Use of domestic minerals for vegetable oil bleaching

Abstract

In this thesis, acid activation and characterization studies were conducted for different clay samples and bleaching capacity of the selected acid activated clay samples for sunflower oil were determined. The samples selected for this study were naturally occuring clays from Ankara and Eskiehir regions. The acid activated zeolite was also used for the purpose to compare its bleaching performance with commercial bleaching clay, Tonsil and the acid activated clays.The clay minerals were activated with hydrochloric acid (HCl) at three acid concentrations (1 N, 3 N, 5 N), activation times (1h, 2h, 3h) and different dry clay/acid ratios. The clay samples from the Ankara and Eskiehir regions were defined as montmorillonite according to X- ray diffraction (XRD). XRD results proved that acid activation caused structural changes in the treated montmorillonites, montmorillonite peaks gradually disappearing and yielding to an amorphous montmorillonite structure.The TGA results showed a significant weight loss between 30 C - 200 C ( 15%) for the Ankara clay and between 20 - 200 (12%) for the Eskiehir clay. This was most probably due to the removal of free and hydrogen-bonded water molecules. Maximum surface area was obtained for the acid activated Ankara clay treated with 1 N HCl for 3 hours. It was determined to be 849.1 m2/g. Also, maximum surface area was 269.7 m2/g for the acid activated Eskiehir clay treated with 5 N HCl for 1hour. Then the surface area of the acid activated clays decreased sharply with the acid activation. The chemical compositions of the solutions and clays after acid activation were determined using ICP and EDX analysis, respectively. According to the results, the dissolution amount of CaO, Na2O, MgO, K2O, Fe2O3 and Al2O3 increased along with increasing acid concentration and treatment time. The SiO2 content and the Si02/Al2O3 ratio increased as a result of dissolving of aluminium ions. This ratio increased from 6.0 to 7.5 for the acid activated Eskiehir clay and from 2.7 to 3.9 for acid activated Ankara clay.Acid activated clays were tested for the assessment of their bleaching efficiency for sunflower oil in the laboratory. Bleaching tests were carried out with earths prepared at different acid activation conditions such as acid concentration and activation times. The absorbance value was measured at 455 nm and found to be 0.429 for the neutralized sunflower oil. Peroxide value and free-fatty acid content of the neutralized oil were found to be 16.8 meq/kg and 0.07 %, respectively. The oil bleached with the acid activated Ankara clay had a peroxide value of 46.2 meq/kg first, which decreased to 22.4 meq/kg and the free-fatty acid content was observed to be around 0.08 %. For acid activated Eskiehir clay, peroxide value of the bleached oil initially increased up to 31.2 meq/kg, then decreased under the peroxide value of neutralized oil (16.8 meq/kg) and free-fatty acid content of bleached oil approximately was around 0.09 %.The bleaching parameters which were used for testing were 1 % earth concentration and 30 minutes contact time at 100°C bleaching temperature. At these selected parameters, acid activated Eskiehir clay (5 N 1h HCl treatment), Ankara clay (1 N 3h HCl treatment) and zeolite (2 N 6h HNO3 treatment) were compared with the commercial bleaching clay, Tonsil. The smallest value of absorbance and bleaching efficiency were found to be 0.084 and 80 %, respectively with the Eskiehir clay and these values were determined to be 0.083 and 81 % with the Tonsil under the same conditions. The absorbance value and bleaching efficiency of the bleached oil with acid activated Ankara clay were determined to be 0.114 and 73 %, respectively using the selected bleaching parameters. Bleaching performance of Ankara clay was found to be lower when compared with the result of Eskiehir clay.At the selected bleaching point, results of lovibond red and yellow color of bleached oil indicated that the Eskiehir clay and Tonsil were close to each other in bleaching efficiency (Red color: 0.8 and 1.1; yellow color: 20 and 20 for Tonsil and Eskiehir clay, respectively). Zeolite did not reach the required bleaching performance.The bleaching efficiency was 25 % with raw zeolite and it hardly increased to 46 % with the acid activated zeolite. In addition, red and yellow color values were higher than the other clays (red color:2.6; yellow color: 30).As a result, Eskiehir clay gave a better bleaching performance compared to Ankara clay and Zeolite. Maximum bleaching efficiency was achieved after 30 minutes of contact time with 1 % earth concentration at 100 °C bleaching temperature following 5 N 1h HCl treatment for Eskiehir clay.