- Email: [email protected]
Effect of Increasing Course of Temperature and Pressure on Polypropylene Degradation in Supercritical Water*
Chin.J. Chem. Eng., 15(5) 738-741
(2007)
Effect of Increasing Course of Temperature and Pressure on Polypropylene Degradation in Supercritical Water* LIU Xiuru(34 %%);>“, CHEN Liying( % I@ SU Lei( % $$-)a,b, WU Xuehua(5 q)”“, CHEN Keyu( %&?)d and HONG Shiming($% @ @)a,** a
x)a,
Laboratory of High Pressure Physics, Southwest Jiaotong University, Chengdu 61003 1, China Department of Physics, Zhengzhou University of Light Industry, Zhengzhou 450002, China College of Science, Kunming University of Science and Technology, Kunming 650093, China Department of Polymer Science and Technology, Sichuan University, Chengdu 610065,China
Abstract The effect of increasing course of temperature and pressure on polypropylene (PP) degradation in supercritical water was investigated for developing a process of recycling waste plastic. A group of experiments was carried out in a reaction system at a pressure of 26MPa, temperature of 380°C or 400°C for 30min, 70min, and 120min by Course One (the increasing course of temperature and pressure is via gaseous regions to supercritical regions), and the other group was carried out at corresponding holding conditions by Course Two (the increasing course of temperature and pressure is via liquid regions to supercritical regions). The time of the increasing courses was about 30min. Products were analyzed by Ostward-type viscometer, gaseous chromatography, and mass spectrometers (GCIMS). Characterization results suggested that different increasing courses of temperature and pressure would give rise to different results, although they were treated under the similar holding conditions. It was also found that Course Two was more effective on PP degradation in supercritical water. Keywords increasing course, polypropylene degradation, supercritical water
1 INTRODUCTION In recent years, supercritical fluid is focused as a “super green” solvent for the conversion of waste materials into resources. It has been reported that supercritical water could be utilized to treat polyethylene terephthalate (PET)[1,2], polystyrene (PS)[3 - 61, polyethylene (PE)[7], cellulose[8], nitrobenzene[9], carbon particles[lO], municipal solid waste[ll], polypropylene (PP)[12,13], and so on. Up to now, most of the articles dealt with the influences of holding conditions on plastic degradation, such as temperature, pressure, holding time, and material ratio. In fact, the experimental result is not so certain for the same holding conditions if the increasing course of temperature and pressure is different and the time of the increasing course is comparable with the holding time. In a previous study[l4,15], it was observed that the increasing course of temperature and pressure is also an important factor on PP degradation. It is unfortunate that no direct experimental evidence has confirmed this view. In this study, a series of experiments were carried out at certain temperature, pressure, and holding time. Besides holding conditions, details of increasing courses of temperature and pressure for every experiment were also recorded. The experiments were divided into two groups with their increasing course. In the first group, each increasing course was via gaseous regions to supercritical regions, which was called Course One. In the other group, each increasing course was via liquid regions to supercritical regions, which was called Course Two. After characterization of all samples, it was made clear that different inReceived 2006- 10-27, accepted 2007-02-07.
creasing courses would give rise to different results, although they were treated under the same holding conditions, and Course Two was more effective on PP degradation in supercritical water.
2 EXPERIMENTAL The experiments were carried out in a system as shown in Fig.1, including a batch reactor made of special titanium steel tube sealed with Swagelok caps (about 25cm3 in volume), heater, temperature controller, pressure sensor, pump, pipes, and valves etc.
