ES2730430B2 - METHOD FOR THE DETERMINATION OF THE CONTENT OF HEMICELLULOSE, CELLULOSE AND LIGNIN IN BIOMASS AND LIGNOCELLULOSE PASTES - Google Patents

Description

DESCRIPTION

METHOD FOR DETERMINING THE CONTENT OF HEMICELLULOSE,

CELLULOSE AND LIGNIN IN BIOMASS AND LIGNOCELLULOSIC PASTES

FIELD OF THE INVENTION

The present invention belongs to the technical field of the characterization of materials, more specifically to the determination of the content of hemicellulose, cellulose and lignin in biomass and lignocellulosic pastes.

BACKGROUND OF THE INVENTION

In the scientific community there is agreement about the close relationship between the cellulose content (not hemicellulose) of a wood and its performance in pulp. Hence the interest in developing quick and cheap analytical systems that allow the analysis of many wood samples. The composition of lignocellulosic biomass can be determined by chemical, chromatographic, or spectroscopic analysis. For example, Wright and Wallis (1998) discuss the precision of various chemical methods and compare them with high pressure liquid chromatography (Wright, P., Wallis, A. 1998 Rapid determination of cellulose in plantation eucalypt Woods to predict kraft pulp yield TAPPI Journal, February 1998, 126-130). For his part, Schimleck (2007) finds that near infrared spectrometry (NIR) is an alternative to traditional methods of evaluating the properties of wood and suggests that it will play an important role in future clone selection programs, however warns that the method requires exhaustive pre-calibration and that its precision is poor for a specific tree and that it should be used not to characterize individuals but populations (Schimleck, L. 2007. Near-Infrared spectroscopy: A rapid non-destructive method for measuring wood properties, and its application to tree breeding. New Zealand Journal of Forestry Science 38.1, 14-35).

We understand by chemical paste that which is obtained from wood through some chemical process of separation of lignin. Historically, chemical methods have been used that occur in an acid medium (sulphite paste) or in a basic medium (soda method, kraft method). Currently the most widespread is the kraft method, which is based on an attack on the wood with sodium hydroxide and sulphide (white lye). The chemical reaction (cooking) takes place in digesters that may or may not be continuous. In them, wood and white liquor increase the temperature to a set point that is maintained for a stipulated time to obtain a cellulose paste with previously established characteristics. Currently, the control of both pasta production and bleaching is carried out by means of a chemical analysis that determines the oxidizable matter in the paste (kappa number) (number of milliliters of 0.1N potassium permanganate solution that is consumed by 1 gram of pasta) using standard procedures (TAPPI um 235).

The optimization of the pulp production process must take into account both the generation of the raw pulp and its subsequent bleaching. The first seeks to increase the yield of raw pasta and the second seeks to reduce the consumption of bleaching reagents. In this sense, it is of great importance to establish the adequate level of cooking that allows the optimal operation of the bleaching section. For this, a cut kappa number is usually used at the outlet of the digesters.

Since the organic matter removed from the wood during digestion is used to produce energy through the combustion of black liquor and the removal of raw pulp during bleaching has to be treated in the liquid effluent plant, it is not surprising that it exists. some pressure to decrease as much as possible the kappa number at the outlet of digesters. In any case, it must be taken into account that the same kappa number in two pastes does not ensure the same whitenability in them. The experience obtained in the production plants indicates that the firing of low-yield woods (for example, Rostrata eucalyptus) should be completed when the paste has a kappa number 4 or 5 units greater than when high-yield woods are cooked (for example, eucalyptus Globulus).

It is evident, therefore, that the control of the cooking and bleaching processes based on the kappa number is imprecise. In the improvement of the digestion process, additives have been used (for example, anthraquinone or polysulfides) and changes in the functioning of the digester oriented both to decrease the alkaline degradation of carbohydrates (isothermal cooking, low solids cooking, ...) and to avoid the deposition of xylan or lignin in the final phase of digestion (for example, if the pH falls below 12.5). On the other hand, efforts to improve bleaching have been directed at reducing the environmental impact of the reagents used, focusing on chlorine-free technologies (TCF) that make use of oxygen, ozone and hydrogen peroxide.

