Technical Field

[0001] The present invention relates to a method of processing cellulosic materials. In particular, the invention concerns a method of dissolving cellulose from cellulose containing feedstock, such as pulp, by contacting the cellulose containing feedstock with quaternary ammonium salts, such as spirocyclic ammonium salts or quatemised cyclic ammonium salts, which exhibit chemical and thermal stability. The invention also relates to the use of said ammonium salts for cellulose processing and to a method of manufacturing cellulose-based shaped articles.

Background Art

[0002] Lignocellulosic materials and in particular the cellulosic components thereof are scarcely soluble in traditional solvents, such as apolar and polar organic solvents. However, it has been shown that lignocelluloses can be successfully dissolved in ionic liquids (ILs), such as imidazolium or phosphonium-based ionic liquids. By coupling suitable cations and anions it has been possible to design ionic liquids, which are efficient in cellulose dissolution but often lack the thermal and chemical stability required in cellulose processing.

[0003] Both tetraalkylammonium and phosphonium salts (typically chloride, acetate and hydroxide) are known to allow for dissolution of cellulose, either as the pure salts or as electrolyte solutions (in e.g. DMSO, GVL, or water). Phosphonium salts are highly thermally stable, which is advantageous for recycling of the salt. However, they are expensive. They are also unstable under strongly alkaline conditions (as hydroxide salt or in the presence of strong bases, e.g. sodium hydroxide). Unfortunately, the aqueous alkaline conditions are ideal for cellulose processing as these electrolytes do not need to be completely dried during recycling, which avoids significant energy consumption during recycling.

[0004] Tetraalkylammonium salts are typically thermally much less stable than the phosphonium analogues. They are also relatively chemically unstable, e.g. towards alkali, also preventing their use in cellulose processing, due to poor recyclability. However, they are usually significantly cheaper than the phosphonium analogues. Thus, more chemically and thermally stable and low-cost ammonium salts are desired for cellulose processing, along with many other applications.

[0005] The dissolution mechanism of cellulose in quaternary ammonium hydroxide solutions has been studied by Zhong et al. (2017). Wei et al. (2015) found that improved dissolution of cellulose in quaternary ammonium hydroxide electrolytes was achieved with a decrease in temperature to 16 °C. In studies by Miao et al. (2014), cellulose could be dissolved in quaternary ammonium acetate in the presence of DMSO and crown ether. Synergistic effect of quaternary ammonium salts and crown ether in cellulose solution was shown also by Ema et al. (2014).

[0006] CN 107177040 relates to a process for dissolving cellulose, wherein cellulose is dispersed in an aqueous solution of alkyl ammonium hydroxide, the dispersion is frozen and then thawed to obtain a cellulose solution.

[0007] US patent application No. 2014/0212670 Al provides a process of dissolving cellulose in a solvent comprising quaternary phosphonium hydroxides or quaternary ammonium hydroxides. The cellulose is precipitated to obtain a cellulose solidified article or cellulose shaped article.

[0008] US 9,394,375 relates to a method of dissolving biomass in an ionic liquid and an amine, wherein the ionic liquid is preferably an imidazolium halide or acetate. JPWO2014087646 (US 2016009669 Al) relates to dissolution of cellulose using onium salts. In a report by Abe et al. (2015), aqueous solutions of tetraalkylphosphonium and tetraalkylammonium hydroxides were found to dissolve cellulose at room temperature. Fukaya et al (2010) studied ionic liquids containing methylphosphonate anion and alky limidazo hum, alkylpiperidinium or alkylammonium cation for dissolution of cellulose, and provided some thermal stability data of imidazolium methylphosphonates.

[0009] In WO 03/029329 A2 and US 6,824,599 B2, dissolution of cellulose comprises admixing cellulose with an ionic liquid in the absence of water or a nitrogen- containing base. Among a broad range of cations of the ionic liquid, imidazolium cations are preferred while the preferred anion of the ionic liquid is a halide or pseudohalide.

[0010] Marino and Kreuer (2015) studied alkaline stability of quaternary ammonium cations for ionic liquids. Among different quaternary ammonium (QA) molecular structures, which included aromatic cations, alkyl chains of various lengths, aliphatic heterocycles and QAs with removed or rotationally inhibited b-protons, most QA groups, particularly cyclic QAs, were found to exhibit alkaline stability with the exception of aromatic cations. When the thermal decomposition of quaternary ammonium hydroxides was investigated, b-elimination in the morpholine ring was several times faster than in a piperidine ring (Booth et al., 1978).

[0011] In a study by Clough et al (2016), the structural and thermal properties of tetraalkylammonium chlorides were studied. The study included both single-ring and azoniaspiro-type chloride salts. The single-ring chlorides were susceptible to thermal degradation at lower temperatures than their azoniaspiro congeners. [0012] However, the often-observed low stability of quaternary ammonium compounds under alkaline conditions has prevented them being used as cations in ionic liquids and thus as solvent for reactions under alkaline conditions, such as cellulose processing.

[0013] Thus, there is a need to provide more chemically and thermally stable quaternary ammonium salts for various applications, in particular for cellulose processing and dissolution. Improved chemical and thermal stability of quaternary ammonium salts would provide easy recovery and recycling and thus enables to design a fully recyclable and sustainable process.

