Mo Och Domsjo Aktiebolag

Hans O Samuelson

Erik Olof Hagglund

Kjell E Abrahamsson

The method solves the problem of delignifying technical cellulose pulp in a selective manner which will result in very low residual contents of lignin in the pulp and a correspondingly high quantity of lignin dissolved in spent liquors, which are recovered in the chemical recovery system of the pulp mill. The method comprises activating liquid-containing lignocellulosic material in the presence of nitrate with a gas that contains nitrogen dioxide, followed by the alkaline delignification of the lignocellulosic material, and measuring the acidity of the liquid accompanying the material on at least one occasion during the activation. The method is characterized in that the acidity of the liquid is measured subsequent to bringing the time derivative of the nitrate concentration of the liquid, expressed as millimols per liter of liquid per minute, to a level beneath +0.2, and by using the measured acidity value to establish the optimum amount of mineral acid for continuation and termination of the activation, and by charging the whole of this quantity or a part of this quantity of mineral acid to the lignocellulosic material.

Method for controlling activation of lignocellulosic material in the

A process is provided for activating cellulose pulp using NO and/or NO.sub.2 plus oxygen gas in the presence of nitric acid, added in an amount within the range from about 0.1 to about 1.0 gmole per kg of water accompanying the cellulose pulp at a temperature within the range from about 40.degree. to about 120.degree. C. for a time at an activating temperature of 40.degree. to 50.degree. C. of from 15 to 180 minutes, at from 50.degree. to 90.degree. C. of from 5 to 120 minutes, and at higher temperatures of from 1 to 10 minutes, followed by washing, and delignifying bleaching in an alkaline medium with or without oxygen gas and/or peroxide.

Process for activating cellulose pulp with NO and/or NO.sub.2 and oxygen

A process is provided for the activation and delignification of cellulose pulp, which comprises:

Process for the activation and delignification of cellulose pulp

Apparatus for reacting lignocellulosic material with a gas phase comprising a nitrogen oxide and oxygen under controlled gas pressure in the presence of water, for example, as a pretreatment before an alkaline delignification, comprising in combination:

Apparatus for reacting lignocellulosic material with a gas phase

A process is provided for reducing carbohydrate losses in the sulphate pulping of wood using sodium hydroxide and sodium sulfide, by pretreating the wood in the presence of water with oxygen gas and nitrogen oxide such as NO.sub.2 and/or NO and/or polymeric oxides and double molecules thereof, for example, N.sub.2 O.sub.4 or N.sub.2 O.sub.3, for from about 3 to about 110 minutes at a temperature within the range from about 25.degree. to about 100.degree. C., the amount of nitrogen oxide charged, calculated as monomers, being within the range from about 0.05 to about 1 kilomole per 1000 kg bone-dry wood, resulting in one or several of the following advantages: an improved yield of pulp, an improved viscosity, and a reduced requirement for bleaching chemicals in any subsequent bleaching stages.

Process for reducing carbohydrate losses in the sulfate pulping of wood

A process is provided for producing nitrogen oxides from aqueous waste cellulose pulp liquors containing nitrogen compounds including oxygen linked to nitrogen in the molecule, which includes initiating an autocatalytic reaction generating nitrogen oxide in a liquid phase comprising aqueous waste cellulose pulp liquor containing nitrogen compounds including oxygen linked to nitrogen in the molecule at a temperature within the range from about 40.degree. to about 180.degree. C. and at an acid pH within the range from about 0 to about 5 in the presence of nitrate ion NO.sub.3.sup.- in a concentration calculated as nitrogen within the range from about 0.2 to about 5 grams moles per kilogram of water and of lignin in a weight ratio lignin:water within the range from about 0.001:1 to about 1:1; and then continuing the autocatalytic reaction while maintaining a gas phase in contact with the liquid phase having a partial pressure of nitrogen oxide within the range from about 0.005 MPa to about 2 MPa, and withdrawing nitrogen oxide from the gas phase so as to maintain said partial pressure.

