SU787984A1 - Chromodistillation method of mixture analysis - Google Patents

Description

ISt) CHROMEDSTILATION METHOD FOR ANALYSIS OF MIXTURES

one

The invention relates to methods for analyzing liquid mixtures and can be used to determine the physicochemical characteristics of pure substances (vapor pressure, heat of evaporation, etc.) / as well as characteristics of solutions (activity coefficients, boiling temperature distribution of the components of a complex mixture), and

can be used in the chemical, petrochemical and other sectors of the national household.

A chroma-distillation method of separation and analysis of liquid mixtures is known, based on the implementation of condensation and evaporation processes on a column with an inert aggregate in a stream of carrier gas in the presence of a temperature field with a negative gradient of 20.

The disadvantage of this method is the use of detectors developed in chromatography, which are based on processes that occur outside the chromatographic column. This leads to the creation of additional nodes in the chromatograph, complicates and increases the cost of its design. thirty

Closest to the invention is a restrictive chroma-distillation variant based on the implementation of condensation processes and evaporation of a liquid mixture in a column with an inert aggregate in a gas carrier when using a preliminary, before introducing a separable mixture, applying a volatility no less than volatility of all components mixes. The recording of the separation results is carried out with a number of chromatographic detectors 2.

The disadvantage of this method is the use of additional devices not related to the processes occurring in the column. Moreover, all variants of this method do not directly transmit the number of components and require additional calibration - and processing of measurement results (determination of areas and t1d.). In some cases, the separation of components with close volatilities or in the analysis of impurities does not completely lead to chroma-distillation separation using the limiter. In this embodiment, restrictive chroma-distillation does not allow components to be tested in terms of ip temperatures. The purpose of the invention is to obtain data on the absolute content of components in the analyzed mixture without calibration and to carry out the distillation of the components at boiling points. This goal is achieved by the fact that during the analysis the change in the weight of the column with the analyzed mixture is measured. In order to obtain the distribution of the components at boiling points, the identification of fractions is carried out by measuring the evaporation rate of individual substances. FIG. 1 shows a setup for implementing the method; Fig. 2 shows the experimental curves for the change in column weight in the separation of n-alkanes (mixture 1 — signs -, mixture 2 x signs) in FIG. 3 - calibration curve; in fig. 4 and 5 are the output curve g (t) and the distillation curve for household gasoline (designation curve G l, curve 2, 3 0). The chroma distillation separation method allows the application of large amounts of the analyzed liquid mixture. This makes it possible to use column weighing to follow the process, which is not possible in conventional chromatography. Determination of dose in chroma-distilling; promotes better component separation. As a result, the mixture is divided into zones of pure substances, which sequentially leave the column at a concentration of saturated steam. In this case, significant changes in the weight of the column can occur depending on the amount of the mixture injected and its composition. If the column is weighed during the process of blowing an individual substance, then the rate of change of its weight (j) is determined by the ratios af and IT-- bVo, (1) b o is the concentration of the saturated vapor of the i-ro component (g / cm); VQ is the volume of carrier gas flow rate (),. Thus, the graph in the coordinates of g from t, reflecting the 1st results of chromium distillation separation, is represented by a series of intersecting straight lines, the slope of which is determined by the elasticity of the substance at a given temperature and velocity V. The distance between the points of intersection along the ordinate axis gives directly the amount of substance in the initial mixture. The method is carried out as follows. Experiments are carried out on the specified installation. The carrier gas (nitrogen) (see Fig. 1) from the cylinder 1 passes through the pressure regulator 2 either into the chromato-distillation column 5 or through the bypass line with the throttle 6 into the atmosphere. The throttle 6- equalizes the resistance of two parallel lines to prevent abrupt pressure changes at the inlet to the column when switching valves 4 and 7. The speed at the entrance and exit from the column is measured by rheometers 3 AND 8. The pneumatic actuator switches the valves simultaneously. The column is an i-shaped glass tube with a length of 26 cm, diameter 0.5 cm, filled with metal and balls (average diameter of 0.5 mm). The liquid sample of the restrictor is introduced, and then the analyzed mixture is produced in a separate unit with a dosing unit, where the column is placed vertically and purged with a stream of nitrogen. The filled column with the liquid mixture is weighed and connected to the appropriate fittings (with a mild installation) of the installation (see Fig. 1). Then, switching the taps 4 and 7 to purge, the section e and the mixture is blown out for some time, the column is again disconnected and weigh. Thus, take the curve g from t. In these experiments, analytical balances with a measuring accuracy of 0.001 g were used. Typical curves of g versus t when analyzing an n-alka 1 C-j-Cg mixture using the n-hexane limiter are shown in FIG. 2, The experiments were carried out at room temperature 20 ° C, the rate of nitrogen was 30 μumin per minute. The time for purging the ut column varies from 30 s to 10 min. The number of the limiter (Q ogre) is selected so that the mixture of a given composition with the amount of the mixture (Qg,) can be completely separated. In tab. 1 shows the results of the analysis of the prepared mixtures of n-alkanes Cc-C & Ct) by the proposed method.

