Method for producing biopropane from waste oils

Abstract

The present invention discloses a method for producing biopropane from waste oils, characterised in that it comprises the steps of: saponifying the waste oils, thus obtaining carboxylate and glycerol; separating the carboxylate and glycerol; fermenting the glycerol obtained after saponification to obtain 1,3-propanediol; oxidising the 1,3-propanediol to obtain propanedioic acid; saponifying the propanedioic acid to obtain carboxylate; and carrying out pyrolysis of the carboxylate obtained from the waste oils and of the carboxylate obtained from the propanedioic acid to obtain biopropane.

Description

[0001] METHOD FOR THE PRODUCTION OF BIOPROPANE FROM RESIDUAL OILS

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates to the field of technologies for the recovery of household and / or industrial waste and in particular provides a method for the production of biopropane from waste oils.

[0004] BACKGROUND OF THE INVENTION

[0005] A recurring problem in the state of the art is the recovery of both domestic and industrial waste. In particular, the use of household waste oils for biodiesel production has been widely reported.

[0006] Some state-of-the-art documents related to this field disclose methods for waste recovery.

[0007] For example, document US 2012 / 157728 AA discloses a method for producing bio-naphtha from a mixture of fats and oils of natural origin. In one of the disclosed embodiments, the oils and fats are treated and, after treatment, subjected to a saponification reaction from which soap and glycerol are obtained. The soap obtained is subjected to a decarboxylation process from which bio-naphtha is obtained, which is a liquid biofuel similar to gasoline. However, this document does not perform a post-treatment of the glycerol obtained, which results in a lower yield of the biofuel production process.

[0008] Document US 2020 / 370072, for its part, discloses a method for obtaining 1,3-propanediol from the fermentation of glycerol. However, this document does not obtain biopropane from the 1,3-propanediol obtained.

[0009] Consequently, a method is required that can overcome the deficiencies of the state of the art.

[0010] SUMMARY OF THE INVENTION

[0011] The present invention provides a method for the production of biopropane from residual oils, characterized in that it comprises the steps of: performing a saponification of the residual oils, obtaining carboxylate and glycerol; performing a separation of the carboxylate and the glycerol; performing a fermentation of the glycerol obtained after saponification to obtain 1,3-propanediol; performing an oxidation of 1,3-propanediol to obtain propanedioic acid; performing a saponification of the propanedioic acid to obtain carboxylate; and performing a pyrolysis of the carboxylate obtained from the residual oils and of the carboxylate obtained from the propanedioic acid to obtain biopropane.

[0012] BRIEF DESCRIPTION OF THE FIGURES

[0013] Fig. 1 illustrates a flow diagram of a first embodiment of the method that is the subject of the present invention.

[0014] DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will now be described in detail, with reference to the figures accompanying this application.

[0016] The present invention provides a method (1) for the production of biopropane (10) from waste oils (100) comprising the steps of:

[0017] - carry out a saponification (2) of the residual oils (100), obtaining carboxylate (21) and glycerol (22);

[0018] - carry out a separation of the carboxylate (21) and the glycerol (22);

[0019] - carrying out a fermentation (3) of the glycerol (22) obtained after saponification (2) to obtain 1,3-propanediol (31);

[0020] - carrying out an oxidation (4) of 1,3-propanediol (31) to obtain propanedioic acid (41);

[0021] - performing a saponification (2) of the propanedioic acid (41) to obtain carboxylate (21); and

[0022] - carrying out a pyrolysis of the carboxylate (21 ) obtained from the residual oils (100) and of the carboxylate (21 ) obtained from the propanedioic acid (41 ) to obtain biopropane (10).

