Process for treating biomass consisting of citrus pastazzo

Abstract

Process for the treatment of biomass comprising dried and pulverized citrus pulp, said process comprising the following steps: A. mixing the biomass with a process solvent selected from a eutectic solvent comprising a hydrogen bond acceptor and a hydrogen bond donor, an ionic liquid and a mixture of said eutectic solvent and said ionic solvent, and precipitation of cellulose residues; B. separation of the insoluble cellulose residues precipitated in step A; C. separation of the hemicellulose and the pectin from the process solvent; wherein in the aforesaid step C. of the separation of hemicellulose and pectin is performed through the addition of a lower alcohol and water, thus allowing the precipitation of the hemicellulose and the pectin and their subsequent separation with conventional techniques from the liquid phase comprising process solvent, organic solvent and possibly water.

Claims

1. Process for the treatment of biomass consisting of dried and pulverized citrus pulp, said process comprising the following steps: A. mixing the biomass with a process solvent selected from a eutectic solvent consisting of a hydrogen bond acceptor and a hydrogen bond donor, an ionic liquid and a mixture of said eutectic solvent and said ionic solvent, and precipitating cellulose residues; B. separating the insoluble cellulose residues precipitated in step A; C. separating the hemicellulose and the pectin from the process solvent; wherein step C. of the separation of hemicellulose and pectin is performed through the addition of a lower alcohol and water, thus allowing the precipitation of the hemicellulose and the pectin and their subsequent separation with conventional techniques from the liquid phase comprising process solvent, organic solvent and possibly water.

2. Process according to claim 1, wherein the hydrogen bond acceptor is selected from choline acetate and choline chloride and the hydrogen donor bond is selected from urea, citric acid, glycolic acid, diglycolic acid, levulinic acid.

3. Process according to claim 2, wherein ionic liquid is the product resulting from the reaction of:
choline Y.sup.−+X—H=choline X.sup.−+Y—H where X is the anion of a weak organic acid selected from glycolic acid, citric acid, diglycolic acid, levulinic acid, whereas Y is selected from CH.sub.3COO.sup.− and Cl.sup.−.

4. Process according to claim 1, wherein in the DES the weight ratio between the hydrogen bond acceptor and the hydrogen bond donor of the eutectic solvent is at least 1:5 to 5:1.

5. Process according to claim 1, wherein the process comprises a step D. in which the precipitate separated in step B. is washed with water to remove the traces of DES and/or ionic liquid.

6. Process according to claim 5, wherein step D. is repeated 6 times.

7. Process according to claim 5, wherein the aqueous mixture coming from step D. and comprising process solvent and water is recycled to step A. or to the mixture comprising the process solvent coming from step B.

8. Process according to claim 1, wherein the process is performed at a temperature comprised between 20 and 100° C.

9. Process according to claim 1, wherein the mixing temperature of the process solvent in step A. is at least in a range comprised between 15 and 60° C.

10. Process according to claim 1, wherein the lower alcohol is a linear or branched C.sub.1-C.sub.4 aliphatic alcohol.

11. Process according to claim 1, wherein the hydrogen bond acceptor is choline acetate and the hydrogen bond donor is glycolic acid.

12. Process according to claim 1, wherein in the DES the weight ratio between the hydrogen bond acceptor and the hydrogen bond donor of the eutectic solvent is 1:2 to 2:1.

13. Process according to claim 1, wherein in the DES the weight ratio between the hydrogen bond acceptor and the hydrogen bond donor of the eutectic solvent is 1:1.

14. Process according to claim 1, wherein the mixing of the process solvent in step A. is performed at a temperature between 20 and 40° C.

15. The process according to 1, wherein the mixing of the process solvent in step A. is performed at 20° C.

16. Process according to claim 1, wherein the lower alcohol is ethanol or isopropanol.

Description

LIST OF FIGURES

[0022] FIG. 1: Block diagram representing the process for the treatment of biomass according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION

[0023] For the purposes of the present invention, “citrus pulp” has been dehydrated and pulverized before being used in the process of the invention. The main components of this biomass are cellulose (25-30%), hemicellulose (10-15%) and pectin (15-20%).

[0024] For the purposes of the present invention, the process solvent may comprise a eutectic solvent, an ionic liquid or a combination of the eutectic solvent and the ionic liquid.

