HRP20151358A2 - Reaction chamber for in-situ recording of raman spectra at mechanochemical reactions and corresponding method of recording raman spectrums - Google Patents

Abstract

The present invention relates to improved reaction vessels (1) used for carrying out mechanochemical reactions, which are suitable for in-situ recording of Raman spectra of samples in reaction vessels (1) during the grinding process at mills. The basic characteristic of the reaction vessels (1) is that they have a flat transparent surface (2) on the outer layer through which the sample in the reaction vessel (1) is excited.

Description

The field to which the invention relates

The present invention relates to a reaction vessel used for mechanochemical reactions, which is suitable for in-situ recording of Raman spectra of samples in reaction vessels during the grinding process on mills. The invention also relates to a method of recording Raman spectra using the reaction vessel of the invention.

Technical problem

Mechanochemical reactions are often carried out using mechanochemical mills, which can be vibrating (ball) mills, planetary ball mills, etc. Reaction vessels for mechanochemical reactions to carry out the reaction contain appropriate reactants and additives and one or more grinding balls and are completely closed during the process grinding. The mill is a device that moves the reaction vessels so that it causes relative motion of the reaction vessel and the steel balls, which results in the mixing of the reactants and the hitting of the balls on the reactants. The advantages of mechanochemical reactions compared to reactions carried out in solutions are reduced or minimal use of solvents, fast and energy-free reactions and quantitative product yields. Mechanochemical reactions are carried out by mounting reaction vessels with reactants and grinding balls on a mill, which then drives the reaction vessels. In vibrating ball mills, the reaction vessels oscillate at a frequency of typically 30 Hz. In one embodiment of the vibrating mill, the mill arm holding the reaction vessel oscillates from its left end point to its right end point in a horizontal plane. In another version of the vibrating ball mill, the oscillation of the reaction vessel occurs in the vertical plane, i.e. the reaction vessel moves up and down.

Until recently, reaction vessels were made exclusively of opaque materials such as steel, agate, tungsten carbide, zirconium oxide, aluminum oxide, and the like, which prevented in-situ monitoring of the physical and chemical changes that occurred during the implementation of the mechanochemical process. For example, opaque reaction vessels prevent the penetration of the excitation laser beam, necessary for obtaining the Raman spectrum of the sample, inside the reaction vessel where the laser beam should interact with the reaction mixture. With opaque reaction vessels, the excitation laser beam is not able to pass through the wall of the reaction vessel.

Monitoring and understanding the flow and processes that take place during the implementation of mechanochemical reactions is desirable from the aspect of optimizing mechanochemical reactions. Until the development of the first in-situ techniques for monitoring the course of mechanochemical reactions without interrupting the grinding process, monitoring the course of mechanochemical reactions was based on interrupting the grinding process to open the reaction vessel and sample the reaction mixture. Such an approach to monitoring the course of the mechanochemical reaction is flawed because some mechanochemical reactions are not stopped by the end of the grinding process, but continue in the reaction mixture already obtained in this way. As the subsequent analysis that follows sampling and preparation of the sample for appropriate analysis inevitably lags behind the moment of sampling, any change in the sample after sampling gives wrong information in the course of the mechanochemical reaction and can lead to wrong conclusions about the progress and course of the mechanochemical reaction. In addition, the grinding process heats the reaction mixture, which is a consequence of the conversion of the kinetic energy of the grinding balls into the internal energy of the reaction mixture and also of the reaction vessel itself. Stopping the grinding process and dividing it into segments for sampling undoubtedly causes cooling of the reaction mixture and the reaction vessel and its reheating by continuing the grinding process. Thus, the temperature changes of the reaction mixture are different during the interrupted grinding process and during continuous grinding. It is clear that for the application of mechanochemical reactions, it is preferable to carry out the procedure continuously, because it requires less time, but also less human work. For these reasons alone, it is obvious that the approach to monitoring the mechanochemical reactions of grinding that require stopping the grinding process is flawed and cannot provide meritorious information about the processes that occur during grinding.

