Particle size regulation of HZSM-22 and Pt/HZSM-22 for n-dodecane hydroisomerization

doi:10.16085/j.issn.1000-6613.2023-0447

Abstract

Abstract:

ZSM-22 zeolite crystals with different c-axis lengths were synthesized by using supersaturated solution method under static hydrothermal conditions and adjusting the water content in the synthetic solution. The as-synthesized ZSM-22 zeolite crystals were characterized by XRD, SEM, N₂ physical adsorption, NH₃-TPD and Fourier transformed infra-red spectroscopy of pyridine adsorption(Py-FTIR). By loading Pt on the ZSM-22 zeolite crystals, the Pt/ZSM-22 bifunctional catalysts were prepared, in which ZSM-22 zeolite crystals played the role of acid supports and the 0.5% Pt acts as (de)hydrogenation active sites. The hydroisomerization of n-alkanes was carried out with n-dodecane as the probe molecules. The effect of water content in the zeolite synthesis solution on the hydroisomerization performance of Pt/ZSM-22 catalyst was investigated. The results indicated that the less the water, the smaller the ZSM-22 crystals. However, a few cristobalite and ZSM-5 crystals were formed when the content of water in the synthetic solution was reduced to a certain value. HZSM-22 synthesized in the solution with the molar composition of SiO₂∶Al₂O₃∶K₂O∶DEA∶H₂O=1∶0.01∶0.08∶0.29∶28 showed the highest medium and strong Brønsted acid amount in the three HZSM-22 samples, and shorter c-axis length. The bifunctional catalyst Pt/HZSM-22 prepared with this kind of HZSM-22 crystals showed the best catalytic performance. The conversion of n-dodecane was 73.24%, the yield of iso-alkanes was 57.92%, and the selectivity of iso-alkanes was 79.09%.Moreover, the selectivity of mono-branched iso-dodecane with methyl branching positioned in the center of the chain, 5-methylundecane, was up to 17.66% at 320℃.

Key words: supersaturated solution method, ZSM-22 molecular sieve, c-axis length, n-dodecane, hydroisomerization

摘要：

通过调控合成液中的水含量，采用过饱和溶液法，在静态水热条件下合成了三种不同c轴长度的ZSM-22分子筛，对其进行了X射线衍射、扫描电子显微镜、N₂物理吸附、NH₃-程序升温脱附和吡啶吸附傅里叶变换红外光谱（Py-FTIR）表征。并以所制备的ZSM-22分子筛为酸性载体，在其上负载0.5%（质量分数）的金属Pt作为加（脱）氢活性位点，制备成Pt/ZSM-22双功能催化剂。以正十二烷为探针分子，进行正构烷烃加氢异构化反应，考察了分子筛合成液中水含量对Pt/ZSM-22催化剂加氢异构化性能的影响。结果表明，随着合成液中水含量减少，ZSM-22分子筛粒径减小。但是当水含量低到一定值时，会有方英石和ZSM-5杂晶生成。当分子筛合成液摩尔组成为SiO₂∶Al₂O₃∶K₂O∶DEA∶H₂O=1∶0.01∶0.08∶0.29∶28时，获得的HZSM-22在所合成的三种分子筛中拥有最多的中、强Brønsted酸量以及较短的c轴长度，对应的双功能催化剂Pt/HZSM-22表现出最佳催化性能。在320℃时，正十二烷转化率为73.24%，异构烷烃收率为57.92%，异构烷烃选择性为79.09%，尤其是中心位置甲基异构体5-甲基十一烷的选择性达到了17.66%。

关键词: 过饱和溶液法, ZSM-22分子筛, c轴长度, 正十二烷, 加氢异构化

CLC Number:

TQ032.4

CHEN Feng, WANG Xuande, HUANG Wei, WANG Xiaodong, WANG Yan. Particle size regulation of HZSM-22 and Pt/HZSM-22 for n-dodecane hydroisomerization[J]. Chemical Industry and Engineering Progress, 2024, 43(3): 1309-1317.

陈风, 王宣德, 黄伟, 王晓东, 王琰. HZSM-22的粒径调控及Pt/HZSM-22的正十二烷加氢异构催化性能[J]. 化工进展, 2024, 43(3): 1309-1317.

Figures/Tables 9

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样品	相对结晶度/%	晶体平均长度/μm	比表面积/m²·g^-1	微孔比表面积/m²·g^-1	外比表面积/m²·g^-1	微孔孔容/cm³·g^-1	介孔孔容/cm³·g^-1
HZSM-22-38	87.7	9.22	52	47	5	0.02	0.04
HZSM-22-28	97.4	7.26	72	60	12	0.02	0.04
HZSM-22-23	100	5.99	92	77	15	0.03	0.05

样品	相对结晶度/%	晶体平均长度/μm	比表面积/m²·g^-1	微孔比表面积/m²·g^-1	外比表面积/m²·g^-1	微孔孔容/cm³·g^-1	介孔孔容/cm³·g^-1
HZSM-22-38	87.7	9.22	52	47	5	0.02	0.04
HZSM-22-28	97.4	7.26	72	60	12	0.02	0.04
HZSM-22-23	100	5.99	92	77	15	0.03	0.05

样品	酸度			酸类型
样品	总酸量	弱酸量	强酸量	总Brønsted酸量	中、强Brønsted酸量	总Lewis酸量	中、强Lewis酸量
HZSM-22-38	537	366.4（166.92℃）	170.6（412.67℃）	99.6	65.3	7.1	3.4
HZSM-22-28	540	366.9（160.07℃）	173.1（401.61℃）	109.3	100.6	37.1	11.9
HZSM-22-23	549	370.4（152.42℃）	178.6（399.06℃）	99.3	78.8	30.4	8.8

样品	酸度			酸类型
样品	总酸量	弱酸量	强酸量	总Brønsted酸量	中、强Brønsted酸量	总Lewis酸量	中、强Lewis酸量
HZSM-22-38	537	366.4（166.92℃）	170.6（412.67℃）	99.6	65.3	7.1	3.4
HZSM-22-28	540	366.9（160.07℃）	173.1（401.61℃）	109.3	100.6	37.1	11.9
HZSM-22-23	549	370.4（152.42℃）	178.6（399.06℃）	99.3	78.8	30.4	8.8

参数	Pt/HZSM-22-38	Pt/HZSM-22-28	Pt/HZSM-22-23
转化率/%	32.90	73.24	66.05
总选择性/%	81.93	79.09	64.52
总收率/%	26.96	57.92	42.62
单支链选择性/%	70.51	60.29	46.76
多支链选择性/%	13.52	18.79	17.75
单多选择性比	5.22	3.21	2.63
产物选择性/%
2-甲基十一烷	23.55	15.83	13.03
3-甲基十一烷	16.37	14.58	11.19
4-甲基十一烷	11.08	10.92	8.16
5-甲基十一烷	18.30	17.66	13.35
6-甲基十一烷	1.22	1.30	1.04
2,4-二甲基癸烷	1.18	0.29	0.31
2,5-二甲基癸烷	0.96	1.31	1.25
2,6-二甲基癸烷	0.76	4.30	4.25
2,7-二甲基癸烷	2.44	2.76	2.68
2,8-二甲基癸烷	0.43	3.23	2.96
2,9-二甲基癸烷	1.51	3.58	3.46
3,3-二甲基癸烷	1.85	0.34	0.37
3,7-二甲基癸烷	2.42	0.50	0.31
3,8-二甲基癸烷	0.41	0.87	0.91
甲基乙基壬烷	1.55	1.62	1.27
其他	0	0	0