2. EXPERIMENTAL

Materials

PFAD was obtained from Bau Palm Oil Mill, Sarawak. Rice husk was obtained from Selangor, Malaysia, washed and air dried prior to use. Sodium hydroxide pallets (NaOH), sulfuric acid (H2SO4) 99% and methanol were purchased from Merck and used as received.

Preparation of Huskcatacid andHuskcatbase

Dried rice husks (1000g) was heated at 800 °C to form calcined rice husk (RHA), and further treated with NaOH (20%) to produce activated ash ARHA (200g). The activated ash was impregnated with concentrated H2SO4 vi a sulfonation for 24 h. The excess acid was decanted, and the residual wet solids were heated at 120 ºC for 18 h (Kaster et al., 2012) to form heterogeneousHuskcatacid .
Solid base catalyst Huskcatbase was prepared by soaking the activated ash (RHA) in NaOH solution (5M) for 2 h, followed by filtration. Sample was then heated at 700 ºC for 10 min (Perrichon and. Durupty, 1988; Refaat, 2011) to afford Huskcatbase .

Characterization of Huskcatacid andHuskcatbase

The X-Ray Diffraction (XRD) patterns of calcined ash was obtained on a Rigaku Miniflex X-ray diffractometer equipped with a scintillation counter to generate pattern at ambient temperature. Surface morphology of the catalyst was observed under Scanning Electron Microscope (SEM) (JEOL 7500F-1) with magnification 10000x. Quantitative element composition of the catalysts was characterized using Energy Dispersive X-ray (EDX) (JEOL JSM-6390 LA). Specific surface area and total pore volume of the catalysts were determined using Brunauer-Emmett-Teller (BET) (Quantachrome ASIQC0000-3) with liquid nitrogen adsorption at 77 K.

Esterification and transesterification reaction of PFAD

Due to high content of FFAs, the production of biodiesel from PFAD was performed via esterification followed by transesterification process. During esterification, Huskcatacid (0.5 g, 5%) was added into methanol (10.0 mL) and heated at 65 ºC for 1 h in a round bottom flask. Preheated PFAD (10.0 g) was added into the flask and heating was continued for 24 h at 120 ºC. The mixture was cooled to room temperature, filtered, and washed with methanol. The filtrate was evaporated to eliminate water and excess methanol to obtain esterified PFAD as a brown oil.
In transesterification process, Huskcatbase (1%, 0.1 g) was added into a 10.0 mL methanol and heated at 65ºC for 1 h in a 3-neck round bottom flask. The esterified oil (10.0 g) was added into the flask and continued heating for 1 h. The mixture was cooled to room temperature, filtered, and washed with methanol. The filtrate was evaporated to remove excess methanol and formed layers of glycerol and biodiesel [23], whereby the upper layer was collected as biodiesel. The effect of reaction times (15 min, 30 min, 45 min, 60 min) employing ratio 1:1 (methanol: oil) and 1% of catalyst was investigated. The acid value and FFA (%) of the esterified oil was calculated using Equation 1 and Equation 2 (Banani et al., 2015).
Acid value (mgKOH/g) = (NKOH x MWKOH x Vt)/ Ws Eq. 1
where, NKOH is the normality of KOH used, MWKOH is the molecular weight of KOH (56.11 g/mol), Vt is the volume of titrant used, and Wsis the mass of sample, g.
FFA % = AVs/2 Eq. 2
where, AVs = Acid value of PFAD, mgKOH/g

Analysis of Biodiesel

The esterified oil and biodiesel analysis were examined using Fourier Transform Infrared (FTIR) (Thermo Scientific Nicolet iS10) with zinc-selenide (Zn-Se) disc as the transmitter. The composition of the biodiesel was analyzed using Gas Chromatography Mass Spectroscopy (GCMS) (Shimadzu GC-MS model QP2010 Plus) with helium as gas carrier with constant flow rate at 0.94 mL/min and linear velocity at 36.6 cm/sec. Chromatographic separation was operated on a nonpolar capillary column, BPX-5 (30.0 m x 0.25 µm x 0.25mm). MS was operated using electronic impact (70 eV) in selected ion monitoring (SIM) mode. The injector port was operated in splitless mode. The temperature of both injector and interface were at 250 °C. The oven temperature was maintained at 10 °C/ min, which initiated at 110 °C and held for 1 min. The temperature was increased to 220 °C at 20 °C/min and held for 8 min.