CN108004030A - The method that biodiesel is prepared using oily sludge two-step method - Google Patents

Abstract

The invention relates to the technical field of biodiesel preparation, in particular to a method for preparing biodiesel by using oily sludge two-step method, using oily sludge from urban sewage treatment plants as raw material, performing esterification reaction and in-situ transesterification to prepare biodiesel Diesel, mainly including sludge pretreatment, in situ esterification/ester exchange, cooling extraction, washing, filtration evaporation and cooling, alkali transesterification steps to obtain maximum biodiesel yield.

Description

Method for preparing biodiesel by utilizing oily sludge two-step method

technical field

The invention relates to the technical field of biodiesel preparation, in particular to a method for preparing biodiesel by utilizing oily sludge in two steps.

Background technique

Today's world energy crisis and environmental crisis make the development of new clean energy a top priority. Making biodiesel from municipal sludge is one of the solutions. Experts estimate that the energy contained in urban sewage is ten times the energy used to treat urban sewage, and more than 50% of the energy contained in urban sewage is transferred to sludge through sewage treatment, and sludge contains 10%-20% Therefore, it is feasible to produce biodiesel from sludge. On the other hand, biodiesel, as a clean and renewable energy source, uses soybeans, rapeseed, sunflower, palm oil, coconut oil, etc. as raw materials, and the cost accounts for 70%-80% of the total cost of biodiesel products. The high production cost has hindered the supply of biodiesel, lost its competitive advantage compared with traditional fossil energy, and caused international problems such as the food crisis. In the context of scarce arable land resources in China, we need to find more sources of raw materials for biodiesel. Sludge from urban sewage treatment plants is a very good raw material. It is not only rich in resources, but also low in cost. It can greatly reduce the production cost of biodiesel while ensuring the supply of raw materials. At the same time, it also solves the difficulty of sludge treatment. The problem. Among the various sludges produced in urban sewage treatment plants, the use of oily sludge to produce biodiesel will be a more promising application. Compared with primary sludge and secondary sludge, its biodiesel production is higher Higher, more conducive to large-scale put into actual production. However, in the two-step method, the selection of catalysts and the control of base transesterification reaction conditions still need to be studied.

Contents of the invention

The purpose of the present invention is to overcome the defects of the above-mentioned background technology, and to provide a method for preparing biodiesel by utilizing oily sludge two-step method, using oily sludge from urban sewage treatment plants as raw material for esterification and in-situ transesterification Production of biodiesel to obtain maximum biodiesel yield.

Technical scheme of the present invention: utilize the method for preparing biodiesel with oily sludge two-step method, described oily sludge is realized by in-situ esterification and alkali transesterification, and the steps are as follows:

1) Sludge pretreatment: use the activated sludge method to generate oily sludge, and collect oily sludge with a solid content of 11±5%;

2), in-situ esterification/transesterification: using methanol as an acyl acceptor, sulfuric acid or 435 lipase is used as a catalyst, and the esterification reaction is carried out in a Schott bottle in an orbital shaker under the conditions of 45-60 ° C and 4.17 Hz for 5-18 hours, thereby obtaining a mixed solution;

3), cooling: cooling the above mixed solution to room temperature;

4), extraction: using hexane as the extractant to extract the mixed liquid collected after cooling in situ transesterification, and collect the supernatant;

5), cleaning: cleaning the supernatant with a cleaning solution, and collecting the upper hexane phase;

6), Filtration, Evaporation and Cooling: Make the above-mentioned hexane phase pass through a filter device containing water-removing agent ALT-201, collect the filtrate, evaporate the filtrate, weigh the esterification product after cooling, and weigh the fatty acid methyl ester and acylglycerols for quantification;

7) Base transesterification: using methanol as an acyl acceptor and 0.3-0.9% sodium hydroxide or potassium hydroxide as a catalyst to carry out transesterification reaction on the above product, remove excess methanol after the reaction to obtain biodiesel products.

