Production of mid-chain branched detergent-range olefins over shape-selective acid catalysts

For the purpose of producing mid-chain mono-methyl branched olefins, a range of acid catalysts (MFI, BEA, TON and amorphous silica-alumina) were screened for the dimerization of 1-hexene, under generally mild conditions, viz. 150 - 170°C, 20 - 40 bar and 1 - 4h-1 WHSV. It was postulated that shape-selective catalysts with defined pore sizes might improve selectivity towards mid-chain mono-methyl branched olefins. Such olefins are potential feedstocks for selectively branched detergents which have improved surfactant properties while retaining good biodegradability. NMR and GC-MS analyses of hydrogenated dimer product fractions indicated that all catalysts produce branched products, and that these products are predominantly multi-branched (i.e. with two or more branches per C12 molecule). Overall, the findings of this study suggest a similar degree of branching of two for all catalysts. Selective poisoning of the external surface of the MFI-90 catalyst using bulky bases effectively eliminated the catalytic activity, suggesting that in the case of MFI zeolite, the hexene dimerization reaction occurs largely (if not exclusively) on the external crystal surfaces which are not shape-selective.In conclusion, BEA and amorphous silica-alumina pore being too large to induce shape selectivity and MFI and TON dimerization being limited to the external, non-selective, surface sites, the production of mono-methyl branched 1-hexene dimers was not accomplished.

Grantor dc:publisher.institution

Department of Chemical Engineering

Year dc:date.issued

2006

Author dc:creator

• Sumani, Mmontshi Lebohang Oliver

Advisor dc:contributor.advisor

• Fletcher, Jack

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/10977

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/10977