The time of exit of the lonpejqe zones is plotted on graphs g from t of extrapolation of linear portions of the curves corresponding to the output of individual substances. The accuracy of measurements is determined by the accuracy of temperature and speed, weighting accuracy and graphic errors.

According to the proposed scheme is defined. neither the average error does not exceed +3 rel.%. Obviously, automating the measurements and carrying out continuous weighing of the column without interrupting the flow periodically can lead to improved analysis results. In order to improve the conditions for separation of the mixture along with the use of a limiter, a temperature field with a negative gradient should be used. In this case, the sharpness of the relative elasticity of the components is found by the slope of the graphs g from t. In contrast to the quantitative measurements of the composition, these data are subject to a greater influence of the parameters.

Table

conditions are improved for condensation of components at the front edge of the strip as it moves along the bed. Then you can reduce the number of the entered limiter and in a number of cases from it

5 refuse.

The proposed method allows re. shat the problem of determining the physicochemical characteristics of individual substances. So, the slope of the graphs is g from t,

0 as follows from formula (1), directly related to s.

B tab. 2 a comparison was made of the calculated and experimental research institutes of the saturated vapor pressure Pf g /

proportional concentration in Р5 H / RT, where R is gas, is constant; T is the temperature of the experiment (K); M is the molecular weight.

Claims (2)

Table 2 ditch experience. Therefore, the average measurement error is -x 10 rel.%. The weight chromatography distillation analysis method makes it relatively easy to obtain data on the distribution of the components of the complex cjviecH at boiling points. Unlike the known β-method, where calibration is carried out by the magnitude of the detector signal, in the proposed method the identification (determination of the boiling points tK.nn) is carried out by the evaporation rate dg / dt, which is connected in accordance with equation (1) the elasticity of the substance at a given temperature of gasoline distillation, obozachenna se on FIG. 5, obtained on a standard LAPS instrument, on which curves of distillation are routinely taken in laboratory practice. The advantage of the proposed method is that the output curve immediately reflects the integral characteristic of the evaporated mixture. The amount of mixture that boils between two temperatures is determined by the difference in the corresponding coordinates on the output curve. In the well-known method dp of this, it was necessary to carry out an additional integration operation. The proposed method of analysis allows, without any calibration, to directly obtain the absolute content of the components in the original cm s, this eliminates the detection system in the chromatograph, simplifies the operations required for performing the analysis, and reduces the cost of the equipment performing the analysis way. Claim 1. Chromedistillation method for ana LIS mixtures, based on tour of experience. Preliminary experiments were carried out with individual substances and a calibration graph was constructed in coordinates Eg 1 from t ,, „(Fig. 3). The distillation of domestic gasoline is carried out on the described installation with the same column. Pentane is used as a limiter (see Fig. 4 and 5). In tab. Figure 3 shows the conditions for the acceleration of domestic gasoline. Table 3 Research institutes for condensation and evaporation of a LIQUID mixture in a column with an inert filler, a current of carrier gas, in which a substance is introduced into the column by introducing its mixture into the column; the volatility of all components of the mixture is different By the fact that, in order to obtain data on the absolute content of components in the analyzed mixture without calibrating and performing the boiling of the components at boiling points, the change in the weight of the column with the analyzed mixture is measured during the analysis. 2. The method of claim 1, wherein the identification of the fractions of the mixture is carried out by measuring the rate of evaporation of individual substances. Sources of information taken into account in the examination 1. The author's certificate of the USSR 11536429, cl. From 01 N 31/08, 1974. 2. USSR author's certificate 600441, cl. G 01 N 31/08, 1976 (prototype). / J, m CTIZ Hl411 } 2 Iff f "3ff 36" 2 8 f 6O 66 7g 79 8 90 96 t yt / ff j IMSJU ( Ij one HJ ioti .. FIG. 2 4 9 n No.Wy t9ytU4e itf9tftKH M "T