A method for continuous production of furfural from corncob

Abstract

The application relates to the technical field of biomass utilization, and relates to a continuous preparation technology of furfural from corncob, which comprises the following steps: S1: corncob is crushed into powder, then is mixed with sulfur trioxide, and is subjected to steam explosion under steam pressure; S2: acid catalysis-extraction reaction; S3: the once-extracted phase is subjected to solid-liquid separation, the liquid phase is subjected to secondary extraction by using an extracting agent, and a secondary extraction phase is obtained; S4: the once-extracted phase and the secondary extraction phase are combined and are sent into a rectifying tower for rectification, and furfural with a purity greater than 99% is obtained. The application has the beneficial effects that: 1. after the corncob is crushed, the corncob is mixed with sulfur trioxide and is subjected to steam explosion, hemicellulose can be effectively stripped from lignin, the subsequent reaction of preparing furfural from hemicellulose by acid catalysis can be more easily carried out, and the yield is higher; 2. in the method, acetic acid and aluminum chloride are used as mixed acid catalysts, the reaction temperature is reduced by 20-40 DEG C compared with one-pot method, and the reaction pressure is reduced by 0.4-0.7 MPa.G compared with one-pot method, so that the requirement of the reaction on equipment is reduced.

Description

Technical Field

[0001] This invention relates to the field of biomass utilization technology, and in particular to a method for the continuous preparation of furfural from corn cobs. Background Technology

[0002] Since its industrial production began in 1929, furfural has been produced using a one-step process. This one-step process involves the hydrolysis of hemicellulose to pentose and the dehydration and cyclization of pentose within the same hydrolysis vessel. The industrial biomass-based furfural production route involves a one-step process from corn cobs to furfural under dilute sulfuric acid catalysis. The process route is as follows: Figure 2 As shown.

[0003] The commonly used process conditions are to react at high temperature (140-185℃) and high pressure for 3-10 hours, with H2SO4 dosage of about 3%. Due to various limitations, the maximum furfural yield in industrial production can reach 45%-55% of the theoretical value, corresponding to a corn cob consumption of 10-12 tons of corn cobs / ton of furfural. The disadvantages of this method are: low yield, the need to discharge slag for each batch of reaction, inability to achieve continuous production, and the high corrosiveness of equipment caused by the use of sulfuric acid.

[0004] In the two-step production process, the hydrolysis of hemicellulose to produce pentose and the dehydration and cyclization of pentose are carried out separately. The first step involves the hydrolysis of hemicellulose to produce pentose. Because hemicellulose has a low degree of polymerization and is easily hydrolyzed, appropriate pre-hydrolysis conditions can ensure almost complete hydrolysis of the hemicellulose while preserving the cellulose intact. The second step utilizes the pentose obtained in the first step to produce furfural. The advantage of this process is its full utilization of raw materials. The yield of the two-step process can reach over 80% in small-scale trials, which are generally conducted in reactors smaller than 100 mL. Once the reactor is scaled up, the yield drops sharply, and it has not been widely used in industrial applications. Furthermore, the two-step process cannot avoid the problem of coking during the pentose-to-furfural process, severely hindering continuous production. Nevertheless, with increasing societal demands for environmental protection and comprehensive utilization of raw materials, the two-step furfural production process is an inevitable trend in the development of the furfural industry. Summary of the Invention

[0005] To address the problems mentioned in the background art, the present invention provides a method for the continuous preparation of furfural from corn cobs, comprising the following steps:

[0006] S1. Crush the corn cobs into powder, then mix them with sulfur trioxide, and perform steam explosion under steam pressure;

[0007] S2. Disperse the corn cob powder after steam explosion in a portion of the mixed acid solution, denoted as solution A; mix the other portion of the mixed acid solution with the extractant, denoted as solution B; pass solution B into a self-circulating reactor and heat it to the set temperature, then pass solution A in to carry out the acid catalytic-extraction reaction. Collect the reaction solution and use the extractant for primary extraction to obtain a primary extract phase containing most of the furfural, as well as a primary raffinate phase.

