METHOD FOR HYDROLYZING CELLULOSE INTO SUGAR TO PRODUCE SPHERICAL CAPACITIVE CARBON

Abstract

A method for hydrolyzing cellulose into sugar to produce spherical capacitive carbon for the deep utilization of biomass and carbon materials. The present disclosure includes the following steps of: (1) crude cellulose pretreatment; (2) alkaline hydrolysis of cellulose; (3) separation of the cellulose from a hydrolyzed sugar liquor; (4) drying of an alkali-containing hydrolyzed sugar; (5) sintering of spherical capacitive carbon; (6) capacitive carbon post-processing; and (7) alkali recycling. In the method, biomass is used as a raw material, high-purity cellulose and hydrolyzed sugar are obtained through deep hydrolysis, the spherical capacitive carbon is sintered with the hydrolyzed sugar instead of sucrose and starch, and alkali is recycled. Pollution and waste are not generated, and more than 80% of the alkali can be recycled.

Claims

1. A method for hydrolyzing cellulose into sugar to produce spherical capacitive carbon, comprising the following steps: step 1, crude cellulose pretreatment: soaking and stirring a crude cellulose raw material in a dilute hydrochloric acid solution, filtering, rinsing filter residues with clean water until neutral, and drying the filter residues to obtain cellulose; step 2, alkaline hydrolysis of cellulose: adding the cellulose obtained in step 1 into a lye, cooking the cellulose at 120-150° C. for 6-10 h, and partly hydrolyzing the cellulose into sugar; step 3, separation of the cellulose from a hydrolyzed sugar liquor: subjecting a hydrolysate obtained in step 2 to solid-liquid separation, washing filter residues with water and drying to obtain purified cellulose; step 4, drying of an alkali-containing hydrolyzed sugar: using a filtrate separated in step 3 as an alkali-containing hydrolyzed sugar liquor, and evaporating and drying the alkali-containing hydrolyzed sugar liquor to obtain the alkali-containing hydrolyzed sugar; step 5, sintering of spherical capacitive carbon: supplementing the alkali-containing hydrolyzed sugar with an activator and a co-activator, grinding, stirring and mixing evenly, heating a resulting mixture to 700-800° C. in an inert atmosphere, and carbonizing-activating for 60-90 min to form a spherical capacitive carbon agglomerate; step 6, capacitive carbon post-processing: crushing the spherical capacitive carbon agglomerate, soaking in hot water, filtering, reserving a filtrate, pickling and washing filter residues with water, drying and grinding to obtain a finished product of spherical capacitive carbon; and step 7, alkali recycling: drying a hot water soaked filtrate in the capacitive carbon post-processing in step 6, recovering the alkali, and recycling the alkali used in the alkaline hydrolysis of cellulose in step 2 and/or the activator in the sintering of spherical capacitive carbon in step 5.

2. The method for hydrolyzing cellulose into sugar to produce spherical capacitive carbon according to claim 1, wherein in step 1, the crude cellulose raw material is coarse pulp produced by a pulp mill or cellulose extracted from biomass by other methods.

3. The method for hydrolyzing cellulose into sugar to produce spherical capacitive carbon according to claim 1, wherein step 1 comprises the following operations: adding the crude cellulose raw material to a 3-10 wt % dilute sulfuric acid solution in a solid-liquid mass ratio of 1:(3-5) to soak and stir for 6-10 h, filtering, rinsing the filter residues with clean water until neutral, and drying to obtain the cellulose.

4. The method for hydrolyzing cellulose into sugar to produce spherical capacitive carbon according to claim 1, wherein in step 2, the cellulose is added to a 3-5 wt % lye in a solid-liquid ratio of 1:(3-5).

5. The method for hydrolyzing cellulose into sugar to produce spherical capacitive carbon according to claim 4, wherein in step 2, the lye is an aqueous NaOH solution.

6. The method for hydrolyzing cellulose into sugar to produce spherical capacitive carbon according to claim 1, wherein in step 5, the alkali-containing hydrolyzed sugar, the activator, and the co-activator have a mass ratio of 1:(0.5-0.8):(0.3-0.6).

7. The method for hydrolyzing cellulose into sugar to produce spherical capacitive carbon according to claim 6, wherein the activator comprises alkaline potassium and sodium salts, and the co-activator comprises urea.

8. The method for hydrolyzing cellulose into sugar to produce spherical capacitive carbon according to claim 7, wherein the potassium salt is potassium carbonate, and the sodium salt is sodium carbonate.

