Method for extracting cellulose from waste biomass and recovering the organic solvents used

Abstract

Method for extracting cellulose from waste biomass and recovering the organic solvents used, suitable for optimizing the extraction of cellulose by employing solid plant biomass waste, commonly found in the agricultural sector; said method comprising the use of at least two organic solvents suitable for reducing the toxicity levels of the extraction plant, further increasing the safety of the operators and recycling most of the compounds used; the first of the two organic solvents being gamma-valerolactone (GVL), suitable for being recovered according to a process involving the use of super-critical CCh; the second of the two organic solvents being ethanol, which is suitable for being recovered by distillation; such recovery processes being decidedly different from each other, a three-way valve is suitable for being operated by a specialized operator, in order to select the most suitable branch of the plant to recover the organic solvent chosen.

Description

[0001] DESCRIPTION

[0002] appended to the INVENTION PATENT application entitled:

[0003] " METHOD FOR EXTRACTING CELLULOSE FROM WASTE BIOMASS AND RECOVERING THE ORGANIC SOLVENTS USED"

[0004] *****

[0005] Field of the art

[0006] The invention relates to an innovative method for extracting cellulose by employing multiple organic solvents which are suitable for being selected according to the preferences of personnel and the needs of the plant, subsequently allowing the recovery thereof by exploiting the branch of the most suitable plant, further reducing the environmental impact and obtaining efficient results while using waste biomass for the extraction of said cellulose.

[0007] Known art

[0008] Cellulose is a very common organic compound in nature, because it forms the support fabric of plant tissue as well as the most important polysaccharides.

[0009] Said substance is defined as insoluble since the bonds between the carbon atoms forming it are so tight as not to allow the entry of water molecules.

[0010] To date, cellulose is the most widespread and abundant substance on our planet. Thanks to its structure, plants have an intrinsic robustness and can thrive, giving rise to forests and woods.

[0011] Overall, the plant species living on Earth today produce more than 100 billion tons of cellulose every year. This is a truly remarkable and extremely useful amount, since a large part of said cellulose becomes a raw material for producing food and for manufacturing everyday objects.

[0012] In addition to being commonly used in the paper production sector, cellulose is further used in the pharmaceutical, cosmetic, textile and construction sectors. In the latter context, cellulose, or rather cellulose fibers, are used as a material forthermal insulation and sound insulation.

[0013] To date, the most used processes for obtaining cellulose pulp are: the Kraft process, the sulfite process and the soda process. If the cellulose is to be used for producing white paper, it is necessary to resort to a bleaching treatment with chlorine and hypochlorites.

[0014] Chemical pulping processes consist of the use of various chemical reagents and heat to soften lignin.

[0015] The first of these is the Kraft pulping process, also known as the sulfate process: 80% of the world's wood pulp production is processed using this method.

[0016] The Kraft process has become the most used method thanks to the fact that the fibers processed with sulfate have a better durability than those obtained as a result of other available technologies.

[0017] This process can be used for all types of wood, allowing an effective recovery of the raw materials used.

[0018] The Kraft process consists of combining wood chips with white liquor. Under high pressure and temperature conditions, this solution dissolves lignin, releasing cellulosic fibers; following the reaction, a black liquor and a cellulose pulp are obtained.

[0019] Although this process is based on efficient and well-established technology, it was conceived at a time when environmental problems were not as severe as they are today.

[0020] The production of cellulose by means of the Kraft process involves the use of aggressive inorganic solvents in aqueous solution such as caustic soda and sulfur-based compounds that make this processing method an obsolete industrial process with a no longer negligible environmental impact.

[0021] To date, no methods have been found to remedy the problems highlighted, such as the case of patent PL3568519, published on May 31, 2021, which describes the use of comb polymers, obtainable by polymerization of unsaturated monomers, asscale inhibitors in the production of cellulose pulp by means of the sulfate process, also called the Kraft process; said invention still does not solve the problems related to the use of aggressive solvents.

