CN1303252C - Process of preparing ethyl aldehydic acid by electrolyzing - Google Patents
Process of preparing ethyl aldehydic acid by electrolyzing Download PDFInfo
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- CN1303252C CN1303252C CNB200410016566XA CN200410016566A CN1303252C CN 1303252 C CN1303252 C CN 1303252C CN B200410016566X A CNB200410016566X A CN B200410016566XA CN 200410016566 A CN200410016566 A CN 200410016566A CN 1303252 C CN1303252 C CN 1303252C
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Abstract
The present invention relates to an improved method for preparing glyoxalic acid by electrolyzing glyoxal, which comprises a step of electrolyzing and oxidizing the glyoxal anode to prepare the glyoxalic acid and a step of purifying a first product of the glyoxalic acid, wherein the initial constitute of an electrolyte, the electrode superficial velocity of the electrolyte, the temperature of the electrolyte, the electrode parameter and the purifying method of the first product of the glyoxalic acid belong to the prior art. The present invention is characterized in that the electrolysis is carried out by using a method of pulse constant current or a method of changed current. Compared with the existing method of pulse constant current the method of changed current, the present invention raises the electrolytic current efficiency and the selectivity of the product glyoxalic acid.
Description
Technical Field
The invention relates to a method for preparing glyoxylic acid, in particular to a method for preparing glyoxylic acid by electrolyzing glyoxal.
Background
Glyoxylic acid (CHOCOOH) is an important chemical raw material and can be used for preparing vanillin, allantoin and other fine chemical products. The electrolytic production of glyoxylic acid is classified into anodic oxidation (CN1318653A) and cathodic reduction (us 3,779,875 and CN 1281063A). The prior art has the defects that the current efficiency of electrolysis and the selectivity of a product (glyoxylic acid) are not high, and the prior art has room for improvement.
Disclosure of Invention
The invention aims to provide a method for preparing glyoxylic acid by electrolyzing glyoxal in a pulse current mode so as to improve the current efficiency of an electrolysis process and the chemical selectivity of glyoxylic acid.
The idea of the invention is that:
as the redox reaction is generated in the process of preparing the glyoxylic acid by electrolyzing and oxidizing the mixture of the glyoxal and the hydrochloric acid anode solution: the hydrochloric acid radical chloride ions are firstly oxidized on the anode into chlorine molecules with strong oxidizing property, and the chlorine molecules and the raw material glyoxal aresubjected to redox reaction to oxidize the glyoxal into glyoxylic acid. The anode electrolysis reaction formula is as follows:
the reaction rate of chlorine molecules and glyoxal is slow during electrolysis. When the electrode is continuously electrified, part of chlorine gas can not react with glyoxal in time to generate product glyoxylic acid and then escapes from the anolyte, so that the current efficiency is reduced. And the adoption of the pulse electrolysis method of powering on and powering off can reduce the chlorine gas from escaping from the anolyte and promote the chlorine gas generated by electrolysis to react with glyoxal completely to generate glyoxylic acid as much as possible. Thereby improving the current efficiency of the electrolysis process.
In the later period of electrolysis, the content of glyoxylate in the anolyte is much higher than that of glyoxal, and if the existing constant current electrolysis method of continuous electrification is still adopted, a large amount of chlorine generated by electrolysis can continuously oxidize the target product glyoxylate into oxalic acid, so that the current efficiency of the electrolysis process and the selectivity of glyoxylate are also reduced. The adoption of pulse electrolysis can greatly reduce the content of chlorine in the anolyte and reduce the combination of chlorine and glyoxylic acid, thereby improving the selectivity of glyoxylic acid in the electrolysis process.
According to the above concept, the present invention proposes the following technical solutions:
the method for preparing the glyoxylic acid by electrolysis comprises thefollowing steps: the method is characterized in that the electrolysis is carried out in a pulse constant current or variable current mode, wherein:
(1) the pulse frequency f of the pulse electrolysis is 0.01-100 Hz;
(2) the pulse carrier-to-air ratio is: 0.01 to 100;
(3) the pulse waveform is square wave, and the current when electrified is constant current or variable current;
when the pulse current is constant current, the apparent current density range is as follows: 200 to 5000A/m2；
When the pulse current is variable current, the current variation scheme is as follows:
① the ratio of the concentration of glyoxylic acid to the concentration of glyoxal is 0-6: 1I
② the ratio of the concentration of glyoxylic acid to the concentration of glyoxal is 6: 1-40: 3 α xI
In the formula: the concentration is mass percent concentration, I is apparent current density, and the range is as follows: 200 to 5000A/m2α is 0.3 to 0.9, preferably 0.5 to 0.9.