Therefore, the development of techniques for monitoring mechanochemical reactions that do not require interrupting the milling process is desirable for a better understanding of these processes and later for their optimization in order to obtain the desired products in the shortest time and with the least consumption of other resources such as energy and initial materials and raw materials. Two techniques that exist today, which enable the monitoring of mechanochemical reactions without disturbing the grinding process, are based either on high-energy X-ray diffraction or on Raman spectroscopy.

Raman spectroscopy is a recognized method of characterizing samples and is often used in scientific and applied research that includes chemical, pharmaceutical, biochemical, biological and physical research. It is a spectroscopic method where the laser beam interacts with the sample and the inelastic scattered radiation is analyzed. Raman scattered radiation is only a small part of the radiation that is scattered on the sample. Approximately one photon in a million from the initial excitation laser beam is inelastically scattered by the sample giving a Raman signal. Therefore, it is of particular importance to enable the collection of as many Raman scattered photons as possible when this scattering occurs during milling, and the excitation laser beam enters through the wall of the reaction vessel to interact with the sample and the scattered radiation exits the reaction vessel to be collected and analyzed by spectrometer.

By collecting the Raman spectrum of the sample, in principle, an insight into the vibrational spectrum of the sample is obtained, which depends on the composition of the sample. Different samples therefore have different Raman spectra, and changes in the composition of the sample can be measured and monitored over time, by recording time-resolved Raman spectra. By default, Raman spectra of a sample are recorded so that the excitation laser beam is directly incident on the sample and Raman scattered radiation is collected directly from the sample. For the application of Raman spectroscopy to mechanochemical reactions, direct contact of the excitation laser beam with the sample is not possible because the reaction mixture is contained in a reaction vessel that oscillates during the grinding process.

For the implementation of the aforementioned mechanochemical reactions in mills, transparent reaction vessels have recently been used, which enabled partial in-situ monitoring of chemical reactions using X-ray diffraction. Such reaction vessels are typically made of polymethyl methacrylate (glass plastic). Such reaction vessels consist of two complementary parts that are joined to form a closed reaction vessel and typically have the shape of a cylinder on the outside, while on the inside they enclose a chamber that is completely rounded. Such transparent reaction vessels can be used to record the Raman spectra of the reaction mixture in-situ during the implementation of the mechanochemical process.

To record Raman spectra, the excitation laser beam passes through the wall of a transparent reaction vessel and enters the reaction vessel where it interacts with the sample or reaction mixture. The excitation laser beam is scattered on the sample, and one part of the scattered radiation belongs to the Raman scattered radiation, which has a changed energy from the excitation radiation. Raman radiation is of interest for this patent application because it is characteristic of the chemical composition of the sample, and by changing the chemical composition of the sample, a different Raman spectrum is obtained. Changes in the Raman spectra of the reaction mixture make it possible to monitor the course of the reaction during the grinding process. For example, as long as the spectrum of the reaction mixture changes, the reaction occurs under the influence of grinding. The cessation of changes in the spectrum of the reaction mixture indicates the cessation of the chemical reaction and the completion of the reaction. Thus, in-situ Raman spectroscopy can be used to determine the time required to complete a mechanochemical reaction, and thus the mechanochemical process can be time optimized.

However, although the very use of transparent reaction vessels enables obtaining spectra from the sample in-situ during grinding and without interrupting the grinding process, it has been shown that such reaction vessels are not suitable for monitoring the course of mechanochemical reactions in reaction mixtures that give a weak Raman scattering effect. Therefore, there was a need for an improvement, that is, for a solution that will enable better quality in-situ recording of Raman spectra during mechanochemical reactions.

State of the art

The use of a plastic reaction vessel for mechanochemical reactions was described earlier [scientific paper: Friščić et al. Nature Chem., 5 (2013) 66-73]. The material of the reaction vessel used in this scientific work is polymethyl methacrylate (PMMA, also known as fiberglass, Plexiglas or Perspex). Raman spectra collected in-situ and without interrupting the grinding process were also collected using such transparent reaction vessels [scientific papers: Gracin et al. Angew. Chem. Int. Ed. 53 (2014) 6193-6197; Batzdorf et al. Angew. Chem. Int. Ed. 54 (2014) 1799-1802, Juribašić et al. Chem. Commun. 50 (2014) 10287-10290; Tireli et al. Chem. Commun. 51 (2015) 8058-8061].

