US2658029A

US2658029A - Distillation method and apparatus

Info

Publication number: US2658029A
Application number: US253538A
Authority: US
Inventors: Untermann Walter; Sondermann Karl; Offenbach Kreis; Milbers Arthur
Original assignee: Metallgesellschaft AG
Current assignee: GEA Group AG
Priority date: 1951-10-27
Filing date: 1951-10-27
Publication date: 1953-11-03
Anticipated expiration: 1970-11-03

Description

Nov. 3, 1953 W. UNTERMANN ET AL DISTILLATION METHOD AND APPARATUS Filed Oct. 27, 1951 ,guuuuu Patented Nov. 3, 1953 UNITED STATES PATENT OFFICE DISTILLATION METHOD AND APPARATUS corporation of Germany Application October 27, 1951, Serial No. 253,538

16 Claims. 1

This invention relates to a new method and apparatus for the distillation of mixtures of substances.

The separation of mixtures of substances may be efiected by continuous distillation with the use of evaporation and rectification equipment. In conventional evaporation and rectification equipment the rectification column receives a gaseous mixture of substances from the evaporation chamber. From this mixture one or more spe cific distillation cuts are obtained in as concentrated a form as is possible. These cuts may be taken from the column as top or side withdrawals. The sump product discharging from the evaporator should be freed from those products which are to be obtained as distillates to the greatest possible extent. In most of the conventional equipment heretofore used the gaseous mixture of substances which entered the rectification column could contain only a, small portion of the substances which were to be obtained as distillation products. For this reason many attempts have been made to efiect the evaporating in the evaporation chamber in such a manner that the substances to be obtained as distillates are present in relatively high concentrations even prior to entrance into the rectification column. These attempts did not produce satisfactory results, however, particularly when the distillation fraction, recovery of which was desired, was only present in a small amount in the initial product.

One object of this invention is to overcome the aforementioned difiiculties.

A further object of the invention is a method and apparatus for the distillation of mixtures of substances which will allow the concentration of the distillation cut to be obtained, even prior to entrance into the rectifying equipment, and to free the discharging sump product practically entirely from these substances. These and still further objects become apparent from the following description read in conjunction with the drawing which diagrammatically shows an embodiment of an evaporation and rectifying device in accordance with the invention.

In accordance with the invention the evaporation is carried out in multiple consecutive stages. These stages are separated into a group of first stages and a group of last stages. The

number of individual first stages should amount to one eighth to seven eights the entire number of stages, including all the first and last stages, and should preferably amount to about threequarters of the entire number of stages. The evaporation products from the first stages are passed, combined with each other, to a, rectification column. The evaporation products of the last stages are fed to a separate rectifying or cooling device such as a separate reflux condenser.

' The reflux from the main rectifying column, i. e. the rectifying column which receives the combined evaporation products from the first stages, is advisedly returned to that individual evaporation stage in the multiple number of first evaporation stages, having a concentration of the substance to be recovered as said distillate therein approximately equal to the concentration of said substance in said condensate. The initial mixture from which the distillate is obtained should be added to the individual evaporation stage which has approximately the same concentration of the substance which is obtained as a distillate as does this initial mixture. In the same manner the reflux and/or the distillate from the last stages is returned to the individual stage or stages whose sump has most nearly the same concentration of the substance to be obtained as distillate as does this returned reflux or distillate from the last stages. Thus the fresh initial mixture which is added and the reflux or distillate from the last stages are returned to those individual stages whose sump has a concentration of the substance to be finally obtained as a distillate which most nearly equals the concentration of this substance in the returned product.

If a separate cooler is used for the last stages, then the condensation products from this cooler are returned to the individual stage having a corresponding concentration of the substance to be obtained as a distillate. If the vapors from the last evaporation stage are conducted into a separate rectifier instead of a separate cooler, the reflux and/or the head products may be conducted to the individual evaporation stages in which there is approximately the same concentration of the desired fraction in the sump.

