SK288853B6 - Apparatus for concentrating volatile organic compounds by adsorption and desorption and a method for concentrating volatile organic compounds by adsorption and desorption - Google Patents

Abstract

The process consists of two steps. In a first step, the adsorption of the volatile organic compounds is carried out, whereby stripping gas is fed from the blower (1) to the storage tank (4) of the volatile organic compound, the stripped gas of the volatile organic compound formed is passed to the first heat exchanger (5). a heat exchanger (8) with a porous bed formed by the adsorbent (7) for adsorbing the volatile organic compound. Subsequently, the stripped gas is fed to the cooler (9) and after passing through the cooler (9) it is returned via the blower (1) to the storage tank (4). After the adsorption process is completed, a second step is carried out - the process of desorption of volatile organic compounds, in which stripping gas is fed from the blower (1) to the storage tank (4), the stripped gas from the storage tank (4) being fed to the first heat exchanger ( 5) and subsequently a second heat exchanger (8) with a heating controlled oil thermostat (6) to the temperature necessary for the desorption process of the volatile organic compound from the adsorbent (7). Subsequently, the stripped gas is fed to a condenser (9) where it is cooled and condensed to separate the liquid phase with desorbed organic volatile compound molecules into the condensate tank (10). The stripped gas is returned from the cooler (9) via the blower (1) to the storage tank (4). After desorption is complete, the concentration of the organic volatile compound in the condensate is measured.

Description

Technical field

The invention relates to an apparatus for concentrating volatile organic compounds by adsorption and desorption and to a method for concentrating volatile organic compounds by adsorption and desorption.

Prior art

Ibrahim I. El-Sharkay and colleagues in their article Adsorption of ethanol on original and surface-treated powdered activated carbon investigated the adsorption isotherms and kinetics of ethanol adsorption on the adsorbents used. The adsorbents used were the original Maxsorb III coal, the surface-treated KOH-Maxsorb III and the H ₂ treated Maxsorb III. Adsorption isotherms and kinetics were measured using a magnetic suspension adsorption unit. The experiments were performed at 30, 40, 50, 60 and 70 ° C. Two types of equations were used to characterize the adsorption isotherms, namely the Dubinin-Astakhov and Dubinin-Radushkevich equations. The adsorption kinetics of these pairs were presented according to the Fickian diffusion model. Experimental results show that of all three investigated adsorbents, H ₂ surface-treated Maxsorb III has the highest sorption capacity, namely 1.23 kg / kg.

F. Taylor and colleagues constructed an experimental device, which they describe in their work entitled Kinetics of continuous fermentation and with ethanol stripping. In a series of experiments and mathematical models, they describe the effect of yeast glucose consumption with increasing ethanol concentration in the fermentation process. The apparatus includes, among other components, a 30-liter fermenter, a packed column, a blower, and a condenser to recover ethanol vapor. The device works continuously for 185 days. Ethanol packing columns are washed twice a week. The data show that in continuous steady state fermentation, the primary inhibitory effect of ethanol is on cell yield, which drops sharply above 60 g ethanol / l, while the rate of glucose consumption is almost unaffected. In conclusion, the authors state that the proposed device is generally applicable to continuous fermentation.

In their work entitled Purification of ethanol by ozonation, adsorption on activated carbon and gas stripping, S. Onuki and colleagues describe the possibility of removing by-products formed during distillation. The work was focused on the purification of ethanol produced from corn for industrial and pharmaceutical use. Ethanol samples were taken using the SPME (headspace microextraction with solid phase) technique and analyzed by gas chromatography with a mass detector. The study focused on 10 types of volatile organic compounds. Ozone treatment effectively removes styrene and 2-pentylfuran. Activated carbon adsorbs ester compounds. Gas stripping (air, N ₂ and CO ₂ ) removes acetaldehyde, 1,1-diethoxyethane. It was the combination of these three procedures that removed 8 of the 10 volatile organic compounds monitored.