The preferred technical scheme is as follows: the anode used in the electrolysis is a fixed bed anode, the parameters of which are shown in CN1318653A, the electrolysis is carried out in a pulse variable current mode, and the current variation scheme is as follows:
① the ratio of the concentration of glyoxylic acid to the concentration of glyoxal is 0-6: 1I
② the ratio of the concentration of glyoxylic acid to the concentration of glyoxal is 6: 1-40: 3 α xI
In the formula: the concentration is mass percent concentration, I is apparent current density, and the range is as follows: 200 to 5000A/m2，α＝0.5～0.9。
The initial product of the anode electrolyte containing the glyoxylic acid obtained by the technical scheme does not need to separate the glyoxylic acid, and can obtain the glyoxylic acid product meeting the requirements (the content of the glyoxylic acid is more than or equal to 40.0 percent, and the content of the glyoxal is less than or equal to 3.0 percent) only by the conventional reduced pressure evaporation.
Detailed Description
The method for preparing the glyoxylic acid by electrolysis comprises the following steps:
1. anodic electrolytic oxidation of glyoxal:
adding glyoxal, hydrochloric acid and deionized water into an anode mixing tank at one time to form the anode electrolyte. And adding 20% sulfuric acid water solution into the cathode mixing tank at one time to form the catholyte. The anolyte and the catholyte are respectively sent into a fixed bed anodic electrolytic tank with a cation exchange membrane by a pump for pulse electrolytic reaction. The anode electrolyte containing the glyoxylic acid generated by the reaction is sent back to the anode mixing tank and then sent to the electrolytic tank for electrolytic reaction, and the electrolysis is stopped after the ratio of the concentration of the glyoxylic acid to the concentration of the glyoxal in the anode primary product reaches 40: 3 after the electrolysis is repeated for many times.
Research shows that chlorine gas continuously escapes from the anolyte in the process of preparing glyoxylic acid by anodic oxidation of glyoxal. The chlorine gas is oxidized from chloride ions of hydrochloric acid on the anode, and the chlorine gas generated by electrolysis also serves as an oxidant for electrolytically oxidizing glyoxal to synthesize glyoxylic acid. Therefore,when chlorine gas escapes from the anode liquor, part of the electric energy can not be used for the synthesis of the glyoxylic acid, namely, the current efficiency of the electrolysis process is reduced. In order to reduce the escape of chlorine, the invention adopts a method of intermittently electrifying the cathode and the anode and continuously reducing the current density, namely a pulse variable current electrolysis method, so that the redundant chlorine generated by electrolysis can fully react with the raw material glyoxal when the cathode and the anode are not electrified. Thereby improving the utilization rate of the chlorine gas, namely the current efficiency of the electrolysis process. In the later period of electrolysis, because the concentration of glyoxylic acid in the anolyte is high and the content of glyoxal is very low, a large amount of chlorine generated by electrolysis can further oxidize the product glyoxylic acid into oxalic acid. Resulting in a great decrease in the current efficiency of the electrolysis process and the chemical selectivity of glyoxylic acid. The generation amount of chlorine can be greatly reduced by adopting a pulse variable current electrolysis method, and the chance of continuously oxidizing glyoxylic acid into oxalic acid can be reduced under the condition of ensuring that glyoxal is oxidized into glyoxylic acid as much as possible. The invention adopts a pulse variable current electrolysis mode as follows:
(1) the pulse frequency f of the pulse electrolysis is 0.01-100 Hz;
(2) the pulse duty ratio range is as follows: 0.01 to 100;
(3) the pulse waveform is square wave, the current change scheme of the current when the power is on is as follows:
when the ratio of the concentration of the glyoxylic acid to the concentration of the glyoxal is more than or equal to 0 and less than or equal to 6: 1, the ratio is I,
when the ratio of the concentration of the glyoxylic acid to the concentration of the glyoxal is more than 6: 1 and less than or equal to 40: 3 is α xI,
in the formula: the concentration is mass percent, I is apparent current density, and the range is as follows: 200 to 5000A/m2，α＝0.5～0.9。
2. Purification of glyoxylic acid primary products
The glyoxalic acid product can be obtained by adopting the conventional reduced pressure evaporation without separating the glyoxalic acid from the initial product of the anode electrolyte containing the glyoxylic acid, wherein the content of the glyoxylic acid is more than or equal to 40.0 percent, and the content of the glyoxal is less than or equal to 3.0 percent.
