CN114345337A - Preparation method of lactic acid - Google Patents

Abstract

The invention discloses a preparation method of lactic acid, which comprises the following steps: mixing glycerol, a catalyst, alkali and water, and carrying out catalytic reaction in an inert atmosphere to obtain the lactic acid; the catalyst comprises nitrogen-doped carbon-coated copper and cuprous oxide nanoparticles. The preparation method of the lactic acid disclosed by the invention has the characteristics of simple process, low material cost, high yield and selectivity, and difficult aggregation, good stability and excellent catalytic performance of the nitrogen-doped carbon-coated copper and cuprous oxide nano particles as the catalyst in the reaction of preparing the lactic acid by catalyzing glycerol.

Description

A kind of preparation method of lactic acid

technical field

The invention belongs to the field of chemistry, and in particular relates to a preparation method of lactic acid.

Background technique

Lactic acid is an organic acid with a wide range of uses in the fields of food, medicine, cosmetics, agriculture and chemical industry. At the same time, lactic acid can also be used as a monomer to synthesize polylactic acid and prepare biodegradable bioplastics. Lactic acid has been widely used in the manufacture of disposable food packaging bags, food containers, wrapping paper, shopping bags, toilet paper, agricultural films, etc. , so the market demand for lactic acid has been increasing. At present, the industrial production of lactic acid mainly includes starch fermentation and chemical synthesis. The starch fermentation method has problems such as high cost, low yield of lactic acid and complicated product separation and purification. The chemical synthesis method requires the use of highly toxic hydrocyanic acid, and there is a huge production risk. Therefore, the development of green and efficient methods to prepare lactic acid is still an urgent hot issue in the industry.

Glycerol is a by-product in the production of biodiesel, and 1 ton of glycerol is produced for every 10 tons of biodiesel produced. With the rapid development of the biodiesel industry, a large amount of glycerol by-products has accumulated, and how to convert glycerol into high value-added chemicals has always been a hot issue in the chemical industry. The study found that converting glycerol into lactic acid through catalytic reaction can not only achieve efficient utilization of glycerol, but also obtain lactic acid with high added value.

The traditional methods for preparing lactic acid by catalytic dehydrogenation of glycerol mainly include homogeneous catalysis and heterogeneous catalysis. The homogeneous catalyst is not easy to separate from the reaction system, while the heterogeneous catalyst is easy to separate, so the heterogeneous catalysis method is more conducive to the industrial production of lactic acid. The catalysts used in the heterogeneous catalysis method mainly include precious metal catalysts and Cu-based catalysts. Among them, Cu-based catalysts are cheap and have many applications in the catalytic dehydrogenation of glycerol to lactic acid. The Cu-based catalysts reported in the literature include Cu ₂ O nanoparticles, Cu nanoparticles, Cu/carbon nanofibers, Cu/ZrO ₂ , Cu/hydrotalcite and Cu/MgO, etc. However, the catalytic conversion of glycerol to lactic acid is carried out under high temperature aqueous phase conditions. Under such reaction conditions, Cu nanoparticles have poor stability, and there is a problem that the catalyst is easily aggregated, resulting in deactivation of the catalyst and cannot be recycled. There is currently no method for stably catalyzing glycerol to prepare lactic acid in the industry, therefore, the market is in urgent need of developing a method for stably preparing lactic acid.

SUMMARY OF THE INVENTION

In order to overcome the problems existing in the above-mentioned prior art, one of the purposes of the present invention is to provide an application of nitrogen-doped carbon-coated copper and cuprous oxide nanoparticles; the second purpose of the present invention is to provide a preparation of lactic acid method.

In order to achieve the above object, the technical scheme adopted by the present invention is:

A first aspect of the present invention provides the application of nitrogen-doped carbon-coated copper and cuprous oxide nanoparticles (Cu-Cu ₂ O@NC) in catalyzing glycerol to prepare lactic acid.