[0023] In a preferred embodiment, the method (1 ) may comprise performing a first saponification operation (2) on a first quantity of residual oils (100) and performing a second saponification operation (2) on a second quantity of residual oils (100). In this preferred embodiment, for example and without limiting the scope of the present invention, the saponification (2) of the propanedioic acid (41 ) may be performed in conjunction with the second saponification operation (2) of the second quantity of residual oils (100). However, other embodiments of the method (1 ) that is the object of the present invention are possible. For example, and without limiting the scope of the present invention, the saponification (2) of the propanedioic acid (41 ) may be performed independently of the saponification (2) of the residual oils (100).In another embodiment, without limiting the scope of the present invention, the saponification (2) of the residual oils (100) can be carried out substantially continuously. In this last embodiment, the propanedioic acid (41) obtained after the oxidation (4) of 1,3-propanediol (31) can be introduced substantially continuously into the saponification process (2) of the residual oils (100).

[0024] In the context of the present invention, without limiting its scope, biopropane will be understood as a biofuel based on propane and having properties similar to liquefied petroleum gas.

[0025] In a preferred embodiment, without limiting the scope of the present invention, the method (1) may additionally comprise the step of filtering the residual oils (100) prior to the step of performing saponification (2), separating particulate material from the residual oils (100). The technique used to perform said filtration does not limit the scope of the present invention and may depend, for example, on the specific implementation of the method (1) that is the object of the present invention, as well as the origin and nature of said residual oils (100). In a more preferred embodiment, without limiting the scope of the present invention, the filtration of the residual oils (100) can be carried out at a temperature between 50 ° C and 80 ° C.

[0026] In another preferred embodiment, without limiting the scope of the present invention, the saponification step (2) of the residual oils (100) can be carried out using NaOH as a base, according to the reaction illustrated in scheme 1:

[0027] Scheme 1: Saponification reaction of residual oils

[0028] In a more preferred embodiment, without limiting the scope of the present invention, the saponification step (2) of the residual oils (100) can be carried out at a molar ratio of NaOH to fatty acids of between 0.5 and 2.5. In another more preferred embodiment, without limiting the scope of the present invention, the saponification step (2) of the residual oils (100) can be carried out at a temperature of between 20 °C and 40 °C, more preferably between 25 °C and 35 °C.

[0029] In a preferred embodiment, without limiting the scope of the present invention, the separation of the carboxylate (21 ) and glycerol (22) obtained after the saponification (2) of the residual oils (100) may comprise a decantation step to obtain a liquid phase, corresponding to glycerol (22) and water, and a solid phase, corresponding to carboxylate (21 ). In a more preferred embodiment, without limiting the scope of the present invention, the method (1 ) may additionally comprise pressing the solid phase obtained after decantation, in order to obtain a higher concentration of carboxylate (21 ).

[0030] In a preferred embodiment, without limiting the scope of the present invention, the carboxylate (21) can be dehydrated, ground and / or sieved prior to the step of performing the pyrolysis (5). The particle size of the carboxylate (21) after the dehydration, grinding and / or sieving steps does not limit the scope of the present invention.

[0031] In another preferred embodiment, the fermentation (3) of glycerol (22) can be carried out under anaerobic or micro-aerobic conditions. In an exemplary embodiment, without limiting the scope of the present invention, the fermentation (3) of glycerol (22) can be carried out using a Klebsiella pneumoniae DSM 2026 strain, at a pH between 5.0 and 8.0 and at a temperature between 34 °C and 39 °C.

[0032] In a further preferred embodiment, without limiting the scope of the present invention, the oxidation (4) of 1,3-propanediol (31) can be done using a Jones oxidation reaction at room temperature, according to the reaction scheme illustrated in scheme 2:

[0033] Scheme 2: Oxidation of a primary alcohol by the Jones reaction

[0034] In a more preferred embodiment, without limiting the scope of the present invention, after the oxidation reaction (4) it is possible to carry out an extraction of propanedioic acid (41 ) using petroleum ether and solvent evaporation. In a preferred embodiment, without limiting the scope of the present invention, the saponification (2) of the propanedioic acid (41 ) can be carried out using NaOH as a base, wherein the saponification (2) of the propanedioic acid (41 ) is carried out at a molar ratio of propanedioic acid (41 ) to NaOH of 1.5.