It has been found. advantageous to arrange all the evaporation stages in the evaporator system annularly or consecutively in a straight line in a receptacle. It is also possible, in accordance with the invention, to have the last evaporation stages in a second still, in which case the direct condensate or concentrated head product may be returned to a. stage in the manner described above or the vapors may be fed to the preceding evaporation stages.

A closed evaporation system has been found in accordance with the present invention in combination with a rectification column, particularly advantageous for high vacuum distillation. Such a closed system, however, may also be used for all pressure distillation purposes, The closed evaporation system may have a connected concentration column, and only'the head product may be obtained as distillate; It is also possible, particularly in connection with pressure distillation, to remove further fractions as side withdrawals from the rectification column. Several such self-contained evaporation and rectification units may be connected in: series in or- 4 her of individual stages, enter the main rectification column combined with each other. In the last stage, the concentration of the substances to be recovered as distillate is relatively low. The low concentrations must be substantially removed. The vapors formed by evaporation during this removal consist to a great extent of substances which are not to be present in the cut distillation product. In order not to charge the rectifying column with these substances these vapors are fed separately to a reflux condenser or a smaller rectifying column, the vapor withdrawal of which discharges into the vapor space of the first evaporation stages. If a reflux condenser is usedfor the last evaporation stages, the reflux is fed to a prior individual evaporation stage which preferably has the same concentration of the substance to be recovered as distillate. Instead of the reflux condenser, a small rectification column may advantageously be used. The reflux from this column is fed to the first evaporation stages, while the top product enters the main rectification column in the form der to separate any desired number of fractions 7 by distillation from an initial product.

In order to effect the distillation in accordance with the invention the starting mixture which is to be distilled is caused to flow to one of the individual evaporation stages in the first evaporation stage. The quantity of liquid from the starting mixture which is not evaporated is allowed to overflow through the subsequent individual evaporation stages so that it will pass through all the subsequent individual stages and be" discharged from the last individual stage of the last evaporation stage. After discharge it may be passed through further evaporation and rectification in accordance with the invention for the separation of further fractions; from the rectification column generally constitutes a multiple of the amount of distillate which is obtained. The reflux from the main rectification may contain a much higher concentration of the substances which are to be obtained as distillate than does the initial starting mixture. This highly concentrated reflux from the main rectification is led to that individual evaporation stage in the first evaporation stage having a concentration of the substance to be recovered as said distillate therein approximately equal to the concentration of said substance in said condensate, and is partially evaporated. The unevaporated portion overflows to the following subsequent individual stages. As the substances to be recovered as distillate are again evaporated from the reflux passed to the said individual stage, as it passes through the subsequent stages, a point is reached in an individual stage along the path of flow in which the concentration of these substances is about the same as concentration in the initial starting mixture. Fresh initial starting mixture is always conducted to this stage after adjusting equilibrium in the distillation system. The closer this stage is to the last stages, the higher the reflux ratio. The fresh initial starting mixture is thus always conducted to the stage in which the reflux has again evaporated to such an extent that the distillate substance concentration is approximately equal to it. From this evaporation stage the initial starting material and the remaining reflux flow together through the remaining individual evaporation stages until the point of discharge from the last stage. The vapors from the first evaporation stages which are preferably equal to about three-fourths of the 130 3841 nu of vapors combined with the vapors of the first evaporation stages. The discharging sump from this evaporation and rectification can now automaticall'y be fedto another identical system or similar system for the separation of further fractions. In this connection the series-com of an apparatus and which has flow lines. The

evaporation stages in this embodiment are shown in a row. These stages may also be connected in a circle without requiring any change in the flow diagram.

