CN102757413B - Method for preparing furfural by taking corncob as raw material - Google Patents

Abstract

The invention relates to the field of furfural production, in particular, the invention relates to a method for preparing furfural from corncobs. The method comprises the following steps: 1) crushing the corncobs, and mixing them uniformly with a sulfuric acid solution with a concentration of 0.1 to 0.5 wt %; 2) heating the mixture in step 1), adding additives such as phenols and aromatic amines to inhibit polymerization agent, stirring and mixing evenly; wherein the addition of the additive accounts for 0.05% to 0.5% of the total mass of the corncob; 3) the hydrolysis reaction occurs in the corncob hydrolysis reactor to generate furfural, and the middle part of the reactor is provided with a wire partition, and the The mixture containing additives in step 2) is added to the wire separator in the corncob hydrolysis reaction kettle, the hydrolysis temperature is 150-190°C, the water rises after gasification, contacts with the mixture, and a hydrolysis reaction occurs, and the gaseous hydrolysis product Furfural escapes to give a furfural condensate. The invention improves the yield from the existing 50%-60% to about 80% through the optimization of the experimental conditions and the improvement of the steps.

Description

A method for preparing furfural from corncobs

technical field

The invention relates to the field of furfural production, in particular, the invention relates to a method for preparing furfural from corncobs.

Background technique

Furfural (Furfural or 2-furfuraldehyde), CAS No. 98-01-1, molecular formula C ₅ H ₄ O ₂ , molecular weight 96.08, is a colorless transparent oily liquid with a taste similar to almond oil, low volatility, and Certain toxicity, irritating to the skin, direct contact should be avoided. The boiling point is 161.7°C (760mmHg); the melting point is -36.5°C; the relative density (d ²⁵ ₂₅ ) is 1.16; the flash point is 59°C. Furfural is slightly soluble in cold water. The solubility in water at 20°C is 8.3%. It is soluble in hot water. When the critical temperature is above 122.7°C, furfural and water can be miscible in any ratio.

Furfural not only has important industrial uses, but also can undergo chemical unit reactions such as hydrogenation, oxidation, chlorination, nitration, and condensation to prepare a large number of derivative products. At present, there are more than 1,600 derivatives made from furfural. , It is widely used in industrial production, and its downstream products cover petrochemical, synthetic resin, food industry, pharmaceutical industry, pesticide industry, synthetic fiber and other industries.

So far, furfural can only be produced by hydrolysis of plant fiber raw materials such as agricultural and forestry waste, corncobs, bagasse, etc., and the process is simple. my country is a big country of corn production, and the output of corncobs is quite considerable. The sulfuric acid catalytic hydrolysis process of corncobs is the mainstream production technology of furfural industry in my country. The main method is that the pentosans contained in hemicellulose are first hydrolyzed to pentoses under acid catalysis, and the resulting pentoses are hydrolyzed. The sugar is then dehydrated by acid catalysis to produce furfural. However, due to the occurrence of various side reactions during the hydrolysis of corn cob, there are problems such as low furfural yield and serious pollution of three wastes (waste water, waste gas, waste residue). Furfural is prone to polymerization under acidic conditions, and the resinous substance produced It will block the pipeline, which reduces the yield of furfural on the one hand, and on the other hand, the pipeline must be cleaned regularly, so that the production cycle is prolonged. The side reactions of polymerization and condensation in the furfural production process belong to the cationic ring-opening polymerization of oxygen heterocyclic compounds. Point out in the literature that multiple inhibitors (such as triphenylphosphine, thiourea or diphenylamine, etc.) are commonly used in the synthesis of organic compounds, phosphorus salts and other phosphorus compounds, and are commonly used polymerization inhibitors in cationic polymerization. The principle of polymerization inhibition is the reaction between additives and cationic active chains, thereby inhibiting the reaction between cationic active chains and monomers, but these documents only believe that such reactions can occur from the perspective of organic reaction mechanisms. These substances were added to increase their yields and suppress side reactions reported.

For this reason, the present invention selects suitable polymerization inhibitor (such as triphenylphosphine, thiourea or diphenylamine etc.) to suppress side reactions such as the cationic ring-opening polymerization reaction of furfural, oxidation, and then effectively improves the utilization ratio of corncob and furfural Yield, and the experimental device was improved, the amount of polymerization inhibitor used in the experiment of extracting furfural from corncobs, and the hydrolysis temperature in order to reduce side reactions and increase extraction rate were investigated, in order to obtain a higher recovery rate.