Preferably, the preparation method of the nitrogen-doped carbon-coated copper and cuprous oxide nanoparticles comprises the following steps:

1) mixing copper salt, 4,4'-bipyridine, terephthalic acid, alcohol solvent and amine solvent, and carrying out solvothermal reaction to obtain copper organic skeleton precursor;

2) calcining the copper organic framework precursor to obtain the nitrogen-doped carbon-coated copper and cuprous oxide nanoparticles.

Preferably, in the step 1), the copper salt includes at least one of copper nitrate, copper chloride, and copper sulfate; further preferably, in the step 1), the copper salt is copper nitrate.

Preferably, in the step 1), the alcohol solvent includes at least one of methanol, ethanol, and butanol; further preferably, in the step 1), the alcohol solvent is methanol.

Preferably, in the step 1), the amine solvent includes at least one of N,N-dimethylformamide and N,N-dimethylacetamide; further preferably, in the step 1), The amine solvent is N,N-dimethylformamide.

Preferably, in the step 1), the temperature of the solvothermal reaction is 100°C-140°C; further preferably, in the step 1), the temperature of the solvothermal reaction is 115°C-125°C.

Preferably, in the step 1), the time of the solvothermal reaction is 36h-60h; further preferably, in the step 1), the time of the solvothermal reaction is 42h-54h.

Preferably, in the step 1), the mass ratio of copper salt, 4,4'-bipyridine, terephthalic acid, alcohol solvent and amine solvent is 1: (0.3-0.34): (0.6-0.8) :(30-50):(30-50).

Preferably, in the step 1), the copper organic framework precursor is Cu ₂ (BDC) ₂ (BPY).

Preferably, in the step 2), the roasting temperature is 300°C-800°C; further preferably, in the step 2), the roasting temperature is 400°C-700°C.

Preferably, in the step 2), the calcination is carried out in an inert atmosphere; further preferably, in the step 2), the calcination is carried out in a nitrogen atmosphere.

A second aspect of the present invention provides a method for preparing lactic acid, comprising the following steps:

Mix glycerol, catalyst, alkali and water, and carry out catalytic reaction under inert atmosphere to obtain the lactic acid;

The catalyst includes nitrogen-doped carbon-coated copper and cuprous oxide nanoparticles.

Preferably, the molar ratio of the glycerol to the base is 1:(1.01-1.5); further preferably, the molar ratio of the glycerol to the base is 1:(1.03-1.4); even more preferably, the glycerol and the base are The molar ratio of the base is 1:(1.05-1.3).

Preferably, the base includes at least one of alkali metal hydroxide and alkaline earth metal hydroxide; further preferably, the base includes at least one of sodium hydroxide and potassium hydroxide.

Preferably, the mass ratio of the glycerol to water is 1:(1-50); further preferably, the mass ratio of the glycerol to water is 1:(1.5-30); even more preferably, the glycerol and The mass ratio of water is 1:(2-20); more preferably, the mass ratio of the glycerol to water is 1:(2.3-19).

Preferably, the mass ratio of the catalyst to glycerol is (0.02-0.5):1; further preferably, the mass ratio of the catalyst to glycerol is (0.05-0.2):1.

Preferably, the temperature of the catalytic reaction is 160°C to 240°C; further preferably, the temperature of the catalytic reaction is 180°C to 220°C.

Preferably, the time of the catalytic reaction is 20min-120min; further preferably, the time of the catalytic reaction is 30min-100min.

Preferably, the inert atmosphere is a nitrogen atmosphere.

Preferably, the pressure of the catalytic reaction is 0.1 MPa to 2.0 MPa; more preferably, the pressure of the catalytic reaction is 0.5 MPa to 1.5 MPa; still more preferably, the pressure of the catalytic reaction is 0.8 MPa to 1.2 MPa ; More preferably, the pressure of the catalytic reaction is 0.9MPa～1.1MPa.