The invention has the following advantages:
because of adopting the pulse electrolysis method, the ratio of the content of the glyoxylic acid to the content of the glyoxal in the anode primary product reaches 40: 3, and the whole electrolysis process has extremely high current efficiency and selectivity of the glyoxylic acid.
The current efficiency and glyoxylate chemoselectivity referred to in the present invention are defined as:
current efficiency is the theoretical amount of electricity consumed to produce a unit mole of glyoxylic acid/the amount of electricity actually consumed to produce a unit mole of glyoxylic acid
Selectivity to glyoxylate is equal to the amount of glyoxylic acid produced (mol)/the amount of glyoxylic acid consumed (mol).
The invention is further illustrated by the following examples, which are intended to provide a better understanding of the invention. The scope of protection of the invention is therefore not limited bythe examples given. In addition, all the percentages in the examples are by mass.
Example 1
Flat lead with a purity of 99.99% was used as the cathode. The fixed bed anode thickness was 25 mm. Apparent area of the electrode is 0.02m2. The CM001 type cation exchange membrane is used as a diaphragm. The concentration of glyoxal and the concentration of hydrochloric acid in the anolyte were 7% and 8% at the start of electrolysis. The catholyte is a 20% aqueous solution of sulfuric acid. The electrolyte is circularly operated by using a magnetic pump as power, and the apparent flow rates of the electrodes of the cathode and the anode are both 0.3 m/s. The temperature of the anolyte is 32 +/-1 ℃. The ratio of the load to the space of the pulse electrolysis is 10, the pulse frequency f is 0.2Hz, and the apparent current density of the electrode is 2000A/m when the current is electrified2. The electrolysis result is: the current efficiency was 76.4% and the glyoxylate selectivity was 87.5%. The content of glyoxylic acid in the anode primary product is 8.5 percent, the content of glyoxal is 0.61 percent, and the ratio of the content of glyoxylic acid to the content of glyoxal is 13.9.
Example 2
The same apparatus and anolyte as in example 1 were used. Wherein the pulse carrier-to-air ratio is 1, and the pulse frequency f is 0.2 Hz. The apparent current density of the electrode at the time of energization was 2000A/m2. The electrolysis result is: the current efficiency was 84.2% and the glyoxylate selectivity was 92.7%. The content of glyoxylic acid in the anode primary product is 8.7 percent, the content of glyoxal is 0.59 percent, and the content of glyoxal in the anode primary product is 8.7 percentThe ratio of the content of aldehyde acid to the content of glyoxal was 14.7.
Example 3
The same apparatus and anolyte as in example 1 were used. Wherein the pulse carrier-to-air ratio is 1, and the pulse frequency f is 5 Hz. The apparent current density of the electrode at the time of energization was 2000A/m2. The electrolysis result is: the current efficiency was 80.7% and the glyoxylate selectivity was 89.3%. The glyoxylic acid content of the anode primary product is 8.6 percent, the glyoxal content is 0.60 percent, and the ratio of the glyoxylic acid content to the glyoxal content is 14.3.
Example 4
The same apparatus and anolyte as in example 1 were used. Wherein the pulse carrier-to-air ratio is 1, and the pulse frequency f is 0.2 Hz. When the concentration ratio of the glyoxylic acid to the glyoxal in the anolyte is 0, 6: 1]The pulse current density is: 2000A/m2(ii) a When the concentration ratio of the glyoxalic acid to the glyoxal in the anolyte is (6: 1, 40: 3)]Time, current density: 1000A/m2. The electrolysis result is: the current efficiency was 87.4% and the glyoxylate selectivity was 94.0%. The content of glyoxylic acid in the anode primary product is 8.9 percent, the content of glyoxal is 0.57 percent, and the ratio of the content of glyoxylic acid to the content of glyoxal is 15.6.
