Patent Description:
The process consists in the separation of a standard cellulose pulp into distinct fractions with different draining and morphological characteristics, as well as the use of one fraction to produce primary fines enriched pulp designated to nanofibrillar production and a high drainability pulp designated to paper market, containing low primary fines content.

The process in reference combines the unitary operations of pulp cooking, bleaching, fiber separation, drying of the high drainage pulp fraction and thickening the high primary fines content pulp to a certain consistency so as to be able to proper nanofibrillating it.

The production of cellulosic pulp involves several chemical and physical processes that result in the separation of the components of the wood raw material (usually composed of cellulose fibers and fibrils, hemicelluloses, lignin molecules and extractives or resins components).

Originally, there is broad size distribution of cellulosic particles in the above-mentioned raw materials associated with the anatomical structures, and part of it has reduced length. During the processes, mechanical friction in equipments such as pressure reducers, pumps and stirrers which, in addition to the chemical embrittlement caused by cooking and bleaching liquors, causes the generation or increase of the content of these particles in the total resulting fibers. Those particles are named as primary cellulosic fines, being differentiated to any fine particles produced in papermaking process due to the fact that they never suffered the effect of any kind of refining, which are called secondary fines.

These fines produced in the pulping and bleaching process, along with the content of naturally occurring fines in raw materials, compose the total of particles present in the cellulosic pulp of which approximate dimensions are less than <NUM> micrometers in length.

The fines are defined as particles capable of linearly traversing sieves of which mesh is less than <NUM> (apertures of <NUM> micrometers) or which are less than <NUM> micrometers in length (Tappi T261 cm-<NUM>, <NUM> - Fines fraction by weight of paper stock by wet screening).

These particles have high specific area as well as high hydrophilic capacity, wherein their presence makes it difficult to drain the cellulosic paste in pulp and paper machines.

However, their small dimensions showed them to be a good starting material for the production of nanofibrillated cellulose, wherein the application of a cellulose paste enriched with fines for this purpose takes place with lower energy cost and or better-quality potential when compared to the use of the standard cellulosic pulp.

The production of nanofibrillated cellulose consists of processing steps, wherein refining is the main treatment. But there are also combinations of refining treatments with chemical and/or enzymatic treatments. The energy consumption, however, is high due to the high refining energy consumption, and the cost of chemicals or enzymes for the production of nanofibrillated cellulose. Due to this problem, it is important to develop new alternatives that can reduce energy consumption. In this new process described herein, it was studied the potential of minimizing refining energy consumption by changing the raw material for the production of nanofibrillated cellulose. While most of the existing processes use regular (non-fractioned or segregated) cellulose pulp for the production of nanofibrillated cellulose, in this new process it is defined a process for fractionating the original cellulose pulp to obtain a fraction rich in primary fines and shorter fibers, which is then the base raw material for the production of nanofibrillated cellulose.

International application <CIT>, entitled "Energy efficient process for preparing nanocellulose fibers", describes a process that combines mechanical treatment (refining) with chemical (ozone) and/or enzymatic treatment. The described process is directed to increase energy efficiency, which is measured by the depolymerization degree of the pulp and by the refining energy consumption to reach a certain level of secondary fines (reaching a very high level of fines is not a starting pulp material but a way to define the quality of the nanocellulose obtained after the refining process, generating high amount of secondary fines). The described process is based on initiating from an original common cellulosic pulp, which is composed of fibrous elements and not segregated or fractionated. At no time the raw material for producing nanofibrillated cellulose is a source of primary fines type elements associated with separation of pulp phases, contrary to what is proposed in the process described herein.

Another method of producing nanofibrillated cellulose is described in International application <CIT>, entitled "High efficiency production of nanofibrillated cellulose". Different from the present invention, this document describes refining treatments of the cellulosic pulp in its original form (and not in the form of primary fines enriched pulp). The method consists of the treatment of the pulp in two steps, wherein the first step is conducted with refining elements different from those used in the second step.

International application <CIT>, entitled "Cellulose fibers, nanofibrils and microfibrils: the morphological sequence of MFC components from a plant physiology and fiber technology of view" also describes the dimensions of micro and nanofibrillated celluloses produced from original common pulp, and not the benefits from generating a new and unique starting material.

International application <CIT>, also describes the high refining energy consumption in the production of nanofibrillated cellulose and presents the use of a bleaching agent (as an additive), but it does not describe, at any time, the use of primary fines enriched pulp as raw material in place of non-fractioned cellulose.

