DE102017211311A1 - Process control with color sensor - Google Patents

Abstract

The present invention relates to a method for monitoring and optionally controlling a chemical reaction occurring within a reaction medium, wherein a color measurement is performed in a gas phase outside the reaction medium, which is carried out with a color sensor, which is not in physical contact with the gas phase.

Description

The present invention relates to a method for monitoring and optionally controlling chemical reactions in which a gaseous reactant is used and / or a gaseous reaction product is formed.

In chemical process analysis, an attempt is made to enable timely capture of substance-specific parameters in process engineering processes using chemical, physical and biological techniques and methods. The aim is to provide substance-specific and quality-relevant information and data for process optimization (for example time savings, cost reduction, reduction of emissions, etc.), for constant product quality and for compliance with environmental regulations.

Frequently, chemical reactions take place in very corrosive or toxic or dangerous reaction media (eg in the presence of concentrated acids and / or strong oxidizing agents). Also, corrosive or toxic gases (eg, Cl ₂ ) are often used as reactants, or such corrosive or toxic gases are produced as reaction products (eg nitrous gases NO _x ). These conditions make efficient process analysis difficult because, for example, measuring instruments can be damaged by such corrosive gases and liquids. In such cases, it is quite common for the chemical reaction to be manually controlled by an operator (eg, by manual control of the feed rate and rate of one or more reactants).

The use of color sensors in industrial processes with a high degree of automation, in which the color of a production or transport goods plays a role, is known. For example, color sensors can assign a label to the packaging, check imprints, recognize colored markings or check the color of surfaces. Typical applications are the pharmaceutical, cosmetics and food industries. There, color sensors are often used to identify products based on color markings and, if necessary, to sort them.

A color sensor illuminates the object to be examined with a light source (for example, a white light source such as a white light LED) and then analyzes the reflected light, e.g. by filtering the reflected color components according to wavelengths and evaluating the respective intensities. For example, color sensors operate on the tristimulus process. For this purpose, the reflected white light is decomposed into its red, green and blue components and their respective components are detected. Alternatively, color sensors are also known which determine the color values of objects via the so-called spectral method using a spectrophotometer.

An object of the present invention is the most efficient and easy to carry out tracking and optionally controlling a chemical reaction in which a gaseous reactant is used and / or a gaseous reaction product is formed. The pursuit or control of the chemical reaction should still be possible reliably even when corrosive or toxic gases are involved.

The object is achieved by a method for monitoring and, if appropriate, controlling a chemical reaction taking place within a reaction medium, wherein a gas phase is subjected to a color measurement outside the reaction medium and the color measurement is carried out with a color sensor which is not in physical contact with the gas phase.

In the context of the present invention, it has surprisingly been found that with a color sensor (ie a sensor which performs a color measurement with evaluation of the light reflected from the object) not only for surfaces of solid objects, but also for gases, as a reactant or reaction product in a chemical Reaction are involved, reliable color values or color properties can be determined. A physical contact of the color sensor with the gas phase, which is to be subjected to the color measurement, is not required. The color sensor can therefore be mounted outside the chemical reactor system. Damage to the sensor due to contact with corrosive gases does not take place. On the basis of the results of the color measurement (for example in the form of the intensities or relative proportions of the primary colors red, green and blue in the light reflected from the gas phase), the course of the chemical reaction can be followed. Depending on the results of the color measurement, optionally one or more process parameters (such as temperature, pressure, addition and / or addition rate of one or more reactants) may be controlled to optimize the course of the reaction.

It is preferably a chemical reaction in which at least one gaseous colored reactant is used and / or at least one gaseous colored reaction product is formed. A gaseous colored reactant or gaseous colored reaction product is, for example, a nitrosic gas (also referred to as nitric oxide or NO _x ), Cl ₂ , Br ₂ , RuO ₄ , or a mixture of at least two such gases. The gaseous reaction product may be the desired reaction product. Alternatively, it is also possible that the gaseous reaction product is formed by an undesirable side reaction.