M. Hashi and colleagues in their article entitled Obtaining Ethanol from a Steam Mix by CO ₂ Stripping: Adsorption Prediction and Modeling describe that removal of ethanol by carbon dioxide stripping and adsorption can be used in fermentation processes that produce bioethanol. This removal of ethanol is intended to reduce the inhibition of product growth in fermentation processes. To better understand the bioethanol adsorption process, they used a mathematical model to predict the adsorption efficiency of WV-1500 activated carbon in the presence of carbon dioxide, ethanol and water. The model takes into account the change in temperature during adsorption and heat loss to the environment. They confirmed the functionality of the proposed model by comparison with experimental adsorption data. Experimental data were obtained from a series of adsorption experiments for ethanol-CO ₂ and ethanol-H ₂ O-CO _{2 systems} to investigate the ability to extract ethanol from the matrix using the CO ₂ equipment designed by them.

In industrial applications, adsorption is most often used for gas cleaning (gas drying, CO ₂ , SO ₂ removal, hydrocarbon separation - methane, ethylene, ethane, propylene, propane, oxygen and nitrogen production) and liquid purification (decolorization of petroleum products and sugar .. .).

At present, there is an effort in industrial practice as well as in scientific circles to design simple devices for concentrating volatile organic compounds. These are devices that are able to adsorb volatile organic compounds and subsequently desorb them. The desorption process is crucial in many cases because it is necessary to recover the adsorbed substances in the unaltered state and in a concentration several times higher than the original one. Ethanol as a major product of fermentation processes is a frequently discussed substance in this field. In most production processes, ethanol is in the form of solutions.

The essence of the invention

The invention relates to an apparatus and a method for concentrating volatile organic compounds by adsorption and desorption.

A volatile organic compound is an organic compound which has a vapor pressure of 20 kPa and more at 20 ° C or which has a corresponding volatility under the particular conditions of use.

The present shortcomings of the concentration of volatile organic compounds are solved by the present invention, which makes it possible to remove volatile organic compounds by adsorption on adsorbents or by stripping and their subsequent desorption, thus obtaining the adsorbed substances again in the unaltered state in several times higher than the original.

The apparatus and method of the present invention make it possible to carry out the adsorption and subsequent desorption in a closed cycle to concentrate the volatile organic compound, as schematically shown in Figure 1.

The device for concentrating volatile organic compounds by adsorption and desorption according to the invention consists in that the individual elements of the device are connected one after the other in one cycle, as shown in detail in FIG. 2. The device consists of a blower 1 for supplying stripping gas to a storage tank 4 for generating an aerosol - stripped gas formed by stripping a stock solution of volatile organic compounds in a storage tank 4 by means of an aerator 3 located in a storage tank 4 of a volatile organic compound solution. At the supply of stripping gas to the storage tank 4, there is a throttle valve 2 to control the flow of stripping gas. Behind the storage tank 4, a first heat exchanger 5 and a second heat exchanger 8 are connected in series, which are equipped with an oil thermostat 6 to reach the desired temperature of stripped gas supplied from the storage tank 4 in the second heat exchanger 8. The second heat exchanger 8 is filled with adsorbent 7. adsorption or desorption of stripped gas supplied from the first heat exchanger 5. A cooler 9 is connected to the second heat exchanger 8 to cool the stripped gas from the second heat exchanger 8 after desorption of volatile organic compounds in the second heat exchanger 8. The cooler 9 is connected to the condensate tank 10 from the cooler 9 and to the blower 1 by discharging the stripped gas from the cooler 9.

The volatile organic substance is alcohols with one -OH group, especially ethanol. Adsorbents are activated carbons, polymeric sorbents or zeolites. Stripping gases are air, CO ₂ , N ₂ .

Oil is used as the heating medium in the first and second heat exchangers 5 and 8, and a cooling liquid is used as the cooling medium in the cooler 9. Other media can also be used in the case of the process of concentrating various volatile organic compounds.

