Method for producing a phosphorylated lignin, phosphorylated lignin, and use thereof

Abstract

The present invention relates to a method for producing a phosphorylated lignin with reduced washing water consumption. The invention also relates to the phosphorylated lignin obtained by the method, and to the use thereof.

Description

[0001] “PROCESS OF PRODUCTION OF A PHOSPHORYLATED LIGNIN, LIGNIN

[0002] PHOSPHORYLATED AND ITS USE”

[0003] FIELD OF INVENTION

[0004]

[0001] The present invention is directed to a process for producing phosphorylated lignin with lower consumption of washing water. The invention also relates to the phosphorylated lignin obtained by the process and its use.

[0005] HISTORY OF THE INVENTION

[0006]

[0002] In recent years, there has been growing interest in obtaining processes that reduce the consumption of renewable resources such as water and reduce environmental impact.

[0007]

[0003] Prieur and collaborators (PRIEUR, B. et al. Phosphorylation of lignin: characterization and investigation of the thermal decomposition. RSC advances, v. 7, n. 27, p. 16866-16877, 2017.) investigates the thermal decomposition of phosphorylated lignin and reveals a phosphorylation process that uses lignin dissolved in tetrahydrofuran (THF) and phosphorus pentoxide, using water to transform the excess phosphorus pentoxide used in the process into phosphoric acid. However, Prieur does not reveal optimal proportions in order to reduce water consumption in washing the phosphorylated lignin obtained to remove the phosphoric acid generated.

[0008]

[0004] Document US3081293 discloses a lignin and phosphorus compound prepared by the reaction of lignin and phosphorus pentoxide at a temperature between room temperature and approximately 200°C for 10 min to 72 hours, in which the reaction is carried out in a solvent. However, US3081293 does not solve the problem of synthetic routes for producing modified lignin that do not use a stoichiometric amount of the components during the synthesis of the modified lignin, as well as the amount of the phosphorylating agent per lignin hydroxyl units. The present invention uses quantities and composition of components in the chemical modification of lignin, including a reduced amount of water required to transform the excess phosphorus pentoxide into phosphoric acid, which is subsequently neutralized. Furthermore, the recovery of the solvent during the modification process of the present invention, through vacuum distillation, still allows the reuse of the solvent.

[0009]

[0005] In this way, the processes for obtaining phosphorylated lignin that report washing with water for the complete removal of the phosphoric acid that is formed during the addition of water to the reaction medium. In the present invention, an initial wash of the material is carried out with an alkaline aqueous solution of pH between 10 - 12, which drastically reduces the number of necessary washes, with a process for producing phosphorylated lignin that becomes beneficial to the environment while being economically more viable.

[0010] SUMMARY OF THE INVENTION

[0011]

[0006] A first embodiment of the present invention is directed to a process for producing a phosphorylated lignin comprising the steps: a) Providing at least one aprotic solvent; b) Adding a lignin to form a mixture of lignin and aprotic solvent; c) Heating the mixture of aprotic solvent and lignin to a maximum of 80% of the boiling point of the aprotic solvent at the pressure used; d) Adding the phosphorylating agent to the mixture of lignin and aprotic solvent at a molar ratio of between 0.5:1 and 5:1 of phosphorylating agent / total hydroxyl of the lignin, providing a reaction mixture of aprotic solvent, lignin and phosphorylating agent; e) Heating the reaction mixture to a maximum of 90% of the boiling point of the aprotic solvent at the pressure used.f) Maintaining the reaction of the reaction mixture to obtain a reaction product comprising a phosphorylated lignin, which has a thermal resistance index (THRI) higher than the lignin initially used as raw material, preferably between 100-200. e C; g) Cooling of the reaction product to a temperature range lower than 15 eC; h) Addition of water in a ratio of 1 - 5 moles of water to 1 mole of phosphorylating agent; i) Maintaining the reaction product under stirring for 15-30 minutes, providing a reaction mixture; j) Distillation of the reaction mixture to recover the aprotic solvent to obtain a recovered distilled solvent and a distillation residue comprising phosphorylated lignin; k) After distillation and recovery of 25-85% of the initial volume of aprotic solvent from the reaction mixture, the distillation residue comprising phosphorylated lignin is dispersed in an aqueous alkaline solution with pH>10. l) Recovery of phosphorylated lignin from the dispersion of step k).

