聚乙烯高压热解及其反应机理研究

顾菁; 程磊磊; 王亚琢; 张原翔; 袁浩然

doi:10.19906/j.cnki.JFCT.2021028

聚乙烯高压热解及其反应机理研究

doi: 10.19906/j.cnki.JFCT.2021028

顾菁^{1, 2, 3, 4, 5,},
程磊磊²,
王亚琢^{1, 2, 3, 4, 5},
张原翔²,
袁浩然^{1, 2, 3, 4, 5, ,}

1.
中国科学院广州能源研究所，广东广州 510640
2.
南方海洋科学与工程广东省实验室(广州)，广东广州 511458
3.
中国科学院可再生能源重点研究室，广东广州 510640
4.
广东省新能源和可再生能源研究开发与应用重点研究室，广东广州 510640
5.
佛山市科恒博环保技术有限公司，广东佛山 528200

基金项目: 国家重点研发计划项目（2018YFC1901200），国家自然科学基金（51976223）和南方海洋科学与工程广东省实验室（广州）人才团队引进重大专项（GML2019ZD0101）资助

详细信息

通讯作者:
E-mail: yuanhaoran81@gmail.com

中图分类号: X705
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出版历程
- 收稿日期: 2020-10-21
- 修回日期: 2020-11-27
- 网络出版日期: 2021-03-19
- 刊出日期: 2021-03-19

High-pressure pyrolysis and its mechanism of polyethylene

GU Jing^{1, 2, 3, 4, 5
,},
CHENG Lei-lei²,
WANG Ya-zhuo^{1, 2, 3, 4, 5},
ZHANG Yuan-xiang²,
YUAN Hao-ran^{1, 2, 3, 4, 5
, ,}

1.
Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences (CAS), Guangzhou 510640, China
2.
Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China
3.
CAS Key Laboratory of Renewable Energy, Guangzhou 510640, China
4.
Guangdong Provincial Key Laboratory of New and Renewable Energy Research and Development, Guangzhou 510640, China
5.
Foshan Kehengbo Environmental Protection Technology Co. LTD, Foshan 528200, China

Funds: The project was supported by the National Key Research and Development Program of China (2018YFC1901200), National Natural Science Foundation of China (51976223) and Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) （GML2019ZD0101）.

摘要

摘要: 塑料废弃物数量日益增加，实现低能耗、高值化利用是促进塑料废弃物回收利用的关键。在380 ℃设定温度和(1−5) ×10⁵ Pa初始压力条件下分别开展聚乙烯高压热裂解和催化热解实验，记录反应过程温度曲线，分析聚乙烯高压热裂解/催化热解产物分布。研究结果表明，反应过程中反应物相态是影响热解反应历程的重要因素；因反应路径而异，压力变化对聚乙烯热裂解和催化热解产生不同程度的影响。聚乙烯高压热裂解实验过程中存在飞温现象，飞温峰值随初始压力的增加呈现单调增加的趋势；峰值温度的升高带来聚乙烯断链程度的加深，即获得更多小分子量产物。在相同设定温度和初始压力条件下的聚乙烯高压催化热解实验中不存在飞温现象，利用锌负载的ZSM-5催化剂实现聚乙烯高选择性制备芳香烃，液体产物中单环芳烃占比达82.53%，积炭产率在1.5%以下。
- 聚乙烯 /
- 高压 /
- 热裂解 /
- 催化热解 /
- 飞温现象
Abstract: With the increasing waste disposal problems, high-value utilization technology using less energy is important to incentivize better recycling of plastic waste. Polyethylene high-pressure thermal cracking and catalytic pyrolysis experiments were conducted at a set temperature of 380 ℃ and low initial pressures (1−5) × 10⁵ Pa. The process temperature curves were recorded and the hydrocarbon distribution of products was analyzed. The results suggest that the phase state in the pyrolysis system is a critical issue for reaction pathways. Thus, the pressure changes have different effects on the thermal cracking and catalytic pyrolysis of polyethylene. There is a phenomenon of thermal runaway during the polyethylene high-pressure pyrolysis process. The peak temperature represents a monotonous increase with the increasing initial pressure; the higher peak temperature leads to deeper cracking of polyethylene, giving more low-molecular-weight products. In the high-pressure catalytic pyrolysis experiments under the same other conditions, no thermal runaway is observed. The Zn-supported ZSM-5 catalyst converts polyethylene into aromatics, and the selectivity for monocyclic aromatics in the liquid phase is up to 82.53%. Moreover, the coke yield is less than 1.5%.
- polyethylene /
- high pressure /
- thermal cracking /
- catalytic pyrolysis /
- thermal runaway