[0022] The object of the patent, is therefore to employ solid plant biomass waste for the production of cellulose, optimizing the extraction method itself, definitively replacing the aggressive chemical solvents thanks to the use of at least two organic solvents, which can be recovered following a distillation or separation process by means of supercritical CO₂, depending on the solvent chosen.

[0023] Description of the invention

[0024] According to the present invention, a method is created for extracting cellulose from waste biomass and recovering the organic solvents used which effectively solves the aforementioned problems.

[0025] The object of the present invention is to describe an innovative method for extracting cellulose from waste biomasses suitable for optimizing the extraction of cellulose, using the fragments of solid plant biomass waste, commonly widespread in the agricultural sector.

[0026] The process which is the subject matter of the invention envisages the use of at least two possible organic solvents, which are suitable for reducing the toxicity levels of the extraction plant, further increasing the safety of the operators and recycling

[0027] most of the compounds used.

[0028] The process of extracting cellulose from waste biomass comprises a plurality of steps, which ensure its correct execution.

[0029] The first step is the insertion, within the extraction plant in question, of 600 kg of solid plant biomass from agricultural waste.Subsequently, said solid plant biomass is pre-treated by means of a chipping machine, suitable for reducing the size of the biomass into particles less than 2 millimeters thick.

[0030] Following their reduction, said particles are moved inside a reactor, which is suitable for subsequently allowing the extraction of a solid / liquid mixture; said reactor is characterized by a capacity of at least 4 cubic meters.

[0031] In an embodiment thereof, said reactor for extracting the solid / liquid mixture comprises two batch containers, installed in parallel, suitable for alternating their operating steps, allowing the cleaning of one of the two containers at each extraction cycle of said cellulose from waste biomass.

[0032] Meanwhile, the mixing of the organic solvent with water in a 1:1 ratio is carried out inside a container having a volume of 3 cubic meters; said mixing is controlled by two flow rate and ratio controllers specially installed upstream of said container. By way of non-limiting example, in mixing the organic solvent with water, a catalyst based on sulfuric acid from 1% to 5% on a dry solid base is further added within said reactor.

[0033] The biomass particles and the organic solvent reside inside said reactor, for a time interval ranging from 45 to 60 minutes; in said interval the temperature reaches 150°C while the pressure maintains the typical atmospheric values at sea level. The temperature is controlled by adjusting the steam flow rate, inside the sleeve of said reactor, while the pressure is regulated by opening the vapor vent valve by an automatic controller.

[0034] The separation of the solid / liquid mixture, following the extraction of said mixture by means of a pump for liquid fractions, occurs by means of a filter press suitable for separating said mixture into a liquid and a solid; said liquid, rich in lignin, obtained by the separation, is called quenched liquor while said solid, rich in cellulose, is called cellulose pulp and represents 53% of the 600 kg of biomass

[0035] 5previously fed into the plant. Said cellulose pulp represents the main result of the present method for extracting cellulose from waste biomass.

[0036] In order to optimize the separation of the solid / liquid mixture for obtaining the cellulose pulp, a water stream in a dry solid / water ratio of 1 / 4 is used inside said filter press; said water stream is suitable to reach temperatures ranging from 60°C to 80°C, by using a shell and tube heat exchanger.

[0037] Subsequently, said quenched liquor is treated, in order to split the cellulose solute from the organic solvent used, selecting through the use of a three-way valve, one of the two branches of the plant through which to continue the treatment step. Each branch is suitable for treating a different organic solvent, allowing an efficient recovery thereof, respectful of the environment but above all low-cost. If the organic solvent used was gamma-valerolactone (GVL), which turns out to be an excellent chemical product since it is suitable for preserving the degree of crystallinity of the cellulose fibres, the quenched liquor would be directed towards the first branch of the extraction plant, using said three-way valve.

[0038] In said first branch, the carbon dioxide is compressed, using pressures above 250 bar, in order to make said carbon dioxide liquid. The obtained CO₂, defined as supercritical and having a high extractive power, is suitable for being mixed with said quenched liquor, loading itself with soluble substances, such as GVL in this case.

