Dechlorination of Polyvinyl Chloride under Superheated Steam with

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Catalysis and Kinetics

Dechlorination of polyvinyl chloride under superheated steam with catalysts and adsorbents Abdul Muaz Hapipi Bin Mohd Yusoff, Hiroki Suda, Md Azhar Uddin, and Yoshiei Kato Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b00838 • Publication Date (Web): 11 Jun 2018 Downloaded from http://pubs.acs.org on June 12, 2018

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“Title”

Dechlorination of polyvinyl chloride under superheated steam with catalysts and adsorbents “Author_Name” A. Muaz Hapipi1, Hiroki Suda1, Md. Azhar Uddin1, Yoshiei Kato*1

“Author_Address” 1 : Graduate School of Environmental and Energy Science, Okayama University, 1-1 Tsushimanaka, 3-chome, Kita-ku, Okayama 700-8530 Japan *Corresponding author:[email protected]

“Keywords” Polyvinyl chloride, Dechlorination, Superheated steam, Plastic waste, Pyrolysis, Catalyst, Adsorbent

1 Environment ACS Paragon Plus

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“Abstract” The chlorine removal from polyvinyl chloride (PVC) with the addition of catalysts such as solid acid catalysts and adsorbents such as alkali and metal oxide including multiple one were described using superheated steam and nitrogen as pyrolysis media in this research. The effect of the dechlorination temperature indicated that the treatment temperature was an important factor to control the carbonization and dechlorination ratio of PVC. The addition of a single metal oxide such as TiO2, MgO and CoO showed better dechlorination ability compared with β-zeolite and NaOH. CoO had the higher dechlorination ability than TiO2 and MgO. Metal oxide supported adsorbent of ZnO/CoO, MgO/CoO and NiO/CoO systems were prepared by impregnation method in order to increase decomposition and chlorine capture ability of the adsorbent during dechlorination. The ZnO/CoO adsorbent achieved the highest dechlorination ratio and especially increased the dechlorination ratio of PVC at ZnO ≧ 25 wt% under superheated steam atmosphere compared with CoO alone. CoCl2・2H2O was observed in the XRD pattern of 25ZnO/CoO and 50ZnO/CoO adsorbents after PVC dechlorination. The PVC dechlorination in nitrogen atmosphere had the same results as superheated steam with no additive and CoO adsorbent at 473 K. However, the addition of 25ZnO/CoO adsorbent at 473 K had lower dechlorination ability than superheated steam. It is supposed to result from the formation of CoCl2・2H2O in superheated steam atmosphere. To obtain similar dechlorination ratio and solid production yield to no additive, 25ZnO/CoO and 50ZnO/CoO adsorbents was able to decrease the pyrolysis temperature from 523 to 473 K.


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“Main_Text” 1. Introduction In recent year, the use of plastics materials in daily life has been increased because of their low price and good durability, which resulted in the huge amount of plastic waste released in the world. This plastic waste is considered as an important source of energy due to the presence of the organic compounds which can be served as hydrocarbon raw material or fuel if treated correctly.1-6 However, the disposal of plastic wastes becomes a major environmental issue because plastic waste is normally non-biodegradable and contains polyvinyl chloride (PVC).1,6-8 Generally, 7 to 10% of total plastic waste contains PVC.9,10 Thermal degradation (pyrolysis, gasification, hydrogenation, etc.) and incineration was the main technology used for PVC recycling.3,11 Because of their high chlorine content, PVC is resistant to incineration. Incineration of PVC also emit greenhouse gas such as CO2 and other toxic pollutants.3,5,11-16 However, thermal degradation of PVC generates a lot of HCl and other toxic substances which cause corrosion of the equipment and other environmental problems.9,13,15,17-26 For the reasons described above, dechlorination of PVC is an essential step before being used in another chemical process for the conversion into energy, fuel, and other useful chemicals.16,27 Pyrolysis is considered one of the most efficient way for PVC dechlorination.1,3,6,14,28-30 It is a thermal process which decomposes organic materials in the absence of air.16,31-33 During this process, HCl was eliminated and the formation of conjugated double bonds occurs.13 HCl product can be used for vinyl chloride production.34 In order to promote the dechlorination of PVC, there are many studies on adding solid acid catalyst such as zeolite18, 26, 32,33 and alkali adsorbents like NaOH 11, 12, 15, 17, 18, metal oxides 13, 18, 19,20, 26,33, 34, 35, 36, 37

