FR2885413A1 - Liquid substance e.g. chemical composition, crystallization temperature measuring method for use in distilling column, involves cooling substance using refrigerant coil and another refrigerant unit for accelerating cooling of substance - Google Patents

Abstract

The method involves cooling a liquid substance using a refrigerant coil (14) and another refrigerant unit to accelerate cooling of the substance. The substance is then cooled using the coil until the start of crystallization and a characteristic temperature of the substance is detected by finding a singular point of a swing curve of the temperature by a sensor. The coil operation is stopped after the detection stage to heat the substance after a delay. A crystallization temperature of the substance is determined by changing a characteristic temperature corresponding to a point of the curve. An independent claim is also included for a device for measuring a crystallization temperature of a liquid substance.

Description

Method and device for measuring the crystallization temperature

  The present invention relates to a method and a device for characterizing a substance by measuring the crystallization temperature. The invention relates more particularly to a device for semi-continuously measuring the crystallization temperature of a partially or totally purified chemical compound.

  Crystallization temperature is a commonly used parameter for product characterization. It is significantly modified by the impurities contained in a body and thus gives a relevant indication of its degree of purity.

  The measuring devices existing in the prior art are static laboratory apparatus requiring sample taking and manipulative work to perform a measurement outside the production line. They have many disadvantages such as packaging problems, destruction of the sample, the discontinuity of the measurement, the late reactivity on the manufacturing process.

  US Pat. No. 4,024,753 discloses a method and equipment for continuous and automated analysis of the crystallization point of liquid substances. This complex method requires pressure measurements, the use of an isomorphous crystalline body and mainly concerns relatively volatile petroleum products. It is applicable for substances whose crystallization temperature varies between -30 C and the ambient temperature. This method can not be extended to other areas.

  It is also known from US Pat. No. 4,383,770 an instrument for determining the freezing point of a liquid on a road. This instrument comprises means for cooling the collected liquid as well as means for heating this liquid. The instrument is used to cool the liquid sample until a solid forms and then warm the sample. During this operation, a temperature probe gives the temperature variations from which the freezing point of the collected liquid can be determined. Such an instrument may be accurate but requires a sampling and is primarily intended for measuring the freezing temperature of salt water or rainwater, in order to know whether to salt a when the ambient temperature is likely to reach less than 0 ° C. The heating and cooling means are not suitable for other uses, especially for a wider temperature range.

  No. 4,601,587 describes a process for determining the crystallization temperature that is unsuitable for industrial use, in which the temperature is not measured continuously. Above all, this type of process does not offer a precision of measuring the crystallization temperature.

  The patent application WO 03/083462 (or FR 2 837 925) of the same applicant proposes a method for measuring the crystallization and melting temperatures completely automatically, directly on the production line, without sampling and so semicontinuous. However, this method does not prevent certain measurement inaccuracies, due in particular to the supercooling phenomenon.

  The present invention therefore aims to overcome the disadvantages of the prior art by providing a method for measuring the crystallization temperature with high accuracy, to cause crystallization repeatedly and is adapted to industrial requirements.

  This object is achieved by a process for the characterization of a substance by semi-continuous measurement of its crystallization temperature, comprising a stirring step in a first envelope of the substance to be characterized, in liquid form, and a measurement step in continuous temperature of the substance to be characterized using at least a first thermal sensor placed inside the first envelope, the first sensor being connected to an acquisition system reporting the evolution of the measured temperature as a function of time, the method characterized in that it further comprises: a first step of cooling the substance by respective actuation of the first coolant-type cooling means provided within the first envelope; so as to generate at least one crystallized substance initiation film, and second refrigerant type cooling means dispersed from said substance only by a wall of the first envelope, intended to accelerate the cooling of the substance, the temperature of the first and second cooling means being lower than the crystallization temperature of said substance, a second cooling step from the substance using only the first cooling means to the beginning of mass crystallization, - a step of detecting a first characteristic temperature during the second cooling step by determining a singular point of the curve of evolution of the temperature measured as a function of time by the first thermal sensor which is arranged at a determined distance from the first cooling means, - a step of stopping the first cooling means following said detection step, followed after a given time delay a step of heating said substance, step of determining the crystallization temperature of the substance during the time delay by reading a second characteristic temperature corresponding to a peak of the temperature evolution curve measured as a function of time by the first thermal sensor.