At I1, the material which is to be distilled enters a distribution system from which it can be conducted simultaneously to one or more of the evaporation stages, l-l-Z, which are arranged in a receptacle 13. The material is, for example, brought into' a central evaporation stage 4. Due to-the overflow openings l5, all the evaporation stages are filled up to the upper level of the overflow device 28. The evaporation of the material which is to be distilled begins advisedly by means of a heating system in each evaporation stage. The vapors from the first evaporation stages [-9 combine in the vapor space M and enter the rectifying column 23, which is filled with plates, packing or the like, in the direction shown by arrow 8, and may have any conventional construction. The head or side product which is to be obtained, is withdrawn at L! and 20 respectively. The reflux flows again to the evaporator at 2i to the first individual evaporation stage, in the direction shown by arrow 22. The reflux, in most cases, is a multiple of the quantity which is to be obained as concentrated distillate. This reflux now displaces from evaporation stages I-4 the initial product which has been added at the beginning, and is again partly evaporated in each stage so that it has, for instance, after evaporation in stage 3,

approximately the same concentration in the substances of the distillation product, as does the initial product. From stage 4, the remaining reflux flows jointly with the starting product The units may through the other evaporation stages 4-I2, thus being further evaporated in the different stages. In the same manner as over first evaporation stages l-9, there is a closed vapor space M, over last evaporation stages 9-!2 there is also such a closed vapor space 29. The evaporation chambers are separated from each other by partition I6 and the last evaporation stages Ill-I2 evaporate the remaining quantities of the substances to be obtained as a distillate from the initial product. The final product from stage 12, which is freed of these substances, can be subjected at 28 to further treatment, for instance in a further unit which is built and operated in the same or a similar manner. During the evaporating in the last evaporation stages, the liquids enter the reflux condenser 26 combined, in the direction shown by arrow 24, and the vapors flow into the vapor space I4 through, for instance, a line 25 in the direction shown by the arrow. The reflux 22 obtained in the reflux condenser is fed to evaporation stage 8 so that, by this recycling, the remaining quantities of the distillate substance to be recovered are again evaporated in concentrated form in first stages 8 and 9.

We claim:

1. Method for the distillation of mixtures of substances which comprises establishing a multiple number of individual series-connected evaporation stages, including a group of first evaporation stages and a group of last evaporation stages, said first group of evaporation stages containing about one eighth to seven eighths of the entire number of individual stages passing any uncondensed vapor from said last group of stages to said common main rectification, subjecting such a mixture of substances to evaporation in all said connected stages, subjecting the vapors evaporated from said first group of stages to a common main rectification while separately condensing the vapors obtained from the evaporation in said last group of evaporation stages. returning the reflux from said common rectification to that individual evaporation stage having a concentration of the substance to be recovered as said distillate therein approximately equal to the concentration of said substance in said condensate, returning the condensate from said last group of stages to at least one of said first group of stages passing any uncondensed vapor from said last group of stages to said common main rectification, and recovering at least one distillate from said common rectificaticn.

2. Method according to claim 1, in which said condensate from said last group of stages is return d to at least one of said first group of stages having a concentration of the substance to be recovered as said distillate therein approximately equal to the concentration of said substance in said condensate.

Method. according to claim '1, in which said first group of evaporation stages contains about three-fourths of the entire number of stages.

4. Method according to claim 1, in which a fresh quantity of such a mixture of substances is added to the evaporation stage having approximately the same concentration of the substance recovered as said distillate as it has.

5. Method according to claim 1, in which said evaporation is effected under vacuum.

6. Method according to claim 1, in which said evaporation is effected under pressure.

7. Method according to claim 1, in which said condensation of the vapors obtained from the the last individual stage and subjected to at least one additional distillation in accordance with the method with the recovery of at least one additional distillate.

10. Apparatus for carrying out the method according to claim 1, comprising means defining a first evaporation chamber having a main rectification column position for receiving evaporated vapors therefrom, said first evaporation chamber being subdivided into multiple individual adjacent evaporation chambers series-connected by over-flows defined therebetween, conduit means for passing a liquid to at least one of said individual evaporation chambers, liquid conduct means positioned for passing reflux from said main rectification column to at least one of the individual evaporation chambers defined in said first evaporation chamber, means defining a last evaporation chamber having condensing means positioned for receiving the vapors therefrom, said last evaporation chamber defining multiple individual adjacent evaporation chambers seriesconnected by over-flows defined therebetween, the first individual chamber defined in said last evaporation chamber being series-connected to the last individual evaporation chamber defined by said first evaporation chamber, liquid conduct means positioned for removing liquid from said last individual chamber, conduit means positioned for passing uncondensed vapor from said condensing means to said main rectification chamber, defined by said last evaporation chamber, and liquid conduct means positioned for passing condensate from said condensing means to at least one of said individual chambers defined by said first evaporation chamber.

