酸、碱处理对HY沸石酸性和环己酮肟液相贝克曼重排反应的影响

Effect of Alkali and Acid Modification on HY Zeolite and Its Catalytic Performance in Liquid-phase Beckmann Rearrangement Reaction of Cyclohexanone Oxime

采用FT-IR、 NH3-TPD和27Al MAS NMR等催化剂表征手段和间歇反应方法,系统研究了NaOH溶液(0.2~0.4mol/L)的碱改性和NaOH溶液与硝酸溶液(0.2 mol/L)的碱-酸组合改性对一种氢型Y沸石(Si/Al=7.5)的物化性质和环己酮肟液相贝克曼重排反应性能的影响.结果表明,碱改性具有脱硅作用,可使Y沸石的表面Bro¨nsted酸中心和Lewis酸中心数量显著增加.酸处理具有脱铝作用,可以选择性地脱除Y沸石中的一部分非骨架铝,从而降低碱改性催化剂的Lewis酸性.用0.2 mol/L NaOH溶液和0.2 mol/L硝酸溶液通过碱-酸组合改性得到的催化剂DeSiAl-Y-0.2在环己酮肟液相重排反应中表现出较好性能.在以苯甲腈为溶剂、反应温度和时间分别为130℃和3 h的条件下,其环己酮肟转化率和己内酰胺选择性都达到了82.9%,分别比Y沸石母体提高了18%和1.5%.在DeSiAl-Y-0.2催化剂上初步开展了反应条件和溶剂效应的研究工作,从中可以看出研制用于环己酮肟液相重排反应的Y型沸石催化剂的关键在于提高其己内酰胺选择性.

The influences of an alkali modification with NaOH solution(0.2~0.4 mol/L) and a combinational alkaliacid modification with NaOH solution and nitric acid solution(0.2 mol/L) on the physicochemical properties of a HY zeolite(Si/Al=7.5) as well as its catalytic performancein the liquid-phase Beckmann rearrangement reaction of cyclohexanone oxime were systematically studied with multiple catalyst characterization methods such as FT-IR, NH3-TPD, and 27 Al MAS NMR, and batch reaction method. Results show that alkali modification has a desiliconisation effect whichcan significantly increase the number of Bro¨nsted acid and Lewis acid centers on the surface of Y zeolite. The acid treatment has a dealumination effect which can selectively remove part of the non-framework aluminum in the Y zeolite and consequently reduce the Lewis acidity of the alkali-modified catalyst. A catalyst De SiAl-Y-0.2 obtained by the combinational alkali-acid modification with 0.2 mol/L NaOH solutionand 0.2 mol/L nitric acid solution, shows better performance in the liquid-phase Beckmann rearrangement reaction of cycloheanone oxime. When benzonitrile was used as solvent and the rearrangement reaction was carried out at 130 ℃ for 3 h, both the conversion of cyclohexanone oxime and selectivity of caprolactam of the catalyst reached 82.9%, increased by 18% and 1.5%, respectively, if the corresponding values of HY zeolite parent was compared with. Preliminary researches on reaction conditions and solvent effects were also carried out with DeSiAl-Y-0.2 catalyst. These researches show that the key to the preparation of a Y zeolite catalyst for the liquid-phase Beckmann rearrangement reaction of cyclohexanone oxime is to increase its caprolactam selectivity.