Summary of the Invention It is an object of the invention to provide an improved method of dissolving cellulose from cellulose containing feedstocks, where the cellulose containing feedstock is contacted with at least one quaternary ammonium compound having a cation of formula I

wherein the nitrogen substituents X and Y are independently identical or different, substituted or unsubstituted, C ₂ -C ₂ o alkylene chains, optionally interrupted by heteroatoms (O, N, S) and by alicyclic or aromatic rings or combinations thereof, to dissolve cellulose from the cellulose containing feedstock. Another object of the invention is to provide a method of manufacturing cellulose-based shaped articles by dissolving cellulosic material in a liquid phase formed by a quaternary ammonium compound having a cation of formula I as defined above, separating any non-dissolved matter from the liquid phase, recovering a solution comprising cellulose in said liquid phase, precipitating cellulose from the liquid phase to form cellulose-based shaped articles, recovering the liquid phase, and recycling the liquid phase for dissolution of cellulose.

[0014] In a further aspect, the invention concerns a method of manufacturing cellulose-based shaped articles by subjecting a solution comprising a cellulosic material dissolved in a quaternary ammonium compound of the above kind to a spinning method, such as an air-gap spinning, a wet spinning or a dry-jet spinning method, where the solution is spun to articles. In another aspect, the invention concerns a solution comprising a cellulosic material dissolved in the quaternary ammonium compound of the above kind, suitable for use in a method for the manufacture of cellulose-based shaped articles.

[0015] A further object of the invention relates to the use of quaternary ammonium salts having a cation of formula I as defined above for dissolution of cellulose.

Brief Description of the Drawings

[0016] FIGURE 1 top: diffusion-edited 1H-NMR spectrum of a 55 % 6-azonia-2- methyspiro[5.5]undecane hydroxide solution containing 15% MCC. Only polymeric signals are visible, allowing for visualization of cellulose peaks. FIGURE 1 bottom: 1H NMR spectra of a 55% 6-azonia-2-methylspiro[5.5]undecane hydroxide solution and a 15% MCC solution thereof, superimposed on one another.

[0017] FIGURE 2 top: diffusion-edited 1H-NMR spectrum of the 6- azoniaspiro[5.5]undecane acetate electrolyte in DMSO containing 5 wt% MCC. Only polymeric signals are visible, allowing for visualization of cellulose peaks. FIGURE 2 bottom: 'H-NMR spectrum of the 6-azoniaspiro[5.5]undecane acetate electrolyte in DMSO-d ₆ containing 5 wt% MCC.

[0018] FIGURE 3 illustrates thermogravimetric analysis (TGA) of 6- azoniaspiro[5.5]undecane bromide (black), 6-azoniaspiro[5.5]undecane acetate (green), Butyltriethylammonium bromide (blue) and butyltriethylammonium acetate (red). Embodiments

[0019] The present invention is based on the finding that spirocyclic ammonium salts or quatemised saturated cyclic ammonium compounds are able to dissolve cellulose, particularly under aqueous conditions, and exhibit interesting properties in cellulose dissolution. In particular, salts of spirocyclic ammonium and quatemised saturated cyclic ammonium compounds not only dissolve cellulose but exhibit chemical and thermal stability under conditions of cellulose processing, such as under alkaline conditions.

[0020] Thus, by contacting cellulose containing feedstock with a liquid phase or solution comprising or consisting essentially of spirocyclic ammonium salts or quatemised saturated cyclic ammonium compounds, optionally in the presence of a co-solvent, it is possible to dissolve cellulose from cellulose containing feedstocks, such as chemical pulp, thermomechanical pulp, kraft pulp, and other cellulose raw-materials.

[0021] It is also possible to dissolve cellulose in a liquid phase or solution, to separate the dissolved organic material, and then to recover the spirocyclic ammonium salt or quatemised saturated cyclic ammonium and recycle it to cellulose dissolution.

[0022] In an embodiment it is possible to manufacture cellulose-based shaped articles by dissolving cellulose in a liquid phase comprising or consisting essentially of the spirocyclic ammoniums salts or quatemised saturated cyclic ammonium compounds, separating any non-dissolved matter from the liquid phase, recovering a solution comprising cellulose in said liquid phase, precipitating cellulose from the liquid phase to form cellulose-based shaped articles, recovering the liquid phase, and recycling the liquid phase for dissolution of cellulose.

[0023] More specifically, the present invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0024] Considerable advantages are achieved by the present invention. Thus, the invention provides a sustainable method for dissolving of cellulose, enabling easy recovery and recyclability of the dissolving agents. The compounds used in the present invention provide high thermal and chemical stability, allowing better recyclability in dissolution processes of cellulose. The compounds are simple to produce and thus cost-effective. They also provide an option to work under aqueous conditions, which eliminates the need for pre-drying steps and allows for less energy-intensive recycling of dissolution media. Compared to ubiquitously used N-methylmorpholinium-N -oxide (NMMO), they also provide the advantage of not posing an explosion hazard.

[0025] The thermal stability of the salts comprising a cation of formula I and a cation, preferably selected from the group of halide, acetate, and hydroxide, was shown to be significantly higher than for the acyclic tetraalkylammonium homologues. In addition, particularly the acetate salts were shown to dissolve cellulose as DMSO or dimethylformamide (DMF) electrolytes. Likewise, the azoniaspiro hydroxide salts were surprisingly shown to dissolve high amounts of cellulose at low temperatures as the aqueous electrolyte solutions, although their acyclic homologues as electrolytes were incapable of dissolving any significant amounts of cellulose.

[0026] As was discussed above, it is an aim of the present invention to provide an improved method of dissolving cellulose from cellulose containing feedstocks or cellulosic materials.