  Thus, the invention advantageously makes it possible to rapidly cool the substance in a first step and then to cool it more slowly, so as to make the evaluation of the crystallization temperature very accurate.

  In addition, several cycles of evaluation of this temperature can be carried out consecutively, by automatic control of the heating or cooling of the product.

  According to another feature, the method comprises an analysis of the profile of the temperature versus time curve which is performed on a computer or a microprocessor comprising a memory for the digital acquisition of the measurements provided by the first thermal sensor.

  According to another particularity, the singular point corresponding to the first characteristic temperature is detected during a positive evolution io the temperature measured by the first sensor.

  According to another feature, the actuation of the first cooling means comprises the opening of at least one valve for circulating a cooling fluid in at least one coil and the actuation of the second cooling means comprises the opening of at least one least one valve for circulating a refrigerant in a second envelope surrounding the first envelope.

  According to another feature, the step of stopping the first cooling means comprises closing at least one valve to stop the circulation of a refrigerant, the heating step being performed by circulating a heating fluid in the second envelope.

  According to another feature, the heating step is carried out until a temperature threshold is reached for a temperature measured by a second thermal sensor at a reduced distance from the first cooling means, this reduced distance being from order of less than 5 mm and less than the determined distance provided for the first thermal sensor, the heating step then being stopped to prevent the disappearance of the crystallized substance initiation film.

  Thus, the invention makes it possible to repeat a cycle of evaluation of the crystallization temperature of the substance to be characterized, avoiding overheating in order to maintain a crystallized substance initiation film formed on the outside of the coil of the first cooling means.

  According to another particularity, the process comprises beforehand, before the first cooling step, a step of introducing the substance into the first envelope and a step of heating the substance to a temperature greater than the crystallization temperature of said substance , the introduction step using at least one valve of a set of pneumatic valves for circulation of the substance by suction.

  Another object of the invention is to provide an apparatus for accurately and automatically measuring semi-continuously the crystallization temperature of a substance to be characterized.

  o For this purpose, the invention relates to a device for semicontinuously measuring the crystallization temperature of a liquid substance to be characterized, comprising: - a double envelope assembly for receiving in a first envelope said substance, a second envelope surrounding the first casing for receiving a cooling fluid or a heating fluid, - means for controlling the passage from heating to cooling the substance, for circulating a fluid in the second casing, - at least a first thermal sensor placed inside. of the first envelope, the first sensor being connected to an acquisition system reporting the evolution of the measured temperature as a function of time, characterized in that it comprises cooling means, of refrigerant coil type, provided for the interior of the first envelope so as to generate at least one crystallized substance initiation film e, and in that the control means are connected to the acquisition system, the acquisition system operating as a function of the temperature measured by the first sensor said control means for controlling: - the circulation of a refrigerant in the cooling means and the circulation of a refrigerant fluid in the second envelope as long as a first target temperature higher than the crystallization temperature of said substance is not reached; and - only the circulation of a refrigerant in the cooling means when the temperature measured by the first sensor becomes lower than said first set temperature; the acquisition system being provided with means for evaluating the temperatures measured by the first sensor to detect the start of mass crystallization of the substance.

  According to another particularity, the first sensor is disposed at a determined distance from the cooling means, the acquisition system being arranged to actuate, via said control means, the stopping of the cooling means during mass crystallization and then actuating after a delay determined via the control means a circulation of a heating fluid in the second envelope.

  According to another feature, the device according to the invention comprises a connection between the first sensor and a memory of a central unit provided in the acquisition system, said memory storing in the form of data the measurements of said sensor, a software of exploitation of these data using means for calculating the central unit for repeatedly evaluating the temperature difference in the same time interval, said central unit being connected to said control means for stopping the cooling means after the detection by said calculating means of a first characteristic temperature corresponding to the beginning of mass crystallization of the substance in the first envelope.

  According to another particularity, the central unit comprises at least one output to a digital / analog converter followed by a conditioner for producing an image output signal of one of the measured characteristic temperatures.

