Recovery of used frying palm oil by acidified ash from rice husk

Abstract

The objective of this study is to improve the quality of fried palm oil by rice husk ash (RHA) adsorption. The RHA was prepared with and without acid treatment. For acid treatment, rice husk was soaked in two different acids, one was 10 M HNO 3 for 24h, and other was 3M
HCl for 3 h. Rice husk (200g) was suspended in 500 ml of acid, thereafter, it was washed with distilled water to obtain pH 7 before incineration at 550 degC for 12h. For untreated-RHA, rice husk was incinerated at the same temperature without acid treatment. The RHA (20 g)
was mixed with 100 g used oil and stirred at 500 rpm on electrical heater at 80oC for 30 min to perform adsorption process. The RHA was filtered out and filtrate oil was analyzed for total polar compound (TPC), free fatty acid (FFA), peroxide value (PV), color L* a* b*, and viscosity. Results showed that the acids-treated RHA with HCl and HNO3 could significantly (p<0.05) reduce TPC of the original used oil from 10.17% to 4.39% and 4.17% respectively, whilst untreated-RHA could significantly (p<0.05) reduce TPC to 7.87%. The acids-treated RHA significantly (p<0.05) increased L* brightness) value of used oil from 41.30 to 88.93 (HCl) and 88.85 (HNO3), whereas to 83.21 for the untreated-RHA. However, the PV and FFA improvement of used oil after adsorption process using untreated-RHA was significant (p<0.05) higher than those of both acids-treated RHA. The both acids treatments of RHA had no significant difference (p>0.05) for all determining quality parameters of the used oil.