[0027] In the present method, it is possible in principle to use any known cellulose containing feedstock, individually or in any desired mixtures with one another. Examples of cellulose containing feedstocks include but are not limited to chemical, mechanical or chemomechanical pulps produced from wood or a non-wood source, for example chemical pulp having a cellulose content of 90 % by mass or more, preferably a bleached or unbleached chemical pulp, produced by a known pulping process, such as kraft, pre- hydrolysis kraft, soda anthraquinone (AQ), sulphite, organosolv, alkaline sulfite anthraquinone methanol (ASAM), alkaline sulfite anthraquinone (ASA), S0 ₂ -ethanol- water (SEW), and monoethanolamine (MEA) pulping In one embodiment, bleached pulp is used. In a preferred embodiment dissolving pulp is used. In another embodiment, a paper pulp, i.e. a chemical pulp containing at least 0.1 % and up to 10 % by weight, preferably up to 5 % by weight, of hemicelluloses is used.

[0028] In one embodiment, the solution additionally comprises a lignin or of lignin- containing pulp.

[0029] The wood raw-material can be selected from tree, such as wood from deciduous and coniferous wood species and mixtures thereof, and from perennial and annual plants. A particularly preferred raw-materials is formed by wood obtained from spruce, pine, larch, eucalyptus, birch, poplar, aspen, alder and tropical mixed hardwood. [0030] A further cellulose containing feedstock is formed by recycled cellulosic or lignocellulosic materials, for example recycled papers, such as newspapers, and recycled packagings, such as recycled paper boards.

[0031] A still further cellulose containing feedstock is formed by recycled textile materials, such as used clothes. Thus, the present technology can be used for separation of cellulose and synthetic materials, such as polyester, or polyester monomers. Thus, dissolution of mixed textile materials, such as polycotton, into these mixtures, in particular for separating polyester or its monomers after partial or complete saponification in an alkaline medium, such as a hydroxide, for example alkali metal hydroxide, or a hydroxide electrolyte solvent. During dissolution of cellulosic material, typical reactions for alkaline aqueous conditions may take place, such as hydrolysis of ester or amide bonds. A further application involves separation of textiles and dyes.

[0032] The objects of the invention are achieved by a process which comprises the step of dissolving cellulose from cellulose containing feedstock, which process comprises the step of contacting the cellulose containing feedstock with a spirocyclic ammonium salt or with a quatemised saturated cyclic ammonium compound or electrolytes thereof. Preferably the ammonium salt has a cation of formula I

wherein the nitrogen substituents X and Y are independently identical or different, substituted or unsubstituted, C ₂ -C ₂ o alkylene chains, optionally interrupted by heteroatoms (O, N, S) and by alicyclic or aromatic rings or combinations thereof, to dissolve cellulose from the feedstock.

[0033] In the formula I, substituents X and Y may each independently be optionally substituted C ₂ -C ₂₀ alkylene chains, such as optionally substituted C4-C10 alkylene chains, or optionally substituted C ₄ -C ₆ alkylene chains, preferably in both N-centered rings.

[0034] The cyclic structures can be formed by mono- or polycyclic ring structures, including fused ring structures. Typically, the rings have 5 to 7 members. [0035] In spirocyclic ammonium salts having a cation of the formula I, the two or more rings that fused together via a quaternary nitrogen atom are thus, independently, rings of 3 to 10 atoms, preferably of 4 to 7 atoms, such as of 5 or 6 atoms. The number of members in each ring can be either the same or different.

[0036] According to an embodiment, one or more of the ring atoms of the fused rings are substituted with a substituent group, such as alkyl, substituted alkyl, alkenyl, hydroxyalkyl, alkoxy or substituted alkoxy, mono- or dialkyl amino, aminoalkyl or substituted aminoalkyl group.

[0037] In the present context, the term“alkyl” refers to saturated, straight or branched hydrocarbon radicals containing one to eight carbon atoms. In certain embodiments, alkyl groups contain 1-6 carbon atoms, or 1-5 carbon atoms. In some embodiments, alkyl groups contain 1-4 carbon atoms, 1-3 carbon atoms, or 1-2 carbon atoms. Examples of alkyl radicals include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, pentyl, hexyl, and the like.

[0038] The term ’’alkenyl”, as used herein, refers to straight or branched hydrocarbon radicals having at least one carbon-carbon double bond. In certain embodiments, alkenyl groups contain 2-12 carbon atoms. In some embodiments, alkenyl groups contain 2-8 carbon atoms, 2-6 carbon atoms, or 2-5 carbon atoms. In some embodiments, alkenyl groups contain 2-4 carbon atoms, or 2-3 carbon atoms. Examples of alkenyl radicals include, but are not limited to, ethenyl, propenyl, butenyl, l-methyl-2- buten-l-yl, and the like.

[0039] In the present context, “aromatic rings” includes but is not limited to aromatic groups having 5 to 18 ring atoms, in particular 5 to 12 ring atoms, for example 5 to 8 ring atoms, such as the benzyl ring.

[0040] Compounds of the above structure are obtainable by methods known from the literature.

[0041] Anions used in the compounds of formula I may in principle be any species, for example hydroxide, halide, and acetate, such as anions selected from the group consisting of bromide, chloride, fluoride, fluoride trihydrate, hydroxide, and acetate, preferably from hydroxide and acetate. The thermal stability of the salts comprising a cation of formula I and an anion preferably selected from the group of halide, acetate, and hydroxide, was shown to be significantly higher than for the acyclic tetraalkylammonium homologues.