The mass ratio of the oily sludge in the step 1) to the methanol and sulfuric acid solution in the step 2) is: oily sludge:methanol:sulfuric acid=1:15.8:0.037.

Add 1% saturated sodium chloride solution to the mixed solution during the extraction process in step 4).

When the in-situ esterification/transesterification catalyst in the step 2) is a sulfuric acid catalyst, the cleaning solution in the step 5) is selected from at least one of potassium bicarbonate solution and sodium bicarbonate solution, and the potassium bicarbonate solution And the mass concentration of sodium bicarbonate solution is 2-4%.

When the in-situ esterification/transesterification catalyst in step 2) is an enzyme catalyst, distilled water is used as the cleaning solution in step 5).

The cleaning in step 5) is carried out in a separatory funnel, and the number of cleanings is 3-5 times.

In the step 6), the water removing agent ALT-201 is selected from at least one of anhydrous sodium sulfate, anhydrous magnesium sulfate and anhydrous calcium chloride.

The evaporation treatment in the step 6) is carried out in a vacuum rotary evaporator, the temperature of the evaporation treatment is 45-60°C, the pressure is 0.01-0.02Mpa, and the time is 20-25min.

The alkali transesterification in the step 7) is carried out in a closed Schott bottle, which is placed in an orbital shaker with an adjustable temperature and a frequency of 4.17 Hz.

The ratio of alcohol to ester in the step 7) is 6.5-12:1, and the reaction is carried out at 45-60° C. for 60-90 min.

Compared with prior art, the present invention has the advantage:

1. The two-step method of the present invention produces biodiesel, and the sludge pretreatment adopts the activated sludge method to obtain oily sludge, and adopts esterification reaction and in-situ transesterification method, which improves the output of fatty acid methyl ester and relatively reduces The cost of producing biodiesel from sludge improves the reaction efficiency.

2. Saturated sodium chloride solution is added to the extraction process of the mixed liquid after the in-situ esterification/transesterification reaction of the present invention to reduce the solubility of the product in the solution, obtain as much product as possible, and suppress the occurrence of emulsification.

3. The two-step method used in the present invention to produce biodiesel is based on the sludge raw material produced in large quantities by urban sewage treatment plants every year, and then utilizes oily sludge to produce biodiesel with higher fat content and higher calorific value, and simultaneously solves the problem of sewage Pollution problems that may be caused by the sludge produced by the treatment plant.

4. The two-step biodiesel production method catalyzed by acid or enzyme catalyst used in the present invention is not only beneficial to the production of higher quality biodiesel, but also effectively inhibits the occurrence of saponification.

Description of drawings

(a) and (b) in Figure 1 are the comparison of the conversion rate of fatty acid methyl ester between secondary sedimentation sludge and oily sludge when acid catalyst and enzyme catalyst are used, respectively.

Figure 2 shows the alkaline esterification of grease sludge esterification products and its effect on the conversion rate of free fatty acids (FFA) and the yield of fatty acid methyl esters (FAME):

Among the figure: FFA (%): the massfraction of free fatty acid (oleic acid) in fatty acid methyl ester;

FAME (%): the output of fatty acid methyl ester;

^a After 8 hours of in-situ acid-esterification reaction;

^b After in situ enzyme-esterification reaction 16h later.

Detailed ways

The present invention will be further described below through specific embodiments and accompanying drawings. The embodiments of the present invention are for better understanding of the present invention by those skilled in the art, and do not limit the present invention in any way.

The experimental methods used in the following examples are conventional methods unless otherwise specified. The reagents and materials used in the following examples can be obtained from commercial sources unless otherwise specified.

Oily sludge samples were collected from Dongjiao Wastewater Treatment Plant located in Dongli District, Tianjin.

Example 1

1. Sludge pretreatment

Municipal sewage treatment plants use the activated sludge method to produce oily sludge and secondary sedimentation sludge, from which the required oily sludge and secondary sedimentation sludge are collected. The solid content of the oily sludge is 11%.