A gaseous reactant is understood as meaning a reactant which is at least partially in the gaseous state under the temperature and pressure conditions prevailing during the color measurement in the gas phase. A gaseous reaction product is understood as meaning a reaction product which is at least partially in the gaseous state under the temperature and pressure conditions prevailing during the color measurement in the gas phase. For example, if the chemical reaction is carried out at elevated temperature and / or reduced pressure, a reaction product which would be in the form of a liquid under normal pressure and / or room temperature may be present in the form of a gas.

Under the gas phase, which is subjected to the color measurement, a gaseous volume element is to be understood, which is irradiated with the light source of the color sensor and whose color properties are to be determined with the color sensor.

The position of this gaseous phase or of this gaseous volume element at which the colorimetry is carried out is selected so that a gaseous reaction product and / or an unreacted gaseous reactant inevitably passes through this region and is therefore detected by the color sensor. Usually, the gas phase at which the color measurement is made, above the reaction medium. The colorimetric gas phase is preferably still within the reactor system. The reactor system comprises the chemical reactor in which the chemical reaction takes place and leads attached to the chemical reactor, through which gaseous reaction products and / or unreacted reactants are removed from the chemical reactor. For example, the gas phase subjected to the color measurement may still be inside the reactor. It is also possible that the color measurement is carried out on a gas phase, which is present in a tubular discharge of the reactor. Via this tubular discharge, the gaseous reaction product or unreacted reactant is removed from the reactor.

If a colored gaseous reaction product such as a nitrosous gas (reddish brown color) formed in the chemical reaction in the reaction medium, this gas rises and is usually discharged from the reactor. Even when rising in the reactor or alternatively after leaving the reactor via a discharge pipe, the colored gas can pass the area which is subjected to the color measurement with the color sensor. In order to avoid physical contact between the color sensor and the gaseous reaction product, the color sensor is preferably located outside the reactor and outside the discharge tube, if one exists. In order for the light emitted by the light source of the color sensor to reach the gas phase to be subjected to the colorimetry in the highest possible intensity, the wall of the reactor or the tube wall of the discharge tube is preferably at least partially or even completely made of a light-transparent material (eg glass or a transparent plastic ). Preferably, the transparent material is colorless. However, in the context of the present invention, it is also possible for the transparent material to be colored. By means of a preferably continuous color measurement, color values (eg RGB values) for the examined gas phase can be determined as a function of time. On the basis of the time course of these color values, it can be recognized whether and in what amount the gaseous colored reaction product (eg NO _x ) forms and whether, if appropriate, a process parameter (such as pressure, temperature, added amount or rate of addition of a reactant, etc.) has to be changed, to optimize the reaction and thus the formation of the colored reaction gas. In addition, the course of the color measurement reveals when the reaction is complete and further addition of reactants is no longer required. The consumption of reactants can be optimized thereby.

Also via a gaseous reactant, which is preferably colored, the course of a reaction using the color sensor can be well observed and optionally controlled. For example, if the colored gaseous reactant does not completely react with the other reactants, the unreacted gaseous reactant is released from the reaction medium again, rising and usually being removed from the reactor. Even when rising in the reactor or alternatively after leaving the reactor via a discharge tube, the colored gaseous reactant can pass the region which is subjected to color measurement with the color sensor. From the results of the color measurement can be seen how well or completely react the reactants with each other, and if necessary, to change a process parameter to improve the efficiency of the chemical reaction.

The reaction medium is the medium in which the chemical reaction takes place. The reaction medium is, for example, a liquid reaction medium (for example in the form of a homogeneous liquid, a dispersion or a melt).

In the context of the present invention, a chemical reaction means not only the reaction between two or more reactants, but also the chemical decomposition of a single reactant.

The chemical reaction usually takes place in a suitable chemical reactor to which at least one (e.g., tubular) drain is attached, via which the gaseous reaction product and / or an unreacted gaseous reactant is removed from the reactor.

In the chemical reaction, for example, a noble metal such as Pt, Pd, Rh, Ir, Ru, Ag or Au (eg in elemental form or in the form of a precious metal-containing alloy) and / or a noble metal compound (eg noble metal salts or complexes) implemented , The noble metal or the noble metal compound may be present as a solid or in dissolved form.