Raman spectra were recorded using opaque reaction vessels, but with a transparent window.

Thus, European patent application EP2784488A1 refers to a reaction vessel for Raman spectrophotometry and a method using such a vessel. On page 3, line 4, paragraph (0016), the reaction vessel from drawings 1 to 5 is described. It is stated that the housing 10 includes a transparent window 11, through which one can see the inside of the reaction vessel 12 in which the electrolyte solution E is obtained. This window serves for Raman spectrophotometry of the electrochemical reaction occurring in the reaction vessel. Such a reaction vessel is not adapted to work in the grinding process.

US patent application US2004/0166310 relates to the use of stabilized zirconium oxide for a window through which to monitor various chemical reactions in various reaction vessels. The invention provides a transparent observation window on different reaction vessels. According to patent claim 10, such a window is used, among other things, for optical methods of monitoring reactions involving spectroscopy. The patent application does not indicate the possibility of using such a reaction vessel for grinding processes.

Presentation of the essence of the invention

The present invention represents an improved reaction vessel for in-situ recording of Raman spectra in mechanochemical reactions. The invention relates to reaction vessels for in-situ recording of Raman spectra of samples during the grinding process on mills, where the outer surface of the reaction vessel is cylindrical and the inner surface of the reaction vessel is completely rounded, and where the cylindrical part of the outer surface of the reaction vessel has one or more flat transparent surfaces on the layer of the roller for the passage of the excitation laser beam into the interior of the reaction vessel and the exit of the Raman scattered radiation. It is preferable that the mills are vibration mills.

The reaction vessels of the present invention enable the collection of improved Raman spectra during the grinding process in comparison to the hitherto known reaction vessels for the collection of Raman spectra and grinding procedures. The improvement of the Raman spectra refers to an approximately 2.3 times higher ratio of the Raman signal from the sample to the reaction vessel when the reaction vessels of the present invention are used compared to the transparent reaction vessels known so far (Figures 4a, 4b and 4c and Table 1). Also, the Raman signal of the sample is approximately 25% higher when using the reaction vessel of the subject invention where the excitation laser beam enters the reaction vessel vertically through its flat part compared to a reaction vessel with a fully rounded wall. Also, the recording of Raman spectra can be done in-situ, without the need to interrupt the grinding or to open the reaction vessel containing the sample or to remove the sample outside the reaction vessel in any other way in order to record its Raman spectrum.

With the reaction vessels of the subject invention, a better ratio of the Raman signal of the reaction mixture noise was achieved, and also a better ratio of the Raman signal of the reaction mixture and the Raman signal of the reaction vessel Namely, the material of the transparent reaction vessel gives a Raman signal that is impossible to avoid because the air on the way to the reaction mixture inside the reaction vessel vessel partially interacts with the material of the reaction vessel and is partially dispersed on the material of the reaction vessel. However, by changing the design of the reaction vessel, the Raman signal-to-noise ratio of the sample and the Raman signal of the reaction vessel can be improved, and this is the subject of the present invention.

It is preferable that the reaction vessel is entirely made of transparent material. The transparent material can be chosen from among others polymethyl methacrylate, polyethylene or polycarbonate.

It is desirable that the surface of the flat surface on the outer surface of the reaction vessel is such that it is sufficient for the excitation laser beam to enter the reaction vessel vertically through this flat and transparent surface/wall of the reaction vessel. Namely, the surface of the flat surface of the reaction vessel of the subject invention should be large enough that the laser beam falls on it all the time while the reaction vessel of the invention moves on the mill.

According to the design of common laboratory mills and the amplitudes of movement of the arm holding the reaction vessel on the mill, the flat transparent surface is 1 mm long to the entire length of the reaction vessel roller. It is desirable that the length of the flat surface of the roller is from 10 mm to 20 mm. It is essential that the flat transparent surface of the roller is at least the length of the reaction vessel mounted on the mill from the right end point to the left end point of the mill arm on which the reaction vessel is mounted.