[0042] The compounds comprising a cation of formula I can be used in the methods of the invention individually or in any desired mixtures with one another. Further, the salts comprising a cation of formula I can be used in the methods of the invention as pure salts or as electrolyte solutions (in e.g. water, DMF or DMSO).

[0043] In an embodiment of the invention for dissolving cellulose, the method comprises admixing cellulose or cellulosic material with a liquid phase comprising or consisting essentially of a compound containing a cation of the formula I above and thus dissolving a significant portion of the cellulose in the liquid phase.

[0044] In an embodiment, 0.1 to 50 parts of cellulosic material or cellulose containing feedstock is contacted with 50 to 500 parts of a compound comprising cations of the above kind, optionally in the presence of a co-solvent, in order to solubilise the cellulosic material or cellulose containing feed stock. Typically, 1 to 10 parts of cellulose containing feedstock is contacted with 50 to 100 parts of the ammonium salt comprising a cation of formula I,

[0045] The method according to the invention can be conducted at a relatively low temperature, i.e. at l50°C or below, or within a temperature range from 10 °C to 80 °C, such as from 20 °C to 60 °C.

[0046] In an embodiment of the invention, a co-solvent or a mixture of co-solvents for the purpose of increasing the solubility or technical processability of the cellulose containing feedstock is added to the ammonium salt solvent to form an electrolyte solution.

[0047] In a preferred example the co-solvent or co-solvents are aprotic and polar. In one example the co-solvent or co-solvents may be selected from the group consisting of dimethylsulfoxide (DMSO), 1,3 dimethyl-2-Imidazolidinone (DMI), 1, 3 -dimethyl-3,· 4,5,6- tetrahydro-2(l//)-pyrimidinone (DMPU), dichloromethane (DCM), cyrene, N- methylpyrrolidone (NMP), /V-butylpyrrolidone (NBP), or other N-alkylpyrrolidones, sulpholane, propylene carbonate (PC), ethylene carbonate (EC), dimethylcarbonate (DMC) and other dialkylcarbonates, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2Me-THF), gamma-Y alerolactone (GYL) and other cyclic lactones, ethyl acetate, acetone, acetonitrile, dimethylformamide (DMF), dimethylacetamide (DMA), l,l,3,3-tetramethylurea (TMU), ethanol, hexamethylphosphoramide (HMPA), acetone, dioxane, and pyridine.

[0048] The amount of co-solvent and the amount of the ammonium salt in the electrolyte solution can be varied so that in one example 0.1 to 50 parts of ammonium salt is mixed with 50 to 500 parts of the co-solvent or co-solvents.

[0049] The content of co-solvent amounts to between 1 and 90%, preferably between 5 and 85%, or advantageously between 50 and 80% of the total weight of the electrolyte solution. The content of the ammonium salt amounts to between 1 and 70%, or between 20 and 60%, such as between 30 and 50% of the total weight of the solution.

[0050] The content of the cellulose containing feedstock in the mixture comprising a co-solvent, a spirocyclic ammonium salt or a quaternary saturated cyclic ammonium compound, and cellulose containing feedstock is typically from 5 to at most 50 % by weight of the mixture, or from 10 to 40 %, for example about 10 to 20 %.

[0051] In one embodiment of the method of the invention, cellulose dissolution is achieved by either ammonium acetates or ammonium hydroxides of the spirocyclic ammonium compounds or the quatemised saturated cyclic ammonium compounds, wherein said ammonium salts are in the form of electrolyte solutions, preferably in the form of electrolyte solutions in DMSO, DMF or water.

[0052] In an embodiment, the dissolved portion of the cellulose is recovered by mixing with a precipitant such as water, dilute acid, aqueous solutions of ammonium salts other organic solvent or aqueous organic solutions. Examples of aqueous solutions include ethanolic and methanolic solutions and similar solutions of water and miscible acids or organic solvents, preferably polar agents.

[0053] Irrespective of the way in which the dissolved material is recovered from the solution, it is preferred to recycle the quaternary ammonium salt. Easy recyclability is due to the heightened thermal and chemical stability of the cyclic ammonium salts provided, in particular of the acetate, hydroxide and halide salts.

[0054] As discussed above, the invention also relates to a method of manufacturing cellulose-based shaped articles by dissolving cellulose in a liquid phase comprising or consisting essentially of a compound having a cation of formula I as defined above, separating any non-dissolved matter from the liquid phase, recovering a solution comprising cellulose in said liquid phase, precipitating cellulose from the liquid phase to form cellulose-based shaped articles, recovering the liquid phase, and recycling the liquid phase for dissolution of cellulose. [0055] Any non-dissolved matter may be separated from the liquid phase for example by filtration before precipitating the cellulose with an anti-solvent.

[0056] In a method of manufacturing cellulose-based shaped article by subjecting a solution comprising cellulose dissolved as explained above to a spinning method, the solution is preferably shaped into a fibre or film. [0057] The solution comprising cellulosic material dissolved in a liquid phase by the method of the invention is stable and easy handle. Thus the invention also provides a solution comprising cellulosic material dissolved in a liquid phase, wherein said solution is suitable for use in a method for the manufacture of cellulose-based shaped articles, particularly by subjecting said solution to a spinning method. The solution (spinning solution, spinning dope) allows for a stable spinning process for the manufacture of highly competitive fibre properties.

