Solvothermal Alcoholysis Method for Recycling High-Consistency Silicone Rubber Waste

In
this work, we investigated the potential use of high-consistency
silicone rubber (SR), which is a synthetic solid material used in
numerous industrial applications, to produce a range of liquid alkoxysiloxane
derivatives R­(OSiMe2)xOR, with x = 1 (P1), 2 (P2), 3 (P3), and 4 (P4). We describe
a simple and convenient solvothermal alcoholysis method for the chemical
recycling of post-consumer SR in the presence of fatty alcohols under
catalyst-free or catalytic conditions. This process proceeds easily
both without and with a catalyst. Alkali-metal aryloxides supported
by a methylsalicylato ligand (MesalO) gave the highest conversions
of SR to products P1–P4. Magnesium and zinc aryloxides
enabled efficient conversions of products P2–P4 to P1. Binary metal catalysts of general
formula [M2M′2(MesalO)6] (M
= Mg or Zn; M′ = Li, Na, or K), which had a combination of
the catalytic properties shown by alkali-metal aryloxides and magnesium/zinc
aryloxides, were produced and used to synthesize P1–P4. The results show that magnesium–sodium/potassium aryloxides
had the best catalytic activities. Their use led to the formation
of two dominant products, namely, P1 and P2, with conversion
yields of 79 and 17%, respectively. Particular emphasis is placed
on the operating conditions and high activity of the catalyst used.
Key factors that affect the catalytic activity and reaction mechanism
are also highlighted.