CH625885A5 - Method and appliance for detecting the presence of an electroactive volatile material - Google Patents

Description

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2nd

PATENT CLAIMS 14, Device according to claim 13, characterized in

1. A method for detecting the presence of a net that the electrodes (57, 58) are platinum wires.

a liquid-in-solution electroactive volatile device according to one of claims 10 to 14,

material, characterized in that the liquid is characterized in that the device for contacting

speed with an inert gas stream and then the inert gas stream with 5 bringing gas and electrolyte, an electrode chamber which includes an electrolyte which detects the presence of an electroactive (65) and which contains the electrode device (66) volatile substance, and with one of the electrochemical detergent Device for contacting tectors. connected gas outlet from gas and liquid (55)

2. The method according to claim 1, characterized in that is.

that the output value of the electrochemical detector with the 16. device according to one of claims 9 to 15,

Amount of the electroactive component which is characterized in the electrolytes in that the device for contacting

is introduced in a linear relationship. bring gas and liquid a device for

3. The method according to claim 1, characterized in that the inert gas is bubbled through the liquid. that in the electrochemical detector there is a liquid electrolyte 17. Device according to one of claims 9 to 15, which flows over an electrode which is characterized by 15 in that the device for contacting the electrolyte with a second electrode in a conductive connection. a device for guiding the gas and liquid, the two electrodes with an electric one of the inert gas looking over a thin film of the liquid and a current detection device.

are electrically connected in a circle. 18. Device according to one of claims 9 to 15,

4. The method according to claim 3, characterized in that the device for contacting that the flow velocities of the inert gas and the introduction of gas and liquid comprises a device, electrolytes are constant and that the current detection device in which the liquid during the Contact with the inert gas is selected so that it is forced to display a quantitative indication of the flow in a helical path. Changes in the current flowing in the electrical circuit provides.

5. The method according to any one of claims 1 to 4, characterized 25

characterized in that both the liquid and the inert gas through a device for contacting gas is one of the many difficult problems with which the ana and liquid flow. lytiker is faced with the analysis of substances that are not

6. The method according to claim 5, characterized in that it contains only the constituents to be determined, but also that the liquid in a helical path through the one or more constituents which can interfere with the analysis of the device for contacting gas and liquid. There is a stream in which this occurs. the analysis of a reaction mixture where the detection or

7. The method according to any one of claims 1 to 6, characterized by the determination of a specific component by the fact that the liquid is a medium in which there are other substances, the starting materials, reaction pro-chemical reaction. 35 products or even accidental impurities,

8. Device for carrying out the method according to the sword.

Proof 1, characterized by a device for contacting it. It is known from US Pat. No. 3,150,516, a volatile material dissolved in a contacting liquid of gas and liquid with the aid of an inerting of the liquid with an inert gas, an electrochemical liquid Drive out carrier gas and the expelled gases afterwards

Detector and a device for contacting 40 using a chromatography column and a thermal conductivity

Gas and electrolyte for contacting the inert gas, ability cell to be analyzed. According to the invention, a much

after it uses the device for contacting gas-rich and robust detector, which has passed through for the and liquid, with the electrolyte of the electro-use in a technical plant.

chemical detector. The invention relates to a method and a pre

9. The device according to claim 8, characterized by a 45 direction for detecting the presence of a in a Flüs gas flow device for generating an inert gas flow. electroactive volatile matter in solution

10. The device according to claim 8 or 9, characterized thereby. The method according to the invention is in claim 1 and is characterized in that the electrochemical detector defines an electrode. The device according to the invention is defined in claim 8, device (66) with a first electrode (57) and a two. With the expression "electroactive material" is a mate -ten electrode (58), means a device for generating an electr so rja] that, when introduced into the electrolyte of an electrolyte stream over the surface of the first electrode and to the trochemical system with the electrolyte, thus forms a connection between the electrolyte The first and second kung occurs as a change in the electrical state of the electrode and an electrical circuit that is brought about with the two elec systems. Can be connected in series using suitable chemical electrodes and comprises a voltage source (61) and components in a current detection device (62) which is connected to the electrochemical system. 55 closed circuit, it is possible to change the electrical