[0039] Following the compression, the expansion of said supercritical CO₂ occurs, in order to allow the return thereof to the gaseous state, extracting the GVL and thus the previously collected soluble substances.

[0040] The recirculation of the obtained gaseous CO₂ makes the subsequent recoveries of GVL when used as an organic solvent possible.

[0041] To make such gamma-valerolactone available again as an organic solvent for the subsequent extractions of cellulose from biomass, the relative tank is filled.If the organic solvent used was ethanol, it is necessary to send the quenched liquor inside the second branch of the cellulose extraction plant.

[0042] In said second branch, the mixture obtained from the previous mixing step is heated, in order to cause the mixture of cellulose and ethanol, i.e., the quenched liquor, to boil, exploiting the two different boiling points of ethanol and cellulose solute.

[0043] Following the heating of the mixture, the evaporation of the ethanol occurs thanks to its lower boiling point with respect to the solute consisting of the cellulose. The evaporated ethanol vapors are then collected inside at least one distillation column, inside which they are suitable for being subjected to condensation, making said organic solvent available again for the subsequent extractions of cellulose from biomass; such condensation is ensured by the presence of a coil suitable for cooling the vapors contained inside said distillation column.

[0044] In an embodiment thereof, said three-way valve is adapted to be remotely operated, by remote control, from a common monitoring station which can manage and constantly monitor the organic solvent recovery processes.

[0045] Alternatively, said three-way valve is suitable for automatically selecting, and in total autonomy, one of the two branches of the plant for the recovery of organic solvents, detecting the organic solvent which was initially selected to perform the extraction of cellulose from waste biomass, using common probes suitable for detecting the level of solvents within the respective containment tanks.

[0046] The advantages offered by the present invention are apparent in the light of the description set forth herein and will be further clarified by the accompanying figures and the detailed description.

[0047] Description of the figuresThe invention will be described below in at least one preferred embodiment by way of non-limiting example and with the aid of the accompanying figures, in which:

[0048] - FIGURE 1 shows a plant diagram suitable for simplifying the understanding of the present cellulose extraction method, In Figure 1 the components necessary for the correct operation of the cellulose extraction plant which is the subject matter of the invention have been highlighted.

[0049] The two branches 30, 40 suitable for treating the recovery of the two types of organic solvents 8 which can be used are further highlighted,

[0050] - FIGURE 2 shows the flow chart underlying the present method for extracting cellulose from waste biomass 10, suitable for using and recycling organic solvents 8.

[0051] Detailed description of the invention

[0052] The present invention will now be illustrated by way of non-limiting or binding example, using the figures which illustrate some embodiments in relation to the present inventive concept.

[0053] With reference to FIG.l, the plant suitable for allowing to carry out the cellulose extraction method described in the present patent application is illustrated.

[0054] The waste biomass 10 is inserted within the plant for it to be treated, reducing its size until it reaches particles SI less than 2 millimeters thick; the fragmentation of the biomass is carried out by using a chipping machine 20.

[0055] Said particles SI reach a reactor 11 by means of a plurality of conveyor belts. In the reactor 11, a mixture comprising an organic solvent 8 and water 9 in a 1: 1 ratio is further converged.A container 12 is used for mixing the solvent 8 and the water 9 before they reach said reactor 11 installed downstream.

[0056] Said particles SI, together with the mixture of solvent 8 and water 9, form a solid / liquid mixture S3 which is sent inside the reactor, where they station for a time interval ranging from 45 to 60 minutes at 150°C.

[0057] The reactor 11 installed in the plant in question advantageously comprises an outer sleeve 13 and a vapor vent valve managed by an automatic pressure controller 5. The solid / liquid mixture S3 obtained is subsequently sent to a filter press 15 by means of a pump 14 for liquid fractions. Following the filtration performed by said filter press 15, the cellulose pulp S4 and a liquid called quenched liquor S5 are obtained.

[0058] To optimize the separation of the solid / liquid mixture S3, a heated water flow S6 is employed, inside said filter press 15. Said water flow S6 can be heated up to 80°C, thanks to the use of a shell and tube heat exchanger 16.

