Technical field

[0001 ]The present invention relates generally to a method for processing black liquor and further the use of resulting components as a fuel.

Background

[0002]Black liquor is a by-product from the manufacture of chemical pulp (sulfate process). It is an alkaline solution of the partially degraded carbohydrates and lignin, but also various sulfur and sodium salts. In the normal case the black liquor is transferred to a stage for regeneration of the process chemicals. In the recovery boiler black liquor is burned. In the recovery boiler the chemicals for the white liquor are recovered and reformed from black liquor, which contains lignin from previously processed wood. The black liquor is burned, generating heat, which is usually used in the process and/or in making electricity.

[0003]The white liquor is mixed with the wood at the beginning of the pulping

process. The combustion of the organic material is a necessary "fuel" for the conversion of the salts, and also produces steam, which is used for the warming of the process and can further be used for producing electricity alternatively for drying purposes. However, there is usually more than necessary of the organic material, and the large amount that is burnt is often a bottleneck for many plants. In order to solve this problem, the process called LignoBoost ^tm is developed, to pick out some of the lignin from black liquor before it goes to the recovery boiler. LignoBoost is a technology for extracting high quality lignin from a kraft pulp mill. Lignoboost is today probably mainly used as fuel in district heating plants and other similar low value applications. At least one use of lignin from LignoBoost ^tm today is as fuel in district heating plants, etc. - i.e. a low value application. LignoBoost ^tm plants are also relatively expensive. WO 2006/031 175 discloses a method for separation of lignin from black liquor comprising the following steps: a) Precipitation of lignin by acidifying black liquor and thereupon dewatering, b) suspending the lignin filter cake obtained in step a) whereupon a second lignin suspension is obtained and adjusting the pH level to approximately the pH level of the washing water of step d) below, c) dewatering of the second lignin suspension, d) addition of washing water and performing a displacement washing at more or less constant conditions without any dramatic gradients in the pH, and e) dewatering of the lignin cake produced in step d) into a high dryness and displacement of the remaining washing liquid in said filter cake, whereby a lignin product is obtained which has an even higher dryness after the

displacement washing of step e).

[0004]Zakzeski et al in "Catalytic Lignin Valorization Process for the Production of Aromatic Chemicals and Hydrogen" ChemSusChem 2012, vol 5, page 1602- 1609 discloses a catalytic process to valorize lignin for use both as fuel and as raw material. There is disclosed dissolution a system comprising both an alcohol and water to perform a degradation reaction.

[0005] Helander et al in "Catalytic Lignin Valorization Process for the Production of Aromatic Chemicals and Hydrogen", Bioresources, 2013, vol 8, page 2270- 2282 discloses a process for separating lignin from black liquor using a membrane with a cut-off of 1000 Da.

[0006] In the prior art there is room for an improvement, in particular regarding the yield of low molecular products resulting from the processing of black liquor.

[0007]One issue at least for some applications is how to prepare a lignin

containing fraction which is more homogenous and has lower molecular weight compared to the state of the art.

[0008] Another problem is how to speed up the reaction. Summary

[0009] It is an object of the present invention to obviate at least some of the

disadvantages in the prior art and provide an improved method of extracting lignin from black liquor and prepare a liquid fuel.

[0010]After extensive research the inventors have unexpectedly found that lignin after filtration and lowering the pH is soluble in an alcohol (compound comprising at least one OH group and from one up to three carbon atoms) together with ammonia. By using this reaction scheme a number of advantages are obtained.

[001 1 ] In a first aspect there is provided a method for processing black liquor

comprising the sequential steps of: a) filtering the black liquor using a filter with a molecular mass cut off from 1000 to 10000 Da and recovering the fraction of the black liquor passing through the filter, b) lowering the pH by at adding at least one from CO2 and an acid to

precipitate organic matter and recovering the precipitated organic matter, c) dissolving the precipitated organic matter in a solution of ammonia and at least one alcohol comprising at least one OH group and from one up to three carbon atoms to obtain a solution, d) subjecting the solution to at least one of hydrogenation, catalytic cracking, and thermal cracking, and e) separating components resulting after step d).

[0012] In a second aspect there is provided a fuel comprising at least one

component, which component is manufactured with the method described above.

[0013] Further aspects and embodiments are defined in the appended claims, which are specifically incorporated herein by reference. [0014]There is provided a cheaper way to pick lignin from the black liquor, which gives a material that is more homogeneous and low molecular weight compared to the state of the art. There is provided a method of making an anhydrous solution of lignin that can be hydrogenated and used for fuel.

Glycerol is in one embodiment used as a solvent. Today there is a surplus of glycerol, since it is obtained as a byproduct in the manufacture of biodiesel and fatty acids from vegetable oils (triglycerides). The final product will be an organic liquid with high fuel value, which is suitable as fuel in combustion engines.

[0015]Advantages of the invention include that the reaction is faster because the shorter polymer chains that are used after filtration react faster. The yield of desired low molecular products is increased. The lower molecular weight lignin is soluble in the mixture of an alcohol and ammonia.

[0016]Another advantage compared to dissolution of lignin in for instance ethanol and water is that a homogenous solution is obtained at a lower temperature. The lower temperature has several advantages including lower energy consumption.

Brief description of the drawings

[0017]The invention is now described, by way of example, with reference to the accompanying drawings, in which:

[0018]Fig. 1 shows a schematic picture of heating and subsequent hydrogenation of a compound.

Detailed description

[0019] Before the invention is disclosed and described in detail, it is to be

understood that this invention is not limited to particular compounds, configurations, method steps, substrates, and materials disclosed herein as such compounds, configurations, method steps, substrates, and materials may vary somewhat. It is also to be understood that the terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting since the scope of the present invention is limited only by the appended claims and equivalents thereof.