[0008] S3. The primary raffinate phase is subjected to solid-liquid separation, and the liquid phase is extracted a second time using an extractant to obtain a secondary extract phase;

[0009] S4. Combine the primary and secondary extraction phases and send them to a distillation column for distillation to obtain furfural with a purity greater than 99%.

[0010] Preferably, the pulverization process involves crushing the corn cob into powder of 40 mesh or less.

[0011] Preferably, the ratio of corn cob powder to sulfur trioxide is 1000:(1-10), the steam pressure is 0.1-0.6 MPa.G, and the steam explosion time is 0.5-3 h.

[0012] Preferably, the ratio of corn cob powder to sulfur trioxide is 1000:(1-3), the steam pressure is 0.1-0.3 MPa.G, and the steam explosion time is 0.5-2 h.

[0013] Preferably, the mixed acid solution is composed of acetic acid, aluminum chloride and water, wherein the mass fraction of acetic acid is 5-15%, the mass fraction of aluminum chloride is 0.5-2%, and the mass ratio of the corn cob powder after gas explosion to the mixed acid solution is (0.1-1.5):10.

[0014] Preferably, the mixed acid solution is composed of acetic acid, aluminum chloride and water, wherein the mass fraction of acetic acid in the mixed acid solution is 5-10%, the mass fraction of aluminum chloride is 0.5-1%, and the mass ratio of the corn cob powder after gas explosion to the mixed acid solution is (0.3-0.8):10.

[0015] Preferably, in the acid catalytic extraction reaction, the mass ratio of the mixed acid solution to the extractant is (1-4):1, the set temperature is 140-180℃, the flow rate of solution A entering the self-circulating reactor is 20-100mL / min, and the flow rate of the extractant entering the self-circulating reactor is 10-100mL / min.

[0016] Preferably, in the acid catalytic extraction reaction, the mass ratio of the mixed acid solution to the extractant is (2-3):1, the set temperature is 150-170℃, the flow rate of solution A into the self-circulating reactor is 30-60 mL / min, and the flow rate of the extractant into the self-circulating reactor is 10-30 mL / min.

[0017] Preferably, the extractant is any one or two of trichloroethane and toluene.

[0018] Preferably, the self-circulating reactor has a length-to-diameter ratio of (5-10):1, is equipped with 5-10 sieve plates, the sieve plates have holes with a diameter of 2-4 mm, the ratio of hole area to sieve plate cross-sectional area is 1:(2-4), and the self-circulation flow rate is 1-5 L / min.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. After the corn cob is crushed, it is mixed with sulfur trioxide and steam-exploded, which can effectively separate hemicellulose from lignin, making the subsequent acid-catalyzed reaction of hemicellulose to furfural easier and yielding a higher result.

[0021] 2. This method uses acetic acid and aluminum chloride as mixed acid catalysts, which reduces the reaction temperature by 20-40℃ and the reaction pressure by 0.4-0.7 MPa.G compared to the one-pot method, thus reducing the equipment requirements for the reaction.

[0022] 3. This method uses a solid-liquid mixture of mixed acid and corn cob powder as the feed to a self-circulating reactor. During the reaction, coking products are generated and adhere to the corn cob powder, and are discharged from the reactor with the solution. Compared with the current two-step method of first hydrolyzing xylose solution and then acid-catalyzing xylose solution to prepare furfural, this method avoids the by-product coking products adhering to the reactor wall and clogging the reactor, and provides a new approach for the continuous preparation of furfural.

[0023] 4. In this method, the extractant is continuously introduced and extracted in the reactor, and most of the generated furfural enters the extractant, which effectively slows down the polymerization of furfural into coke in the acidic environment of the aqueous phase and improves the yield.