11. Apparatus according to claim 10, in which the individual evaporation chambers'defined by said first evaporation chamber are equal in number to about three-fourths the total number of individual evaporation chambers defined by said first and last evaporation chamber.

12. Apparatus according to claim 10, in which said first and last evaporation chambers are defined by a partition in a main evaporation chamber, subdivided in multiple adjacent series-connected individual evaporation chambers by partial partitions defining over-flow spaces therethrough.

13. Apparatus according to claim 10, in which said individual evaporation chambers of said first and last evaporation chambers are defined in a series-connected straight line.

14. Apparatus according to claim 10, in which the individual evaporation chambers of said first and last evaporation chamber are defined in a series-connected circle.

15. Apparatus according to claim 10, in which said condensing means positioned above said last evaporation chamber is a reflux condenser having a conduit positioned for passing reflux therefrom to at least one of said individual chambers defined by said first evaporation chamber, and vapor conduit means positioned for passing uncondensed vapor passing therethrough to said first evaporation chamber.

16. Apparatus according to claim 10, in which said last evaporation chamber and condensing means therefore are defined in a subsequent, separate distillation still.

WALTER UN'IERMANN. KARL SON'DERMANN. ARTHUR MILBERS.

References Cited in the file of this patent UNITED STATES PATENTS Number Number Name Date McAfee Mar. 23, 1926" Wilson Feb. 21, 1933 Carney May 8, 1934 Goldsbarry et a1. Dec. 11, 1951 FOREIGN PATENTS Country Date Great Britain of 1884 Switzerland Nov. 6, 1891 France Feb. 1, 1910 Great Britain Jan. 30, 1918,

Claims

1. METHOD FOR THE DISTILLATION OF MIXTURES OF SUBSTANCES WHICH COMPRISES ESTABLISHING A MULTIPLE NUMBER OF INDIVIDUAL SERIES-CONNECTED EVAPORATION STAGES, INCLUDING A GROUP OF FIRST EVAPORATION STAGES AND A GROUP OF LAST EVAPORATION STAGES, SAID FIRST GROUP OF EVAPORATION STAGES CONTAINING ABOUT ONE EIGHT TO SEVEN EIGHTS OF THE ENTIRE NUMBER OF INDIVIDUAL STAGES PASSING ANY UNCONDENSED VAPOR FROM SAID LAST GROUP OF STAGES TO SAID COMMON MAIN RECTIFICATION, SUBJECTIG SUCH MIXTURE OF SUBSTANCES TO EVAPORATION IN ALL SAID CONNECTED STAGES, SUBJECTING THE VAPORS EVAPORATED FROM SAID FIRST GROUP OF STAGES TO A COMMON MAIN RECYIFICATION WHILE SEPARATELY CONDENSING THE VAPORS OBTAINED FROM THE EVAPORATION IN SAID LAST GROUP OF EVAPORATION STAGES RETURNING THE REFLUX FROM SAID COMMON RECTIFICATION TO THAT INDIVIDUAL EVAPORATION STAGE HAVING A CONCENTRATION OF THE SUBSTANCE TO BE RECOVERED AS SAID DISTILLATE THEREWITH APPROXIMATELY EQUAL TO THE CONCENTRATION OF SAID SUBSTANCE IN SAID CONDENSATE, RETURNING THE CONDENSATE FROM SAID LAST GROUP OF STAGES TO AT LEAST ONE OF SAID FIRST GROUP OF STAGES PASSING ANY UNCONDENSED VAPOR FROM SAID LAST GROUP OF STAGES TO SAID COMMON MAIN RECIFICATION, AND RECOVERING AT LEAST ONE DISTILLATE FROM SAID COMMON RECIFICATION.