International application <CIT> also discloses the high energy consumption in the production of microfibrillated cellulose and presents a solution with combinations of processes by alternating refining and washing, thus obtaining an increase in consistency to minimize energy consumption.

International application <CIT>, provides a method of fractionating biomass into different chemical components and cellulose. The fractionation mentioned herein refers to the separation of the biomass components: cellulose, from lignin and hemicelluloses, and therefore, it does not have any similarity with the present invention. The use of the cellulose extracted is the production of nanocrystalline cellulose, which is not an object of the present invention either.

The research paper published by <NPL>, describes a study in which mechanical pulp is separated and the shorter particles are directed to nano-ligno-cellulose production through homogenization. It totally differs from the present invention considering the initial raw material (mechanical pulp) and even more in the final product produced: nano-lignin-cellulose, due to the high contents of lignin in its composition. Also, the type of processing is different, it being performed through homogenization and not through refining energy application.

The refining mechanical treatment is, in general, the most commonly used process for generation of nanofibrillated cellulose, which results in significant changes in the morphological characteristics. The publications known from the state of the art, although mentioning fines as secondary fines, are only those generated during the refining treatment, whereas in the present invention the fines are in its totality primary fines, fractionated from an original cellulose, thus being the raw material for the production of nanofibrillar cellulose.

It is an object of the present invention to provide a process of producing fibrillated nanocellulose with low energy consumption and a high drainability market pulp comprising the steps of:.

The structure and operation of the present invention, together with further advantages thereof may be better understood by reference to the accompanying drawings and the following descriptions:.

Although the present invention may be susceptible to various embodiments, there are shown in the drawings and in the following detailed discussion, preferred embodiments with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the present invention to what is illustrated and described herein.

The present invention refers to a process of producing nanofibrillated cellulose with lower energy consumption, and a market pulp with high drainability. The energy consumption set herein is based on the same treatment performed on a reference (standard or common) pulp, compared to different levels of trial pulps according to what is proposed in the present invention.

The energy consumption reduction is possible with the production of a raw material of cellulose primary fines obtained by fractionating of cellulose pulp, followed by a refining treatment.

Although the fibrillated nanocellulose production process involves a similar unitary operation, the present invention refers to the new use of pre-fractionated raw material combined with unique process parameters for the production of cellulosic material having nanometric dimensions with significant reduction of energy consumption.

The preferred embodiment of this invention relates to a process of producing fibrillated nanocellulose with low energy consumption and a high drainability market pulp comprising the steps of:.

In step a), the resulting mass rich in cellulosic and hemicellulosic polymer chains comprising a very reduced amount of lignin and extractives may be bleached cellulose, semi-bleached cellulose and combinations thereof.

The process may consider any cellulosic pulp fiber derived from short or long fiber woods such as Eucalyptus, Corymbia, Birch, Aspen, Pinus, etc., their residues such as bark, sawdust, etc., and also any type of recycled fibers, preferably of Eucalyptus and Corymbia genders.

The pre-selected material is then fractionated in step c) preferably through a fractionating system, but not limited to pressurized basket screening systems, fines particulate recovering washers or hydrocyclones, in one or more steps, wherein combinations of the aforementioned equipment may be used.

The high-primary fines material fraction obtained from step c) is then subjected to thickening and nanofibrillar cellulose production process, in which it will be subjected to refining energy so that its element sizes are reduced to nanometric fractions.

The fraction of fibers with lower primary fines content, containing a massic amount of fines of about <NUM> to <NUM>%, preferably between <NUM>% and <NUM>, with significant lower resistance to drainability and water retention value.

In step d), the high primary fines content pulp is characterized by °SR between <NUM> and <NUM>; and water retention values between <NUM> and <NUM> per cent.

In step g), the absolute variables specific from Eucalyptus treatments in the High Drainage Pulp after pulp dryer are: fines content between <NUM>% to <NUM>,<NUM>%, preferably between <NUM> to <NUM>; water retention value between <NUM> and <NUM>/g, more preferable between <NUM> and <NUM> and °SR between <NUM> and <NUM>, more preferable between <NUM> and <NUM>. <FIG> describes briefly the processual steps from raw material selection until the production of the Nanofibrillated cellulose and the high drainage pulp.

<FIG> describes the increase in the fines content in two different kraft mills, showing the crescent profile of fines content according to the course of the process. The profile may be slightly different case by case for each mill due to the kind of equipments, intensity of cooking and mechanical energy suffered by the fibers.