[0024] 5. This method uses a self-circulating reactor. Compared with the continuous extraction reaction of furfural using an extraction tower, the self-circulating reactor has a simple structure and no dynamic seal. Without changing the reactor's structural dimensions, the mixing effect of the aqueous phase and the extraction phase can be improved by adjusting the circulation rate. It has greater operational flexibility and stronger adaptability to raw materials. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process of the present invention.

[0026] Figure 2 The existing technology provides a flowchart of the process route for producing furfural.

[0027] Among them, 1. Crusher; 2. Gas explosion tank; 3. Dissolving and stirring tank; 4. Self-circulating pump; 5. Self-circulating reactor; 6. Aqueous phase condenser; 7. Extraction phase condenser; 8. Aqueous phase filter; 9. Extraction phase filter; 10. Extractor; 11. Distillation column; Detailed Implementation

[0028] Unless otherwise stated, all raw materials and reagents used in this invention are commercially available or can be prepared by known methods. Example 1

[0029] like Figure 1 As shown, a method for continuous preparation of furfural from corn cobs is characterized by comprising the following steps:

[0030] S1. Add corn cobs with 10% moisture content to crusher 1 and crush them to below 40 mesh. Add them to steam explosion tank 2 and add sulfur trioxide at a ratio of 1.5:1000. Pass steam into steam explosion tank 2 until the pressure is 0.3 MPa.G and maintain the pressure while stirring for 2 hours.

[0031] S2. Add mixed acid to the dissolving and stirring tank 3. The mixed acid contains 10% acetic acid and 0.5% aluminum chloride. The mass ratio of the corn cob powder after gas explosion to the mixed acid is 0.3:10. Start the dissolving and stirring tank 3 for stirring. In the self-circulating reactor 5, the ratio of extractant to mixed acid is 3:1. Heat to 150℃. The self-circulating flow rate is 2L / min. The mixed acid and corn cob mixture (solution A) enters the self-circulating reactor 5 at a flow rate of 60mL / min. Collect the reaction solution and perform a primary extraction using extractant (chloroform, the same below) to obtain a primary extract phase containing most of the furfural and a primary raffinate phase. The flow rate of the extractant entering the self-circulating reactor is 30mL / min. The primary extract phase is cooled by the extract phase cooler 7 and then enters the extract phase filter 9.

[0032] S3. The primary raffinate phase is cooled by the aqueous phase condenser 6 and then enters the aqueous phase filter 8 for solid-liquid separation. The liquid phase enters the extractor 10 and the aqueous phase is extracted with the extractant to obtain the secondary raffinate phase.

[0033] S4. The secondary extract phase from extractor 10 and the primary extract phase from extract phase filter 9 are combined and enter distillation column 11. Furfural with a purity of 99.5-99.8% is obtained by distillation. The extractant is recycled back to the circulating reactor. The corn cob consumption of the distilled furfural is 8.5g corn cob / 1g furfural. Example 2

[0034] The difference between this embodiment and embodiment 1 is that steam is introduced into the steam explosion tank 2 to a pressure of 0.4 MPa.G, while other conditions are exactly the same as in embodiment 1. Furfural with a purity of 99.5-99.8% is obtained by distillation, and the corn cob consumption is 8.5g corn cob / 1g furfural. Example 3

[0035] The difference between this embodiment and embodiment 1 is that steam is introduced into the steam explosion tank 2 to a pressure of 0.5 MPa.G, while other conditions are exactly the same as in embodiment 1. Furfural with a purity of 99.5-99.8% is obtained by distillation, and the corn cob consumption is 8.6 g corn cob / 1 g furfural. Example 4

[0036] The difference between this embodiment and Embodiment 1 is that the temperature is raised to 160°C, while other conditions are exactly the same as in Embodiment 1. Furfural with a purity of 99.5-99.8% is obtained by distillation, and the corn cob consumption is 8.2g corn cob / 1g furfural. Example 5