, aluminum foil

27

and sodium sulfide 38 to PVC. However, these are limited


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to some additives for each investigation and the dechlorination of PVC was not compared between various kinds of additives. As for the addition of multiple metal oxides, there are two examples such as additive of SiO2-Al2O3 19 and Al-Mg composite oxide 39, although the research target is to enhance the liquid products. There is no study on obtaining the solid product by the low temperature dechlorination. Besides, the effect of pyrolysis temperature on the dechlorination of PVC was investigated between 553 and 593 K by Yuan et al.40 and it was shown that the higher temperature enhanced the PVC dechlorination. However, it was not under the low pyrolysis temperature condition such as below 550 K, which may affect the solid product yield. On the other hand, some of the authors carried out the dechlorination of RDF

41,42

,

chlorides in incineration ash 43 and the carbonization of biomass 44 by superheated steam which has gained much attention due to simplicity of equipment and higher heat transfer property. The effects of superheated steam on the dechlorination and the additives were not clear in these studies. In this study, the effects of PVC dechlorination on treatment temperature and time with no additive were initially examined at the relatively low pyrolysis temperatures and the dechlorination was secondary compared between various additives such as solid acid catalyst, alkali and metal oxides adsorbents including multiple complex compounds which enhanced the dechlorination at the same pyrolysis temperature. Compared with superheated steam and nitrogen atmospheres, the effectiveness of superheated steam was discussed on the PVC dechlorination. If the dechlorination can be carried out at low temperature, it can reduce organic volatile, increase solid product yield and save energy. The purpose of this study is to investigate the


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process conditions for the removal of chlorinated compounds from PVC using catalysts and adsorbents under superheated steam atmosphere.

2. Experimental PVC powder (Kishida Chemical Co., Ltd., 99.0% purity) has been used as feedstock in this experiment. The chlorine content of PVC was 55.9% (analytical data). 5 g of PVC powder with or without catalyst/adsorbents was compressed to the pellet using a hydraulic press to make it easy to put it in the sample basket. Dechlorination experiment was carried out using superheated steam apparatus (Dai-ichi High Frequency Co., Ltd., Hi-Heater 2005S) as shown in Figure 1. The device consists of a boiler, superheated steam generator, and reaction chamber. Steam was produced by the boiler and then the temperature was risen to the setting temperature using a superheated steam generator. Two thermocouples (A, B) were attached to the reaction chamber (A) and sample (B) to measure chamber and sample temperatures. The flow rate of superheated steam was kept to 10 kg/h. After the reaction was complete, the sample was cooled down to 343 K and the residue was ground with a blender before further analysis. The effect of dechlorination atmosphere was studied under nitrogen gas using electric furnace (As One Co. Ltd., TMF-500N). The schematic diagram of the apparatus is shown in Figure 2. The flow rate of nitrogen was fixed to 6 kg/h. The temperatures of the reaction chamber (A) and sample (B) were measured by two thermocouples. The experimental conditions of this study are summarized in Table 1. For the temperature effect, the dechlorination treatment was carried out at 473, 498, 523 and 573 K of sample temperature measured for 60 min. 30, 60, and 90 min of treatment times were utilized for 523 K


