EP0081611B1 - Verfahren zur elektrochemischen Reduktion von Terephthalsäure - Google Patents

Verfahren zur elektrochemischen Reduktion von Terephthalsäure Download PDF

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Publication number
EP0081611B1
EP0081611B1 EP81305832A EP81305832A EP0081611B1 EP 0081611 B1 EP0081611 B1 EP 0081611B1 EP 81305832 A EP81305832 A EP 81305832A EP 81305832 A EP81305832 A EP 81305832A EP 0081611 B1 EP0081611 B1 EP 0081611B1
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EP
European Patent Office
Prior art keywords
terephthalic acid
mercury
cathode
process according
lead
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EP81305832A
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English (en)
French (fr)
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EP0081611A1 (de
Inventor
John Andrew Donohue
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BP Corp North America Inc
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BP Corp North America Inc
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Priority to DE8181305832T priority Critical patent/DE3172636D1/de
Priority to EP81305832A priority patent/EP0081611B1/de
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B3/00—Electrolytic production of organic compounds
    • C25B3/20—Processes
    • C25B3/25—Reduction

Definitions

  • This invention relates to a process for the electrochemical reduction of terephthalic acid to p-hydroxymethylbenzoic acid (pHMBA) and more particularly to improvements in the electrical efficiency of the said reaction and to operation by treatment of the cathode to obtain a mercury overlay as an amalgam on the cathode surface and the addition of a soluble salt of mercury, which regenerates the amalgam overlay, to the electrolysis catholyte solvent.
  • pHMBA p-hydroxymethylbenzoic acid
  • German Offenlegungsschrift 24 28 878 teaches a process for production of p-hydroxymethylbenzoic acid esters by electrochemical reduction of dimethylterephthalate on solid electrode cathodes (lead, zinc, cadmium, graphite and amalgamated metals-lead, copper, etc.) with methanol as solvent.
  • solid electrode cathodes lead, zinc, cadmium, graphite and amalgamated metals-lead, copper, etc.
  • methanol as solvent.
  • the poisoning effect has plagued the application of electrolytic reduction processes to aromatic carboxylic acids. Natarajan, et al., Electrochem.
  • an object of the present invention to develop an electrochemical process for the manufacture of p-hydroxymethylbenzoic acid from terephthalic acid which avoids the above disadvantages. It is an object of the present invention to provide a process for production of p-hydroxymethylbenzoic acid wherein the production of by-product impurities, namely 4-carboxybenzaldehyde, dihydroxymethylbenzene and toluic acid is minimised. It is a further object of this invention to increase the current efficiency of the electrochemical reduction process over that of previously known methods for electrochemical reduction of terephthalic acid to p-hydroxymethylbenzoic acid.
  • a process for the preparation of p-hydroxymethylbenzoic acid which comprises electrochemical reduction of an electrolyte comprising a solution of terephthalic acid having a pH of at least 6.5 in an electrolysis cell wherein a) the cathode comprises a solid phase metal having a surface comprising an amalgam of mercury, said metal of said cathode having a hydrogen overvoltage which is greater than the potential for the reduction of terephthalic acid to p-hydroxymethylbenzoic acid, and b) sufficient mercury is added to the electrolyte as a mercury compound to maintain said process.
  • Addition of a mercury compound is essential since, for example, without the addition of mercury, current efficiency decreases in continuous operation and cathode amalgam surfaces lose amalgamation.
  • current efficiency is defined as ratio of consumption in Faradays (c/mol) used to make product to total Faradays (c/mol) used times 100.
  • amalgam is defined as referring only to an alloy of mercury.
  • the present invention provides a process for the electrochemical preparation of p-hydroxymethylbenzoic acid with improved current efficiency and minimal production of by-product impurities.
  • the process comprises performing the cathodic reduction in an electrolysis cell having a cathode compartment and an anode compartment.