Contents of the invention

The object of the present invention is to provide a kind of method that takes corn cob as raw material to prepare furfural, and this method has solved the low utilization rate of corn cob, many side reactions in the production process, the problem that furfural yield is low, in order to realize above-mentioned purpose, The technical solution of the invention is to add a polymerization inhibitor (such as triphenylphosphine, thiourea or diphenylamine) in the furfural production process to suppress side reactions and increase the yield of furfural.

The method for preparing furfural as raw material with corn cob of the present invention comprises the following steps:

1) After the corn cob is crushed, it is uniformly mixed with a sulfuric acid solution having a concentration of 0.1 to 0.5 wt%, to obtain a corn cob mixture;

2) heating the mixture in step 1), adding phenols and aromatic amine inhibitors, stirring and mixing evenly to obtain a mixture containing additives;

Wherein the addition amount of the additive accounts for 0.05% to 0.5% of the total mass of the corn cob;

3) In the corncob hydrolysis reaction kettle, furfural is generated by hydrolysis reaction, and the middle part of the reaction kettle is provided with a wire partition, and the additive-containing mixture in step 2) is added to the wire partition in the corncob hydrolysis reaction kettle. On the plate, the hydrolysis temperature is 150-190°C. The water under the metal wire partition rises after gasification, contacts with the mixture, and undergoes a hydrolysis reaction. The gaseous hydrolysis product furfural escapes and condenses to obtain a furfural condensate.

According to the method for preparing furfural from corn cobs of the present invention, the mass ratio of sulfuric acid solution to corn cobs in the step 1) is 10:1˜5:1.

According to the method for preparing furfural from corn cobs of the present invention, the stirring temperature in the step 2) is 80-100°C.

According to the method for preparing furfural from corncobs of the present invention, the polymerization inhibitor in the step 2) includes one of 1-naphthol, triphenylphosphine, naphthylamine, thiourea, diphenylamine and hydroquinone one or two.

According to the method for preparing furfural from corn cobs of the present invention, the hydrolysis reaction time in the step 3) is 3.5-5 hours.

According to the method for preparing furfural from corn cobs of the present invention, the step 3) adopts a temperature program, and the temperature is raised from 40° C. to 150-190° C. within 30 minutes.

According to the method for preparing furfural from corncobs of the present invention, in the step 3), the wire separator is arranged in the middle of the reactor, for separating water from the mixture containing the polymerization inhibitor in the step 2).

Through the method of the invention, the yield of furfural is increased from 50.0% to 60.0% in the traditional process to 74.4 to 86.0%. The main steps of the method are: 1) After crushing corn cobs to a certain particle size, mix them with dilute sulfuric acid at a certain liquid-solid ratio; 2) After heating the mixture to boiling, add a polymerization inhibitor and stir evenly, and then transfer to the autoclave ; 3) carry out the hydrolysis reaction in the autoclave, control the reaction conditions and the temperature rise program of the autoclave, and obtain the furfural-containing condensate after the steam is condensed.

In the present invention, by adding polymerization inhibitor (such as triphenylphosphine, thiourea or diphenylamine etc.) to suppress side reaction, improve furfural yield, the addition of this polymerization inhibitor needs strict If the amount of addition is too small, the effect of inhibiting side reactions will not be achieved. If the amount of addition is too high, not only will it not inhibit side reactions, but will cause other side reactions, thereby reducing the yield of furfural. Therefore, strictly The added amount of the polymerization inhibitor is controlled to account for 0.05-0.5% of the total mass of the corn cob.

In addition, the inventors of the present invention have also improved the reaction device. During conventional furfural hydrolysis, the mixture of corn cob and sulfuric acid is added to the hydrolysis pot for cooking. Remove the system in time, and the furfural partially dissolved in the liquid phase undergoes an oxidation reaction or polycondensation reaction under acidic conditions, resulting in a very low extraction rate of furfural, generally 50% to 60%; in the present invention, a The metal wire separator prevents the mixture of corncob and sulfuric acid from directly contacting with water, but rises through water vaporization into water vapor and undergoes a hydrolysis reaction in contact with the mixture of corncob and sulfuric acid. Through this improvement, the concentration of sulfuric acid is changed from the existing The 5% in the technology is reduced to 0.5%, and the reaction temperature can be increased to 150-190°C to keep the reaction system boiling, and the generated furfural can be taken away by water vapor in time, so not only can the extraction rate of the reactant be improved, but also Various side reactions of the product furfural in the mixture solution can be avoided, thereby further increasing the yield of furfural.

Finally, the present invention increases the yield from the existing 50% to 60% to about 80% through the optimization of the experimental conditions and the improvement of the steps, which has a good effect.