thermocouple
I
n
valve 2
-
I
$
I I pressure sensor
temperature control
Figure 1 The SCW experimental system
PP powder (Wuhan Phenix Co. China), with the mean molecular weight (Mw) of about 8OOOO was used as starting materials. Distilled water was the solvent in all experiments.The mass ratio of water to PP was 5 : 1. Holding temperature was 380°C and 400”C,
* Supported by the National Natural Science Foundation of China (No.59972022) and the Opening Foundation of the Environmental Engineering Key Discipline, Zhejiang University of Technology (No.563 10503011). ** To whom correspondence should be addressed. E-mail: [email protected]
Effect of Increasing Course of Temperature and Pressure on Polypropylene Degradation in Supercritical Water
pressure was about 26MPa, and holding time was 30, 75, and 120min, respectively. The amount of water was decided using the equation of state to obtain the desired pressure. Especially, the details of the increasing courses of temperature and pressure were recorded for every experiment, The time of increasing course of temperature and pressure is about 30min, which is comparable with the holding time. M, of reaction products was obtained by measuring the viscosity with Ostward-type viscometer at a constant temperature of 135"C. Decahydronaphthalene with purity higher than 98% (Shanghai Chemical Reagent Co., China) was used as the normative solvent. And the concentration of the sample is 20mg-ml-'. The composition of the yield was analyzed using gas chromatography and mass spectrometers (HP 6890 series GC System, HP 5973 MASS selective detector). The experimental conditions are as follows. The column, HP-SMS, is 250pm in diameter and 30m long, and the film thickness is 0.25pm. Helium was used as the carrier gas with an exit flow rate of 0.8ml.minand T increased from 50°C to 120iC at 5"C+min-', from 120°C to 280°C at 10"C.min- . Injector: direct
739
injection, 270°C. EI: 70ev. Scan: 2W50Oamu.
3 RESULTS AND DISCUSSION Figures 2(a), (c), and (e) express the increasing courses of temperature and pressure of corresponding samples, and all of them are via gaseous regions to supercritical regions (Course One). Figs.2(b), (d), and (f) present the increasing courses of temperature and pressure of corresponding samples, and all of them are via liquid regions to supercritical regions (Course Two). The holding conditions and the results are shown in Table 1. It can be seen that the phases of the samples gained by Course Two were almost different from those gained by Course One. For example, the phase of Sample 2 is grease, while that of Sample 1 is solid, and then the phase of Sample 6 is oil, while that of Sample 5 is grease. It is cogitable that the oil phase product is more decomposed than grease, and grease is more decomposed than solid. So the results imply that Course Two is more effective on PP degradation in supercritical water.
Ly/ G[,; J G i !20bG 1 !i2o ,
'"1__.41 25
g
.I
30 I
I
25,
400
0
m
10
k 5
G
0
100
300
200
15
g
10
0
100
200
300
temperature, 'C
200 300 temperature, 'C
(a) Sample 1
(b) Sample 2
(c) Sample 3
30 I
2
400
temperature, 'C
30
I
t
1
2 10
0
100 200 300 temperature, "C
400
0
(d) Sample 4
30 I
2 10 & 0
5
200 400 temperature, "C
100
400
I
400
200
600
600
temperature, "C
(f) Sample 6
(e) Sample 5
Figure 2 The increasing course of temperature and pressure of the samples -gas-liquid equilibrium curve; rn increasing course of the sample Table 1 The holding conditions and the results ~
~
~~
Sample No. 1
Course' One
P,MPa 26
T, "C 380
No.2
Two
26
No.3
One
26
No.4
Two
26
t, min
30
Phase solid
380
30
grease
6027
380
75
grease
5762
380
75
grease
3325
M w
12895
400 120 grease 826 No.6 Two 26 400 120 oil 198 0 Course One: the increasing course of temperature and pressure is via gaseous regions to supercritical regions; Course Two: the increasing course of temperature and pressure is via liquid regions to supercritical regions. NOS
One
26
Chin. J. Ch. E. 15(5) 738 (2007)
Chin. J. Ch. E. (VO~.15, No.5)
740
Table 1 also shows that M , of the products are different in two kinds of experiments. The Mw of products obtained by Course Two decreased faster than those gained by Course One although they were treated at the same holding conditions. For example, at 380°C, 26MPa, for 30min, M, of Sample 2 decreased from 80000 to 6027, while Sample 1 was decomposed to 12895. In other words, Course Two is more effective on PP degradation than Course One.
Figure 3 shows the GC/MS result of Sample 6. And the main products are shown in Table 2. It indicated that PP was decomposed to products with low molecular weight by solvolysis of supercritical water, such as hydrocarbon of methane series, hydrocarbon of ethylene series, and cycloparaffinic hydrocarbons. On comparing with the product of Sample 5 , which was grease phase, Sample 6 was more decomposed, although treated at the same holding conditions.
