WO2011149341A1

WO2011149341A1 - Process for the treatment of lignocellulosic biomass

Info

Publication number: WO2011149341A1
Application number: PCT/NL2011/050348
Authority: WO
Inventors: Wiebren De Jong; Miguel Alberto Tavares Cardoso; Jacob Van Spronsen; Geert-Jan Witkamp
Original assignee: Technische Universiteit Delft
Priority date: 2010-05-25
Filing date: 2011-05-24
Publication date: 2011-12-01
Also published as: NL2004761C2

Abstract

The invention is directed to a process for the treatment of lignocellulosic biomass to recover one or more components or derivatives of components thereof, said process comprising treating said biomass at a temperature of at least 75°C in a mixture of an ionic liquid and an organic acid, thereby producing a treatment mixture containing cellulose and wherein cellulose is precipitated from the said treatment mixture with an organic alcohol or water, and optionally separated therefrom.

Description

Title: Process for the treatment of lignocellulosic biomass

The present invention is directed to a process for the treatment of lignocellulosic biomass in order to recover one or more components or derivatives thereof, such as furfural.

The decrease in the resources of fossil fuels together with the global warming alarms have led to an intensified search for alternative sources for production of chemical compounds to supply the modern society. The concept of biorefinery is becoming increasingly important since it has the potential to be a real alternative for large-scale production of fuels and platform chemicals that compete directly with oil derivatives, presenting a neutral carbon dioxide balance.

In this biorefinery context, biomass resources such as wood and straw have not yet been properly valorised since these materials are mostly incinerated to produce heat.

In addition, production of platform chemicals from lignocellulosic biomass, especially wood, minimizes the competition with the food chain and presents higher yields when compared to first generation biofuels. The challenge now is to make this process attractive from an economical point-of-view.

One of the major difficulties when dealing with these raw materials is related to the need of pre-treatments to dissociate the biomass structure. Lignocellulose consists mainly of cellulose (35 -50%), hemicellulose (20 -35%) and lignin (5-30%). These components are assembled in a complex three-dimensional structure remarkably resistant against chemicals and microbial attacks that makes them very difficult to hydrolyze, which is key for its future utilization.

An effective dissociation of these components and their separation can lead to the production of several high value products prior to the production of fuels. This integrated approach increases the competitiveness of the biorefinery industry and can make it attractive even considering the actual oil prices (2009).

Ionic liquids offer a new and attractive route for the dissociation of lignocellulosic biomass. Besides the amount of biomass that can be dissolved in some ionic liquids (that can reach 8 % w/w), their complete recycling and significant environmental advantages make this class of compounds the best possible choice for a new pre-treatment to

dissociating and fractionating the lignocellulosic biomass prior to biorefinery processing.

As indicated, it is known to use ionic liquids for the dissociation and the fractionation of lignocellulosic biomass, such as straw or wood, and also as a catalyst for hemi-cellulose hydrolysis.

The complete dissociation of both wood and wheat straw in ionic liquids can be followed by the fractionation of the several components that constitute the biomass.

The obtained results show that this is a promising process for the pre-treatment of lignocellulosic biomass, regardless the type (wood or straw). Moreover, since the ionic liquids can be almost 100% recycled, this is a low cost, fast, simple and environmentally friendly pre-treatment that can increase significantly the competitiveness of modern

biorefineries.

Using this process, the lignocellulosic biomass is separated into its constituents, which means that after hydrolysis the cellulose can be separated from the reaction mixture by precipitation with an organic alcohol or a small amount of water, and that the lignin can be separated by further precipitation with water. The hemicellulose in the remaining solution can be further converted into furfural via acid hydrolysis into xylose, followed by dehydration to furfural (see attached reaction scheme, Fig. 1).

In order to make the process more economically viable there is a need for an improved hydrolysis and conversion of the biomass into its constituents and more in particular into derivates of the constituents, such as furfural. Further, there is a need for a process that can be operated under such mild conditions, that the amount of unwanted side reactions and byproducts is diminished.

The present invention is based on the surprising discovery that the use of an organic acid, preferably acetic acid, as catalyst and as co-solvent with the ionic liquid, leads to an improved process in that respect and more in particular leads to increased furfural yield.

Accordingly the present invention is directed to a process for the treatment of lignocellulosic biomass to recover one or more components or derivatives of components thereof, said process comprising treating said biomass at a temperature of at least 75°C in a mixture of an ionic liquid and an organic acid, thereby producing a treatment mixture containing cellulose and wherein cellulose is precipitated from the said treatment mixture with an organic alcohol or water, and optionally separated therefrom.