Description of drawings

Fig. 1 is the distillation unit of the theoretical content of furfural of the present invention;

Fig. 2 is a structural schematic diagram of a high-pressure reactor for preparing furfural by hydrolyzing corncobs of the present invention.

Reference sign

1. Autoclave 2. Water inlet valve 3. Water outlet valve 4. Constant flow pump

5. Thermostat 6. Gas outlet valve 7. Thermocouple 8. Metal wire separator

9. Condenser 10. Receiving graduated cylinder

Detailed ways

1. Whether the extraction of raw materials is complete and the theoretical content determination method of furfural

The invention provides a method for determining whether the extraction of raw materials is complete and the theoretical content of furfural obtained, specifically as follows.

The furfural detection method that the present invention relates to is expressed as follows:

For the determination of furfural content in corncob raw materials, refer to GB/T2677.9-94 Determination of polypentose content in papermaking raw materials. The device used is shown in Figure 1. Weigh 0.5g of the sample (the polypentose content in the sample is higher than 12%, weigh 0.5g, and the one with lower than 12% weighs 1g) 0.5g, accurate to 0.1mg, and put it into a 500mL round bottom In the flask, add 10g of sodium chloride, install a condenser and a separatory funnel, add a certain amount of 12% hydrochloric acid in the separatory funnel, adjust the temperature of the electric furnace, make the content of the round bottom flask boil, and control the distillation rate to be every 10min Distill 30 mL of distillate, that is, add 30 mL of 12% hydrochloric acid into the flask from the separatory funnel, and when a total of 300 mL of distillate is distilled, use aniline acetate solution to check whether the furfural is completely distilled. For this purpose, use a test tube to collect 1 mL of distillate from the lower end of the condenser, add 1 to 2 drops of phenolphthalein indicator, and drop 1 mol/L sodium hydroxide solution to neutralize until it is slightly red, then add 1 mL of freshly prepared aniline acetate If the solution turns red after standing for 1 minute, it proves that the furfural has not been distilled completely, and distillation still needs to be continued. If it does not turn red, it means that the distillation is completed. The tetrabromide method was used to titrate the furfural content in the distillate.

Furfural is a pentacyclic aldehyde-based unsaturated compound, which undergoes an addition reaction with bromine. The reaction principle is as follows:

KBrO ₃ +5KBr+6HCl→6KCl+3Br ₂ +3H ₂ O

The excess bromine reacts with KI to form a redox reaction, free iodine, and then titrate with sodium thiosulfate.

2KI+Br ₂ →2KBr+I ₂

2Na ₂ S ₂ O ₃ +I ₂ →2NaI+Na ₂ S ₄ O ₆

According to GB/T 2677.9-94, use a pipette to draw 200mL of distillate into a 500mL conical flask, add 25.0mL of sodium bromate-sodium bromide solution, quickly stopper the bottle, and place it in a dark place for 1 hour. After reaching the specified time, add 10mL of 10% potassium iodide solution, quickly stopper the bottle, shake well, place in the dark for 5min, titrate with 0.1000mol/L sodium thiosulfate standard solution, when the solution turns light yellow, add 0.5 % starch solution 2 ~ 3mL, continue to titrate until the blue color disappears.

Draw another 200mL of 12% hydrochloric acid solution, and conduct a blank test according to the above operation.

Furfural content X (%) is calculated according to the following formula

$\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 0.024</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 500</span>}}{\mathrm{<span\; class="notranslate">\; 200</span>}\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, V ₁ - the volume of 0.1000mol/L sodium thiosulfate standard solution consumed by the blank test, mL;

V ₂ - the volume of 0.1000mol/L sodium thiosulfate standard solution consumed by the sample, mL;

c-sodium thiosulfate standard solution concentration, mol/L

m - absolute dry mass of sample, g;

0.024-furfural quality equivalent to 0.1ml sodium thiosulfate standard solution, g.

2. Example of extracting furfural in corn cob under different experimental conditions

The device of the present invention comprises an autoclave 1, a water inlet valve 2, a water outlet valve 3, a constant flow pump 4, a thermostat 5, a gas outlet valve 6, a thermocouple 7, a condenser 9 and a receiving measuring cylinder 10. In addition, in the autoclave The middle part of 1 is also provided with a wire partition 8, which is used to separate water and the mixture containing the polymerization inhibitor.

The following are examples of extracting furfural according to the method of the present invention and comparative examples without using a polymerization inhibitor.

