According to an example aspect of the present invention, there is provided a method for producing an oxidised lignin based high performance surface active agent in techno-economically feasible manner within kraft pulp mill without interfering the main process.

The present invention relates to novel lignin-derived compounds and compositions comprising the same and their use as redox flow battery electrolytes. The invention further provides a method for preparing said compounds and compositions as well as a redox flow battery comprising said compounds and compositions. Additionally, an assembly for carrying out the inventive method is provided.

The invention relates to processes for manufacturing pulp and more specifically to improved processes for manufacturing dissolving pulp. The processes have primarily been developed to be used in connection with large scale kraft processes, i.e. they have been designed to be incorporated into a plant. A liquor derivable from the process and comprising xylan, lignin, alkali and water is also disclosed as well as a dissolving pulp produced by the process.

The invention is related to improved polysulfide production process wherein a specific second filtration process (F.sub.x) is installed before the polysulfide reactor (R.sub.c). According to the inventive method a cross flow filter (F.sub.x) is used as the second filtration process reaching astonishing low levels of residual solids in the white liquor as well as extended availability of the second filtration process. The subsequent polysulfide reactor, either in form of an electrolytic cell or in form of a bed of active carbon, could then also be operated at increased availability. The invention increases the production volume of polysulfide and the retentate from the cross filtering process may be bled out continuously to a process position ahead of a first filtering or clarification stage, capturing most of the increased content of lime mud particles in the retentate and causing less disturbance of the process with a minimum of tanks and pumps.

Residual lignin recovered from biological conversion processes and pulp and paper industry wastes can be converted to water-soluble products by alkaline oxidation under oxygen pressure at high solids loading within the temperature range 130-180 C. No problems associated with repolymerization reactions are encountered at solids loading between 10-30% where the initial molar ratio of hydroxide base to lignin residual is at last 0.4, possibly because of enhanced reactivity in the oxidation reaction of aromatic groups in self-associate structures. The water-soluble oxidation products can be fractionated to recover a low molecular weight fraction in which pH can be adjusted using CO2 without forming precipitates. Sodium carbonate byproduct can be recovered from the pH adjusted reaction mixture using acetone precipitation. The low molecular weight fraction of the pH adjusted oxidation products can be used as feed for anaerobic digestion to biomethane.

According to an example aspect of the present invention, there is provided a method of replacing with sodium make-up chemicals sodium losses caused by outflows in a pulp mill which employs a kraft process for producing cellulosic pulp, wherein the pulp mill includes a unit for conversion of sulphurous compounds, which is fed with sulphurous substances of the kraft process to convert said sulphurous substances into oxidized sulphurous compounds, said method comprising using sodium sulphate possibly together with other sodium salts as the main make-up chemical, to achieve an essentially sodium hydroxide free feed of sodium make-up chemicals, and at least a part of the sulphur contained in the sodium sulphate make-up chemical being used for producing oxidized sulphurous compounds in said unit for conversion of sulphurous compounds.

In a process for oxidation of white liquor, in particular of white liquor used in a process of production of paper or cellulose, the oxygen required for the oxidation is supplied to the reactor or the reactors in which the oxidation is carried out at least partially in the form of oxygen-containing nanobubbles. Due to the relatively long lifetime of the nanobubbles this very efficiently provides oxygen also for oxidation reactions in the white liquor proceeding at different rates.

A method for transforming a black liquor, comprising the following steps: a) supplying a black liquor, b) gasifying the black liquor by means of supercritical water gasification in the presence of a hydrogenated carbon-free fuel, by means of which reaction products are formed, c) cooling the reaction products, by means of which a gaseous mixture is obtained which comprises at least methane and a green liquor comprising at least sulphur in the form of NaHS, Na.sub.2S and H.sub.2S.