Classifications

• • 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
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
  • C25B11/036—Bipolar electrodes
• • 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
  • C25B3/01—Products
  • C25B3/05—Heterocyclic compounds
• • 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
  • C25B3/01—Products
  • C25B3/07—Oxygen containing compounds
• • 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
  • C25B3/23—Oxidation
• • 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
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/13—Single electrolytic cells with circulation of an electrolyte
  • C25B9/15—Flow-through cells
• • 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
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/70—Assemblies comprising two or more cells

Definitions

• the invention relates to electrochemical cells, particularly for carrying out electrochemical reactions involving a gaseous reactant or in which gas is supplied for another purpose such as purging or sweeping away a product of reaction, or as a buffering agent or to inhibit unwanted reactions.
• the invention is more specifically, but not exclusively, concerned with an electrochemical cell for electro-organic synthesis, for example the electrochemical oxidation of unsaturated and poly-unsaturated hydrocarbons,
• the electrochemical production of propylene oxide is particularly interesting, and will be discussed in greater detail by way of example.
• propylene is converted to propylene halohydrin by reaction with, halogen generated in situ by the anodic oxidation of the halide salt of an alkali metal in aqueous solution.
• the propylene halohydrin is converted to propylene oxide by reaction with the hydroxyl group at the cathode from which hydrogen is liberated.
• the general' scheme of reaction when sodium bromide is used as the electrolyte is:
• the gap between the electrode discs was made small (0.2 to 0.5 mm), to enable low bromide concentrations to be handled with low ohmic losses.
• a current efficiency of 70% or just above and an energy consumption of 0.23 - 0.30 kwh/ gmol propylene oxide are reported for a small capillary gap cell, but scaling up this cell for industrial production would involve difficulties.
• Fleischmann et al (Symposium on Electrochemical Engineering I, Newcastle 1971, Editor J.D. Thornton) have studied the synthesis of propylene oxide using a bipolar packed bed cell.
• the cell consisted of a packed bed made up of a mixture of conducting and non-conducting particles.
• the conducting particles become bipolar by using dilute electrolyte in the cell and applying sufficient voltage gradient between the contact electrodes so as to overcome the resistance drop in the electrolyte.
• glass coated with graphite as the conducting particles and glass beads as the non-conducting particles, all particles having a diameter of about.0.05 cm, the energy consumption of .such a cell was found to be high, in the range of 2.5 - 3 kwh/gmol propylene oxide.
• a bipolar rod flow cell was used by King et al, CTrans. Inst. Chem. Eng., 53, 1975) for the production of propylene oxide.
• the cell consisted of vertical rows of electrically-conductive rods, separated from one another by a small gap.
• the electrolyte was fed to the top rods, flowed downvmrds over the vertical rows and was collected from the bottom rods for re circulation.
• the gaseous reactant, propylene was passed up the space between the vertical rows, in continuous contact with the electrolyte film.
• the current efficiency of this cell was of the order of 70% and the energy consumption is estimated in the range 0.35 - 0.4 kwh/gmol propylene oxide.
• An object of the invention is to provide an electrochemical cell specifically (but not exclusively) for the production of propylene oxide and which can be designed to meet up. to the following requirements better than the previously proposed cells:
• an electrochemical cell comprises electrodes disposed over a perforated generally horizontal plate, an electrolyte inlet and an electrolyte outlet spaced apart on opposite sides of the electrodes across the perforated plate, and a cell housing which is divided by the perforated plate into an upper chamber and a lower chamber.
• the lower chamber is a gas supply chamber from which, in use, gas passes up through perforations in the plate and bubbles through electrolyte on the plate to collect in the upper chamber.
• the electrolyte inlet and electrolyte outlet of the cell are each advantageously formed by a weir.
• the top of the inlet weir is higher than the top of the outlet weir which in turn is higher than the top of the electrodes.
• the electrolyte is made to flow over the inlet weir and between the electrodes as it passes across the perforated plate, while spent or reacted electrolyte flows out over the outlet weir at a chosen rate.
• These weirs may be formed by upstanding plates integral with or fixed on the perforated plate.
• the electrodes may rest on the perforated plate which, in this instance, will be made of electrically insulating material.
• the perforations in the plate can be arranged in rows each spaced about mid-way between adjacent electrodes. Perforations in the form of generally circular bores having a diameter of about 1 mm have been found satisfactory, but perforations of other form and size can be used.
• the bottom of the lower chamber of the cell housing can serve as a receptacle for a pool of spent or reacted electrolyte which flows via a downcomer tube leading from the aforementioned outlet weir into the pool from which electrolyte is removed via an outlet and may be recycled.
• Fresh electrolyte can be supplied to the aforementioned inlet weir via an incomer tube which extends down through the upper chamber of the cell housing into the electrolyte retained by the inlet weir.