[0025] For the purposes of the present invention, eutectic solvents refer the so-called deep eutectic solvents or DES. In other words, it is a combination of a hydrogen bond acceptor and a hydrogen bond donor. Preferably in the process of the invention the hydrogen bond acceptor is selected from between choline acetate and choline chloride, while the hydrogen bond donor is selected from urea, glycolic acid, diglycolic acid, citric acid, levulinic acid and imidazole. In a particularly preferred embodiment, the DES used is the combination of choline acetate and urea or choline acetate and glycolic acid or choline acetate.

The production of the eutectic solvent is preferably performed in a temperature range comprised between 20 and 100° C., more preferably between 25 and 90° C., even more preferably between 30 and 80° C., and according to a particularly preferred embodiment at 50° C.

[0026] For the purposes of the present invention, by an ionic liquid used as a process solvent it is meant the product resulting from the reaction of:

choline Y.sup.−+X—H=choline X.sup.−+YH

where X is the anion of an organic weak acid preferably selected from glycolic acid, citric acid, diglycolic acid, levulinic acid. In particular, the ionic liquid contains choline ion in the presence of the conjugated base of glycolic acid or diglycolic acid or levulinic acid. In a particularly preferred embodiment, the ionic liquid used is choline glycolate.

[0027] The ionic liquid formation reaction is preferably performed in a temperature range comprised between 20 and 80° C., more preferably between 20 and 60° C. even more preferably between 20 and 50° C. and according to a particularly preferred embodiment at 25° C. Furthermore, the ratio between the reagents is preferably 1:1.

Preferably, the process solvent used in the process according to the present invention is halogen-free, so that the disposal thereof at the end of industrial processing has a lower environmental impact.

[0028] DESs are prepared by simple mixing the two components at room temperature and pressure, reducing preparation costs and production time.

[0029] DESs can in turn react to form the above-mentioned ionic liquid. Since the ionic liquid formation reaction is an equilibrium reaction, this explains the fact that the process solvent is a mixture of DES and ionic liquid.

[0030] In particular, the mixture of the eutectic solvent and the ionic liquid, when choline acetate is used as the hydrogen acceptor, preferably comprises choline X.sup.−, acetic acid and eutectic solvent, where the hydrogen bond acceptor and the hydrogen bond donor are preferably halogen-free, the hydrogen bond acceptor is preferably choline acetate and the hydrogen bond donor is preferably selected from: glycolic acid, diglycolic acid, citric acid, levulinic acid and urea, more preferably the hydrogen bond donor is selected from acid glycolic.

[0031] According to the present invention the weight ratios between the components of the eutectic solvent, donor and acceptor of hydrogen bonds, preferably are comprised between 1:5 and 5:1, more preferably from 1:3 to 3:1, even more preferably from 1:2 to 2:1 and according to a particularly preferred solution said ratio is 1:1. The molar ratio between the reagents for DESs choline chloride combined with urea or choline acetate combined with urea is preferably 1:2.

[0032] For the purposes of the present invention, lower alcohol means a C2-C4 alcohol preferably ethanol or isopropanol, more preferably ethanol.

[0033] Advantageously, the lower alcohol added to a solution comprising hemicellulose and/or pectin and the process solvent and optionally water favours the selective precipitation of organic material, preferably hemicellulose and pectin, allowing it to be separated and used in subsequent processing.

[0034] According to the present invention, the lower alcohol solubilises the process solvent and possibly water by promoting the precipitation of hemicellulose and pectin.

[0035] For the purposes of the present invention, the separation of precipitated hemicellulose and pectin is carried out with conventional techniques such as, for example, filtration, fractional precipitation, or, preferably, centrifugation.

[0036] A further advantage of the invention is that the separation of the hemicellulose and pectin from the reaction mixture containing the process solvent facilitates recycling the process solvent and obtaining a mixture of hemicellulose and pectin in a purer form.

[0037] In step A. the mixing of the biomass with the process solvent takes place preferably in a temperature range comprised between 15 and 60° C., more preferably between 20 and 50° C. even more preferably between 20 and 40° C. and according to a particularly preferred embodiment at 25° C.

[0038] The manufacturing process comprises a step prior to step A. in which the biomass is ground and dried, reducing it to powder. This facilitates mixing with the process solvent and the subsequent separation steps.

[0039] Preferably, in step B. any separation of the insoluble cellulosic residues from the mixture containing the process solvent, is carried out with conventional procedures such as, for example, filtration, fractional precipitation, or, preferably, centrifugation.