6500000 6000000
I
5500000 5000000 4500000
4000000 a
3500000
'
3000000 2500000 2000000 1500000 1000000
2.00
4.00
6.00
8.00 10.00 12.00 14.00 16.00 18.00 20.00 22.00 24.00 26.00 28.00 30.00 32.00
time,min Figure 3 The result analyzed by gas chromatography and mass spectrometry (400"C, 26MPa,120min) Table 2 The main components o troduct of Sample 6 detected by GC-MS
Time,min 1.40 1.55 2.11 2.46 3.04 3.79
4.15 4.58 4.83 5.39 5.68 5.96 6.53 6.91 7.51 7.60 8.36 8.70 9.06 9.61 October, 2007
Component pentane 2-methylpentane
3-dimethylc yclopentane
Area,% 0.35 0.52 0.35
1,1,3-trirnethylcyclopentane
0.37
4-methylheptane 3,5,5-trimethyl1-hexene 2,4-dimethylheptane 2,4-dimethyl-1-hepene 1,2,4-trimethylcyclohexane 2,4,4tetramethylcyclopentene 2,3,5-trimethyl1,3-hexadiene 1,1,3,5-tetramethylcyclohexane 4-acetyl-1,5-dimethylpyrazole 1,1,3,5-tetramethylcyclohexane 1-octadecene 3,s-dimethyloctane 1-ethyl-3-methylbenzene 1,2,4-trimethylbenzene 4-methylnonane 1,2,4-trimethylbenzene
2.37 2.12 1.33 1.35 0.47 1.31 0.61 1.96 0.76 0.38 0.47 0.69 0.81
4.85 0.38 2.45
Time,min 10.66
11.oo 11.95 12.21 13.03 13.99 14.40 15.24 16.26 16.45 17.61 18.79 21.47 23.23 23.44 25.58 26.18 28.15 28.88
Comuonent 2,4-diethyl1-methylcyclohexane 2,6-dimethylnonane 1-methyl-3-propylbenzene 2-ethyl-1,4-dimethylbenzene 1-decene 2,4-dimethyl1,3,Strimethylcyclohexane 2,3,3-trimethyl-4-nonene 2,4-diethylcyclohexane 1,4-diethy1-2-methylbenzene 1-ethy1-3,5-dimethylbenzene 1,1,3-trimethylcyclohexane
2,3-dihydro-1,6-dimethyl-lH-indene 2,3-dihydro1,1,5-trimethyl1H-indene 4,6-dimethyldodecane 2,7,1O-trimethyldodecane 1,4-dimethylbenzene 1,2-dihydr0-2,S,8-trimethylnaphthalene 1,4,6-trimethylnaphthalene 1,2-diethyl-3-methylcyclohexane
Area,% 0.35 1.46 0.70
1.so 2.38 0.82 1.07 0.41 0.53 1.05
0.47 0.81 0.38 0.56 0.45 0.42 0.41 0.61 0.71
Effect of Increasing Course of Temperature and Pressure on Polypropylene Degradation in SupercriticalWater
It is well known that the properties of the fluid in liquid regions are quite different from those in gaseous regions, especially in near-critical point, such as density, viscosity, diffusion coefficient, dielectric constant, ionization degree, solubility, and so on. Fig.4 shows a schematic drawing of the relation of density, temperature, and pressure of general fluid in near-critical and supercritical fluid. It can be seen that the density turns higher gradually by Course One, while the density turns smaller gradually by Course Two. The other properties will also be changed differently along with the different courses. These differences may bring about different influences on PP degradation. In general experiments, the increasing courses of temperature and pressure are almost via gaseous regions to supercritical regions. The reason of increasing courses via liquid regions to supercritical regions is a randomly or manipulatively additive pressure rise during the process. This change could induce certain changes of the component and state in the sample. The changed state may have an active effect on PP degradation in the following reaction process. Moreover, it takes about 30min in the increasing course, which is comparable to the holding time at appointed temperature and pressure, so the effect cannot be ignored in the whole reaction. In previous reports on the similar methods, the time of increasing course of temperature and pressure is comparatively short, so the above-mentioned phenomenon may not be so obvious. Nevertheless, in the modem industry, rapid increasing course will give rise to certain problems, such as labor security, additional cost, and so on. So it is still necessary to study the effect of increasing course of temperature and pressure on plastic degradation.
perature and pressure is a very important factor on PP degradation in supercritical water. Under the experimental conditions, Course Two (the increasing course of temperature and pressure is via liquid regions to supercritical regions) is more effective than Course One (the increasing course of temperature and pressure is via gaseous regions to supercritical regions) on PP degradation in supercritical water. Therefore, controlling the increasing course of temperature and pressure is a promising way to advance efficiency and decrease cost in the industrial process for recycling of waste plastics.