As indicated, with few exceptions, the cellulose pulp production process control system revolves around the measure of the degree of delignification achieved. Traditionally this measurement has been made by redox titration and resulted in the kappa number of the pastes.

Alternatives based on chromatographic or spectroscopic methods have recently been proposed. An example is patent US4944841 that suggests using gas chromatography to control the lignin content in the paste. However, the most abundant are those based on infrared spectroscopy. Some examples of this are the US4743339 patent that monitors black liquor and the US7604712 patent that monitors pasta. In any case, they continue to use the kappa number as a criterion in decision-making in the control of the production process.

Given the difficulty of implementing these expensive control systems, cellulose pulp production plants generally control the cooking process afterwards, that is: the analysis of the raw pulp obtained (kappa number) serves to modify the conditions of the upstream digester (alkalinity, sulfidity, temperature, time). In these facilities, the control of the wood is scarce, there are no routine analyzes that evaluate its quality. Instead, specialized company departments often take samples of lumber that is purchased in large batches to determine its pulp yield under conditions similar to those that will be used in the industrial plant. Therefore, there are catalogs of wood properties that were acquired in large quantities at specific times. This information was useful until that batch of wood was consumed, then lost much of its usefulness.

Changes in wood can also be expected after weeks or months in the open air in storage parks of processing plants. Those changes are not taken into account.

On the other hand, in general, the control of the bleaching process is also carried out a posteriori by means of the kappa number of the pastes obtained in the successive stages. It is common for the raw pulp after undergoing an alkaline scrubbing and washing process to have a kappa number close to 20. In an ECF bleach based on an O-D0-PO-D1 sequence (delignification with oxygen, chlorine dioxide, hydrogen peroxide and chlorine dioxide) the kappa number can be reduced to 1 or less. In absolute terms the The greatest decrease occurs in the first stage (O), but in relative terms the most effective are the chlorine dioxide stages (D0 and D1) that can decrease kappma by more than 60%.

In general terms, it can be verified that the scientific research and the patents described are oriented towards a real-time control of the characteristics of black liquor and paste in the digester. This proposal is expensive to implement and expensive to maintain, being hardly justifiable in economic terms if, as proposed in the present invention, there is a control of the characteristics of the wood used as raw material. From the point of view of the present invention, the control of digestion must move towards the wood, since if it is properly characterized, the operating conditions in the digester can be easily inferred. In this context, it is necessary to identify the wood and pulp obtained from it by means of a parameter (V / C) that adequately informs of its composition, avoiding confusing measurements such as the kappa number.

It is worth noting the patent ES2359163T3, which proposes a digestion control system that is not based on the kappa number. It is proposed to analyze the paste at the exit of the digester to determine the proportion that is not soluble in a 5% NaOH solution (called parameter R5). According to the authors of this patent, this parameter R5 can replace the kappa number in the characterization of the pastes. The monitoring of the pulps with parameter R5 allows to obtain pulps with uniform characteristics even if the wood that feeds the digester is modified.

The purpose is to monitor the cellulose content in the pulps, assuming that pulps with similar cellulose contents will show similar characteristics when transformed into paper.

The aforementioned method measures the amount of cellulose in the raw pulp through the 5% soluble fraction in NaOH, this being an arbitrary decision, so the reliability of this method is highly questioned, since it is based on correlations empirical that are established later.

DESCRIPTION OF THE INVENTION

The present invention introduces a new standard or characteristic property of lignocellulosic biomasses (herbaceous, wood or pasta), the V / C index, measurable by thermogravimetric analysis and that can be correlated with its composition and, consequently, with those characteristics dependent on it. such as its ability to produce pasta of a given kappa or the proper digestion conditions to produce a certain yield. Likewise, the V / C parameter finds application in the characterization of cellulosic pulps, replacing with advantage the current standard, the kappa number.

With this invention a quick and cheap determination of the content of hemicellulose, cellulose and lignin of lignocellulosic materials is achieved, particularly those used in the production of pasta, allowing a control of the biomass before entering the digester and the pasta raw once obtained.

The main novelty of the present invention is the characterization of lignocellulosic biomasses according to their tendency to produce volatiles or carbonaceous residues. For this it is necessary to use thermogravimetric analysis.