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to investigate the effect of dechlorination time of PVC in the superheated steam atmosphere. On the other hand, in nitrogen heating, the experiments at 473 and 523 K were done for 60 min of dechlorination time. In the case of dechlorination using catalysts, 0.5 g of TiO2 and β-zeolite were added to the PVC powder (5.0 g), respectively, and mixed sufficiently before compression. NaOH was used as alkali adsorbent, and MgO and CoO were used as metal oxide adsorbents. The mixture of PVC (5.0 g) and NaOH was 1:1 mole ratio, while the mixture of PVC and the metal oxide adsorbents (MgO, CoO) were 1:0.5 and 1:1 mole ratios. The experiment with metal oxide supported adsorbents was also carried out with MgO-CoO, NiO-CoO and ZnO-CoO systems. 50 wt% of MgO, NiO and ZnO were added to CoO support where we wrote them as 50MgO/CoO, 50NiO/CoO and 50ZnO/CoO, respectively. The adsorbents preparation procedure by impregnation method was schematically shown in Figure 3. The effect of ZnO loading amount was studied with 10ZnO/CoO, 25ZnO/CoO and 50ZnO/CoO. All the reaction with the above catalysts and adsorbents were carried out at 473 K for 60 min. The total weight of the metal oxide (MgO, NiO, ZnO) and CoO support was fixed to 5.8 g. The sample after the dechlorination was treated with hot water and then filtered to obtain inorganic chlorine solution. Organic chlorine content from the remaining sample after filtration was analyzed by Eschka method.45-47 Chlorine contents of both inorganic and organic solution was analyzed using Mercury thiocyanate absorption spectrophotometry method.48 The solid product yield and dechlorination ratio were defined as Eqs. (1) and (2), respectively. Yield [%] = (Wf/W0) x 100

(1)

Dechlorination ratio [%] = {(W0Cl0-WfClf)/(W0Cl0)}x100

(2)


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where, W0 and Wf are the masses of the initial and final PVC sample [g], respectively, Cl0 and Clf are the total chlorine contents in the initial and final PVC sample [wt%], respectively. The Wf is given by subtracting mass of additives such as solid catalysts, alkali and metal oxides from the mass of treated sample before the filtration. Thus, the adsorbent separation after the treatment was not carried out in this study. The total chlorine content means the sum of organic and inorganic chlorine contents in the sample.

3. Results and discussion 3.1 Effects of dechlorination temperature and residence time on PVC dechlorination The PVC dechlorination with no additive was examined in this section. The effects of the dechlorination temperature on solid product yield and dechlorination ratio are shown in Figure 4. The treatment time was 60 min. Generally, product yield decreased with the temperature because the reaction rate increased.40 Product yield decreased to 37.4% at 573 K. The dechlorination ratio of PVC at 473, 498, 523 and 573 K were 12.9, 42.7, 79.8, and 96.5%, respectively. Almost all chlorine was released at 573 K.49 These results indicated that the temperature was an important factor that controlled dechlorination process. Remaining of the chlorine compounds in PVC after the experiment without additives was in the state of organic chlorine. The color of PVC samples without additive before and after the experiment is shown in Fig. 5. The treatment time was 60 min. The color changed from white at the raw PVC to brown at 473 K and became darker at higher temperatures from 493 to 573 K, although it is a little bit difficult to distinguish in the photograph. The color change is supposed to be influenced by conjugated double bond of polyene as shown by Braun.50


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Figure 6 shows the effect of treatment time on the solid product yield and dechlorination ratio of PVC. The sample temperature was fixed to 523 K. Solid product yield was constant after 30 min of dechlorination due to no degradation of PVC. This indicates that one hour is enough time for the dechlorination of PVC. The gas product at the treatment time of 30 min and sample temperature of 473 K was measured by a GC-FID (Shimadzu, GC-8A). The detected gas was only HCl in this condition. However, the other gas products might be detected under the higher dechlorination ratio.

3.2 Effect of solid acid catalysts on PVC dechlorination Solid acid catalysts, alkali compound and metal oxides are often used in decomposition of the plastic.7,11,27,32 Figure 7 shows the effect of the addition of solid acid catalysts ( β-zeolite, TiO2) on the solid product yield calculated from Eq. (1), organic chlorine (=organic chlorine content in the treated sample after the filtration [wt%]), inorganic chlorine (=inorganic chlorine content in the treated sample before the filtration [wt%]) and dechlorination ratio calculated from Eq. (2). Only a small change was observed in the solid product yield with the addition of solid acid catalyst. TiO2 showed the higher dechlorination ratio between the two catalysts. Compared with no addition, β-zeolite addition resulted in a small increase of dechlorination ratio probably because the presence of water in superheated steam lowered the catalytic activity of zeolite. None of inorganic chlorine was observed using these catalysts and these results agree with Lopez et al. 51 which reported that the acid site of the catalyst improved PVC dechlorination but lacked chlorine capture ability. Thus, due to no detection of inorganic chlorine, the sample was dechlorinated by the emission of HCl in the atmosphere.

