PROCESS FOR ACIDIC HYDROLYSIS OF A PARTICULATE SOLID MATERIAL CONTAINING HEMICELLULOSE， CELLULOSE AND LIGNIN， AND BASIC PROCESS CONTROL FOR SUCH

A process for the conversion of a particulate solid material comprising hemicellulose， cellulose and lignin， said process being conducted in at least one reactor comprising said particulate solid material and interstitial space. The process comprises two hydrolysis steps using hydrochloric acid， separated by a displacement step wherein a water-immiscible displacement liquid displaces part of the hydrochloric acid containing hydrolysate products from the interstitial space in the reactor， and wherein the reactor has at least one exit connected to a flow-through section， and wherein said flow-through section comprises non-invasive measurement means. The non-invasive measurement can detect the change in effluent from the reactor: from acid aqueous hydrolysis solution to displacement fluid and/or from displacement fluid to acid aqueous hydrolysis solution.