[0012]

[0007] A second embodiment of the invention relates to phosphorylated lignin obtained from said process.

[0013]

[0008] A third embodiment of the invention concerns the use of phosphorylated lignin obtained from said process.

[0014] FIGURES

[0015]

[0009] Figure 1 is a statistical analysis representing the presence of aliphatic OH of the phosphorylated lignin obtained by the process of the present invention and an unmodified kraft lignin.

[0016]

[0010] Figure 2 illustrates FTIR results comparing the spectra of examples 1, 2, 3 and 4 of the present invention and an unmodified kraft lignin.

[0017]

[0011] Figure 3 illustrates TGA results of Examples 1, 2, 3 and 4, as well as that of unmodified kraft lignin.

[0018]

[0012] Figure 4 illustrates the first derivative of the TGA results of Examples 1, 2, 3 and 4, as well as that of unmodified kraft lignin.

[0019]

[0013] Figure 5 represents the statistical difference illustrating the significant difference in the initial degradation temperature of Example 1 of the lignin obtained by the process of the present invention in relation to the reference kraft lignin (KL).

[0020] DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention is directed to a process for producing a phosphorylated lignin comprising the steps: a) Providing at least one aprotic solvent; b) Adding a lignin to form a mixture of lignin and aprotic solvent; c) Heating the mixture of aprotic solvent and lignin to a maximum of 80% of the boiling temperature of the aprotic solvent at the pressure used; d) Adding the phosphorylating agent to the mixture of lignin and aprotic solvent at a molar ratio between 0.5:1 and 5:1 moles of phosphorylating agent / total hydroxyl of the lignin, providing a reaction mixture of aprotic solvent, lignin and phosphorylating agent; e) Heating the reaction mixture to a maximum of 90% of the boiling temperature of the aprotic solvent at the pressure used.f) Maintaining the reaction of the reaction mixture to obtain a reaction product comprising a phosphorylated lignin, which has a thermal resistance index (THRI) higher than the lignin initially used as raw material, preferably between 100-200. e C; g) Cooling of the reaction product to a temperature range between 15°C and 15°C. eC; h) Addition of water in a ratio of 1 - 5 moles of water to 1 mole of phosphorylating agent; i) Maintaining the reaction product under stirring for 15 - 30 minutes, providing a reaction mixture; j) Distillation of the reaction mixture to recover the aprotic solvent to obtain a recovered distilled solvent and a distillation residue comprising phosphorylated lignin; k) After distillation and recovery of 25-85% of the initial volume of aprotic solvent from the reaction mixture, the distillation residue comprising phosphorylated lignin is dispersed in an aqueous alkaline solution with pH> 10. l) Recovery of phosphorylated lignin from the dispersion of step k).

[0021]

[0015] The aprotic solvent or solvent mixture used in the process of the present invention may be an aprotic solvent that has a RED less than or equal to 1.0 according to the Hansen solubility parameter. For example, and in a non-limiting manner, the aprotic solvent may be an aprotic solvent selected from Dimethyl sulfoxide (DMSO), Dimethylformamide (DMF), Tetrahydrofuran (THF), dioxane and mixtures thereof.

[0022]

[0016] Step b) of the process of the present invention comprises adding a lignin to form a mixture of lignin and aprotic solvent. The aprotic solvent can be added to the lignin or, preferably, the lignin can be added to the aprotic solvent. In either case, the addition of the aprotic solvent to the lignin or of the lignin to the aprotic solvent can be carried out under agitation, for example, by mixers, or the addition of one to the other can be carried out first and then stirring is carried out.

[0023]

[0017] Furthermore, step b) of the process according to the present invention may comprise the addition of lignin between 20% and 50% by mass of the total mass of the mixture of lignin and aprotic solvent. Step b) may be carried out at a temperature between 15 e C up to a value equivalent to 50% of the boiling point of the solvent used and, preferably, 15-30 e C, at a residence time of between 20-40 minutes.

[0024]

[0018] The lignin used in the present invention for the modification reaction via phosphorylation may have a total hydroxyl content between 3 - 8 mmol / g. Accordingly, the lignin used may have a solids content above 95%, a pH between 3 - 7 and an ash content of less than 5%. Characteristically, the lignin may be a softwood or hardwood lignin from kraft processes, or a technical lignin generated after pyrolysis of wood biomass.