3.3 Effect of alkali adsorbent on PVC dechlorination


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The effect of NaOH additive on the dechlorination ratio of PVC is shown in Figure 8. The mixture of PVC (5.0 g) and the NaOH was 1:1 mole ratio. The addition of NaOH increased the dechlorination ratio from 12.9 to 21.1%. Some increase in the inorganic chlorine was observed with the addition of NaOH, which means that NaOH reacted with generated HCl and formed an inorganic chloride (NaCl).35 Normally, the addition of alkali adsorbent only increases the chlorine capture ability and does not increase the dechlorination ratio as observed in the results. The increase in dechlorination ratio was estimated due to the neutralization reaction between HCl and NaOH which was an exothermic reaction. In this experiment, the reaction temperature increased from 473 to 483 K. It is assumed that PVC degradation starts with the breaking of C-Cl bond because of their lower binding energy compared with C-C and C-H bond and the increase in the reaction temperature will enhance the cracking of C-Cl bond and led to higher dechlorination ratio.1,6,12,38

3.4 Effect of metal oxides loading amount on PVC dechlorination It is reported that the addition of metal oxide affects the degradation of PVC.36, 37 The effect of metal oxide adsorbents such as MgO and CoO on PVC dechlorination is shown in Figure 9. The mixture of PVC and the catalyst were 1:0.5 and 1:1 mole ratios as shown in Table 1. With loading amount of PVC: MO (M=Mg, Co) =1:0.5 mole ratio, 35.0% of dechlorination ratio was obtained with MgO, while CoO was 28.3%. MgO showed almost no effect of the loading amount from 1:05 to 1:1, but the PVC dechlorination ratio by CoO loading increased from 28.3 (1:0.5) to 56.7 % (1:1). On the contrary, the solid product of CoO decreased from 87.1 (1:0.5) to 70.3% (1:1). The increase in CoO loading amount promoted not only the dechlorination ratio but also PVC decomposition. There was almost no inorganic chlorine


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observed as shown in Figure 9. This indicates that there was no reaction between metal oxide and HCl to form inorganic salt and the dechlorination proceeded by the HCl emission in the atmosphere. As reviewed by Yu et al.,36 the dechlorination with metal oxide is due to the selective cleavage of one or more C-Cl bonds.

3.5 Effect of metal oxides supported adsorbents on PVC dechlorization Metal oxides supported adsorbent was used to increase the dechlorination and decomposition of the adsorbent. These multicomponent adsorbents can increase the dechlorination and chlorine capture ability compared with single component adsorbent which either has a good dechlorination ability or chlorine capture ability.19, 39 As the dechlorination ratio of the CoO loading (1:1) was highest in the result of section 3.4, three kinds of CoO supported adsorbents was prepared by impregnation method as shown in Figure 3. The effects of 50ZnO/CoO, 50MgO/CoO and 50NiO/CoO adsorbents on PVC dechlorination are shown in Figure 10. The addition of metal oxides supported absorbents increased the decomposition and dechlorination ratio compared with no additive. The addition of ZnO achieved the highest values of the decomposition and dechlorination ratio. MgO and NiO addition decreased the decomposition and dechlorination ratio compared with CoO alone. The dechlorination ratio of CoO, 50ZnO/CoO, 50MgO/CoO and 50NiO/CoO were 56.7, 69.6, 48.1 and 27.6%, respectively. Inorganic chlorine content was measured for 50ZnO/CoO and 50MgO/CoO adsorbents, which means that this adsorbent has chlorine capture ability. XRD patterns of 50ZnO/CoO, 50MgO/CoO and 50NiO/CoO adsorbents before the dechlorination are shown in Figure 11. The sample temperature and treatment time were 473 K and 60 min, respectively. The peak of zinc cobaltite (ZnCo2O4) was observed in the 50ZnO/CoO.


