A method for lignin separation and usage of lignin

Abstract

The present invention relates to a method for separating lignin, a lignin product obtainable by said method and its usage.

Description

[0001] A METHOD FOR LIGNIN SEPARATION AND USAGE OF LIGNIN

[0002] Field of the invention

[0003] The present invention relates to a method for separating lignin, a lignin product obtainable by said method and its usage.

[0004] Background

[0005] Lignin is a renewable raw material that has had technical limitations, although certain remarkable applications can now be highlighted. The cellulose and paper industry produce huge amounts of lignin each year and over 90 % of this material is normally directly burned at the same factories in an energy-recovery step. In total a minor part of lignin from sulfite pulping and kraft lignins are commercially exploited currently, and thus it is a promising field for obtaining commercially valuable products from lignin derivatives for the future. A major part of sulphite lignins are converted into lignosulfonates.

[0006] Precipitation of lignin from liquors in sulfite and sulfate pulp manufacturing is known. Sulfite liquor has, most usually, a low pH and contains lignosulfonates. Sulfate liquor has a high pH and contains sulfate lignin. The traditional way of handling such lignin products has been to evaporate these and to use it as fuel internally as mentioned above e.g. in a recovery boiler with subsequent rework of the remains from the melt (oxide, carbonate and sulphide) into new cooking chemicals (e.g. sodium sulphide and sodium hydroxide).

[0007] Kraft lignin (KL) and lignosulfonates (LS) are thus as such known. The application and manufacture (using precipitation) of lignin is disclosed in e.g. W02006031175A1 (Lignoboost) and in SE2150944A1 and WO2023287340A1 (Suncarbon). In the last mentioned, sulfate lignin is precipitated from an acidic biomass stream, such as pyrolysis oil.

[0008] Further, SU1006389A appears to mention liquors from sulfate and sulfite. In addition, TAPPI 23rd Alkaline Pulping Conference, Jacksonville, Florida, October 14-16, 1969, RECOVERY OF CHEMICALS IN COMBINED KRAFT AND NSSC PULP MILLS, WILLIAMSON DF;

[0009] HOUGH GW; MASON Fl, seems to point away from said combination. In addition, there is CN 102140174A which discloses a method for preparation of a lignin product by mixing sulfate pulping waste liquor and sulphite pulping waste liquor. Further, there are aldehyde compounds added to enhance the precipitation.

[0010] There is a thus however a need for lignin material useful in certain application areas that provide new benefits and which may be flexible when it comes to its application areas. Also, a simpler way of providing a lignin product as mentioned previously would be of benefit. Saving raw material would be of benefit. Further, in normal mills, there is also normally a recovery boiler present that calls for maintenance which in turn is very costly. Also, its installation thereof is extremely costly. A simplified process would also be desirable.

[0011] Summary of the invention

[0012] The present invention solves / alleviates one or more of the above problems by providing according to a first aspect a method for separating lignin from a combined stream comprising the following steps: a) providing a stream from a sulfate pulp manufacturing process, preferably black liquor, b) providing a stream from a sulfite pulp manufacturing process, preferably brown liquor, c) and whereupon combining both said streams, preferably involving also mixing, and thereupon the mixed stream is kept at a temperature above about 110 °C, preferably from about 120 °C to about 180 °C, most preferred from about 140 °C to about 160 °C, especially preferred at about 150 °C, during from about 0.5 to about 5 hours, preferably from about 0.75 to about 1.25 hours, most preferred during about 1 hour, whereby this provides: d) precipitation of lignin, preferably by not adding one or more additives, such as one or more helping agents, thus providing a lignin product.

