CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority to co-pending U.S. Provisional Patent Application Serial No. 63/304724, filed 31 January 2022.

TECHNICAL FIELD

[0001] This disclosure relates generally to chemical engineering, and, more specifically, to a method and apparatus for using organic solvents, such as methanol, to explosively separate clean, free, and depolymerized lignin from cellulosic materials and the harvesting of both.

BACKGROUND

[0002] This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, these statements are to be read in this light and are not to be understood as admissions about what is or is not prior art.

[0003] Lignin is the most abundant natural aromatic polymer. Lignin has a high storage capacity for phenolic compounds, and as such is a potential source for polymers and biomaterials. However, access to those polymers and biomaterials is difficult, as lignin is both complex and not very reactive.

[0004] One method of accessing the locked-in polymers and biomaterials is through depolymerization of the lignin. Steam has been used to explosively separate lignin from biomass fibers. Steam separation is advantageous because water is cheap and plentiful. However, steam explosion of biomass requires a fairly great amount of heat and also requires a nickel catalyst, which poses an initial expense as well as a back-end removal expense. Thus, there is a need for a lignin/cellulosic material separation process that requires less heat input and can be performed without the need of a catalyst. The present novel technology addresses this need.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 is a process flowsheet for production of clean depolymerized lignin and clean cellulose from biomass.

DETAILED DESCRIPTION

[0006] For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended.

[0007] The present novel technology relates to a process for the explosive separation of lignin from cellulosic material using an organic solvent, such as methanol; the depolymerization of the so-separated lignin; and the extraction of clean lignin from the depolymerization yield.

[0008] First, a quantity of biomass feedstock, such as wood chips and/or rice straw, are placed in a tank and soaked in an organic solvent. In this example, the feedstock is soaked in methanol, as methanol has a relatively low boiling point (as compared to water). The fibers may be soaked for a predetermined amount of time at room temperature, or at some elevated temperature below the solvent boiling point to speed the kinetics of the soaking process.

[0009] The soaked fibers are then moved to a high-pressure tank and additional solvent is added, wherein the pressure is increased and the mixture is superheated; the increased pressure is sufficiently great such that the solvent remains in liquid form when superheated. In some embodiments, the additional solvent is preheated before introduction into the high-pressure tank.

[0010] The pressure within the tank is then rapidly reduced, such that the solvent rapidly boils. The solvent soaked within the now-swelled fibers rapidly boils and explodes the fibers. The escaping evolved solvent vapor is collected in a knockout tank fluidically connected to the high-pressure tank, condensed back into a liquid state, and recycled for reuse.

[0011] While the process has similarities to known methods of steam explosion of fibers, the novel process enjoys the advantages of not requiring the removal of water for downstream processing. Further, the organic solvent may be chosen for being more effective in swelling natural fibers (like, for example, methanol). Also, the organic solvent may be selected for having a boiling point lower than that of water, so that similar pressures that drive the explosion process can be achieved at lower temperatures with lower associated energy costs.

[0012] Next, the separated lignin is depolymerized. The vapor-exploded fibers with solvent are placed in a high-pressure reactor vessel, which may or may not be the same vessel as the vapor explosion unit described above. Additional ingredients such as catalysts (such as nickel or the like), hydrogen, nitrogen, and/or acid are added to the reactor, which is then heated to temperatures that are super-critical and thus generate high pressures, typically between 20 bars and 300 bars. The super-critical conditions with their attendant high temperatures increase the rate of the lignin depolymerization reaction.

[0013] Methanol is the solvent used in the current example. Methanol is attractive because it is readily available, readily swells the fibers, has a low boiling compared to other alcohols but remains a liquid with a relatively low vapor pressure, and is one of the components in the composite board resin system that has been developed using the depolymerized lignin, thereby alleviating the need to fully remove the methanol. However, other solvents such as ethanol, isopropyl alcohol, mixtures of the above-listed alcohols, and the like, may also be useful, where the associated process would be similar with different temperatures and pressures required for both the vapor-explosion and lignin depolymerization reaction.

[0014] The depolymerization reaction is most commonly done using a metal catalyst, such as supported nickel. However, lignin depolymerization may also be achieved at super-critical temperatures using just high-pressure hydrogen without any metal catalyst. This removes the cost of catalyst preparation as well as the cost of recovery of the catalyst from the reaction products.

[0015] Once the lignin depolymerization reaction is complete, a filter press or the like is used to separate the lignin-free fibers from the solvent phase containing the depolymerized lignin. Any remaining solvent in the fibers is removed by drying, where the solvent is then recaptured and returned to the process. The liquid phase from the filter press is then put into a flash evaporator and/or a distillation unit to remove some, but not necessarily all, of the solvent thereby concentrating the depolymerized lignin and any other components in the liquid phase. Solvent may be recovered and recycled back to the process.

[0016] The resulting brown liquor contains the depolymerized lignin as well as other components, such as sugars, hemi-cellulose, small amounts of small cellulose fibers that made it past the filter press, some silica and other inorganic material, and the like. Any remaining cellulose fibers and inorganic particulates like silica may be removed in a settling tank or by mild centrifugation.

[0017] The above methodology may be applied to a variety of agricultural and forestry sources of biomass, including wheat straw, corn stover, sugar cane bagasse, and the like. The only real requirement is that the biomass have a significant amount of lignin.

[0018] It is generally desirable to remove the hemi-cellulose and sugars from the brown liquor. An aqueous salt solution with sufficient molarity forms a two-phase mixture at room temperature with organic solvents (such as, in this case 1 M NaCI in methanol at room temperature to yield a two-phase mixture). The sugars and hemi-cellulose are primarily in the aqueous phase, while the depolymerized lignin remains primarily in the organic phase. Thus, liquid-liquid extraction be employed to separate the sugars and hemi-cellulose from the brown liquor, resulting in clean depolymerized lignin.

[0019] The sugars and hemi-cellulose are then separated from the salt solution using membrane technology, where the aqueous salt solution is then recycled to the process. The sugars and hemi-cellulose are a product of the process in addition to the clean depolymerized lignin and the clean cellulose fibers. [0020] While the novel technology has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It is understood that the embodiments have been shown and described in the foregoing specification in satisfaction of the best mode and enablement requirements. It is understood that one of ordinary skill in the art could readily make a nigh-infinite number of insubstantial changes and modifications to the above-described embodiments and that it would be impractical to attempt to describe all such embodiment variations in the present specification. Accordingly, it is understood that all changes and modifications that come within the spirit of the novel technology are desired to be protected.