4.64 13.00

1.36 13.10 4.72 1.53 8.92 3.88 56.19 3.04 0.10 0.31 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2.31 4.53

0.72 11.79 0.00 0.60 7.35 0.00 62.88 4.58 0.00 0.00 0.82 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.56 9.70

1.13 9.47 6.10 0.96 5.55 5.12 56.32 1.71 0.71 1.94 0.74 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.55 8.70

0.00 10.98 0.00 0.66 8.92 0.00 60.48 3.66 0.00 0.00 0.75 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.54 13.00

0.41 7.50 0.00 0.87 5.84 0.00 51.68 2.71 0.00 0.31 0.42 3.00 1.54 0.56 4.76 0.52 2.07 0.30 6.78 10.73

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Table 4 Comparison of liquid products formed during the degradation of EPS in reported literature (by wt.% of the oil) with 20% Zn–Al2O3.

Reaction conditions Temperature Time Polymer to Catalyst ratio Contents of products (wt.%) Yield Oil Yield Gas Residue Contents of liquid (wt.%) Benzene Toluene Ethylbenzene Styrene Benzene, (1-methylethyl)alpha-Methylstyrene Benzene, 1,10 -(1,3-propanediyl)bis Other a b c d e

Current method

Literature method

20(%) Zn–Al2O3

9(%) K2O/Si-MCM-4a

HY-700b

HHc

HDM (147)d

Fe–K/Al2O3e

450 120 1:0.3

400 30 2:1

375 90 1:0.01

450 120 –

360 90 1:0.01

400 90 1:0.01

91.53 8.47 0.00

85.67 4.86 9.47

68.00 18.80 13.20

90.20 4.80 5.00

59.00 22.70 18.30

92.20 6.40 1.40

0.72 11.79 7.35 62.88 0.00 4.58 0.00 2.98

– – – 59.13 – – – 26.54

0.20 4.90 4.90 45.29 0.68 6.32 0.48 5.24

0.24 6.44 7.54 53.06 1.019 6.49 – 15.42

0.04 3.38 2.50 39.95 0.35 6.80 1.53 4.45

0.09 5.72 1.84 65.83 0.37 7.74 3.50 7.10

Ref [19]. Ref [46]. Ref [20]. Ref [6]. Ref [9].

performance as compared to Al2O3 and thermal degradation process. The yield of low molecularly products like benzene, toluene, ethylbenzene, and methylbenzene have been reported by the degradation of styrene monomer produce during the reaction [50]. Impregnated catalyst of 20% Zn–Al2O3 was found with the best catalytic selectivity of desirable compounds with toluene 11.79 wt.%, ethylbenzene 7.35 wt.%, styrene monomer 62.88 wt.%, and a-methyl styrene 4.58 wt.%.

The yield of 20% Zn–Al2O3 was compared with that of literature reported methods, 20% Zn–Al2O3 was found with better catalytic activity from many of the reported modified or impregnated catalysts [6,23,24,30]. The behavior of 20% Zn–Al2O3 catalyst was somewhat identical with Fe–K/Al2O3 catalyst [9] in catalytic activity and selectivity. The analysis data of literature reported methods are given in Table 4 for wt.% of the PS in comparison with 20% Zn–Al2O3.

Fig. 7. GC–MS chromatogram of the WPS degraded products using thermal degradation.

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Fig. 8. GC–MS chromatogram of the WPS degraded products using Al2O3 support as a catalyst.

Fig. 9. GC–MS chromatogram of the WPS degraded products using 20% Zn–Al2O3 catalyst.

4. Conclusions Impregnated metal (Mg, Al, Zn, Cu, and Fe) catalysts were prepared and characterized by SEM, XRD, and N2 adsorption/ desorption methods. The surface area of metal impregnated catalyst over Al2O3 increased. The metal impregnated catalysts were investigated for the catalytic degradation of WPS. The activity and selectivity of liquid products increased with impregnated

catalyst as compared to thermal degradation of WPS. The liquid products obtained by the use of different impregnated catalysts were analyzed by GC–MS. The results were compared with the literature catalytic degradation methods. The results show that 20% Zn–Al2O3 is a good catalyst due to its high catalytic activity and selectivity of the products. At optimum catalytic degradation conditions the conversion of WPS was 100% with the yield of liquid products 91.53 wt.% and styrene 62.88 wt.%.

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