[0013] The above method of the present invention providing precipitation of two streams creates a new material for applications in materials and / or a as a solid fuel. In addition, helping agents such as aldehyde compounds may be omitted for enhancing the precipitation set out above. Further said method has huge consequences in the form of the possibility for co-localization of sulfite- and sulfate pulp manufacturing facilities and at the same time abolishing the need for a recovery boiler which is a heavy investment in a mill and which normally incinerates evaporated sulfate liquor (black liquor) or sulfite liquor (brown liquor). The method of the present invention thus solves / alleviates this problem. Thus, process steps may be omitted as a recovery boiler, normally present in a mill, may be omitted when using the present invention. Further, in addition Sustainability Development Goals (SDGs) 8, 9 and / or 12 may be affected in a positive way using said method. Thus, the method according to the present invention has a positive impact when it comes to sustainability and in particular some of the global sustainability goals which in total are 17.

[0014] SDG Targets: 8.2 Achieve higher levels of economic productivity through diversification, technological upgrading and innovation, including through a focus on high-value added and labour- intensive sectors.

[0015] 9.4 By 2030, upgrade infrastructure and retrofit industries to make them sustainable, with increased resource-use efficiency and greater adoption of clean and environmentally sound technologies and industrial processes, with all countries taking action in accordance with their respective capabilities.

[0016] 9.5 Enhance scientific research, upgrade the technological capabilities of industrial sectors in all countries, in particular developing countries, including, by 2030, encouraging innovation and substantially increasing the number of research and development workers per 1 million people and public and private research and development spending.

[0017] 12.2 By 2030, achieve the sustainable management and efficient use of natural resources.

[0018] The present invention also is in line with aims of the current Ell bio-economy strategy and with Ell Green deal.

[0019] Said precipitation of the method according to the first aspect may also in parallel, be assisted by coagulation, thus there may also be a precipitation and / or coagulation ongoing in said step d) of the method of the first aspect of the present invention.

[0020] The present invention also provides according to a second aspect a lignin product obtainable by a method according to the first aspect. The lignin product obtainable by said method, is a new type of technical lignin with characteristics from both kraft lignin (such as the one obtained using e.g. the Lignoboost process (commercialized at StoraEnso, Sunila, Finland and at Domtar, Canada) and lignosulfonate (such as the one obtainable from Domsjb or Borregaard sulfite mills). The characteristics may also be controlled by the mixing relationship of streams: sulfite vs. sulfate. The lignin product provided according to the said second aspect by the present invention is thus also very flexible when it comes to the usage thereof, due to its characteristics, in comparison with earlier known lignin product (such as the ones described above earlier).

[0021] The present invention also provides according to a third aspect use of the lignin product according to the second aspect. Usage areas are all the ones that technical lignin is presently used within, but said lignin product of the second aspect has a clear advantage as it mimics both of the above mentioned earlier lignin products. This may e.g. have an advantage in continued modification into adhesives or when used in compatibilization to plastics. Said lignin product according to the second aspect may further be used as set out for the third aspect as follows: as a free-radical scavenger, an anti-oxidant, as an anti-viral or antibiotic or anti-cancerogenic compound, as a dietary enhancing agent, as a technical lignin, in a battery or in an intermediary product for making a battery or a component thereof, in production of chemicals, in glue applications, in a lacquer (which could be biodegradable), in concrete manufacturing for preventing lumping and settling of unsolved particles, as a dispersant agent for use in connection with pesticides, such as for stabilization, as a binding agent such as for use in coal briquettes or ceramics or wood-related materials, such as for use in plywood or particle boards, or in agriculture as animal feed or soil stabilizer, as an emulsifier, as a heavy-metal sequestrant, as a moisture-retention agent, as a dustsuppressor (such as to avoid air-borne particles in e.g. public works, unpaved roads, airports, sports facilities or racing circuits), in leather-tanning, in gypsum-board manufacturing, in asphalt emulsions (for replacing bitumen of fossil origin and for stabilizing said emulsion), in wax emulsions, in dyes , in pigments, in composites, in coatings, in carbon fibre manufacturing, as a co-polymer component (for use in manufacturing of bio-plastics), for use in purification of water, food or chemicals, in gasoline vapor emission control, in lubricants, in inks, in rubber compositions, in polyurethane elastomers, as compatibilizer in e.g. plastics, in production of fossil petroleum in an oil field, in mining applications, in pavement markings, in soaps, in detergents, in textiles, as cleaning and decontamination agent, as a chelating agent, in the manufacture of containers, such as bottles, as fuel, such as bio-fuel, in a solid or liquid fuel plant to recover heat and steam therefrom, or in heating applications. Said lignin product may also be used as such or as a precursor when making a derivative (i.e. modifying said lignin product) that may be useful in one or more of the application areas mentioned above.

