EP2703758A1

EP2703758A1 - Method for drying filter cake

Info

Publication number: EP2703758A1
Application number: EP20130150720
Authority: EP
Inventors: Zhuoxian Wang; Jianjun Zhu
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2012-08-29
Filing date: 2013-01-09
Publication date: 2014-03-05
Also published as: CN103629910A

Abstract

In order to overcome the problems that earlier methods have experienced, a method for drying filter cake is proposed, comprising the steps of:
a) feeding wet filter cake into at least one drier (E101);
b) feeding drier gas into said drier (E101);
c) recovering solvent-containing gas from said drier (E101);
d) feeding said solvent-containing gas to at least one cryogenic condensation system (E102);
e) feeding at least one inert gas to said cryogenic condensation system (E102);
f) condensing solvent from said solvent-containing gas;
g) recovering solvent-free gas from said cryogenic condensation system (E102); and
h) feeding said solvent-free gas to said drier (E101).

Description

Technical field of the present invention

The present invention relates to a method for drying filter cake.

Background of the present invention; prior art

As a unit operation drying is widely applied in the chemical industry, particularly in pharmaceutical and fine chemical production processes. It is common that the solid products or reaction intermediates are filtered after synthesis and crystallization.
Significant amounts of solvents such as acetone, ether, isopropanol, etc. are used in the filter cakes which need to be further dried. Compared to other methods, pneumatic drying at relatively low temperatures is a more efficient drying process and is widely used in the pharmaceutical and fine chemical industries.
In a conventional pneumatic drying process a gas stream passes through a filter cake in a drier. The solvent diffuses into the gas stream and vents out from the filter cake. The solvent-containing gas is normally further treated before being released into the atmosphere.
Conventionally, absorption and/or adsorption methods are employed in the treatment of the gas to absorb volatile solvents. The conventional pneumatic drying process consumes a significant amount of inert gas such as nitrogen.
The production of inert gases such as nitrogen can be expensive due energy cost whether through cryogenic air separation technology or adsorption methods. Further to abate volatile organic compounds (VOCs) in the offgas by convention methods such as scrubbing is still a challenge to meet the appropriate environmental regulations.

Disclosure of the present invention: object, solution, advantages

Starting from the disadvantages and shortcomings as described above and taking the prior art as discussed into account, an object of the present invention is to overcome the problems that earlier methods have experienced.
This object is accomplished by a method comprising the features of claim 1. Advantageous embodiments and expedient improvements of this improved terephthalic acid production method are disclosed in the dependent claims.
Basically, the present invention relates to a method for drying wet filter cake containing solvents in at least one drier by contacting the wet filter cake with a drier gas thereby forming a solvent-containing gas. The solvent-containing gas is fed to at least one cryogenic condensation system where the solvent is condensed from the solvent-containing gas. The recovered solvent is stored for potential other uses, and the recovered solvent-free gas is fed back to the drier to assist in the drying process. In this manner, there is no emission of the solvents into the atmosphere.
In one embodiment of the present invention there is disclosed a method for drying filter cake comprising the steps of:

a) feeding wet filter cake into at least one drier;
b) feeding drier gas into said drier;
c) recovering solvent-containing gas from said drier;
d) feeding said solvent-containing gas to at least one cryogenic condensation system;
e) feeding at least one inert gas to said cryogenic condensation system;
f) condensing solvent from said solvent-containing gas;
g) recovering solvent-free gas from said cryogenic condensation system; and
h) feeding said solvent-free gas to said drier.