ACKNOWLEDGEMENT The authors would like to thank Academician Fu-Qian Jing, Southwest Jiaotong University, People’s Republic of China,for his kind support, and Prof. Takashi Moriyoshi, Research Institute for Solvotherma1 Technology, Japan, for his support in the experimental apparatus. REFERENCES 1 2
3 4 5
6
7 8 9 10 I1 12
T‘arbitrary unit)
Figure 4 The schematic drawing of the relation of density (subscript n shows increasing order), pressure and temperature for general fluids
CONCLUSIONS On the basis of the above-mentioned results, it could be concluded that the increasing course of tem4
741
13
14
15
Chen, J.Y., Ou, C.F., “Depolymerization of polyethylene terephthalate resin under pressure”, Appl. Polym. Sci., 42, 1501--1507(1991). Cao, W.L., Zhang, J.C., Li, Y., “Application of supercritical fluids technique in the degradation of PET waste”, J . Berj’ing Univ. Chem. Technol., 26(4), 73-74(1999). (in Chinese) Chen, K.Y., Wang, H.J., Tao, W., “The decomposition of PS in supercritical water”, Environ. Sci. Technol., 21(3), 19-21(1998). (in Chinese) Douglas, L.W., Sungyu, L., “Kinetics and mechanism of styrene monomer recovery from waste polystyrene by SCW partial oxidation”, Adv. Envir. Res., 6(1),9-16(2001). Liu, Y.R., Qiang, J.L., “Pyrolysis of polystyrene waste in a fluidized-bed reactor to obtain styrene monomer and gaseousoline fraction”, Fuel Process. Technol., 63(3), 45-55 (2000). Zheng, F., Janusz, A., “A comparative study of polystyrene decomposition in supercritical water and air environments using diamond anvil cell”, Appl. Polym. Sci., 81,3565-3577(2001). Takehiko, M., Heiji, E., “Characteristics of polyethylene cracking in supercritical water compared to thermal cracking”, Polym. Degrud. Stub., 65(3), 373-386( 1999). Mitsuru, S., Zhen, F., Yoshiko, F., “Dissolution and hydrolysis of cellulose in subcritical and supercritical water”, Ind. Eng. Chem. Res., 39(8), 2883-2890(2000). Zhang, G.M., Inez, H., “Supercritical water oxidation of nitrobenzene”,Ind. Eng. Chem. Res, 42(2), 285-289(2003). Masakazu, S., Masahiko, K., Hisao, O., “Oxidation of carbon particles in supercritical water: Rate and mechanism”, Ind. Eng. Chem. Res., 43(3), 69*699(2004). Takehiro, M., Motonobu, G., Akio Kodama, “Supercritical water oxidation of a model municipal solid waste”, Ind. Eng. Chem. Res., 39(8), 2807-2810(2000). Meng, L.H., Huang, Y.D., Zhang, Y., Liang, Z.H., “Comparative study on thermal decomposition of PP and supercritical water decomposition of polypropylene”, Muter. Sci. Technol., 11(3),3 11-3 14(2003). (in Chinese) Wang, J., Shen, M.Q., Gong, Y.L., Ma, P.S., “Study of polypropylene degradation in supercritical water”, Polym. Muter. Sci. Eng., 20(2), 6568(2004). (in Chinese) Wu, X.H., Su, L., Liu, X.R., Chen, L.Y., Chen, K.Y., Hong, S.M., “The effect of additive BPO on the depolymerization of HDPE in supercritical water”, Polym. Muter. Sci.Eng., 22(1), 135-138(2006). (in Chinese) Su, L., Wu, X.H., Liu, X.R., Chen, L.Y., Chen, K.Y., Hong, S.M., “An investigation of polypropylene degradation in supercritical water adding dibenzoyl peroxide”, Chin. J . Chem. Eng., 13(6), 845--848(2005).