Comparative example
The same apparatus and anolyte as in example 1 were used. Constant current electrolysis is adopted. The apparent current density of electrolysis is 2000A/m2. The electrolysis result is: the current efficiency was 69.8% and the glyoxylate selectivity was 76.5%. The content of glyoxylic acid in the anode primary product is 8.2 percent, the content of glyoxal is 0.61 percent, and the ratio of the content of glyoxylic acid to the content of glyoxal is 13.4.
Claims (2)
1. The electrolytic process of preparing glyoxalic acid includes two steps of preparing glyoxalic acid by anodic electrolytic oxidation of glyoxal and purifying glyoxalic acid product, and features that the electrolysis is performed in constant or variable pulse current mode,
wherein: (1) the pulse frequency f of the pulse electrolysis is 0.01-100 Hz;
(2) the pulse carrier-to-air ratio is: 0.01 to 100;
(3) the pulse waveform is square wave, and the current is constant current or variable current when electrified;
when the pulse current is constant current, the apparent current density range is as follows: 200 to 5000A/m2；
When the pulse current is variable current, the current variation scheme is as follows:
when the ratio of the concentration of the glyoxylic acid to the concentration of the glyoxal is more than or equal to 0 and less than or equal to 6: 1, the ratio is I,
when the ratio of the concentration of the glyoxylic acid to the concentration of the glyoxal is more than 6: 1 and less than or equal to 40: 3 is α xI,
wherein: the concentration is mass percentage concentration, I is apparent current density, and the range is as follows: 200 to 5000A/m2，α＝0.3～0.9。
2. The method according to claim 1, wherein the anode used for electrolysis is a fixed bed anode.
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| Application Number | Priority Date | Filing Date | Title |
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| CNB200410016566XA CN1303252C (en) | 2004-02-26 | 2004-02-26 | Process of preparing ethyl aldehydic acid by electrolyzing |
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| CNB200410016566XA CN1303252C (en) | 2004-02-26 | 2004-02-26 | Process of preparing ethyl aldehydic acid by electrolyzing |
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| CN1560326A CN1560326A (en) | 2005-01-05 |
| CN1303252C true CN1303252C (en) | 2007-03-07 |
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| CN109852987B (en) * | 2018-12-24 | 2021-02-02 | 万华化学集团股份有限公司 | Method for preparing sodium glyoxylate by coupling reverse osmosis technology |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4217336A1 (en) * | 1992-05-26 | 1993-12-02 | Hoechst Ag | Glyoxylic acid prodn. by electrochemical redn. of oxalic acid |
| EP0578946A2 (en) * | 1992-05-26 | 1994-01-19 | Hoechst Aktiengesellschaft | Electrochemical process for reducing oxatic acid to glyoxylic acid |
| CN1318653A (en) * | 2001-04-17 | 2001-10-24 | 华东理工大学 | Ethanedial electrolyzing and oxidizing process of synthesizing glyoxalic acid |
| CN1322860A (en) * | 2001-04-17 | 2001-11-21 | 华东理工大学 | Oxalic acid electroreduction process of preparing glyoxalic acid |
| CN1322859A (en) * | 2001-04-17 | 2001-11-21 | 华东理工大学 | Paired electrolysis procss of preparing glyoxalic acid |
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- 2004-02-26 CN CNB200410016566XA patent/CN1303252C/en not_active Expired - Fee Related
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4217336A1 (en) * | 1992-05-26 | 1993-12-02 | Hoechst Ag | Glyoxylic acid prodn. by electrochemical redn. of oxalic acid |
| EP0578946A2 (en) * | 1992-05-26 | 1994-01-19 | Hoechst Aktiengesellschaft | Electrochemical process for reducing oxatic acid to glyoxylic acid |
| CN1318653A (en) * | 2001-04-17 | 2001-10-24 | 华东理工大学 | Ethanedial electrolyzing and oxidizing process of synthesizing glyoxalic acid |
| CN1322860A (en) * | 2001-04-17 | 2001-11-21 | 华东理工大学 | Oxalic acid electroreduction process of preparing glyoxalic acid |
| CN1322859A (en) * | 2001-04-17 | 2001-11-21 | 华东理工大学 | Paired electrolysis procss of preparing glyoxalic acid |
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