[0022] When it comes to said anti-oxidant application area, said lignin product according to the second aspect may have anti-oxidant activity in red blood cells. In animal feed said lignin product may be useful in a prebiotic composition. Said product may improve the growth of beneficial bacteria and morphological structures in the intestines of animals. On the other hand, lignin fragments have also shown bactericidal properties so that they may help control intestinal pathogens in livestock products. When it comes to the lignin products usage as a dietary enhancing agent, it may absorb bile acid and may thus have an impact on lipid metabolism. When using said lignin product as a binding agent, it may be used when briquetting mineral dust and then it may bind fines, shavings and turnings. Binding agents based upon said lignin product may also be used in development of eco-friendly renewable materials. When using said lignin product as a cleaning and decontamination agent, e.g. in water or in soil, this may prevent scaling problems. Also, this usage may enhance the provision of ions thus making them more available for plants. Said usage may involve said lignin product in a ppm-scale. When modifying said lignin product as set out above, owing to its aromatic nature, said product may be subjected to a wide range of reactions (and modifications): alkylation, dealkylation, oxyalkylation, amination, carboxylation, acylation, halogenation, nitration, hydrogenolysis, methylolation, oxidation and reduction, sulfomethylation, sulfonation, silylation, phosphorylation, and nitroxide formation or a combination thereof.

[0023] Detailed description of the invention

[0024] It is intended throughout the present description that the expressions “sulfite” or “sulfate” are equivalent with sulphate or sulphite, respectively. Said expressions may be used interchangeably in the present specification.

[0025] According to a preferred embodiment of the first aspect, active heating is used in step c) for keeping said mixed stream at said temperatures or said temperature ranges, wherein said heating may be provided by a stream emanating directly from a chemical pulp digester, such as a cooking vessel.

[0026] According to a preferred embodiment of the first aspect the streams comprises from about 10 to about 25 wt%, preferably from about 12 to about 20 wt% of raw material that when combined provides a lignin product. If one or both streams are evaporated before being combined they may contain from about 25 to about 80 wt%.

[0027] According to a preferred embodiment of the first aspect the flow rate of the streams is at least 10 m3 / h, preferably from about 20 to about 400 m3 / h, and the temperature of said streams is at least 40 °C, preferably from about 45 to about 100 °C.

[0028] According to a preferred embodiment of the first aspect the stream from a sulfate pulp manufacturing process, and the stream from a sulfite pulp manufacturing process emanate from separate mills, wherein preferably one or both streams are undergoing evaporation before being transported.

[0029] According to a preferred embodiment of the first aspect said method comprises adding one or more helping agents to one or both streams set out in a) and b), or in the combined stream in step c), for enhancing the precipitation of lignin. Said helping agents may be e.g. coagulants such as cationic polymers (or others that have affinity for lignins such as tannins). They may also be electrolytes, preferably such that already is present in the process and wherein evaporated overphase (supernatant) after separating lignin from said sulfite and sulfate streams will have a higher electrolyte contents but may also have simpler salts with preferably two or multivalent cations. It is also possible to modify the pH with an acid such as using sulfuric acid or using alkali such as using sodium hydroxide in order to modify the precipitation. The different streams may be heated before being combined, and they also may be pre-evaporated to change the relationships between the different streams.

[0030] According to a preferred embodiment of the first aspect said method comprises a further step e) separating said lignin product, preferably using filtration, to provide a lignin product, which most preferred is in a solid form, and at the same time providing a left-over supernatant.

[0031] According to a preferred embodiment of the first aspect said method comprises a further step f) washing and subsequent drying of said lignin product to provide a powder.

[0032] According to a preferred embodiment of the first aspect said supernatant is evaporated for chemical recovery, thus providing cooking chemical(s) for sulfite and / or sulfate pulping.

