Production method of L-glucan

Provided is a method for easily industrially producing levoglucan in high yield and high purity using pulp as a raw material. The method comprises: (1) dipping a pulp having a glucose content as constituent sugars of at least 80% by weight and a Krapon lignin content of not more than 1% by weight in an aqueous solution of a divalent metal salt; (2) thermally treating by heating so as to pyrolyze the impregnated pulp to form gaseous levodextran and neither form carbon or form membranous carbon and neither form carbon monoxide or form no more than 5 parts by weight of carbon monoxide per 100 parts by weight (absolutely dry) of pulp; and (3) recovering the gaseous L-glucan by cooling the gaseous L-glucan to a temperature that is or is lower than the boiling point of the L-glucan. 提供一种使用纸浆作为原料以高产率和高纯度容易地工业生产左旋葡聚糖的方法。该方法包括：(1)在二价金属盐的水溶液中对具有至少80重量％的作为组成糖的葡萄糖含量和不超过1重量％的克拉松木质素含量的纸浆浸渍处理；(2)通过加热进行热处理，从而热解浸渍处理过的纸浆以形成气态左旋葡聚糖，并且也不形成炭或形成膜状炭，并且不形成一氧化碳或形成每100重量份(绝干重量)纸浆不超过5重量份的一氧化碳；和(3)通过将气态左旋葡聚糖冷却至左旋葡聚糖的沸点或低于其沸点的温度来回收所述气态左旋