[0059] Once said cellulose pulp S4 has been obtained, which represents the final result of the extraction process which is the subject matter of the invention, the recovery of the organic solvent 8, still stored within said quenched liquor S5, is carried out.

[0060] In fact, the quenched liquor S5 comprises both the solute, consisting of cellulose fibers, and the chosen organic solvent 8.

[0061] A three-way valve 1 is suitable for directing said quenched liquor S5 in the branch 30, 40 most suitable for carrying out the recovery process.

[0062] A first branch 30 is used to recover the gamma-valerolactone (GVL) when it has been used as an organic solvent 8, exploiting the supercritical CO₂.

[0063] 9A second branch 40 of the present plant is used to recover the ethanol used as an organic solvent 8, exploiting a distillation process.

[0064] Said three-way valve 18 can be remotely controlled by a monitoring station 19, in order to make the present system manageable even remotely, minimizing costs and reducing unforeseen events.

[0065] With reference to FIG.2, the flow chart suitable for marking the steps necessary to ensure the correct operation of the cellulose extraction method which is the subject matter of the invention is illustrated:

[0066] - insertion 100, within the extraction plant in question, of 600 kg of solid plant biomass 10 from agricultural plant waste;

[0067] - pretreatment 200 of said solid plant biomass 10 by means of a chipping machine 20, suitable for reducing the size of the biomass 10 into particles SI less than 2 millimeters thick;

[0068] - mixing 300 the chosen organic solvent 8 with water 9 in a 1:1 ratio within a container 12 having a volume of 3 cubic meters; said mixing 300 being controlled by at least two flow rate and composition controllers 6 specially installed upstream of said container 12;

[0069] - displacement 400, of said particles SI, within a reactor 11 suitable for subsequently permitting the extraction of a solid / liquid mixture S3; said reactor 11 having a capacity of 4 m3; said displacement step 400 further moving, within said reactor 11, the chosen organic solvent 8 and water 9 previously mixed in a 1:1 ratio in the mixing step 300;

[0070] - stationing 500, of the particles SI of biomass 10, within said reactor 11, for a time interval ranging from 45 to 60 minutes; in said time interval thetemperature reaches 150°C while the pressure maintains the typical atmospheric values at sea level;

[0071] - temperature control 550, by adjusting the saturated vapor flow rate inside the sleeve 13 of said reactor 11;

[0072] -- pressure control 570, by opening the vapor vent valve by an automatic controller 5;

[0073] - extraction 600 of a solid / liquid mixture S3 from said reactor 11, by using a pump 14 for liquid fractions;

[0074] - separation 700 of said solid / liquid mixture S3, by means of the use of a filter press 15 suitable for separating said solid / liquid mixture S3 into a liquid called quenched liquor S5, rich in lignin, and into a solid, rich in cellulose; said solid, called cellulose pulp S4, representing 53% of the 600 kg of biomass 10 previously fed into the plant and being suitable for representing the main result of the present method for extracting cellulose from waste biomass 10;

[0075] - use 650 of a water stream S6 with a dry solid / water ratio of 1 / 4 within said filter press 15, in order to optimize the separation 700 of the solid / liquid mixture S3 to obtain the cellulose pulp S4; said water stream S6 being suitable to reach temperatures ranging from 60°C to 80°C by using a shell and tube heat exchanger 16;

[0076] ■■■• treatment 800 of said quenched liquor S5, in order to split the cellulose solute from the organic solvent 8 used, selecting through the use of a three- way valve 18, one of the two branches of the plant through which to continue the treatment step 800; each branch 30, 40 being suitable for treating a different organic solvent 8:--- compression 900 of the carbon dioxide, within the first branch 30 belonging to the extraction plant in question, if the organic solvent 8 used is gamma¬ valerolactone (GVL), by using pressures above 250 bar, in order to make said carbon dioxide liquid; said CO₂, defined as supercritical, and having a high extractive power, is suitable for being mixed with said quenched liquor S5, loading itself with soluble substances, hence with GVL;

