Bio-Based Phenol from Cashew Nutshells by Catalytic Hydrocardanol Trans-Alkylation Using H-ZSM-5 Zeolite

Area of Science:

• Chemical Engineering
• Sustainable Chemistry
• Catalysis

Background:

• Cardanol, a byproduct of cashew nutshell liquid, is a sustainable source for bio-based chemicals.
• Phenol production traditionally relies on fossil fuels, necessitating sustainable alternatives.
• Hydrocardanol, the hydrogenated form of cardanol, offers improved thermal stability.

Purpose of the Study:

• To investigate hydrocardanol as a feedstock for phenol production via trans-alkylation.
• To optimize reaction conditions for maximizing phenol yield using H-ZSM-5 zeolite.
• To compare the efficiency of hydrocardanol versus cardanol in phenol synthesis.

Main Methods:

• Trans-alkylation of hydrocardanol with toluene using H-ZSM-5 (SiO2/Al2O3 = 80) in a batch reactor.
• Analysis of phenol yield and byproducts at full hydrocardanol conversion.
• Model reaction studies with phenol and 1-pentadecene to elucidate reaction mechanisms.
• Validation of the process in a fixed-bed flow reactor.

Main Results:

• H-ZSM-5 achieved a 53.7% phenol yield from hydrocardanol, significantly higher than 27.1% from cardanol.
• The saturated side chain of hydrocardanol suppressed undesirable self-alkylation, leading to higher phenol selectivity.
• Phenol realkylation was identified as a key limitation; reducing the hydrocardanol-to-toluene ratio mitigated this.
• A fixed-bed flow reactor achieved >95% phenol yield and >99% carbon balance.

Conclusions:

• Hydrocardanol is a superior feedstock for bio-based phenol production compared to cardanol via trans-alkylation.
• Optimized conditions and reactor design can lead to highly efficient and selective phenol synthesis.
• This process offers a sustainable route to phenol, utilizing agricultural waste and improving resource circularity.