  According to another particularity, the control means comprise an actuator of solenoid valves.

  According to another feature, the device according to the invention comprises a set of at least two pneumatic valves allowing both the introduction into the first envelope and the evacuation of the substance.

  According to another feature, the jacketed assembly comprises a rotatable member mounted on a rotor, the movable member having two magnetic elements secured to the rotor, said assembly being associated with a magnetic drive apparatus having a plurality of separate magnets distributed around an axis parallel to the axis of rotation of the movable member.

  According to another feature, the acquisition system is also connected to a second sensor and arranged to actuate via the control means a circulation of a heating fluid in the second envelope and stop the circulation of warming fluid in the second envelope as soon as possible. that the temperature measured by the second sensor reaches a second set temperature higher than the crystallization temperature.

  The invention also relates to a use of the device for controlling a unitary separation / purification operation or a process resulting in the formation of a relatively pure product, via the exploitation of crystallization determined by said device.

  This objective is achieved by a use of the device according to the invention, characterized in that the device, installed directly on a production line, serves to control and optimize a synthesis unit or separation / purification of the product to be characterized such that a distillation column.

  The invention, with its features and advantages, will emerge more clearly on reading the description given with reference to the accompanying drawings in which: - Figure 1 shows a schematic view of an embodiment of the device according to the invention; FIG. 2 shows an arrangement used according to the invention of the sensors around the coil; - Figures 3A and 3B respectively show a side view and a top view of a device according to the invention connected to a pipe; FIG. 4 represents an example of a cyclic process according to the invention making it possible to evaluate, in particular, the crystallization temperature of the substance to be characterized; FIG. 5 shows the presence on the coil of a crystallized substance initiation film; FIG. 6 illustrates the evolution of the temperature measured by the first sensor as a function of the steps of the method according to the invention.

  The invention will now be described with reference to FIG. 1. By way of example, the valves (EV2, EV3, EV4, EV5, EV6, EV7) used to regulate the circulation of heat transfer fluids and the circulation of heating fluid can be solenoid valves.

  The device (1) illustrated in FIG. 1 allows the semi-continuous measurement of the crystallization temperature (TC) of a liquid substance to be characterized introduced into a jacketed assembly (A, B). This assembly is intended to receive in a first envelope (A) the substance, while the second envelope (B) surrounding the first envelope (A) can receive a cooling fluid or a heating fluid. The assembly is therefore equipped with pipe connection members. The capacity of the first envelope may be about 500 ml to receive a sufficient volume of substance sample to be characterized.

  A multi-valve system (EV2, EV3, EV4, EV5, EV6, EV7) is controlled for example by an actuator. The control means (5) of the device (1) including such an actuator make it possible to control the passage from heating to cooling of the substance, in particular by triggering or stopping the circulation of a fluid in the second envelope (B). The measuring device (1) according to the invention further comprises refrigerant-type cooling coil means (14). A coil (14) is provided inside the first envelope (A) so as to generate at least one initiating film (F) of crystallized substance, by cooling effect of the outer walls of the coil (14). The presence of such a film (F) of crystallized product makes it possible to initiate the crystallization phase without wasting time because of the frequent phenomena of supercooling. This coil (14) conveying water or other coolant dives into the mass of substance to be characterized. The advantage of the coil (14) is to provide a slow cooling, to avoid triggering a mass crystallization, detrimental to the quality of the measurement.

  To ensure the measurement of the crystallization temperature (TC), at least a first thermal sensor (10) is placed inside the first envelope (A) and connected to an acquisition system (3) reporting the evolution the measured temperature as a function of time. The thermal sensor (10) is for example a temperature probe with transmitter. The analog or digital signal delivered by the transmitter is fed to the acquisition system of the system measurements (3). In the example of FIG. 1, three probes of type Ptl 00 class A make it possible to control the temperature inside the first envelope (A) as well as an analysis of the temperature changes. Two separate first sensors (10, 11) can be used to measure the temperature of the mass and provide redundancy of the information. Of course, only one first sensor (10) can also be used. In a preferred embodiment of the invention, another sensor (12), for example a structural probe similar to the probes forming the first sensors, controls the temperature near the coil (14).