[0033] Preferred features of each aspect of the invention are as for each of the other aspects mutatis mutandis. The prior art document (s) mentioned herein are incorporated to the fullest extent permitted by law. The invention is further described in the following example, together with the appended figures, which do not limit the scope of the invention in any way.

[0034] Embodiments of the present invention are described as mentioned in more detail with the aid of examples of embodiments, together with the appended figures, the only purpose of which is to illustrate the invention and are in no way intended to limit its extent.

[0035] Figures

[0036] Figure 1 discloses a schematic view of a normal conventional pulp mill involving sulfite (Figure 1a) and sulfate (Figure 1b) pulping (prior art) and its contents, with e.g. recovery boilers present.

[0037] Figure 2 reflects the method according to the present invention, also with optional evaporation steps. The black and brown liquor may emanate from mills placed remotely from the facility for manufacturing the lignin product obtainable by the present invention, or said liquors may be available in the near vicinity of said facility. If available nearby said liquors may be transported via pipelines. If the liquors are taken from one or more remote mills, the liquors may be transported using a tank boat or a truck equipped with a tank, potentially preceded by an evaporation step for creating less material to transport. After said streams i.e. said black and brown liquor (potentially evaporated), have been mixed they are conveyed into a separating unit where both a supernatant liquid phase and a precipitated solid phase emerges (arises). The supernatant may then be subject to evaporation and chemical recovery, whereby cooking chemicals for sulfate and sulfite pulping are recovered. The precipitate may then undergo washing and drying. The technical lignin then obtained will have novel properties compared to existing kraft lignin or lignosulfonic acids. Instead of using said technical lignin for subsequent further processing, or doing it in parallel with subsequent processing, said material recovered after precipitation may be used for energy and steam by using a solid fuel boiler and also as part of chemical recovery.

[0038] Figure 3, a, b, c, d and e show photos and optical micrographs at 100x magnification.

[0039] Figure 4, shows water contact angle as a function of time after dispensing a 10 microliter deionized water (pH 10) drop onto the tablet surfaces.

[0040] Figure 5 shows 5a: water (at pH 10) drop on tablet of ”KL_ref” sample. Water contact angle after 1 second was 42.5 degrees and 5b: water (at pH 10) drop on tablet of ”KL+LS_ref” sample. Water contact angle after 1 second was 45.3 degrees.

[0041] Figure 6 shows 6a: water (at pH 10) drop on tablet of “LS_ref” sample. Water contact angle after 1 second was 31.2 degrees and 6b: water (at pH 10) drop on tablet of “KL 150C,1h” sample. Water contact angle after 1 second was 56.2 degrees.

[0042] Figure 7 shows water (at pH 10) drop on tablet of “KL+LS 150C,1h” sample. Water contact angle after 1 second was 76.0 degrees.

[0043] Figure 8 shows FTIR spectra for reference and autoclaved samples, the whole measured range 650 to 3800 cm-1

[0044] Figure 9 shows FTIR spectra for reference and autoclaved samples, the so-called fingerprint region, plotted 600 to 1800 cm-1.

[0045] Figure 10 shows FTIR spectra for reference and autoclaved samples, the intermediate region, plotted 1800 to 2300 cm-1.

[0046] Figure 11 shows FTIR spectra for reference and autoclaved samples, the high wavenumber region, plotted 2700 to 3800 cm-1.

[0047] Examples Example 1

[0048] Two process streams, namely spent liquors from sulfate (black liquor, BLL) at high pH and sulfite (brown liquor, BRL) at low pH pulping containing kraft lignin (KL) and lignosulfonate (LS) are contacted directly after the respective pulping processes. Both BLL and BRL have KL and LS concentrations of about 12-20% solids. The BLL stream is preferably first taken to a process step whereby tall oil is separated from the BLL stream. The BLL and BRL streams are mixed, see Figure 2, and precipitation occurs. The supernatant contains salts and soluble lignin that will be converted to new cooking liquors for both kraft pulping and sulfite pulping using their respective, existing caustisizing cycles after evaporation. The precipitate between BLL and BRL is the new technical lignin product and is filtrated off and dried to a powder which is a final product for technical applications or is partially used as fuel in an industrial solid fuel boiler to receive high pressure steam at the plant. When BLL and BRL is mixed at process temperatures there will likely be flash steam produced because of the high temperature and an exothermic reaction. This can be taken care of in a flash steam vessel and steam will be used in the plant.