[0025]

[0019] Step c) of the process of the present invention may consist of heating the mixture of aprotic solvent and lignin to a maximum of 80% of the boiling temperature of the aprotic solvent at the operating pressure. For example, if carried out at atmospheric pressure such as 1 atm., the heating of the mixture of aprotic solvent and lignin occurs to a maximum of 80% of the boiling temperature of the aprotic solvent at 1 atm. If such heating occurs at a pressure lower or higher than 1 atm., the heating, accordingly, occurs to 80% of the boiling temperature of the aprotic solvent at the determined operating pressure.

[0026]

[0020] Preferably, step d) provides a reaction mixture formed by the addition of the phosphorylating agent to the mixture of lignin and aprotic solvent, providing a reaction mixture formed by the aprotic solvent, lignin and phosphorylating agent. Preferably, the addition of the phosphorylating agent is carried out at a molar ratio of between 0.5:1 and 5:1 moles of the phosphorylating agent used in relation to the amount of moles of total hydroxyl of the lignin. Furthermore, step d) can be carried out for, for example, between 20 - 40 minutes.

[0027]

[0021] The phosphorylating agent used in step d) of the process of the present invention may be a phosphorylating agent selected from: phosphorus pentoxide, phosphoric anhydride, hypophosphorous acid, phosphorus oxychloride, and mixtures thereof.

[0028]

[0022] Step e) of the process of the present invention may consist of heating the reaction mixture to a maximum of 90% of the boiling point of the aprotic solvent at the operating pressure. For example, if carried out at a pressure of 1 atm., the heating of the reaction mixture occurs to a maximum of 90% of the boiling point of the aprotic solvent at a pressure of 1 atm. If such heating occurs at a pressure lower or higher than 1 atm., the heating, accordingly, occurs to 90% of the boiling point of the aprotic solvent at the determined operating pressure.

[0029]

[0023] As already stated, the aprotic solvent used in the process of the present invention may be a mixture of aprotic solvents. In this case, a mixture of aprotic solvents may potentially present aprotic solvents with different boiling points or even the formation of a eutectic mixture. In any case, the present invention provides that the temperature of steps c) or d) is, respectively, at 80% and 90% of the boiling temperature of the most volatile aprotic solvent or of the eutectic mixture, if more volatile, in the mixture. Thus, for example, if a mixture of two or more aprotic solvents is used in the invention, the maximum temperature of 80% for step c) and 90% for step e) is calculated based on the boiling temperature of the solvent that has the lowest boiling temperature at that operating pressure.Furthermore, if a eutectic mixture is formed that eventually has the lowest boiling point for that operating pressure, this is chosen as the reference for determining the operating temperature in steps c) and e). For example, if steps c) and e) are operated at 1 atm., heating in steps c) and e) occurs, respectively, to a maximum of 80% and 90% of the boiling point of the aprotic solvent at a pressure of 1 atm. If such heating occurs at a pressure lower or higher than 1 atm., heating, accordingly, occurs up to 90% of the boiling point of the aprotic solvent at the determined operating pressure, or of its eutectics, whichever is lower, as already explained.

[0030]

[0024] Step f) of the process may comprise maintaining the reaction of the reaction mixture, formed by the mixture of aprotic solvent, lignin and phosphorylating agent, to obtain a reaction product comprising a phosphorylated lignin that has a heat-resistance index (THRI) greater than that of unmodified lignin. It is known that the THRI is a measurement of a material's ability to resist a heat flow. Thus, the higher this parameter, the more heat resistance the material will have and, consequently, the greater its performance as a flame retardant, one of the possible applications of phosphorylated lignin.

[0031]

[0025] In any case, after the period of formation of the phosphorylated lignin, the process of the present invention may comprise step g) of cooling the reaction product to a temperature range to a temperature lower than 15 e W.

[0032]

[0026] The process may further comprise step h) of adding water to the reaction product in a ratio of 1-5 moles of water for each 1 mole of phosphorylating agent added in step d) of the present process. The addition of water to the reaction product of step h) may be carried out in, for example, up to 60 minutes. After the addition of water in step h), the mixture of water and reaction product may be kept under mixing for, for example, 15-30 minutes, preferably 30 minutes, providing an aqueous reaction mixture.

