**3. Experimental**

Solid HPAs possess a discrete ionic structure, comprising fairly mobile basic structural units,

order to increase the specific area of HPAs or, even better, to increase the number of accessible acid sites of the HPAs, a variety of supports like activated carbon [23-26], silica [27-32], zeolite

HPAs and HPAs supported on different supports have been used as acid catalysts for biodiesel

Transesterification of waste cooking oil with high acid value and high water content was performed using heteropolyacid H3PW12O40.6H2O (PW) as homogeneous catalyst. PW was found to be the most promising catalyst, which exhibited the highest ester yield (87%) for transesterification of waste cooking oil and an ester yield of 97% for esterification of long-chain palmitic acid. The PW acid catalyst showed higher activity under the optimized reaction conditions compared with the conventional homogeneous catalyst sulfuric acid, and it can easily be separated from the products by distillation of the excess methanol and can be reused

Biodiesel production in the presence of 20 wt% myristic acid from soybean oil was carried out over heteropolyacid immobilized on mesoporous Ta2O5 materials. Different catalysts were prepared. The network structures of the hybrid materials and the functions of the incorporated

Biodiesel synthesis from waste cooking oil was carried out over 12-tungstosilicic acid on SBA-15. The heteropolyacid was prepared using impregnation method. The effect of different reaction parameters like percentage loading, catalyst amount, mole ratio, time and tempera‐ ture were studied for the supreme conversion. The catalyst was recycled up to four times after

In this work, we report the transesterification of waste cooking oil with different alcohols over heteropolyacids immobilized on SBA-15. We also studied the effect of free fatty acid addition

The McDonald's Corporation is the world's largest chain of fast-food restaurants, serving around 68 million customers daily in 119 countries across 35,000 outlets [49]. The waste cooking oil in about 90% of McDonald's restaurants is used for after-market uses, including biodiesel. The used cooking oil from the restaurants is collected, recycled into biodiesel, and put back into distributors' trucks to fuel their deliveries to McDonald's restaurants. In a few countries, McDonald's waste cooking oil are a closed-loop system. Since 2013, McDonald's developmen‐ tal licensee in the United Arab Emirates operates a 100% closed-loop biodiesel system. More than 25,000 liters of waste cooking oil are being collected from McDonald's approximately 108 restaurants each month and converted into biodiesel. Waste cooking oil is stored at the

alkyl groups on the catalytic activity of the materials have been put forward [46].

simple workup without notable loss in the activity [48].

into waste cooking oil. A kinetic model is proposed.

**2. Waste cooking oil raw converted to biofuel**

of, e.g., zeolites and metal oxides [20-22]. HPAs have low specific surface areas (1–10 m2

[33-38] and polymeric matrix [39-43] have been used as support to immobilize HPAs.

, H3O+

, H5O2 +

, etc.) unlike the network structure

/g). In

e.g., heteropolyanions and counter cations (H+

production [44-48].

288 Biofuels - Status and Perspective

several times [45].

### **3.1. Catalyst preparation**

Mesoporous silica SBA-15 was prepared according to the literature [51] An ethylene oxide (EO)/propylene oxide (PO) triblock copolymer (P123) with composition EO20PO70EO20 and with an average molecular weight of 5800 was used as the template. The synthesis consisted of 2.0 g of triblock P123 dissolved in 60 cm3 of 2 mol.dm-3 aqueous HCl and 15 cm3 of distilled water under stirring. Then, 4.4 g of tetraethyl orthosilicate (TEOS) was added dropwise to the solution at room temperature. The mixture was stirred for 24 h at 313 K, and then the temper‐ ature was raised to 373 K and kept at 373 K for another 24 h in a Teflon-lined autoclave. Finally, the resulting precipitate was filtered, washed carefully with distilled water, air-dried, and calcined at 773 K in air for 5 h to remove the template and to obtain the final product SBA-15.

The heteropolyacid was immobilized on SBA-15 by the grafting technique. The grafting of tungstophosphoric acid (PW) was carried out by mixing 2.0 g dried SBA-15 with 3-aminopro‐ pyltriethoxysilane (23.4 µL) containing freshly distilled toluene refluxing for 48 h. The obtained solid material was immersed in an aqueous solution of PW with stirring for 5 h. The solid was then dried in vacuum to obtain the heteropolyacid anchored mesoporous catalyst [52].

### **3.2. Catalyst characterization**

The textural characterization of the catalysts was based on the nitrogen adsorption isotherm, determined at 77 K with a Micromeritics ASAP 2010 apparatus.

The FTIR spectra were recorded with a Bio-Rad FTS 155 instrument.

The amount of W in silica catalysts was measured by dissolving the catalyst in H2SO4/HF 1:1 (v/v) and analyzing the obtained solution using inductively coupled plasma analysis (ICP), which was carried out in a Jobin-Yvon ULTIMA instrument.

The X-ray diffraction (XRD) patterns of the heteropolyacid, silica and catalysts were obtained by using a Bruker powder diffractometer with built-in recorder, using Cu Kα radiation, nickel filter, 30 mA and 40 kV in the high voltage source, and scanning angle between 0.7° and 5° of 2θ at a scanning rate of 1°/min.

Transmission electron microscopy (TEM) analyses were performed on a Hitachi S-2400 scanning electron microscope, at a current voltage of 25 kV.

Catalyst acidity was measured by means of potentiometric titration [53].

### **3.3. Catalytic experiments**

The catalytic experiments were carried out in a stirred batch reactor at 60°C. In a typical experiment, the reactor was loaded with 30 mL of methanol and 0.2 g of catalyst. Reactions were started by adding 2.5 ml waste cooking oil (WCO).

Stability tests of the catalyst were carried out by running four consecutive experiments, using the same reaction conditions. Between the catalytic experiments, the catalyst was separated from the reaction mixture by filtration, washed with acetone and methanol and dried at 70° C overnight.

In order to study the reusability, the PW-NH2-SBA-15 catalyst was filtered from the reaction mixture. After this operation, it was soaked in hexane overnight and it was dried overnight.

Undecano was used as the internal standard. Samples were taken periodically and analyzed by GC, using a Hewlett Packard instrument equipped with a 30 m x 0.25 mm HP-5 column.