The drier can advantageously be at least one pneumatic drier, and/or the drier gas may expediently be any inert gas such as nitrogen or carbon dioxide. Air may also be employed as the drier gas.
Any suitable drier that can safely dry the filter cake containing the solvents can be employed in the present invention. The filter cake may favourably be from a production process such as those selected from the group consisting of pharmaceutical and fine chemical production processes.
The solvents that may typically be found in the wet drier cake are selected from the group consisting of acetone, ether and isopropanol. Other solvents depending upon the production processes employed may typically be present such as methanol, ethanol, ethers, acetone, tetrahydrofuran (THF) and halohydrocarbons selected from the group consisting of CH₃Cl, CH₂Cl₂, CHCl₃ and CCl₄, etc.
The dried filter cake can preferably be recovered and/or may preferably be re-employed in at least one production process.
The inert gas that is fed to the cryogenic condensation system can advantageously be selected from the group consisting of nitrogen and carbon dioxide. Other inert gases may expediently be used depending upon the process conditions employed by the cryogenic condensation system. For example, air may be used in place of nitrogen or carbon dioxide. This inert gas may favourably be fed as at least one liquefied gas.
The solvent-free gas that is recovered from the cryogenic condensation system can preferably be fed back to the drier and/or can preferably be withdrawn using at least one blower assembly.
The solvent-free gas may advantageously be directed through at least one gas buffer unit to provide additional treatment of the gas before it re-enters the drier. The inert gas that is recovered from the cryogenic condensation system may expediently be vented to the atmosphere and/or used in at least one other process operation.
In this manner, the volatile organic compounds that comprise the solvent materials from the wet filter cake are removed from the filter cake and recovered without being emitted into the atmosphere.
The present invention further relates to a drying system being operable according to the method as described above.

Brief description of the drawings

For a more complete understanding of the present inventive embodiment disclosures and as already discussed above, there are several options to embody as well as to improve the teaching of the present invention in an advantageous manner. To this aim, reference may be made to the claims dependent on claim 1; further improvements, features and advantages of the present invention are explained below in more detail with reference to preferred embodiments by way of non-limiting example and to the appended drawing figure taken in conjunction with the description of the embodiments, of which:

Fig. 1: is a schematic of a closed pneumatic drying system according to the present invention, with the system being operable according to a method of the present invention.

Detailed description of the drawings; best way of embodying the present invention

Turning to Fig. 1, a closed pneumatic drying process is shown. The closed pneumatic drying process comprises a conventional pneumatic drier E101, a cryogenic condensation unit E102 and a gas blower or compressor P101 which is used for gas recycling, and a condensate storage tank V101.
Wet filter cake can be loaded into the pneumatic drier E101 continuously through line 10. This loading may also be by batch processing. The dried solid material is downloaded through line 20. The dry inter gas is blown into the drier E101 through line 70.
The solvent-containing gas is fed through line 30 to the cryogenic condensation system E102 wherein the volatile organic solvents are condensed. The condensed solvents are fed to the condensate storage tank V101 through line 100.
There may be additional contaminants that accompany the solvents on the filter cake depending upon the type production process practiced upstream of the filter cake. So in addition to the solvents, volatile organic reactants that have not been completely converted during the reaction; any volatile by-products that formed during the reaction and solid particles (cake powder) may be present in the gas stream leaving from the filter cake.
In certain instances, at least one additional filter (not shown) may be employed downstream of the filter cake (upstream of the cryogenic condensation system) to prevent possibly choking the cryogenic condensation system by removing the solid particles from the gas stream.
The cryogenic condensation may be any system that provides cryogenic conditions. For example, a system that comprises one or two finned tube type heat exchangers, in which the gas-gas heat exchange efficiency can be enhanced significantly, can be employed. A cryogenic condensation system such as the CIRRUS VEC system available from Linde AG is a preferable cryogenic condensation system for use in the present invention.
The treated gas stream from the cryogenic condensation system E102 is pressurized by the gas recycling blower P101 through lines 40a and 40b.
Optionally, a gas buffer V102 can be added between the cryogenic condensation system E102 and the gas recycling blower P101 in which some solvent liquid can be separated from the gas stream and introduced into the solvent storage tank V1 01 by way of line 120. In other words, line 120 is provided for the transport of condensate to the condensate storage tank V101.
The gas buffers are present in the loop to balance the pressure throughout the loop. The gas buffer V102 may also be employed to separate liquid droplets from the recycled gas from the cryogenic condensation system E102.
To maintain pressure balance, a part of the treated gas stream can be vented into the atmosphere without any further treatment. The gas recycling blower P101 is selected to provide the necessary blowing power to overcome the process resistance or pressure drop in the system.
Another gas buffer V103 can be optionally employed after the gas recycling blower P101 in which additional inert gas is fed through line 50 to maintain pressure balance and the overall gas flow rate.
The concentration of the solvent in the gas stream in line 40a strongly depends upon the operating temperature of the condensation system. The operation system of the cryogenic condensation system is precisely set so that the required solvent concentration is reached while inhibiting the formation of frosting/icing the system.
In the cryogenic condensation system, liquefied nitrogen or carbon dioxide can be used either directly or indirectly as the coolant. For direct coolant use, the liquefied gas is introduced into the cryogenic condensation system through line 80 while vaporized gas vents out of the system through line 90.
The vaporized gas can be recovered and reused for other purposes or simply vented to the atmosphere. In the event that the solvent has a high freezing point, it can be problematic to directly use a cryogenic liquefied gas as the coolant. When low concentrations of the gas stream in line 40a are not required because of process conditions, it is not necessary to use cryogenic coolants such as liquefied gases like nitrogen or carbon dioxide.
In these circumstances, it is preferable to use cold heat transfer fluid to condense the solvent in the cryogenic condensation system as these temperatures may be more carefully controlled. Preferably, the cold heat transfer fluid transfers cold energy either from a cryogenic liquefied gas in a specially designed system or from a mechanical refrigeration unit.
While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of the present invention will be obvious to those skilled in the art. The appended claims in this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.