11. The device as claimed in claim 10, characterized in that the system is in a state and thus the presence of the net proves that the device for generating an inert gas flow of electroactive material. An electrical display component which is electrically connected to a suitable and the device for generating an electrolyte current is designed such that it comprises a constant flow rate electrochemical system, e.g. deliver an electrochemical. 60 see detector which is for use in the context of the inventions

12. The device according to claim 11, characterized in that it is suitable. For use in the context of the invention that the current detection device (62) is designed in such a way that suitable electrochemical detectors are included, they have a quantitative indication of the current change in two types, namely that of an electrical circuit delivers. Develops and demonstrates potential when it

13. The device according to one of claims 9 to 12, 65 ven material comes into contact, and the one in which the electrode device (66) has the effective electrical resistance of the system in the case of legs (56) around which the Both electrical contact changes with the electroactive material, the Wi-electrodes (57, 58) being wound helically. change in the state by changing a current

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is shown, which flows in a circuit containing a voltage source, which is connected to the system.

In general, the measured value of a detector of the latter type is linearly related to the amount of electroactive material introduced into the electrolyte of the electrochemical detector, so that detectors of this type are more suitable for quantitative detection of electroactive materials.

As the inert gas which is brought into contact with the solution of a volatile electroactive material, a gas is suitable which is inert with respect to the components of the solution and the electrolytes of the electrochemical detector (hereinafter referred to as detection device), i.e. a gas that does not interfere with the analysis. Nitrogen is suitable in most cases, but air is often equally suitable. The inert gas stream can be contacted with the solution of the volatile electroactive material and with the electrolyte in any suitable manner, for example by bubbling the gas through them or by contacting them with a thin film composed of them.

A preferred embodiment of the electrochemical detection device has a liquid electrolyte which flows over an electrode which is conductively connected through the electrolyte to a second electrode, the two electrodes being connected in series with an electrical voltage source and a current detection device. The presence of electroactive material in the inert gas stream is detected by a change in the current flowing in the electrolyte and the electroactive material.

The change in the current flow can occur simply because the volatile substance dissolves in the electrolyte or because it reacts with the electrolyte in such a way that components are created or destroyed that can be discharged at one of the two electrodes. Depending on the nature of the volatile electroactive component, the electrolyte is chosen so that it produces the desired effect.

It has been shown that the electrochemical detection device is sensitive to the flow rate of the inert gas and that, where it is a detection device in which a liquid electrolyte flows over the surface of the electrodes, it is also sensitive to the flow rate of the electrolyte. Therefore, where the method is used to determine the concentration of the electroactive volatile in the liquid, the flow rates of the inert gas and the electrolyte must be kept substantially constant. A change in one of the two flow velocities of one of these substances produces a change in the output size of the detection device.

Where the method according to the invention uses a detection device with a flowing electrolyte, the electrodes are preferably made of noble metal, for example platinum. The electrolyte expediently flows from a storage container in such a way that it forms a thin layer which constantly moves between and over the surfaces of the two electrodes. Where the method is used to measure the concentration of the electroactive substance in the liquid, there is preferably a constant electrolyte level in the storage container or a pump which replaces the storage container provides a constant electrolyte flow.

Any suitable voltage source can be used in the outer circuit of the current detection circuit.

if desired, the voltage can be changed, for example to reduce the disruptive influence of other components or contaminants in the system. Conventional current measuring devices can be used, for example a potentiometer for measuring the voltage drop across a resistor arranged in the circuit. The method according to the invention can be used both for batch-wise and for continuous analysis and forms a valuable test method that can be used to improve or control production. It is particularly suitable for the continuous analysis of continuous production processes, since the method according to the invention is able to provide a quick indication of the condition of the checked liquid. If desired, the method can be adapted to provide automatic control of any process, such as maintaining a desired level in the liquid.