The chemical reaction can take place, for example, during a precious metal recycling. In these chemical reactions very corrosive reaction media (eg concentrated acids or alkaline oxidizing melts) and / or corrosive gaseous reactants (eg Cl ₂ ) are often used. Also often arise corrosive gases (eg nitrous gases).

The chemical reaction may be, for example, the reaction of a noble metal (eg, Pt, Pd, Rh, Ir, Ru, Ag, Au or an alloy containing at least one of these noble metals) or a noble metal compound (eg, a noble metal salt or a noble metal complex) in or with an acidic or alkaline oxidizing medium. The acidic medium may contain, for example, aqua regia, nitric acid (in particular concentrated nitric acid), Cl ₂ -containing hydrochloric acid, or a mixture of at least two of these components. The alkaline oxidizing medium is, for example, an alkaline oxidizing melt, for example a melt containing an alkali metal hydroxide such as NaOH and a nitrate salt (eg an alkali metal nitrate such as NaNO ₃ ).

For example, the chemical reaction involves the release or formation of a nitrous gas.

In an exemplary embodiment, the chemical reaction comprises the oxidation of a noble metal (eg, Pt, Pd, Rh, Ir, Ru, Ag, Au, or an alloy containing at least one of these noble metals) in a suitable reaction medium (eg, aqua regia) and the release Formation of a nitrous gas. The oxidized noble metal forms a soluble noble metal compound (for example in the form of a complex compound such as a chloride complex).

In a further exemplary embodiment, the chemical reaction comprises the decomposition of at least one substance selected from the group consisting of nitrates, nitrites, nitric acid and nitrous acid and the release or formation of a nitrous gas.

In another exemplary embodiment, the chemical reaction involves the oxidation of silver or a metal having a lower standard potential than silver in the electrochemical series (eg, Cu, rhenium, tin, antimony, bismuth or nickel, or an alloy containing at least one of these metals contains) in nitric acid and the release or formation of a nitrous gas.

In a further exemplary embodiment, the chemical reaction comprises the acidic workup of the solidified product of an alkaline oxidizing melt of a noble metal, in particular a melt containing an alkali or alkaline earth metal hydroxide (eg NaOH) and a nitrate salt (eg an alkali metal nitrate such as NaNO ₃ ). The acidic workup (by adding an acid such as hydrochloric acid), for example, proceeds with release or formation of a nitrous gas. For an improved release of the nitrous gas, the acidic work-up of the solidified melt can take place under heating.

Suitable color sensors are known to the person skilled in the art and are commercially available. By way of example reference can be made to the full-spectrum sensors of the LR-W model series from Keyence.

The color measurement is for example an RGB color measurement.

The color measurement may e.g. carried out by the tristimulus method or the spectral method. These methods are known in principle to the person skilled in the art. In the tristimulus method, the reflected light is filtered into its red, green and blue color components and the intensities or relative proportions of the respective color components in the reflected light are determined.

The color sensor is, for example, a full-color sensor.

The color sensor uses e.g. a white light LED as a light source. The color sensor may also use a combination of a red LED, a green LED and a blue LED as light sources.

Depending on the color sensor used, its detection range or scanning range can vary. For example, the color sensor has a detection range of up to 200 cm, e.g. 5 mm to 200 cm or 10 mm to 100 cm or 10 mm to 50 cm.

The light spot diameter of the color sensor is, for example, in the range of 1 mm to 50 mm.

Preferably, the color measurement is carried out continuously during the chemical reaction.

Preferably, the color sensor is positioned stationary so that the color measurement during the chemical reaction is always made on the same gas phase (i.e., the same volume element within the reactor system).

As a result of the color measurement carried out on the gas phase, for example, the intensities or relative proportions of the primary colors red, green and blue in the reflected light are obtained.

Based on the results of the color measurement, the course of the chemical reaction can be followed. Depending on the results of the color measurement, optionally one or more process parameters (such as temperature, pressure, amount added, and / or rate of addition of one or more reactants) may be changed to optimize the course of the reaction.

The results of the color measurement are forwarded, for example, to a control unit which, in terms of programming, is set up in such a way that it changes one or more process parameters, if appropriate, taking into account defined specifications or predetermined setpoint values.

