Process of producing nanofibrillated cellulose with low energy consumption
The present invention refers to the separation of cellulose pulp into distinct fractions with different draining and morphological characteristics, as well as the use of part of these fractions for the production of nanocellulose. The process in reference combines the unitary operations of fiber separation, thickening to a certain consistency, draining and drying of the cellulosic pulp with the high drainage ability and production of nanocellulose from high primary fines content pulp. The process may consider any cellulosic pulp fiber derived from short or long fiber woods such as Eucalyptus, Corymbia, Birch, Aspen, Pinus, recycled fibers, etc., their residues such as bark, sawdust, etc.
1. Process of producing nanofibrillated cellulose and a market pulp characterized by comprising the steps of:
a) cooking and bleaching of biomass generating a cellulosic material comprising a reduced amount of lignin and extractives;
b) separating a fiber line from the cellulosic material, wherein the fiber line comprises fines which are in its totality primary fines, and the fiber line has the following characteristics: b.1) average fiber length of 0.3 to 2.5 mm; and b.2) primary fines content of 3% to 30% by mass of the fiber line;
c) fractionating the separated fiber line of step b) by means of a fractionating system into at least two streams, a high-primary fines content material stream and a low primary fines content pulp stream;
d) separating the high-primary fines content material stream obtained in step c), wherein the high-primary fines content material stream has a content of 10% to 90% of primary fines by mass of the high-primary fines content material stream and consistencies of 0.02% to 1%;
e) thickening the high-primary fines content material stream of step d) until its consistencies reach 2% to 15%;
f) submitting the thickened material of step e) to a nanofibrillated cellulose production process, wherein it is subjected to mechanical refining energy, being the energy consumption used for the generation of the nanofibrillar cellulose smaller than in comparison with non-fractionated or segregated cellulosic pulp starting material;
g) separating the low primary fines content pulp stream of c) which comprises pulp with a °SR reduction of 15% to 50%, and water retention value reduction between 7% and 35% when compared to the cellulosic material; and
h) drying of the low primary fines content pulp of step g) in pulp drying machines.
2. Process, according to claim 1 , characterized in that the resulting cellulosic material of step a) is selected from bleached cellulose, semi-bleached cellulose, and combinations thereof.
3. Process, according to claim 1 , characterized in that step c) is carried out through a fractionating system selected from the group comprising pressurized basket screening systems, fine particulate recovering washers, hydrocyclones and combinations thereof.
4. Process, according to claim 1 , characterized in that the refining energy of the nanofibrillated cellulose production process of step f) is associated with enzymatic treatment.
5. Process, according to claim 1 , characterized in that the high primary fines content pulp of step d) has °SR between 20 and 95, and water retention values between 140 and 690 percent.