Chin. J. Ch. E. 15(5) 738 (2007)
(2007)
Effect of Increasing Course of Temperature and Pressure on Polypropylene Degradation in Supercritical Water* LIU Xiuru(34 %%);>“, CHEN Liying( % I@ SU Lei( % $$-)a,b, WU Xuehua(5 q)”“, CHEN Keyu( %&?)d and HONG Shiming($% @ @)a,** a
x)a,
Laboratory of High Pressure Physics, Southwest Jiaotong University, Chengdu 61003 1, China Department of Physics, Zhengzhou University of Light Industry, Zhengzhou 450002, China College of Science, Kunming University of Science and Technology, Kunming 650093, China Department of Polymer Science and Technology, Sichuan University, Chengdu 610065,China
Abstract The effect of increasing course of temperature and pressure on polypropylene (PP) degradation in supercritical water was investigated for developing a process of recycling waste plastic. A group of experiments was carried out in a reaction system at a pressure of 26MPa, temperature of 380°C or 400°C for 30min, 70min, and 120min by Course One (the increasing course of temperature and pressure is via gaseous regions to supercritical regions), and the other group was carried out at corresponding holding conditions by Course Two (the increasing course of temperature and pressure is via liquid regions to supercritical regions). The time of the increasing courses was about 30min. Products were analyzed by Ostward-type viscometer, gaseous chromatography, and mass spectrometers (GCIMS). Characterization results suggested that different increasing courses of temperature and pressure would give rise to different results, although they were treated under the similar holding conditions. It was also found that Course Two was more effective on PP degradation in supercritical water. Keywords increasing course, polypropylene degradation, supercritical water
1 INTRODUCTION In recent years, supercritical fluid is focused as a “super green” solvent for the conversion of waste materials into resources. It has been reported that supercritical water could be utilized to treat polyethylene terephthalate (PET)[1,2], polystyrene (PS)[3 - 61, polyethylene (PE)[7], cellulose[8], nitrobenzene[9], carbon particles[lO], municipal solid waste[ll], polypropylene (PP)[12,13], and so on. Up to now, most of the articles dealt with the influences of holding conditions on plastic degradation, such as temperature, pressure, holding time, and material ratio. In fact, the experimental result is not so certain for the same holding conditions if the increasing course of temperature and pressure is different and the time of the increasing course is comparable with the holding time. In a previous study[l4,15], it was observed that the increasing course of temperature and pressure is also an important factor on PP degradation. It is unfortunate that no direct experimental evidence has confirmed this view. In this study, a series of experiments were carried out at certain temperature, pressure, and holding time. Besides holding conditions, details of increasing courses of temperature and pressure for every experiment were also recorded. The experiments were divided into two groups with their increasing course. In the first group, each increasing course was via gaseous regions to supercritical regions, which was called Course One. In the other group, each increasing course was via liquid regions to supercritical regions, which was called Course Two. After characterization of all samples, it was made clear that different inReceived 2006- 10-27, accepted 2007-02-07.
creasing courses would give rise to different results, although they were treated under the same holding conditions, and Course Two was more effective on PP degradation in supercritical water.
2 EXPERIMENTAL The experiments were carried out in a system as shown in Fig.1, including a batch reactor made of special titanium steel tube sealed with Swagelok caps (about 25cm3 in volume), heater, temperature controller, pressure sensor, pump, pipes, and valves etc.
