Compatibility of Biodiesels and Their Blends with Typical Rubbers and Copperish Metals

The swelling of ‘O’ rings of 3 typical rubbers (NBR, FKM, EPDM) and the corrosion of 2 typical copperish metal pieces (Copper, Brass) were investigated. The fuel samples included 14 kinds of biodiesels, 1 kind of diesel, and 4 kinds of blends respectively for 2 kinds of biodiesels. The changes in mass and size of ‘O’ rings were measured with an electronic balance and a vernier caliper. The surface corrosion of copperish metals was recorded with photos. It was found that the swelling of NBR in pure biodiesels were generally larger than those in diesel. The mass and size of FKM almost did not change in both pure biodiesels and diesel. The swelling of EPDM became less in pure biodiesels than that in diesel. When the blend ratios of biodiesels were less than 10%, the change rates in mass, inner diameter and section diameter of NBR, FKM and EPDM were similar between blended fuels and diesel. Base on the comparisons between change rates in mass and fuel properties, it was revealed that the swelling of rubbers should not be directly related to acid value, sulfur content and H2O content of biodiesels, and were still controlled by the differences in polarity characteristics between fuels and the immersed rubber sample. Acid value played a critical role in the corrosion of copperish metals. The blends with low ratios of biodiesels still had corrosive effects on copperish metals. The reason was considered as the combined effects of the acid in biodiesels and the sulfur in diesels.