9. The method for hydrolyzing cellulose into sugar to produce spherical capacitive carbon according to claim 1, wherein in step 2, the lye is an aqueous NaOH solution.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 is a concise block diagram of the technical route of the present disclosure.

[0032] FIG. 2 is a photograph of a coarse pulp manufactured from bagasse in a paper mill of Example 1, and the coarse pulp is used as a raw material.

[0033] FIG. 3 is a photograph of the hydrolysis of pure cellulose after pickling and water washing in a lye in Example 1.

[0034] FIG. 4 is a photograph of high-purity cellulose obtained after alkaline hydrolysis of cellulose in Example 1.

[0035] FIG. 5 is a photograph of an alkali-containing hydrolyzed sugar obtained after alkaline hydrolysis of cellulose in Example 1.

[0036] FIG. 6 is a scanning electron microscopy (SEM) image of spherical capacitive carbon prepared in Example 1.

[0037] FIG. 7 is a BET test report of the specific surface of spherical capacitive carbon prepared in Example 1.

[0038] FIG. 8 is a photograph of a solid alkali activator recovered in Example 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] The technical route and operational details of the present disclosure will be further described below with reference to specific examples and drawings.

[0040] In the pulp and paper industry, chemical bonds are broken among cellulose, lignin and hemicellulose in the raw material through the chemical hydrolysis of biomass. The main component of the separated coarse pulp is cellulose, which contains a small amount of unseparated impurities such as hemicellulose and lignin. In the present disclosure, dry pulp from paper mills or cellulose separated by organic solvent method and ionic liquid method is used as a raw material, hydrolyzed into sugar in a lye, and the sugar is sintered into spherical capacitive carbon. The technical route is shown in FIG. 1, including the following seven steps: (1) crude cellulose (pulp) pretreatment; (2) alkaline hydrolysis of cellulose; (3) separation of the cellulose from a hydrolyzed sugar liquor; (4) drying of an alkali-containing hydrolyzed sugar; (5) sintering of the spherical capacitive carbon; (6) capacitive carbon post-processing; and (7) alkali recycling.

[0041] The specific operations of each step are described as follows:

[0042] (1) Crude Cellulose (Pulp) Pretreatment

[0043] The coarse pulp is ground into powder, added to a 3%-10% dilute sulfuric acid solution in a solid-liquid ratio of 1:3 to 1:5, stirred and soaked at 60-80° C. for 6-8 h. Hemicellulose is dissolved in an acid liquor, and the acid liquor and pure cellulose are separated by a centrifuge, rinsed with deionized water until neutral, and dried to obtain purified cellulose.

[0044] (2) Alkaline Hydrolysis of Cellulose

[0045] The cellulose is added to a 3%-5% NaOH solution in a solid-liquid ratio of 1:3 to 1:5, and cooked at 120-150° C. for 6-10 h to hydrolyze the cellulose until partially hydrolyzed into sugar.

[0046] (3) Separation of the Cellulose from a Hydrolyzed Sugar Liquor

[0047] A hydrolysate is subjected to solid-liquid separation in the centrifuge, and the cellulose in the centrifuge is washed with deionized water until neutral to obtain highly purified cellulose; a separated alkali-containing hydrolyzed sugar liquor is reserved for the next step.

[0048] (4) Drying of an Alkali-Containing Hydrolyzed Sugar

[0049] The alkali-containing hydrolyzed sugar liquor is poured into a stainless steel tray, dried in an oven at 115-125° C. for 6-10 h, and ground into powder; alternatively, the alkali-containing hydrolyzed sugar liquor is converted into a dry powder by spray drying.

[0050] (5) Sintering of the Spherical Capacitive Carbon

[0051] A solid alkali-containing hydrolyzed sugar obtained in step 3 was added to activator K.sub.2CO.sub.3 (or Na.sub.2CO.sub.3) and co-activator urea in a ratio of 1:(0.5-0.8):(0.3-0.6), ground, stirred, mixed evenly, put in a graphite crucible, heated to 700-800° C. in an electric furnace in an inert atmosphere for 60-90 min.

[0052] (6) Capacitive Carbon Post-Processing

[0053] Furnace carbon blocks are crushed, soaked in hot water, and filtered, a filtrate is reserved, and filter residues are pickled once and washed with water several times until neutral, and dried to obtain the spherical capacitive carbon.