  The fact of using a cooling coil (14) and being able to control the temperature in its vicinity makes it possible to guarantee the presence of a primer necessary to repeatedly cause the crystallization of the sample and to limit the phenomenon of supercooling and its influences on the quality of the measurement. It has indeed been found that, for the same operating conditions, it is possible to observe a significant error caused by the substantial supercooling when the crystallization is not initiated, the error being greater than a degree Celsius in the case, for example, of a phenol derivative.

  Referring to Figure 1, the inlet (21) of the coil (14) is connected to a valve (EV4) actuated by the control means (5) to trigger or not the refrigerant circulation whose temperature is much lower at the expected temperature of crystallization of the substance. The flow rate in the coil (14) is low and can be of the order of 25 dm3lh of liquid (for example cold water at 20 C at most, aqueous solution, methanol, organic liquid). The coolant fluid said coolant can also be a gas. More generally, the volume flow rate can be variable and determined by the dimensioning of the device (1). The output (22) of the coil (14) is for example connected to a connection connection with two separate valves (EV5, EV6). In the example of Figure 1, the coolant exiting the coil (14) is directed either to the double jacket assembly to fill the second envelope (B) or to a discharge outlet (40) (sewer). ), or to its source (recycling).

  With reference to FIGS. 2 and 5, the first thermal sensor (10) for measuring the crystallization temperature is arranged at a determined distance (d1) from the coil-type cooling means (14), this distance (dl) to be sufficient to not disturb the quality of the measurement. On the other hand, a second thermal sensor (12) is arranged at a reduced distance (d2) from the coil (14), for example to less than 5 mm so as to control heating steps of the substance, in particular to make it possible to repeat cycles of measuring the crystallization temperature without overheating, so as not to remove the priming film (F) generated on the outer surface of the coil (14).

  The acquisition system (3) is connected to the control means (5) and actuates the latter, as a function of the temperature measured by the first sensor (10). The measuring principle consists, after removal of the liquid sample, to force its crystallization by cooling by raising the temperature curve of the agitated mass in the first envelope (A). The determination of the crystallization temperature is done by analysis of the temperature profile which is recorded. The sample can then be warmed and melted for subsequent sampling.

  It will be understood that the acquisition system (3) initially makes it possible to initiate the circulation of a refrigerant fluid in both the coil (14) and the second casing (B) in order to lower the temperature of the mass of substance present in the first envelope t0 (A). The refrigerant circulation is thus ensured by opening the circulation valves (EV4, EV5, EV7) corresponding to the circuit starting from the source (Si) of heat transfer fluid, successively passing through the coil (14) and the second envelope (B), then opening towards the exit (40) of rejection. This first cooling circuit is operated via the control means (5) as long as a first set temperature higher than the crystallization temperature of said substance is not reached. It is the first sensor (10) that measures this temperature. By way of example for a phenol derivative having a crystallization temperature of 49-50 ° C., the first set temperature may be about 60 ° C.

  The acquisition system (3) then makes it possible to circulate the cooling fluid only in the coil (14), the temperature of the mass of substance measured by the first sensor (10) then being greater than or equal to the crystallization temperature and less than the first set temperature. For this, the control means (5) actuate the closure of the valve (EV5) located between the outlet (22) of the coil (14) and the second shell (B) and the opening of the valve (EV6) arranged between the outlet (22) of the coil (14) and the outlet (40) of rejection. According to this second cooling circuit, only the coil (14) is crossed.