[0035] In another preferred embodiment, without limiting the scope of the present invention, the pyrolysis (5) of the carboxylate (21) is carried out using a fluidized bed reactor, with a temperature between 550 °C and 700 °C. However, other pyrolysis methods (5) are also applicable to the method (1) of producing biopropane (10) that is the object of the present invention, without limiting the scope of the protection requested.

[0036] According to the previously detailed description, it is possible to obtain a method (1) that allows overcoming the deficiencies of the state of the art.

[0037] It should be understood that the different options described for the technical characteristics of the method (1) can be combined with each other, or with other alternatives known to a person normally versed in the matter, without this limiting the scope of the protection requested.

[0038] LIST OF REFERENCES

[0039] 1 Biopropane production method

[0040] 10 Biopropane

[0041] 100 Residual oils

[0042] 2 Saponification

[0043] 21 Carboxylate

[0044] 22 Glycerol

[0045] 3 Fermentation

[0046] 31 1,3-propanediol

[0047] 4 Oxidation

[0048] 41 Propanedioic acid

[0049] 5 Pyrolysis

[0050] Below are examples of the application of the method (1) that is the subject of this application. These examples are provided only for a better understanding of the technology, but in no case should they be understood as limiting the scope of the protection requested. In addition, details of technical characteristics described in different examples may be combined with each other, or with other options previously described or known to a person normally versed in the art, in any manner foreseen, without this limiting the scope of protection.

[0051] APPLICATION EXAMPLES

[0052] Example 1: Pretreatment of waste oils

[0053] Collected frying waste oil was subjected to a filtration process to remove particulate matter. The process was carried out at temperatures between 50°C and 80°C to facilitate filtration. Filtration was performed using a vacuum filtration system consisting of a Büchner funnel, a Kitasato flask, filter paper, and a vacuum pump. At this stage, drying of the oil was not required.

[0054] Example 2: Implementation of pretreatment of waste oils

[0055] 500 ml of residual frying oil was measured into a beaker, which was heated on a hot plate until temperatures between 60°C and 70°C were reached, then vacuum filtered using the system described in the previous example.

[0056] Example 3: Saponification process:

[0057] Carboxylates were produced through the saponification of previously filtered residual frying oils obtained from examples 1 and 2. The process additionally generated glycerol and water as secondary products.

[0058] The process started with an amount of oil calculated from the stoichiometry of the triglyceride saponification reaction (Scheme 1) under a molar ratio of 0.5 to 2.5 NaOH / fatty acid. The mass of NaOH used was calculated from the stoichiometry of the reaction, assuming approximately a 10% excess. The calculated mass of NaOH was diluted in water to reach a concentration of 23% m / v.

[0059] For saponification, the NaOH solution was added to the oil under constant stirring at room temperature for approximately 10 minutes. The reaction mixture was then allowed to settle for 24 hours, until phase separation was observed, with the solid phase corresponding to the carboxylate and the liquid phase to glycerol.

[0060] Example 4: Separation of carboxylate and glycerol The decanted mixture obtained from the previous example was subjected to a separation to separate the carboxylate from the glycerol. To do this, the solid phase, corresponding to the carboxylate, was separated from the liquid phase, corresponding to the glycerol.

[0061] Because some of the glycerol remains in the carboxylate extracted from the separatory funnel, an additional extraction process was performed to remove this remaining glycerol. To do this, the warm carboxylate was pressed to drain the glycerol / water mixture and separate it from the solid phase.

[0062] Example 5: Drying of carboxylate

[0063] The solid phase obtained from Examples 3 and 4 was conditioned for use in the carboxylate pyrolysis step. For this purpose, the solid phase was dried in a convective tunnel at 70°C to 100°C for 20 to 30 hours. The dried product was ground and sieved, collecting the fraction remaining between the 500 and 250 µm sieves, according to the requirements of the subsequent pyrolysis study.