  • the anode and cathode compartments can be separated by a cation exchange diaphragm, although the presence of a separating diaphragm is not an essential element of the invention. If a separating diaphragm is used, the cathode and anode and the separating diaphragm are preferably in parallel planes.
  • several of the elementary electrolysis cells can be combined in the manner of a filter press.
  • any metal with a higher hydrogen overvoltage than the potential for the reduction of terephthalic acid to p-hydroxymethylbenzoic acid is suitable, but metals which will form an alloy with lead and an amalgam with mercury are preferred.
  • material forming the cathode are lead and alloys of lead with cadmium, antimony, tin or bismuth.
  • the cathode is prepared by abraiding in a suitable manner the surface of the solid cathode to remove any metal oxidation and then contacting the abraded metallic surface with mercury to form the amalgam.
  • lead it is sufficient to abrade the surface of the lead solid to remove all forms of lead oxide and any other impurities.
  • Liquid mercury of 99.9% purity is used as a bath for the abraided solid lead cathode.
  • the lead amalgam is formed in the surface of the lead at room temperature upon contacting the mercury bath.
  • the anode of the electrolysis cell usually consists of a solid electrically conducting material which is electrochemically stable in the anolyte and under the operating conditions considered.
  • a solid electrically conducting material which is electrochemically stable in the anolyte and under the operating conditions considered.
  • metals and metalloids such as platinum, platinised titanium, graphite, lead and its alloys, particularly with silver, antimony or tin.
  • any known cation exchange membrane can be used to separate the catholyte from the anolyte, but membranes of the homogeneous type are preferred. These membranes optionally can be reinforced with a screen. For carrying out electrolysis operations over a long period, it is naturally preferred to use membranes which do not swell and which are stable to the action of the various constituents of the catholyte and the anolyte. Examples of such membranes are those of Nafion (trademark of E. I. DuPoint de Nemours & Co.).
  • the catholyte can comprise a neutral solvent, a weakly basic solvent or an aprotic solvent i.e., acetonitrile, to which a source of protons has been added.
  • neutral solvents are water, methanol and other alcohols mixed with water to obtain necessary solvent properties.
  • basic solvents are ammonia, methylamine, ethylenediamine which are diluted suitably to maintain a weak basic condition.
  • the catholyte consists of a solvent, preferably water, and terephthalic acid with a soluble ammonium salt and ammonia. At the start of electrolysis, the catholyte contains sufficient ammonia to form a diammonium salt of terephthalic acid.
  • Concentration of ammonia as ammonium hydroxide is within the range of from about 1 gram of ammonium hydroxide per 2 grams of terephthalic acid to about 1 gram of ammonium hydroxide per gram of terephthalic acid and wherein the pH of the resulting solution is at least 6.5, preferably with a pH within the range of from about 8.5 to about 9.5.
  • concentrations of terephthalic acid and ammonium salt can be either constant when the reaction is carried out continuously, or variable when the reaction is carried out discontinuously.
  • the concentration of terephthalic acid is less than the saturation concentration at the temperature of electrolysis; generally, this concentration is greater than 2% by weight, and preferably greater than 3% when the current density is high, these values relating particularly to the constant concentration when the reaction is carried out continuously and to the final concentration when the reaction is carried out discontinuously.
  • the concentration of ammonium salt is usually between about 0.1% to about 10% by weight, and preferably between about 0.1 % to about 1.0% by weight, these values relating particularly to the total solution of water, terephthalic acid and other solution components when the reaction is carried out continuously and to the final solution when the reaction is carried out discontinuously.
  • the ammonium salt can be any ammonium salt but a salt selected from the group consisting of ammonium chloride, ammonium sulfate and ammonium carbonate is preferred.
