Study on co⁃pyrolysis characteristics and kinetics of waste PE and PET plastics

doi:10.19491/j.issn.1001-9278.2024.03.015

Abstract

Abstract:

The cap （PE） and body （PET） of the discarded 550 mL mineral water bottle of Nongfu Spring were used as raw materials. The laboratory⁃scale fixed⁃bed reactor and thermogravimetric analyzer were used to conduct pyrolysis experiments to explore the synergistic effects of co⁃pyrolysis of waste PE and PET plastics and the kinetic behaviors in which co⁃pyrolysis process was separated into two degradation stages. The results showed that co⁃pyrolysis of PE and PET plastics promoted the production of liquid pyrolysis oil and improving the selectivity of hydrocarbons in pyrolysis oil. When the mixing ratio of PE and PET was 2∶1， the highest pyrolysis oil yield of 84.72 % was achieved. The increment of pyrolysis temperature promoted the occurrence of secondary reactions like Diels⁃Alder and aromatization reactions， generating more aromatic products. The average apparent activation energies of the two degradation stages of co⁃pyrolysis process were 191.05 kJ/mol and 215.22 kJ/mol. The reaction mechanisms of these two stages were aligned with order⁃based model and contracting volume （R3） model， respectively.

Key words: polyethylene, polyethylene terephthalate, waste plastic, co?pyrolysis, kinetics

CLC Number:

TQ325.1⁺2

LUO Guanqun, ZHAO Le, PAN Yaqi. Study on co⁃pyrolysis characteristics and kinetics of waste PE and PET plastics[J]. China Plastics, 2024, 38(3): 86-93.

Figures/Tables 12

项目	成分	PE	PET
元素分析（质量分数）/%	C	84.33	60.27
	H	14.82	4.69
	O*	0.70	34.25
	N	0.15	0.79
工业分析（质量分数）/%	水分	0	0
	挥发分	98.78	84.18
	固定碳	0.16	14.43
	灰分	1.05	1.39

Tab.1. Ultimate and proximate analysis of PE and PET

Fig.1. Schematic diagram of pyrolysis reaction system

反应机理类型	模型名称/代码	$f (α)$	$g (α)$
幂函数模型	$P n$	$α 1 / n$	$n α (n - 1) / n$
反应阶数模型	一阶模型 O1	$1 - α$	$- l n 1 - α$
	二阶模型 O2	$1 - α 2$	$1 - α - 1 - 1$
	三阶模型 O3	$1 - α 3$	$1 - α - 2 - 1 / 2$
几何模型	一维模型 D1	$1 / 2 α$	$α 2$
	二维模型 D2	$- l n 1 - α - 1$	$1 - α l n 1 - α + α$
	收缩面模型 R2	$2 1 - α 1 / 2$	$1 - 1 - α 1 / 2$
	收缩体模型 R3	$3 1 - α 2 / 3$	$1 - 1 - α 1 / 3$
成核与生长模型	Avrami⁃Erofeev A2	$2 1 - α - l n 1 - α 1 / 2$	$- l n 1 - α 1 / 2$
	Avrami⁃Erofeev A3	$3 1 - α - l n 1 - α 2 / 3$	$- l n 1 - α 1 / 3$
	Avrami⁃Erofeev A4	$4 1 - α - l n 1 - α 3 / 4$	$- l n 1 - α 1 / 4$

反应机理类型	模型名称/代码	$f (α)$	$g (α)$
幂函数模型	$P n$	$α 1 / n$	$n α (n - 1) / n$
反应阶数模型	一阶模型 O1	$1 - α$	$- l n 1 - α$
	二阶模型 O2	$1 - α 2$	$1 - α - 1 - 1$
	三阶模型 O3	$1 - α 3$	$1 - α - 2 - 1 / 2$
几何模型	一维模型 D1	$1 / 2 α$	$α 2$
	二维模型 D2	$- l n 1 - α - 1$	$1 - α l n 1 - α + α$
	收缩面模型 R2	$2 1 - α 1 / 2$	$1 - 1 - α 1 / 2$
	收缩体模型 R3	$3 1 - α 2 / 3$	$1 - 1 - α 1 / 3$
成核与生长模型	Avrami⁃Erofeev A2	$2 1 - α - l n 1 - α 1 / 2$	$- l n 1 - α 1 / 2$
	Avrami⁃Erofeev A3	$3 1 - α - l n 1 - α 2 / 3$	$- l n 1 - α 1 / 3$
	Avrami⁃Erofeev A4	$4 1 - α - l n 1 - α 3 / 4$	$- l n 1 - α 1 / 4$

Tab.2. The commonly used reaction mechanism functions for solid pyrolysis

Fig.2. Product yield and distribution of co⁃pyrolysis of PE and PET at different mixing ratios

Fig.3. Product yield and distribution of co⁃pyrolysis of PE and PET at different pyrolysis temperatures （PE∶PET=1∶1）

Fig.4. TG and DTG curves of co⁃pyrolysis of PE and PET at different heating rates （PE∶PET=1∶1）

样品	升温速率（ $β$ ）/℃·min^-1	最大失重速率所对应的温度/℃
样品	升温速率（ $β$ ）/℃·min^-1	$T 1$	$T 2$
PE	5	-	463.04
	10	-	477.00
	20	-	493.01
PET	5	422.97	-
	10	436.93	-
	20	446.10	-
PE和PET	5	424.91	439.91
	10	440.82	463.82
	20	455.06	472.06

样品	升温速率（ $β$ ）/℃·min^-1	最大失重速率所对应的温度/℃
样品	升温速率（ $β$ ）/℃·min^-1	$T 1$	$T 2$
PE	5	-	463.04
	10	-	477.00
	20	-	493.01
PET	5	422.97	-
	10	436.93	-
	20	446.10	-
PE和PET	5	424.91	439.91
	10	440.82	463.82
	20	455.06	472.06

Tab.3. Characterisitic parameters of pyrolysis/co⁃pyrolysis of PE and PET at different heating rates

Fig.5. Variations of ∆W with pyrolysis temperatures at different heating rates （PE∶PET=1∶1）

升温速率/ ℃•min^-1	温度区间/℃
升温速率/ ℃•min^-1	第一失重阶段	第二失重阶段
5	346.91~438.91	438.91~494.91
10	348.82~452.82	352.82~5028.82
20	355.06~467.06	467.06~546.06

Tab.4. Degradation stage separation at different heating rates

Fig.6. Estimation of Ea of different degradation stage for co⁃pyrolysis of PE and PET by KAS

Fig.7. Estimation of Ea of different degradation stage for co⁃pyrolysis of PE and PET by KAS

Fig.8. Experimental master plots and mechanism function curves

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