2. In situ esterification/transesterification

In a closed Schott bottle, with mass concentration of 99% methanol as acyl acceptor, respectively with mass concentration of 98% sulfuric acid catalyst and The 435 lipase catalyst performs in-situ esterification/esterification of oily sludge and secondary sedimentation sludge respectively. The mass ratio of oily sludge to methanol and sulfuric acid solution is: oily sludge:methanol:sulfuric acid=1:15.8 : 0.037, reacted in a Schott bottle in an orbital shaker under the conditions of 45°C and 4.17Hz for 18h, after the sample started to react, the Collect at 14 and 18 hours and at 0, 0.5, 1, 2, 4, 8, 16, 20, 24, 28, 32 and 38 hours.

3. Extraction

After the reaction in the above steps, each sample was cooled to room temperature, and the mixed solution collected after the above-mentioned in situ esterification/ester exchange was extracted 3 times with hexane (30ml) as the extractant, and the supernatant was collected after the extraction, and discarded Substratum.

A 1% saturated solution of sodium chloride was added to the mixture during extraction.

4. Cleaning

For reactions catalyzed by acid catalysts, wash with sodium bicarbonate 2% and distilled water until the water remains colorless in the phenolphthalein indicator;

For reactions catalyzed by enzymes, wash the hexane phase with distilled water only;

Washing was carried out in a separatory funnel, and the number of washings was 3 times.

5. Filtration, evaporation and cooling

Make the above-mentioned hexane phase pass through a filter device containing anhydrous sodium sulfate as a dewatering agent, collect the filtrate and evaporate the filtrate. The evaporation treatment is carried out in a vacuum rotary evaporator. The temperature of the evaporation treatment is 45 ° C and the pressure is 0.01 Mpa, the time is 20min, after cooling, the esterification product is weighed, and fatty acid methyl ester and acylglycerol are quantified;

6. Base transesterification

For the above two mixtures of free fatty acid esters and acylglycerols obtained by using acid and enzyme catalysts respectively, 99% methanol was used as the acyl acceptor and 0.5% sodium hydroxide (NaOH) was used as the catalyst for transesterification. It was carried out in a Schott bottle, and the Schott bottle was placed in an orbital shaker with an adjustable temperature and a frequency of 4.17 Hz. The alcohol-ester ratio was 6.5:1, and the reaction was carried out at 45°C for 90 minutes. After the reaction, in the rotary evaporator, the excess methanol is quickly removed by adopting methods such as accelerating the rotation speed (increasing the evaporation area), increasing the temperature of the water bath (increasing the escape energy of liquid molecules), reducing the pumping pressure (reducing the number of gas molecules), and Glycerol is recovered after phase separation. The methyl ester phase was washed with deionized water (80° C.), and the organic phase was dried over anhydrous sodium sulfate (Na ₂ SO ₄ ) and filtered to obtain fatty acid methyl esters and glycerides. (The above experiments were done with two parallel experiments on oily sludge and secondary sedimentation sludge, and the experimental results are shown in (a) and (b) in Figure 1.

The content of fatty acid methyl ester obtained by acid catalyst and enzyme catalyst was observed in two time periods of 18h and 38h respectively. In both cases, the FAME conversion rate of the oily sludge reached the highest value at 8h and 15h, which were 63.9% and 58.7%, respectively, but on the contrary, the FAME conversion rate of the secondary sedimentation sludge was 11% and 16%, it can be concluded that the acid catalyst has a better catalytic effect on oily sludge, and the enzyme catalyst has a better effect on secondary sedimentation sludge. The catalytic effect of sedimentation sludge will be close to the latter. Comparing the fatty acid methyl ester conversion rate of oily sludge and secondary sedimentation sludge, the conversion rate of the former is 6 and 3.6 times that of the latter under the two catalysts, respectively. This difference may be caused by the difference in lipid composition between the two. The ratio of lipid components is the determining factor affecting the yield of FAME, because biodiesel production requires some saponifiable lipids, especially glycerol and free fatty acids. Therefore, it is a better choice to use oily sludge to produce biodiesel.