In a first aspect of the invention, the method for determining the content of hemicellulose, cellulose and lignin in biomass and lignocellulosic pastes comprises the following steps:

(a) analyze a sample of biomass and / or lignocellulosic paste by means of a thermogravimetric analysis;

(b) represent the thermogravimetric data obtained in step (a) indicating the percentage of mass loss (TG curve) and the speed of mass loss (DTG curve) for each time and temperature;

(c) perform the calculation of the V / C index from the thermogravimetric data using the formula:

V / C = V / (100-V)

where V is the mass of the volatilized sample and C is the mass of the charred sample, calculated as C = 100 - V;

(d) determine the amount of hemicellulose, cellulose, and lignin in the sample using linear relationships that depend on the parameter V / C.

The data obtained in the method of the invention allow calculating the V / C index, the composition of lignocellulosic biomass and the optimal treatment conditions during cooking.

This allows anticipating the level of severity of the cooking process, avoiding trial and error tests when the type of biomass is changed and, consequently, improving the economic balance of the industrial installation. In the case of wood from young crops, the method can be extended to a large number of samples and would allow establishing the potential production of cellulose in the adult phase, therefore, it would be useful in the selection of clones in the nursery.

Another aspect of the invention relates to that the biomass and lignocellulosic pastes can be woods, cellulosic pastes, herbaceous or residual materials.

Another aspect of the invention is the possibility of carrying out the analysis of the lignocellulosic biomass sample from step (a) in an inert or oxidizing atmosphere.

Another aspect of the invention relates to that the analysis of the lignocellulosic biomass sample from step (a) can be carried out at heating rates between 5 and 20 ° C / min, preferably at 10 ° C / min.

Another aspect of the invention is the application of the method at the end of the digestion and the successive bleaching stages of the biomass and lignocellulosic pastes.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows a flow diagram of the calibration process of the thermogravimetric system described in the invention.

Figure 2 shows a flow diagram of the determination of the V / C index in biomass and its application in the determination of parameters of interest in the cooking process.

Figure 3 shows a flow diagram of the determination of the V / C index in pastes and their application in the determination of parameters of interest in the cooking and bleaching process. Figure 4 shows a flow chart of one of the preferred embodiments of this invention directed to the data processing modules.

Figure 5 shows a block diagram of a computing system that automates the calculation modules.

Figure 6 shows the relationship between the parameter V / C (measured in an inert atmosphere) and the cellulose and lignin contents of the eucalyptus woods (a and b) and the cellulose content of the raw pulp c).

Figure 7 shows the relationship between the kappa index and the V / C index of pulps obtained from high-yield (E2) and low-yield (E12) woods.

Figure 8 shows the linear relationship between the pulp yield of a wood up to kappa number 16 (squares) or 20 (circles) and the parameter V / C in atmosphere a) inert and b) oxidizing.

Figure 9 shows the linear relationship between the active alkali used in cooking and the V / C index of the wood to obtain kappa 16 index pulps.

DESCRIPTION OF MODES OF REALIZATION

Having described the present invention, it is further illustrated by the following examples.

It is important to note that a calibration process is carried out prior to the use of the V / C index. It follows the method 100 described below and whose flow diagram is represented in Figure 1.

In step 110, the biomass or pulp samples are subjected to thermogravimetric analysis and their results are used to obtain the V / C index according to procedures 220 and 230 for biomass and 320 and 330 for cellulosic pulps, which will be detailed below.

In step 120, the biomass or paste samples are subjected to chemical analysis (HPLC, gas chromatography) to determine the content of their main components.

In step 130, the biomass samples will be cooked with different active alkalis and various factor H values to produce pastes of preset kappa indices.

In step 140, the data obtained from thermogravimetric and chemical analyzes will be used to obtain the necessary correlations between the V / C index and the parameters of interest outlined in methods 200 and 300, which will be detailed below.

In accordance with the technique's calibration method 100, it can be applied to any other biomass (pine wood, cellulosic pulps, herbaceous, etc.) with the following protocol: a) select samples of the biomass of interest that cover a range of compositions broad enough;

b) chemically analyze those samples to determine the contents of their main components (for example, using HPLC);

c) carry out thermogravimetries in nitrogen and air;

d) measure the V / C parameter; and

e) correlate the cellulose and lignin contents with the parameter V / C.