The beneficial effects of the present invention are:

The lactic acid preparation method disclosed by the invention has the advantages of simple process, low material cost, high yield and high selectivity, and the catalyst nitrogen-doped carbon-coated copper and cuprous oxide nanoparticles are not easy to aggregate and have good stability in the glycerol-catalyzed preparation of lactic acid. and excellent catalytic performance.

Specifically, the present invention has the following advantages:

1. The present invention uses nitrogen-doped carbon-coated copper and cuprous oxide nanoparticles (Cu-Cu ₂ O@NC) as catalysts, and uses N-doped C to coat Cu and Cu ₂ O nanoparticles to avoid reactions During the process, the aggregation of Cu and Cu ₂ O nanoparticles grows, so that the Cu-Cu ₂ O@NC catalyst can be recycled for many times and has better stability. The preparation method of the Cu-Cu ₂ O@NC catalyst is simple, the cost is low, the material source is wide, and the industrial mass production can be carried out.

2. The Cu-Cu ₂ O@NC catalyzed glycerol disclosed in the present invention can realize the efficient preparation of lactic acid, and the method has the advantages of high glycerol conversion rate, high yield of lactic acid, short reaction time and excellent catalyst stability. The method has good industrial application scenarios.

Description of drawings

Figure 1 shows the XRD characterization of the catalyst Cu-Cu ₂ O@NC-400.

Figure 2 shows the XRD characterization of the catalyst Cu-Cu ₂ O@NC-400 after 8 cycles of use.

Detailed ways

The specific implementation of the present invention will be further described below with reference to examples, but the implementation and protection of the present invention are not limited thereto. It should be pointed out that, if there are any processes that are not described in detail below, those skilled in the art can realize or understand them with reference to the prior art. If the reagents or instruments used do not indicate the manufacturer, they are regarded as conventional products that can be purchased in the market.

The preparation of the catalyst will be further described below with reference to examples.

Catalyst Preparation Example

The preparation steps of Cu-Cu ₂ O@NC catalyst are as follows:

1) Synthesis of Cu ₂ (BDC) ₂ (BPY): 0.72 g of copper nitrate, 0.23 g of 4,4'-bipyridine, 0.50 g of terephthalic acid, 30 mL of methanol and 30 mL of DMF were sequentially added to a 100 mL beaker, and then Stir at room temperature for 1 h. The above mixed solution was transferred to a hydrothermal reactor and reacted at 120°C for 48h. Finally, the copper organic framework precursor Cu ₂ (BDC) ₂ (BPY) was obtained by centrifugal filtration, washing and vacuum drying.

2) Preparation of Cu-Cu ₂ O@NC: Cu ₂ (BDC) ₂ (BPY) was calcined at 400 °C, 550 °C, and 700 °C for 2 h under N ₂ atmosphere, respectively, to obtain catalyst Cu-Cu ₂ O@NC-400, Cu-Cu ₂ O@NC-550, Cu-Cu ₂ O@NC-700 (T in Cu-Cu ₂ O@NC-T represents the calcination temperature).

Figure 1 shows the XRD characterization of the catalyst Cu-Cu ₂ O@NC-400. In Fig. 1, the diffraction peaks at 43.2°, 50.4° and 74.1° are assigned to Cu; the diffraction peaks at 36.4° and 61.3° are assigned to Cu ₂ O. The above results indicate that the active components on the prepared catalyst are Cu and Cu ₂ O nanoparticles.

The preparation of lactic acid from glycerol catalyzed by copper nanoparticles will be further described below with reference to examples.

Example 1

The method for preparing lactic acid in this example comprises the following steps:

A 5wt% glycerol aqueous solution was added to a 100mL high temperature and high pressure reactor, then Cu-Cu ₂ O@NC-400 catalyst (the addition amount was 2% of the mass of the glycerol aqueous solution) was added, and NaOH (the molar ratio of glycerol and NaOH was 2%) was added. 1: _1.2 ), finally sealed the reactor, replaced the air in the reactor with N ₃ times, then filled with N to the pressure in the reactor to be 1MPa, heated to 180 ° C, and reacted for 100min. After the reaction, sampling was carried out for gas phase and Liquid phase analysis to determine glycerol conversion and lactate selectivity. The conversion of glycerol was tested to be 90% and the selectivity to lactic acid was 80%.