[0054] (7) Alkali Recycling

[0055] A hot water soaked filtrate reserved in step 6 is put into a tray with a tetrafluoroethylene coating, evaporated and dried in a blast drying oven at 110-135° C. to recover the activator K.sub.2CO.sub.3 (or Na.sub.2CO.sub.3), which is recycled as the activator of step 5 and the hydrolyzed lye of step 2.

[0056] FIG. 1 is an operational flowchart of the technical solution of the present disclosure, where the part in the bold dashed line is the content of steps 1 to 7 of the present disclosure, and two other products, lignin-derived capacitive carbon sintered with black liquor of alkali lignin and short carbon fibers sintered with high-purity cellulose, can refer to the prior art.

[0057] The implementation methods and effects of the present disclosure will be described below with reference to specific examples.

Example 1

[0058] The spherical capacitive carbon was produced with the coarse pulp manufactured from bagasse in Nanning Paper Mill as an initial raw material (as shown in the photograph in FIG. 2). The following operational steps were as follows:

[0059] (1) Coarse Pulp Pretreatment

[0060] In a solid-liquid mass ratio of 1:5, 100 g of coarse pulp was weighed, ground into powder, put in a 5 wt % sulfuric acid solution, soaked and stirred at 80° C. for 6 h, centrifuged, and filtered; the cellulose in the centrifuge was rinsed three times with deionized water until neutral, spin-dried, and dried in an oven at 110° C. to a constant weight to obtain 92 g of dry cellulose.

[0061] (2) Alkaline Hydrolysis of Cellulose

[0062] In a solid-liquid mass ratio of 1:4, 92 g of cellulose was added to 368 g of 5 wt % NaOH solution (containing 18.4 g of NaOH), and cooked at 140° C. for 8 h to hydrolyze the cellulose, which was partially converted into sugar.

[0063] (3) Separation of the Cellulose from a Hydrolyzed Sugar Liquor

[0064] A hydrolysate was subjected to solid-liquid separation in the centrifuge, and a alkali-containing hydrolyzed sugar liquor was separated (shown in FIG. 3); the cellulose in the centrifuge was washed with deionized water until neutral, spin-dried, and dried in the oven at 110° C. to a constant weight to obtain highly purified cellulose (shown in FIG. 4), which weighed 48 g.

[0065] (4) Drying of an Alkali-Containing Hydrolyzed Sugar

[0066] The centrifuged alkali-containing hydrolyzed sugar liquor was put into a stainless steel tray, dried in an oven at 115° C. for 10 h, and ground into powder to obtain a solid alkali-containing hydrolyzed sugar (as shown in FIG. 5), which weighed 54 g (containing 18.4 g of NaOH).

[0067] (5) Sintering of the Spherical Capacitive Carbon

[0068] In a mass ratio of 1:0.7:0.5, 37.8 g of activator K.sub.2CO.sub.3 and 27 g of co-activator urea were added to 54 g of solid alkali-containing hydrolyzed sugar obtained in step 4, ground, stirred, mixed evenly, put into a graphite crucible, heated to 750° C. in an electric furnace in an inert atmosphere, held for 90 min, and discharged.

[0069] (6) Capacitive Carbon Post-Processing

[0070] Furnace carbon blocks were crushed, soaked in hot water, and filtered, a filtrate was reserved, and filter residues were pickled once and washed with water several times until neutral, and dried to obtain the spherical capacitive carbon, which weighed 12.6 g.

[0071] (7) Alkali Recycling

[0072] The hot water soaked filtrate reserved in step 6 was put into a tray with a tetrafluoroethylene coating, evaporated and dried to a constant weight in a blast drying oven at 130° C.; the recovered activator was a mixture of K.sub.2CO.sub.3 and Na.sub.2CO.sub.3, the former was K.sub.2CO.sub.3 added in step 5, and the latter was Na.sub.2CO.sub.3 convened from NaOH used for alkaline hydrolysis in step 2. In this example, 18.4 g of NaOH and 37.8 g of K.sub.2CO.sub.3 were used, and a total of 45.7 g of the mixture of potassium carbonate and sodium carbonate was recovered (as shown in FIG. 8), which could be recycled as the activator in step 5.

[0073] FIG. 6 is an SEM image of the spherical capacitive carbon prepared in this example.

[0074] FIG. 7 is a BET test report of the specific surface of the spherical capacitive carbon prepared in this example. In this example, 48 g of high-purity cellulose and 12.6 g of spherical capacitive carbon were obtained from 100 g of coarse pulp. The products were tested by multi-point MBET; the specific surface was 2,368 m.sup.2/g, and the total pore volume was 1.35 mL/g, which exceeded the highest standards of the national standard for capacitive carbon (2,000 m.sup.2/g and 0.80 mL/g, respectively).