List of reference numerals

10: line
20: line
30: line
40a: line
40b: line
50: line
60: line
70: line
80: line
90: line
100: line
110: line
120: line
E101: drier, in particular pneumatic drier
E102: condensator or condensation system or condensation unit, in particular cryogenic condensator or cryogenic condensation system or cryogenic condensation unit
P101: compressor or blower, in particular gas blower, for example gas recycling blower
V101: condensate storage tank or solvent storage tank
V102: buffer unit or buffer, in particular gas buffer and/or buffer tank
V103: buffer unit or buffer, in particular gas buffer and/or buffer tank

Claims

A method for drying filter cake, comprising the steps of:
a) feeding wet filter cake into at least one drier (E101);

b) feeding drier gas into said drier (E101);

c) recovering solvent-containing gas from said drier (E101);

d) feeding said solvent-containing gas to at least one cryogenic condensation system (E102);

e) feeding at least one inert gas to said cryogenic condensation system (E102);

f) condensing solvent from said solvent-containing gas;

g) recovering solvent-free gas from said cryogenic condensation system (E102); and

h) feeding said solvent-free gas to said drier (E101).
The method according to claim 1 wherein said drier (E101) is at least one pneumatic drier.
The method according to claim 1 or 2 wherein said drier gas is selected from the group consisting of nitrogen and carbon dioxide.
The method according to at least one of claims 1 to 3 wherein said filter cake is from a production process selected from the group consisting of pharmaceutical and fine chemical production processes.
The method according to at least one of claims 1 to 4 wherein said solvent is selected from the group consisting of acetone, ether, isopropanol, methanol, ethanol, tetrahydrofuran and halohydrocarbons selected from the group consisting of CH₃Cl, CH₂Cl₂, CHCl₃ and CCl₄.
The method according to at least one of claims 1 to 5 wherein said solvent-free gas is fed through at least one buffer tank (V102, V103) before entering said drier (E101).
The method according to claim 6 wherein said buffer tank (V102, V103) removes liquid droplets from said solvent-free gas.
The method according to at least one of claims 1 to 7 wherein a blower (P101) is used to draw said solvent-free gas from said cryogenic condensation system (E102).
The method according to at least one of claims 1 to 8 wherein solvent-free gas is supplemented with additional inert gas prior to entering said drier (E101).
The method according to at least one of claims 1 to 9 wherein said dried filter cake is recovered.
The method according to at least one of claims 1 to 10 wherein said inert gas is fed to said cryogenic condensation system (E102) as at least one liquefied gas.
The method according to at least one of claims 1 to 11 wherein said inert gas fed to said cryogenic condensation system (E102) is selected from the group consisting of nitrogen, carbon dioxide and air.
The method according to at least one of claims 1 to 12 wherein said inert gas is vented to the atmosphere or recovered for at least one other process operation.
The method according to at least one of claims 1 to 13 wherein said cryogenic condensation system (E102) uses a cryogen either directly or indirectly as a coolant.
The method according to at least one of claims 1 to 14 wherein liquefied gas is introduced into said cryogenic condensation system (E102) and vaporized gas vents out of said cryogenic condensation system (E102).