The width of the flat surface should be sufficient for the laser beam to enter the reaction vessel through the flat surface in all positions in which the reaction vessel can be found with respect to the laser beam during the grinding process. So in all positions of the reaction vessel from the left end point of the mill arm to the right end point. The width of the flat surface on the reaction vessel can range from 1 mm to 20 mm. It is preferable that the width of the flat surface is 3 mm to 10 mm.

It is preferable that there is only one flat transparent part of the surface sufficient for the passage of the laser beam on the reaction vessel. In that case, the rest of the cylindrical part of the reaction vessel could easily be placed in the arm of the mill, and the mechanochemical reactions resulting from the shaking of the mill would continue to be carried out efficiently.

The thickness of the walls of the reaction vessel should be as small as possible so that the Raman signal from the reaction vessel in the Raman spectrum is as small as possible, but still sufficient for the reaction vessel to have adequate strength. It is desirable that the thickness of the wall of the reaction vessel is adapted to the properties of the excitation laser beam. For example, in designs where the excitation laser beam is focused at a certain distance from the tip of the laser probe, it is desirable that the thickness of the wall of the reaction vessel at the place where the reaction vessel has a flat surface is smaller than that certain distance of the focus of the laser beam from the tip of the laser probe. This ensures that the focus of the laser beam is in the interior of the reaction vessel where there is a reaction mixture whose Raman spectra are measured.

In the event that the transparent reaction vessel of the invention consists of two complementary parts that are joined to form a closed reaction vessel with a lining and a smooth internal shape, it is preferable that each of the two complementary parts of the reaction vessel has a flat surface on the outer surface of the reaction vessel that are of equal width so that by closing the reaction vessel, one continuous flat transparent surface is realized on the outer surface of the closed reaction vessel.

An embodiment is possible in which the flat part of the folded and closed reaction vessel does not extend the entire length of the reaction vessel, but the reaction vessel is completely rounded at its ends that touch the mill arm when the reaction vessel is mounted on the mill. In this case, each of the two complementary parts has a flat part of the outer wall extending from the part where each of the two parts of the reaction vessel is open. Thus, when the reaction vessel is closed, the total length of the flat surface of the outer wall of the reaction vessel is equal to or greater than the amplitude of the reaction vessel while mounted on the mill in operation.

In this way, it is achieved that the laser beam enters through the flat part of the reaction vessel in all positions of the reaction vessel during grinding.

It is preferable to use a reaction vessel with a flat surface during the experiment of collecting in-situ Raman spectra in such a way that the excitation laser beam enters the reaction vessel vertically through the flat surface, it is easily possible to collect the Raman spectrum by using a reaction vessel with a completely rounded outer wall, if the laser beam for Raman excitation enters the reaction vessel vertically through the flat and transparent outer wall, the highest quality Raman spectrum of the sample is obtained. A comparison of Raman spectra obtained by different recording methods is shown in drawings 4a, 4b and 4c. The results of the signal strength analysis obtained by these three recording methods are given in Table 1.

The subject invention also relates to a method of collecting Raman spectra of the reaction mixture during the grinding process and without interrupting the grinding process, which uses the reaction vessel of the subject invention in such a way that the reaction vessel of the subject invention is mounted on a vibrating ball mill so that its transparent surface is flat in the horizontal plane and facing down. In doing so, the laser probe is placed under the reaction vessel in such a way that the excitation laser beam enters the reaction vessel vertically through its flat surface, and Raman scattered radiation is collected so that it exits the reaction vessel through the same flat surface.

Brief description of the drawing

Drawing 1 - Technical drawing of the reaction vessel showing a flat part on the surface of the reaction vessel

Drawings 2a and 2b - Technical drawings of half of the reaction vessel, i.e. one complementary part of the reaction vessel showing a flat part on the surface of the reaction vessel

Drawings 3a and 3b - Represent the side and side sections of the reaction vessel

Drawings 4a, 4b and 4c - Represent the test results of reaction vessels with a rounded outer surface and a flat outer surface

A detailed description of at least one way of realizing the invention

In the following, one of the preferred embodiments of the reaction vessel of the present invention will be described.

