Study On Synthesis And Properties Of Terpenyl Gallates As Biodiesel Stabilizers

Biodiesel was a new alternative energy which has the advantages of environmental friendliness and renewability. The stability of biodiesel could be improved by addition of different antioxidants. A series of new stabilizers, terpenyl gallates, were designed in this study. The synthesis and identification of terpenyl gallates, preparation of biodiesel used for stability evaluation were studied. The effects of terpenyl gallates on room temperature stability and high temperature stability were studied based on comparison with alkyl gallates, synthetic antioxidants, natural gallates and complex stabilizers. The stabilization mechanism of biodiesel acted by stabilizers of terpenyl gallates was discussed. This study could provide a primary foundation for searching relationship of molecular structure of stabilizers with their properties, and selecting highly effective stabilizers for biodiesel.A new synthetic route of terpenyl gallates was advanced. Gallic acid was acetylated at first, esterificated respectively with six terpenyl alcohols by DCC dehydration and ultrasound assistance at room temperature, and then deacetylated by hydrazine hydrate to form corresponding terpenyl gallates. The chemical structures of six terpenyl gallates obtained were all identified. The synthetic method had lower reaction temperature, shorter reaction time, and higher conversion. The total yield of farnesyl gallate, geranyl gallate, linalyl gallate, nerolidyl gallate, menthyl gallate, and hydroabietyl gallate was respectively 86.2 %, 85.3 %, 76.3 %, 87.5 %, 79.2 % and 82.5 %.In order to search a suitable research carrier for biodiesel stability, the preparation of biodiesel by transesterification and assistance of low-power-density ultrasound at room temperature was studied. The yield of biodiesel was 85.9 %-86.4 % at the condition of molar ratio of soybean oil to methanol 1: 6, mass ratio of potassium hydroxide to soybean oil 0.01:1, ultrasonic power density 0.032 W·cm-3, reaction time 20-60 min, and reaction temperature 30℃. The quality of obtained biodiesel reached the requirement of biodiesel standard.The effect of terpenyl gallates on room temperature stability was studied by evaluation of peroxide value, acid value, refractive index of biodiesel. The sequence of stabilization to biodiesel was: farnesyl gallate> linalyl gallate> nerolidyl gallate> menthyl gallate> geranyl gallate> hydroabietyl gallate. The inhibition rate of farnesyl gallate and methyl gallate at the sixth month was respectively 31.6 % and 76.6 %. Meanwhile, the inhibition rate of farnesyl gallate added citric acid as synergistic agent could rise to 74.1 %. The effect of terpenyl gallates on high temperature stability was studied by evaluation of acid value of biodiesel. There were slight differences between six terpenyl gallates on high temperature stability of biodiesel. Geranyl gallate and farnesyl gallate were slightly better. The regression equations of stability were deduced. The stabilization mechanism of biodiesel acted by terpenyl gallates was discussed at last.