[0033]

[0027] Step j) of the present process comprises distilling the reaction mixture to recover the aprotic solvent to obtain a recovered distilled solvent and a distillation residue comprising phosphorylated lignin. Thus, distillation step j) of the process of the present invention can be carried out under a pressure of 1 atm. or under reduced pressure.

[0034]

[0028] Distillation is preferably conducted depending on the boiling temperature and the solvent, as well as the pressure used in the distillation.

[0035]

[0029] The process of the present invention also has a dispersion step k) which can be carried out after distillation and recovery of at least 70% of the initial volume of aprotic solvent from the reaction mixture. The dispersion step k) of the present process, after the distillation of step j), also includes the collection of the residue obtained from the distillation, comprising phosphorylated lignin, in which it is taken to a distillation residue dispersion step, which can be carried out at a pH greater than 10. To obtain such a pH range, a pH adjustment can be carried out with alkalizing agents selected from alkaline hydroxides, carbonates, amines, ammonium hydroxide. For example, for a distillation residue comprising phosphorylated lignin normally obtained from distillation step j) it can be dispersed at 10% mass / mass in an alkalizing agent solution with pH=12.

[0036]

[0030] In any case, the step of washing the distillation residue to obtain a phosphorylated lignin advantageously consumes a smaller volume of washing water.

[0037]

[0031] Furthermore, the process according to the present invention comprises a step m) of washing the phosphorylated lignin obtained in step f) with water until a pH >3 is reached. Preferably, step m) is carried out after step i) of recovering the phosphorylated lignin from the dispersion and aqueous alkaline solution of step k). In this way, the phosphorylated lignin is recovered from the dispersion of step k) and removed for washing with water. The process, object of the present invention, thus obtains lower water consumption values ​​in the washing process.

[0038]

[0032] Advantageously, reducing water consumption presents several benefits, such as lower environmental impact, making the process more economically viable, since it drastically reduces consumption to obtain the product within the specification (pH>3).

[0039]

[0033] In this way, the process according to the present invention may further comprise a step m) of filtering and drying the phosphorylated lignin.

[0040]

[0034] In another embodiment, the use of phosphorylated lignin obtained by the process of the present invention is described for applications in thermoplastics, thermosets, rubber, paper, water treatment and agriculture. In a preferred embodiment, the use of phosphorylated lignin obtained by the process of the present invention as a flame retardant is disclosed.

[0041] Examples

[0042] Example 1

[0043]

[0035] In a 2 L flask, 890 grams of THE and 100 grams of lignin were added within 30 minutes at room temperature with stirring at 300 rpm. The system was heated to 60°C and 68 grams of phosphorus pentoxide were added to the mixture. Then, a reflux system was coupled and the reaction was maintained until the THRI of the final product was greater than the lignin used. After the reaction period, the temperature of the system was cooled to a range of 3-10°C with an ice bath around the flask and then 35 grams of water were added gradually to minimize exotherm. The system was kept mixed for 30 minutes. The temperature was raised to 40°C and a vacuum distillation system was coupled to distill and recover the THF solvent. Then, the distillation residue was dispersed in an aqueous NaOH solution with a pH between 10 - 12 and filtered.After filtration, the material was thoroughly washed until a pH of 2-5 was reached. The material was then dried in a vacuum oven for 48 hours at 40°C. Phosphorylated lignin was thus obtained from the phosphorylation reaction of lignin with phosphorus pentoxide, considering a 1:1 moles of pentoxide / total OH of lignin ratio.

[0044]

[0036] Phosphorylated lignin was obtained according to the following consumption illustrated in Table 1:

[0045] Table 1

[0046] Example 2

[0047]

[0037] In a 2 L flask, 890 grams of THF and 100 grams of lignin were added within 30 minutes at room temperature with stirring at 300 rpm. The system was heated to 60°C and 170 grams of phosphorus pentoxide were added. Then, the reflux system was coupled and the reaction was maintained for 8 hours. After the reaction period, the temperature of the system was cooled to a range of 3-10°C with an ice bath around the flask and then 86 grams of water were added to minimize the exotherm. The system was kept mixed for 30 minutes. The temperature was raised to 40°C and the vacuum distillation system was coupled to distill the THF solvent. After the distillation step for solvent recovery, the material was dispersed in an aqueous NaOH solution with a pH between 10-12 and filtered. After filtering, the material was washed until a pH of between 2 and 5 was reached. The material was then dried in a vacuum oven for 48 hours at 40°C.