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As zinc cobaltite compound (ZnCo2O4) has a catalytic activity as indicated by Bazuev et al.,52 the dechlorination is supposed to be accelerated when using this adsorbent and to be led to the increase in the inorganic chlorine formation. Figure 12 shows the XRD patterns of CoO and 50ZnO/CoO supported adsorbents after dechlorination. Here, the sample temperature and treatment time were also 473 K and 60 min, respectively. In 50ZnO/CoO supported adsorbent, ZnCO2O4 disappeared and cobalt chloride (CoCl2) and cobalt chloride dihydrate (CoCl2∙2H2O) came to the surface after the reaction of PVC with ZnCO2O4, ZnO, CoO and superheated steam (H2O). As the formation of this metal chloride compound also acts as catalyst for PVC decomposition,37,53-55 it might accelerate the dehydrochlorination of PVC.

3.6 Effect of ZnO loading amount on PVC dechlorination The effect of ZnO loading amount to CoO support on PVC dechlorination is shown in Figure 13. ZnO loading was 10, 25 and 50 wt%. The solid product yield, organic and inorganic chlorine contents decreased with the increasing ZnO loading amount and became almost constant when ZnO loading exceeded 25 wt%. As for the sample with 25ZnO/CoO adsorbent, the dechlorination ratio defined by Eq.(2) and solid product yield expressed as Eq. (1) were 70.3 and 41.6 %, respectively. By substituting these values and Cl0 = 57 wt% in Eqs. [1] and [2], the Clf value was given as 41 wt%. Although the solid product yield decreased rapidly compared with the sample of 10ZnO/CoO adsorbent, the chlorine was preferentially emitted in the atmosphere due to Clf /Cl0 < 1. The reason why inorganic chlorine content decreased in spite of increasing ZnO loading was unknown. However, the dechlorination ratio increased with the increase in ZnO, which means that the increasing ZnO loading does not trap chlorine as the inorganic chlorine form but allowed HCl to escape in the atmosphere.


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Chlorine recovery ratio [%] defined as Eq. (3) was calculated to evaluate the chlorine capture properties with ZnO loading amount and the results are shown in Table 2. Chlorine recovery ratio = (chlorine capture ratio/ chlorine release ratio) × 100

(3)

where chlorine capture ratio is the chlorine capture [%] as the inorganic chlorine and chlorine release ratio is the initial chlorine [%] – organic chlorine [%]. From Table 2, the chlorine recovery ratio in the sample became 50 - 100%.

3.7 Effects of atmosphere on PVC dechlorination To examine the effect of atmosphere on PVC dechlorination, the experiments on no addition, CoO (1:1) and 25ZnO/CoO were carried out under nitrogen and superheated steam atmospheres at 473 K. Figure 14 shows the results where SS and N2 are the superheated steam and nitrogen atmospheres, respectively. The solid product yield and dechlorination ratio with no addition and CoO adsorbent were almost the same for both SS and N2 atmospheres. However, in the case of 25ZnO/CoO adsorbent, superheated steam had higher values of decomposition and dechlorination ratio compared with nitrogen atmosphere. Figure 15 shows the XRD patterns of the samples with 25ZnO/CoO adsorbent after 60 min of dechlorination at 473 K. The atmospheres were SS and N2 and the treated sample was measured before the filtration. The inorganic chlorine in the sample of SS was in the form of CoCl2 and CoCl2∙2H2O while only CoCl2 was detected in N2 atmosphere. The sample colors of SS and N2 were reddish black due to the existence of CoCl2 ∙2H2O (red-violet in color) and a little bit bluish black resulted from CoCl2 (blue in color), respectively. As CoCl2 ∙ 2H2O is more stable than CoCl2 under SS atmosphere, the CoCl2∙2H2O formation in SS is supposed to promote the high dechlorination ratio compared with N2 atmosphere.


