CN110016686B

CN110016686B - Method for producing hydrocarbons by electrolysis of mixed carboxylic acids

Info

Publication number: CN110016686B
Application number: CN201910276275.0A
Authority: CN
Inventors: 王庆法; 袁刚; 张香文; 王涖; 邹吉军; 刘国柱; 李国柱
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2019-04-08
Filing date: 2019-04-08
Publication date: 2021-01-15
Anticipated expiration: 2039-04-08
Also published as: CN110016686A

Abstract

The invention discloses a preparation method of hydrocarbon substances, which takes an inert electrode as a working electrode and a counter electrode, takes a solution of a mixture of unit fatty acid and dibasic fatty acid dissolved in an aprotic or aprotic solvent as an electrolyte, and carries out electrolysis under the condition that the working voltage is not lower than 3.0V to obtain the hydrocarbon substances,wherein the unit fatty acid has a structural formula of R¹-COOH, wherein the dicarboxylic acid has the formula HOOC-R²-COOH, wherein the hydrocarbon product comprises the formula R¹‑(R²)_n‑R¹And/or a hydrocarbon product having a double bond, branched or carbocyclic structure, wherein n is a natural number. The invention adopts an electrochemical method to prepare hydrocarbons, the monocarboxylic acid and the dicarboxylic acid are renewable green raw materials, an aqueous solution system can be completely adopted, the obtained hydrocarbon products are naturally separated, and the product purity is high.

Description

Method for producing hydrocarbons by electrolysis of mixed carboxylic acids

Technical Field

The invention belongs to the technical field of electrochemical synthesis, and particularly relates to an electrocatalytic preparation method of hydrocarbons with increased carbon chains.

Background

With the rapid increase of the global population, the continuous increase of the requirements of people on the living quality, the gradual exhaustion of non-renewable fossil and the gradual protrusion of the problem of environmental pollution, the research and development of renewable carbon neutral chemical products have strategic significance for relieving the petroleum crisis, improving the environmental pollution condition and realizing the sustainable development

In organic synthesis, the construction of a carbon skeleton is an extremely important step, which involves the growth of carbon chains. The traditional carbon chain lengthening method is usually accompanied with the use of toxic and harmful reagents, or the carbon chain lengthening capability is weaker, such as only one carbon atom can be increased.

The electrochemical organic synthesis method has the following outstanding advantages: the method has the advantages of simple required instruments, fewer preparation procedures, mild reaction conditions, shorter time for obtaining reaction products, simple post-treatment of products, no need of additional catalyst, high atom economy, green reaction process and the like. The Kolbe reaction can utilize monocarboxylic acid R-COOH to electrolyze to obtain R-R alkane. Palkovits et al electrolyze R at a current of 200mA¹-COOH and HOOC-R²-COOH toTo R¹-R¹And esters. But using monocarboxylic acids R¹-COOH and dicarboxylic acid HOOC-R²Subjecting the mixture of-COOH to electrolysis to obtain a compound of formula R¹-R²-R¹And other hydrocarbons with carbon chain growth that do not meet the Kolbe reaction law are not reported at present.

The invention firstly provides a method for preparing hydrocarbon substances by electrocatalysis by taking mixed carboxylic acid from biomass as a raw material.

Disclosure of Invention

The invention adopts a unit with wide biomass sources and a dicarboxylic acid mixture as raw materials for preparing hydrocarbon substances by electrocatalysis for the first time. The technical scheme of the invention is as follows:

the invention discloses a preparation method of hydrocarbon substances, which takes an inert electrode as a working electrode and a counter electrode, takes a solution of a mixture of unit fatty acid and dibasic fatty acid dissolved in a protic or aprotic solvent as an electrolyte, and carries out electrolysis under the condition that the working voltage is not lower than 3.0V to obtain the hydrocarbon substances, wherein the structural formula of the unit fatty acid is R¹-COOH, wherein the dicarboxylic acid has the formula HOOC-R²-COOH, wherein the hydrocarbon product comprises the formula R¹-(R²)_n-R¹And/or a hydrocarbon product having a double bond, branched or carbocyclic structure, wherein n is a natural number.