[0038] The modified lignin was obtained by the phosphorylation reaction with phosphorus pentoxide considering a ratio of 2.5:1 (moles of pentoxide / total OH of lignin).

[0048]

[0039] Phosphorylated lignin was obtained according to the following consumption illustrated in Table 2:

[0049] Table 2

[0050] Example 3

[0051]

[0040] In a 2 L flask, 890 grams of THE and 100 grams of lignin were added within 30 minutes at room temperature with stirring at 300 rpm. The system was heated to 60°C and 339 grams of phosphorus pentoxide were added. Then, the reflux system was coupled and the reaction was maintained for 8 hours. After the reaction period, the temperature of the system was cooled to a range of 3-10°C with an ice bath around the flask and then 172 grams of water were added to minimize the exotherm. The system was kept mixed for 30 minutes. The temperature was raised to 40°C and the vacuum distillation system was coupled to distill the THE solvent. After the distillation step for solvent recovery, the material was dispersed in an aqueous NaOH solution with a pH between 10-12 and filtered. After filtering, the material was thoroughly washed until reaching a pH between 2 and 5.The material was then dried in a vacuum oven for 48 hours at 40°C. The modified lignin was obtained by the phosphorylation reaction with phosphorus pentoxide considering a ratio of 5:1 (moles of pentoxide / total OH of lignin).

[0052]

[0041] Phosphorylated lignin was obtained according to the following consumption illustrated in Table 3:

[0053] Table 3

[0054] Example 4

[0055]

[0042] In a 2 L flask, 890 grams of THE were added. Then, 100 grams of lignin were added within 30 minutes at room temperature with stirring at 300 rpm. The system was heated to 60°C, and 34 grams of phosphorus pentoxide were carefully added to the reaction. Then, the system was coupled to reflux, and the reaction was maintained for 8 hours. After the reaction period, the temperature of the system was cooled to a range of 3-10°C with an ice bath around the flask, and then 18 grams of water were gradually added to minimize exotherm. The system was kept mixed for 30 minutes. The temperature was raised to 40°C, and the vacuum distillation system was coupled to distill the THE. After the distillation step for solvent recovery, the material was dispersed in an aqueous NaOH solution with a pH between 10-12 and filtered. After filtering, the material was thoroughly washed until a pH of between 2 and 5 was reached.The material was then dried in a vacuum oven for 48 hours at 40°C.

[0043] The lignin was modified through the phosphorylation reaction with phosphorus pentoxide considering a ratio of 2:1 (moles of pentoxide / total OH of lignin).

[0056]

[0044] Phosphorylated lignin was obtained according to the following consumption illustrated in Table 4:

[0057] Table 4

[0058] Example 5

[0059]

[0045] In a 50 L reactor, 20,000 grams of THE were added. Then, 2,000 grams of lignin were added within 30 minutes at room temperature with stirring at 100 rpm. The system was heated to 50°C, and 1,360 grams of phosphorus pentoxide were carefully added to the reaction. The reaction was maintained for 8 hours at 60°C without using reflux. After the reaction period, the system temperature was cooled to 25°C, and 688 grams of water were added to the reactor. The system was kept mixed for 30 minutes. The temperature was raised to 65°C, and the THE distillation process began. 14 liters of THF were distilled after 2 hours. After this step, the material was dispersed in an aqueous NaOH solution with a pH between 10 and 12 and filtered. After filtration, the material was thoroughly washed until a pH of between 2 and 5 was reached. The material was then dried in a vacuum oven for 48 hours at 40°C.

[0060]

[0046] The lignin modified through the phosphorylation reaction with phosphorus pentoxide considering a 1:1 ratio (moles of pentoxide / total OH of lignin).

[0061]

[0047] Phosphorylated lignin was obtained according to the following consumption illustrated in Table 5:

[0062] Table 5

[0063] Characterization of the obtained phosphorylated lignin

[0064]

[0048] The chemical composition, including the percentage of insoluble, soluble and total lignin, the molar masses (Mn and Mw) and the amounts of hydroxyl of examples 1, 2, 3 and 4 can be seen in Tables 6-9. For comparison purposes, information regarding the reference kraft lignin was also presented. In the tables below, the average values ​​represent a quadruplicate analysis of the conditions evaluated. The average values ​​refer to the chemical composition, molar masses and amounts of hydroxyls of the examples presented, as well as of the reference kraft lignin.