The method according to the invention is particularly valuable for monitoring and controlling the progress of diazo processes of a continuous or discontinuous nature. In the diazotization process commonly used for the production of azo dyes i5 and pigments, a primary aromatic amine is reacted with nitrous acid to form a diazo compound. In order to ensure complete diazotization of the amine, it is important that sufficient nitrous acid is added, but at the same time, because of the possibility of side reactions, it is generally undesirable to have a significant excess. The presence of nitrous acid in an aqueous solution gives rise to volatiles in the form of various oxides of nitrogen. The method according to the invention permits the detection of these volatile substances and is able to measure their concentrations.

The device according to the invention is preferably used in connection with a gas flow device for generating an inert gas flow through the devices for bringing gas and liquid as well as gas and electrolyte into contact.

According to a preferred embodiment of the device according to the invention, the electrochemical detection device comprises an electrode device with a first and a second electrode, a device which causes an electrolyte to flow over the surface of the first electrode, and a connection between the first and second electrode and an outer circuit, which can be connected in series with the two electrodes and contains a voltage source and a current detection device. Alternative embodiments for the electrochemical detection device which make use of non-flowing electrolytes and are suitable for use in the context of the invention are described in Journal of Electroanalytical Chemistry, Volume 75 (1977), pages 45 255-277.

The device for contacting gas and liquid preferably comprises a device which causes

that the inert gas passes through the liquid in the form of bubbles or flows over the surface of a thin layer of the liquid.

The device for contacting gas and electrolyte expediently comprises an electrode chamber which contains the electrode device and a line which connects the device for contacting gas and liquid 55 to the electrode chamber and which is arranged such that the inert gas directs over the surface of the first electrode after it has been brought into contact with the liquid.

The electrode device expediently has the fio shape of a coil former on which the two electrodes, preferably in the form of wires, are wound helically, so that the electrolyte can coat both electrodes at the same time. The electrodes are preferably made of noble metal, for example platinum. 65 The electrolyte feed device preferably supplies a constant electrolyte flow via the electrode device and expediently comprises a storage container for the electrolyte, which sits above the electrode chamber, so that the

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Electrolyte can flow under the influence of gravity over the coil body on which the electrodes are wound.

Where the device is to be used to provide a quantitative indication of the electroactive volatile substance, the storage container preferably has a refill device for achieving a constant electrolyte level. As a further possibility, the electrolyte can be supplied with the aid of a pump, preferably a peristaltic or similar pump, which is set up in such a way that it supplies an essentially constant electrolyte current.

The current detection device is preferably selected as one that provides a quantitative indication of the change in the current flow in the outer circuit, for example as a potentiometer (compensation measuring device) placed over a resistor arranged in the circuit.

The gas flow device can comprise an impeller, which serves to press and / or suck the gas through the device or comprise a source of the inert gas which is pressurized internally, both devices preferably being set up in such a way that they deliver electricity at a constant flow rate.

In the following preferred embodiments of the invention are described in connection with the attached drawing. On this shows

1 is a schematic representation of a device according to the invention,

2 shows in cross section an alternative embodiment of the device for contacting gas and liquid to that shown in FIG. 1,

3 shows a section along line X-X in FIG. 2,

4 shows a section along line Y-Y in FIG. 2,

Flg. 5 in cross section a variant of the device shown in FIG. 2 for creating a gas / liquid contact and

Flg. 6 in cross section a further variant of the device for contacting gas and liquid shown in FIG. 2.

In the device shown in FIG. 1, a vessel 51 contains a first reagent stirred with a magnetic stirrer 52, while a burette 53 contains a solution of a second reagent which reacts with the first reagent and a free electroactive volatile substance after the equivalence point has been exceeded in the Can generate excess. A gas / liquid contacting device includes a gas inlet 54 and a jacket 64, the gas inlet 54 being connected to an pressurized inert gas source (not shown) such that gas is introduced into the solution of the first reagent within the Mantels 64 is possible. A line 55 forms a passage for the gas from the jacket 64 to an electrode chamber 65 containing an electrode device 66. The electrode device 66 consists of a coil former 56 made of non-conductive material, which carries two helically wound platinum electrodes 57 and 58. The electrodes are electrically connected in series at terminals with a voltage source 61 and a current measuring device 62. A liquid electrolyte from a storage container (not shown) can reach the electrodes 57 and 58 through an inlet 63.