  The acquisition system (3) is provided with means for evaluating the temperatures measured by the first sensor (10) to detect the start of mass crystallization of the substance which occurs during cooling by the single coil (14) . The acquisition system (3) of the device (1) according to the invention is arranged to actuate via said control means (5) stopping the cooling means (14) during mass crystallization. The acquisition system (3) also ensures, after a determined delay (600) for determining the crystallization temperature, the actuation via the control means (5) of a circulation of a heating fluid in the second envelope (B). In other words, a few moments after the detection of the crystallization, the system (3) automatically activates the control means (5), for example a logic actuator, to open the valves (EV2 EV3) of the assembly. double jacket (A, B), so that a circulation of the hot fluid is allowed in the second envelope (B). For example, the refrigerant circulation is temporarily stopped as soon as a first characteristic temperature (TO) representative of a start of crystallization and during the time delay (600) is detected, so as not to disturb the measurement during the crystallization stage. , but then resumes after reopening of the valve (EV4) at the outlet of the heat transfer fluid source (SI). The heating circuit starts from a source (S2) of hot fluid such as a gas or water vapor (steam heating 3 bars), having for example a temperature of 150 C for crystallization at about 50 C a phenol derivative.

  A link between the first sensor (10) and a memory (32) of a central unit provided in the acquisition system (3) and provided to allow said memory (32) to store as data the measurements of the first sensor (10). In one embodiment of the invention, a software for exploiting these data implementing means for calculating the central unit makes it possible to evaluate the difference in temperature repeatedly over a same time interval. The central unit can be connected to the control means (5) to stop the cooling in the coil (14) after the detection by said calculating means of the first characteristic temperature (TO) which is detected by a positive evolution of the temperature during cooling by the single coil (14). This first characteristic temperature (TO) is the crystallization start temperature and can not be considered as the desired value for the crystallization temperature because the product is supercooled at this time of the process. The detection of this temperature (TO) is advantageously used to completely stop the cooling.

  The central unit includes at least one output to a digital-to-analog converter followed by a conditioner for producing an image output signal of one of the measured characteristic temperatures. The acquisition system (3) can be provided with display means for presenting on a graph the evolution curve of the measured temperature. In one embodiment of the invention, the acquisition system (3) is provided with an operating software that allows the programming of the measurement modes. In a variant of the invention, the acquisition of the output temperature data is performed digitally via a fieldbus. The system (3) may be a simple automaton, having at least one microprocessor whose calculation means make it possible to obtain in particular the crystallization temperature.

  With reference to FIGS. 3A and 3B, the measuring device (1) is for example equipped with a double-envelope type tank (A, B). Two optional borosilicate portholes (51, 52) associated with PTFE seals or the like provide visual control of the substance sample to be characterized. The device (1) can be installed in branch on a pipe (5) in a preferred embodiment but not limited to the invention. The process fluid containing the product to be characterized flows in said pipe (5) and is sampled occasionally in the tank during a forced flow operation of a sample by pressure difference. The device according to the invention is for example devoid of pumping device and uses the line flow as motive power. In the piping collection sleeve (5), an upwardly curved tube (510) serves as a collection pipe while another downwardly curved tube (520) serves to empty the tank. These curved tubes (510, 520) spaced apart from each other generate a pressure difference between their ends, which forces the flow. The opening, with stirring, for about 90 seconds of the filling and emptying pneumatic valves (V1, V10) ensures complete rinsing and the preparation for the following analysis. The device (1) comprises a set of at least two pneumatic valves (V1, V10) allowing both the introduction into the first envelope (A) and the evacuation of the substance, by suction.

  The double jacket assembly (A, B) comprises a movable member (15) in rotation mounted on a rotor. This movable member (15) comprises for example two magnetic elements made integral with the rotor. The assembly is associated with a magnetic drive apparatus (4) having a plurality of distinct magnets distributed around an axis (7) parallel to the axis of rotation of the movable member (15). In the embodiment of FIG. 3A, the tank is thus agitated by means of a movable member (15) composed of 2 magnetized bars mounted on a rotor. The magnetic drive is provided by a disc provided with four magnets in line with the four poles of said movable member (15). The stirring speed commonly used is of the order of 250 rpm. The choice of materials and magnetic technology ensure extreme durability of the parts in friction, a complete waterproofness and a total absence of maintenance. Stirring is maintained during all phases of the measurement.

  In one embodiment of the invention, the acquisition system (3) makes it possible to actuate via the control means (5) a circulation of a heating fluid in the second envelope (B) and to stop the circulation of fluid in the second envelope (B) as soon as the temperature measured by the second sensor (12) reaches a second setpoint temperature higher than the crystallization temperature. This second setpoint temperature may be substantially equal to the first setpoint temperature since the goal is to maintain a range of temperature range sufficiently limited that the cooling generated by the coil (14) can maintain the presence of the priming film (F), as shown in Figure 5.