Likewise, the width of the fibers also decreases due to the chemical peeling reactions also contributing to the increase and generation of the fiber category so called primary fines.

<FIG> shows the microscopic aspect of the fibers (in the right) and primary fines (in the left). A high amount of short fibers and small elements is present in the primary fines sample and barely seen in the samples whose material was removed, allowing the high drainability of the pulp trough physical and chemical improved flow through the void volumes created.

<FIG> shows the impact of the primary fines (measured by Britt Jar in mass percentage) in drainability aspects represented by Schopper Rigler degree (°SR) and water retention value. The values clearly indicates the high impact of the presence of primary fines in the drainability of the fibers.

<FIG> shows the morphological characteristic of the high drainage pulp, with reduced primary fines content to its half, and increase of fiber length and width.

<FIG> show the drainability and absorption properties characterization of pulp generated in pilot scale with lower fines content. The properties of the so called High drainage pulp in terms of resistance to drainage (°SR), water retention value, bulk and water absorption demonstrates that considerable gains in the drainability properties are present, signifying high potential for energy consumption reduction in the drying of this pulp in pulp and paper machines. The absence of fines also creates higher bulk pulp, allowing the pulp to absorb more water per gram of pulp.

<FIG> shows the possible gains in dryness after pulp machine press, allowing the energy saving in between <NUM> to <NUM>% for pulp drying.

<FIG> shows the properties of the high primary fines content pulp, generated through pilot processes. In <FIG>), the primary fines content shown has values obtained from one of the conditions used in pilot trials, and can be higher or lower depending of the need and technology set up used. The impact on drainability as demonstrated in items b and c is enourmous, showing very high drainage and water retention values caused by the presence of the primary fines in the pulp. The items d and e show the average fibers length and width measured, demonstrating that the fibers contained in the materials are also shorter and narrower that the regular ones.

<FIG> shows examples of images showing the width of the nanofibrils generated from increasing primary fines content samples.

The average of its width was done by evaluating <NUM> measurements for each sample, from at least <NUM> high resolution images and resulted in very similar width for all the samples, showing that the quality of the nanofibrillated cellulose is the same, as seen in <FIG>.

<FIG> shows the characterization of the potential of modifying properties in a given standard pulp by adding Nanofibrillar cellulose in terms of Tensile Strength and Resistance to drainage increase.

As can be seen from <FIG>, there is no difference between the quality of the nanofibrillated cellulose generated from standard pulp and from the high primary fines content pulp.

<FIG> shows the energy consumption in kWh per metric ton consumed to generate a given quality of nanofibrillar cellulose in a pilot plan with capacity to produce <NUM> tons/day. By convention, and based on literature and machine construction for nanocellulose obtainment trough refining energy (please see reference <CIT>) when <NUM>% of the particles size in length is smaller than <NUM> micrometers, obtained in morphological measurements, the product can be considered a nanofibrillated cellulose according to the definition of having at least one of its three dimensions between <NUM> and <NUM> nanometers according to ISO/TS <NUM>:<NUM> - Nanotechnologies - Standard terms and their definition for cellulose nanomaterial.

Claim 1:
Process of producing fibrillated nanocellulose with low energy consumption and a high drainability market pulp characterized by comprising the steps of:
a) cooking and bleaching of biomass generating a mass rich in cellulosic and hemicellulosic polymer chains comprising very reduced amount of lignin and extractives;
b) separating a fiber line from the mass of step a), wherein said fiber line has the following characteristics: b.<NUM>) average fiber length of <NUM> to <NUM>; and b.<NUM>) primary fine content of <NUM>% to <NUM>% of fines by mass;
c) fractionating of the segregated 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, so called high drainage pulp;
d) separating the high-primary fines content material stream obtained in step c), wherein said stream has a content of <NUM>% to <NUM>% of primary fines by mass and consistencies of <NUM>,<NUM>% to <NUM>%;
e) thickening of the high-primary fines content material stream of step d) until its consistencies reach <NUM> to <NUM>%;
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 common cellulosic pulp starting material;
g) separating the low primary fines content pulp stream of step c), wherein said pulp presents a massic amount of fines of about <NUM> to <NUM>, with significant lower resistance to drainability and water retention value, wherein the °SR presents a reduction of <NUM>% to <NUM>% and the water retention value presents a reduction between <NUM>% and <NUM>; and
h) drying of the low primary fines content pulp of step g) in drying pulp machines.