Deactivation of HZSM-5 during the catalytic co-pyrolysis of biomass and plastic

doi:10.16085/j.issn.1000-6613.2020-1767

Abstract

Abstract:

The reuse and regeneration of HZSM-5 zeolite in the catalytic co-pyrolysis of corn stover/high-density polyethylene was investigated using a tube reactor. The effect of acid washing treatment of corn stover on the catalytic activities of HZSM-5 zeolite was studied. The composition of the obtained bio-oil was analyzed by GC-MS, and the properties of fresh, spent, and regenerated HZSM-5 catalysts were measured using TG, ICP-MS, SEM/EDS, BET, and NH₃-TPD, respectively. The results showed that aromatics were the main products for the catalytic co-pyrolysis of corn stover/high-density polyethylene with fresh HZSM-5. With the increase of HZSM-5 reuse times, the yield of aromatics decreased gradually, and the BET area, pore volume, and acidity of the catalyst decreased sharply, indicating the reduced catalytic activities of HZSM-5. The acid washing pretreatment of corn stover enhanced the formation of oxygen-containing intermediates, which accelerated the deactivation of HZSM-5 zeolite. The catalytic activity of the regenerated HZSM-5 over acid washing corn stover/high-density polyethylene was recovered, while the catalytic activity of the regenerated HZSM-5 over raw corn stover/high-density polyethylene was slightly lower than that of fresh HZSM-5. This was due to the fact that alkali/alkaline earth metals were significantly accumulated over the HZSM-5 catalyst, which couldn’t be removed by calcination and thus could deposit on the strong acid sites, causing the “poisoning” deactivation of the catalyst. The above results suggest that the deactivation of HZSM-5 caused by coke can be regenerated by calcination, while that caused by alkali/alkaline earth metals is difficult to recover. The acid-washing pretreatment can effectively eliminate the effect of alkali/alkaline earth metals, which is beneficial to prolong the lifetime of the catalyst.

Key words: biomass, plastics, pyrolysis, HZSM-5, deactivation, alkali/alkaline earth metals

摘要：

利用管式炉热解装置进行HZSM-5在线共催化热解玉米秸秆/高密度聚乙烯过程中的循环和再生利用实验，对玉米秸秆进行酸洗预处理，考察原料酸洗预处理对HZSM-5催化性能的影响。采用GC-MS（气相色谱-质谱联用仪）对生物油的化学组成进行分析，并对反应前、反应后以及再生催化剂进行TG（热重分析）、ICP-MS（电感耦合等离子体发射光谱仪）、SEM/EDS（场发射扫描电镜）、BET、NH₃-TPD（程序升温脱附技术）等表征分析。研究表明，HZSM-5催化玉米秸秆/高密度聚乙烯热解的主要产物为芳烃，随着催化剂重复利用次数的增加，芳烃含量逐渐降低，催化剂的比表面积、孔容、酸性等也随之降低，说明催化剂的活性逐渐降低；原料经酸洗预处理后有利于热解中间体的生成，加速了催化剂的结焦失活速率；催化热解酸洗玉米秸秆/高密度聚乙烯的催化剂经焙烧再生后其活性基本恢复至原有水平，而催化热解未处理玉米秸秆/高密度聚乙烯的催化剂再生后其活性有所降低，碱/碱土金属在HZSM-5催化剂上发生累积，从而引起酸性位点“中毒”失活，而原料经酸洗预处理后可有效降低催化剂上碱/碱土金属的累积量，有利于延长催化剂的使用寿命。

关键词: 生物质, 塑料, 热解, HZSM-5, 失活, 碱/碱土金属

CLC Number:

ZHANG Donghong, REN Xiajin, CAI Hongzhen, YI Weiming, LIU Shanjian, LIN Xiaona. Deactivation of HZSM-5 during the catalytic co-pyrolysis of biomass and plastic[J]. Chemical Industry and Engineering Progress, 2021, 40(8): 4259-4267.

张东红, 任夏瑾, 蔡红珍, 易维明, 柳善建, 林晓娜. 生物质/塑料共催化热解过程中HZSM-5失活分析[J]. 化工进展, 2021, 40(8): 4259-4267.

Figures/Tables 10

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样品	工业分析（干燥基）/%			元素分析（干燥无灰基）/%
样品	灰分	挥发分	固定碳	N	C	H	O（差值法）
玉米秸秆	7.55	75.64	16.81	1.55	46.61	5.29	46.55
酸洗玉米秸秆	3.15	84.28	12.57	0.48	47.91	6.01	45.6

样品	工业分析（干燥基）/%			元素分析（干燥无灰基）/%
样品	灰分	挥发分	固定碳	N	C	H	O（差值法）
玉米秸秆	7.55	75.64	16.81	1.55	46.61	5.29	46.55
酸洗玉米秸秆	3.15	84.28	12.57	0.48	47.91	6.01	45.6

样品	K/mg·kg^-1	Ca/mg·kg^-1	Na/mg·kg^-1	Mg/mg·kg^-1
玉米秸秆	9397	2857	160	1188
酸洗玉米秸秆	28	348	39	87

样品	K/mg·kg^-1	Ca/mg·kg^-1	Na/mg·kg^-1	Mg/mg·kg^-1
玉米秸秆	9397	2857	160	1188
酸洗玉米秸秆	28	348	39	87

样品	Na/mg·kg^-1	Mg/mg·kg^-1	K/mg·kg^-1	Ca/mg·kg^-1
新鲜 HZSM-5	326	50	38	65
CS/HDPE共催化热解所用HZSM-5
Run 1	311	159	798	344
Run 5	408	324	2078	481
再生HZSM-5	321	350	2126	580
ACS/HDPE共催化热解所用HZSM-5
Run 1	290	40	56	54
Run 5	428	103	99	206
再生HZSM-5	363	78	143	260