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图 1 聚乙烯高压热解实验装置

Figure 1 Polyethylene high-pressure pyrolysis experimental device

1: nitrogen cylinder; 2: reducing valve; 3: gas inlet valve; 4: cylinder; 5: heater assembly; 6: gas release valve; 7: magnetic agitator; 8: pressure gage; 9: reactor controller; 10: computer; 11: gas collecting unit

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图 2 聚乙烯高压热裂解（(a)−(e)）和高压催化热解过程（f）温度曲线

Figure 2 Temperature curves of polyethylene high-pressure pyrolysis ((a)−(e)) and high-pressure catalytic pyrolysis (f) processes

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图 3 聚乙烯高压热裂解（a）和催化热解（b）实验产物产率

Figure 3 The product yields of polyethylene high-pressure pyrolysis (a) and catalytic pyrolysis (b) experiments

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图 4 聚乙烯热裂解液体产物GC-MS色谱图（npa：正构烷烃，ol：α-烯烃）

Figure 4 GC-MS chromatograms of liquid products obtained from the thermal cracking of polyethylene (npa: n-paraffins, ol: α-olefins)

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图 5 聚乙烯催化热解液体产物GC-MS色谱图

Figure 5 GC-MS chromatograms of liquid products obtained from the catalytic pyrolysis of polyethylene

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图 6 聚乙烯高压热裂解（a）和催化热解（b）过程机理图

Figure 6 Reaction mechanism of polyethylene high-pressure thermal cracking (a) and catalytic pyrolysis (b)

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表 1 实验原料的LDPE特性

Table 1 Property of LDPE feedstock

Form	Powder
Molar mass	average M_n ~ 1700 by GPC average M_w ~ 4000 by GPC
Viscosity	1.5 Poise (25 ℃, Brookfield Thermosel) (lit.)
Melting point	92 ℃
Acid number	<0.05 mg KOH/g
Transition temp	softening point 106 ℃ (ring and ball)
Density	0.92 g/mL at 25 ℃

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表 2 实验原料LDPE元素分析

Table 2 Ultimate analysis of LDPE feedstock

Raw material	Ultimate analysis w/%
Raw material	C	H	N	S	O
LDPE	85.22	14.08	0	0	0

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表 3 聚乙烯高压热裂解/催化热解过程参数

Table 3 Process parameters of polyethylene high-pressure pyrolysis and high-pressure catalytic pyrolysis

Entry	Starting value of thermal runaway/℃	Peak temperature /℃	Peak pressure/ 10⁵ Pa	Final pressure at room temperature/10⁵ Pa	Partial pressure of gaseous product at room temperature/10⁵ Pa
P-1	~293	417.8	9.5	4	3
P-2	~303	427.0	15	5	3
P-3	~303	437.6	18	6.5	3.5
P-4	~305	450.0	22	7.5	3.5
P-5	~311	452.3	24	9	4
C-1	−	380.3	34.5	12	11
C-2	−	381.9	39	13	11
C-3	−	383.3	43.5	13.5	10.5
C-4	−	383.1	50	15	11
C-5	−	381.0	52	16.5	11.5