[0065] Table 6: Total lignin (%), Carbon content (%), Hydrogen content (%) and Nitrogen content (%):

[0066] Table 7: Weight molar mass (Mw) and Average molar mass (Mn):

[0067] Table 8: Aliphatic OH; Carboxylic OH and Total OH:

[0068] Table 9: Syringyl, Condensed Guaiacyl, Uncondensed Guaicyl and p-hydroxyphenyl:

[0069]

[0049] Analysis of the data presented in Tables 6-9 reveals that, in terms of the percentage of insoluble, soluble and total lignin, no significant difference was observed when comparing the reference sample with the samples obtained in the examples of the present invention. However, this does not mean that there was no change in the lignin hydroxyls, in which the lignin result demonstrates the composition of phosphorylated lignin after acid hydrolysis, which does not mean that structures with modifications in hydroxyls are not subject during analysis, being very similar to the results of kraft lignin. Except for example 3, which presented slightly lower values. This result suggests that the chemical structure of lignin was not significantly altered after the phosphorylation reaction, since it was carried out under the most critical condition of the highest phosphorus pentoxide / lignin molar ratio, as demonstrated in Example 3.In terms of molar masses, a clear trend was observed: an increase in the phosphorus pentoxide / lignin molar ratio led to an increase in molar masses, particularly Mw. Without being bound by theory, this increase may be related to two factors: the incorporation of phosphate groups into the lignin structure and, to a greater extent, the occurrence of condensation reactions via phosphate bridges during the phosphorylation reaction. Regarding chemical composition, phosphorylated lignins exhibited a lower carbon concentration, which was more pronounced for conditions with lower reactant / lignin molar ratios, and the variation in hydrogen concentration was not significant. The reduction and slight increase in carbon concentrations, respectively, are related to the addition of phosphorus to the lignin structure, which alters the original composition of the reference lignin.Finally, in relation to the quantities of different types of hydroxyls, high degrees of conversion were observed for aliphatic and carboxylic hydroxyls, hydroxyls that are more accessible in the structure of the reference lignin, represented in the graph in figure 1, indicating a statistical difference between the examples of the average results of aliphatic OH, where the averages followed by the same letter differ from each other evaluated by Tukey's comparison with 95% reliability.

[0070]

[0050] In the case of phenolic hydroxyls, lower degrees of conversion were observed. This type of hydroxyl is less accessible, since they are more sterically hindered, and in the phosphorylation reaction, the phosphate groups are attached via derivatization of the hydroxyls. Figure 1 shows the statistical analysis of the mean difference with 95% reliability by the Tukey test, showing that experiments 1, 2, and 3 have an impact on the reduction of aliphatic hydroxyls by the phosphorylation reaction, proving the effectiveness of the process used on lignin hydroxyls.

[0071] FTIR spectra

[0072]

[0051] The FTIR results are presented in Figure 2, in which the spectra of examples 1, 2, 3 and 4 cited in the document (PKL20231, PKL20232, PKL20233, PKL20234, respectively) are compared. In order to perform a qualitative analysis of the functional groups that were introduced into the modified lignin via the phosphorylation reaction, the spectrum of the reference hardwood kraft lignin (KL) is also presented. Comparing the spectra of the mentioned examples with that of the reference lignin, it is possible to observe a slight decrease in the intensity in the band associated with the stretching of hydroxyls (3380 cm-1), indicating that there was consumption of hydroxyls to the detriment of the attachment of phosphate groups. Furthermore, an increase in the intensity of the band centered at 1212 cm-1 was observed in the spectra of the examples. This band, in the case of the reference lignin, is associated with the ether bond stretching mode (C-OC).However, in this region, stretching of double bonds between phosphorus and oxygen atoms (P=O) present in phosphate groups is also observed. Therefore, the increase in intensity demonstrates the incorporation of phosphate groups into the structure of the reference lignin, confirming the chemical modification by phosphorylation.

[0073] Thermal analysis (TGA / DTG)

[0074]

[0052] The TGA results are presented in Figure 3, where the thermograms of Examples 1, 2, 3 and 4 are illustrated, as well as of the unmodified kraft lignin. Duplicate thermal analyses were therefore performed on each of the mentioned examples in order to evaluate the effect of phosphorylation on the thermal properties. Analysis of the thermograms allows us to verify that phosphorylation led to a gain in residual char (amount of carbonized mass observed after the end of the thermal analysis). It is worth noting that, in general, the amount of residual char is directly proportional to the phosphorus pentoxide / lignin molar ratio used.

