Synthesis of ZSM-5 from impure and beneﬁciated Grahamstown kaolin: Effect of kaolinite content, crystallisation temperatures and time
Isa, Yusuf Makarﬁ
Mdleleni, Masikana M.
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Copyright: 2016. Elsevier. Due to copyright restrictions, only the abstract is available. For access to the full text item, please consult the publisher's website. The definitive version of the work is published in Applied Clay Science, Vol 119. Pp 213-221. http://dx.doi.org/10.1016/j.clay.2015.10.008
Raw kaolin obtained from Grahamstown, South Africa was beneﬁciated using wet sieving and ﬁltration before use in the synthesis of ZSM-5 zeolite via hydrothermal treatment at various temperatures (120–190 °C) and times (24–96 h) under autogenous pressure. The impacts of kaolinite content and crystallisation parameters (i.e. temperature and time) on ZSM-5 formation were investigated. The mineralogical phases, morphology, sur-face area and porosity characteristics of the synthesised materials were investigated using XRF, XRD, FT-IR, HRSEM-EDS and N2 physisorption (BET) analyses. Catalytic tests were carried out in a ﬁxed bed reactor, WHSV of 8 h−1 and a temperature of 350 °C at atmospheric pressure using 1-hexene as a feed. Beneﬁciation decreased the impurity content in the clay and increased kaolinite content which resulted in the formation of pure ZSM-5 zeolite. XRD and HR-SEM revealed that ZSM-5 synthesised from raw kaolin contained quartz and formed a ZSM- 5/quartz coated composite. Temperature and time were critical in controlling phase purity and crystallinity of ZSM-5. At a synthesis temperature of 190 °C ZSM-5 transformed into a more thermodynamically stable quartz phase. The optimum condition for synthesising pure ZSM-5 from this clay was found to be 150 °C for 48 h. Morphology, surface area and porosity of ZSM-5 changed with an increase in crystallisation time. ZSM-5 with a high external surface area and presence of mesopores were observed in products synthesised at 150 °C for 24 h. Microporosity further developed as time increased and the ZSM-5 became more crystalline. The catalyst performance studies indicated that the ZSM-5 synthesised from raw and beneﬁciated kaolin at crystallisation conditions 150 °C and 48 h had good 1-hexene transformation activity and high selectivity to gasoline range hydrocarbons. The presence of quartz in the catalyst enhanced catalyst stability and selectivity to C10+ hydrocarbons.
Mohiuddin, E. et al. 2016. Synthesis of ZSM-5 from impure and beneﬁciated Grahamstown kaolin: Effect of kaolinite content, crystallisation temperatures and time. Applied Clay Science. 119: 213-221.