In this embodiment of the reaction vessel of the present invention, the reaction vessel 1 consists of two complementary parts 7 which are joined to form a closed reaction vessel with a lining and a smooth internal shape. Each of the complementary halves 7 has one part of the outer wall that is flat, while the remaining part of the reaction vessel is rounded 3. The two complementary parts 7 are joined so that in the assembled and closed reaction vessel the flat parts of both halves are aligned so that a flat part of the closed reaction vessel 2 is obtained along the entire length of reaction vessel 1.

The closed reaction vessel 1 is 65 mm long and is suitable for hand holding most standard mechanochemical mills. The radius of the reaction vessel on the part where the reaction vessel is rounded is 12.5 mm from the axis of the reaction vessel to the outer edge. The flat part of the wall of the closed reaction vessel 2 has a width of "b"=9 mm and is located along the entire length of the reaction vessel "/". In the part where the flat part of the reaction vessel 2 is located, the thickness of the wall of the reaction vessel "d" is smaller than in the part of the reaction vessel where the wall is rounded. The distance from the central axis of the reaction vessel to the outer flat wall of the reaction vessel 2 is 11.5 mm.

The inner surface of the reaction vessel 4 is cylindrical in the central part of the reaction vessel, while the ends are hemispherical. In the central cylindrical part of the reaction vessel, the radius of the reaction vessel is 9.5 mm. This ensures that the inner wall of the reaction vessel 4 is free of sharp edges or edges where material could collect during the grinding process, which would make it impossible to evenly mix and grind the contents of the reaction vessel. The internal volume of the reaction vessel is approximately 14 cm3.

In the performance of the mechanochemical experiment, where the course of the mechanochemical reaction is monitored in-situ using Raman spectroscopy, the reaction vessel 1, for monitoring the course of the mechanochemical reaction on the mill, is placed so that its flat transparent surface 2 is horizontal and facing downwards. The laser probe is placed so that the excitation laser beam enters the reaction vessel perpendicular to the flat surface 2. The laser probe is also equipped with optical fibers that collect the scattered radiation and lead it to the spectrometer for analysis. The spectrometer is connected to a computer which, with the help of a specialized computer program, records the spectra and enables their processing and storage. During spectrum collection, the reaction vessel 1 is attached to the arms of the mill and oscillates at a frequency of typically 30 Hz in the horizontal plane so that the flat part of the reaction vessel 2 is always horizontal and so that the laser beam is always perpendicular to this flat surface 2 in each position of the reaction vessel 1 The probe with the laser is stationary during spectrum collection, while the reaction vessel 1 oscillates above it.

By using the transparent reaction vessels 1 of the present invention, it is possible to record high-quality time-resolved Raman spectra during the grinding process and without interrupting the grinding process.

The temporal resolution of the spectra that can be achieved ranges from milliseconds to several seconds or minutes. The time resolution during the recording of time-resolved Raman spectra is characteristic for a particular mechanochemical experiment that is to be monitored in-situ, and is determined so that each individual spectrum that is collected is informative about the composition of the sample, i.e. so that the contributions of different of the compounds found in the reaction mixture and so that changes in the spectra collected over time can be observed. If the Raman response of the sample is weaker, it is necessary to increase the time of collecting an individual spectrum, while this time can be reduced if the sample or reaction mixture gives a strong Raman scattering of the excitation laser beam. In the same recording conditions, which are determined by the power of the excitation laser beam and the spectrum collection time, by modifying the transparent reaction vessels that are the subject of this invention, the collection of a higher quality Raman spectrum is achieved, which is manifested by the fact that the spectrum collected using the reaction vessel 1 of the subject invention has a better signal ratio from the sample and noise and a better ratio of the signal of the sample in relation to the signal of the reaction vessel itself than is the case when using unmodified transparent reaction vessels.

When testing the efficiency of the reaction vessel 1 of the subject invention, the same sample (benzoic acid) was imaged in three different ways: with the laser entering vertically through the flat bottom of the reaction vessel 2, through the flat bottom of the reaction vessel 2, but not perpendicular to the flat surface 2, through the rounded (round) wall of the reaction vessel 3. Other recording conditions (total measurement time of each spectrum, power of the excitation laser beam) were identical in each of the three recordings.