[0064] Example 6: Implementation of obtaining carboxylate:

[0065] In a 1-liter beaker, 309.69 g of residual frying oil were added, calculated according to the reaction stoichiometry of scheme 1. Subsequently, under constant stirring (800 - 1000 rpm), the 23% m / v NaOH solution (60 g of NaOH in 200 ml of distilled water) prepared at room temperature was added and allowed to react for 10 minutes. Subsequently, the reaction mixture was allowed to settle for 24 hours. After this time, the solid phase (carboxylate) was collected manually and dried in a convective tunnel at 75 ° C for 24 h. The dried product was ground and sieved, collecting the fraction that remained between the 500 and 250 pm sieves. The total saponification yield was determined, obtaining values ​​greater than 95%.

[0066] Example 7: Glycerol conditioning

[0067] The liquid phase obtained from Examples 3 and 4, corresponding to the residual glycerol, was conditioned to be subsequently carried out in the biotechnological fermentation process to produce 1,3-propanediol. For this, ethanol was poured onto the liquid phase in order to extract the glycerol. Upon adding the ethanol, a brown-colored liquor was obtained that contained dissolved glycerol, water and other colored impurities. In addition, a pale yellow precipitate was formed, corresponding to residual carboxylate.

[0068] Following ethanol extraction, the liquid fraction was filtered to separate the remaining carboxylates, followed by evaporation of all ethanol in a rotary evaporator. The resulting liquid concentrate was cooled in an ice-water mixture and subsequently neutralized with a 20% w / v hydrochloric acid solution until a pH of approximately 6.0 was obtained, thereby precipitating the fatty acids and carboxylates dissolved in the concentrated liquor. The precipitated residues, corresponding to fatty acids and carboxylates, were separated by vacuum filtration.

[0069] The liquid fraction was heated to between 100°C and 110°C, after which activated carbon was added, and the mixture was stirred for approximately 10 minutes to adsorb the colored impurities. This mixture was then hot filtered to remove the activated carbon, yielding a pale yellow solution. Finally, this solution was distilled to remove as much water as possible from the glycerol. The final glycerol-rich liquid obtained had a viscous, pale yellow appearance.

[0070] Example 8: Implementation of glycerol conditioning

[0071] 300 ml of a liquid mixture (residual glycerol / water) was poured onto 600 ml of ethanol to extract the glycerol. Upon adding the ethanol, a pale yellow precipitate formed, corresponding to the salts of the fatty acids (sodium carboxylates), and a brown liquid fraction or liquor containing the dissolved glycerol, water, and other colored impurities. This mixture was subsequently filtered to separate the carboxylates, followed by evaporation of all the ethanol in a rotary evaporator. The resulting liquid concentrate was cooled in an ice-water mixture and subsequently neutralized with 500 ml of a 20% w / v hydrochloric acid solution until a pH of around 6.0 was obtained, thus generating the precipitation of the fatty acids that were dissolved in the concentrated liquor.The precipitated fatty acids were separated by vacuum filtration, and the liquid fraction was heated to 105 °C. Activated carbon was added to adsorb colored impurities and stirred for 10 minutes. This mixture was then hot filtered to remove the activated carbon, yielding a pale yellow solution. Finally, this solution was distilled to remove as much water as possible from the glycerol. The final glycerol-rich liquid obtained had a viscous, pale yellow appearance.

[0072] Example 9: Obtaining 1,3-propanediol from glycerol

[0073] Glycerol fermentation was performed using the Klebsiella pneumoniae strain DSM 2026, which was purchased in lyophilized condition. It had to be rehydrated and reactivated according to the DSM2026 data sheet from the DSMZ (Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH) strain bank. This last step was performed in two plate reactivation media, one according to the DSM 2026 data sheet and the other on Columbia agar medium, to select the medium that allowed obtaining the highest cell density. The results obtained allowed defining Columbia agar medium as the ideal one to obtain the highest cell density. Subsequently, pre-inoculums with the strain acclimated to culture conditions for the production of 1,3-propanediol were prepared in flasks with 50% of the useful volume of the culture medium used by Mitrea et al. (Mitrea, L., Florina, L., Bouari, C. and Vodnar, D. 2020.Separation and Purification of Biogenic 1 ,3-Propanediol from Fermented Glycerol through Flocculation and Strong Acidic Ion-Exchange Resin. Biomolecules, 10, 1601 -1607), el cual contiene glicerol dentro de su composición.