  • the catholyte can also contain reaction by-products in small amounts, generally less than 1% by weight.
  • An aqueous acid solution is preferably used as the anolyte, though any other anolyte capable of providing electrical conductivity between the two electrodes can be used.
  • Aqueous solutions of sulphuric or phosphoric acids are usually employed in a concentration generally of 0.1 to 5 mols/liter, and preferably 0.5 to 2 mols/liter.
  • the current density at the cathode is within the range of from about 1 to about 200 amperes per decimeter squared (Aldm2), preferably from about 20 to about 100 A/dm 2 .
  • the flow of the catholyte in a closed circuit is usually achieved by means of a pump.
  • the circuit can in addition contain attached devices such as a heat exchanger or an expansion vessel.
  • the expansion vessel enables terephthalic acid to be added to the catholyte and also some catholyte to be withdrawn in order to extract the p-hydroxymethylbenzoic acid. By-product hydrogen is also removed.
  • the anolyte can also be circulated, preferably in an anolyte circuit similar to that of the catholyte, so that the pressure on either side of the separating diaphragm can be substantially the same.
  • At least one spacer is preferably present in the anode and cathode compartment if a cation exchange membrane is used. These spacers serve to prevent deformations of the cation exchange membrane and prevent contact between this membrane and the electrodes. These spacers also help to render uniform the spacing between the membrane and electrodes which contains the electrolyte.
  • These spacers are generally manufactured from synthetic polymers which are chemically inert and which do not conduct electricity; they can be made in the form of interlaced, intertwined, knotted or welded yarns (e.g., woven fabrics, grids or nets) or they can be in the form of plates possessing holes or grooves. In practice, these spacers are oriented along planes which are parallel to those of the electrodes and the separating diaphragm.
  • Terephthalic acid reduction can be monitored to obtain 100% conversion. Less than 100% conversion is preferable. Less than 96% conversion is more preferable. Undesirable by-products are produced at high conversion levels. Increased amounts of impurities such as dihydroxymethylbenzene and toluic acid can result at terephthalic acid conversion levels of greater than 95-96%. Percent conversion is preferably balanced to obtain maximum conversion to p-hydroxymethylbenzoic acid and minimum conversion to undesirable by-products.
  • Terephthalic acid under ambient conditions being virtually insoluble in water, requires a weak base as a reactant to form a soluble salt in water.
  • suitable weak bases are ammonia, methylamine and ethylenediamine but any similar weak base can be used.
  • a weak base such as ammonia and a salt such as an ammonium salt are added initially to the catholyte, the ammonia in a concentration sufficient to dissolve the terephthalate acid in the solvent, i.e., water, liquid ammonia, etc. but which is preferably water, and an ammonium salt to carry the current.
  • a monoammonium salt of terephthalic acid is added to maintain a basic condition sufficient to cause additions of terephthalic acid to dissolve, with pH above 6.5 and preferably with a pH within the range of about 8.5 to about 9.5, to insure complete solubility of the terephthalic acid.
  • a mercury compound preferably a solvent-soluble mercury salt
  • a mercury compound is added to the catholyte in an amount sufficient to maintain the continuous process, to provide a minimum concentration of mercury metal ion of from about 5 to 1000 parts per million (ppm) expressed as the metal. Concentrations of mercury metal ions greater than 1000 ppm can be used if suitable. Examples of mercury salts soluble in aqueous solutions are mercuric acetate, mercuric bromide, mercuric chlorate, mercuric chloride, mercuric cyanide. Mercuric acetate is preferred because of high solubility and easy availability.
  • the p-hydroxymethylbenzoic acid is isolated from the electrolyte by known means, which optionally can be by the difference in water solubility between that of terephthalic acid and p-hydroxymethylbenzoic acid.
  • the catholyte is acidified and filtered hot, within a temperature range of from about 75°C to about 100°C, to remove terephthalic acid.