[0058] The present invention also relates to the use of a series of azoniaspiro compounds or quatemised saturated cyclic ammonium compounds having a cation of formula I for dissolution of cellulose. The compounds particularly include the halide, acetate, and hydroxide salts of said compounds

[0059] In an embodiment, the ammonium salts for use in the methods of the invention are selected from the group consisting of

6-azonia-2-methylspiro[5 5]undecane bromide;

6-azonia-2-methylspiro[5 5]undecane bisulfate;

6-azonia-2-methylspiro[5 5]undecane hydroxide;

6-azonia-2-methylspiro[5 5]undecane acetate;

6-azonia-2-methylspiro[5.5]undecane fluoride trihydrate;

6-azoniaspiro[5 5]undecane bromide;

6-azoniaspiro[5 5]undecane chloride;

6-azoniaspiro[5 6]dodecane bromide; - 6-azonia[5.6]dodecane acetate;

- 5-azoniaspiro[4.5]decane acetate;

- 6-azoniaspiro[5.5]undecane hydroxide;

- 6-azoniaspiro[5.5]undecane acetate; and

6-azoniaspiro[5.5]undecane fluoride trihydrate

[0060] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0061] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases“in one embodiment” or“in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0062] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0063] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0064] The following non-limiting examples illustrate the invention.

Example 1: Synthesis of 6-azonia-2-methylspiro[5.5]undecane bromide

4.96 g (50 mmol) of 3-methylpiperidine, 11.85 g (50 mmol, 97% purity) of 1,5- dibromopentane and 10 g (100 mmol) of KHCO3 were dissolved/dispersed in 100 ml of EtOH and refluxed for 48 hours. Afterwards, the mixture was allowed to cool off, diluted with 100 ml of MeCN to precipitate most of the still-in-solution KBr, the solids were filtered off and the solution concentrated to about 30 ml. Next, 200 ml of diethyl ether were added to precipitate the product. The mixture was transferred to the freezer (-20°C) for 5 hours, then the product filtered off, washed with diethyl ether and dried in high vacuum overnight. This yielded 11.2 g of a white, free-flowing powder, corresponding to 90% of theoretical yield.

Example 2: Synthesis of 6-azonia-2-methylspiro[5.5]undecane bisulfate

To a stirred solution of 5 mg (20.14 mmol) of 6-azonia-2-methylspiro[5.5]undecane bromide in 5 ml of water, ca. 4 g (3 ml, 31.5 mmol) of dimethyl sulfate were added and the mixture heated to 60 °C for 3 hours to allow for complete evaporation of the generated methyl bromide. 50 ml of water and one drop of concentrated sulfuric acid were added to the mixture and the solution stirred at l20°C overnight, in order to quantitatively hydrolyze the methyl sulfate to the bisulfate. After concentration, the product was a highly viscous, yellow oil.

Example 3: Synthesis of 6-azonia-2-methylspiro[5.5]undecane hydroxide

To a stirred solution of 10.1 g (32 mmol) of barium hydroxide octahydrate in 100 ml of water at 70 °C, a solution of 5.34 g (20.14 mmol) 6-azonia-2-methylspiro[5.5]undecane bisulfate in 20 ml of water was quickly added and stirred for half an hour, letting the solution cool down naturally. The very fine BaS0 ₄ precipitate was filtered off (sinter funnel, pore size 4), and then the solution evaporated using a rotary evaporator (50°C bath temperature). This yielded 4.6 g of the raw product, which was then treated with 2 g of water to create a formally 70% solution (actual azoniaspiro content around 55% due to residual water). Then, to remove small salt particulates, the solution was syringe filtered (0.6 pm filter based on PTFE) to give 3.44 g of a clear, yellow, Ba-free solution. Example 4: Homogenisation of cellulose using an aqueous solution of 6-azonia-2- methylspiro[5 5]undecane hydroxide

To 150 mg of microcrystalline cellulose (Avicel ^® PH-101), 850 mg of the solution generated in Example 3 were added and the resulting dispersion stirred at 50 °C for four hours. The amber, clear and highly viscous liquid was then treated with 0.2 ml of D ₂ 0 and transferred to an NMR tube.

The 1H NMR spectrum showed no significant decomposition of the azoniaspiro compound. Spectra recorded at 50 °C clearly show signals corresponding to cellulose, diffusion edited proton spectra recorded at 50 °C reveal chemically unaltered but clearly dissolved cellulose (Figure 1). Example 5: Synthesis of 6-azoniaspiro[5.5]undecane acetate, an electrolyte solution in DMSO-d6 thereof and its application as cellulose solvent for NMR studies

The synthesis of 6-azoniaspiro[5.5]undecane acetate follows examples 1-3, with the difference that instead of 3-methylpiperidine, piperidine was used, and instead of barium hydroxide, barium acetate was employed. The product was then concentrated and dried in a high vacuum rotary evaporator at 90 °C for 8 hours to remove generated acetic acid and residual water.

Then, 6-azoniaspiro[5.5]undecane acetate and DMSO-d6 were weighed in a 1 :4 ratio, and the initially heterogeneous mixture homogenized via application of heat. The azoniaspiro salt does recrystallize upon cooling, but is easily dissolved again through gentle heating. 50 mg of microcrystalline cellulose (Avicel ^® PH- 101) were added to 950 mg of the above mentioned electrolyte solution, then the mixture stirred at 80 °C for 16 hours. Finally, the clear amber liquid was transferred to an NMR tube and characterized spectroscopically (Figure 2). Example 6: Synthesis of 6-azoniaspiro[5.5]undecane bromide

To 600 ml of chloroform, 86.0 g (100 ml, 1 mol, 99% purity) of piperidine, 234.6 g (139 ml, 1 mol, 98% purity) of l,5-dibromopentane and 130.6 g (175 ml, 1 mol, 99% purity) of diisopropylethylamine were added and the mixture heated under reflux for 15 hours, during which time the product precipitates from solution. Then, the mixture was filtered while still warm and the product washed twice with 200 ml of chloroform each and once with 200 ml of acetone. Finally, the product was dried in vacuo to give 232 g (991 mmol, 99% yield) of free-flowing, pure -white, powdery 6-azoniaspiro[5.5]undecane bromide.

