柠檬酸改性原位晶化催化剂的性能及传质扩散行为研究

采用不同浓度的柠檬酸溶液对原位晶化催化剂进行了改性脱铝研究,利用XRD、荧光衍射、氮气吸附、吡啶红外吸附等表征手段对脱铝后的催化剂进行了分析表征,分析表征结果表明柠檬酸能显著调变催化剂孔结构,有效改变中强酸和总酸量。ACE的反应评价结果表明,采用柠檬酸改性后催化剂的裂化能力显著增强,转化率提高3.23%（质量分数）以上、油浆收率降低1.13%（质量分数）以上、液化气质量分数增加2.7%以上、柴油质量分数降低1.94%以上、焦炭选择性变好。说明柠檬酸改性可显著提高原位晶化催化剂酸性位可接近性,从而改善反应选择性,柠檬酸质量分数为0.5%时具有最佳的反应结果。以菲为探针分子测试的催化剂穿透曲线验证了这一点。

Study on performance and mass transfer and diffusion behavior of citric acid modified in situ crystallization catalyst

Catalytic cracking is a process of mass transfer and diffusion of heavy oil macromolecules in the catalyst.It is also a process of acid catalytic reaction.Therefore,the well-developed pore structure and appropriate acidity are important research directions in the design and development of catalytic cracking catalyst.Y zeolite is an important component of FCC catalyst and an important acid supplier.For Y zeolite,there are many ways to adjust its acidity,such as metal modification,hydrothermal super stable acid treatment,etc.Hydrothermal super stable method is often used in industry.Through hydrothermal super stable method,part of framework aluminum of molecular sieve is removed and Al in framework is replaced by Si.As a result,the density of acid center of active component Y zeolite decreases,the acid strength increases and the secondary pores are more abundant.However,the framework of the zeolite will be destroyed significantly after hydrothermal treatment and a large amount of non-framework aluminum will block the pores,which is more likely to coke on the surface of the catalyst and form carbon deposition affecting the distribution of reaction products.Using acid to control the acidity of catalyst has the advantages of flexible control and mild reaction.In this paper,the specific surface,pore volume and acidity of the in-situ crystallized super stable catalyst with different concentrations of citric acid were studied.The characterization results showed that with the increase of concentration of citric acid,the specific surface and pore volume increased and the subsequent change was not obvious.After modification with citric acid,the total acid content of the catalyst decreased,but the medium strong acid content increased.The results of ACE reaction evaluation showed that the cracking enhanced.The conversion yield increased by more than 3.23%,the slurry yield decreased by more than 1.13%,the LPG increased by more than 2.7%,the diesel decreased by more than 1.94%and the coke selectivity improved.It was indicated that citric acid modification could significantly improve in-situ crystallization.The acidity of the catalyst was approachable to improve the selectivity of the reaction.The best reaction result was obtained when the concentration of citric acid was 0.5%.Using phenanthrene as probe molecule,the mass transfer and diffusion rate of samples modified with different concentrations of citric acid were tested.The test results showed that the mass transfer and diffusion rate of probe molecule in the catalyst was faster than that of the contrast agent,which indicated that the citric acid modified catalyst cleaned up the non-framework aluminum deposited on the surface of the catalyst and made the pore channel of the catalyst more stable.The test result was in good correspondence with the response evaluation result.