Using this process improved dissociation of the lignocellulosic biomass, preferably wheat straw, pine wood, bagasse and rice husks, is obtained. Also a higher yield of furfural from the hemicellulose fraction is obtained.

As indicated above, the biomass is initially treated (hydrolysed) using a solvent mixture comprising an ionic liquid and an organic acid, preferably in a weight ratio of 1:10 to 10:1.

As ionic liquid all ionic liquids are suitable that are liquid at the reaction temperature, namely at 75°C or above. These ionic liquids may be of natural or synthetic origin. Examples thereof are l-butyl-3-methyl- imidazoliumchloride, 1 -ethyl- 3-methyl-imidazoliumchloride, 1 -butyl- 3- methyl-imidazoliumacetate,

In principle all organic acids are suitable. However, preferred are the organic acids having a relatively short alkyl chain such as acetic acid, citric acid, lactic acid, propionic acid, butanoic acid, or other organbic acids, such as ethyl- or propyl- sulfonic acid, and the like. The hydrolysis takes place at 75°C or above, preferably at a temperature between 90 and 175°C. It has been found that a higher temperature, within this range, has a favorable effect on the process and the yield, without negatively influencing the selectivity and accordingly the production of by-products.

The hydrolysis takes place during a period of between 5 min and 10 hours. After the hydrolysis the reaction mixture contains three main components, namely cellulose, lignin and hemicelluloses.

The cellulose is first precipitated from the reaction mixture, preferably by adding a lower alcohol (Ci to Ce) or a small amount of water. The cellulose can then be recovered from the mixture, for example by a suitable liquid- solid separation, such as filtration or centrifugation.

Subsequently, lignin can be precipitated by adding water (in a larger amount than for precipitating the cellulose) and be recovered in the same way.

The remaining solution of hemicellulose in the solvent mixture of ionic liquid and organic acid can then be reacted further to produce xylose and furfural by dehydration of the xylose.

The present invention is also embodied in a process for producing furfural from lignocellulosic biomass, which process comprises treating said biomass at a temperature of at least 75°C in a mixture of an ionic liquid and an organic acid, followed by precipitation of cellulose from the treatment mixture with an organic alcohol, and separation of the cellulose from the reaction mixture, followed by precipitation of lignin from the reaction mixture with water and separation of the lignin from the reaction mixture and acid treatment of the mixture thus obtained to produce xylose from the hemicelluloses in the mixture, which xylose is subsequently dehydrated to produce furfural. Description of the figures:

Figure 1 shows the reaction scheme of the lignocellulose hydrolysis and treatment;

Figure 2 shows a picture of the residues on the first filter (cellulose precipitation by addition of ethanol) and second filter (lignin precipitation by addition of water) for the straw sample at 100 °C and different amounts of acetic acid added (0, 2, 4 and 6 ml); and

Figure 3 shows a SEM-image of straw before (left) and after treatment with acetic acid (6 ml, 125 °C).

The invention is now elucidated on the basis of some, non-limiting examples. EXAMPLES

First, dissolution experiments were done using two types of lignocellulosic biomass i.e., (i) the low lignin containing wheat straw, and (ii) the high lignin containing pine wood. For this, 0.5 g of lignocellulosic biomass and 10 g of [emim][Cl] were weighted into a 50 ml Erlenmeyer with magnetic stirrer (200 rpm). The Erlenmeyer was heated to 125°C under nitrogen during 5 hours.

The acidity (pH) was measured at several time intervals.

Afterwards, the suspension was filtered and visually inspected. On contrary to literature data, we found that not all biomass was dissolved. Although the solution was transparent after 5 hours, fibers were found on the filter after filtration. In literature, the solution was not filtered, which might explain why complete dissolution was assumed.

Moreover, the pH measurements indicated that the solution became more acidic over time. Based on these two observations, it was concluded that lignocellulosic biomass does not dissolve in [emim][Cl], but hydrolyzes in the [emim] [Cl], and that the hydrolyzed reaction products (lignin, hemicellulose, cellulose) dissolve in the ionic liquid.

In order to hydrolyze the lignocellulosic biomass completely under mild conditions and to dissolve the hydrolyzed products, we investigated the acid catalyzed hydrolysis of lignocellulosic biomass in [emim] [CI] .