Example 2

1. Sludge pretreatment

Municipal sewage treatment plants use the activated sludge method to produce oily sludge, from which oily sludge is collected, and the solid content of the oily sludge is 14%.

2. In situ esterification/transesterification

In a closed Schott bottle, with mass concentration of 99% methanol as acyl acceptor, respectively with mass concentration of 98% sulfuric acid catalyst and 435 lipase catalyst carries out sludge in-situ esterification/ester exchange to oily sludge, and the mass ratio of oily sludge to methanol and sulfuric acid solution is: oily sludge: methanol: sulfuric acid=1:15.8:0.037, using sulfuric acid as Catalyst, react in a Schott bottle in an orbital shaker at 60°C and 4.17Hz for 5h.

3. Extraction

After the reaction, each sample was cooled to room temperature, and the mixed solution collected after the in-situ esterification/ester exchange was extracted 5 times with hexane (30 ml) as the extractant, the supernatant was collected, and the lower layer was discarded. A 1% saturated solution of sodium chloride was added to the mixture during extraction.

4. Cleaning

For reactions catalyzed by acid catalysts, wash with potassium bicarbonate solution (4%) and distilled water until the water in the phenolphthalein indicator remains colorless;

For reactions catalyzed by enzymes, wash the hexane phase with distilled water only;

Washing was carried out in a separatory funnel, and the number of washings was 5 times.

5. Filtration, evaporation and cooling

Make the above-mentioned hexane phase pass through a filter device containing water-removing agent anhydrous magnesium sulfate or anhydrous calcium chloride, collect the filtrate and evaporate the filtrate. The evaporation treatment is carried out in a vacuum rotary evaporator, and the temperature of the evaporation treatment is 60 ° C. , the pressure is 0.02Mpa, the time is 25min, after cooling, the esterification product is weighed, and the fatty acid methyl ester and acylglycerol are quantified;

6. Base transesterification

For the above two mixtures of free fatty acid esters and acylglycerols obtained by using acid and enzyme catalysts respectively, 99% (wt) methanol was used as the acyl acceptor, and the base transesterification was carried out in a closed Schott bottle, and KOH was selected according to the situation. Or NaOH is used as a catalyst, and the reaction is carried out under the following four reaction conditions respectively:

(1), KOH 0.9%, alcohol-ester ratio 6.5:1, 60°C, time 90 minutes;

(2), KOH 0.7%, alcohol-ester ratio 8:1, 50°C, time 60 minutes;

(3), NaOH 0.5%, alcohol-ester ratio 12:1, 60°C, time 60 minutes;

(4), NaOH 0.3%, alcohol-ester ratio 12:1, 60°C, time is 60 minutes;

The above alcohol-to-ester ratio refers to the molar ratio of methanol to the mixture of free fatty acid ester and acylglycerol.

Experiments were performed in closed Schott jars in a temperature-controlled orbital shaker (4.17 Hz). After the reaction, in the rotary evaporator, the excess methanol is quickly removed by adopting methods such as accelerating the rotation speed (increasing the evaporation area), increasing the temperature of the water bath (increasing the escape energy of liquid molecules), reducing the pumping pressure (reducing the number of gas molecules), and Glycerol is recovered after phase separation. The methyl ester phase was washed with deionized water (80° C.), and the organic phase was dried over anhydrous sodium sulfate (Na ₂ SO ₄ ) and filtered to obtain fatty acid methyl esters and glycerides.

The conclusion drawn from this experiment is that higher yields of fatty acid methyl esters can be obtained by applying different base transesterification conditions. As shown in Figure 2, in Experiments 2 and 3 using acid catalysts, the production of fatty acid methyl esters was increased by nearly 2%, which means that a part of triacylglycerol was converted into fatty acid methyl esters. In addition, while changing the reaction conditions of base transesterification, the content of free fatty acid under the catalysis of acid catalyst and enzyme catalyst was significantly reduced, and the yield of methyl ester was significantly increased, thereby improving the yield and quality of biodiesel.