  • the p-hydroxymethylbenzoic acid is obtained by cooling the mother liquor, optionally after concentrating under reduced pressure. The cooling is carried out at temperatures below 40°C and preferably below 25°C, the degree of concentration and the cooling temperature naturally vary according to the degree of purity desired for the p-hydroxymethylbenzoic acid.
  • the process of the invention possesses numerous advantages in addition to the advantages of continuous operation; it makes it possible to use catholyte solutions which facilitate workup and recovery of the p-hydroxymethylbenzoic acid; it allows electrolysis cells to be produced which are compact and easy to dismantle; it allows gases to be removed easily which are produced at the anode, especially oxygen, and are capable of causing high resistance between the electrodes due to gas bubbles; it makes it possible to use high current densities and to achieve easily the supply of electricity in series between the various elementary electrolysis cells in an assembly of several cells; it makes it possible to use cells with vertical electrodes.
  • the anolyte and the catholyte can be circulated very rapidly, enabling lower concentrations of terephthalic acid to be employed and, as a result, better degrees of conversion can be obtained in continuous operation.
  • Examples VIII and IX illustrate the invention, Examples I-VII being for purposes of comparison.
  • the chemical yields indicated are yields of p-hydroxymethylbenzoic acid relative to initial quantities of terephthalic acid present. Concentrations of solutions are expressed as the number of grams of solute per liter of solution.
  • Batch reduction of terephthalic acid to p-hydroxymethylbenzoic acid was carried out in an electrolysis cell in the following manner.
  • the cell was mounted in an oil bath which was used to heat the electrolyte to reaction temperature before starting and to cool the electrolyte once the reaction had started.
  • the oil bath was fitted with an electric heater, a source of cooling comprising coils filled with cooling water and a mechanical stirring means.
  • the cell was a 600 ml glass beaker fitted with a stopper of fluorocarbon rubber. Holes through the stopper gave entrance to a thermometer, the anode leads and the cathode leads.
  • the anode support was a glass anolyte tube which was fitted with a fluorocarbon plastic holder to support the anode and a semi-permeable membrane.
  • the anode was a circular platinum screen about 2.5 cm in diameter.
  • the membrane was of sulfonated fluorocaron polymer.
  • the glass tube served as the anolyte chamber.
  • the fluorocarbon plastic holder was inclined at an angle from the horizontal to permit gases rising from the cathode to escape.
  • the cathode was a metal disc about 6 cm in diameter.
  • the cathode was of electrolytically pure lead of 99.9% purity.
  • a magnetic stirring bar was placed on top of the cathode disc in the bottom of the glass beaker which served as the electrolysis cell.
  • the catholyte solution was placed in the cell with the cathode and with the stirring bar in place.
  • the anode was inserted in the anolyte chamber, the chamber was filled with anolyte and inserted in the fluorocarbon stopper.
  • the anolyte chamber was thereupon checked for membrane leakage and placed on the cell.
  • the thermometers were inserted in the fluorocarbon stopper and the cell was assembled.
  • Heat can be applied to the completed cell by means of an oil bath to reach the necessary temperature at which time the heat application is stopped.
  • the cooling system is thereupon activated and as soon as the cell temperature began to drop, the electrolysis reaction is started by applying a source of direct current. Alternatively, the reaction could be started at room temperature and reach operating temperature without direct heating. Alternatively, the cell could be operated without the presence of a semipermeable membrane.
  • Example II The procedure of Example I was repeated using ammonium chloride and ammonium sulfate as the ammonium salts. The results are in Table II.
  • ammonium chloride is a more suitable electrolyte salt with a lead cathode than either ammonium carbonate or ammonium sulfate.
  • the chloride ion is at least twice as effective as the carbonate or sulfate ions.
