Patent Application
20170173551
A subject-matter of the present invention is a high output, compact and economical catalytic screening device intended to evaluate the performances of heterogeneous catalysts.
Heterogeneous catalysis represents the branch of catalysis in which the catalyst occurs in another phase, within the thermodynamic meaning of the term, than the reactants and products of the catalysed reaction. The catalyst is typically in the solid state and catalyses a reaction in which the reactants and products are in the liquid phase or in the gas phase.
It is useful to evaluate the performance of a catalyst. In order to do this, there exist several performance criteria which can be assessed. For example, it is possible to determine the degree of conversion of a reactant, that is to say the number of moles of reactants which have reacted divided by the number of moles of this reactant initially present in the reactor (case of a closed reactor), or the ratio of the molar flow rate of this reactant which has reacted to the molar flow rate of this reactant entering the reactor (case of an open reactor), or alternatively the yield of reaction products.
Devices for evaluating the performance of heterogeneous catalysts are known in particular from the document WO 02/092219. However, these devices are sophisticated, bulky and particularly expensive.
The present invention is targeted at overcoming these disadvantages.
It provides in particular a device for evaluating at least one performance criterion of heterogeneous catalysts, comprising:
The device according to the invention additionally comprises a gas chromatograph and each reaction region is located in an injector of the chromatograph.
Thus, instead of using a laboratory reactor normally employed for the measurements of catalytic performance, the device according to the invention is based on the rerouting of the use of an injector of a gas chromatograph in order to use it as fixed bed catalytic reactor. It is thus possible to simultaneously use several injectors in parallel, which makes it possible to accelerate the catalytic tests by adopting a high output catalytic screening methodology. In addition, the device exhibits the advantage of complete reversibility of use if the user no longer desires to use it as catalytic screener but again in its original function of chromatograph.
The device preferably comprises at least two reaction regions.
Each catalyst can be in the solid state and each reactant can be in the gas state.
The performance criterion can be chosen from the degree of conversion of a reactant and the yield of reaction products.
Each reaction region is advantageously a liner of the injector.
Each liner can comprise a catalytic bed.
The device can comprise several injectors positioned in parallel.
The device can comprise a module capable of independently regulating the temperature and the pressure of each reaction region (i.e., each injector) and the feed flow rates of each reaction region.
The gas chromatograph can additionally comprise a sampling system, at least one chromatographic column and at least one detection system, in particular a detection system conventionally used in gas chromatographs, for example a flame ionization detector (FID), a thermal conductivity detector (TCD) or any other detector known to a person skilled in the art.
The device can comprise a source of carrier gas, the carrier gas being intended to dilute and transport the reactant or reactants in each reaction region.
The reactant or reactants and the carrier gas entering each reaction region can result from an evaporator, followed by a system for distributing the streams.
Another subject-matter of the invention is a process for evaluation of at least one performance criterion of heterogeneous catalysts, employing the device described above.
The process according to the invention comprises:
Another subject-matter of the invention is the use of a device described above as a catalytic screener or as a chromatograph, it being possible to use the device in a reversible manner as a catalytic screener or as a chromatograph.
Other characteristics and advantages of the present invention will become more clearly apparent on reading the following description, given by way of illustrative and nonlimiting example and made with reference to the appended drawings, in which:
The liquid methanol is introduced into an evaporator 4 according to a predetermined flow rate (for example 100 μl.min−1), the evaporator 4 being simultaneously fed with carrier gas (for example helium, using an He cylinder, at a flow rate of 160 ml.min−1) by means of a weight flow controller 5. The two compounds (gaseous helium and liquid methanol) enter the evaporator 4, which comprises a tube filled with silicon carbide, the diameter of the particles of which is, for example, 125 μm, and which is maintained at 120° C. The objective is, at this point of the device 1, to vaporize the methanol and to ensure that the gaseous reaction mixture to be distributed over the different reactors is homogeneous. By way of example, four reactors R1, R2, R3 and R4 have been represented in
The outlet of the evaporator 4 is connected to a stream distributor equipped with an inlet and four outlets, to which four tubes of fused silica, with an internal diameter equal to 0.1 mm and of a length of 40 cm, are connected, in order to generate an individual pressure drop thirty times greater than that produced by the catalytic bed (2.25×103 Pa per reactor R1, R2, R3 and R4). The pressure drop generated by this stream distributor is from approximately 9 to 10 bar.
The reaction mixture thus results from a module. The module, which will be linked immediately above the reactors R1, R2, R3 and R4, makes it possible to prepare the feed mixture which will be injected into the reactors R1, R2, R3 and R4 and to distribute it equitably between the different routes. It is possible to prepare therein a gaseous reactant mixture but also to vaporize liquids before mixing with gases and introduction into the reactors. The module is thus a kind of oven comprising evaporators, tubes, mixing regions, devices for controlling and regulating the flow rates, and heating elements, such as electrical resistances. The configuration of this module can be adjusted as a function of the reactions to be studied.
The module makes it possible in particular to regulate the temperature of each reactor R1, R2, R3 and R4 and the feed flow rates. It is also possible to control the pressure of the reaction by adding a blow-off valve at the reactor outlet. Software can ensure the control of the module, for example with inputs of temperature setpoints or of flow rates, or also the indication of true values. The regulation of the temperature can be an external control or a control provided by the chromatograph itself.