[0037] The difference between this embodiment and Embodiment 1 is that the temperature is raised to 170°C, while other conditions are exactly the same as in Embodiment 1. Furfural with a purity of 99.5-99.8% is obtained by distillation, and the corn cob consumption is 8.3g corn cob / 1g furfural. Example 6

[0038] The difference between this embodiment and embodiment 4 is that the self-circulation flow rate is 3L / min, while the other conditions are exactly the same as in embodiment 4. The distillation yields furfural with a purity of 99.5-99.8%, and the corn cob consumption is 7.8g corn cob / 1g furfural. Example 7

[0039] The difference between this embodiment and embodiment 4 is that the self-circulation flow rate is 4L / min, while other conditions are exactly the same as in embodiment 4. Furfural with a purity of 99.5-99.8% is obtained by distillation, and the corn cob consumption is 7.6g corn cob / 1g furfural. Example 8

[0040] The difference between this embodiment and embodiment 4 is that the self-circulation flow rate is 5L / min, while the other conditions are exactly the same as in embodiment 4. Furfural with a purity of 99.5-99.8% is obtained by distillation, and the corn cob consumption is 7.7g corn cob / 1g furfural. Example 9

[0041] The difference between this embodiment and embodiment 7 is that the flow rate of the mixed acid and corn cob solution (solution A) into the self-circulating reactor 5 is 50 mL / min, and the other conditions are exactly the same as in embodiment 7. The distillation yields furfural with a purity of 99.5-99.8%, and the corn cob consumption is 7.4 g corn cob / 1 g furfural. Example 10

[0042] The difference between this embodiment and embodiment 7 is that the flow rate of the mixed acid and corn cob solution (solution A) into the self-circulating reactor 5 is 40 mL / min, and the other conditions are exactly the same as in embodiment 7. The distillation yields furfural with a purity of 99.5-99.8%, and the corn cob consumption is 7.1 g corn cob / 1 g furfural. Example 11

[0043] The difference between this embodiment and embodiment 7 is that the flow rate of the mixed acid and corn cob solution (solution A) into the self-circulating reactor 5 is 30 mL / min, and the other conditions are exactly the same as in embodiment 7. The distillation yields furfural with a purity of 99.5-99.8%, and the corn cob consumption is 7.2 g corn cob / 1 g furfural. Example 12

[0044] The difference between this embodiment and Example 10 is that the flow rate of the extractant into the self-circulating reactor is 20 mL / min, while the other conditions are exactly the same as in Example 10. Furfural with a purity of 99.5-99.8% is obtained by distillation, and the corn cob consumption is 7.4 g corn cob / 1 g furfural. Example 13

[0045] The difference between this embodiment and Example 10 is that the flow rate of the extractant entering the self-circulating reactor is 10 mL / min, and the other conditions are exactly the same as in Example 10. The distillation yields furfural with a purity of 99.5-99.8%, and the corn cob consumption is 7.9 g corn cob / 1 g furfural.

[0046] As can be seen from Examples 1, 2, and 3, the steam explosion pressure has little effect on the unit consumption of corn cobs;

[0047] As can be seen from Examples 1, 4, and 5, the higher the temperature, the lower the unit consumption; however, the unit consumption does not change much after the temperature exceeds 160°C.

[0048] As can be seen from Examples 6, 7, and 8, the self-circulation flow rate is 4 L / min, and the corn cob consumption is the lowest.

[0049] As can be seen from Examples 9, 10 and 11, reducing the flow rate of the mixed acid and corn cob solution is beneficial to reducing the corn cob consumption, but the reduction in consumption is no longer significant when the flow rate is below 40 mL / min.

[0050] As can be seen from Examples 12 and 13, reducing the extractant flow rate significantly increases the corn cob consumption per unit.

[0051] Based on the above examples, it can be seen that with a reaction temperature of 160℃, a self-circulating flow rate of 4L / min, an extraction phase flow rate of 30mL / min, and a mixed acid and corn cob solution flow rate of 40mL / min, the corn cob consumption can reach a relatively low level, which is more than 30% lower than the current one-pot method.