[0075]

[0053] Figure 4 shows the first derivatives of the thermograms presented in Figure 3. In general, when comparing the reference lignin with the examples mentioned, it is observed that phosphorylation led to an increase in the temperature at which the most significant mass loss process occurs at the maximum rate (temperature corresponding to the maximum of the largest peak) and to a reduction in the mass loss rate of this same process. Unlike the gain in residual char, it was not possible to notice a trend between the results obtained and the phosphorus pentoxide / lignin molar ratio.

[0076]

[0054] Thus, the residual char gain observed in Figure 2, the shift in the temperature where the mass loss rate of the most significant event is maximum, and the reduction in the mass loss rate are factors that improve the flame retardancy property of the reference lignin. Therefore, the phosphorylated lignins obtained by the process of the present invention have the potential to be applied as flame retardants. In this sense, among all the examples, the one that exhibited the best performance was Example 1, in which a phosphorus pentoxide / lignin molar ratio of 1:1 is used.

[0077]

[0055] From the thermogram, the THRI can be calculated according to equation 1, where T5 and T 30 are, respectively, the temperatures at which the material lost 5 and 30% of its original mass during a mass loss analysis.

[0078] THRI — 49 x [T5 + 0.6 x (T30 — T5)]

[0079] (1 )

[0080]

[0056] Using equation 1, T5, T30 were extracted from the thermograms shown in Figure 3, and THRI calculated for the reference sample and for each of the examples. All phosphorylated samples showed, on average, a THRI higher than the reference lignin, indicating that phosphorylation led to increased heat flow resistance and flame retardancy property, as illustrated in Table 10.

[0081] Table 10

[0082]

[0057] Figure 5 shows a statistical difference using the Tukey test with 95% reliability, showing a significant difference in the initial degradation temperature of example 1 (PKL20231) in relation to kraft lignin (KL), where a phosphorus pentoxide / lignin molar ratio of 1:1 is used. It is desirable that the initial degradation temperature increases when the lignin is modified using phosphorylating reagents, with this effect being positive for acting as a flame retardant material.

[0083]

[0058] In this way, it is demonstrated that the present process for obtaining phosphorylated lignin, with the performance of an initial wash of the material with an alkaline aqueous solution of pH between 10 - 12, drastically reduces the number of necessary washes of the phosphorylated lignin obtained, being a process for producing phosphorylated lignin that becomes beneficial to the environment although economically more viable than those reported in the art.

Claims

CLAIMS 1. Process for producing a phosphorylated lignin characterized by comprising the steps: a) Providing at least one aprotic solvent; b) Adding a lignin to form a mixture of lignin and aprotic solvent; c) Heating the mixture of aprotic solvent and lignin to a maximum of 80% of the boiling temperature of the aprotic solvent at the pressure used; d) Adding the phosphorylating agent to the mixture of lignin and aprotic solvent at a molar ratio of between 0.5:1 and 5:1 moles of phosphorylating agent / total hydroxyl of the lignin, providing a reaction mixture of aprotic solvent, lignin and phosphorylating agent; e) Heating the reaction mixture to a maximum of 90% of the boiling temperature of the aprotic solvent at the pressure used.f) Maintaining the reaction of the reaction mixture to obtain a reaction product comprising a phosphorylated lignin, which has a thermal resistance index (THRI) greater than the lignin used as raw material, preferably between 100-200. e C g) Cooling of the reaction product to a temperature range between to a temperature lower than 15 e C; h) Addition of water in a proportion of 1 - 5 moles of water to 1 mole of phosphorylating agent; i) Maintenance of the reaction product under stirring for 15-30 minutes, providing a reaction mixture; j) Distillation of the reaction mixture to recover the aprotic solvent to obtain a recovered distilled solvent and a distillation residue comprising phosphorylated lignin; k) After distillation and recovery of 25-85% of the initial volume of aprotic solvent from the reaction mixture, the distillation residue comprising phosphorylated lignin is dispersed in an aqueous alkaline solution with pH>10. I) Recovery of phosphorylated lignin from the dispersion of step k).