  The method of characterization by semi-continuous measurement of the crystallization temperature of a substance will now be described in connection with FIGS. 1 and 4.

  By taking the non-limiting example of a phenol derivative (the process being suitable for any crystallization temperature range), the double-jacketed assembly is pre-started with a heating of the apparatus until a temperature above the crystallization temperature, for example 80 C, and start stirring at 250 rpm.

  The sampling can then begin during an introduction step (6) using at least one valve of a set of pneumatic valves (V1, V10, FIGS. 3A and 3B) for circulation of the substance by suction, with the opening of these product valves for 90 seconds combined with the triggering of a circulation of cold water in the coil (14). Stirring of the liquid substance can be increased to 820 rpm, for example. This step (6) of introducing the substance into the first envelope (A) and the step (60) of heating the substance are each controlled by means of the acquisition system (3) which triggers the means of control for opening the pneumatic valves (V1, V10) and the valves (EV2, EV3) for hot fluid circulation from the source (S2) of hot fluid.

  Thus, the lowering of the temperature begins immediately after the introduction of the sample into the first envelope (A). With reference to FIG. 4, a first cooling step (61) of the substance is carried out with the actuation of two separate cooling means, on the one hand the cooling fluid coil (14), and on the other hand means of cooling. cooling of the coolant type separated from said substance only by a wall (100) of the first envelope (A). These cooling means formed by the second envelope (B) or similar cooling means can accelerate the cooling of the substance to a temperature of the order of 60 C, the stirring can be maintained (820 tr / min).

  When the temperature measured by the first sensor (10) falls below this first setpoint temperature, a second cooling step (62) of the substance using the single coil (14) takes place until the onset of crystallization. in mass (exothermicity).

  This cooling is slower (coil only) and vigorous agitation. (820 rpm) is maintained.

  The method according to the invention then comprises a step (63) for detecting a first characteristic temperature (TO) produced during the second cooling step (62). The detection is carried out by determining a singular point of the curve of evolution of the temperature measured as a function of time by the first thermal sensor (10), for example by detecting a positive evolution of the curve despite the cooling by the single coil (14). In one embodiment of the invention, an analysis of the profile of the temperature curve as a function of time is performed on a computer or a microprocessor, belonging for example to the acquisition system (3) and comprising a memory (32) for the digital acquisition of the measurements provided by the first thermal sensor (10). As soon as the beginning of crystallization is detected (detection of the first characteristic temperature), the acquisition system (3) triggers, via the control means (5), a step (64) for stopping the cooling by the coil ( 14). A time delay (600) of a definite duration can be performed while crystallization of the mass continues. During this time delay (600), a control of the accuracy of the evaluation of the crystallization temperature (TC) can be carried out, the crystallization point being measured with less vigorous stirring (250 rpm), in the absence of cooling.

  After the delay (600) which lasts about 5 minutes to validate the temperature profile, a step (65) for heating the substance is performed via a hot fluid passing through the second envelope (B). This heating, for example with steam (150 C) simultaneously with a circulation of water (25 I / h) in the coil for control priming film, is stopped when the temperature measured in the vicinity of the coil by the second sensor ( 12) reaches the second setpoint temperature. A new cycle can then begin with a new sampling (the substance remained liquid being evacuated and replaced). The step (6) of introduction of the substance is therefore repeated and again followed by rapid cooling, as shown in FIG.

  With reference to FIG. 6, an increase in the temperature of the mass measured by the first sensor (10) is observed after the step (63) of detecting the first characteristic temperature (TO) because of the exothermic nature of the crystallization . When the measured temperature begins to decrease again (presence of a peak), said timer (600) can be triggered. The timer (600) therefore starts at the moment when the determination of the crystallization temperature (TC) can be carried out most accurately. At the end of the timer (600), the maximum value recorded during the phase of low temperature evolution (offset) may be selected to correspond to the desired value of the crystallization temperature (TC) of the substance. In one embodiment of the invention, if a new summum is detected (other than the first summum), then the current timing value is reset. This ensures that the measured value (TC) corresponds to the desired peak.