The process for concentrating volatile organic compounds by adsorption and desorption is carried out in a closed cycle according to the invention in the same plant as follows:

The adsorption of volatile organic compounds takes place first at ambient temperature. From the blower 1, the stripping gas is fed to a storage tank 4 of a stock solution with a low concentration of organic volatiles. The stripping gas flow is controlled by a throttle valve 2. The stripping gas entering the storage tank 4 passes through the aerator 3, thereby forming an aerosol-stripped volatile organic compound gas in the storage tank 4, which is led to the first heat exchanger 5 and subsequently the second heat exchanger 8. with a porous bed of the adsorbent 7, in which the process of adsorption of the volatile organic compound from the stripped gas takes place on the surface of the adsorbent 7. The adsorption process is carried out at ambient temperature. The stripped gas freed of part of the volatile organic compound after its adsorption in the second heat exchanger 8 is led to the cooler 9 and after passing through the cooler 9 is returned through the blower 1 in the form of stripping gas to the storage tank 4. The adsorption process continues in the same way and repeated until until the adsorbent is flooded with a volatile organic compound. At the end of the adsorption process, the stock solution is pumped out of the storage tank 4 and the decrease in volume and concentration of the volatile organic compound in the stock solution is measured. The loss of volatile organic compound at this point is due to binding to the adsorbent.

Subsequently, the second part of the cycle takes place - the desorption process, in which the stripped gas from the storage tank 4 is led to the first heat exchanger 5 with heating controlled by an oil thermostat 6 and then to the second heat exchanger 8 heated to the temperature required to be in the second exchanger. heat 8, the process of desorption of the volatile organic compound from the adsorbent 7 into the stripped gas took place in an increased concentration, regenerating the adsorbent 7. The temperature range during desorption is limited by the boiling point of the volatile organic compound and the temperature of heat 8, the stripped gas is led to a condenser 9, where it is cooled, and after cooling in the condenser 9, the liquid phase with the desorbed molecules of the organic volatile compound is separated by condensation into a condensate tank 10. The cooling temperature in the condenser 9 must be below the dew point temperature of the organic volatile compound. The stripping gas is returned from the cooler 9 via the blower gas blower 1 to the storage tank 4 for stripping the stock solution. The desorption process continues in the same manner and is repeated until the desired concentration of organic volatile compound in the condensate is reached.

Overview of figures in the drawings

Figure 1 schematically shows the principle of adsorption and subsequent desorption in a closed cycle in order to form a condensate with a higher content of volatile organic compound.

Figure 2 shows a diagram of an apparatus for a closed cycle adsorption and desorption process.

Examples of embodiments of the invention

Example 1

Volatile organic compounds were first adsorbed at ambient temperature. From the blower 1, stripping gas was fed to a storage tank 4 of a low ethanol stock solution with a volume of 1 L. In all the above examples, air was used as stripping gas. The stripping gas flow is controlled by throttle valve 2 and has been set to 5 1 / min. The stripping gas entering the storage tank 4 passed through the aerator 3, thereby forming an aerosol-stripped ethanol gas in the storage tank 4, which was fed to a first heat exchanger 5 and then a second heat exchanger 8 with a porous bed of adsorbent 7 in which the process took place. adsorption of ethanol from the stripped gas on the surface of the adsorbent 7. In all the above examples, activated carbon from various manufacturers was used as the adsorbent. The adsorption process was performed at ambient temperature. The stripped gas freed of part of the ethanol after its adsorption in the second heat exchanger 8 was led to the cooler 9 and after passing through the cooler 9 it was returned through the blower 1 to the storage tank 4. The adsorption process continued in the same way and repeated until the adsorbent was flooded with ethanol. . After 12 hours, the adsorption was stopped and the stock solution was removed from the storage vessel. Subsequently, the volume drop in the storage tank 4 was measured, and the ethanol concentration in the stock solution was measured pycnometrically. The loss of ethanol at this point was due to binding to the adsorbent.