Example 2

[0075] Example 2 was the same as Example 1. The spherical capacitive carbon and the short carbon fiber were produced with the coarse pulp manufactured from bagasse in Nanning Paper Mill as an initial raw material. The difference was that the activator used in step 5 was changed from K.sub.7CO.sub.3 to Na.sub.2CO.sub.3. The activation ability of Na.sub.2CO.sub.3 was not as good as that of K.sub.7CO.sub.3, but the cost was low. After the recycling in step 7, the activator was Na.sub.2CO.sub.3 alone, instead of a mixture of Na.sub.2CO.sub.3 and K.sub.2CO.sub.3.

[0076] (1) Coarse Pulp Pretreatment

[0077] In a solid-liquid mass ratio of 1:5, 100 g of coarse pulp was weighed, ground into powder, put in a 5 wt % sulfuric acid solution, soaked and stirred at 80° C. for 6 h, centrifuged, and filtered; the cellulose in the centrifuge was rinsed three times with deionized water until neutral, spin-dried, and dried in an oven at 110° C. to a constant weight to obtain 92 g of dry cellulose.

[0078] (2) Alkaline Hydrolysis of Cellulose

[0079] In a solid-liquid mass ratio of 1:4, 92 g of cellulose was added to 368 g of 5 wt % NaOH solution (containing 18.4 g of NaOH), and cooked at 140° C. for 8 h to hydrolyze the cellulose, which was partially converted into sugar.

[0080] (3) Separation of the Cellulose from a Hydrolyzed Sugar Liquor

[0081] A hydrolysate was subjected to solid-liquid separation in the centrifuge; the separated cellulose was washed with deionized water until neutral, spin-dried, and dried in the oven at 110° C. to a constant weight to obtain highly purified cellulose, which weighed 51 g.

[0082] (4) Drying of an Alkali-Containing Hydrolyzed Sugar Liquor

[0083] The alkali-containing hydrolyzed sugar liquor separated from the centrifuge was put into a tray, evaporated and dried to a constant weight in a blast drying oven at 120° C. to obtain a solid alkali-containing hydrolyzed sugar; the solid alkali-containing hydrolyzed sugar was ground into powder, which weighed 55 g.

[0084] (5) Sintering of the Spherical Capacitive Carbon

[0085] In a mass ratio of 1:0.7:0.5, 38.5 g of activator Na.sub.2CO.sub.3; and 27.5 g of co-activator urea were added to 55 g of solid alkali-containing hydrolyzed sugar obtained in step 4, ground, stirred, mixed evenly, put into a graphite crucible, heated to 740° C. in an electric furnace in an inert atmosphere, and held for 90 min.

[0086] (6) Capacitive Carbon Post-Processing

[0087] Furnace carbon blocks were crushed, soaked in hot water, and filtered, a filtrate was reserved, and filter residues were pickled once and washed with water several times until neutral, and dried to obtain the spherical capacitive carbon, which weighed 16.6 g.

[0088] (7) Alkali Recycling

[0089] The hot water soaked filtrate reserved in step 6 was put into a tray with a tetrafluoroethylene coating, evaporated and dried to a constant weight in a blast drying oven at 130° C.; the recovered activator was a mixture of Na.sub.2CO.sub.3, and the NaOH used for alkaline hydrolysis in step 2 had been converted into Na.sub.2CO.sub.3. In this example, 18.4 g of NaOH and 38.5 g of Na.sub.2CO were used in total, and a total of 46.7 g of sodium carbonate was recovered, with a recovery rate of 82%.

[0090] In this example, 51 g of high-purity cellulose and 16.6 g of spherical capacitive carbon were obtained from 100 g of coarse pulp. The products were tested by multi-point MBET; the specific surface was 1,824 m.sup.2/g, and the total pore volume was 0.822 mL/g.

