Presentation Profile
Precise Back Titration Method for Determination of Bromine Number
Currently Scheduled: 10/11/2022 - 12:00 PM - 12:45 PM
Room: Rose
Main Author
Tore Fossum - Tor Systems
- Alan Cummings - Lummus Technology
Abstract:
Unsatisfactory repeatability and reproducibility of bromine number by ASTM D1159 and bromine index D2710 prompted the investigation of an alternate method that would deliver more precise and accurate results. The precision of a classical titration is due to being able to determine the equivalence point exactly. However, bromine number is not an equivalence point titration. It is instead a titration to a diminished rate of bromine uptake. Measuring this rate is dependent on the voltametric or amperometric detection of the apparatus, on the rate of delivery of titrant, the geometry of the detecting electrodes, and on the reactivity of the sample to free bromine. Finding the bromine number reliably is a challenge in one lab with one instrument, but getting uniform results with various manufacturer's instruments in different labs has been difficult. Therefor we propose a method where the bromine reagent is added at one time in excess, allowed to react with the olefin, and the remaining bromine titrated using a classical redox equivalence endpoint. A blank of the same amount of bromine is compared to the remaining bromine to give the bromine number. The endpoint is a standard equivalence redox inflection which should be reliably detected no matter which lab or which manufacturer's instrument is used. We present results with a variety of hydrocarbon samples and standards by the classical D1159 compared to the back titration method. A discussion will follow, with plans for an ILS at the next ASTM D02 meeting in December. Potential participants are invited to attend.
