JPS6044002B2 - Method for reducing non-volatile impurities in liquid during distillation operations - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reducing non-volatile impurities in a liquid during a distillation operation.

The distillation operation of distilling a liquid to obtain product liquids from the top and bottom of the column is well known.
Another well-known method is separation by evaporation, in which a liquid containing non-volatile impurities is evaporated by heating and the vapor is condensed to obtain a liquid free of non-volatile impurities.

In the present invention, when a liquid containing non-volatile impurities is distilled using a thermosiphon reboiler and product liquids are obtained from the top and bottom of the column, the above-mentioned It is possible to reduce the non-volatile impurities in the bottom product liquid at the same time as the distillation operation without separating the non-volatile impurities in the liquid by evaporation separately from the distillation operation, and also to reduce the non-volatile impurities in the liquid at the bottom of the column. The purpose is to reduce the loss of the bottom product liquid as much as possible without increasing the amount of heat.

In a distillation operation, the vapor emitted from the top of the column does not contain non-volatile impurities from the feed liquid unless mist etc. are present, so the condensate obtained by cooling this vapor and condensing it usually does not contain non-volatile impurities.

A portion of this condensate becomes a product liquid at the top of the column, and the remainder is returned to the top of the distillation column as a reflux liquid. Therefore, all of the non-volatile impurities contained in the feed liquid remain in the bottom product liquid, so the concentration of non-volatile impurities in the bottom product liquid is higher than the non-volatile impurity concentration in the feed liquid. For example, if the bottom product liquid amount is 112 times the feed liquid amount, the nonvolatile impurity concentration in the bottom product liquid will be twice the nonvolatile impurity concentration in the feed liquid. Normally, when a thermosyphon reboiler is used, the product liquid at the bottom of the column is extracted from the bottom of the distillation column. Further, a liquid with an amount of 20 to 4 times the amount evaporated in the reboiler is supplied from the bottom of the distillation column to the reboiler, is partially evaporated in the reboiler, and is returned to the bottom of the distillation column as a gas-liquid mixed phase fluid. Therefore, when the distillation column is operated under certain conditions, the concentration of non-volatile impurities in the bottom product liquid will be greater than the concentration of non-volatile impurities in the feed liquid, as described above.

In the present invention, a gas-liquid separator is installed at the outlet of the thermosiphon reboiler, and the gas-liquid multiphase fluid at the outlet of the thermosiphon reboiler is separated into vapor and liquid in this gas-liquid separator, and only the vapor is sent to the bottom of the distillation column. The liquid is returned to the thermosiphon type reboiler and is continuously or intermittently drawn out in small amounts separately.

The amount of liquid supplied from the bottom of the distillation column to the thermosiphon reboiler is approximately the same amount as the amount of evaporation within the thermosiphon reboiler, and the steam generated in the reboiler is the liquid that circulates through the thermosiphon reboiler and the gas-liquid separator. It also enters a gas-liquid separator where the vapor is separated and returned to the bottom of the distillation column.

Therefore, in the case of a normal thermosiphon reboiler,
Distillation column bottom liquid of 20 to 4 times the amount of liquid evaporated in the reboiler is supplied from the bottom of the distillation column to the thermosiphon reboiler, and the same amount of gas-liquid multiphase fluid is supplied from the thermosyphon reboiler to the distillation column. However, in the method of the present invention, it is returned to the bottom of the tower. In the method, the bottom liquid in an amount approximately equal to the amount evaporated in the reboiler is supplied to the thermosiphon reboiler together with the liquid that circulates through the gas-liquid separator and the reboiler, that is, 20 to 4 times the amount of liquid that evaporates in the reboiler. The bottom of the distillation column is filled with steam evaporated by the reboiler. Only the Qi will be returned. The steam returned to the bottom of the distillation column does not contain non-volatile impurities unless it is mixed with mist, so the non-volatile impurities contained in the liquid supplied from the bottom of the distillation column to the thermosyphon reboiler are gas-liquid. It will remain in the circulating fluid separated in the separator.