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表 4 聚乙烯高压热裂解气体产物组分分布

Table 4 Gas products distribution obtained from the high-pressure pyrolysis of LDPE

Runs	P-1	P-2	P-3	P-4	P-5
Hydrogen	3.84	5.04	5.88	7.54	8.61
Methane	24.26	25.69	26.74	26.28	29.00
Ethane	19.01	20.53	20.62	21.31	21.44
Ethylene	7.26	7.43	8.53	7.69	7.59
Propane	18.23	16.26	15.37	16.12	14.12
Propene	15.25	14.19	14.12	13.14	11.67
C₄ alkanes	5.66	5.20	4.09	3.57	3.63
C₄ olefins	5.56	4.85	3.75	3.64	3.11
C₅₊ hydrocarbons	0.94	0.81	0.91	0.71	0.83
note: the temperature set in the above table is 380 ℃; X in the label “P-X ” is the initial pressure value

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表 5 聚乙烯高压热裂解液体产物组分分布

Table 5 Liquid products distribution obtained from the high-pressure pyrolysis of LDPE

Runs	P-1	P-2	P-3	P-4	P-5
n-Paraffins	67.59	66.37	65.18	65.25	64.14
Isoparaffins	−	0.38	0.95	1.14	1.18
Cycloparaffins	5.73	5.76	5.67	6.27	8.59
α-olefins	24.59	22.97	21.48	19.57	18.01
Cycloolefins	−	1.56	2.58	3.41	3.27
Other olefins	2.09	2.23	2.49	2.19	2.54
Aromatics	−	0.73	1.65	2.17	2.27
Average carbon number	14.12	13.57	12.84	11.16	11.05
note: the temperature set in the above table is 380 ℃; X in the label “P-X ” is the initial pressure value

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表 6 聚乙烯催化热解气体产物组分分布

Table 6 Gas products distribution obtained from the catalytic pyrolysis of LDPE

Runs	C-1	C-2	C-3	C-4	C-5
Hydrogen	26.27	24.98	23.51	19.82	20.26
Methane	6.82	6.29	5.37	6.03	5.88
Ethane	4.83	4.92	5.15	5.08	5.39
Ethylene	4.25	3.49	2.49	2.09	1.96
Propane	32.02	34.82	36.85	39.77	39.37
Propylene	7.58	5.28	4.26	3.92	3.00
Butane	5.18	6.26	6.44	7.09	7.26
Isobutane	7.17	9.18	10.49	11.52	11.56
C₄ olefins	3.36	2.47	2.76	1.79	2.26
C₅₊ hydrocarbons	2.52	2.31	2.68	2.89	3.06
note: the temperature set in the above table is 380 ℃; X in the label “P-X ” is the initial pressure value

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表 7 聚乙烯催化热解液体产物组分分布

Table 7 Liquid products distribution obtained from the catalytic pyrolysis of LDPE

Runs	C-1	C-2	C-3	C-4	C-5
Aromatics	84.51	83.10	83.25	81.54	79.21
Benzene	5.62	4.84	5.32	4.28	4.36
Toluene	25.04	24.16	22.10	20.75	20.89
Ethylbenzene	4.63	4.53	4.46	4.39	4.40
Xylene	24.78	25.64	24.97	25.36	24.58
Other MAHs	22.46	21.87	24.25	24.75	23.29
PAHs	1.98	2.06	2.15	2.01	1.69
Other hydrocarbons	15.49	16.90	16.75	18.46	20.79
n-Paraffins	6.54	6.32	7.01	6.95	7.91
Isoparaffins	4.80	5.21	6.04	5.96	7.01
Olefins	0.74	0.83	0.98	1.26	1.44
Cycloparaffins	3.21	4.49	2.72	3.61	4.00
Cycloolefins	0.20	0.05	0.00	0.68	0.43
note: the temperature set in the above table is 380 ℃; X in the label “P-X ” is the initial pressure value

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