When using the device, the solution in the vessel 51, for example an acidified solution of an aromatic primary amine, is stirred while reagent solution, for example sodium nitrite solution, is added from the burette 53. The inert gas is passed through the solution in the vessel 51 at a constant flow rate in gas bubbles with the aid of the gas inlet 54, leaves the jacket 64 through the line 55 and thus comes into contact with the liquid electrolyte, for example a 0.5% aqueous solution Potassium iodide solution which flows over the electrodes at a low constant rate, for example of 0.5 ml per minute. A voltage of 600 mV is applied between the electrodes. When sufficient solution has been added to the solution in the vessel 51 to form free volatile substance, the latter is taken along in the stream 5 of the inert gas and then brought into contact with the electrolyte film flowing over the electrodes. The resulting change in the current flowing in the electrical circuit is then recorded on the current measuring device 62, which gives a quick indication of the end point of the di-iaootation reaction.

When monitoring a continuous production process, the solution in the vessel 51 is replaced by a flowing stream of a reaction mixture, the changes in the composition of which can be observed on the current measuring device 15. Under these circumstances, however, it is more expedient to provide another embodiment of a device for creating a gas / liquid contact. This embodiment may include a vessel through which the liquid and gas are substantially countercurrently directed so as to cause electroactive volatiles to transition from the liquid to the gas. In order to achieve intimate contact, the liquid preferably flows through the device for creating this contact as a thin film. The inert gas outlet of the device for making this contact is preferably connected directly to the electrode chamber, where the presence of any electroactive volatile substance in the inert gas stream is to be detected.

Preferred embodiments of such devices for creating a gas / liquid contact are shown in FIGS. 2-6 shown.

As can best be seen in FIG. 2, a vertical cylindrical vessel 1 is closed at its upper end with a cylindrical block 2 which is axially pierced at 3 and provided with an internal thread at 4. A pipe 5, which is connected to an inert gas source (not shown) which is pressurized and is held by a clamping sleeve 6, forms an inlet for an inert gas, and a radial bore 7 in the block 2 forms an outlet for the inert gas. 40 The lower part of the block 2 has a reduced outer diameter and offers a surface 8 which, together with the inner surface of the vessel 1, forms a channel into which liquid can be fed via an inlet opening 10. The inlet opening 10 comprises a vertical slot in the vessel 1, which is connected to a partially threaded bore 11 in a block 12 attached to the side of the vessel 1. The axis of the bore 11 runs parallel to a tangent to the outer circumference 8 of the block 2, as can be seen better in FIG. 3. The lower part of the block 2 runs conically, the surface 13 being at an angle to the axial gas inlet pipe 5.

The vessel 1 is supported at its lower end by a frame 14 which is formed from two flat plates 15 and 16 which are slotted and put together so that they support one another in a vertical plane and form a cross in a horizontal plane , as can be seen better in FIG. 4. The frame 14 sits in a container 17 which is provided with an overflow pipe 18.

When using the device, a volatile 60 electroactive substance is fed in a liquid flow through the inlet opening 10 and passes through the channel 9 substantially in the circumferential direction with respect to the inner surface of the upper end of the vessel 1 and the outer surface 8 of the block 2. In this way, the Liquid flow communicated a substantially circular movement and this, together with the gravity acting on the liquid, results in a substantially continuous film of liquid which is in a substantially helical path around the inner surface of the

5

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Vessel 1 and this flows down. This film of moving liquid runs into and out of the container 17 via the overflow pipe 18. Swirling of the liquid in the container 17 is slowed down by the frame 14. The lower part of the vessel 1 is closed off by the liquid in the container 17, i.e. poetry.

An inert gas is fed into the vessel 1 through the axial tube 5, and the resulting axial inert gas jet strikes the surface of the liquid in the container and thereafter runs essentially upward in countercurrent to the downward flowing liquid in the vessel 1. The inert gas then passes through outlet 7.