Example 3

[0091] A method for hydrolyzing cellulose into sugar to produce spherical capacitive carbon was provided, including the following steps:

[0092] step 1, crude cellulose pretreatment: the crude cellulose raw material was added to a 10 wt % dilute sulfuric acid solution in a solid-liquid mass ratio of 1:3 to soak and stir for 10 h and filtered; the filter residues were rinsed with clean water until neutral and dried to obtain cellulose; the crude cellulose raw material was coarse pulp manufactured by pulp mills or cellulose extracted from biomass;

[0093] step 2, alkaline hydrolysis of cellulose: the cellulose obtained in step 1 was added into a 5 wt % aqueous NaOH solution in a solid-liquid ratio of 1:3, cooked at 120° C. for 10 h, and partially hydrolyzed into sugar, and a hydrolysate was obtained;

[0094] step 3, separation of the cellulose from a hydrolyzed sugar liquor: the hydrolysate obtained in step 2 was subjected to solid-liquid separation, and filter residues were washed with water and dried to obtain purified cellulose;

[0095] step 4, drying of an alkali-containing hydrolyzed sugar: a filtrate separated in step 3 was used as an alkali-containing hydrolyzed sugar liquor, and the alkali-containing hydrolyzed sugar liquor was evaporated and dried to obtain the alkali-containing hydrolyzed sugar;

[0096] step 5, sintering of spherical capacitive carbon: the dried alkali-containing hydrolyzed sugar was supplemented with activator potassium carbonate/sodium carbonate and co-activator urea, where the alkali-containing hydrolyzed sugar, the activator and the co-activator had a mass ratio of 1:0.5:0.3; all materials were ground, stirred and mixed evenly, the resulting mixture was heated to 700° C. in an inert atmosphere, and carbonized-activated for 80 min to form spherical capacitive carbon;

[0097] step 6, capacitive carbon post-processing: the spherical capacitive carbon agglomerate was crushed, soaked in hot water, and filtered, a filtrate was reserved, and filter residues were pickled and washed with water, dried to obtain a finished product of spherical capacitive carbon;

[0098] step 7, alkali recycling: a hot water soaked filtrate in the capacitive carbon post-processing in step 6 was dried, the alkali was recovered, and the alkali used in the alkaline hydrolysis of cellulose in step 2 and the activator in the sintering of spherical capacitive carbon in step 5 were recycled.

Example 4

[0099] A method for hydrolyzing cellulose into sugar to produce spherical capacitive carbon was provided, including the following steps:

[0100] step 1, crude cellulose pretreatment: the crude cellulose raw material was added to a 4 wt % dilute sulfuric acid solution in a solid-liquid mass ratio of 1:4 to soak and stir for 8 h and filtered; the filter residues were rinsed with clean water until neutral and dried to obtain cellulose; the crude cellulose raw material was coarse pulp manufactured by pulp mills or cellulose extracted from biomass;

[0101] step 2, alkaline hydrolysis of cellulose: the cellulose obtained in step 1 was added into a 3 wt % aqueous NaOH solution in a solid-liquid ratio of 1:5, cooked at 150° C. for 6 h, and partially hydrolyzed into sugar, and a hydrolysate was obtained;

[0102] step 3, separation of the cellulose from a hydrolyzed sugar liquor: the hydrolysate obtained in step 2 was subjected to solid-liquid separation, and filter residues were washed with water and dried to obtain purified cellulose;

[0103] step 4, drying of an alkali-containing hydrolyzed sugar: a filtrate separated in step 3 was used as an alkali-containing hydrolyzed sugar liquor, and the alkali-containing hydrolyzed sugar liquor was evaporated and dried to obtain the alkali-containing hydrolyzed sugar;

[0104] step 5, sintering of spherical capacitive carbon: the dried alkali-containing hydrolyzed sugar was supplemented with activator potassium carbonate/sodium carbonate and co-activator urea, where the alkali-containing hydrolyzed sugar, the activator and the co-activator had a mass ratio of 1:0.8:0.6; all materials were ground, stirred and mixed evenly, the resulting mixture was heated to 800° C. in an inert atmosphere, and carbonized-activated for 60 min to form spherical capacitive carbon;

[0105] step 6, capacitive carbon post-processing: the spherical capacitive carbon agglomerate was crushed, soaked in hot water, and filtered, a filtrate was reserved, and filter residues were pickled and washed with water, dried to obtain a finished product of spherical capacitive carbon;

[0106] step 7, alkali recycling: a hot water soaked filtrate in the capacitive carbon post-processing in step 6 was dried, the alkali was recovered, and the alkali used in the alkaline hydrolysis of cellulose in step 2 and the activator in the sintering of spherical capacitive carbon in step 5 were recycled.

[0107] Although the present disclosure has been disclosed above with preferred examples, they are not intended to limit the present disclosure. Any person skilled in the art can make some modifications and improvements without departing from the spirit and scope of the present disclosure. Therefore, the protection scope of the present disclosure should be subject to that defined by the claims.