One of the preferred embodiments of this invention is directed to cellulosic pulp producing biomasses. In it the V / C index is calculated according to the method 200 described below and whose flow diagram is represented in Figure 2.

In step 210 of thermogravimetric analysis, a 5-15 mg sample of biomass is placed on a thermobalance. Thermogravimetric analysis is carried out in nitrogen or air from room temperature up to 750 ° C with a heating rate of 10 ° C / min. As a result of this analysis, thermogravimetric data will be obtained indicating the percentage of loss of mass (TG curve) and the speed of mass loss (DTG curve) for each time and temperature.

In step 220, the DTG curve is deconvolved. For this, five pseudo-components are used in an inert atmosphere (nitrogen) and seven in an oxidative atmosphere (air).

In the first case (nitrogen) four pseudo-components represent the volatilized fractions of hemicellulose, amorphous cellulose, crystalline cellulose and lignin, and the fifth the volatilized fraction of carbon obtained from the pyrolysis of the previous fractions.

In the second case (air), four pseudo components represent the volatilized fractions of hemicellulose, amorphous cellulose, crystalline cellulose and lignin, and the other three represent the oxidation of the carbons produced by hemicellulose, cellulose and lignin.

To achieve a good fit, the thermal degradation of the pseudo-components is simulated with autocatalytic kinetics (Prout-Tompkins type):

gives

----- = k (1 - car r (í tt m)

cit

where a represents the degree of conversion, n the order of reaction, m the order of nucleation (measure of the degree of autocatalysis), and k the kinetic constant, which, in turn, depends on the frequency factor k ⁰ , the activation energy E and temperature T according to the equation of

Arrhenius

Once the initial values of the pseudo-component masses and the kinetic parameters (frequency factor, activation energy, reaction order, nucleation order) have been established, deconvolution is achieved through an optimization process in the that the difference between the experimental values supplied by the thermogravimetric analysis and the sum of the thermal degradations of the referred pseudo-components is minimized. As a result of this adjustment process, the optimal values of the kinetic parameters and the contents of the pseudo-components are obtained in the analyzed sample, in particular the hemicellulose, amorphous cellulose, crystalline cellulose and lignin masses that have been volatilized. This process can be done with programs like Matlab or with a spreadsheet.

In step 230, the V / C index calculation is carried out. For this, the mass of the volatilized sample V is first calculated by adding the masses of the first four pseudo-components (they represent the volatilized masses of hemicellulose Hv, amorphous cellulose Cav, crystalline cellulose Ccv and lignin Lv). Then the carbonized sample mass is calculated: C = 100 - V. In short: V / C = V / (100-V).

In step 240, the sample hemicellulose, cellulose and lignin contents are calculated. This calculation can be carried out in two different ways: by means of the specific carbon productions of each of the biomass components (Method 1), and by means of the V / C index (Method 2).

Method 1: This method is already known and allows calculating the amounts of hemicellulose H, cellulose C and lignin L using the volatilized hemicellulose, cellulose and lignin masses (Hv; Cv and Lv) previously obtained in the thermogravimetric analysis, thus avoiding calculate the V / C parameter as an intermediate step. For this, we would have to optimize the equation H C L = 100, where H = c1Hv; C = c2 (Ccv + Cav); L = c3Lv, where parameters c1, c2 and c3 represent the intrinsic tendencies of the pseudo-components to form carbon. Taking the standard initial values according to the analyzed biomass, an adjustment procedure similar to that of step 230 can be established to calculate their optimal values and, consequently, the contents of hemicellulose, cellulose and lignin in the sample. For this you can use a spreadsheet.

Method 2: In this method, object of the invention, the composition is obtained directly from the V / C index determined in step 230. For this, it is necessary to proceed to a previous calibration according to method 100, which, after chemical analysis and thermogravimetric of various biomasses, allow establishing the constants f1 to f5 of the following linear relationships between the contents of hemicellulose H, cellulose C and lignin L with the V / C index.

H = f1 + f2 (V / C)

C = f3 + f4 (V / C)

L = f5-f6 (V / C)

In step 250, the potential yield of a biomass paste is calculated from the V / C index.

In step 270, the necessary alkali is calculated to obtain a paste with a preset kappa index starting from the V / C index.

In step 260, the necessary H index is calculated to obtain a paste of a prefixed kappa index starting from the V / C index.