In the event that the inert gas shows a tendency to carry liquid droplets or splashes to the gas outlet 7, the main part of the entrained liquid is deposited on the surface 13 of the block 2, from where it flows back into and from the liquid flow flowing down the vessel 1 is collected and carried away.

The inlet opening 10 for the liquid is adjacent to the point where the block 2 closes the vessel 1. In this way, liquid fed through the inlet opening 10 is prevented from flowing upward and all surfaces are continuously washed by the liquid, so that solids which would encrust the surfaces do not separate.

It is easy to see that the figures in Figs. 2-4 shown device for creating a gas / liquid contact can be modified in many ways. For example, the inlet opening 10 shown as a slot in the side wall of the vessel 1 can also be made circular and simple by drilling a hole in the vessel 1. Furthermore, the surface 13 of the block 2 need not be flat and smooth, as shown, but may be preferably concave, curved and provided with grooves or other depressions in order to improve its ability to collect any liquid carried in the inert gas. Other frame shapes can also be used, or the frame can be omitted and instead, other holding devices for the vessel 1, for example a clamping device, can be used.

Suitable flow rates for the liquid and the inert gas can be determined by a simple experiment.

It has been shown that with a diameter of the in FIGS. 2-4 shown vessel 1 of the device for creating a gas / liquid contact of approximately 6 cm, the liquid flow can expediently be approximately 25 1 / min with an inert gas flow over the liquid of approximately 2 1 / min. These numbers are only intended as a guide, and a wide range for the flow rates of both the liquid and the inert gas is possible.

In the device for creating a gas / liquid contact shown in FIG. 5, which is designed in particular for cases in which the inert gas is air, the same parts are provided with the same reference numerals with the parts shown in FIG. 1. The inner surface of the vessel 1 has a screw thread with a rectangular cross-section, and the socket 2 has an outer diameter such that its outer surface 8, together with the threaded inside of the vessel 1, forms a channel 9 with a rectangular cross-section. The inlet opening 10 is a radial bore through the vessel 1 into the channel 9. The liquid supplied through the inlet opening 10 is forced into a path along the channel 9 and in this way assumes a helical movement downwards on the inner wall of the vessel 1 , the thread serving as a guide and ensuring the continuity of the liquid film. The lower end 19 of the vessel 1 is open and the liquid falls from there into a suitable collecting vessel.

Instead of the gas inlet pipe 5 shown in FIG. 2, the device for creating a gas / liquid contact shown in FIG. 5 uses an impeller 20, with which air is drawn through the open end 19 of the vessel 1 and out through the gas outlet 7, whereby the impeller gives the air flow in the vessel 1 a swirling motion and causes it to run essentially in countercurrent to the liquid descending on the inner wall of the vessel 1.

6 shows a device for creating a gas / liquid contact, also in particular for use in air as an inert gas, in which the liquid containing the electroactive volatile substance is caused on the outer surface of a cylindrical part which is coaxial with the vessel 1 attached, flows down. With the in Figs. 2 and 3 shown parts identical parts are again provided with the same reference numerals. In this embodiment, a cylindrical part 21, which does not need to be solid, as shown, but could also be a hollow rod or a tube, carries a thread 22 with a rectangular cross-section 20 on the outside and is coaxial with the vessel 1 appropriate. A sleeve 23 is fitted onto the upper end of the part 21 in such a way that it covers the upper end of the thread 22 and creates a channel 9 with a rectangular cross section, in which liquid can be seen through an axial bore 24 and a radial bore 25 in the cylinder 25 Part 21 is fed. The liquid fed into the channel 9 in this way is brought to flow along the thread 22 and flows until it reaches the lower end of the part 21, from where it falls freely into a collecting vessel. With the help of a fan, which is arranged either in the gas outlet pipe 7 30 of the vessel 1 or in the gas outlet pipe of the electrode chamber to which the device for creating a gas / liquid contact is connected, air can be drawn into the vessel 1.