Preferably, the molar ratio of the unit fatty acid to the dibasic fatty acid in the unit fatty acid and dibasic fatty acid mixture is any ratio or 0.1:1-1:0.1, and the total concentration of the carboxylic acid solution is generally not lower than 0.01 mol/L.

Preferably, the protic or aprotic compound solvent is one or more of deionized water, methanol, acetone or acetonitrile.

Preferably, a supporting electrolyte is further added to the electrolytic solution, and the supporting electrolyte is an alkaline substance or a neutral substance.

Preferably, the inert electrode is metallic platinum or graphite.

Preferably, the faradaic efficiency of the production process and the selectivity to product hydrocarbons are increased by selecting a platinum electrode as the working electrode.

Preferably, the faradaic efficiency of the production process and the selectivity to product hydrocarbons are increased by increasing the operating voltage.

The present invention may or may not use a reference electrode. A reference electrode is used in a common laboratory, and the reference electrode is not needed in industrial production.

The invention has the beneficial effects that:

1. the method has the advantages of adopting the mixture of the monocarboxylic acid and the dicarboxylic acid as the raw material to prepare the hydrocarbons, using the current as the reaction reagent and the catalyst, not needing to add dangerous and toxic additives, having simple reaction process, generating less waste in the reaction process, having short reaction period, high reaction conversion rate, lower reaction cost compared with the traditional method, not discharging tail gas harmful to the environment, having green reaction process and the like, and having the reaction under normal temperature and normal pressure.

2. The conventional Kolbe reaction is electrolysis of monocarboxylate (RCOOH) in methanol solution and yields the product (R-R) after its decarboxylative dimerization. The invention uses an electrochemical method to produce monocarboxylic acid (R)¹-COOH) with dicarboxylic acid (HOOC-R)²-COOH) as raw material to synthesize hydrocarbon product whose main component is R¹-(R²)_n-R¹And/or hydrocarbons having double bonds, branches, or carbocycles, have not been previously reported.

3. The present invention uses a mixture of monocarboxylic acids and dicarboxylic acids as a feedstock to produce hydrocarbons. The monocarboxylic acid and the dicarboxylic acid are renewable green raw materials, have the advantages of wide source, low price, biodegradability, no toxicity and the like, and can be obtained by fermenting cellulose, hemicellulose, plant starch and the like.

4. The method of the invention can completely adopt an aqueous solution system as the electrolyte to prepare the hydrocarbon substances. The water is used as an environment-friendly solvent, the water is used as the solvent, the requirement of 'green chemistry' is met, the generated hydrocarbon liquid is insoluble in water, and the density of the hydrocarbon liquid is smaller than that of the water, so that the hydrocarbon liquid can be naturally separated from the water solution. Therefore, the collection process of the product after electrolysis is more simplified compared with the traditional preparation method, not only saves a large amount of time, but also reduces the energy consumption of the whole process, and has the advantages of environmental friendliness, low cost and high product purity. Is easy for industrialized production.

Detailed Description

The following specific examples illustrate the processes described in the present invention, but the present invention is not limited to these examples.

The invention adopts electrocatalysis to catalyze and decarboxylate the mixture of the unit and the dicarboxylic acid to obtain the hydrocarbons. The hydrocarbons generated after the reaction are naturally separated from the aqueous solution, so that the collection is easy and the purity is high. The whole electrolysis process can be carried out in an aqueous solution of a carboxylic acid.

Example 1

Medicine preparation: deionized water (18.2 M.OMEGA., Merck Milli-QaddvantageA 10 ultrapure water system), the carboxylic acid used, potassium hydroxide, and potassium sulfate were purchased and used directly without further purification.

