The invention relates to a process for isolation of hemicelluloses from biomass pulping process waters or spent liquors with removal of suspended solids, concentration of the product and purification of the product by removal of inorganic salts and low molecular weight substances. It is characterized in that the hemicellulose isolation process conditions at several separation/purification stages are adjusted separately by e.g. pH adjustment. The invention further relates to a plant for carrying out the process. With such process and plant it is possible to recover most of the suspended solids, especially xylan and other hemicelluloses.

The problem of runaway smelt explosions due to a sudden influx of smelt into a dissolving tank is mitigated by a system comprising an ultrasonic transducer configured to emit ultrasonic waves toward the dissolving tank at a frequency above 20 kilohertz. A system comprising the ultrasonic transducer may further comprise sensors and a data processor configured to regulate the properties of the ultrasonic waves in response to process conditions affecting the smelt flow.

The problem of runaway smelt explosions due to a sudden influx of smelt into a dissolving tank is mitigated by a system comprising an ultrasonic transducer configured to emit ultrasonic waves toward the dissolving tank at a frequency above 20 kilohertz. A system comprising the ultrasonic transducer may further comprise sensors and a data processor configured to regulate the properties of the ultrasonic waves in response to process conditions affecting the smelt flow.

The disclosure provides methods and compositions for reducing the viscosity of black liquor. Also provided are methods of inhibiting deposition of scale and methods of processing black liquor. In some embodiments, the compositions include a carboxylate-containing polymer and an inorganic salt. In some embodiments, the compositions include a carboxylate-containing polymer, an inorganic salt, and a surfactant.

Embodiments herein relate to a system (200; 300; 400; 500) for obtaining methanol from foul condensate (101) of a pulping process. The system (200; 300; 400; 500) comprises a primary stripper (102) arranged to strip the foul condensate (101) from pollutants, whereby a first methanol-containing condensate is obtained from the polluted stripper off gases (SOGs). The system (200; 300; 400; 500) also comprises a first acidification unit (202) arranged to acidify the first methanol-containing condensate. Further, the system (200; 300; 400; 500) comprises a secondary stripper (204) arranged to strip the acidified first methanol-containing condensate from pollutants to obtain a second methanol-containing condensate, and a distillation column (107) arranged to distil the second methanol-containing condensate from the secondary stripper (204) so as to obtain methanol. Embodiments herein also relate to a method performed in a system (200; 300; 400; 500) for obtaining methanol from foul condensate (101) of a pulping process.

A method to purify black liquor soap (BLS) from sulfur compounds is disclosed. In the BLS desulfurization method, a BLS composition is heated in an inert atmosphere and sulfur is removed via aqueous extractions with inorganic base in the absence of other chemicals such as brine, sulfate salts and carbonate salts. The purified BLS composition exhibits favorable properties, including reduced sulfur content, lower color, and improved odor characteristics. The resulting tall oil compositions, depitched tall oil compositions, tall oil distillation fractions, and products derived therefrom also show reduced sulfur content, lower color, and improved odor characteristics.

A method for producing an alkali metal/alkaline earth metal hydroxide includes: subjecting a solution containing R.sup.ACOOM.sup.B and/or (R.sup.ACOO).sub.2M.sup.C and water to an electrochemical reaction to cause a Kolbe electrolysis reaction at an anode to generate at least R.sup.AR.sup.A, carbon dioxide, and an M.sup.B+ ion and/or M.sup.C2+ ion; and neutralizing the M.sup.B+ ion and/or M.sup.C2+ ion by using an OH.sup.? ion generated by electrolysis of water at a cathode. R.sup.A represents a hydrocarbon group, M.sup.B represents an alkali metal, and M.sup.C represents an alkaline earth metal.

A method for producing an alkali metal/alkaline earth metal hydroxide includes: subjecting a solution containing R.sup.ACOOM.sup.B and/or (R.sup.ACOO).sub.2M.sup.C and water to an electrochemical reaction to cause a Kolbe electrolysis reaction at an anode to generate at least R.sup.AR.sup.A, carbon dioxide, and an M.sup.B+ ion and/or M.sup.C2+ ion; and neutralizing the M.sup.B+ ion and/or M.sup.C2+ ion by using an OH.sup.? ion generated by electrolysis of water at a cathode. R.sup.A represents a hydrocarbon group, M.sup.B represents an alkali metal, and M.sup.C represents an alkaline earth metal.

A system for producing aqueous sulphuric acid is provided, the system including a first heat exchanger configured to cool aqueous sulphuric for producing cooled aqueous sulphuric acid; a pre-cooling unit comprising an inlet or inlets for receiving the gas containing sulphur trioxide and the cooled aqueous sulphuric acid, an outlet for letting out aqueous sulphuric acid and the gas containing sulphur trioxide, and a first nozzle for spraying the cooled aqueous sulphuric acid onto the gas containing sulphur trioxide. The system further includes a condensation tower comprising a first inlet for receiving the cooled gas containing sulphur trioxide and aqueous sulphuric acid from the pre-cooling unit and means for circulating the aqueous sulphuric acid within the condensation tower by spraying. An associated method and pre-cooling unit suitable for cooling gas comprising sulphur trioxide from at least 400 C. to at most 150 C. are also provided.

A system for producing aqueous sulphuric acid is provided, the system including a first heat exchanger configured to cool aqueous sulphuric for producing cooled aqueous sulphuric acid; a pre-cooling unit comprising an inlet or inlets for receiving the gas containing sulphur trioxide and the cooled aqueous sulphuric acid, an outlet for letting out aqueous sulphuric acid and the gas containing sulphur trioxide, and a first nozzle for spraying the cooled aqueous sulphuric acid onto the gas containing sulphur trioxide. The system further includes a condensation tower comprising a first inlet for receiving the cooled gas containing sulphur trioxide and aqueous sulphuric acid from the pre-cooling unit and means for circulating the aqueous sulphuric acid within the condensation tower by spraying. An associated method and pre-cooling unit suitable for cooling gas comprising sulphur trioxide from at least 400 C. to at most 150 C. are also provided.