For the calculations of steps 250, 260 and 270, a previous calibration according to method 100 is necessary.

Another of the preferred embodiments of this invention is aimed at determining the V / C index in pastes and its application in determining parameters of interest in the cooking and bleaching process. In this example the V / C index is calculated according to the method 300 described below and whose flow diagram is represented in figure 3.

In step 310 of thermogravimetric analysis, a 5-15 mg sample of the material to be analyzed is placed on a thermobalance. Thermogravimetric analysis is carried out in nitrogen or air from room temperature up to 750 ° C with a heating rate of 10 ° C / min. As a result of this analysis, thermogravimetric data will be obtained indicating the percentage of loss of mass (TG curve) and the speed of mass loss (DTG curve) for each time and temperature.

In step 320, the DTG curve is deconvolved. For this, five pseudo-components are used in an inert atmosphere (nitrogen) and seven in an oxidative atmosphere (air).

In the first case (nitrogen) four pseudo-components represent the volatilized fractions of hemicellulose, amorphous cellulose, crystalline cellulose and lignin, and the fifth the volatilized fraction of carbon obtained from the pyrolysis of the previous fractions.

In the second case (air), four pseudo components represent the volatilized fractions of hemicellulose, amorphous cellulose, crystalline cellulose and lignin, and the other three represent the oxidation of the carbons produced by hemicellulose, cellulose and lignin.

To achieve a good fit, the thermal degradation of the pseudo-components is simulated with autocatalytic kinetics (Prout-Tompkins type):

where a represents the degree of conversion, n the order of reaction, m the order of nucleation (measure of the degree of autocatalysis), and k the kinetic constant, which, in turn, depends on the frequency factor k ⁰ , the activation energy E and temperature T according to the equation of

Arrhenius

Once the initial values of the masses of the pseudo-components and of the kinetic parameters (frequency factor, activation energy, reaction order, order) have been established nucleation), deconvolution is achieved through an optimization process in which the difference between the experimental values supplied by the thermogravimetric analysis and the sum of the thermal degradations of the referred pseudo-components is minimized. As a result of this adjustment process, the optimal values of the kinetic parameters and the contents of the pseudo-components are obtained in the analyzed sample, in particular the hemicellulose, amorphous cellulose, crystalline cellulose and lignin masses that have been volatilized (Hv , Cav, Ccv, Lv). This process can be done with programs like Matlab or with a spreadsheet.

In step 330, the V / C index calculation is performed. For this, the mass of the volatilized sample V is first calculated by adding the masses of the first four pseudo-components (they represent the volatilized masses of hemicellulose Hv, amorphous cellulose Cav, crystalline cellulose Ccv and lignin Lv). Then the carbonized sample mass is calculated: C = 100 - V. In short: V / C = V / (100-V).

In step 340, the hemicellulose, cellulose and lignin contents of the sample are calculated. This calculation can be carried out in two different ways: by means of the specific carbon productions of each of the biomass components (Method 1), and by means of the V / C index (Method 2).

Method 1: This method is already known and allows calculating the amounts of hemicellulose H, cellulose C and lignin L using the volatilized hemicellulose, cellulose and lignin masses (Hv; Cv and Lv) previously obtained in the thermogravimetric analysis, thus avoiding calculate the V / C parameter as an intermediate step. For this, the equation H + C + L = 100 would have to be optimized, where H = c1Hv; C = c2 (Ccv + Cav); L = c3Lv, where parameters c1, c2 and c3 represent the intrinsic tendencies of the pseudo-components to form carbon.

Taking the standard initial values according to the biomass analyzed, an adjustment procedure similar to that of step 330 can be established to calculate their optimal values and, consequently, the contents of hemicellulose, cellulose and lignin in the sample. For this you can use a spreadsheet.

Method 2: In this method, object of the invention, the composition is obtained directly from the V / C index determined in step 330. For this, it is necessary to proceed to a previous calibration according to method 100, which, after chemical analysis and thermogravimetric of various biomasses, allow establishing the constants f1 to f5 of the following linear relationships between the contents of hemicellulose H, cellulose C and lignin L with the V / C index.

H = f1 + f2 (V / C)

C = f3 + f4 (V / C)

L = f5-f6 (V / C)

In step 350, the kappa index of the paste is calculated from the V / C index.