Process for producing nitrogen oxides from aqueous waste cellulose pulp

A process is provided for delignifying bleaching lignin-containing cellulose pulp which comprises:

Process for delignifying bleaching lignin-containing cellulose pulp by

A two-stage process is provided for the conversion of lignocellulosic material, for instance, wood, to cellulose pulp, first oxidizing the lignocellulosic material to form aldonic acid end groups, preferably bound with 1,4-glycosidic bonds, in the polysaccharides, in an alkaline medium in the presence of the oxidized form of a redox additive which is converted into a reduced form in reaction with the wood and/or products formed from the wood, withdrawing the alkaline medium and then reoxidizing the reduced form of the redox additive in the absence of the lignocellulosic material at a rate to maintain the oxidized form of the redox additive in a major proportion in the alkaline medium during oxidation of the lignocellulosic material by contacting the withdrawn alkaline medium with oxygen-containing gas, and then continuing the digestion in an alkaline medium at a temperature within the range from about 160.degree. to about 200.degree. C., also in the presence of a redox additive, but without any addition of oxygen.

Process for the conversion of lignocellulosic material to cellulose pulp

A process for delignifying bleaching cellulose pulp in three stages, an activating stage, and first and second alkaline stages, NO and/or NO.sub.2 and O.sub.2, and optionally HNO.sub.3, being supplied to the water-containing pulp in the activating stage; in the first alkaline stage, alkali being supplied as carbonate, primarily HCO.sub.3.sup.-, with oxygen gas having a partial pressure, on average, of from 0 to 0.2 MPa, the lignin content of the pulp being lowered in this stage so that the Kappa number of the pulp after the stage is from 10 to 60% of the Kappa number of the pulp entering the activating stage; in the second alkaline stage, alkali being supplied as carbonate, primarily CO.sub.3.sup.=, with oxygen gas at a partial pressure, on average, of from 0.1 to 3 MPa.

Process for the delignifying bleaching of cellulose pulp by activating

A two-stage oxygen bleaching of chemical cellulose pulp is provided, in which an alkaline oxygen bleaching stage is preceded by a nitrogen dioxide activating stage in which oxygen is added to the activating stage in an amount such that nitrogen monoxide formed as an intermediate during the activation process is consumed, so regulating the amount of oxygen added that when the activation reaction is practically complete, substantially all of the nitrogen dioxide and nitrogen monoxide has been consumed.

Process for the oxygen bleaching of cellulose pulp

A process is provided for the bleaching delignification of cellulose pulp with oxygen gas in the presence of alkali, wherein the pulp is first activated with nitrogen dioxide and then washed, preferably with water. The invention is characterized in that the acid solution obtained is used to pretreat the digested pulp subsequent to washing the pulp with waste liquor obtained from the oxygen gas bleaching delignification stage.

Process for alkaline oxygen gas bleaching of cellulose pulp

A process is provided for the alkaline oxygen delignification and bleaching of chemical cellulose pulp while inhibiting degradation of carbohydrates in the pulp, due to the presence of one or more aromatic diamines, preferably having the diamine groups directly linked to an aromatic ring.

Alkaline oxygen delignification and bleaching of cellulose pulp in the

A process for pulping hardwood to produce cellulose pulp in good yield and of high quality, with a low requirement for causticized pulping liquor, which comprises in a first pulping stage pulping the hardwood in an alkaline pulping liquor containing sodium sulfide at a pH of about 10.5 to about 13 and at a temperature within the range from about 110.degree. to about 170.degree. C while generating hydrogen sulfide in situ by reaction of sodium sulfide with organic acids liberated in the pulping; and then in a second pulping stage, following directly after the first pulping stage, continuing the pulping at a pH higher than said first stage pH, within the range of about 12.5 to about 14 and at a temperature higher than said first stage temperature within the range from about 145.degree. to about 190.degree. C, in the presence of added alkaline pulping liquor comprising sodium hydroxide and sodium sulfide until cellulose pulp is produced.

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Gothenburg, Sweden

Hans O Samuelson