[0049] Example 2

[0050] Two process streams, as in Example 1 , are contacted but evaporation is first used on one or both BLL and BRL streams to adapt the composition of the precipitated technical lignin produced.

[0051] Example 3

[0052] Two process streams, as in Example 1, are contacted and different additives, such as acid or alkali to change pH, flocculants or coagulants is used on one or both BLL and BRL streams or during the precipitation to increase the precipitation efficiency and the properties of the technical lignin produced. Flocculants can be polymeric flocculants, such as cationic polymers, and coagulants can be divalent or trivalent salts, such as alum, or preferably, evaporated supernatant from the new process cycle.

[0053] Example 4 Two process streams, as in Example 1 , are contacted and different filtration and decantation devices are used to increase efficiency in precipitation and subsequent washing of the precipitate. These are preferentially used in a counter-current set-up with use of thin or thickevaporated supernatant. A portion of the supernatant or precipitated product in dispersion can be spray-dried to achieve a technical lignin product.

[0054] Example 5

[0055] Two types of technical lignins in powder form were used to show the extent of precipitation and properties of the precipitate: a lignosulfonate and a kraft lignin. These were acquired from TCI and Sigma Aldrich, CAS # 8061-51-6 and 8068-05-1 , respectively. The lignosulfonate powder was dissolved in 1 molar sulfuric acid and at 5 gram / liter and the kraft lignin in 1 molar sodium hydroxide, also at 5 gram / liter.

[0056] The two solutions were mixed and directly formed a precipitate. After sedimentation, the product was filtered off on paper filtrate and collected. The product was air-dried at room temperature. The total solids from the original solutions were 10 grams / liter and the precipitated product was weighed out. The yield of precipitated product was 86 % and 45% after washing the filter cake with four 50 mL aliquots of deionized water. The remaining filtrate had a pH of between 5 and 6. The discrepancy between washed and non-washed filter cake accounts for remaining salt from sodium hydroxide and sulfuric acid (i.e. sodium sulfate) and some dissolution of the precipitated product at a neutral pH.

[0057] A portion of the product was dissolved in 1 molar sulfuric acid and another portion in 1 molar sodium hydroxide. A third portion was put in water at neutral pH. The precipitate was fully dissolved in the alkaline solution and were dissolved to a proportion of 17% in the acidic solution. The precipitated product was dissolved in water at neutral pH to a proportion of 25%.

[0058] The precipitated product had properties resembling both the lignosulfonate and the Kraft lignin but can also have new unique properties.

[0059] Example 6

[0060] Kraft lignin (alkali lignin from Sigma-Aldrich) and lignosulfonate (from Sigma-Aldrich) in powder form were used as examples of lignins that would be present in industrial process streams from kraft pulping (black liquor containing kraft lignin, hemicelluloses and salts) and from sulfite pulping (brown liquor containing sulfonated lignin, hemicelluloses and salts).

[0061] Lignosulfonate (LS) is soluble across the normal pH range whereas kraft lignin (KL) is soluble only at alkali pH. Solutions at 5 g / L of each KL and LS were prepared at pH 10 in deionized water. A series of precipitation experiments were performed as detailed in Example 1-3.

[0062] Example 6 prepares KL and LS solutions in the same manner but these are now autoclaved at 150 degrees C for 1 hour in glycerol bath. Autoclaves were fitted with 2 L of solutions, and were closed but not evacuated and the atmosphere was normal air at normal pressure.

[0063] Four different samples were prepared:

[0064] 1. LS solution at 10 g / L, total volume 2 L.

