SOURCE:

Faculty: Physical Sciences
Department: Pure And Industrial Chemistry

CONTRIBUTORS:

Ogbu, I. M
Ajiwe, V.I.E

ABSTRACT:

Two types of biodiesels (methyl esters and butyl esters) were synthesized from Cucurbita pepo, Afzelia africana and Hura crepitans seed oils using acid catalysis. Solid acid catalysts were prepared from biowastes (seed cake/shell) from the oil seeds via partial carbonization to aromatize the materials and subsequent sulfonation to introduce –SO3H group on them. Ten different solid acid catalysts (0HuSO3H, 30HuSO3H, 60HuSO3H, 90HuSO3H, 120HuSO3H, 0ASO3H, 30ASO3H, 60ASO3H, 90ASO3H and 120ASO3H) were obtained by varying the resident time of the carbonization before sulfonation. The catalysts were characterized using FTIR, TGA, SEM and XRD and were applied on the biodiesel synthesis alongside H2SO4. Various process parameters such as quantity of catalyst, stirring rate, temperature and time were investigated on the biodiesel production. Different esters/diesel blends were made from each biodiesel sample by diluting it with petrodiesel at various ratios and their fuel properties were tested in line with ASTM methods. From the results, the oil yields of the crops: 42.43 % (C. pepo), 21.80 % (A. africana) and 39.87 % (H. crepitans) were quite promising for commercial biodiesel production. Modified biowaste catalyst from the seed shell/cake exhibited high acid density up to 2.34 mmol/g and were effective for biodiesel synthesis; the most effective one gave 96 % biodiesel yields compared to 98 % of H2SO4 and showed advantage of easy separation after reaction and being recycled. The activities of the catalysts varied with the carbonization time; 30 to 60min. was optimal for acid site density, pore sizes and hydrolytic stability. SEM images of the catalysts showed that carbonization (at 500 oC) of the biowastes beyond 60 min. before sulfonation resulted in collapse of carbon framework and pores on the catalysts. TGA/DTG curves showed that the catalysts were thermally stable up to 230 oC after which –SO3H group started dissociating from the carbon structure. At alcohol/oil ratio of 6:1, optimal conditions for methyl ester synthesis from the oil samples were found to be 60 oC, 3 % catalyst (H2SO4), and 300 rpm stirring rate. Butyl esters required up to 80 oC and 400 rpm. The experimental data suggested that the esterification reaction followed second order model. The results of the fuel properties of the biodiesels and their blends indicated their suitability for biodiesel production. Methyl esters/diesel blends of 10:90 had viscosity that placed them in 2D grade diesel (2-4.3 mm2/s) suitable for fuelling mobile equipment while the higher blends fell within 4D grade diesel (5.0-34.0 mm2/s) suitable for powering stationary equipment. For the butyl esters, up to 50:50 blends fell within 2D grade. The cetane number, 64.25 (H. crepitans), 59.76 (C. pepo) and 43.44 (A. africana) were quite high for efficient combustion in diesel engine. The flash points, 102 oC (C. pepo), 88 oC (A. africana) and 150 oC (H. crepitans) signified low fire risk during transportation and storage. Other fuel properties including acid value (<0.6 mg KOH/g), pour point, ash content and density were within ASTM D6751 limits for biodiesels. H. crepitans exhibited the best fuel properties in terms of high cetane number, flash point and cold-flow properties. Most C. pepo and A. africana samples congealed below 5oC indicating that they might not be suitable for cold weather (below 5 oC). Butyl esters of the oil samples showed better fuel properties compared to the methyl esters in terms of viscosity and heating value. The FTIR results indicated that the bond structures of the vegetable oil esters were similar to those of petrodiesel and were stable up to 300 oC, signifying their thermal fitness as biodiesels.