Example 7: Synthesis of 6-azoniaspiro[5.5]undecane chloride

A mixture of 8.6 g (10 ml, 100 mmol, 99% purity) piperidine, 14.4 g (13 ml, 100 mmol, 98% purity) l,5-dichloropentane and 8.0 g (100 mmol, 98% purity) of a 50 wt% sodium hydroxide solution was heated to 100 °C under reflux for 5 hours, then 100 ml of isopropanol added and the heterogeneous mixture left to cool off. Next, precipitated NaCl was filtered off and the solvent evaporated, then the residue taken up in circa 20-25 ml of hot ethanol and the product precipitated via the addition of 150 ml of methyl-tert-butyl ether. The product was filtered off, washed with some more methyl-tert-butyl ether and dried in vacuo to give 18.4 g (97 mmol, 97% yield) of white, powdery 6- azoniaspiro[5 5]undecane chloride.

Example 8: Synthesis of 6-azoniaspiro[5.6]dodecane bromide

5.0 g (50 mmol, 99% purity) of azepane, 11.85 g (50 mmol, 97% purity) of 1,5- dibromopentane and 8.4 g (100 mmol) of sodium bicarbonate were refluxed for 24 hours in 100 ml of ethanol, followed by evaporation of the solvent and extraction of the product with 3x100 ml of hot acetonitrile. The acetonitrile was evaporated and the product taken up in 15 ml of methanol, then precipitated via addition of 100 ml of methyl-tert-butyl ether. Finally, the product was filtered, washed and dried in vacuo to give 10.1 g (40.7 mmol, 91% yield) of pure 6-azoniaspiro[5.6]dodecane bromide.

Example 9: Synthesis of 6-azonia[5.6]dodecane acetate

To 4.0 g (16.1 mmol) of 6-azonia[6.5]dodecane bromide in 50 ml of methanol, 2.68 g (16.1 mmol, 99% purity) of silver acetate were added and the resulting mixture stirred at room temperature and light exclusion for 8 hours. Then, generated silver bromide was filtered off and the filtrate concentrated in vacuo to give 3.55 g (15.6 mmol, 97% yield) of slightly off-white 6-azonia[6.5]dodecane acetate. An optional purification step comprises leaving the product to stand open to the sun and atmosphere for 72 hours, then dissolving it in 10 ml of methanol, filtering off photo-reduced residual silver via use of a syringe filter (PTFE-based, 0.64 pm) and evaporating the solvent.

Example 10: Synthesis of 5-azoniaspiro[4.5]decane acetate

To 200 ml of isopropanol, 8.60 g (10 ml, 100 mmol, 99% purity) piperidine, 21.8 g (100 mmol, 12.1 ml, 99% purity) 1 ,4-dibromobutane and 27.7 g (200 mmol) potassium carbonate were added and the resulting mixture heated under reflux for 16 hours. Next, 20.1 g (100 mmol) of lauric acid were added and refluxing continued for another 3 hours, followed by filtration of the mixture while still hot, washing the filter cake with 75 ml of hot isopropanol and concentrating the filtrate in vacuo to give waxy 5- azoniaspiro[4.5]decane laurate, which was dissolved in 50 ml of warm water. To this solution, 9.0 g (150 mmol) of glacial acetic acid were added dropwise, and then the biphasic mixture cooled to 4 °C and solidified lauric acid filtered off. The filter cake was washed with 20 ml of cold water and the filtrate concentrated in vacuo, the residue taken up in 100 ml of chloroform and filtered again, then the filtrate concentrated and the residue dried in vacuo to yield 16.4 g (82.3 mmol, 82% yield) of solid 5-azoniaspiro[4.5]decane acetate.

Example 11: Synthesis of 6-azoniaspiro[5.5]undecane hydroxide

To a solution of 50 g (213.5 mmol) 6-azoniaspiro[5.5]undecane bromide in 25 ml of distilled water, 27.0 g (214 mmol, 20.3 ml) of dimethyl sulfate were added, resulting in strong and long-lasting effervescence. The generated methyl bromide was neutralized by directing it through a washing bottle filled with a cold mixture of ethanol and concentrated ammonia. Once effervescence ceased, the reaction mixture was heated to 50 °C and another 12.0 ml (126.5 mmol, 16.0 g) of dimethyl sulfate were added to it in 3 aliquots of 4 ml each, waiting for an hour between each addition. After confirming that the halide content in the reaction mixture is low (negative silver nitrate test), 1.0 ml (18 mmol) of 96% sulfuric acid was added and the mixture stirred openly at 130 °C for 12 hours in order to hydrolyze methyl sulfate to the bisulfate anion. After addition of 50 ml of distilled water and cooling down to 60 °C, a solution of 113.1 g (358.5 mmol) barium hydroxide octahydrate in 200 ml of hot water were added and the resulting heterogeneous mixture stirred while allowing it to cool to room temperature. Barium sulfate was filtered off and the filtrate concentrated to around 90 g total weight, cooled to 4 °C and filtered again. This gave 85.5 g of a slightly viscous and colorless solution containing 35.5 wt% of 6- azoniaspiro[5.5]undecane hydroxide (83% yield based on 6-azoniaspiro[5.5]undecane bromide).