[0065] 2. KL solution at 10 g / L, total volume 2 L.

[0066] 3. Mixture of 1 L of each of LS and KL solution so that the total concentration was also 10 g / L and the total volume 2 L.

[0067] The autoclaves were heated to 150 C by increasing the temperature by 2 degrees C per minute and kept at 150° C once the target temperature was reached.

[0068] The samples were analyzed after autoclavation.

[0069] Table 1 Samples, pH and concentration of non-soluble matter after autoclavation.

[0070] The non-soluble fraction was filtered off, dried and made into tablets for further analyses by water contact angle and Fourier Transform Infrared Spectroscopy (FTIR). These results are further highlighted below and in Figures 3 - 11.

[0071] The experiment clearly showed a chemical reaction between KL and LS at conditions that are present at industrial process and with no use of extra chemicals to initiate chemical reactions. This is further illustrated by the following figures: Figure 3 shows photo images of the 2 cm diameter tablets and close-up micrographs using a DPM 100 USB optical microscope. Photos and optical micrographs at 100x magnification of reference material and non-soluble fractions after autoclavation: (a) KL reference, used as received, (b) LS reference, used as received, (c) KL+LS, a 50 / 50 w / w mixture of KL and LS powder, used as received, (d) KL after autoclavation (sample 2 in Table 1), and (e) KL+LS after autoclavation (sample 3 in Table 1). Sample 1 had a too small non-soluble fraction to evaluate.

[0072] Water contact angle measurements were used to assess the wettability, and thus is further illustrated in Figure 4. In Figure 4, Water contact angle as a function of time after dispensing a 10 microliter deionized water (pH 10) drop onto the tablet surfaces is shown. The samples show decreasing degree of hydrophilic character in which the “KL+LS 150C,1 h” sample has a contact angle above 80 degrees at the time of dispensing.

[0073] In Figure 5a, water (at pH 10) drop on tablet of ”KL_ref’ sample. Water contact angle after 1 second was 42.5 degrees. Further in Figure 5b, water (at pH 10) drop on tablet of ”KL+LS_ref” sample. Water contact angle after 1 second was 45.3 degrees. Then in Figure 6a, water (at pH 10) drop on tablet of “LS_ref’ sample. Water contact angle after 1 second was 31.2 degrees. Figure 6b further shows water (at pH 10) drop on tablet of “KL 150C, 1 h” sample. Water contact angle after 1 second was 56.2 degrees. Lastly in Figure 7, water (at pH 10) drop on tablet of “KL+LS 150C,1 h” sample. Water contact angle after 1 second was 76.0 degrees.

[0074] Figure 8 further shows FTIR spectra for reference and autoclaved samples, the whole measured range 650 to 3800 cm-1Figure 9 further shows FTIR spectra for reference and autoclaved samples, the so-called fingerprint region, plotted 600 to 1800 cm-1. In the fingerprint region there are more prominent absorption peaks for the KL and LS reference materials, which is also apparent for the “KL+LS_ref” sample. There are peaks at 1030 cm-1due to C-0 stretching, at 1150 cm-1, most likely due to C-O-C asymmetric stretching, at 1509 and 1591 cm-1due to aromatic ring and skeletal vibration, respectively. These peaks are also present in the reacted “KL 150C,1 h” sample but all these are much less apparent for the “KL+LS 150C,1h” sample.

[0075] In Figure 10, FTIR spectra for reference and autoclaved samples are shown, the intermediate region, plotted 1800 to 2300 cm-1. The intermediate region between 1800 and 2300 cm-1shows almost the same appearance for all the measured samples and cannot distinguish the samples apart. Designation of specific peaks with functional groups and molecular vibrations in this region was not made. Finally, in Figure 11 FTIR spectra for reference and autoclaved samples are reflected, the high wavenumber region, plotted 2700 to 3800 cm-1.