[0040] Step B. of the process according to the present invention provides for the separation of the insoluble material in the process solvent from the mixture comprising the process solvent, hemicellulose, pectin and any other components. In this way in step B. the cellulose is separated from the rest of the mixture comprising the process solvent.

[0041] The process preferably comprises a step D. in which the precipitate separated in step B. is washed with water to dissolve any inorganic material and to remove the traces of DES and/or ionic liquid. In particular, the washing is repeated at least from 2 to 10 times, preferably 6 times in order to facilitate the elimination of any residues of the process solvent within the cellulose mixture. Subsequently, step D. provides for centrifuging the aqueous mixture which allows to obtain cellulose with a high degree of crystallinity, eliminating any water residues.

[0042] Preferably, the washing water containing residues of the process solvent is recycled in step A.

[0043] The cellulose is purified compared to the starting biomass from amorphous substances contained in the biomass, preferably hemicellulose. The degree of purification is expressed as the increase in crystallinity of the cellulose compared to the starting biomass. The crystallinity is measured by powder X-ray diffractometry. In particular, cellulose shows an increase in the degree of crystallinity, compared to the starting biomass, comprised between 4% and 40%, preferably between 5% and 30%.

[0044] In other words, the increase in purity of the cellulose in the process according to the present invention is attributable to a more efficient separation of the cellulose from other materials.

[0045] In particular, step C., following the addition of ethanol, provides for the separation of the precipitated hemicellulose and pectin from the mixture with conventional techniques, preferably by centrifugation from the eutectic solvent and/or ionic liquid. Preferably, step C of the process according to the present invention provides for the separation of the process solvent, organic solvent and water from the rest of the mixture comprising hemicellulose, pectin and any other residues. In this way, it is possible to recycle the process solvent, water and organic solvent in steps A. and C. respectively.

[0046] Laboratory examples are shown below in order to better clarify the different steps of the process according to the invention and the high added value products obtained.

EXAMPLE 1

[0047] In this example, 150 mg of dried and ground citrus pulp and 1.5 g DES choline acetate combined with glycolic acid were used in a 1:1 molar ratio.

Step A:

[0048] preparation of 150 mg of dried and ground citrus pulp;
mixing of DES with citrus pulp for 24 hrs at 25° C.;
centrifugation of the mixture and obtaining a precipitate of cellulose and a mixture of DES, pectin, hemicellulose.

Step B:

[0049] separation of precipitated cellulose.

Step D:

[0050] washing of the cellulose precipitate six times with water at 20° C. The mixture containing water and DES is used in step C of the process;
centrifugation of the aqueous mixture;
separation of the cellulose from the aqueous mixture resulting in cellulose with a higher degree of crystallinity than the starting biomass.

Step C:

[0051] addition of a certain amount of ethanol equal to 10 ml to the mixture containing DES, pectin, hemicellulose;
separation of pectin and precipitated hemicellulose.

EXAMPLE 2

[0052] In this example, 150 mg of dried and ground citrus pulp and 1.5 g of DES choline chloride combined with urea, in a 1:2 molar ratio, were used.

Step A:

[0053] preparation of 150 mg of dried and ground citrus pulp;
mixing of DES with citrus pulp for 24 hrs at 25° C.;
centrifugation of the mixture and obtaining a precipitate of cellulose and a mixture of DES, pectin, hemicellulose.

Step B:

[0054] separation of precipitated cellulose.

Step D:

[0055] washing of the cellulose precipitate six times with water at 20° C. The mixture containing water and DES is used in step C of the process;
centrifugation of the aqueous mixture;
separation of the cellulose from the aqueous mixture resulting in cellulose with a higher degree of crystallinity than the starting biomass.

Step C:

[0056] addition of a certain amount of ethanol equal to 10 ml to the mixture containing DES, pectin, hemicellulose;
separation of pectin and precipitated hemicellulose.

EXAMPLE 3

[0057] In this example, 150 mg of dried and ground citrus pulp and 1.5 g DES choline acetate combined with urea, in a 1:2 molar ratio, were used.

Step A:

[0058] preparation of 150 mg of dried and ground citrus pulp;
mixing of DES with citrus pulp for 24 hrs at 25° C.;
centrifugation of the mixture and obtaining a precipitate of cellulose and a mixture of DES, pectin, hemicellulose.