A 33.0 g portion thereof was further concentrated to 17.3 g via rotary evaporation at 50 °C, then cooled to 4 °C and subjected to syringe filtration (PTFE-based, 0.64 pm) to give 16.3 g of a slightly yellow, quite viscous solution with a 6-azoniaspiro[5.5]undecane hydroxide content of 64 wt%. Example 12: Synthesis of 6-azoniaspiro[5.5]undecane acetate

To a solution of 10.0 g (39.8 mmol) 6-azoniaspiro[5.5]undecane bisulfate in 20 ml of distilled water, a solution of 10.2 g (39.8 mmol) barium acetate in 20 ml of distilled water was added under stirring and the resulting heterogeneous mixture stirred for 15 minutes, then precipitated barium sulfate filtered off and the filtrate concentrated at 100 °C in vacuo to give 8.0 g (37.8 mmol, 95% yield) of white, solid 6-azoniaspiro[5.5]undecane acetate.

Example 13: Synthesis of 6-azoniaspiro[5.5]undecane fluoride trihydrate

To 5.0 g (10.36 mmol) of a 35.5 wt% 6-azoniaspiro[5.5]undecane hydroxide solution, 0.434 g (10.4 mmol, 374 mΐ) of a 48 wt% hydrofluoric acid solution were added under stirring and the resulting solution concentrated via rotary evaporation at 50 °C until distillation became very slow to give 2.35 g (10.34 mmol, 99% yield) of translucent, crystalline 6-azoniaspiro[5.5]undecane fluoride trihydrate.

Example 14: Synthesis of 6-azonia-2-methylspiro[5.5]undecane hydroxide

10.0 g (100 mmol, 99% purity) of 3-methylpiperidine, 14.4 g (100 mmol, 98% purity) of l,5-dichloropentane and 8.0 g (100 mmol) of a 50 wt% sodium hydroxide solution were mixed and heated under reflux for 5 hours, then 100 ml of isopropanol added and left to cool to room temperature under stirring. Next, precipitated sodium chloride was filtered off and the filtrate concentrated in vacuo. The solid residue was taken up in circa 20-25 ml of hot ethanol and the product precipitated via the addition of 150 ml of methyl-tert-butyl ether. The product was filtered off, washed with some more methyl-tert-butyl ether and dried in vacuo to give 19.4 g (95.3 mmol, 95% yield) of white, powdery 6-azonia-2- methylspiro[5 5]undecane chloride.

7.55 g (37.0 mmol) of 6-azonia-2-methylspiro[5.5]undecane chloride were then treated with 4.09 g (40.0 mmol, 2.22 ml) of 96% sulfuric acid, leading to vigorous effervescence and liquefaction of the azoniaspiro salt. The generated hydrogen chloride was neutralized by leading it through a washing bottle filled with cooled 1M sodium hydroxide solution. After cessation of effervescence, the reaction mixture was heated to 150 °C under stirring, and another 0.50 ml (9.0 mmol, 0.92 g) of 96% sulfuric acid added, then the mixture stirred for an hour at 150 °C. After a successful (negative) silver nitrate test, the liquid bisulfate salt was cooled to 80 °C, treated with 20 ml of water and let cool off naturally. Next, a solution of 15.5 g (49.0 mmol) barium hydroxide octahydrate in 50 ml of hot water were added under vigorous stirring and stirring continued for 10 minutes, followed by filtration of barium sulfate and concentration of the filtrate to 16 g total weight. Finally, this solution was cooled to 4 °C and subjected to syringe filtration (PTFE-based, 0.64 pm) to give 14.2 g of a colorless 39.8 wt% solution of 6-azonia-2-methylspiro[5.5]undecane hydroxide (82% yield, based on 6-azonia-2-methylspiro[5.5]undecane chloride used).

Example 15: Comparison of thermal stabilities - azoniaspiro compounds vs classic aliphatic tetraalkylammonium compounds

Thermogravimetric analysis is routinely employed for the determination of a compound’s thermal stability. Comparison of decomposition onset temperatures for 6- azoniaspiro[5.5]undecane bromide and acetate, and butyltriethylammonium bromide and acetate is illustrated in Figure 3.

6-Azoniaspiro[5.5]undecane bromide starts to decompose at 334 °C, almost 120 °C after the acyclic aliphatic congener butyltriethylammonium bromide does (216 °C). Comparing the acetates, which generally tend to decompose sooner due to heightened nucleophilicity and basicity of the acetate anion vs. the bromide anion, it is apparent that decomposition of the 6-azoniaspiro[5.5.]undecane acetate sets in over 50 °C later (213 °C) than it does for butyltriethylammonium acetate (157 °C). It is worth mentioning that the azoniaspiro acetate is almost as thermally stable as the aliphatic acyclic tetraalkylammonium bromide.

Example 16: Dissolution of microcrystalline cellulose (Avicel® PH- 101) using aqueous 6-azoniaspiro[5.5]undecane hydroxide solutions A 64 wt% solution of 6-azoniaspiro[5.5]undecane hydroxide was adjusted to 60, 50, 49, 40, 30, 20 and 10 wt% hydroxide content using distilled water and the solubility of Avicel ^® PH-101 therein tested at room temperature.

Table 1

The higher the hydroxide content, the quicker samples start to colorize, changing from a light yellow over a deep orange to a brownish shade of color.