[0052] The control method of this invention is automatic control through a controller. The control circuit of the controller can be implemented by simple programming by those skilled in the art. The power supply is also common knowledge in the field. Furthermore, since this invention is mainly used to protect mechanical devices, the control method and circuit connection will not be explained in detail here.

[0053] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for continuous preparation of furfural from corn cobs, characterized in that, Includes the following steps: S1: Crush the corn cobs into powder, sieve them, then mix them with sulfur trioxide and steam-explode them under steam pressure; S2: Disperse the corn cob powder after steam explosion in a portion of the mixed acid solution, denoted as solution A; mix the other portion of the mixed acid solution with the extractant, denoted as solution B; pass solution B into a self-circulating reactor and heat it to the set temperature, then pass solution A in to carry out the acid catalytic-extraction reaction. Collect the reaction solution and use the extractant for primary extraction to obtain a primary extract phase containing most of the furfural, as well as a primary raffinate phase; S3: The primary raffinate phase is subjected to solid-liquid separation, and the liquid phase is extracted a second time using an extractant to obtain a secondary extract phase; S4: Combine the primary and secondary extraction phases and send them to a distillation column for distillation to obtain furfural with a purity greater than 99%. The mixed acid solution is composed of acetic acid, aluminum chloride and water, wherein the mass fraction of acetic acid is 5-15% and the mass fraction of aluminum chloride is 0.5-2%, and the mass ratio of the corn cob powder after gas explosion to the mixed acid solution is (0.1-1.5):

10. The extractant is any one or two of trichloroethane and toluene; The self-circulating reactor has a length-to-diameter ratio of (5-10):1, is equipped with 5-10 sieve plates, and the sieve plates have holes with a diameter of 2-4 mm. The ratio of the hole area to the cross-sectional area of ​​the sieve plate is 1:(2-4), and the self-circulation flow rate is 1-5 L / min.

2. The method for continuous preparation of furfural from corn cobs according to claim 1, characterized in that, The pulverizing process breaks the corn cob into powder of less than 40 mesh.

3. The method for continuous preparation of furfural from corn cobs according to claim 1, characterized in that, The ratio of corn cob powder to sulfur trioxide is 1000:(1-10), the steam pressure is 0.1-0.6 MPa.G, and the steam explosion time is 0.5-3 h.

4. The method for continuous preparation of furfural from corn cobs according to claim 1, characterized in that, The ratio of corn cob powder to sulfur trioxide is 1000:(1-3), the steam pressure is 0.1-0.3 MPa.G, and the steam explosion time is 0.5-2 h.

5. The method for continuous preparation of furfural from corn cobs according to claim 1, characterized in that, The mixed acid solution is composed of acetic acid, aluminum chloride and water, wherein the mass fraction of acetic acid in the mixed acid solution is 5-10% and the mass fraction of aluminum chloride is 0.5-1%, and the mass ratio of corn cob powder after gas explosion to the mixed acid solution is (0.3-0.8):

10.

6. The method for continuous preparation of furfural from corn cobs according to claim 1, characterized in that, In the acid-catalyzed extraction reaction, the mass ratio of the mixed acid solution to the extractant is (1-4):1, the temperature is set at 140-180℃, the flow rate of solution A into the self-circulating reactor is 20-100 mL / min, and the flow rate of the extractant into the self-circulating reactor is 10-100 mL / min.

7. The method for continuous preparation of furfural from corn cobs according to claim 1, characterized in that, In the acid-catalyzed extraction reaction, the mass ratio of the mixed acid solution to the extractant is (2-3):1, the set temperature is 150-170℃, the flow rate of solution A into the self-circulating reactor is 30-60 mL / min, and the flow rate of the extractant into the self-circulating reactor is 10-30 mL / min.

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