thermocouple
I
n
valve 2
-
I
$
I I pressure sensor
temperature control
Figure 1 The SCW experimental system
PP powder (Wuhan Phenix Co. China), with the mean molecular weight (Mw) of about 8OOOO was used as starting materials. Distilled water was the solvent in all experiments.The mass ratio of water to PP was 5 : 1. Holding temperature was 380°C and 400”C,
* Supported by the National Natural Science Foundation of China (No.59972022) and the Opening Foundation of the Environmental Engineering Key Discipline, Zhejiang University of Technology (No.563 10503011). ** To whom correspondence should be addressed. E-mail: [email protected]
Effect of Increasing Course of Temperature and Pressure on Polypropylene Degradation in Supercritical Water
pressure was about 26MPa, and holding time was 30, 75, and 120min, respectively. The amount of water was decided using the equation of state to obtain the desired pressure. Especially, the details of the increasing courses of temperature and pressure were recorded for every experiment, The time of increasing course of temperature and pressure is about 30min, which is comparable with the holding time. M, of reaction products was obtained by measuring the viscosity with Ostward-type viscometer at a constant temperature of 135"C. Decahydronaphthalene with purity higher than 98% (Shanghai Chemical Reagent Co., China) was used as the normative solvent. And the concentration of the sample is 20mg-ml-'. The composition of the yield was analyzed using gas chromatography and mass spectrometers (HP 6890 series GC System, HP 5973 MASS selective detector). The experimental conditions are as follows. The column, HP-SMS, is 250pm in diameter and 30m long, and the film thickness is 0.25pm. Helium was used as the carrier gas with an exit flow rate of 0.8ml.minand T increased from 50°C to 120iC at 5"C+min-', from 120°C to 280°C at 10"C.min- . Injector: direct
739
injection, 270°C. EI: 70ev. Scan: 2W50Oamu.
3 RESULTS AND DISCUSSION Figures 2(a), (c), and (e) express the increasing courses of temperature and pressure of corresponding samples, and all of them are via gaseous regions to supercritical regions (Course One). Figs.2(b), (d), and (f) present the increasing courses of temperature and pressure of corresponding samples, and all of them are via liquid regions to supercritical regions (Course Two). The holding conditions and the results are shown in Table 1. It can be seen that the phases of the samples gained by Course Two were almost different from those gained by Course One. For example, the phase of Sample 2 is grease, while that of Sample 1 is solid, and then the phase of Sample 6 is oil, while that of Sample 5 is grease. It is cogitable that the oil phase product is more decomposed than grease, and grease is more decomposed than solid. So the results imply that Course Two is more effective on PP degradation in supercritical water.
Ly/ G[,; J G i !20bG 1 !i2o ,
'"1__.41 25
g
.I
30 I
I
25,
400
0
m
10
k 5
G
0
100
300
200
15
g
10
0
100
200
300
temperature, 'C
200 300 temperature, 'C
(a) Sample 1
(b) Sample 2
(c) Sample 3
30 I
2
400
temperature, 'C
30
I
t
1
2 10
0
100 200 300 temperature, "C
400
0
(d) Sample 4
30 I
2 10 & 0
5
200 400 temperature, "C
100
400
I
400
200
600
600
temperature, "C
(f) Sample 6
(e) Sample 5
Figure 2 The increasing course of temperature and pressure of the samples -gas-liquid equilibrium curve; rn increasing course of the sample Table 1 The holding conditions and the results ~
~
~~
Sample No. 1
Course' One
P,MPa 26
T, "C 380
No.2
Two
26
No.3
One
26
No.4
Two
26
t, min
30
Phase solid
380
30
grease
6027
380
75
grease
5762
380
75
grease
3325
M w
12895
400 120 grease 826 No.6 Two 26 400 120 oil 198 0 Course One: the increasing course of temperature and pressure is via gaseous regions to supercritical regions; Course Two: the increasing course of temperature and pressure is via liquid regions to supercritical regions. NOS
One
26
Chin. J. Ch. E. 15(5) 738 (2007)
Chin. J. Ch. E. (VO~.15, No.5)
740
Table 1 also shows that M , of the products are different in two kinds of experiments. The Mw of products obtained by Course Two decreased faster than those gained by Course One although they were treated at the same holding conditions. For example, at 380°C, 26MPa, for 30min, M, of Sample 2 decreased from 80000 to 6027, while Sample 1 was decomposed to 12895. In other words, Course Two is more effective on PP degradation than Course One.
Figure 3 shows the GC/MS result of Sample 6. And the main products are shown in Table 2. It indicated that PP was decomposed to products with low molecular weight by solvolysis of supercritical water, such as hydrocarbon of methane series, hydrocarbon of ethylene series, and cycloparaffinic hydrocarbons. On comparing with the product of Sample 5 , which was grease phase, Sample 6 was more decomposed, although treated at the same holding conditions.