Example 17: Dissolution of microcrystalline cellulose (Avicel® PH- 101) using aqueous 6-azonia-2-methylspiro[5.5]undecane hydroxide solutions Table 2

Example 18: Dissolution of microcrystalline cellulose (Aviccl PH- 101) at room temperature using a solution of 6-azoniaspiro[5.5]undecane hydroxide trihydrate in DMSO Table 3

Example 19: Dissolution of microcrystalline cellulose (Aviccl PH-101) using 6-azoniaspiro[5.5]undecane acetate electrolytes

To a solution of 6-azoniaspiro[5.5]undecane acetate in various co-solvents, Avicel® PH- 101 was added and dissolution thereof performed under specific conditions.

Table 4

Example 20: Dissolution of microcrystalline cellulose (Avicel ^® PH- 101) using 6-azoniaspiro[5.5]undecane fluoride trihydrate and electrolytes thereof

Table 5

Example 21: Regeneration of cellulose from solution using distilled water

A 15% solution of Avicel ^® PH-101 in an originally 49 wt% aqueous

6-azoniaspiro[5.5]undecane hydroxide solution was added dropwise to a lOO-fold mass equivalent of vigorously stirred distilled water, resulting in the (comparatively) slow regeneration of cellulose in undefined shapes. After stirring the mixture for 12 hours at room temperature, cellulose was filtered off and washed with water, then dried in vacuo. A wide-angle x-ray scattering experiment of this regenerated material exhibited a high amount of amorphous material and confirmed the presence of some cellulose II.

The filtrate was concentrated in a rotary evaporator at 50 °C until a

6-azoniaspiro[5.5]undecane hydroxide content of 49 wt% was established again. Example 22: Regeneration of cellulose from solution using aqueous sulfuric acid

A 15% solution of Avicel ^® PH-101 in an originally 49 wt% aqueous

6-azoniaspiro[5.5]undecane hydroxide solution was added dropwise to a 50-fold mass equivalent of vigorously stirred distilled water, which additionally contained 2 mol- equivalents of sulfuric acid, relative to hydroxide content. Regeneration of cellulose was instantaneous, allowing for the production of cellulose beads. These beads were kept in aqueous environment for another 15 hours, then filtered off and washed with distilled water.

The filtrate, containing surplus acid and a 6-azoniaspiro[5.5]undecane bisulfate, was treated with a mol-equivalent of barium hydroxide octahydrate, then the generated barium sulfate filtered off and the solution of 6-azoniaspiro[5.5]undecane hydroxide concentrated to the original 49 wt% again. Example 23: Regeneration of cellulose from solution using aqueous ammonium thiocyanate

A 15% solution of Avicel ^® PH-101 in an originally 49 wt% aqueous 6-azoniaspiro[5.5]undecane hydroxide solution was added dropwise to a 50-fold mass equivalent of vigorously stirred distilled water, which additionally contained 1 mol- equivalent of ammonium thiocyanate, relative to hydroxide content. Regeneration of cellulose was instantaneous, allowing for the production of cellulose beads. These beads were kept in aqueous environment for another 15 hours, then filtered off and washed with distilled water.

The filtrate was evaporated to give 6-azoniaspiro[5.5]undecane thiocyanate.

Example 24: Regeneration of cellulose from solution using aqueous ammonium bicarbonate

A 15% solution of Avicel ^® PH-101 in an originally 49 wt% aqueous 6-azoniaspiro[5.5]undecane hydroxide solution was added dropwise to a 50-fold mass equivalent of vigorously stirred distilled water, which additionally contained 1 mol- equivalent of ammonium bicarbonate, relative to hydroxide content. Regeneration of cellulose was instantaneous, resulting in a loosely aggregated cellulose precipitate. This precipitate was stirred in aqueous environment for another 15 hours, then filtered off and washed with distilled water.

The filtrate, containing 6-azoniaspiro[5.5]undecane bicarbonate, was treated with a mol- equivalent of calcium hydroxide, then calcium carbonate filtered off and the resulting solution of 6-azoniaspiro[5.5]undecane hydroxide concentrated to the original 49 wt% again.

[0065] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0066] The verbs“to comprise” and“to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality. Industrial Applicability

[0067] At least some embodiments of the present invention find industrial application in cellulose processing, particularly dissolution, wherein the recovered cellulosic materials can be put to several uses, for example for the production of paper/ paper pulp/ cardboard/ carboxymethyl cellulose (CMC)/ biofuel/ textiles/ adhesives. The shaped cellulose-based articles produced by the method of this invention can be used as textile fibres, carbon fibre precursors, high-end non-woven fibres, technical fibres, films for packaging with superior properties than cellophane but comparable to polyethylene films, barriers films in batteries, membranes etc.

Acronyms List

DCM Dichloromethane

DMA Dimethylacetamide

DMF Dimethylformamide

DMI 1.3-Dimethyl-2-imidazolidinone

DMPU 1.3-dimethyl-3,4,5,6-tetrahydro-2(l//)-pyrimidinone

DMSO Dimethyl sulfoxide

HMPA Hexamethylphophoramide

IL Ionic liquid

MCC Microcrystalline cellulose

NMMO N -methy lmorpholinium-N -oxide

NMR Nuclear magnetic resonance

PTFE Polytetrafluoroethylene

TGA Thermogravimetric analysis

THF T etrahydrofuran

TMU T etramethylurea Citation List

Patent Literature

CN 107177040

JPWO2014087646 (US 2016009669 Al)

US 2014/0212670 Al

US 6,824,599 B2

US 9,394,375

WO 03/029329 A2

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