• the upper and lower chambers may be formed by upper and lower sections of a box-like cell housing, the sections being separated by the aforesaid plate which is perforated only in the region under the electrodes.
• a rectangular enclosure for the electrodes may thus be formed by the side walls of the upper housing section fitting against upstanding plates forming the inlet and outlet weirs. These side walls can carry inset terminal electrodes of the electrode array.
• the invention also concerns an electrochemical reactor formed by stacking several cells according to the invention in a column whereby the gas-collection chamber of each cell (except the top one) forms the gas-supply chamber for the cell above.
• the perforated plate of each cell except the lowest one
• gas passes up through. the cells from the bottom of the column to the top, bubbling through the electrolyte in each cell.
• the electrolyte outlets and inlets of the successive cells are connected in cascade so that the electrolyte flows down the column from one cell to the next, the electrolyte flowing across the perforated plate of each cell from the inlet to the outlet and then down to the inlet of the cell below.
• Each cell of such a reactor can have the aforementioned preferred features of a single cell unit, such as the electrolyte inlets and outlets being formed By weirs.
• Another aspect of the invention is a method of carrying out an electrochemical process or reaction using a cell according to the invention, this method comprising passing gas up through the perforations in the plate s o that it bubbles into the electrolyte on the plate.
• the method may be operated continuously, i.e. continuously, supplying gas, electrolyte and electric current, or discontinuously, i.e. with an intermittent supply of gas, electrolyte and/ or current.
• Yet another aspect of the invention is a method of carrying out an electrochemical process or reaction using a reactor formed by a column of cells according to the invention, this method comprising flowing electrolyte down the column from. one cell to the next and across the perforated plate of each cell, and passing gas up through the perforations in the successive plates so that the gas bubbles through the electrolyte on each plate.
• This method may also be operated continuously or discontinuously.
• the gas may be a reactant or a mixture of reac.ants, or may serve another purpose, for instance an inert purge gas such as nitrogen may be used to sweep away a product of reaction, or a buffering agent such as CO 2 or NH 3 may be used to control the pH of the electro lyte, for example to inhibit unwanted reactions.
• an inert purge gas such as nitrogen may be used to sweep away a product of reaction
• a buffering agent such as CO 2 or NH 3 may be used to control the pH of the electro lyte, for example to inhibit unwanted reactions.
• the cell according to the invention could be used in the electro-synthesis of other products such as the formation of butylene oxide from butene.
• Fig. 1 is a cross-section of a cell along the line I-I of Fig. 2;
• Fig. 2 is a cross-section along the line II-II of Fig. 1;
• Fig, 3 is a sectional view of the cell of Figs. 1 and 2 along the line III-III of Fig. 1;
• Fig. 4 is a cut-away view similar to Fig. 1, of part of a column formed of several cells connected in cascade.
• the cell of Figs. 1 to 3 comprises a generally rectangular box-like housing composed of an upper section 1 and a lower section 2.
• a plate 3, fixed between flanges 34 of the upper and lower sections 1,2 divides the housing into an upper chamber 4 and a lower chamber 5.
• the joints between the flanges 34 and the plate 3 are sealed by gaskets 6.
• the upper chamber 4 has an electrolyte inlet section 7, an electrode section 8 and an electrolyte outlet section 9.
• the inlet section 7 comprises an incomer tube 10 which passes through the top 35 of the upper section 1 and extends down to near the plate 3, between an upstanding plate 11 and three side walls 36of the section 1.
• the plate 11, which is integral with the plate 3, extends across the width of the chamber 4 and forms an inlet weir which, in use, holds a pool of electrolyte at a level 12, this electrolyte being delivered via the incomer tube 10.
• the electrolyte outlet section 9 comprises an outlet weir plate 13 which also extends across the width of the chamber 4, but is formed by one wall of an enlarged square end 14 of a downcomer tube 15 which passes through a hole 16 in the plate 3.
• the square end 14 is fitted in a corresponding square recess defined by the side walls 36 of the upper section 1 and an upstanding plate 17 integral with the plate 3.
• the top of the outlet, weir plate 13, is lower than the top of the inlet weir plate 11 and, in use, it maintains electrolyte in the electrode section 8 at a level 18.
• the electrode section 8 In the electrode section 8 are disposed seven electrodes 19 in the form of plates held in spaced parallel relationship in vertical grooves 20 in the plates 11 and 17.
• the electrodes 19 are disposed between two terminal electrodes 21 which are inset in the side walls 36 through which pass current leads 22.
• the plate 11 at one end of the spaced electrodes, and the plates 17 and 13 at the other end define, with the side walls 36 of the section 1, an electrolyte receptacle whose bottom is formed by a perforated central part of the plate 3.
• the perforations in the plate 3, indicated at 23, are in the form of circular holes or bores having a diameter of about 1mm, arranged in eight rows each of seven equally-spaced holes disposed mid-way between the adjacent electrodes 19 or 19 and 21.
• the upper, housing section 1 also comprises, in its top 35, a gas outlet pipe 24 for the removal of gas from the upper chamber 4.
• the downcomer tube 15 extends near to the bottom, below the level of an upstanding wall 30 which forms a trap or weir holding a pool of outgoing electrolyte at a level 31.