6500000 6000000
I
5500000 5000000 4500000
4000000 a
3500000
'
3000000 2500000 2000000 1500000 1000000
2.00
4.00
6.00
8.00 10.00 12.00 14.00 16.00 18.00 20.00 22.00 24.00 26.00 28.00 30.00 32.00
time,min Figure 3 The result analyzed by gas chromatography and mass spectrometry (400"C, 26MPa,120min) Table 2 The main components o troduct of Sample 6 detected by GC-MS
Time,min 1.40 1.55 2.11 2.46 3.04 3.79
4.15 4.58 4.83 5.39 5.68 5.96 6.53 6.91 7.51 7.60 8.36 8.70 9.06 9.61 October, 2007
Component pentane 2-methylpentane
3-dimethylc yclopentane
Area,% 0.35 0.52 0.35
1,1,3-trirnethylcyclopentane
0.37
4-methylheptane 3,5,5-trimethyl1-hexene 2,4-dimethylheptane 2,4-dimethyl-1-hepene 1,2,4-trimethylcyclohexane 2,4,4tetramethylcyclopentene 2,3,5-trimethyl1,3-hexadiene 1,1,3,5-tetramethylcyclohexane 4-acetyl-1,5-dimethylpyrazole 1,1,3,5-tetramethylcyclohexane 1-octadecene 3,s-dimethyloctane 1-ethyl-3-methylbenzene 1,2,4-trimethylbenzene 4-methylnonane 1,2,4-trimethylbenzene
2.37 2.12 1.33 1.35 0.47 1.31 0.61 1.96 0.76 0.38 0.47 0.69 0.81
4.85 0.38 2.45
Time,min 10.66
11.oo 11.95 12.21 13.03 13.99 14.40 15.24 16.26 16.45 17.61 18.79 21.47 23.23 23.44 25.58 26.18 28.15 28.88
Comuonent 2,4-diethyl1-methylcyclohexane 2,6-dimethylnonane 1-methyl-3-propylbenzene 2-ethyl-1,4-dimethylbenzene 1-decene 2,4-dimethyl1,3,Strimethylcyclohexane 2,3,3-trimethyl-4-nonene 2,4-diethylcyclohexane 1,4-diethy1-2-methylbenzene 1-ethy1-3,5-dimethylbenzene 1,1,3-trimethylcyclohexane
2,3-dihydro-1,6-dimethyl-lH-indene 2,3-dihydro1,1,5-trimethyl1H-indene 4,6-dimethyldodecane 2,7,1O-trimethyldodecane 1,4-dimethylbenzene 1,2-dihydr0-2,S,8-trimethylnaphthalene 1,4,6-trimethylnaphthalene 1,2-diethyl-3-methylcyclohexane
Area,% 0.35 1.46 0.70
1.so 2.38 0.82 1.07 0.41 0.53 1.05
0.47 0.81 0.38 0.56 0.45 0.42 0.41 0.61 0.71
Effect of Increasing Course of Temperature and Pressure on Polypropylene Degradation in SupercriticalWater
It is well known that the properties of the fluid in liquid regions are quite different from those in gaseous regions, especially in near-critical point, such as density, viscosity, diffusion coefficient, dielectric constant, ionization degree, solubility, and so on. Fig.4 shows a schematic drawing of the relation of density, temperature, and pressure of general fluid in near-critical and supercritical fluid. It can be seen that the density turns higher gradually by Course One, while the density turns smaller gradually by Course Two. The other properties will also be changed differently along with the different courses. These differences may bring about different influences on PP degradation. In general experiments, the increasing courses of temperature and pressure are almost via gaseous regions to supercritical regions. The reason of increasing courses via liquid regions to supercritical regions is a randomly or manipulatively additive pressure rise during the process. This change could induce certain changes of the component and state in the sample. The changed state may have an active effect on PP degradation in the following reaction process. Moreover, it takes about 30min in the increasing course, which is comparable to the holding time at appointed temperature and pressure, so the effect cannot be ignored in the whole reaction. In previous reports on the similar methods, the time of increasing course of temperature and pressure is comparatively short, so the above-mentioned phenomenon may not be so obvious. Nevertheless, in the modem industry, rapid increasing course will give rise to certain problems, such as labor security, additional cost, and so on. So it is still necessary to study the effect of increasing course of temperature and pressure on plastic degradation.
perature and pressure is a very important factor on PP degradation in supercritical water. Under the experimental conditions, Course Two (the increasing course of temperature and pressure is via liquid regions to supercritical regions) is more effective than Course One (the increasing course of temperature and pressure is via gaseous regions to supercritical regions) on PP degradation in supercritical water. Therefore, controlling the increasing course of temperature and pressure is a promising way to advance efficiency and decrease cost in the industrial process for recycling of waste plastics.