Example 2

The method for preparing lactic acid in this example comprises the following steps:

The 10wt% glycerol aqueous solution was added to a 100mL high temperature and high pressure reaction kettle, then Cu-Cu ₂ O@NC-550 catalyst was added (the addition amount was 1.2% of the mass of the glycerin aqueous solution), and KOH (the molar ratio of glycerol and KOH was 1.2%) was added. ₁ :1.05), finally sealed the reactor, replaced the air in the reactor with N ₃ times, then filled with N to the pressure in the reactor to be 1MPa, heated to 220 ° C, and reacted for 60min. After the reaction, sampling was carried out for gas phase and Liquid phase analysis to determine glycerol conversion and lactate selectivity. After testing, the conversion of glycerol was 95%, and the selectivity of lactic acid was 75%.

Example 3

The method for preparing lactic acid in this example comprises the following steps:

The 30wt% glycerol aqueous solution was added to the 100mL high temperature and high pressure reactor, then Cu-Cu ₂ O@NC-700 catalyst (the addition amount was 2% of the mass of the glycerol aqueous solution) was added, and NaOH (the molar ratio of glycerol and NaOH was 2%) was added. 1:1.3), finally sealed the reactor, replaced the air in the reactor with N ₃ times, then filled with N to the pressure in the reactor to be 1MPa, heated to ₂₀₀ ° C, and reacted for 80min. After the reaction, sampling was carried out for gas phase and Liquid phase analysis to determine glycerol conversion and lactate selectivity. After testing, the conversion of glycerol was 100%, and the selectivity of lactic acid was 72%.

Example 4

The method for preparing lactic acid in this example comprises the following steps:

A 5wt% glycerol aqueous solution was added to a 100mL high temperature and high pressure reactor, then Cu-Cu ₂ O@NC-700 catalyst (the addition amount was 0.5% of the mass of the glycerol aqueous solution), and then KOH (the molar ratio of glycerol and KOH was 1: _1.2 ), finally sealed the reactor, replaced the air in the reactor with N ₃ times, then filled with N to the pressure in the reactor to be 1MPa, heated to 220 ° C, reacted for 30min, after the reaction finished, sampling for gas phase and Liquid phase analysis to determine glycerol conversion and lactate selectivity. After testing, the conversion of glycerol was 100% and the selectivity of lactic acid was 73%.

Example 5

The method for preparing lactic acid in this example comprises the following steps:

The 12wt% glycerol aqueous solution was added to the 100mL high temperature and high pressure reactor, then Cu-Cu ₂ O@NC-400 catalyst was added (the addition amount was 1% of the mass of the glycerin aqueous solution), and NaOH (the molar ratio of glycerol and NaOH was 1%) was added. ₁ :1.1), finally seal the reactor, replace the air in the reactor with N ₃ times, then fill with N to the pressure in the reactor to be 1MPa, heat to 220 ° C, and react for 60min. After the reaction, sampling is carried out for gas phase and Liquid phase analysis to determine glycerol conversion and lactate selectivity. The conversion of glycerol was tested to be 95% and the selectivity to lactic acid was 84%.

Example 6

The method for preparing lactic acid in this example comprises the following steps:

The 10wt% glycerol aqueous solution was added to a 100mL high temperature and high pressure reactor, then Cu-Cu ₂ O@NC-400 catalyst (the addition amount was 1.5% of the mass of the glycerol aqueous solution), and then NaOH (the molar ratio of glycerol and NaOH was ₁ :1.1), finally sealed the reactor, replaced the air in the reactor with N ₃ times, then filled with N to the pressure in the reactor to be 1MPa, heated to 220 ° C, and reacted for 90min. After the reaction, sampling was carried out for gas phase and Liquid phase analysis to determine glycerol conversion and lactate selectivity.

