g of oven dried equivalent weight poplar was charged into a batch reactor a h 2 so 4 catalyst at a 0 1m concentration was added the yield of pulp was 53 with a kappa number of 46 the lignin yield was 23 with a purity of 92 the yield of the hemicellulose fraction was 24 aspen chips 193 g oven dried equivalent were charged into a 1 7 liter percolation reactor the reactor was filled with a mibk ethanol water mixture containing 16 mibk 34 ethanol and 50 water containing 0 025m h 2 so 4 the reactor was heated to 140 u00b0 c over 34 minutes without flow of solvent when the pulping temperature was reached pulping solvent of the same composition was pumped through the chip bed at a flow rate of 28 ml min for 56 minutes the chips were then washed in the reactor with neutral solvent at the same flow rate for 60 minutes without heating total severity for the reaction was 4 27 the reactor was drained the chips fiberized and the lignin separated as described above the pulp yield was 52 with a kappa of 28 lignin was isolated in a 17 yield hemicellulose yield was 31 poplar chips from undebarked logs 189 g oven dried equivalent were pulped under the same conditions as example 3 except for a 0 1 m h 2 so 4 catalyst concentration severity for this run was.