Method for producing a lignin product

Abstract

It is disclosed a method for producing a lignin product, comprising the steps of: providing a soluble lignin-containing organic solution; providing an aqueous precipitant solution; adding the precipitant solution to the soluble lignin-containing organic solution to provide a mixture comprising precipitated lignin, mixing the mixture in a dynamic mixer at a speed of about 500 rpm to about 2000 rpm; separating and recovering the precipitated lignin product from the mixture.

Description

[0001] METHOD FOR PRODUCING A LIGNIN PRODUCT

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a method for producing a lignin product. More particularly, the invention relates to an improved method for producing a precipitated lignin product with enhanced solids yield and good filterability in an efficient and controlled way.

[0004] BACKGROUND OF THE INVENTION

[0005] Precipitation of lignin from a lignocellulosic material with water is known. WO 2011 / 154293 Al discloses a process for separation of lignins and sugars from an extraction liquor involving concentrating the extraction liquor, mixing the concentrated liquor with water in equal parts, stirring the resultant mixture to obtain a stable suspending of the lignins in the solution, filtering the solution comprising the suspended lignins.

[0006] WO 2021 / 198555 Al discloses a method for the separation of lignin from an organic solvent, comprising multiple two-step cycles involving a first step of adding an aqueous solution to a lignin-containing organic solvent to precipitate lignin, and a second step of subjecting the resultant lignin-reduced solution to the first step of addition of an aqueous solution. Precipitated lignin is separated and recovered in each step. The multi-step addition of an aqueous solution to a lignincontaining solution provides lignin precipitates with a different molecular weight distribution.

[0007] Current methods for precipitation of lignin from an organic spent cooking liquor obtained from organosolv pulping of a lignocellulosic material do not provide means to affect solids yield, particle size distribution or filterability of solid-liquid mixture. It is challenging to produce a homogeneous mixture containing precipitated lignin at industrial scale, e.g., at high total solids content, without blockages or operational challenges in the system and without unpredictable properties of precipitated mixture. Current batch-wise and continuous methods cause several problems. Batch-wise operation produces various mixture properties, such as unfavorable and unpredictable particle size distribution and challenging separation of solids and liquid. Continuous operation with a static mixer suffers from reduced production capacity and operational challenges due to slow blockage possibilities. BRIEF DESCRIPTION OF THE INVENTION

[0008] We have now found an improved method for efficient and controlled production of a precipitated lignin product having targeted properties.

[0009] The method is based on an organosolv pulping of a lignocellulosic material in which cellulose, lignin and hemicellulose present in the lignocellulosic material are separated in two main streams, i.e., cellulosic pulp and a solution of soluble lignin and hemicellulosic sugars, by using an aqueous organic solvent as a cooking liquor. The cooking liquor is acidic and includes formic acid and acetic acid, water and furfural. During cooking, hemicellulosic sugars and a portion of lignin are dissolved in the cooking liquor.

[0010] In context of the invention, a soluble lignin -containing organic solution obtained from cooking of a lignocellulosic material with an aqueous organic solvent is described here as "a spent cooking liquor". The spent cooking liquor thus contains, e.g.., soluble lignin, hemicellulosic sugars, inorganics, proteins and extractives, and also components of original cooking liquor.

[0011] In the method of the invention, soluble lignin is precipitated from the spent cooking liquor using water as a precipitant solution.

[0012] It was surprisingly found that using a dynamic mixer for combining an aqueous precipitant solution and a soluble lignin-containing organic solution in a controlled way results in enhanced yield of total solids and good filterability of a mixture containing precipitated lignin. The yield and properties of the mixture, such as particle size of lignin precipitate, can be adjusted by changing the rotation speed of the dynamic mixer, and an acid concentration of the aqueous precipitant solution.

[0013] The present invention provides an efficient and economic method for producing and recovering a precipitated lignin in a controlled way.

[0014] BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 shows an apparatus used for precipitation of lignin in the method of the invention.

[0016] Figures 2, 3a-3c, and 4a-4c relate to lignin precipitates precipitated with water. Figures 5a-5b relate to lignin precipitates precipitated with an acidic aqueous solution.

[0017] Figure 2 shows a yield of precipitated lignin in wt.% based on total solids of a mixture containing precipitated lignin vs. rotation speed [rpm] of a dynamic mixer. Figures 3a-3c show particle size distribution of a lignin precipitate in volume (%) vs. mean particle size (gm).

[0018] Figure 4a and figure 5a show mean particle size d(0.5) (gm) vs. rotation speed (rpm) of a dynamic mixer.

[0019] Figure 4b and figure 5b show filterability (kg D.S. / m2h) of a lignin precipitate vs. rotation speed (rpm) of a dynamic mixer.

[0020] Figure 4c and figure 5c show filterability (kg D.S. / m2h) of a lignin precipitate vs. mean particle size (gm).