2. Process according to claim 1, characterized in that it comprises a step m) of washing the phosphorylated lignin with water until a pH >3.

3. Process, according to claim 1, characterized by comprising a step n) of filtration and drying of the phosphorylated lignin.

4. Process according to claim 1, characterized in that the lignin from step b) is added at between 20% and 50% by mass of the total mass of the mixture of lignin and aprotic solvent.

5. Process according to claim 1, characterized in that step b) is carried out at a temperature between 15 e C up to 50% of the boiling temperature of the solvent used, preferably 15-30 e W.

6. Process, according to claim 1, characterized in that the aprotic solvent is an aprotic solvent that presents a lignin solubility determined by the Hansen solubility parameter and has a RED less than or equal to 1, which indicates a high interaction between lignin and solvent.

7. Process according to claim 1, characterized in that the aprotic solvent is a solvent selected from Dimethyl sulfoxide (DMSO), Dimethylformamide (DMF), Tetrahydrofuran (THF), dioxane and mixtures thereof.

8. Process according to claim 1, characterized in that the lignin is a lignin that has a total hydroxyl content between 3 - 8mmol / g.

9. Process, according to claim 1, characterized in that the lignin is a lignin that has a solids content above 95%, pH between 3 - 7 and ash content of less than 5%.

10. Process, according to claim 1, characterized in that the phosphorylating agent is a phosphorylating agent selected from: phosphorus pentoxide, phosphoric anhydride, hypophosphorous acid, phosphorus oxychloride, and mixtures thereof.

11. Process, according to claim 1, characterized in that step d) is carried out within 20-40 minutes.

12. Process, according to claim 1, characterized by step c) of heating the mixture of aprotic solvent and lignin to a maximum of 80% of the value of the temperature of boiling of the aprotic solvent, characterized by the value of the boiling temperature of the aprotic solvent being determined between 0.5 and 2 atm.

13. Process, according to claim 1, characterized by step e) of heating the reaction mixture to a maximum of 90% of the boiling temperature of the aprotic solvent, characterized in that the boiling temperature is determined between 0.5 and 2 atm.

14. Process according to claim 7, characterized in that the temperature of steps c) and d) is, respectively, 80% and 90% of the boiling temperature of the most volatile aprotic solvent in the mixture.

15. Process, according to claim 1, characterized by step h) of adding water to the reaction product, which can be carried out in up to 60 minutes.

16. Process, according to claim 1, characterized in that step i) of maintaining the reaction product under mixing is carried out between 5 and 60 minutes, preferably between 15 and 30 minutes.

17. Process according to claim 1, characterized in that distillation step j) is carried out in accordance with the boiling temperature of the aprotic solvent.

18. Process according to claim 1, characterized in that distillation step j) is carried out under pressure of 1 atm. or under reduced pressure.

19. Process according to claim 1, characterized in that dispersion step k) is carried out after distillation and recovery of at least 70% of the initial volume of aprotic solvent from the reaction mixture.

20. Process according to claim 1, characterized in that dispersion step k) is carried out at a pH greater than 10, and preferably between 10 - 12.

21. Process, according to claim 1, characterized in that the dispersion step k) is carried out with pH adjustment with alkalizing agents selected from alkaline hydroxides, carbonates, amines and ammonium hydroxide.

22. Process, according to claim 1, characterized by step f) for obtaining a reaction product comprising a phosphorylated lignin characterized in that the phosphorylated lignin obtained presents a heat-resistance index (THRI) between 100 and 200. e W.

23. Process, according to claim 1, characterized in that the lignin is a lignin originating from hard or soft wood.

24. Process, according to claim 17, characterized in that the lignin is a kraft lignin, or lignin from a biomass hydrolysis process as well as a product extracted from wood pyrolysis, both from hard and soft woods.

25. Phosphorylated lignin characterized by being obtained by the process as defined in any one of claims 1 to 24.

26. Phosphorylated lignin according to claim 25, characterized by presenting: i) an aliphatic hydroxyl content between 0.10 and 1.20 mmol.g -1 ; and / or ii) a THRI between 150 and 170 e C; and / or iii) a phosphorus content between 0.1 and 5.0%.

27. Use of phosphorylated lignin as defined in any one of claims 25 to 26, characterized in that it is for applications in thermoplastics, in thermosets, in rubber, in paper, in water treatment and in agriculture.

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