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Figure 16 shows the effect of the dechlorination atmosphere and sample temperature on dechlorination properties. At 473 K, there occurred almost no dechlorination difference between no additive of SS and N2 atmospheres. However, decomposition and dechlorination ratio of SS at 523 K were higher than those of N2. It might result from the superior heat transfer ability of superheated steam. The decomposition and dechlorination ratio of 25ZnO/CoO adsorbent in SS at 473 K had almost the same values as those of no addition in N2 at 523 K and had the higher ones than those of 25ZnO/CoO adsorbent in N2. Thus, the SS atmosphere enhanced the dechlorination ratio for the samples with no additive at 523 K and 25ZnO/CoO adsorbent at 473 K compared with the N2 atmosphere under the same condition. The addition of metal oxide supported adsorbent such as 25ZnO/CoO decreased the reaction temperature to obtain the same dechlorination ratio in SS and N2, although SS atmosphere was efficient to the temperature decrease.

3.8 Comparison of dechlorination ability and solid product yield Figure 17 shows the comparison of the dechlorination ratio and solid product yield for the above experimental conditions. Here, MgO and CoO means the data of MgO(CoO):PVC=1:1. The horizontal axis shows the yield of PVC defined as Eq. (4) and the vertical axis indicates the dechlorination ratio of PVC calculated from the remaining organic chlorine in the sample after dechlorination as Eq. (5). η = (Wf/W0)

(4)

1-η(Clorganic/Cl0) = {(W0Cl0-WfClorganic)/(W0Cl0)}

(5)

where Clorganic is the organic chlorine content in the sample after dechlorination [wt%]. Thus, the slope of Clorganic/Cl0=1 in Figure 17 means that the standard value for PVC dechlorination


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without any desirable or undesirable dechlorination. When the data were plotted above the line of Clorganic/Cl0=1, chlorine were removed from the sample on a preferential basis. When chlorine is perfectly removed and the residual carbon and hydrogen remain in the PVC sample, 1-η(Clorganic/Cl0) and η values become 1 and 0.43, respectively, due to 57 wt% chlorine contained in PVC. This is an ideal and perfect dechlorination point and indicated at the tip of the arrow line in Figure 17. In our results, dechlorination in superheated steam atmosphere with mixed metal adsorbent of 25 and 50wt% ZnO loading at 473 K and that without any addition at 523 K showed a higher preferable dechlorination effect as shown in the dotted circle of Figure 17. This means that 25ZnO/CoO and 50ZnO/CoO adsorbents can decrease the pyrolysis temperature by 50 deg to obtain similar dechlorination ratio and solid production yield to no additive.

4. Conclusions The dechlorination of PVC were investigated by using superheated steam with and without catalysts and adsorbents and compared with the results of nitrogen atmosphere. 1.

Temperature was an important factor that affected PVC decomposition and dechlorination.

2.

Metal oxide showed better dechlorination ability compared with solid acid catalyst and alkali adsorbent. CoO had the higher dechlorination ability than MgO.

3.

The addition of ZnO to CoO support increased the dechlorination ratio of PVC at ZnO ≧ 25 wt% under superheated steam atmosphere compared with CoO alone.

4.

Dechlorination in nitrogen atmosphere had the same results as superheated steam with no and CoO additions at 473 K. However, the addition of 25ZnO/CoO adsorbent at 473 K and no addition at 523 K had lower dechlorination ability than superheated steam.


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5.

25ZnO/CoO and 50ZnO/CoO adsorbents can decrease the pyrolysis temperature from 523 to 473 K to obtain similar dechlorination ratio and solid production yield to no additive.