[0021] DETAILED DESCRIPTION OF THE INVENTION

[0022] An object of the present invention is to provide a method for producing a lignin product, comprising the steps of:

[0023] - providing a soluble lignin-containing organic solution,

[0024] - providing an aqueous precipitant solution comprising acid(s) in amount of 0 wt.% to about 40 wt.%,

[0025] - adding the aqueous precipitant solution to the soluble lignin-containing organic solution to provide a mixture comprising precipitated lignin,

[0026] - mixing the mixture in a dynamic mixer at a rotation speed of about 500 rpm to about 2000 rpm,

[0027] - separating and recovering the precipitated lignin product from the mixture.

[0028] The percentages of the various constituents used in the method of the present invention are given on weight basis.

[0029] Figure 1 shows an apparatus used in the method of the invention for precipitation of lignin. Precipitant liquor is led via line A to a dynamic mixer 103 by means of a pump 101. Soluble lignin-containing cooking liquor is led via line B to the dynamic mixer 103 by means of a pump 102. Flow rates of liquors A and B are controlled with pumps 101 and 102. In the dynamic mixer 103, precipitation of lignin is started to provide a mixture comprising precipitated lignin. Properties of the mixture and yield of the lignin precipitate is controlled by rotation speed of the dynamic mixer 103. The mixture is led via line C to a tank 104 where the mixture is gently agitated to avoided settling of the lignin particles. The mixture containing precipitated lignin particles is transferred to a separation step via line D.

[0030] In the context of the present invention, the term "dynamic mixer" means a device comprising a chamber with a moving part for turbulence generation inside the chamber, and own motor to move or rotate the moving part inside the chamber. The chamber volume and the flow rate of the combination of soluble lignin-containing organic solution and an aqueous precipitant solution lead to short residence time in the chamber, e.g., < 45 sec. In an embodiment, the residence time is about 2 sec.

[0031] Soluble lignin-containing organic solution is originated from an organo- solv pulping method of a lignocellulosic material. In an embodiment, the soluble lignin-containing organic solution comprises formic acid, acetic acid, and water. In another embodiment, the soluble lignin -containing organic solution comprises formic acid, acetic acid, water and furfural.

[0032] In an embodiment, the dry matter content of the soluble lignin-containing organic solution is in the range of about 50% to about 90%. In another embodiment, the dry matter is from about 60% to about 85%. In a further embodiment, the dry matter is from about 70% to about 80%.

[0033] In an embodiment of the invention, the aqueous precipitant solution is water. In another embodiment, the aqueous precipitant solution is acidic. In an embodiment, the aqueous precipitant solution contains about 5 wt.% to about 30 wt.% of the acid(s). In another embodiment, the aqueous precipitant solution contains about 10 wt.% to about 20 wt.% of the acid(s). In an embodiment, the acid(s) is an organic acid(s). In an embodiment, the acid(s) is selected at least one of formic acid and acetic acid.

[0034] The precipitant solution is added to the soluble lignin-containing organic solution in a weight ratio of about 0.7:1 to about 2.5:1. In an embodiment, the aqueous precipitant solution is added in a weight ratio of about 1:1 to about 2:1.

[0035] The temperature of the mixture of the soluble lignin -containing organic solution and the precipitant solution in the dynamic mixer is below 90°C.

[0036] The particle size of the lignin precipitate and therefore, the filterability of the mixture containing precipitated lignin and finally, recovery of the lignin precipitate, may be controlled by adjusting of rotation speed of the dynamic mixer, and an acid concentration of the aqueous precipitant solution.

[0037] In the method, the rotation speed of the dynamic mixer is adjusted to a range of about 500 rpm to about 2000 rpm.

[0038] The precipitated lignin product is separated and recovered. In an embodiment, the separation is carried out by filtration.

[0039] If desired, the precipitated lignin product may be washed with water to remove any residual impurities in the product. The invention provides a flexible method that can be easily controlled for precipitation of lignin from an organic spent cooking liquor in which lignin is present in soluble form. The method provides a lignin precipitate with homogeneous properties. Smaller particle sizes and high precipitation yield are achieved by increasing the rotation speed of the dynamic mixer whereas fast filtration and larger particles are achieved by decreasing the rotation speed of the dynamic mixer. This gives flexibility and easy control of the method.

[0040] The following examples are presented for further illustration of the invention without limiting the invention thereto.

[0041] The content of lignin was measured according to technical report of NREL TP-510-42618 (August 2012).

[0042] Example 1

[0043] Soluble lignin-containing spent cooking liquor having a dry matter content of 66% before lignin precipitation was provided. Soluble lignin was precipitated by adding tap water as a precipitant solution to the spent cooking liquor.

[0044] The soluble lignin-containing spent cooking liquor was pumped at a flow rate of about 180 kg / h, and the precipitant solution was pumped at a flow rate of about 360 kg / h to a dynamic mixture. The dynamic mixture was operated at a rotation speed of about 500 rpm to about 2000 rpm.