Therefore, the amount of non-volatile impurities in the liquid circulating through the thermosyphon reboiler and gas-liquid separator increases over time. The concentration of non-volatile impurities in this circulating fluid must be kept lower than the concentration at which non-volatile impurities precipitate from the circulating fluid. It is necessary to extract small amounts separately. By increasing the concentration of non-volatile impurities in the liquid to be extracted to a level close to the concentration at which non-volatile impurities precipitate from the liquid, the amount of liquid to be extracted can be reduced to a very small amount, and product loss can be prevented as much as possible. , it becomes possible to minimize the amount of heat carried away by this extraction liquid. For example, the amount of liquid fed to the distillation column is 2 O/Hr, the heavy metal concentration is 5 ppm (weight), and the bottom product liquid is 12
．． 5T/Hr and the bottom liquid supplied from the bottom of the distillation column to the thermosiphon reboiler is 39T/Hr, the heavy metal concentration in the bottom product liquid is 2.5 ppm (weight).
and halved.

The amount of liquid circulating through the thermosyphon type reboiler and the gas-liquid separator is, for example, 3 of the amount of evaporated liquid in the reboiler of 39T/Hr.
It is 1170T/Hr of Hao, but if the heavy metal concentration of this circulating fluid is 10000ppm, it is 9.75kg/Hr.
All you have to do is draw out the r circulating fluid. This withdrawal amount is only 0.078% of the product liquid at the bottom of the column, resulting in a very small amount of product loss. In the above explanation, it has been described that the product is obtained from the top and bottom of the distillation column, but as is clear from the above explanation, the liquid obtained from the top and bottom of the column does not necessarily have to be a product, but rather It may also be something that is used cyclically within the organization.

In addition, although it has been explained that there is no mist etc. in the steam separated in the gas-liquid separator installed at the outlet of the thermosyphon type reboiler, the concentration of non-volatile impurities in the circulating fluid is extremely high, so It is necessary to prevent mist etc. from entering inside as much as possible. For this reason, if necessary, a mist separator or the like must be installed. As described above, the present invention converts the circulating liquid of the thermosiphon reboiler and the gas-liquid separator installed at its outlet into a concentrated liquid of non-volatile impurities, and performs distillation by extracting a small amount of this concentrated liquid. This method reduces non-volatile impurities in the product liquid that is extracted directly from the bottom of the tower, making it possible to minimize product loss without increasing the amount of heat supplied to the reboiler for evaporation.

The present invention will be explained below with reference to the drawings.

Although FIG. 1 is a process explanatory diagram showing one embodiment of the method of the present invention, the present invention is not limited thereby. A liquid containing non-volatile impurities is supplied to a distillation column 2 through a line 1, and an overhead vapor free of non-volatile impurities is supplied to a condenser 4 through a sheath 3, where it is condensed.

This condensate is taken out through line 5, a part of which is taken out through line 6 as an overhead product liquid containing no non-volatile impurities, and the remainder is returned to the distillation column 2 through line 7 as a reflux liquid. The non-volatile impurities contained in the feed liquid in line 1 remain in the bottom liquid of total distillation column 2.

This column bottom liquid is withdrawn as a column bottom product liquid through line 8, and at the same time, approximately the same amount of liquid as the amount of evaporation in thermosiphon reboiler 9 is supplied to thermosyphon reboiler 9 through line 10. The bottom liquid is sent to the thermosyphon reboiler through line 10 and gas-liquid separator 1.
Most of the liquid separated in step 1 and withdrawn from the gas-liquid separator through line 12 is supplied through line 13. The amount of liquid evaporated in the thermosiphon reboiler 9 is approximately the same amount as the liquid supplied through the line 10. The gas-liquid multiphase fluid exiting the thermosyphon reboiler is line 14.
The gas is supplied to the gas-liquid separator 11 through the gas-liquid separator 11, where it is separated into vapor and liquid. Of these, the steam is returned to the distillation column 2 through line 15, and the liquid is circulated through line 12 and further to line 13 to thermosyphon reboiler 9, and a very small amount is extracted through line 16.
Therefore, the bottom liquid is extracted from the distillation column 2 through the line 10, and the same amount of liquid is evaporated in the thermosiphon reboiler 9 and returned to the distillation column 2 through the line 15. In the circulation, non-volatile impurities in the bottom liquid are removed.