An electrolytic cell: the electrolytic cell used in the reaction is 50mm³The screw can seal the diaphragm-free park glass electrolytic cell. The electrolytic system was a three-electrode system in which a Pt sheet (1 cm. times.1 cm) was used as the working electrode, a Pt mesh (60 mesh, 1 cm. times.1 cm) was used as the counter electrode, and a Hg/HgO (1M KOH) electrode was used as the reference electrode.

1.1g of adipic acid, 2.2g of n-octanoic acid and 15.0mm were weighed out separately³2molcm^-3Sequentially adding the KOH aqueous solution into a beaker, mixing, adding ultrapure water to a constant volume of 30mm^-3. The magnetons are put into a beaker, and are stirred for 10min after being started at 600rpm, and then are added into the electrolytic cell. The cell was placed in a water bath at about 30 ℃ and the three electrodes were connected to a workstation in sequence. Firstly, a Cyclic Voltammetry (CV) test is carried out, wherein the CV scanning range is 0V-4V, and the scanning rate is as follows: 5mV/s, number of scan cycles: 5 circles. Then constant potential electrolysis is carried out for 10min at constant voltage under 3V.

And (3) product treatment: after electrolysis is completed, the resulting oil phase product will naturally float above the solution due to its lower density than water. Taking 0.2mm by using a pipette^-3The upper oily product was placed in a chromatographic flask and weighed. Then move and take 0.2mm^-3The internal standard was placed in the above described chromatography vial and was heavy. Then 1.5mm of^-3Isopropanol into the chromatography flask and shakingShaking the mixture on a shaker and shaking the mixture evenly.

And (3) product analysis: the resultant synthesized product obtained in the chromatography was analyzed by gas chromatography and mass spectrometer. The mass spectrum in the gas chromatograph-mass spectrometer is used for determining what substance the product is, and the gas chromatograph-mass spectrometer is used for quantitatively obtaining the distribution percentage of the product. The results are shown in Table 1. As a result of analysis, C was obtained by electrolyzing a mixture of adipic acid and n-octanoic acid₁₈H₃₀，C₂₂H₄₆The obtained hydrocarbon material not only contains alkane, but also contains cyclic hydrocarbon. The mixture of the monocarboxylic acid and the dicarboxylic acid is jointly electrolyzed, catalyzed and decarboxylated to obtain the hydrocarbon which does not conform to the Kolbe reaction rule of the monocarboxylic acid.

Examples 2 to 15

The composition and selectivity of the product obtained after the electrolysis reaction of the mixture of different monocarboxylic acid and dicarboxylic acid are shown in Table 1. In examples 1 to 8 and 10 to 15, working electrodes were used as in example 1, and the working electrode used in example 9 was a graphite electrode. The rest is the same as example 1.

Table 1 examples 1-15

Claims

1. A preparation method of hydrocarbon substances is characterized in that metal platinum is used as a working electrode, an inert electrode is used as a counter electrode, a solution of a mixture of a unit fatty acid and a dibasic fatty acid dissolved in a protic or aprotic solvent is used as an electrolyte, and the hydrocarbon substances are obtained by electrolysis under the condition that the working voltage is not lower than 3.0V, wherein the structural formula of the unit fatty acid is R¹-COOH, wherein the dicarboxylic acid has the formula HOOC-R²-COOH, wherein the hydrocarbon product comprises the formula R¹-(R²)_n-R¹And hydrocarbon products having a double bond, branched or carbocyclic structure, wherein n is a natural number.

2. The method of claim 1, wherein the molar ratio of the mono-fatty acid to the di-fatty acid in the mono-fatty acid and di-fatty acid mixture is 0.1:1 to 1: 0.1.

3. The method according to claim 1, wherein the protic solvent is one or more of deionized water or methanol, and the aprotic solvent is one or more of acetone or acetonitrile.

4. The method of claim 1, further comprising adding a supporting electrolyte to the electrolyte, wherein the supporting electrolyte is selected from the group consisting of alkaline materials and neutral materials.

5. The method of claim 1, wherein the faradaic efficiency of the production process and the selectivity to product hydrocarbons are increased by increasing the operating voltage.