[0045] After the mixing was completed, the mixture was analysed for total solids, precipitated lignin, filterability and particle size distribution. The effect of rotation speed of a dynamic mixer on yield of the precipitated lignin is shown in Figure 2. It was found that the yield of precipitated lignin increases with increasing rotation speed of the dynamic mixer.

[0046] It was further found that particle size distribution in volume (%) depends on the rotation speed of the dynamic mixer. More particularly, mean particle size in gm increased when rotation speed was slowed down (Figure 3).

[0047] Figure 4a shows that mean particle size of the lignin precipitate decreased when rotation speed of the dynamic mixer was increased. Small particle size of a lignin precipitate reflects the filterability of the lignin precipitate. The smaller the particles are, the slower the mixture containing precipitated lignin is as is shown in Figure 4c. In turn, increase of rotation speed of the dynamic mixture decreases the filterability of precipitated lignin (Figure 4b) due to that fact that the mean particle size is decreased while rotation speed is increased.

[0048] Example 2

[0049] Soluble lignin-containing spent cooking liquor having a dry matter content of 66% before lignin precipitation was provided. Soluble lignin was precipitated by adding tap water as a precipitant solution to the spent cooking liquor.

[0050] Both soluble lignin-containing spent cooking liquor and precipitant solution were pumped at a flow rate of about 250 kg / h to a dynamic mixture at a speed of 1000 rpm. The precipitated lignin was obtained in high yield constituting 58% of dry matter of the mixture. The mixture containing precipitated lignin exhibited a filterability of 0.11 g / cm2min, indicating an easy filterability of the mixture.

[0051] Example 3

[0052] Soluble lignin-containing spent cooking liquor (60°C) having a dry matter content of 55% before lignin precipitation was provided. The acid content of the spent cooking liquor was 77.5% based on the liquid part (i.e., volatile components including acid) of the spent cooking liquor. Soluble lignin was precipitated by adding an aqueous precipitant solution (20°C) containing 10% acid to the spent cooking liquor. The acid content of the resultant mixture was 22.4% based on the liquid part (i.e., volatile components including acid) of the mixture.

[0053] The soluble lignin-containing spent cooking liquor and the aqueous precipitant solution were pumped at a flow rate of 200 kg / h and 400 kg / h, respectively, to a dynamic mixture at a speed of 500 rpm, 1000 rpm, and 1500 rpm and at a temperature of 60°C. Weight ratio of the aqueous precipitant solution and the spent cooking liquor was 2:1 calculated from flow rates.

[0054] Figures 5a-5c show that by adjusting rotating speed, particle size and filterability of the lignin precipitate may be affected using an aqueous acidic precipitant solution.

[0055] Figures 4a-4c and 5a- 5c further show that by adjusting rotating speed of the dynamic mixer and acid concentration of the aqueous acidic precipitant solution, particle size and filterability of precipitated lignin product may be affected.

[0056] It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

Claims1. A method for producing a lignin product, comprising the steps of:- providing a soluble lignin-containing organic solution,- providing an aqueous precipitant solution comprising acid(s) in amount of 0 wt.% to about 40 wt.%,- adding the aqueous precipitant solution to the soluble lignin-containing organic solution to provide a mixture comprising precipitated lignin,- mixing the mixture in a dynamic mixer at a rotation speed of about 500 rpm to about 2000 rpm,- separating and recovering the precipitated lignin product from the mixture.

2. The method of claim 1, wherein the soluble lignin -containing organic solution is a spent cooking liquor from an organosolv pulping process of a lignocellulosic material.

3. The method of claim 1 or 2, wherein the soluble lignin -containing organic solution comprises formic acid, acetic acid, and water, and optionally furfural.

4. The method of any one of the preceding claims, wherein the dry matter of the soluble lignin-containing organic solution is in the range of about 50% to about 90%, specifically about 60% to about 85%, more specifically about 70% to about 80%.

5. The method of any one of the preceding claims, wherein the aqueous precipitant solution is water.

6. The method of any one of claims 1-4, wherein the aqueous precipitant solution contains the acid(s).

7. The method of claim 6, wherein the acid(s) is organic acid(s).

8. The method of claim 6 or 7, wherein the aqueous precipitant solution comprises an acidic process side stream from organosolv pulping process of the lignocellulosic material.

9. The method of any one of claims 6-8, wherein the acid(s) is at least one of formic acid and acetic acid.

10. The method of any one of claims 6-9, wherein the aqueous precipitant solution contains acid(s) in amount of about 5 wt.% to about 30 wt.%, specifically about 10 wt.% to about 20 wt.%.

11. The method of any one of the preceding claims, wherein the aqueous precipitant solution is added to the soluble lignin -containing organic solution in a weight ratio of about 0.7:1 to about 2.5:1, specifically about 1:1 to about 2:1.

12. The method of any one of the preceding claims, wherein the mixture comprising precipitated lignin has a temperature of below 90°C.

13. The method of any one of the preceding claims, wherein the mixture is mixed in the dynamic mixer for about less than 45 sec, specifically about 2 sec.

14. The method of any one of the preceding claims, wherein the separation is carried out by filtration.

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