In step 360 the cellulose crystallinity of the pulp is calculated from the V / C index.

For the calculations of steps 350 and 360, a previous calibration according to method 100 is necessary.

Figure 4 shows a flow chart of one of the preferred embodiments of this invention directed to data processing modules.

Module 410 receives thermogravimetric data on biomass and / or cellulose pulps. Module 420 calculates the V / C index. Module 430 calculates biomass composition from the V / C index or from thermogravimetric data and specific coal productions. Module 440 calculates the composition of pastes from the V / C index or from thermogravimetric data and specific coal productions. Module 450 calculates the paste yield of a given biomass. Module 470 calculates the H factor necessary for the cooking of a biomass to produce a paste of the desired characteristics. Module 490 calculates the active alkali necessary for the cooking of a biomass to produce a paste of the desired characteristics. Module 460 calculates the kappa index of a given V / C index paste. Module 480 calculates the crystallinity of a given V / C index paste.

On the other hand, Figure 5 shows a block diagram of a computing system 500 in which the present invention can be implemented.

The computer system has a central processing unit (processor) 520, an input / output interface 530 and a support circuit 540. In certain embodiments of the In the present invention, where the computer system requires a direct human interface, a display 510 and a data input device 550 such as keyboard or mouse will also be required.

The display 510, the data input device 550, the processor 520 and the support circuit 540 will be connected to a bus (digital system that transfers data between the components of a computer or between several computers) that, in turn, will be connected to memory 560. Program 570 and data storage memories 580 may include volatile (RAM) or nonvolatile (ROM) memory units and may also contain hard drives and backup storage capacity.

The program storage memory 570 stores the associated software and data modules, and in particular will store the modules 410 to 490 described in Figure 4.

Data storage memory 580 will store the results and other data generated by one or more modules of the present invention. This computer system 500 can be a personal computer, minicomputer, or the like. Computer system 500 supports an operating system, for example, stored in program storage memory 570 and executed in processor 520.

Example 1.- Correlation between the composition of eucalyptus woods and its kappa 16 index pulps with the V / C indices.

A selection of woods was made so as to cover the widest possible spectrum of paste yields after cooking by the kraft method.

Once subjected to acetone extraction, all the samples were subjected to two types of analysis: determination of lignin Klason and HPLC to determine the contents of hemicellulose, cellulose and lignin and thermogravimetry to determine the V / C index according to the procedure previously described. For this, 5 mg of each of them were heated in a thermobalance from room temperature to 700 ° C in inert (nitrogen) and oxidative (air) atmospheres. Heating rates were 5, 10 and 20 ° C / min.

The V / C index was found to maintain a linear relationship with the cellulose and lignin contents of the woods and with the cellulose content of the raw pulps (see figure 6). The Data shown in Figure 6 pertain to heating rates of 10 ° C / min and inert atmosphere.

Table 1 collects the information obtained from 12 woods of different species of eucalyptus and their respective raw kappa 16 pastes. The eucalyptus woods are ordered from the highest yielding paste (E1) to the lowest yielding (E12).

Table 1. Parameter V / C (in nitrogen and air) and composition of the eucalyptus woods and of the raw pastes of number kappa 16 obtained after the cooking process.

-Cel: Cellulose; Hem: Hemicellulose; Lig: Lignin

-V / C: ratio between the volatilized and charred mass during heating in nitrogen (N) or in air (A).

-Wood: E1-E8 Globulus; E9-E11 Urograndis; E12 Rostrata.

Once subjected to extraction in acetone, all samples were subjected to two types of analysis: determination of lignin Klason and HPLC to determine the contents of hemicellulose, cellulose and lignin, and thermogravimetry to determine the V / C index according to the method previously described. For this, 5mg of each of them were heated in a thermobalance from room temperature to 700 ° C in inert (nitrogen) and oxidative (air) atmospheres.

The heating rates were 5, 10 and 20 ° C / min, with the exposed data being those obtained at 10 ° C / min. As can be verified, the V / C index maintains a linear relationship with the cellulose and lignin contents of the woods and with the cellulose content of the raw pulps (see figure 6). The exposed data are those that correspond to V / C in an inert atmosphere. Usually the V / C parameter measured in an inert atmosphere changes between 2.0 and 3.5 in woods and between 3.5 and 5.5 in pulps, regardless of the origin of the sample analyzed.

