The spent liquor (SL) of a thermomechanical pulping (TMP) process introduces a high load to the wastewater system of this process. To reduce this load, fly ash from a biomass boiler is used and the application of fly ash improves the performance of biological process. Three different alternatives are introduced to apply fly ash to treat spent liquor.

A catalyst is recovered from an aqueous reaction mixture comprising heterocyclic nitroxyl catalyst and oxidized cellulose, by: separating the oxidized cellulose from the reaction mixture, contacting the reaction mixture with solid hydrophobic adsorbent particles with particle sizes below 350, preferably below 200 m, more preferably below 100 m, said particles being silica particles provided with functionalized hydrophobicity, adsorbing the catalyst to the hydrophobic adsorbent particles, and eluting the catalyst from the adsorbent particles with an organic solvent.

A method for removing inorganic salts from an alcoholic basic lignin solution, comprising the steps of adding an acid to said solution whereby an alcoholic lignin solution is formed, and separating a precipitate comprising an inorganic precipitate from said solution, and a method for separating lignin from an alcoholic basic lignin solution, comprising the steps of adding an acid to said solution whereby an alcoholic lignin solution is formed, separating a precipitate comprising an inorganic precipitate from said solution, removing ethanol from said solution, optionally adjusting the pH of the mixture obtained, and separating lignin from said mixture, and, a method for avoiding foaming during alcohol recovery from an alcoholic mixture comprising lignin, optionally after separation of an inorganic precipitate, which method is characterized in that a pH of 2 to 9 of the alcoholic mixture is adjusted during alcohol recovery

A method used in connection with the recovery of pulping chemicals from spent pulping liquor produced by kraft-type pulping at very high sulphidity. In the method, spent pulping liquor is acidified to a relatively low pH which converts a most or all of the sulphide and hydrosulphide in the liquor to hydrogen sulfide. Sulphur containing gases released from the acidification of the spent pulping liquor, together with other sulphur gases collected at the pulp mill, are converted into an acid compound. This acid compound is employed as an acidification agent in the acidification of the spent pulping liquor. The amount of acid compound generated by the conversion of sulphur containing gases may be sufficient to provide most, if not all, of the acid needed for the acidification of the spent pulping liquor.

A process for recausticizing green liquor in a sulphate or Kraft process for wood pulp production, in which a green liquor consisting of an aqueous solution of sodium carbonate as the major component and sodium sulphide is admixed with calcium oxide in a slaker and undergoes a reaction in a recausticizer to form an aqueous suspension containing sodium hydroxide and calcium carbonate as the major components, which suspension is filtered on a first filter and subsequently, after dilution with water in a dilution vessel, is fed over further filters two or three times and filtered to separate solids suspended therein, characterized in that after a first separation of calcium carbonate as the major component and calcium oxide as the minor component, carbon dioxide is added to the aqueous suspension at least during dilution in a dilution vessel and in particular in the dilution vessel (s) upstream of a second and/or a third filter.

A method of treatment of an aqueous foamable medium, such as a process stream of a pulp and paper mill, the method comprising contacting the aqueous process stream with a defoaming agent comprising: a) at least one C.sub.12 to C.sub.40 Guerbet alcohol; and/or, b) at least one polyol ester.

The spent liquor (SL) of a thermomechanical pulping (TMP) process introduces a high load to the wastewater system of this process. To reduce this load, fly ash from a biomass boiler is used for removing lignin from the SL, and also for decreasing the chemical oxidation demand (COD) and turbidity of the SL.

A method and a liquor filter, in which liquor filter sealing medium is fed via a sealing medium channel (3) into an innermost sealing zone formed by an innermost sealing member (1), an outer seal (2) and the space between them at a causticizing plant of a chemical pulp mill. The sealing medium used is an alkaline sealing liquid and/or gas, which does not substantially dilute the liquor being filtered. Advantageously the sealing medium is filtrate from the liquor filter and/or gas taken from the interior of the liquor filter.

The invention relates methods and processes for the separation and refining of lignin from spent cooking liquor, called black liquor, present in industrial chemical plants, and compositions thereof. A process is provided for separating black liquor into at least two, three, or four streams selected from: (i) a gaseous stream comprising volatile sulfur compounds; (ii) a lignin-comprising stream produced by extracting lignin into a limited solubility solvent S1; (iii) a salt stream, comprising solid sodium and sulfate salts; and (iv) a salt-depleted and lignin-depleted aqueous stream comprising hydrocarbons.

A method of recovering wood pulping chemicals from black liquor produced in a wood pulping process where the process entails burning the black liquor in a recovery boiler to form ash containing high levels of carbonate as well as sodium, potassium and chloride. The ash is dissolved to form a dissolved ash solution that is directed to a first stage crystallization unit that concentrates the dissolved ash solution and which results in the precipitation of sodium sulfate and sodium carbonate. Thereafter the concentrated dissolved ash solution is directed to a second stage crystallization unit which adiabatically cools the concentrated dissolved ash solution to form a glaserite slurry and a purge stream that is rich in chloride. In order to reduce the tendency of sodium carbonate and burkeite to crystallize in the second stage crystallization unit and to encourage pure glaserite to crystalize in the crystallizer, the method entails mixing a sulfate source, such as sodium sulfate or sulfuric acid, to the concentrated dissolved ash solution upstream of the crystallizer.