In the prior art, the method for preparing furfural from corncobs

After drying the crushed corncob at 105°C, weigh 40g, add it into a certain volume of dilute sulfuric acid (concentration of dilute sulfuric acid is 5%), mix well, and transfer the mixture to autoclave 1. When heating to 100-110°C, open the reactor gas outlet valve 6 to exhaust the air for 10-20 minutes, and close the valve. After the hydrolysis temperature reaches 140°C, the gas outlet valve is slightly opened 6, and the timing is started. At this time, a small amount of furfural has been generated in the reaction system, and the aldehyde vapor enters the receiving measuring cylinder 10 after being condensed by the condenser 9 . After the temperature reaches the set value, the aldehyde steaming flow is controlled by adjusting the opening of the gas outlet valve 6, and at the same time, the constant flow pump 4 is turned on to inject deionized water into the autoclave to keep the water injection flow equal to the furfural production flow . Measure the furfural content in the receiving solution every 30 minutes to judge the reaction process of furfural, and stop the reaction when the yield of furfural increases less than 1% within 30 minutes. Close the heating knob and water inlet valve 2, and disassemble the autoclave after cooling down.

Determination of the volume V of the receiving solution and the volume fraction of furfural in the receiving solution Calculate the mass of furfural obtained:

The calculation formula of furfural yield (X) is as follows:

X＝M ₁ /M ₂ ×100% (3)

In the formula, M ₁ is the obtained furfural quality, g; p is the density of pure furfural, 1.158g/mL; V is the volume fraction of furfural, 10 ^-6 ; V is the volume of receiving solution, mL; X is the yield of furfural, %; M ₂ is the theoretical mass of furfural, g. At this moment, it was measured that in the condensate, the yield of furfural was 55%.

Example 1

Dry the crushed corncobs at 105°C, weigh 40g, add a certain amount of dilute sulfuric acid prepared, wherein the concentration of dilute sulfuric acid is 0.5%, and the mass ratio of sulfuric acid solution to corncobs is 8:1 , heated to boiling. Weigh 0.25% of the additive triphenylphosphorus, which accounts for 0.25% of the total amount of corncob, dissolve it in a certain amount of ethanol, add it to the boiling mixture and stir evenly, then transfer it to the autoclave 1, the corncob stays on the wire separator 8, and the sulfuric acid It flows into the lower space and is sealed and heated. When heating to 100-110°C, open the reactor gas outlet valve 6 to exhaust the air for 10-20 minutes, and close the valve. After the hydrolysis temperature reaches 140° C., the gas outlet valve 6 is opened, and timing is started. At this time, a small amount of furfural has been generated in the reaction system, and the aldehyde vapor enters the receiving measuring cylinder 10 after being condensed by the condenser 9 . After the temperature reaches the set value of 180°C, the aldehyde steaming flow rate is controlled by adjusting the opening of the gas outlet valve 6, and at the same time, the advection pump 4 is turned on to inject deionized water into the autoclave to maintain the water injection flow rate and the furfural production flow rate equal. The reaction process of furfural was judged by measuring the furfural content in the receiving solution every 30 minutes. When the furfural yield increased less than 1% within 30 minutes, the reaction was stopped, and the reaction time was 240 minutes. Close the heating knob and water inlet valve 2, and disassemble the autoclave after cooling down.

According to the formula (2) in the existing method, the concentration of furfural in the condensate calculated by (3) is 15.5%. The yield of furfural was 85.8%.

Example 2

With the pulverized corn cob, after drying at 105°C, weigh 40g and add it to a certain volume of prepared dilute sulfuric acid, wherein the concentration of dilute sulfuric acid is 0.5%, and the mass ratio of sulfuric acid solution to corn cob is 8: 1. Heat to boiling. Weigh 0.2% of the total corncob additive diphenylamine, dissolve it in a certain amount of ethanol, add it to the boiling mixture and stir evenly, then transfer it to the autoclave 1, the corncob stays on the wire separator 8, and the sulfuric acid flows into the lower part Space, sealed and heated. When heating to 100-110°C, open the reactor gas outlet valve 6 to exhaust the air for 10-20 minutes, and close the valve. After the hydrolysis temperature reaches 140° C., the gas outlet valve 6 is slightly opened, and timing is started. At this time, a small amount of furfural has been generated in the reaction system, and the aldehyde vapor enters the receiving measuring cylinder 10 after being condensed by the condenser 9 . After the temperature reaches the set value of 180°C, the aldehyde steaming flow rate is controlled by adjusting the opening of the gas outlet valve 6, and at the same time, the advection pump 4 is turned on to inject deionized water into the autoclave to maintain the water injection flow rate and the furfural production flow rate equal. The reaction process of furfural was judged by measuring the furfural content in the receiving solution every 30 minutes. When the furfural yield increased less than 1% within 30 minutes, the reaction was stopped, and the reaction time was 240 minutes. Close the heating knob and water inlet valve 2, and disassemble the autoclave after cooling down.