It should be understood that the embodiments and examples discussed here are only for illustration, and those skilled in the art may make improvements or changes, and all these improvements and changes shall belong to the protection scope of the appended claims of the present invention.

Related literature:

[1]Urrutia C,Sangaletti-Gerhard N,Cea M,et al.Two stepesterification-transesterification process of wet greasy sewage sludge forbiodiesel production[J].Bioresource Technology,2016,200:1044.

[2] Olkiewicz M, Fortuny A, Stüber F, et al. Evaluation of Different Sludges from WWTP as a Potential Source for Biodiesel Production [J]. Procedia Engineering, 2012, 42(42): 634-643.

Claims (10)

1. the method for biodiesel is prepared using oily sludge two-step method, it is characterised in that the oily sludge passes through ester in situ Change reaction and alkali ester exchange reaction is realized, step is as follows：

1), sludge pretreatment：Oily sludge is produced using activated sludge process, collection solids content is 11 ± 5% oily sludges；

2), esterification/ester exchange in situ：Using methanol as acyl acceptor, with sulfuric acid or435 lipase are catalyst, Esterification 5-18h is carried out in the Xiao Te bottles in orbital shaker under the conditions of 45-60 DEG C and 4.17Hz, so as to obtain mixed liquor；

3), cool down：Above-mentioned mixed liquor is cooled to room temperature；

4), extract：Above-mentioned mixed liquor after cooling is extracted using hexane as extractant, is collected supernatant；

5), clean：Supernatant is cleaned with cleaning solution, collects upper strata hexane phase；

6), filter, evaporate and cool down：Make filtration apparatus of the above-mentioned hexane mutually by the ALT-201 containing deicer, collect filtrate, it is right Filtrate evaporation process, after the cooling period weighs esterification products, and fatty acid methyl ester and acylglycerol are quantified；

7), alkali ester exchange：Using methanol as acyl acceptor, mass concentration 0.3-0.9% sodium hydroxides or potassium hydroxide are used as and urge Agent, carries out ester exchange reaction to above-mentioned product, removes excessive methanol after reaction, obtain biodiesel product.

2. according to the method described in claim 1, it is characterized in that, first in oily sludge and the step 2) in the step 1) Alcohol, the mass ratio of sulfuric acid solution are：Oily sludge:Methanol:Sulfuric acid=1:15.8:0.037.

3. according to the method described in claim 1, it is characterized in that, added in the step 4) in extraction process into mixed liquor 1% sodium chloride saturated solution.

4. according to the method described in claim 1, it is characterized in that, when the step 2) Central Plains it is bit esterified/ester exchange catalyst For sulfuric acid catalyst when, cleaning solution is selected from least one of potassium bicarbonate solution and sodium bicarbonate solution in the step 5), The mass concentration of the potassium bicarbonate solution and sodium bicarbonate solution is 2-4%.

5. according to the method described in claim 1, it is characterized in that, when the step 2) Central Plains it is bit esterified/ester exchange catalyst For enzyme catalyst when, cleaning solution uses distilled water in the step 5).

6. according to the method described in claim 1, carried out it is characterized in that, being cleaned in the step 5) in separatory funnel, clearly Number is washed as 3-5 times.

7. according to the method described in claim 1, it is characterized in that, deicer ALT-201 is selected from anhydrous sulphur in the step 6) At least one of sour sodium, anhydrous magnesium sulfate and anhydrous calcium chloride.

8. according to the method described in claim 1, it is characterized in that, evaporation process is in vacuum rotary evaporator in the step 6) Middle progress, the temperature of the evaporation process is 45-60 DEG C, pressure 0.01-0.02Mpa, time 20-25min.

9. according to the method described in claim 1, it is characterized in that, alkali ester exchange is in the Xiao Te bottles of closing in the step 7) Carry out, Xiao Te bottle are placed in adjustable temperature and frequency as in the orbital shaker of 4.17Hz.

10. according to the method described in claim 1, it is characterized in that, alcohol ester ratio is 6.5-12 in the step 7):1, in 45- 60-90min is reacted at 60 DEG C.