[0077] - expansion 910 of said supercritical CO2, in order to allow the return thereof to the gaseous state, extracting the GVL and thus the previously collected soluble substances;

[0078] - recirculation 920 of the obtained gaseous and pure CO₂, for subsequent recoveries 800 of GVL;

[0079] - filling 930 the tank suitable for containing the GVL, in order to make such an organic solvent 8 available again for the subsequent extractions of cellulose from biomass 10;

[0080] - heating 90 the mixture obtained from the previous mixing step 300, if the organic solvent 8 used was ethanol, within the second branch 40 belonging to the extraction plant in question; said heating 90 being suitable for causing the mixture of cellulose and ethanol, i.e., the quenched liquor S5, to boil, in order to take advantage of the two different boiling points of ethanol and cellulose solute;

[0081] - evaporation 91 of ethanol, being characterized by a lower boiling point with respect to the solute consisting of cellulose;

[0082] - collection 92 of the evaporated ethanol vapors, within at least one distillation column;

[0083] 12— condensation 93 of said ethanol vapors, in order to make said organic solvent 8 available again for subsequent extractions of cellulose from biomass 10; said condensation 93 being ensured by the presence of a coil suitable for cooling the vapors contained within said distillation column. Lastly, it is clear that the invention described up to now can be subjected to modifications, additions or variants obvious to those skilled in the art, without departing from the scope of protection outlined by the attached claims.

Claims

1. CLAIMS1. Method for extracting cellulose from waste biomass (10) and for recovering the organic solvents (8) used characterized in that it is suitable for optimizing the extraction of cellulose by employing waste biomass (10) plant solids, commonly found in the agricultural sector; said method comprising the use of at least two organic solvents (8) suitable for reducing the toxicity levels of the extraction plant, further increasing the safety of the operators and recycling most of the compounds used; the first of the two organic solvents (8) being gamma-valerolactone (GVL), suitable for subsequent recovery according to a process involving the use of supercritical CO2; the second of the two organic solvents (8) being ethanol, which is apt to be subsequently recovered by distillation; these recovery processes being decidedly different from each other, a three-way valve (18) is apt to be operated by a specialized operator, in order to select the most suitable branch (30, 40) of the plant to recover the organic solvent (8) chosen; said method being suitable to obtain a ratio of cellulose greater than 50% of the biomass (10) used; said method comprising the steps of:- insertion (100), within the extraction plant in question, of 600 kg of solid plant biomass (10) from agricultural waste;- pretreatment (200) of said solid vegetable biomass (10) by means of a chipping machine (20), suitable for reducing the size of the biomass (10) into particles (SI) with a thickness of less than 2 millimeters;- mixing (300) of the chosen organic solvent (8), with water (9) in a ratio of 1:1, within a container (12) having a volume of 3 cubic meters; said mixing (400) being controlled by at least two flow rate and ratio controllers (6) specifically installed upstream of said container (12);- displacement (400), of said particles (SI), within a reactor (11) suitable for subsequently permitting the extraction of a solid / liquid mixture (S3); saidreactor (11) having a capacity of 4 cubic meters; said displacement step (400) further moving, within said reactor (11), the chosen organic solvent (8) and water (9) previously mixed in a 1: 1 ratio in the mixing step (300); - stationing (500), of the particles (SI) of biomass (10), inside said reactor ( 11 ), for a time interval ranging from 45 to 60 minutes; during said time interval the temperature reaches 150°C while the pressure maintains typical atmospheric values at sea level;- temperature control (550), by adjusting the saturated steam flow rate inside the sleeve (13) of said reactor (11);- pressure control (570), by opening the vapor vent valve by an automatic controller (5);- extraction (600) of a solid / liquid mixture (S3) from said reactor (11), by the use of a pump (14) for liquid fractions;— separation (700) of said solid / liquid mixture (S3), by the use of a filter press (15) suitable for separating said solid / liquid mixture (S3) into a liquid, called quenched liquor (S5), and into a solid, rich in cellulose; said solid, called cellulose pulp (S4), generally representing 53% of the 600 kg of biomass (10) previously fed into the plant and being suitable to represent the main result of the present method of extracting cellulose from waste biomass (10);— use (650) of a water stream (S6) with a dry solid / water ratio of 1 / 4 within said filter press (15), in order to optimize the separation (700) of the solid / liquid (S3) mixture to obtain the pulp (S4); said water stream (S6) being suitable to reach temperatures ranging between 60°C and 80°C by the use of a shell and tube heat exchanger (16);- treatment (800) of said quenched liquor (S5), in order to split the cellulose solute from the organic solvent (8) used, by selecting through the use of a three-way valve (18), one of the two branches (30, 40) of the plant throughwhich to continue the treatment step (800); each branch (30, 40) being suitable for treating a different organic solvent (8);— compression (900) of the carbon dioxide, within the first branch (30) belonging to the extraction plant in question, if the organic solvent (8) used is gamma-valerolactone (GVL), by the use of pressures above 250 bar, in order to make said carbon dioxide liquid; said CO2, defined as supercritical, and endowed with high extractive power, is suitable to be mixed with said quenched liquor (S5), loading itself with soluble substances, hence with GVL;- expansion (910) of said supercritical CO2, in order to allow it to return to the gaseous state, extracting the GVL and thus the soluble substances collected;— recirculation (920) of the obtained gaseous and pure CO2, for subsequent recoveries (800) of GVL;- filling (930) of the tank suitable to contain the GVL, in order to make this organic solvent (8) available again for subsequent extractions of cellulose from biomass (10);- heating (90) of the mixture obtained from the previous mixing step (300), in case the organic solvent (8) used was ethanol, within a second branch (40) belonging to the extraction plant in question; said heating (90) being suitable to cause the boiling of the mixture of cellulose and ethanol, i.e., of the quenched liquor (S5), in order to take advantage of the two different boiling points of ethanol and cellulose solute;- evaporation (91) of ethanol, as it is characterized by a lower boiling point than the solute consisting of cellulose;— collection (92) of the evaporated ethanol vapors, within at least one distillation column;- condensation (93) of said ethanol vapors, in order to make said organic solvent (8) available again for subsequent extractions of cellulose from biomass (10); said condensation (93) being ensured by the presence of a coil suitable for cooling the vapors contained within said distillation column.