[0020] It must be noted that, as used in this specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.

[0021 ] If nothing else is defined, any terms and scientific terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this invention pertains.

[0022] In a first aspect there is provided a method for processing black liquor

comprising the sequential steps of: a) filtering the black liquor using a filter with a molecular mass cut off from 1000 to 10000 Da and recovering the fraction of the black liquor passing through the filter, b) lowering the pH by at adding at least one from CO2 and an acid to

precipitate organic matter and recovering the precipitated organic matter, c) dissolving the precipitated organic matter in a solution of ammonia and at least one alcohol comprising at least one OH group and from one up to three carbon atoms to obtain a solution, d) subjecting the solution to at least one of hydrogenation, catalytic cracking, and thermal cracking, and e) separating components resulting after step d).

[0023] In one embodiment the precipitated organic matter from step b) is washed with water wherein at least one from CO2 and an acid has been added to the water, and wherein the precipitated organic matter is dried after the washing, before entering step c) . The water with which the precipitated matter is washed is acidified. The additional acid wash has the effect of removing metal salts.

[0024] In one embodiment at least one alcohol comprising at least one OH group and from one up to three carbon atoms is added to the precipitated organic matter and heating the mixture to a temperature above 160°C between steps b) and c). The at least one alcohol comprising at least one OH group and from one up to three carbon atoms added between steps b) and c) is not necessarily the same as the one added in step c). It can be the same or a different compound. Also various mixtures of compounds are encompassed both for addition between steps b) and c) as well as for step c).

[0025] In one embodiment the at least one alcohol comprising at least one OH group and from one up to three carbon atoms is at least one compound selected from the group consisting of methanol, ethanol, propanol, and glycerol.

[0026]The pH value during the addition of an acid can be varied. In particular the pH at the end of the pH-lowering step can be varied in order to precipitate different fractions with different properties. The selected pH value at the end depends on the desired end product. In one embodiment the pH value at the end of step b) is in the interval 2-3. In an alternative embodiment the pH value at the end of step b) is in the interval 3-4. In an alternative embodiment the pH value at the end of step b) is in the interval 4-5. In an alternative embodiment the pH value at the end of step b) is in the interval 5-6. In an alternative embodiment the pH value at the end of step b) is in the interval 6-7. In an alternative embodiment the pH value at the end of step b) is in the interval 7-8. In an alternative embodiment the pH value at the end of step b) is in the interval 8-9. It is also encompassed to divide the incoming material, wherein the end pH is different for each part in order to precipitate different fractions of material.

[0027] If the option to heat the precipitate to at least 160°C with addition of at least one alcohol comprising at least one OH group and from one up to three carbon atoms is used, the need for hydrogenation in a subsequent step is decreased. The option to heat above 160°C leads to chemical reactions which can facilitate hydrogenation. Fig. 1 shows a schematic picture of heating and subsequent hydrogenation of a compound. Although lignin is a complex chemical compound, it is represented by the structure in fig 1 .

[0028] In one embodiment the solution of ammonia and at least one alcohol

comprising at least one OH group and from one up to three carbon atoms in step c) is from 10 to 12. When the precipitate in one embodiment is dissolved in a solution comprising ammonia water and glycerol the pH value in the solution of ammonia water and glycerol is also from 10 to 12.

[0029]The ammonia has the effect of making the dissolution in the alcohol

possible and facilitating the dissolution. The result is a homogenous mixture, i.e. a solution. By solution it is meant a solution without or essentially without undissolved lignin, i.e. more than 95wt% or preferably more than 99wt% of the lignin is dissolved. One advantage of using ammonia as a helping substance to perform the dissolution is that already at temperatures below 100°C there is a homogenous system where the lignin is dissolved. The ammonia increases the pH and also further facilitates the dissolution because it does not add metal ions (metal salts) as many other pH increasing additives such as NaOH etc.

[0030] Further the solution of ammonia and at least one alcohol in step c) does not comprise water.

[0031 ]During hydrogenation commonly used catalysts are suitably utilized.

Examples of catalysts include but are not limited to nickel based catalysts including Raney nickel and Urushibara nickel, rhodium based catalysts, including Wilkinson's catalyst, iridium based catalysts including Crabtree's catalyst, as well as catalysts based on ruthenium, platinum, and palladium.

[0032] In one embodiment at least one component from step e) is utilized as a fuel adapted to an internal combustion engine. The fuel adapted to an internal combustion engine is a fuel which is suitable to use in an internal combustion engine.

[0033] In an alternative embodiment the filtering in step a) is performed using a filter with a molecular mass cut off from 1000 to 5000 Da.

[0034] In a second aspect there is provided a fuel comprising at least one

component, which component is manufactured with the method described above. Optionally the fuel further comprises other ingredients. Examples include but are not limited to diesel and gasoline.

[0035]Other features and uses of the invention and their associated advantages will be evident to a person skilled in the art upon reading the description and the examples.

[0036] It is to be understood that this invention is not limited to the particular

embodiments shown here. The embodiments are provided for illustrative purposes and are not intended to limit the scope of the invention since the scope of the present invention is limited only by the appended claims and equivalents thereof.

Example

[0037] Glycerol was flushed with ammonia gas until the pH was 1 1 . Filtrated

acidified lignin was dissolved in 20% (200 mg per ml) by magnetic stirring and heating to 50°C. A black viscous solution was obtained. No precipitate could be detected when the solution was cooled down without stirring.