Figure 3a shows that the Raman signal of the reaction mixture, obtained by imaging where the excitation laser beam enters the reaction vessel vertically through the flat surface 2 located on the outer layer of the reaction vessel, is greater than the Raman signal of the reaction mixture obtained when the excitation laser beam enters the reaction vessel vessel through its rounded wall 3. As the Raman signal of the reaction mixture is greater in the case when the spectrum is recorded so that the excitation laser beam enters the reaction vessel 1 perpendicular to the flat surface 2 on the outer layer, the ratio of the Raman signal of the reaction mixture to noise is better, and ratio of the Raman signal of the reaction mixture and the reaction vessel. It follows from the above that the recording of Raman spectra so that the excitation laser beam enters the reaction vessel 1 vertically through the flat surface 2 enables obtaining better quality Raman spectra of the reaction mixture, which is desirable for the purpose of monitoring the course of mechanochemical reactions.

The Raman spectra in Figures 4a, 4b and 4c show that, apart from the highest signal from the sample, which is the sum of the signal intensities of FP3, FP4 and FP5, recording vertically through flat surface 2 has the best signal ratio of the sample to the reaction vessel. The noise of the measurements shown in drawings 4a, 4b and 4c is approximately the same in all three measurements, as shown by the data listed in Table 1. It follows that by recording Raman spectra using reaction vessel 1 with a flat outer wall, the best ratio of Raman signal to noise in the spectrum is achieved and thus the highest quality Raman spectrum.

Table 1 - Overview of the difference in intensity and signal ratio of the sample and the vessel when excited by laser vertically through the flat part of the vessel, not vertically through the flat part of the vessel and through the rounded part of the vessel

[image]

List of used call signs

1 reaction vessel

2 flat transparent surfaces

3 outer surface of the reaction vessel

4 inner surface of the reaction vessel

7 complementary parts of the reaction vessel

Claims (9)

1. Reaction vessel (1) for in-situ recording of Raman spectra of samples during the grinding process on mills, indicated by the fact that the outer surface of the reaction vessel is cylindrical (3) and the inner surface of the reaction vessel (4) is completely rounded, and where the cylindrical part of the outer surface of the reaction vessel has one or more flat transparent surfaces (2) on the layer of the roller for the passage of the excitation laser beam. 2. Reaction vessel (1) according to claim 1, characterized in that it is completely made of transparent material. 3. Reaction vessel (1) according to claim 1, characterized in that the transparent part of the reaction vessel is made of plastic, such as polymethylacrylate, polyethylene or polycarbonate. 4. The reaction vessel (1) according to claim 1, indicated by the fact that the flat transparent surface (2) is of such a surface that is sufficient for the excitation laser beam to enter through it vertically into the reaction vessel and that the length of the transparent flat surface I is equal to or greater than the amplitude that the reaction vessel has while mounted on the on mill during the grinding process. 5. Reaction vessel (1) according to claim 4, characterized in that the length of the flat surface / roller is from 10 mm to 20 mm. 6. Reaction vessel (1) according to claim 4, characterized in that the width b of the flat transparent surface is from 3 to 10 mm. 7. The reaction vessel (1) according to claim 1, characterized by the fact that in the embodiments when the excitation laser beam is focused at a certain distance from the top of the laser probe, the wall thickness d of the reaction vessel at the point where the reaction vessel has a flat surface (2) is smaller than that certain distances of the focus of the laser beam from the tip of the laser probe. 8. Reaction vessel (1) according to any patent claim from 1 to 4, characterized in that it is for in-situ recording of Raman spectra of samples during the grinding process on vibrating ball mills. 9. A method of collecting Raman spectra of the reaction mixture during the grinding process and without interrupting the grinding process using a reaction vessel (1) according to claim 1, characterized in that the reaction vessel (1) is mounted on a vibrating ball mill so that it is a flat transparent surface (2) of the reaction vessel in the horizontal plane and facing downwards and where the laser probe is placed under the reaction vessel in such a way that the excitation laser beam enters the reaction vessel vertically through its flat surface (2) and the Raman scattered radiation is collected so that it exits the reaction vessel through the same flat surface (2).