Therefore, the greater the amount of liquid supplied to the thermosyphon reboiler 9 through the line 10, in other words, the greater the amount of evaporation in the thermosyphon reboiler 9, the higher the concentration of non-volatile impurities in the bottom product liquid extracted through the line 8. Although the amount of evaporation is small, it is determined by the distillation operating conditions, and there is no need to increase the amount of evaporation especially in order to reduce non-volatile impurities in the product liquid at the bottom of the column. In order to increase the amount of evaporation, for example, the amount of recirculated liquid may be increased, but it is necessary to supply an extra amount of heat to the reboiler corresponding to the increase in the amount of recirculated liquid. If the advantage of reducing non-volatile impurities in the bottom product liquid outweighs the disadvantage of increasing the amount of heat, then the amount of evaporation in the reboiler should be increased. Thermosiphon type reboiler 9
The amount of liquid circulating through the gas-liquid separator 11 is usually 20 to 4 times the amount of liquid evaporated in the thermosyphon reboiler 9.
It is desirable to increase the concentration of non-volatile impurities in this circulating fluid as much as possible, close to the concentration at which non-volatile impurities precipitate from the circulating fluid. In this case, the amount of fluid drawn from line 16 can be reduced as much as possible, and product loss can be minimized. At the same time, it becomes possible to minimize the amount of heat carried away by the extraction liquid.

The method of the present invention will be specifically explained below with reference to Examples.
The method of the invention is not limited only to this example. Example 1 When producing product nitric acid by distilling 30 wt% nitric acid and concentrating it to 62 wt%, it is necessary to discharge water containing almost no nitric acid from the top of the column, but there is no water in the feed liquid. 5p
pm (by weight) of heavy metals, mainly iron, chromium, and nickel, so in order to reduce the heavy metal concentration in the nitric acid solution at the bottom of the column, the process is carried out according to the flow shown in Figure 1. Ta.

Table 1 shows the flow rate, nitric acid concentration, heavy metal concentration, temperature of 7 degrees Celsius, and pressure at each part in this case.

[Brief explanation of the drawing]

FIG. 1 is a process explanatory diagram showing an example of an embodiment of the method of the present invention, in which 1 is a supply line for a liquid containing non-volatile impurities, 2 is a distillation column, 4 is a condenser, and 8 is a bottom liquid. extraction line,
9 is a thermosiphon type reboiler, 11 is a gas-liquid separator,
Reference numerals 16 and 16 respectively indicate extraction lines for liquids containing non-volatile impurities.

Claims (1)

[Claims] 1 A method in which a liquid containing non-volatile impurities is distilled using a thermosiphon reboiler to obtain distillate and bottoms from the top and bottom of the column, respectively.The gas-liquid multiphase fluid coming out of the thermosiphon reboiler is separated into gas and liquid. After separating into vapor and liquid in the distillation vessel, the vapor is returned to the bottom of the distillation column, and the liquid is fed from the bottom of the distillation column to a thermosiphon reboiler. By returning the circulating liquid to the thermosiphon type reboiler and gas-liquid separator, it becomes a concentrated liquid containing non-volatile impurities, and by separately withdrawing a minute amount of this circulating liquid, it is added to the bottom liquid of the distillation column. A method for reducing non-volatile impurities in a liquid in a distillation operation, characterized by reducing non-volatile impurities in a liquid.