According to the formula (2) in the existing method, the concentration of furfural in the obtained condensate calculated by (3) is 15%. The yield of furfural was 80.0%.

Example 3

With the pulverized corn cob, after drying at 105°C, weigh 40g and add it to a certain volume of prepared dilute sulfuric acid, wherein the concentration of dilute sulfuric acid is 0.5%, and the mass ratio of sulfuric acid solution to corn cob is 8: 1. Heat to boiling. Weigh 0.2% of the corncob additive thiourea and directly add it to the boiling mixture, stir evenly and then transfer it to the autoclave 1, the corncob stays on the wire separator 8, the sulfuric acid flows into the lower space, seals and heats. When heating to 100-110°C, open the reactor gas outlet valve 6 to exhaust the air for 10-20 minutes, and close the valve. After the hydrolysis temperature reaches 140° C., the gas outlet valve 6 is slightly opened, and timing is started. At this time, a small amount of furfural has been generated in the reaction system, and the aldehyde vapor enters the receiving measuring cylinder 10 after being condensed by the condenser 9 . After the temperature reaches the set value of 180°C, the aldehyde steaming flow rate is controlled by adjusting the opening of the gas outlet valve 6, and at the same time, the advection pump 4 is turned on to inject deionized water into the autoclave to maintain the water injection flow rate and the furfural production flow rate equal. The reaction process of furfural was judged by measuring the furfural content in the receiving solution every 30 minutes. When the furfural yield increased less than 1% within 30 minutes, the reaction was stopped, and the reaction time was 240 minutes. Close the heating knob and water inlet valve 2, and disassemble the autoclave after cooling down.

The concentration of furfural in the obtained condensate calculated according to the formulas (2) and (3) in the existing method is 12.5-15.4%. The yield of furfural is 70.0-85.1%.

In addition, the inventors of the present invention also investigated the experiment of extracting furfural from corn cobs under different experimental conditions. The experimental steps refer to Example 1, and the results are shown in Table 1.

The experiment of extracting furfural in corn cob under different experimental conditions in table 1

The present invention first optimizes the furfural production process, the optimal reaction temperature is 180°C, the sulfuric acid concentration is 0.5%, and the liquid-solid ratio is 8:1. On this basis, through the combination of theoretical analysis and experimental selection, the antioxidant and polymerization inhibitor for the process of preparing furfural by hydrolysis of corncobs were developed. The addition of additives increased the yield of furfural from 50-60% to 80- 85%, while the amount of sulfuric acid and steam consumption has also been controlled.

Claims (5)

1. a method of preparing furfural taking corn cob as raw material, is characterized in that, said method comprising the steps of:

1) after corn cob is pulverized, the sulphuric acid soln that is 0.1～0.5wt% with concentration mixes, and obtains the mixture of corn cob;

2) by the mixture heating in step 1), add stopper, be uniformly mixed, obtain the mixture containing stopper;

Wherein the add-on of stopper accounts for corn cob total mass 0.05～0.5%;

3) in corn cob hydrolytic reaction pot, there is hydrolysis reaction and generate furfural, the middle part of described reactor is provided with wire dividing plate, by step 2) in join on the wire dividing plate in corn cob hydrolytic reaction pot containing the mixture of stopper, hydrolysis temperature is 150～190 DEG C, after the aqueous vapor below wire dividing plate, rises, and contacts with described mixture, there is hydrolysis reaction, the hydrolysate furfural of gaseous state is overflowed, and condensation, obtains furfural phlegma;

Described step 2) in stopper be selected from one or more in 1-naphthols, triphenylphosphine, naphthylamines, thiocarbamide, pentanoic and Resorcinol.

2. the method for preparing furfural taking corn cob as raw material according to claim 1, is characterized in that, in described step 1), the mass ratio of sulphuric acid soln and corn cob is 10:1～5:1.

3. the method for preparing furfural taking corn cob as raw material according to claim 1, is characterized in that, described step 2) in whipping temp be 80～100 DEG C.

4. the method for preparing furfural taking corn cob as raw material according to claim 1, is characterized in that, in described step 3), hydrolysis time is 3.5～5h.

5. the method for preparing furfural taking corn cob as raw material according to claim 1, is characterized in that, in described step 3), adopts temperature programming, for 30min rises to 150～190 DEG C by 40 DEG C.