[0074] The reactivated strain in agar culture medium at 37 °C and pH 7.0 for 24 h was replated using preinoculums for fermentation and 1,3-propanediol production assays. The assays were performed by adjusting the pH to 7.0 with 12N NaOH. The useful volume for each assay corresponded to 50% in flasks (100 ml) and the preinoculum used corresponded to 10% of the useful volume of the flasks. Commercial glycerol was used as a carbon source at an initial concentration of 40 g / l, but the preinoculum was also previously prepared with the same concentration, finally contributing to the initial concentration of 38.5%, therefore, the initial concentration was 65 g / l of glycerol in the flask. The culture conditions corresponded to 37 °C, pH 7.0 and 150 rpm for 24 h. To perform the fermentation kinetics, samples were taken every 2 h, during the first 12 h and then a sample at 24 h. Subsequently, the samples were centrifuged (10,000 rpm, 2 eC and 20 min), storing the upper phase (liquid), where the reaction products are found: 1,3-propanediol and the unconsumed substrate (glycerol), which were quantified by Gas Chromatography coupled to mass spectrometry (GC-MS), and in the lower phase (solid) the cellular concentration of Klebsiella pneumoniae was determined, using dry weight methodology.

[0075] Example 10: Optimization of the process for obtaining biomass and 1,3-propanediol

[0076] Biomass production was optimized by taking as an optimization condition the highest amount of biomass produced (12.28 g / l) in the shortest possible time (8 h), so as not to affect productivity. On the other hand, the selection of the maximum concentration of 1,3-propanediol obtained was carried out under the same criteria as for biomass, that is, the highest concentration obtained (20.79 g / l) was selected in the shortest possible time (8 h), but without penalizing the concentration of 1,3-propanediol more than 5% with respect to the maximum value obtained (21.95 g / l). The yield obtained with respect to the initial glycerol was calculated with the value at time zero (65 g / l).

[0077] The results showed that using 65 g / l of glycerol, it was possible to achieve a constant production of 20 g / l of 1,3-propanediol for 8 hours. This resulted in a productivity of 2.6 g / l / h of 1,3-propanediol.

[0078] Example 11: Glycerol fermentation in a bioreactor

[0079] The fermentation kinetics of Klebsiella pneumoniae DSM 2026 were carried out by batch tests in a 3I bioreactor using commercial glycerol concentrations (WINKLER) of 20 g / l, 40 g / l and 60 g / l. To carry out these fermentations, the concentration of commercial glycerol in the pre-inoculum was maintained at 40 g / l. In addition to the above, the culture media described by Mitrea et al. (2019) were used for the preparation of the pre-inoculum and kinetics, which had to be adjusted to pH 7.0 with 12 N NaOH.

[0080] For the reaction, a useful volume of 50% of the total bioreactor volume was used. The pre-inoculum used corresponded to 10% of the useful volume of the bioreactor volume, and the fermentation operating conditions were 37°C, pH 7.0, and 150 rpm for 24 h.

[0081] Samples were taken every 2 h for the first 12 h, followed by a sample at 24 h, for a total of 8 samples per fermentation. The sample volume extracted from the bioreactor for biomass, glycerol, and 1,3-propanediol analysis was 5 ml. Each sample was centrifuged (10,000 rpm, 2 e C and 20 min), obtaining the upper (liquid) phase, where the reaction products are found: 1,3-propanediol and the unconsumed substrate (glycerol), which were quantified by GC-MS. In the lower (solid) phase, the cellular concentration of Klebsiella pneumoniae DSM 2026 was determined using dry weight methodology.

[0082] The effect of glycerol concentration was evaluated at increasing concentrations of commercial glycerol, with the aim of optimizing this variable for the production of 1,3-propanediol. Fermentations were carried out on a bioreactor scale using a 3 L steel thaltener, with pH and temperature control.

