Economic evaluation of isolation of hemicelluloses from process streams from thermomechanical pulping of spruce

Hemicelluloses, which are abundant in nature and have potential use in a wide variety of applications, may make an important contribution in helping relieve society of its dependence on petrochemicals. However, cost-efficient methods for the isolation of hemicelluloses are required. This article presents an economic evaluation of a full-scale process to isolate hemicelluloses from process water from a thermomechanical pulp mill. Experimental data obtained in laboratory scale were used for the scale up of the process by computer simulation. The isolation method consisted of two process steps. The suspended matter in the process water was removed by microfiltration and thereafter the hemicelluloses were concentrated by ultrafiltration, and at the same time, separated from smaller molecules and ions in the process water. The isolated hemicelluloses were intended for the production of oxygen barriers for food packaging, an application for which they have been shown to have suitable properties. The solution produced contained 30 g hemicelluloses/L with a purity (defined as the ratio between the hemicelluloses and the total solids) of approx 80%. The evaluation was performed for a plant with a daily production of 4 metric tonnes (t) of hemicelluloses, which is the estimated future need of barrier films at Tetra Pak (Lund, Sweden). The production cost was calculated to be € 670/t of hemicelluloses. This is approx 9 times lowr than the price of ethylene vinyl alcohol, which is produced by petrochemicals and is currently used as an oxygen barrier in fiberbased packaging materials. This indicates that it is possible to produce oxygen barriers made of hemicelluloses at a price that is competitive with the materials used today.