2. Method for extracting cellulose from waste biomass ( 10) and for recovering the organic solvents (8) used, according to the preceding claim 1, characterized in that said reactor (11) for extracting (600) the solid / liquid mixture (S3) comprises two batch containers, installed in parallel, suitable for alternating their phases of operation, allowing the cleaning of one of the two containers at each cycle of extraction of said cellulose from waste biomass (10).

3. Method for extracting cellulose from waste biomass ( 10) and for recovering the organic solvents (8) used, according to any one of the preceding claims, characterized in that said insertion (100) of the organic solvent (8) and water (9), within said reactor (11), further comprises the addition of a sulfuric acid catalyst from 1% to 5% on a dry solid basis.

4. Method for extracting cellulose from waste biomass ( 10) and for recovering the organic solvents (8) used, according to any one of the preceding claims, characterized in that the recycled organic solvent (8) and water (9) recirculations are managed and mixed within the cellulose extraction plant by the use of special composition controllers (4); said composition controllers (4) being suitable for proportioning the use of the recycled substances within the new substances.

5. Method for extracting cellulose from waste biomass ( 10) and for recovering the organic solvents (8) used, according to any one of the preceding claims, characterized in that said three-way valve (18) is suitable for being remotely operated, by remote control, from a common monitoring station(19) which can manage and constantly monitor the organic solvent recovery processes (8).

6. Method for extracting cellulose from waste biomass (10) and for recovering the organic solvents (8) used, according to any one of the preceding claims 1 to 4, characterized in that said three-way valve (18) is suitable for automatically selecting one of the two branches (30, 40) of the plant for the recovery of organic solvents (8), by detecting the organic solvent (8) that was initially selected to perform the extraction of cellulose from waste biomass (10), by means of common probes designed to detect the level of solvents (8) within the respective holding tanks.

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