As already mentioned above, the colorimetric gas phase is preferably still within the reactor system. The reactor system comprises the chemical reactor in which the chemical reaction takes place and leads attached to the chemical reactor, through which gaseous reaction products and / or unreacted reactants are removed from the chemical reactor. The gas phase at which the color measurement is carried out may, for example, still be located inside the reactor (preferably above the reaction medium). The gas phase at which the colorimetry is performed may also be in a drain (e.g., a tubular drain) of the reactor. Since a discharge (e.g., in the form of a tube) from the reactor usually has significantly smaller dimensions than the reactor itself, color measurement in the region of the discharge is easier and more efficient to carry out than in the reactor.

In a preferred embodiment, therefore, the chemical reaction is carried out in a reactor having a discharge (eg in the form of a tube) for gaseous reaction products and / or unreacted gaseous reactants and the gas phase at which the color measurement is carried out is located therein dissipation.

For example, the color sensor is positioned and set to exhibit its maximum sensitivity in the gas phase region undergoing colorimetry. For example, if the gas phase at which the colorimetry is being performed is in the reactor discharge tube, the color sensor is positioned and adjusted to have its maximum sensitivity substantially at the center of the reactor discharge tube (ie, at half the diameter of the tube). This adjustment can easily be made by the person skilled in the art. For example, the focal point of the color sensor can be set to be substantially centered in the colorimetry to be subjected Gas phase (ie the gaseous volume element whose color properties are to be determined with the color sensor) is located.

Moreover, the present invention relates to the use of a color sensor for tracking and optionally controlling a chemical reaction in which at least one gaseous reactant is used and / or at least one gaseous reaction product is formed.

With regard to the preferred properties of the color sensor, the chemical reaction and the gaseous reactants and reaction products, reference may be made to the above statements.

As mentioned above, the color sensor preferably takes a color measurement on a gas phase which is outside (e.g., above) the reaction medium and is passed by the gaseous reaction product and / or an unreacted gaseous reactant.

The invention will be described in more detail with reference to the following examples.

Examples

Comparative Example 1: Manual Process Control

As part of the precious metal extraction precious metals in aqua regia were dissolved in a steel / enamel reactor. The solution was heated and the loss of fumed hydrochloric acid was compensated by addition of new hydrochloric acid. Nitrous gases, recognizable by their reddish-brown color, were liberated. The nitrous gases were removed from the reactor via a glass removal tube and passed to a NOx scrubber.

In the manual control in the comparative example 1 the HCl dosage was about all 60 Minutes started by a trained and experienced operator to realize a relatively continuous process.

The process time until the release of all nitrous gases was 954 Minutes. The amount of HCl added by the operator was 800 Liter.

Comparative Example 2: Manual Process Control

In Comparative Example 2 The same noble metal-containing starting materials were dissolved under the same conditions and in the same steel / enamel reactor as in Comparative Example 1 in aqua regia and the solution was heated.

In the manual control in Comparative Example 2, the HCl dosage was started approximately every 120 minutes by a trained and experienced operator.

The nitrous gases were expelled intermittently, which is unfavorable for a downstream exhaust air purification.

The process time until the release of all nitrous gases was 1433 minutes. The amount of HCl added by the operator was 1100 liters.

Example 1: Process control using a color sensor

In Example 1, the same noble metal-containing starting materials were dissolved under the same conditions and in the same steel / enamel reactor as in Comparative Example 1 in aqua regia and the solution was heated.

A color sensor (full-spectrum sensor LR-W500, Keyence MU-N11 evaluator) was placed at a distance of about 2 cm to the glass discharge tube, which carries the nitrous gases out of the reactor.

The light source of the color sensor, which illuminated the gas phase within the drain tube, was a white light LED. The color sensor operated on the tristimulus method, i. the radiation reflected by the gaseous phase within the discharge tube was split into its red, green and blue components and their relative proportions were determined.

Since the nitrous gases have a reddish-brown color, the course of the reaction can be monitored, in particular, on the intensity profile of the red color component determined during the colorimetry.