[0083] The production of 1,3-propanediol was identical between the highest glycerol concentrations used (40 g / l and 60 g / l), with maximum concentrations of approximately 16 g / l of 1,3-propanediol being observed. However, maximum concentrations of approximately 6 g / l were obtained with 20 g / l of glycerol. Example 12: 1,3-propanediol production results

[0084] Table 1 presents the production parameters of 1,3-propanediol, observing a higher production of 1,3-propanediol with 40 g / L at 12 h of fermentation (15.78 g / L), selecting this condition that achieves a higher conversion of glycerol into 1,3-propanediol in molar ratio, being this 0.48 and 0.47 at 12 h and 10 h respectively. Similarly, the optimal fermentation time of 10 h is defined since a higher volumetric productivity is obtained (1.55 g 1,3-propanediol / L / h).

[0085] Table 1: Production of 1,3-propanediol using Klebsiella pneumoniae

[0086] Example 13: Production of 1,3-propanediol under anaerobic conditions

[0087] The comparison of micro-aerobic and anaerobic fermentation was carried out, with the optimal glycerol condition selected from example 12 (40 g / L), for which nitrogen was continuously bubbled into the bioreactor during fermentation.

[0088] An increase in 1,3-propanediol production was observed from 15.47 g / L under microaerobic conditions to 23.35 g / L under anaerobic conditions. An increase in the molar conversion of glycerol to 1,3-propanediol and volumetric productivity were also observed, being 0.71 mol 1,3-propanediol / mol glycerol and 2.34 g 1,3-propanediol / L / h, respectively, under anaerobic conditions.

[0089] Example 14: Oxidation of 1,3-propanediol

[0090] In a test tube, 60 drops of Jones' reagent were added, followed by 10 ml of 1,3-propanediol. The tube was shaken until a color change was observed, with the liquid turning dark. The dicarboxylic acid formed, i.e., propanedioic acid, was extracted with 50 ml of petroleum ether. The yield of the Jones oxidation is reported to be around 97% according to the literature; this yield was checked gravimetrically and was found to be 95%.

[0091] Example 15: Oxidation of 1,3-propanediol from a bioreactor For the oxidation of 1,3-propanediol obtained from a bioreactor, an Erlenmeyer flask was set up and 100 drops of Jones reagent and 100 ml of the bioreactor culture broth were added. The flask was shaken and its contents were subsequently emptied into a 500 ml separatory funnel, to which 200 ml of petroleum ether were added.

[0092] The separating funnel was shaken and allowed to settle. Subsequently, 30 ml of water was added and the mixture was allowed to settle until phase separation was observed.

[0093] The organic phase, corresponding to the upper phase, was collected in a beaker. The solvent was evaporated under a hood overnight, yielding propanedioic acid.

[0094] The oxidation reaction yield of the bioreactor broth was 95% as calculated by gravimetry.

[0095] Example 16: Saponification of propanedioic acid

[0096] The propanedioic acid obtained from the previous example was saponified with a 1.5 molar ratio of NaOH to obtain the carboxylate. The resulting carboxylate was dried at 105 °C to determine the reaction yield.

[0097] A saponification yield of 73.7% was obtained, calculated by gravimetry.

[0098] Example 17: Pyrolysis of carboxylate

[0099] Biopropane production from carboxylate was carried out at 550-700 °C and with a carrier gas flow that ensured a residence time of over 2 seconds for the gases and devolatilized pyrolytic products in the reactor. Once the aforementioned conditions were established, the feedstock (ground carboxylate from the carboxylate production stage) was injected into the pyrolysis reactor, where propane, butane, and other light olefins are produced, to be carried out of the reactor by the carrier gas. After the products transported by the carrier gas exited, they were taken to a condensation section, which cooled the products, retaining the condensable products.

[0100] The uncondensed product stream was transported to an electrostatic precipitator, precipitating the aerosols and condensables that were not previously condensed. The transported products that were not retained and / or precipitated are pyrolytic gases rich in propane / propene (approximately 26%), butane, pentane, and other olefins.

[0101] Example 18: Integrated process According to the results obtained in the previous examples, the sequence of the integrated method was validated, that is, incorporating each of the essential stages, for the production of biopropane from residual oils.