  An example of an industrial application of the invention is a use for a distillation process with a continuous feed. In one embodiment of the invention, the acquisition system (3), via the microprocessor of the central unit, for example delivers a normalized signal to an actuator to enable the process to be carried out. It is possible to add to the device according to the invention (1) a regulator for conducting the distillation process. In the case of a distillation column, obtaining the characteristic crystallization temperature makes it possible, in addition to controlling the product, to regulate the reflux ratio of the column. The quality of the distillate containing the product to be characterized can be accurately determined using the device (1). The exploitation of the difference between the characteristic temperature obtained with the device (1) of the invention compared to the expected temperatures for the pure product makes it possible to know, for example by means of a graphical method using abacuses or correspondence tables, the level of impurities in the distillate. So; when for example the crystallization temperature determined by the device (1) becomes too low, reflecting the increase in the level of impurities in the distillate, the distillate flow rate can be decreased by means of a regulator connected to the device (1 ) and a control valve, so as to readjust the reflux ratio.

  One of the advantages of the device (1) according to the invention is to respond in a simple manner to the need to regularly control the purity of a product resulting from a process, by providing precise control of the crystallization temperature and by making it possible to repeat measurement cycles in a particularly reliable manner. The type of control provided by the measuring device (1) in practice eliminates the risk of error related to the supercooling phenomenon.

  It should be obvious to those skilled in the art that the present invention allows embodiments in many other specific forms without departing from the scope of the invention as claimed.

Claims (16)