Step B:

[0059] separation of precipitated cellulose.

Step D:

[0060] washing of the cellulose precipitate six times with water at 20° C. The mixture containing water and DES is used in step C of the process;
centrifugation of the aqueous mixture;
separation of the cellulose from the aqueous mixture resulting in cellulose with a higher degree of crystallinity than the starting biomass.

Step C:

[0061] addition of a certain amount of ethanol equal to 10 ml to the mixture containing DES, pectin, hemicellulose;
separation of pectin and precipitated hemicellulose.

EXAMPLE 4

[0062] In this example, 150 mg of dried and ground citrus pulp and 1.5 g DES choline chloride combined with glycolic acid, in a 1:1 molar ratio, were used.

Step A:

[0063] preparation of 150 mg of dried and ground citrus pulp;
mixing of DES with citrus pulp for 24 hrs at 25° C.;
centrifugation of the mixture and obtaining a precipitate of cellulose and a mixture of DES, pectin, hemicellulose.

Step B:

[0064] separation of precipitated cellulose.

Step D:

[0065] washing of the cellulose precipitate six times with water at 20° C. The mixture containing water and DES is used in step C of the process;
centrifugation of the aqueous mixture;
separation of the cellulose from the aqueous mixture resulting in cellulose with a higher degree of crystallinity than the starting biomass.

Step C:

[0066] addition of a certain amount of ethanol equal to 10 ml to the mixture containing DES, pectin, hemicellulose;
separation of pectin and precipitated hemicellulose.

EXAMPLE 5

[0067] In this example, 150 mg of dried and ground citrus pulp and 1.5 g of choline glycolate were used.

Step A:

[0068] preparation of 150 mg of dried and ground citrus pulp;
mixing of ionic solvent with citrus pulp for 24 hours at 25° C.;
centrifugation of the mixture and obtaining a precipitate of cellulose and a mixture of ionic solvent, pectin, hemicellulose.

Step B:

[0069] separation of precipitated cellulose.

Step D:

[0070] washing of the cellulose precipitate six times with water at 20° C. The mixture containing water and ionic solvent is used in step C of the process;
centrifugation of the aqueous mixture;
separation of the cellulose from the aqueous mixture resulting in cellulose with a higher degree of crystallinity than the starting biomass.

Step C:

[0071] addition of a certain amount of ethanol equal to 10 ml to the mixture containing ionic solvent, pectin, hemicellulose;
separation of pectin and precipitated hemicellulose.

EXAMPLE 6

[0072] In this example, 150 mg of dried and ground citrus pulp and 1.5 g DES choline chloride combined with levulinic acid, in a 1:1 molar ratio, were used.

Step A:

[0073] preparation of 150 mg of dried and ground citrus pulp;
mixing of DES with citrus pulp for 24 hrs at 25° C.;
centrifugation of the mixture and obtaining a precipitate of cellulose and a mixture of DES, pectin, hemicellulose.

Step B:

[0074] separation of precipitated cellulose.

Step D:

[0075] washing of the cellulose precipitate six times with water at 20° C. The mixture containing water and DES is used in step C of the process;
centrifugation of the aqueous mixture;
separation of the cellulose from the aqueous mixture resulting in cellulose with a higher degree of crystallinity than the starting biomass.

Step C:

[0076] addition of a certain amount of ethanol equal to 10 ml to the mixture containing DES, pectin, hemicellulose;
separation of pectin and precipitated hemicellulose.

EXAMPLE 7

[0077] In this example, 150 mg of dried and ground citrus pulp and 1.5 g DES choline acetate combined with diglycolic acid, in a 1:1 molar ratio, were used.

Step A:

[0078] preparation of 150 mg of dried and ground citrus pulp;
mixing of DES with citrus pulp for 24 hrs at 25° C.;
centrifugation of the mixture and obtaining a precipitate of cellulose and a mixture of DES, pectin, hemicellulose.

Step B:

[0079] separation of precipitated cellulose.

Step D:

[0080] washing of the cellulose precipitate six times with water at 20° C. The mixture containing water and DES is used in step C of the process;
centrifugation of the aqueous mixture;
separation of the cellulose from the aqueous mixture resulting in cellulose with a higher degree of crystallinity than the starting biomass.

Step C:

[0081] addition of a certain amount of ethanol equal to 10 ml to the mixture containing DES, pectin, hemicellulose;
separation of pectin and precipitated hemicellulose.