  • Example II The procedure of Example I was repated using ammonium chloride and ammonium sulfate as the ammonium salts and mercury as the cathode.
  • the liquid mercury was placed in the bottom of the glass beaker which functioned as the cell holder. Electrical contact was made with the liquid mercury by means of a suitable conductor. Results are in Table III.
  • Example II The procedure of Example I was repeated using a lead amalgam cathode.
  • the lead amalgam was prepared by abraiding the surface of electrolytically pure lead to remove any metal oxidation and then contacting the abraided metal surface with mercury to form the amalgam.
  • Mercury of 99.9% purity was used as the bath for the abraided solid lead cathode.
  • the lead amalgam of mercury formed in the surface of the lead at room temperature. Results are in Table IV.
  • Two continuous reductions of terephthalic acid to p-hydroxymethylbenzoic acid were carried out in an electrolysis cell in the following manner to compare the current efficiency obtained with a lead cathode and with a lead amalgam cathode in continuous operation.
  • One cathode was electrically pure lead.
  • the other cathode was electrically pure lead amalgamated with 99.9% pure mercury.
  • the two compartment electrolysis cell comprised an inlet plate of polyvinylchloride (PVC) which was fitted to a second plate of the same size of lead amalgam which constituted the cathode.
  • PVC inserts between the cathode plate and the semipermeable membrane acted as spacers to separate the cathode and membrane sufficiently to permit catholyte flow.
  • the anode was an electrically pure 1/2-inch (1.27 cm) titanium plate coated with platinum to a thickness of 250 micro-inches (6.3x10- 4 cm). Anode and membrane were separated by PVC spacers to permit the anolyte to flow through the cell.
  • An external reservoir for the anolyte served as an oxygen gas separator.
  • An external reservoir for the catholyte served as a hydrogen gas separator.
  • electrolyte was continuously pumped from the reservoir to the electrolysis cell and returned to the reservoir through a heat exchanger. No addition of a mercury salt was made to either catholyte. Details are in Table V.
  • Ammonium chloride (NH 4 CI) was used as the electrolyte with the lead cathode on the basis of data in Example II indicating NH 4 CI gave higher terephthalic acid (TA) conversion to pHMBA and higher current efficiency than did ammonium sulfate (NH 4 ) 2 S0 4 as an electrolyte.
  • TA terephthalic acid
  • Example V The lead amalgam cathode used in Examples V and VI was re-amalgamated in the procedure of Example IV.
  • the procedure of Example V was repeated without any addition of mercury.
  • the electrolyte was analyzed three times by atomic absorption (AA) of mercury using standard analytical techniques, twice before the 5-hour run and once after the 5-hour run.
  • the first analysis was of the freshly prepared catholyte.
  • the second analysis was after pumping the catholyte through the cell so as to contact the lead amalgam cathode.
  • Mercury content of the catholyte was increased by contact with the lead amalgam cathode and, as indicated by the third analysis, decreased with subsequent reduction of terephthalic acid. Details are in Tabla VII
  • Example V In the procedure of Example V two continuous reductions of terephthalic acid were carried out in an electrolysis cell to compare current efficiency obtained with and without the addition of a mercury salt.
  • the cathode was electrically pure lead amalgamated with 99.9% mercury.
  • Periodic additions of mercuric acetate (Hg(Ac) 2 ) were made each hour to the electrolysis cell during the course of the run.
  • a control run was also made wherein mercuric acetate was not added to the electrolysis cell.
  • the results of continuous operation using ammonium sulfate as the required salt are in Table VIII.
  • Example V The procedure of Example V was repeated in multiple runs using mercuric acetate additions in all runs.
  • the same cathode used in Example VIII was used in Example IX without cleaning and/or amalgamation with a mercury bath.
  • the results of continuous operation using ammonium sulfate and one run with ammonium carbonate as the required salt and with addition of mercuric acetate over a period of days are in Table IX.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