[0102] Under the conditions tested, a propane conversion of approximately 28% was achieved from used frying oil. This result is far superior to other known processes in the state of the art, such as catalytic deoxygenation, which achieves maximum yields of 10%.

Claims

MODIFIED CLAIMS received by the International Bureau on 17 September 2024 (17.09.2024) 1. A method (1) for the production of biopropane (10) from waste oils (100), CHARACTERIZED in that it comprises the steps of: - carry out a saponification (2) of the residual oils (100), obtaining carboxylate (21) and glycerol (22); - carry out a separation of the carboxylate (21) and the glycerol (22); - carrying out a fermentation (3) of the glycerol (22) obtained after saponification (2) to obtain 1,3-propanediol (31); - carrying out an oxidation (4) of 1,3-propanediol (31) to obtain propanedioic acid (41); - performing a saponification (2) of the propanedioic acid (41) to obtain carboxylate (21); and - carrying out a pyrolysis of the carboxylate (21 ) obtained from the residual oils (100) and of the carboxylate (21 ) obtained from the propanedioic acid (41 ) to obtain biopropane (10).

2. The method (1) of claim 1, CHARACTERIZED in that it comprises performing a first saponification operation (2) on a first quantity of residual oils (100) and performing a second saponification operation (2) on a second quantity of residual oils (100); wherein the saponification (2) of the propanedioic acid (41) is performed in conjunction with the second saponification operation (2) on the second quantity of residual oils (100).

3. The method (1) of claim 1, CHARACTERIZED in that it additionally comprises filtering the residual oils (100) prior to the step of performing saponification (2), separating particulate material from the residual oils (100).

4. The method (1) of claim 3, CHARACTERIZED in that the filtration of the residual oils (100) is carried out at a temperature between 50 °C and 80 °C.

5. The method (1) of claim 1, CHARACTERIZED in that the saponification step (2) of the residual oils (100) is carried out using NaOH as a base. MODIFIED SHEET (ARTICLE 19) 6. The method (1) of claim 5, CHARACTERIZED in that the saponification step (2) of the residual oils (100) is carried out at a molar ratio of NaOH to residual oils of between 0.5 to 2.

5.

7. The method (1) of claim 1, CHARACTERIZED in that the separation of the carboxylate (21) and the glycerol (22) obtained after the saponification (2) of the residual oils (100) comprises a decantation step to obtain a liquid phase, which corresponds to glycerol (22) and water, and a solid phase, which corresponds to carboxylate (21).

8. The method (1) of claim 7, CHARACTERIZED in that it additionally comprises pressing the solid phase obtained after decantation.

9. The method (1) of claim 1, CHARACTERIZED in that the carboxylate (21) is dehydrated, ground and sieved prior to the step of performing the pyrolysis (5).

10. The method (1) of claim 1, CHARACTERIZED in that the fermentation (3) is carried out under anaerobic or micro-aerobic conditions. 1 1. The method (1) of claim 1, CHARACTERIZED in that the fermentation (3) is carried out using a strain of Klebsiella pneumoniae DSM 2026, at a pH between 5.0 and 8.0 and at a temperature between 34 °C and 39 °C.

12. The method (1) of claim 1, CHARACTERIZED in that the oxidation (4) of 1,3-propanediol (31) is done using a Jones oxidation reaction at room temperature.

13. The method (1) of claim 12, CHARACTERIZED in that after the oxidation reaction (4) an extraction of propanedioic acid (41) is carried out using petroleum ether and solvent evaporation.

14. The method (1) of claim 1, CHARACTERIZED in that the saponification (2) of the propanedioic acid (41) is carried out using NaOH as a base, wherein the saponification (2) of the propanedioic acid (41) is carried out at a molar ratio of propanedioic acid (41) to NaOH of 1.

5. MODIFIED SHEET (ARTICLE 19) 5. The method (1) of claim 1, CHARACTERIZED in that the pyrolysis (5) of the carboxylate (21) is carried out using a fluidized bed reactor, with a temperature between 550 °C and 700 °C. MODIFIED SHEET (ARTICLE 19)

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