  A method of characterizing a substance by semi-continuous measurement of its crystallization temperature, comprising a step of stirring in a first envelope (A) of the substance to be characterized, in liquid form, and a step of continuous measurement of the temperature of the substance to be characterized by means of at least a first heat sensor (10) placed inside the first envelope (A), the first sensor (10) being connected to an acquisition system (3) ) reporting the evolution of the measured temperature as a function of time, characterized in that it further comprises: - a first step (61) of cooling the substance by respective actuation of first cooling means, of serpentine type ( 14), provided inside the first envelope (A) so as to generate at least one initiating film (F) of crystallized substance, and second fluid-type cooling means refrigerant separated from said substance only by a wall (100) of the first casing (A), provided to accelerate the cooling of the substance, the temperature of the first and second cooling means (14, B) being lower than the temperature of the crystallisation of said substance; second substance cooling step (62) using only the first cooling means (14) until the start of mass crystallization; a step (63) of detecting a first temperature. characteristic (TO) during the second cooling step (62) by determining a singular point of the temperature evolution curve measured as a function of time by the first thermal sensor (10) which is arranged at a determined distance (d1) first cooling means (14), - a step (64) for stopping the first cooling means following said detection step, followed after a first time determined poring (600) of a step (65) for heating said substance, - a step of determining the crystallization temperature (TC) of the substance during the time delay (600) by reading a second characteristic temperature corresponding to a peak of the temperature evolution curve measured as a function of time by the first thermal sensor (10).   The method of claim 1, including analyzing the profile of the temperature versus time curve that is performed on a computer or microprocessor including a memory (32) for digitally acquiring measurements provided by the first sensor. thermal (10).   3. Method according to claim 1 or 2, wherein the singular point corresponding to the first characteristic temperature (TO) is detected during a positive evolution the temperature measured by the first sensor (10).   4. Method according to one of claims 1 to 3, wherein the actuation of the first cooling means comprises opening at least one valve for circulating a refrigerant in at least one coil (14) and the actuation of second cooling means comprises opening at least one valve for circulating a refrigerant in a second envelope (B) surrounding the first envelope (A).   5. Method according to claim 4, wherein the step (64) for stopping the first cooling means (14) comprises closing at least one valve (EV4) to stop the circulation of a refrigerant, the heating step (65) being performed by circulation of a heating fluid in the second envelope (B).   6. Method according to one of claims 1 to 5, wherein the step (65) of heating is carried out until a temperature threshold is reached for a temperature measured by a second heat sensor (12) at a distance reduced (d2) first cooling means (14), this reduced distance (d2) being of the order of less than 5 mm and less than the determined distance (dl) provided for the first thermal sensor (10), the heating step (65) is then stopped to prevent the disappearance of the crystallization substance initiation film (F).   7. Method according to one of claims 1 to 6, comprising beforehand, before the first step (61) cooling, a step (6) of introducing the substance into the first envelope (A) and a step (60) of heating the substance at a temperature above the crystallization temperature of said substance, the introduction step (6) using at least one valve of a set of pneumatic valves (V1, V10) for circulation of the substance by suction .   8. Device (1) for semi-continuous measurement of the crystallization temperature (TC) of a liquid substance to be characterized, comprising: a double envelope assembly (A, B) for receiving in a first envelope (A) said substance, a second envelope (B) surrounding the first envelope (A) for receiving a cooling fluid or a heating fluid, - control means (5) for the passage of heating to cooling of the substance, for circulating a fluid in the second envelope (B), - at least one first thermal sensor (10) placed inside the first envelope (A), the first sensor (10) being connected to an acquisition system (3) reporting the evolution of the temperature measured as a function of time, characterized in that it comprises cooling means, of the cooling fluid coil type (14), provided inside the first envelope (A) so as to generate at minus a boot film age (F) of crystallized substance, and in that the control means (5) are connected to the acquisition system (3), the acquisition system (3) operating as a function of the temperature measured by the first sensor ( 10) said control means (5) for controlling: - the circulation of a refrigerant in the cooling means (14) and the circulation of a refrigerant in the second shell (B) as a first temperature of setpoint greater than the crystallization temperature of said substance is not reached; and - only the circulation of a refrigerant in the cooling means (14) when the temperature measured by the first sensor (10) becomes lower than said first set temperature; the acquisition system (3) being provided with means for evaluating the temperatures measured by the first sensor (10) to detect the start of mass crystallization of the substance.   9. Device (1) according to claim 8, wherein the first sensor (10) is disposed at a determined distance (dl) cooling means (14), the acquisition system (3) being arranged to operate via said control means (5) stopping the cooling means (14) during mass crystallization and then actuating, after a time delay determined via the control means (5), a circulation of a heating fluid in the second envelope (B) .   10. Device (1) according to claim 8 or 9, comprising a connection between the first sensor (10) and a memory (32) of a central unit provided in the acquisition system (3), said memory (32) storing, in the form of data, the measurements of said sensor (10), a software for exploiting these data implementing means for calculating the central unit for repeatedly evaluating, in the same time interval, the difference in temperature, said central unit being connected to said control means (5) for stopping the cooling means after detection by said calculating means of a first characteristic temperature (TO) corresponding to the beginning of mass crystallization of the substance in the first envelope ( AT).   11. Device (1) according to one of claims 8 to 10, wherein the central unit comprises at least one output to a digital / analog converter followed by a conditioner for producing an image output signal of one of the characteristic temperatures measured .   12. Device (1) according to one of claims 8 to 11, wherein the control means (5) comprise an actuator solenoid valves.   13. Device (1) according to one of claims 8 to 12, comprising a set of at least two pneumatic valves (V1, V10) for both the introduction into the first envelope (A) and the evacuation of the substance, by aspiration.   14. Device (1) according to one of claims 8 to 13, wherein the double-jacketed assembly (A, B) comprises a movable member (15) in rotation mounted on a rotor, the movable member (15). having two magnetic elements secured to the rotor, said assembly being associated with a magnetic drive apparatus (4) having a plurality of distinct magnets distributed about an axis (7) parallel to the axis of rotation of the rotor movable member (15).   15. Device (1) according to one of claims 8 to 14, wherein the acquisition system (3) is also connected to a second sensor (12) and arranged to actuate via the control means (5) a circulation a heating fluid in the second shell (B) and stop the flow of heating fluid in the second shell (B) as soon as the temperature measured by the second sensor (12) reaches a second set temperature higher than the crystallization temperature .   16. Use of the device (1) according to any one of claims 8 to 15, characterized in that the device (1), installed directly on a production line, serves to control and optimize a synthesis unit or separation / purification of the product to be characterized, such as a distillation column.