ACKNOWLEDGEMENT The authors would like to thank Academician Fu-Qian Jing, Southwest Jiaotong University, People’s Republic of China,for his kind support, and Prof. Takashi Moriyoshi, Research Institute for Solvotherma1 Technology, Japan, for his support in the experimental apparatus. REFERENCES 1 2
3 4 5
6
7 8 9 10 I1 12
T‘arbitrary unit)
Figure 4 The schematic drawing of the relation of density (subscript n shows increasing order), pressure and temperature for general fluids
CONCLUSIONS On the basis of the above-mentioned results, it could be concluded that the increasing course of tem4
741
13
14
15
Chen, J.Y., Ou, C.F., “Depolymerization of polyethylene terephthalate resin under pressure”, Appl. Polym. Sci., 42, 1501--1507(1991). Cao, W.L., Zhang, J.C., Li, Y., “Application of supercritical fluids technique in the degradation of PET waste”, J . Berj’ing Univ. Chem. Technol., 26(4), 73-74(1999). (in Chinese) Chen, K.Y., Wang, H.J., Tao, W., “The decomposition of PS in supercritical water”, Environ. Sci. Technol., 21(3), 19-21(1998). (in Chinese) Douglas, L.W., Sungyu, L., “Kinetics and mechanism of styrene monomer recovery from waste polystyrene by SCW partial oxidation”, Adv. Envir. Res., 6(1),9-16(2001). Liu, Y.R., Qiang, J.L., “Pyrolysis of polystyrene waste in a fluidized-bed reactor to obtain styrene monomer and gaseousoline fraction”, Fuel Process. Technol., 63(3), 45-55 (2000). Zheng, F., Janusz, A., “A comparative study of polystyrene decomposition in supercritical water and air environments using diamond anvil cell”, Appl. Polym. Sci., 81,3565-3577(2001). Takehiko, M., Heiji, E., “Characteristics of polyethylene cracking in supercritical water compared to thermal cracking”, Polym. Degrud. Stub., 65(3), 373-386( 1999). Mitsuru, S., Zhen, F., Yoshiko, F., “Dissolution and hydrolysis of cellulose in subcritical and supercritical water”, Ind. Eng. Chem. Res., 39(8), 2883-2890(2000). Zhang, G.M., Inez, H., “Supercritical water oxidation of nitrobenzene”,Ind. Eng. Chem. Res, 42(2), 285-289(2003). Masakazu, S., Masahiko, K., Hisao, O., “Oxidation of carbon particles in supercritical water: Rate and mechanism”, Ind. Eng. Chem. Res., 43(3), 69*699(2004). Takehiro, M., Motonobu, G., Akio Kodama, “Supercritical water oxidation of a model municipal solid waste”, Ind. Eng. Chem. Res., 39(8), 2807-2810(2000). Meng, L.H., Huang, Y.D., Zhang, Y., Liang, Z.H., “Comparative study on thermal decomposition of PP and supercritical water decomposition of polypropylene”, Muter. Sci. Technol., 11(3),3 11-3 14(2003). (in Chinese) Wang, J., Shen, M.Q., Gong, Y.L., Ma, P.S., “Study of polypropylene degradation in supercritical water”, Polym. Muter. Sci. Eng., 20(2), 6568(2004). (in Chinese) Wu, X.H., Su, L., Liu, X.R., Chen, L.Y., Chen, K.Y., Hong, S.M., “The effect of additive BPO on the depolymerization of HDPE in supercritical water”, Polym. Muter. Sci.Eng., 22(1), 135-138(2006). (in Chinese) Su, L., Wu, X.H., Liu, X.R., Chen, L.Y., Chen, K.Y., Hong, S.M., “An investigation of polypropylene degradation in supercritical water adding dibenzoyl peroxide”, Chin. J . Chem. Eng., 13(6), 845--848(2005).
Chin. J. Ch. E. 15(5) 738 (2007)