Application of Thiol Amino Acids in a Reductive Liming Process

Thiol containing amino acids cysteine and homocysteine were used as dehairing agents in an alkaline reductive liming process. It is shown that complete dehairing is achieved with amounts of 8 % w/w of the thiol amino acids, rendering them as effective as sodium sulfide on a molar basis. Cysteine and homocysteine can be used to establish a completely sulfide free liming process without fundamental changes of the remaining process parameters. Furthermore a method is presented for the preparation of homocysteine from lower-cost methionine. This method comprises a two step process including the demethylation of methionine in sulfuric acid, resulting in the formation of dimeric homocystine, and the subsequent reduction of homocystine to homocysteine with tin in acidic solution. Identity and purity of the reaction products were proved by HPLC analysis. The effectivity of freshly prepared homocysteine as a dehairing agent is comparable with commercial homocysteine thiolactone.