If desired, the gas outlet 7 may be arranged to extend through the top of the gas / liquid contacting device, and the vessel 1 may be rotatable and internally provided with baffles which act as impellers and air through the Drive vessel 1 or, alternatively, suck. In this way, the air can be given a vortex movement 40 which increases the extent of the mutual contact caused by the vessel.

It is understood that the features of the gas / liquid contact means of Figs. 5 and 6 can be combined so that liquid flows down the inner wall 45 of the vessel 1 and the outer wall of the cylindrical part 21.

The in Figs. 5 and 6 gas / liquid contacting devices are particularly useful in cases where the liquid flow is low, for example less than 11 / min.

The following examples illustrate the operation of the device described above with reference to FIG. 1 in the detection of volatile electroactive substances generated 55 during various chemical reactions.

example 1

Preparation of N-cyclohexylbenzthiazyl-2-sulfenamide.

(a) Device and Conditions 60 An EMF is applied from the voltage source 61 and the bobbin 56 for the electrodes 57 and 58 is sprinkled with an electrolyte which is a 0.8 molar aqueous solution of hydrogen bromide at a rate of 0.5 ml / min. The current measuring device comprises a resistor connected into the electrical circuit, via which a registration potentiometer is connected. Any change in the current flowing in the circuit as a result of absorption of electroactive material by the electrolyte is considered a change

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the potential difference across the resistance is demonstrated. During the reaction, air is supplied through the gas inlet 54 at a speed of 1.5 l / min, so that it leads the volatile substance, which is contained in the reaction medium in the vessel, via line 55 into the electrode chamber 65.

(b) reaction

175 ml of a 10% aqueous solution of sodium mercapobenzothiazole and 25 ml of cyclohexylamine (100%) are placed in the vessel 51 and an aqueous solution of sodium hypochlorite (14% available chlorine) is placed in the burette 53. The level of the gas inlet 54 and the jacket 64 are adjusted so that they reach below the surface of the reactants located in the vessel 51. The stirrer 52 is started up and the sodium hypochlorite solution is slowly added from the burette 53 into the vessel 51. At intervals, readings of the amount of sodium hypochlorite added against the potential difference are made on the writing potentiometer and the results are plotted on a diagram.

Initially there is no change in the potential difference when the sodium hypochlorite is added to vessel 1, but suddenly the potential difference begins to increase at a rate which corresponds to the amount of excess sodium hypochlorite, i.e. is proportional to the sodium hypochlorite added after the point where the potential difference began to increase.

The change in potential difference is believed to result from the formation of N-chlorocyclohexylamine, which is formed by the reaction between sodium hypochlorite and the excess cyclohexylamine when all of the sodium mercaptobenzothiazole is used up. The volatile N-chlorocyclohexylamine is removed from the vessel 1 and absorbed by the electrolyte in the electrode chamber. Since it is electroactive, it leads to an increased current flow in the electrical circuit.

The measured potential difference is directly proportional to the amount of N-chlorocyclohexylamine detected and 5 to the amount of excess sodium hypochlorite. The method therefore does not have only one end point for the reaction, i.e. the point at which the potential difference begins to increase, but after calibration also a measurement of the excess sodium hypochlorite, which can be used in a continuous process for changing the current of the reactants, so that a balanced reaction is obtained.

Example 2

15 Diazotization of aniline

(a) Device and conditions.

These correspond to those in Example 1 with the exception that the electrolyte is a 0.5% (w / w) aqueous solution of potassium iodide.

20 (b) reaction

A solution of 9 g of aniline in 450 ml of 2 molar hydrochloric acid is placed in the vessel 51 and a 30% (weight / weight) solution of sodium nitrite is placed in the burette 53. The sodium nitrite solution is slowly added to the vessel 51 at a rate such that a small constant potential difference is displayed on the writing potentiometer, and the addition continues until the potential difference suddenly begins to increase. The point at which the sudden increase in the potential difference occurs corresponds to the end point of the diazotization as measured using a standard iodine starch paper. The endpoint can be reproduced over a number of experiments and the increase in the measured potential difference is proportional to the excess sodium nitrite from that supplied to point 35 where the potential difference begins to increase.

C.

2 sheets of drawings