The recycling steps of the catalyst Cu-Cu ₂ O@NC-400 in this example are as follows:

The Cu-Cu ₂ O@NC-400 catalyst was centrifuged from the reaction mixture, washed with water 4 times, and used directly for the next reaction. The reaction conditions were the same as the method for preparing lactic acid in this example. The catalyst was recycled 8 times, and Table 1 shows the test results of the catalyst Cu-Cu ₂ O@NC-400 recycling performance.

Table 1: Cyclic performance test results of catalyst Cu-Cu ₂ O@NC-400

Cycle times Glycerol conversion (%) Lactic acid selectivity (%) 1 100 86 2 100 86 3 100 86 4 100 85 5 100 85 6 100 85 7 100 84 8 100 84

The examples of the present invention show that the catalyst Cu-Cu ₂ O@NC has efficient catalytic performance for catalyzing glycerol to prepare lactic acid, the conversion rate of glycerol in the reaction is 90%-100%, and the selectivity of lactic acid is 72%-86%. The catalyst Cu-Cu ₂ O@NC prepared by the invention can still maintain a stable catalytic effect after 8 cycles of use, indicating that the catalyst overcomes the problem that copper nanoparticles are easily aggregated after the reaction under high temperature aqueous phase conditions, which leads to the deactivation of the catalyst. Figure 2 shows the XRD characterization of the catalyst Cu-Cu ₂ O@NC-400 after 8 cycles of use. From the comparison between Figure 1 and Figure 2, it can be seen that the XRD patterns of the catalyst Cu-Cu ₂ O@NC-400 before and after the reaction are almost the same, which further indicates that the catalyst has good stability.

Comparative ratio:

Table 2 shows the cycle times of Cu-based catalysts in the published literature.

Table 2 Cycle times of Cu-based catalysts in published literature

It can be seen from Table 2 that the Cu-based catalysts in the published literature are used less frequently and cannot meet the requirements of stably catalyzing glycerol to prepare lactic acid.

The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above examples, and any other changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principle of the present invention , all should be equivalent replacement modes, and all are included in the protection scope of the present invention.

Claims (10)

1. Application of nitrogen-doped carbon-coated copper and cuprous oxide nanoparticles in preparation of lactic acid by catalyzing glycerol.

2. A method for preparing lactic acid is characterized in that: the method comprises the following steps:

mixing glycerol, a catalyst, alkali and water, and carrying out catalytic reaction in an inert atmosphere to obtain the lactic acid;

the catalyst comprises nitrogen-doped carbon-coated copper and cuprous oxide nanoparticles.

3. The method for producing lactic acid according to claim 2, characterized in that: the molar ratio of glycerol to base is 1: (1.01-1.5).

4. The method for producing lactic acid according to claim 3, characterized in that: the base comprises at least one of an alkali metal hydroxide and an alkaline earth metal hydroxide.

5. The method for producing lactic acid according to claim 2, characterized in that: the mass ratio of the catalyst to the glycerol is (0.02-0.5): 1.

6. the method for producing lactic acid according to claim 2, characterized in that: the mass ratio of the glycerol to the water is 1: (1-50).

7. The method for producing lactic acid according to claim 2, characterized in that: the temperature of the catalytic reaction is 160-240 ℃.

8. The method for producing lactic acid according to claim 2, characterized in that: the time of the catalytic reaction is 20 min-120 min.

9. The method for producing lactic acid according to claim 2, characterized in that: the inert atmosphere is a nitrogen atmosphere.

10. The method for producing lactic acid according to claim 9, characterized in that: the pressure intensity of the catalytic reaction is 0.1 MPa-2.0 MPa.

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