[0076] The high wavenumber region at 2800 to 3600 cm-1shows clear differences between the samples. There were two small but distinguishable peaks at 2840 and 2925 cm-1, which is due to asymmetric and symmetric methyl and methylene stretching. The peak at 2925 cm-1is seen for the reacted “KL 150C,1 h” sample but none of them for the “KL+LS 150C,1 h” sample. A final broad peak is seen from 3100 to 3500 cm-1for the “LS_ref “and “KL+LS_ref’ samples but not for “KL_ref’ and the reacted samples “KL 150C,1 h” and “KL+LS 150C,1 h”. The broad peak is due to OH intra- and intermolecular stretching.

[0077] The conclusion from the FTIR measurements is that it confirms a chemical reaction between KL and LS at 150 degrees C for 1 hour at pH 10, that is a process condition that closely resemble industrial process conditions at which two different lignin-containing process streams can be contacted with each other. A chemical reaction occurs in this case without any additional chemicals present. FTIR measurements support a suggested combination of a sulfonation of the KL followed by, most likely, several condensation reactions.

[0078] Below is reference for designation of FTIR peaks (Javier-Astete R, Jimenez-Davalos J, Zolla G (2021) Determination of hemicellulose, cellulose, holocellulose and lignin content using FTIR in Calycophyllum spruceanum (Benth.) K. Schum. and Guazuma crinita Lam. PLoS ONE 16(10), https: / / doi.org / 10.1371 / iournal.pone.0256559)

[0079] Lignin:

[0080] 3200-3300 OH intra- and intermolecular stretching

[0081] 2920-2925 Symmetric methyl and methylene stretching

[0082] 2850-2860 Asymmetric methyl and methylene stretching

[0083] 1595-1605 Aromatic ring vibration

[0084] 1510-1520 Aromatic skeletal vibration

[0085] 1447 OH in-plane bending

[0086] 1415-1425 C=O stretching and aromatic skeletal vibration

[0087] 1095-1105 Aromatic C-H in-plane deformation

[0088] 1020-1032 C-0 stretching The present invention, with its aspects as set out above, is as said based on mixing different streams, such as black liquor (BLL) from Kraft pulping with brown liquor (BRL) which results in precipitation and possibly also coagulation because of high pH of BLL and low pH of BRL or on precipitation between differently charged species in the two different spent liquors.

[0089] In sulfite pulping the cooking liquor consists is generated by treating various bases (alkali metal or alkaline earth hydroxides) with sulfur dioxide:

[0090] SO2+ MOH MHSO3 (1)

[0091] MHSO3+ MOH ^ M2SO3+ H2O (2)

[0092] Where M is Mg2+or Ca2+and using carbonates in place of hydroxide.

[0093] In sulfate pulping the cooking liquor the active species are NaOH, Na2S and Na2COs, the latter to minor extent.

[0094] In the method of the present invention according to the first aspect, there is thus precipitation and / or coagulation of the two spent liquors into particles that are sedimented, and thereafter preferably filtration occur after which they may then be washed and dried into a powder. The dried powder may then be used as a technical lignin similar to Kraft lignin (KL) or lignosulfonic acid (LS) but will have properties that are a mixture of both, e.g. solubility over a broader pH range where LS fraction will be readily dissolved and the KL fraction will dissolve at high pHs.

[0095] The lignin obtainable by the method according the present invention, as set out in the second aspect, may also be burnt in a solid fuel plant at the mill to recover heat and steam, but may also be used in other application areas as set out in the third aspect of the present invention. The present invention will also allow that the traditional Tomlinson recovery boiler is not used while the cooking liquors are instead recovered from the supernatant mixture resulting from the mixing and precipitation in the method according to the present invention that provides a lignin product. This supernatant mixture may go to evaporation of a liquid and not as spent liquors. This will also reduce the risk for scaling. The chemical recovery of the evaporated supernatant mixture set out above may be similar to Kraft or sodium sulfite chemical recovery but will be based on ashes from solid fuel plants, not a traditional recovery boiler.