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“Figure and Table captions”

Figure 1 Schematic diagram of superheated steam device used for the experiment. Figure 2 Schematic diagram of electric furnace used for the experiment. Figure 3 Adsorbent preparation procedure by impregnation method. Figure 4 Effect of sample temperature on solid product yield and dechlorination ratio. Figure 5 Color change in the sample after dechlorination. Figure 6 Effect of treatment time on solid product yield and dechlorination ratio. Figure 7 Effect of solid acid catalysts on PVC dechlorination. Figure 8 Effect of alkali adsorbent on PVC dechlorination. Figure 9 Effect of metal oxide loading amount on PVC dechlorination. Figure 10 Effect of metal oxide supported adsorbent on PVC dechlorination. Figure 11 XRD pattern of metal oxides supported adsorbents before dechlorination. Figure 12 Comparison of XRD patterns of CoO and 50ZnO/CoO adsorbents. Figure 13 Effect of ZnO loading amount on PVC dechlorination. Figure 14 Effect of dechlorination atmosphere on PVC dechlorination (SS; Superheated steam, N2; Nitrogen). Figure 15 XRD pattern of 25ZnO/CoO adsorbent sample after dechlorination in superheated steam and nitrogen atmospheres (SS; Superheated steam, N2; Nitrogen). Figure 16 Effect of the dechlorination atmosphere at temperature of 473 and 523 K (SS; Superheated steam, N2; Nitrogen). Figure 17 Comparison of dechlorination ratio and solid product yield for all reaction conditions. Table 1 Experimental conditions (SS; superheated steam, N2; nitrogen). Table 2 Chlorine recovery ratio with ZnO loading amount.


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Figure 1 Schematic diagram of superheated steam device used for the experiment.


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Figure 2 Schematic diagram of electric furnace used for the experiment.


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Figure 3 Adsorbent preparation procedure by impregnation method.


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Figure 4 Effect of sample temperature on solid product yield and dechlorination ratio.


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Figure 5 Color change in the sample after dechlorination.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 6 Effect of treatment time on solid product yield and dechlorination ratio.


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Energy & Fuels

Figure 7 Effect of solid acid catalysts on PVC dechlorination.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 8 Effect of alkali adsorbent on PVC dechlorination.


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Energy & Fuels

Figure 9 Effect of metal oxide loading amount on PVC dechlorination.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 10 Effect of metal oxide supported adsorbent on PVC dechlorination.


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Energy & Fuels

Figure 11 XRD pattern of metal oxides supported adsorbents before dechlorination.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 12 Comparison of XRD patterns of CoO and 50ZnO/CoO adsorbents.


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Energy & Fuels

Figure 13 Effect of ZnO loading amount on PVC dechlorination.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 14 Effect of dechlorination atmosphere on PVC dechlorination (SS; Superheated steam, N2;Nitrogen).


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Energy & Fuels

Figure 15 XRD pattern of 25ZnO/CoO adsorbent sample after dechlorination in superheated steam and nitrogen atmospheres (SS; Superheated steam, N2; Nitrogen).


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 16 Effect of the dechlorination atmosphere at temperature of 473 and 523 K (SS; Superheated steam, N2; Nitrogen).


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Energy & Fuels

Figure 17 Comparison of dechlorination ratio and solid product yield


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Table 1 Experimental conditions (SS; superheated steam, N2; nitrogen).

no addition

Sample Temperature [K] 473, 498, 523, 573

Treatment time (min) 30, 60, 90

Catalyst or adsorbent [g] -

Treatment atmosphere SS, N2

β-zeolite

473

60

0.5

SS

TiO2

473

60

0.5

SS

NaOH

473

60

3.0

SS

MgO

473

60

1.6, 3.2

SS

CoO

473

60

2.9, 5.8

SS, N2

50MgO/CoO

473

60

5.8

SS

50NiO/CoO

473

60

5.8

SS

50ZnO/CoO

473

60

5.8

SS

10ZnO/CoO

473

60

5.8

SS

25ZnO/CoO

473

60

5.8

SS, N2


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Energy & Fuels

Table 2 Chlorine recovery ratio with ZnO loading amount. Chlorine recovery ratio [%]

Dechlorination ratio [%]

no addition

10.7

12.9

CoO(1:1)

0.0

56.7

10ZnO/CoO

100.0

46.6

25ZnO/CoO

51.1

70.3


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Dechlorination of Polyvinyl Chloride under Superheated Steam with

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