Doctoral dissertation: A larch biorefinery producing pulp and lactic acid

A proof of concept for a process utilizing larch for production of papermaking pulp and biochemically obtained lactic acid was determined. Wood chips of Siberian larch (Larix sibirica Lebed.) were pre-extracted with water prior pulping. The optimal PE conditions were determined. Both the sugar-rich extract and the pre-extracted wood chips were analyzed in detail. PE at 150 °C for 90 min dissolved about 11% sugars on wood. A mild wash was needed to wash out the dissolved carbohydrates from the wood chips. The pre-extracted and washed wood chips were used for pulping, while the extract was fermented into lactic acid. Polysulfide (PS) and anthraquinone (AQ) were used as pulping additives to compensate for the yield loss caused by the PE. PE allows less alkali and lower H-factor. The larch pulp was bleached, and paper sheets were made. Pulp and paper characteristics were determined. PE-PSAQ pulps could be used in similar applications as other softwoods. The hydrolyzed extract was fermented with different bacteria strains. Fermentation with Bacillus coagulans MXL-9 gave the most attractive results. The lactic acid yield for 97 h cultivation time was 78.5% on initial sugar and 5.8% on wood. A process flowchart for a larch biorefinery was constructed, mass and energy balances were obtained through simulation, and the process was economically evaluated. An existing kraft pulp mill could relatively easy be converted into a larch biorefinery.