Method for controlled delignification of lignocellulosic feedstock, said method comprising the steps of:



providing a reactive phase of pH less than 1, said reactive phase comprising:

water;
sulfuric acid;
a source of peroxide;
a modifying agent, said modifying agent adapted to control the reactivity of the sulfuric acid;


providing a holding phase, said holding phase comprising an organic solvent which does not react with the aqueous acidic composition;
combining said reactive phase and holding phase to form a reaction mixture;
exposing a lignocellulosic material to said reaction mixture for a period of time sufficient to allow delignification of the lignocellulosic material.