In accordance with the invention, the reactors R1, R2, R3 and R4 of the device 1 for evaluation of the performance of the catalyst are injectors of a gas chromatograph. The remainder of the chromatograph may or may not be used.
A gas chromatograph typically comprises:
The operating principle of the chromatograph is as follows. The sample (a volatile liquid or a gas) is first introduced into the injector placed at the column top via a sampler or a microsyringe which will pass through a rubber disc, known as septum, in order to be reencountered in a small chamber upstream of the column, known as insert. The carrier gas passes through the injector and the latter is brought to a temperature appropriate to the volatility of the sample.
Subsequently, once rendered volatile, the different compounds of the sample will be swept along by the carrier gas through the column and be separated from one another as a function of their affinity with the stationary phase. The stationary phase can be a non-volatile or only very slightly volatile liquid (gas-liquid chromatography) or an absorbent solid (gas-solid chromatography). In both cases, the stationary phase will bring about a phenomenon of chromatographic retention with the different compounds, known as solutes. The greater the affinity of the compound with the stationary phase, the more time it will take to exit from the column. The raw experimental quantity is known as retention time. This is the time which elapses between the injection of the sample and the appearance of the maximum signal of the solute at the detector. In order to promote the transportation of all the compounds through the column (elution), it is necessary to determine the satisfactory temperature of the oven. In general, the temperature should be slightly greater than the boiling point of the compounds, so that the compounds do not exit too soon, which would have the consequence of having their peaks mixed up with that of the dead time. It is possible to operate under isothermal conditions, that is to say with a fixed temperature throughout the analysis, or with a temperature programme which varies.
At the outlet of the column, the compounds encounter an essential component which is referred to as detector. This component continuously evaluates the amount of each of the constituents separated within the carrier gas by virtue of the measurement of different physical properties of the gas mixture. The detector sends an electronic signal to a recorder, which will draw the curves of each peak as a function of their intensities (curve of Gaussian type). The set of peaks is referred to as chromatogram.
A gas chromatograph can comprise several analytical routes, in particular from two to four, which are injector+column+detector combinations.
The injectors are housed in a metal block, the temperature of which is regulated in order to ensure good thermal homogeneity of the system. The sample will be vaporized and the solutes will pass through the injector through a glass (sometimes metal) tube, known as a liner, by virtue of the carrier gas, as far as the top of the column. The advantage of the liner is to retain the non-volatile constituents of the sample, unsuitable by nature to chromatography.
In the case of the use of the injector for the determination of catalytic performance, each liner is filled with the solid catalysts to be tested, in the powder form, and is traversed continuously by a gaseous reaction mixture.
As illustrated in
In accordance with the invention, the conventional use of a gas chromatograph is rerouted by using the liner 9 of the injector 8 as catalytic reactor Ri, (
This operation is carried out by replacing the content of the liner 9, normally mineral wool, with the catalytic bed 6 comprising the catalyst 61, as well as, for example, quartz wool 62 and silicon carbide 63, as illustrated in
The present invention is described in more detail by the following example, to which, however, it is not limited.
The dehydration of methanol to give dimethyl ether is carried out according to the following reaction:
CH3OH→CH3OCH3+H2O
Experimental Conditions
The catalyst tested is a gamma alumina γ-Al2O3 sold by Alfa Aesar.
The carrier gas is a mixture comprising 1 mol % of Kr in He, into which the methanol is evaporated in order to obtain the following molar proportions for the reaction mixture: MeOH/He/Kr: 27.4/71.9/0.7 (mol %).
The sum of the gas flow rates is 33 000 ml.h−1.g−1 at 25° C. and atmospheric pressure.
Stability of the Composition of the Reaction Mixture
Before each reaction, a series of six analyses per reactor is carried out in order to confirm the stability of the composition of the reaction mixture. The number of moles of methanol shown for each reactor in Table 1 is a mean of the six analyses:
Good stability is observed for all the reactors.
Conversion of the Methanol
The degree of conversion of the methanol, and also the relative standard deviation between the reactors for six analyses per reactor, is shown in Table 2:
It is found that the reproducibility of the degree of conversion of the methanol from one reactor to the other is excellent.
The yield of dimethyl ether for each reactor is shown in Table 3:
Good reproducibility of the catalytic performance is observed between the different reactors.
The invention thus makes it possible to obtain an economical, compact and simple device for measuring the performance of heterogeneous catalysts, in particular in the gas phase. The different injectors of the chromatograph, rerouted from their original application in order to become reactors, can be used simultaneously in parallel, which makes it possible to greatly accelerate the catalytic tests using the methodology of high output catalytic screening. The technology used in addition exhibits the advantage of complete reversibility of use if it is no longer desired to use it as catalytic screener but again in its original function of chromatograph. It is possible in addition to simultaneously test several catalysts, or just one catalyst under different operating conditions (temperature or contact time, for example). The time necessary in order to carry out the measurements of the catalytic performance of the catalysts is thus significantly reduced and the time for the development of a new heterogeneous catalyst is thus decreased.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1450923 | Feb 2014 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2015/050263 | 2/4/2015 | WO | 00 |