As shown in Table 1, pastes from the same kappa (16) can have compositions that differ by up to 6% in cellulose or hemicellulose. It has been verified that the pastes of a certain kappa index from low yield woods (E11 and E12) that (to eliminate their high lignin contents) have been subjected to high alkalinities in the digester, produce pulps with a higher proportion of cellulose than high-performance woods (see table 1).

The high alkalinity that has been used in its production removes more lignin at the cost of further degrading carbohydrates, mainly hemicellulose, and producing a paste with lower viscosity. Obviously, these pastes will have different physical properties from those obtained from high-performance woods, which have been obtained with less aggressive alkaline digestions and retain an even higher proportion of hemicellulose and a greater degree of polymerization in cellulose.

In this sense, it must be taken into account that the kappa number is a measure of the oxidizable matter present in the paste and that for pastes obtained from broadleaved (eg eucalyptus) the greatest contributions to the total kappa number are made by residual lignin and hexenuronic acids (HexA) formed during cooking (carbonyl groups may also be of importance). Given that the lignin and HexA contents of the pastes evolve inversely to changes in alkalinity in the digester, it is possible that there are pastes with the same kappa number that belong to two different categories: those with low lignin content and high HexA and those with high lignin content and low HexA. Between both extremes all the intermediate possibilities fit. In short, obtaining pastes of the same kappa index from different woods does not guarantee obtaining products of the same composition and physical-chemical behavior.

This fact that has been described is known in the cellulose pulp industry, but in the absence of a new index that solves the deficiencies of the kappa index, the industry must resort to empirical solutions such as those used in plants that have two cooking lines, one specialized in high-performance woods and the other in low-performance woods.

In this type of facility it is known that the raw pastes of the same kappa number obtained in the two production lines have very different behaviors in the subsequent bleaching stages and, therefore, if you want to mix these pastes in a common discharge tub In order to feed the subsequent delignification-bleaching process, it is necessary that the line fed with low-yield wood produces a paste with a number kappa several units higher than that obtained in the high-performance wood line. In this way, process engineers produce pastes of different kappa indices from different woods without knowing, until now, that they were producing pastes of the same V / C index.

The method of the invention is supported by tests carried out, such as those represented in Figure 7, in which pulp of kappa number 16 from high-performance wood (eg Globulus E2) has the same V / C index as a paste of number kappa 21 that comes from a low-yielding wood such as Rostrata eucalyptus (E12).

Example 2.- Determination of the paste yield of various samples of eucalyptus. Thermogravimetric method for the selection of woods based on their paste performance. Usefulness of the V / C parameter in estimating the wood pulp yields of different eucalyptus species.

Table 2. Characterization of the cooking process of different eucalyptus woods and the raw pasta obtained according to the established kappa number.

-Wood: E1-E8 Globulus; E9-E11 Urograndis; E12 Rostrata.

-Active alkali: Measures the content of NaOH and Na2S in the white liquor and is expressed as 10 grams of Na2O in 100mL of white liquor.

-Professional yield: Measured as grams of pulp obtained for every 100g of treated wood.

As described in procedure 100 of the present invention, Table 2 summarizes the results obtained by subjecting various eucalyptus woods (of the Glóbulus, Urograndis and Rostrata varieties) to firings with different levels of active alkali. In all tests, the following variables were stable: hydromodule 3.5: 1, sulfidity 25%, maximum temperature 165 ° C, temperature rise time 90 minutes, temperature rest time 50 minutes (factor H = 578 ). After each test, the following parameters were measured: residual alkali, crude yield, rejection of uncooked, kappa index and viscosity of the paste obtained.

For each wood the yield increased as the kappa number of the pulp obtained decreased. In all cases, a linear relationship was obtained between both parameters. This allowed to establish by interpolation the active alkali that produces pastes with kappa number 16 or 20. It was also found that: i) the viscosity of the obtained paste decreased linearly as the active alkali of cooking increased, and ii) there was a relationship linear between paste viscosity and measured performance.

