摘要
对由高岭土和NaA分子筛成型得到的NaA小球进行焙烧,将部分焙烧后小球进行碱处理和Ca^(2+)交换,采用TG-DTA、XRD、^(27)Al-NMR、甲醇吸附、氮气物理吸附等方法对样品进行表征和评价,考察焙烧温度对其物性和吸附性能的影响。结果表明:在500~700℃焙烧能够使高岭土结构坍塌成为偏高岭土,但不会破坏NaA分子筛结构,经碱处理后偏高岭土几乎全部转变为NaA分子筛,其中经700℃焙烧后碱处理的小球吸附量最高;在750℃焙烧可使NaA分子筛骨架结构发生变化,几乎丧失对甲醇的吸附能力,但经碱处理后不仅偏高岭土转变为NaA分子筛,而且小球内原有的分子筛结构得到了修复,使得小球的甲醇吸附量高于NaA分子筛原粉;焙烧温度超过800℃时,NaA分子筛会转变成更加稳定的三斜霞石或霞石;在750℃焙烧再经碱处理和Ca^(2+)交换制备的5A小球的灼基堆密度和抗压碎强度明显优于700℃以下焙烧制备的5A小球,其原因是较高的温度导致小球内微粒的结合更紧密。
The NaA pellets composed of kaolin and NaA molecular sieve were calcinated and then treated with alkali solution and exchanged with Ca2＋ containing solution. The samples were character- ized by TG-DTA, XRD, 27Al-NMR, BET, and methanol adsorption test. The results show that kaolin in NaA pellet is changed into metakaolin during calcination at 500--700℃, and no destruction of NaA molecular sieve was found. Almost all of metakaolin formed was converted to NaA molecular sieve after alkali treatment. One of the pellets caleinated at 700 ℃ and alkali treated has the highest methanol ad- sorption capability. While the NaA structure was suffered destruction when calcinating at 750 ℃ and lost methanol adsorption ability. The alkali treatment not only can convert metakaolin into NaA molecu- lar sieve, also repair the destroyed NaA molecular sieve structure, resulting in even higher adsorption capacity than uncalcined NaA powder. At calcination temperature above 800℃, NaA is transformed in- to more stable carnegieite and nepheline. The burning base bulk density and crush strength of the 5A pellets obtained via calcination at 750 ℃ and treatment of alkali and Ca＋ exchange are significantly high- er than that of the 5A pellet calcinated below 700 ℃. The reason is that the higher temperature leads to a closer combination of particles in the pellets.
出处
《石油炼制与化工》
CAS
CSCD
北大核心
2016年第4期23-29,共7页
Petroleum Processing and Petrochemicals
关键词
NaA小球
NaA分子筛
5A小球吸附剂
焙烧温度
碱处理
NaA pellet
NaA molecular sieve
5A pellet adsorbent
calcination temperature
alkali treatment