Claims (13)

1. Verfahren zur Herstellung von p-Hydroxymethylbenzoesäure, dadurch gekennzeichnet, daß man einen Elektrolyten, der ein Lösung von Terephthalsäure mit einem pH-Wert von wenigstens 6,5 enthält, in einer Elektrolysezelle einer elektrochemischen Reduktion unterzieht und hierbei (a) eine Kathode aus einem Festphasenmetall versendet, die eine Oberfläche aus Quecksilberamalgam hat und bei der das Metall der Kathode eine Wasserstoffüberspannung aufweist, die größer ist als das Reduktionspotential von Terephthalsäure zu p-Hydroxymethylbenzoesäure, und (b) dem Elektrolyten soviel Quecksilber in Form von Quecksilberverbindungen zusetzt, daß das Verfahren aufrechterhalten bleibt.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß es in einer Elektrolysezelle durchgeführt wird, deren Katholyt ein Lösungsmittel, Terephthalsäure, Ammoniak, ein Ammoniumsalz und eine Quecksilberverbindung enthält.
3. Verfahren nach Anspruch 2, dadurch gekennzeichnet, daß das Ammoniumsalz des Katholyten ausgewählt wird aus Ammoniumchlorid, Ammoniumsulfat und Ammoniumcarbonat, die Konzentration dieses Ammoniumsalzes innerhalb des Bereiches von etwa 0,1 bis etwa 10 Gewichtsprozent der gesamten Lösung liegt, und die Konzentration der Terephthalsäure mehr als 2 Gewichtsprozent der gesamten Lösung ausmacht.
4. Verfahren nach Anspruch 2, dadurch gekennzeichnet, daß die Konzentration des Ammoniaks als Ammoniumhydroxid innerhalb des Bereichs von etwa 1 g Ammoniumhydroxid auf 2 g Terephthalsäure bis zu etwa 1 g Ammoniumhydroxid auf 1 g Terephthalsäure liegt, det pH-Wert der erhaltenen Lösung wenigstens 6,5 bis etwa 9,5 beträgt, die Stromdichte innerhalb des Bereichs von etwa 20 bis etwa 100 A/dm2 liegt und die Reduktion von Terephthalsäure zu p-Hydroxymethylbenzoesäure weniger als 100% ausmacht.
5. Verfahren nach einem der Ansprüche 2 bis 4, dadurch gekennzeichnet, daß die Temperatur des Katolyten innerhalb des Bereichs von etwa 0°C bis etwa 100°C liegt.
6. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die Stromdichte innerhalb des Bereichs von etwa 1 bis 200 Aldm2 liegt.
7. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß das Metall der Kathode ausgewählt ist aus Blei und Bleilegierungen, deren Legierungsmetall ausgewählt ist aus Cadmium, Antimon, Zinn und Wismut.
8. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die Quecksilberverbindung ein lösliches Quecksilbersalz ist.
9. Verfahren nach Anspruch 8, dadurch gekennzeichnet, daß das lösliche Quecksilbersalz ausgewählt ist aus Quecksilber(II)-acetat, Quecksilber(II)-bromid, Quecksilber(II)-chlorat, Quecksilber(II)-chlorid und Quecksilber(11)-cyanid.
10. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß das Metall Blei ist, die Oberfläche der Kathode aus Bleiamalgam besteht und das Lösungsmittel Wasser ist.
11. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die p-Hydroxymethylbenzoesäure aus dem Katholyten durch Ansäuerung des Katholyten, Filtration des Katholyten bei einer Temperatur innerhalb des Bereichs von etwa 75°C bis etwa 100°C zur Entfernung der Terephthalsäure und Abkühlung der Mutterlauge auf eine Temperatur von unter 40°C isoliert wird.
12. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß eine Trennmembran aus einem sulfonierten Fluorkohlenstoffpolymeren verwendet wird.
13. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß es ein kontinuierliches Verfahren ist.
EP81305832A 1981-12-10 1981-12-10 Verfahren zur elektrochemischen Reduktion von Terephthalsäure Expired EP0081611B1 (de)

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Application Number Priority Date Filing Date Title
DE8181305832T DE3172636D1 (en) 1981-12-10 1981-12-10 Process for electrochemical reduction of terephthalic acid
EP81305832A EP0081611B1 (de) 1981-12-10 1981-12-10 Verfahren zur elektrochemischen Reduktion von Terephthalsäure

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EP81305832A EP0081611B1 (de) 1981-12-10 1981-12-10 Verfahren zur elektrochemischen Reduktion von Terephthalsäure

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EP0081611A1 EP0081611A1 (de) 1983-06-22
EP0081611B1 true EP0081611B1 (de) 1985-10-09

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GB599140A (en) * 1944-02-17 1948-03-05 Hoffmann La Roche Improvements in or relating to the electrolytic reduction of organic compounds
DE2642496C2 (de) * 1976-09-22 1984-04-19 Basf Ag, 6700 Ludwigshafen Verfahren zur Herstellung von p-Hydroxymethylbenzoesäure

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