Given that both the tendency to produce volatiles (or carbon) from a wood and its yield in pulp depend on the composition, it is expected that there is some kind of relationship between both variables. Figure 8 shows that this relationship exists and is especially Simple: woods with higher V / C parameters are also those that produce the highest paste yield, both for kappa number 16 and for kappa number 20.

In short, the cellulose content affects the formation of volatiles and the production of pulp in the same proportion. This fact is of great interest for the selection of high-performance clones since an alternative to infrared spectroscopy (NIR) would be available as a quick and cheap analysis of the cellulose content in forest plantations. In this sense, the advantages of thermogravimetry seem evident since its results are not affected by so many variables.

Example 3.- Determination of the optimal active alkali to obtain a cellulose paste with a predetermined kappa index.

Figure 9 shows the linear relationship between the active alkali of various firings and the V / C indexes of the eucalyptus woods used to obtain kappa index 16 pastes. This fact shows that the thermogravimetric control of the eucalyptus wood allows establish a priori the optimal operating conditions in the cooking process.

Example 4.- Procedure for the application of thermogravimetric control in the cellulose pulp industry

The application of the thermogravimetric control of wood and cellulose pulps according to the present invention has two great advantages over the current one: i) the company can acquire woods on the market based on economic criteria since the ignorance of their behavior during the firing will not imply expensive previous analyzes to guide the engineer during his firing, and ii) the firing conditions will be established prior to the digestion of the wood, without waiting for subsequent analyzes of the kappa number of the pulp obtained to inform of the necessary changes in active alkali or factor H.

The procedure for applying the present invention would be as follows:

i. Adaptation to the digestion system of the industrial plant

For its application in a specific industrial installation, the method proposed in the present invention requires a process of adaptation to the cooking procedures used therein.

The objective would be to introduce the necessary corrections into the already known standard correlations between type of wood, cooking conditions and characteristics of the pulp obtained. Several controlled firings would be necessary, carried out in the factory's digesters, applied to the usual woods in order to produce the usual pastes. As a final result of this process, thermogravimetric data of woods and pulps will be obtained, which will be related to each other by means of cooking processes specific to each industrial factory. Apply calibration method 100.

ii. Application in the selection of high-yield paste clones

A wood sample (in the order of milligrams) will be taken to carry out the corresponding thermogravimetric analysis and calculate the V / C parameter. The latter will report the cellulose and lignin content and the potential paste yield.

iii. Optimization of digestion conditions

Once the wood's V / C parameter has been determined and the adaptation tests to the factory's firing process have been carried out, the control engineer can adopt the appropriate digestion conditions to obtain a preset V / C paste or kappa number. To confirm that the digestion process is operating properly, a thermogravimetric analysis of the raw pasta obtained will be performed. This will confirm that the V / C parameter setpoint has been reached and, if not, the necessary measures can be taken to achieve this.

Claims (6)

1. Method for determining the content of hemicellulose, cellulose and lignin in biomasses and lignocellulosic pastes, characterized in that it comprises the following steps: (a) analyzing a sample of biomass and / or lignocellulosic paste by means of a thermogravimetric analysis; (b) represent the thermogravimetric data obtained in step (a) indicating the percentage of mass loss (TG curve) and the speed of mass loss (DTG curve) for each time and temperature; (c) perform the calculation of the V / C index from the thermogravimetric data using the formula: V / C = V / (100-V) where V is the mass of the volatilized sample and C is the mass of the charred sample, calculated as C = 100 - V; (d) determine the amount of hemicellulose, cellulose, and lignin in the sample using linear relationships that depend on the parameter V / C. 2. Method according to claim 1, characterized in that the biomass and lignocellulosic pastes are selected from the group comprising woods, cellulosic pastes, herbaceous or residual materials. 3. Method according to claim 1, characterized in that the analysis of the lignocellulosic biomass sample from step (a) can be carried out in an inert or oxidizing atmosphere. 4. Method according to claim 1, characterized in that the analysis of the lignocellulosic biomass sample from step (a) can be carried out at heating rates between 5 and 20 ° C / min. 5. Method according to claim 4, characterized in that the analysis of the lignocellulosic biomass sample from step (a) can be carried out at a heating rate of 10 ° C / min. 6. Method according to any of claims 1 to 5, characterized in that it can be used at the end of the digestion and the successive bleaching stages of the biomass and lignocellulosic pastes.