The continuously determined color values of the gas phase were forwarded to a control unit, which was programmed in such a way that it dosed additional hydrochloric acid via a control valve with a decrease in the intensity of the red color component. Thus, the process conditions (e.g., metering rate) could be automatically adjusted to the current reaction history and the formation of NOx maintained at a consistently high level. The red color fraction of the light reflected from the gas phase showed a very constant intensity profile for the duration of the chemical reaction, which in turn means that during the chemical reaction a very uniform release of NO x took place. Upon completion of the reaction (i.e., no further release of nitrous gases), the intensities of red, blue and green color components returned to "white light".

1 shows the intensity curves of the red, blue and green color components during and after the reaction.

The process duration until the release of all nitrous gases was 782 minutes. The metered amount of HCl was 555 liters. Both the process time and the consumption of HCl could be significantly improved compared to the manual process control. Also, for the operation of the NOx scrubber, it is advantageous if it is charged during the process time with the most consistent amount of nitrous gases.

Process duration and the consumed HCl amounts of Comparative Examples 1-2 and Example 1 of the invention are listed again in Table 1 below. Table 1: Process time and amount of HCl consumed example 1 Vgl.bsp. 1 Vgl.bsp. 2 Duration of expulsion of nitrous gases [min] 782 954 1433 Amount of HCl used [l] 555 800 1100

With the method according to the invention, the operating staff is significantly relieved, manual intervention is no longer necessary. It results in faster turnaround time, higher plant capacity, lower chemical consumption and lower energy costs.

Comparative Example 3: Process control using a chemical NOx sensor

In Comparative Example 3, it was tested whether an automatic process observation and optionally control of the chemical reaction described in Example 1 and Comparative Examples 1 and 2 is also possible by a chemical NOx sensor.

The chemical NO _x sensor was mounted in the exhaust duct of the reactor. Due to the contact of the sensor with the corrosive gas atmosphere, its life was only 2 weeks.

Claims (15)

A method for monitoring and optionally controlling a chemical reaction occurring within a reaction medium, wherein a gas phase outside the reaction medium is subjected to a color measurement and the color measurement is performed with a color sensor that is not in physical contact with the gas phase. The procedure according to Claim 1 , wherein in the chemical reaction at least one gaseous colored reactant is used and / or at least one gaseous colored reaction product is formed. The procedure according to Claim 2 wherein the gaseous colored reaction product or an unreacted colored reactant passes the gas phase which is subjected to the colorimetry. The method of any one of the preceding claims, wherein the chemical reaction involves the reaction of a noble metal or noble metal compound and the reaction medium is an acidic reaction medium. The method of any one of the preceding claims, wherein the chemical reaction comprises the release of a nitrous gas. The procedure according to Claim 5 wherein the chemical reaction comprises the oxidation of a metal, preferably a noble metal, and the release of a nitrous gas, and / or wherein the chemical reaction is the decomposition of at least one substance selected from the group consisting of nitrates, nitrites, nitric acid and nitrous acid and the release a nitrous gas. The procedure according to Claim 5 wherein the chemical reaction comprises acid processing the solidified product of a melt containing an alkali or alkaline earth metal hydroxide and a nitrate salt to release the nitrous gas. The method of any of the preceding claims, wherein the color measurement is by the tristimulus method or the spectral method; and / or wherein the color sensor is a full color sensor. The method of any of the preceding claims, wherein the color measurement is continuous. The method according to one of the preceding claims, wherein the results of the color measurement are forwarded to a control unit, which is set up by the program in such a way that, taking into account defined specifications, it optionally changes one or more process parameters. The method of any one of the preceding claims, wherein the color sensor is mounted outside the reactor system. The process of any one of the preceding claims, wherein the chemical reaction is carried out in a reactor having a discharge for gaseous reaction products and / or unreacted gaseous reactants and the gaseous phase undergoing the colorimetry being in that discharge. The method of any one of the preceding claims, wherein the focal point of the color sensor is adjusted to be substantially centered in the colorimetric gas phase. Use of a color sensor for tracking and optionally controlling a chemical reaction in which at least one gaseous reactant is used and / or at least one gaseous reaction product is formed. Use according to Claim 14 wherein the color sensor makes a color measurement on a gas phase which is outside the reaction medium and which is passed by the gaseous reaction product and / or by an unreacted gaseous reactant.

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