Experiments with 0.5 g of biomass, 10 g of [emim] [CI] and 0, 2, 4, and 6 ml acetic acid were carried out at 100, 125 and 150 °C. The reaction mixture was stirred (200 rpm) for 5 hours under nitrogen. Thereafter, 20 ml ethanol was added in order to precipitate the cellulose. After cooling to room temperature, the suspension was filtered over a 0.22 fm filter.

Next, water was added (ratio 1:2 with respect to filtrate) in order to precipitate the lignin, and the suspension was filtered again using a 0.22 fm filter. The precipitates were analyzed by using Scanning Electron Microscopy (SEM) from Jeol, type JSM-5400. The furfural content of the remaining filtrate was analyzed by using High Performance Liquid

Chromatrography (HPLC) from Waters, type Waters 510 HPLC pump & Waters Symmetry Cis-column.

At 100°C most of the wood did not dissolve, but the straw partly hydrolyzed and dissolved in the ionic liquid. The residues on the first filter (cellulose precipitation by addition of ethanol) and second filter (lignin precipitation by addition of water) for the straw sample at 100°C and different amounts of acetic acid added are shown in Figure 2. It can be noticed that straw dissolved better with increasing amount of acetic acid (less straw-like fibers on the first filter). Moreover, the amount of lignin precipitated increased with an increasing amount of acetic acid added (increased color on the second filter).

At 125°C the straw dissolved completely, and the precipitate at the first filter (after ethanol addition) had a fiber-like structure from cellulose. Moreover, furfural started to be formed. The results for the furfural production are presented in Table 1. The amount of furfural produced increased with increasing acetic acid concentration. The wood did not completely dissolve at 125 °C, because it is more difficult to hydrolyze lignin-rich material in [emim][Cl]. The trend of increasing furfural production with increasing acetic acid concentration was also observed in this case. However, the amount of furfural produced is much lower compared to the results with straw, which is consistent with the lower rate of hydrolysis of wood in the ionic liquid as compared to straw⁵.

Figure 3 shows the SEM-images of the straw before and after reaction at 125 °C (with 6 ml acetic acid added). It can be seen that the fiber size of the original material is in the order of 500 fm, whereas the size of the fibers of the precipitated cellulose after reaction are in the order of 100 fm.

Table 1. Furfural produced as a function of temperature and amount of acetic acid (HAc) added

Claims

1. Process for the treatment of lignocellulosic biomass to recover one or more components or derivatives of components thereof, said process comprising treating said biomass at a temperature of at least 75°C in a mixture of an ionic liquid and an organic acid, thereby producing a treatment mixture containing cellulose and wherein cellulose is precipitated from the said treatment mixture with an organic alcohol or water, and optionally separated therefrom.

2. Process according to claim 1, wherein the organic acid is acetic acid, citric acid, lactic acid, propionic acid, butanoic acid, or other organic acids, such as ethyl- or propyl- sulfonic acid.

3. Process according to claim 1 or 2, wherein the ionic liquid is selected from the group consisting of l-butyl-3-methyl- imidazoliumchloride, 1 -ethyl- 3-methyl-imidazoliumchloride, 1 -butyl- 3- methyl-imidazoliumacetate,

4. Process according to claims 1-3, wherein the ratio of ionic liquid to organic acid (wt/wt) is between 10 : 1 tot 1 : 10.

5. Process according to claims 1-4, wherein the temperature is between 90 and 175°C.

6. Process according to claims 1-5, wherein the time treatment time is between 5 min and 10 hours.

7. Process according to claims 1-6, wherein lignin is precipitated from the treatment mixture, after the precipitation of cellulose with water and optionally recovered therefrom.

8. Process according to claim 7, wherein the treatment mixture, after recovery of cellulose and lignin, which mixture contains hemicellulose is treated under acidic conditions to produce xylose.

9. Process according to claim 8, wherein the xylose is subsequently dehydrated to produce furfural.

10. Process according to claims 1-9, wherein the lignocellulosic biomass has been selected from the group of wheat straw, pine wood, bagasse and rice husks.

11. Process for the production of furfural from lignocellulosic biomass, said process comprising treating said biomass at a temperature of at least 75°C in a mixture of an ionic liquid and an organic acid, followed by precipitation of cellulose from the treatment mixture with an organic alcohol, and separation of the cellulose from the reaction mixture, followed by precipitation of lignin from the reaction mixture with water and separation of the lignin from the reaction mixture and acid treatment of the mixture thus obtained to produce xylose from the hemicelluloses in the mixture, which xylose is subsequently dehydrated to produce furfural.