• an outlet pipe 32 for removing the electrolyte which has flowed over the weir wall 30.
• the lower housing section 2 also has a gas inlet pipe 33 for delivering gas into the lower chamber 5. Electrolyte in the bottom of the chamber 5 prevents this gas from escaping via the outlet pipe 32 or the downcomer tube 15, so that the gas passes up through the perforations 23 in the plate 3 and bubbles into the electrolyte between the electrodes 19, and 19 and 21 in the electrode section 8.
• the electrolyte outlet pipe 32 is connected to the incomer tube 10 by an electrolyte circulating system, and the gas outlet pipe 24 is connected to the inlet pipe 33 by a gas circulating system.
• the electrolyte is circulated at a chosen rate so that fresh electrolyte from the incomer tube 10 flows over the inlet weir, namely the plate 11, across the electrode section 8, i.e. through the parallel channe defined between the electrodes 19, and 19 and 21, and out over the outlet weir plate 13.
• the gas is also circulated at a chosen rate, which can be adjusted independently of the electrolyte flow rate.
• the product of the electrochemical reaction may be taken off as a gas and removed from the gas stream before recirculating, or may be : taken off dissolved in the electrolyte, in which case it is removed from the electrolyte before recycling.
• the product will partition itself between the electrolyte and the gas phase and may therefore advantageously be removed through the ⁇ as outlet pipe 24 and separated by condensation.
• a cell as shown in Figs. 1 to 3 was used for the production of propylene oxide.
• the electrodes were plates of graphite each 6.3 cm high, 8.3 cm long and
• the electrolyte 5 litres of 0.2M or 0.2M NaBr solution, was flowed at a constant rate, in the range from about 20 to 45 cm 3 /sec. Propylene gas was also circulated, using a supply of fresh propylene at. a constant rate in the range from about 5 to 40 cm 3 /sec. Before supplying a constant current (at from 1 to 2A and a constant voltage from 25 to 40V) , the propylene was circulated for several minutes, to remove air from the cell housing and to saturate the electrolyte solution. Operation was carried out at ambient temperature and atmospheric pressure and the pH of the electrolyte was maintained between about 11 and 12 by adding HBr solution. Gas and liquid samples were checked at 1/2 hourly intervals.
• a foaming agent (“Decon", Trademark) was added with a view to promoting rapid mass transport of the reactants to the electrodes, and to increase the solubility of propylene.
• the results showed a high current efficiency, about 80.%, and a low energy consumption, 0.2 to 0.3 kwh/gmol of propylene oxide when operating at low temperature, low current and low gas flowrate using dilute NaBr.
• an energy consumption of 0.26 kwh/gmol of butylene oxide was achieved at a current efficiency approaching that obtained with propylene oxide.
• FIG. 4 As shown in Fig. 4, several cells similar to that of Figs. 1 to 3 can be stacked in a column with the electrolyte flow system connected in cascade.
• the same parts are designated by the same references as before, some parts of the intermediate cells being designated by double references.
• the upper section 1 of the housing of the top cell and the lower section 2 of the housing of the bottom cell are exactly the same as the upper and lower sections 1 and 2 of Figs. 1 and 2.
• the perforated plate 3 forming the bottom of one cell also forms the top of the gas collection chamber 4 of the cell below and its perforations 23 act as the gas outlet for that chamber;
• the downcomer tube 15 for the discharge of electrolyte from one cell forms the incomer tube 10 of the cell below;
• the gas collection chamber 4 of eac cell (except the top one), forms the gas supply chamber 5 for the cell above; and so forth.
• gas is supplied at the bottom of the column, via the inlet pipe 33, passes up through the successive cells, bubbling up through the electrolyte in each electrode section 8, and is removed from the top of the column via the outlet pipe 24.
• Electrolyte is supplied at the top 35 of the column via the top incomer tube 10 and, as indicated by the arrow, cascades down from one cell to the next, flowing across the electrode section 8 of each cell, and is removed from the bottom of the column via the outlet pipe 32.
• current is supplied to the electrodes of each cell and the operation may be continuous or discontinuous.
• Electrodes can be used, depending on the reaction: ..in particular, dimensionally-stable metal electrodes will be preferred for some reactions. Also, the electrodes need not be bipolar. In some instances, spaced parallel electrodes can be disposed transverse to the general direction of flow of electrolyte across the perforated plate.
• perforations can be provided in this plate and, instead of being disposed between the adjacent electrodes, for certain reactions these perforations could lead into porous or foraminous electrodes disposed on the perforated plate.
• the preferred electrolyte inlet and outlet weirs other means could be provided to enable a flow of the electrolyte generally across the perforated plate, while maintaining a given electrolyte level.

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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)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

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ID=10452254

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Cited By (2)

Citations (1)

• 1978
  • 1978-10-13 JP JP54500004A patent/JPS6217038B2/ja not_active Expired
  • 1978-10-13 WO PCT/GB1978/000025 patent/WO1979000323A1/en unknown
  • 1978-10-13 DE DE7878900203T patent/DE2862342D1/de not_active Expired
  • 1978-10-24 CA CA314,004A patent/CA1103201A/en not_active Expired
• 1979
  • 1979-07-30 EP EP78900203A patent/EP0007951B1/en not_active Expired

Patent Citations (1)

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