[0096] Various embodiments of the present invention have been described above but a person skilled in the art realizes further minor alterations that would fall into the scope of the present invention. The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments but should be defined only in accordance with the following claims and their equivalents. For example, any of the above-noted methods may be combined with other known methods. Other aspects, advantages and modifications within the scope of the invention will be apparent to those skilled in the art to which the invention pertains. -

Claims

Claims1. A method for separating lignin from a combined stream comprising the following steps: a) providing a stream from a sulfate pulp manufacturing process, preferably black liquor, b) providing a stream from a sulfite pulp manufacturing process, preferably brown liquor, c) and whereupon combining both said streams, preferably involving also mixing, and thereupon the mixed stream is kept at a temperature above about 110 °C, preferably from about 120 °C to about 180 °C, most preferred from about 140 °C to about 160 °C, especially preferred at about 150 °C, during from about 0.5 to about 5 hours, preferably from about 0.75 to about 1.25 hours, most preferred during about 1 hour, whereby this provides: d) precipitation of lignin, preferably by not adding one or more additives, such as one or more helping agents, thus providing a lignin product.

2. A method for separating lignin according to claim 1 wherein active heating is used in step c) for keeping said mixed stream at said temperatures or said temperature ranges, wherein said heating may be provided by a stream emanating from a chemical pulp digester, such as a cooking vessel.

3. A method for separating lignin according to claim 1 wherein the streams comprise from about 10 to about 25 wt%, preferably from about 12 to about 20 wt% of raw material that when combined provides a lignin product, and if one or both streams are evaporated from about 25 to about 80 wt%.

4. A method for separating lignin according to claim 1 wherein the flow rate of the streams is at least 10 m3 / h, preferably from about 20 to about 400 m3 / h, and the temperature of said streams is at least 40 °C, preferably from about 45 to about 100 °C.

5. A method for separating lignin according to claim 1 wherein the stream from a sulfate pulp manufacturing process, and the stream from a sulfite pulp manufacturing process emanate from separate mills, preferably wherein one or both streams are undergoing evaporation before being transported.

6. A method for separating lignin according to claim 1 comprising adding one or more helping agents to one or both streams set out in a) and b), or in the combined stream in step c), for enhancing the precipitation of lignin.

7. A method for separating lignin according to claim 1 or 6 comprising a further step e) separating said lignin product, preferably using filtration, to provide a lignin product, which most preferred is in a solid form, and at the same time providing a left-over supernatant.

8. A method for separating lignin according to claim 7 comprising a further step f) washing and subsequent drying of said lignin product to provide a powder.

9. A method for separating lignin according to claim 7 wherein said supernatant is evaporated for chemical recovery, thus providing cooking chemical(s) for sulfite and / or sulfate pulping.

10. A lignin product obtainable by a method according to any one of claims 1 to 8.

11. Use of a lignin product according to claim 10 wherein said product is used as a free-radical scavenger, an anti-oxidant, as an anti-viral or antibiotic or anti-cancerogenic compound, as a dietary enhancing agent, as a technical lignin, in a battery or in an intermediary product for making a battery or a component thereof, in production of chemicals, in glue applications, in a lacquer, in concrete manufacturing for preventing lumping and settling of unsolved particles , as a dispersant agent, for use in connection with pesticides, such as for stabilization, as a binding agent such as for use in coal briquettes or ceramics or wood-related materials or in agriculture as animal feed or soil stabilizer, as an emulsifier, as a heavy-metal sequestrant, as a moisture-retention agent, as a dustsuppressor, in leather-tanning, in gypsum-board manufacturing, in asphalt emulsions, in wax emulsions, in dyes , in pigments, in composites, in coatings, in carbon fibre manufacturing, as a co-polymer component for use in manufacturing of bio-plastics, for use in purification of water, food or chemicals, in gasoline vapor emission control, in lubricants, in inks, in rubbercompositions, in polyurethane elastomers, as compatibilizer in e.g. plastics, in production of fossil petroleum in an oilfield, in mining applications, in pavement markings, in soaps, in detergents, in textiles, as cleaning and decontamination agent, as a chelating agent, in the manufacture of containers, such as bottles, as fuel, such as bio-fuel, in a solid or liquid fuel plant to recover heat and steam therefrom, or in heating applications.

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