Subsequently, the second part of the cycle took place - the desorption process, in which stripped gas from the storage tank 4 was led to the first heat exchanger 5 and then the second heat exchanger 8 with heating controlled by an oil thermostat 6 set at 150 ° C necessary for the second heat exchanger 8, the process of desorption of ethanol from adsorbent 7 into stripped gas took place in increased concentration, while adsorbent 7 was regenerated. After desorption in the second heat exchanger 8, the stripped gas was led to cooler 9, where it was cooled and after cooling in cooler 9 the liquid was separated by condensation. phase with desorbed ethanol molecules into the condensate tank 10. The cooling temperature in the condenser 9 must be below the dew point temperature of the organic volatile compound. The stripped gas was returned from the cooler 9 via the blower 1 to the storage tank 4 for stripping the stock solution. The desorption process was continued in the same manner and repeated until the desired concentration of ethanol in the condensate was reached. During desorption after 30 min. from the beginning and subsequently after 3 hours (end of desorption), the condensate was collected, its volume was measured and the ethanol concentration was determined pycnometrically. After desorption, the activated carbon was weighed. 3 measurements were performed under the same conditions. The measured quantities and their values are given in Table 1.

Table 1

Values of measured values of adsorption and desorption - adsorbent activated carbon (AC 1, 80 g)

ADSORPTION DESORPTION AC 1 V-SS [1] EtOH-R1 m AV-SS [ml] EtOH-R 2 [%] V-COND1 [ml] EtOHCOND1 [%] V-COND2 [ml] EtOHCOND2 [%] m-AC [g] 1. measurement 1 2.0 31 1.5 19 29.8 27 26.0 83.0 2. measurement 1 2.0 31 1.5 19 29.7 27 26.0 82.3 3. measurement 1 2.0 32 1.6 20 28.0 27 25.7 82.6

V-SS - volume of stock solution at the beginning of the process,

EtOH-R1 - ethanol concentration in the stock solution at the beginning of the process,

Δ V-SS - change - reduction of stock solution volume after adsorption,

EtOH-R2 - ethanol concentration in stock solution after adsorption,

V-COND1 - condensate volume after 30 min. desorption,

EtOH-COND1 - ethanol concentration in V-COND1,

V-COND2 - volume of condensate after desorption,

EtOH-COND2 ethanol concentration in V-COND2, m-AC - mass of activated carbon after desorption.

Example 2

In Example 2, the procedure was the same as in Example 1, except that another type of activated carbon, designated AC2, was used as the adsorbent 7. The measured quantities and their values are given in Table 2.

Table 2

Values of measured values of adsorption and desorption - adsorbent activated carbon (AC2, 80 g)

ABSORPTION DESORPTION AC2 V-SS [1] EtOH-R1 [%] Δ V-SS [ml] EtOH-R2 m V-COND1 [ml] EtOHCOND1 [%] V-COND2 [ml] EtOHCOND2 [%] m-AC [g] 1. measurement 1 2.0 28 1.7 18 25.7 26 23.6 82.7 2. measurement 1 2.0 30 1.8 18 24.8 25 22.7 84.0 3. measurement 1 2.0 29 1.7 19 25.2 26 23.1 83.0

V-SS - volume of stock solution,

EtOH-R1 - ethanol concentration in stock solution,

Δ V-SS - change of stock solution volume after adsorption,

EtOH-R2 - ethanol concentration in stock solution after adsorption,

V-COND1 - condensate volume after 30 min. desorption,

EtOH-COND1 - ethanol concentration in V-COND1,

V-COND2 - volume of condensate after desorption,

EtOH-COND2 ethanol concentration in V-COND2, m-AC - mass of activated carbon after desorption.

In Examples 3 to 7, several types of activated carbon (LGCO 85, LGCO100, Applichem, Centralchem, PGChem) were used, the results obtained using these types differing slightly. Therefore, the average result values are briefly shown in Tables 3 to 7.

Example 3

In Example 3, the procedure was the same as in Example 1, with the following differences: Different types of activated carbon were used as the adsorbent 7. The initial ethanol concentration in the stock solution was 1.1%. The duration of desorption was 4 hours. The achieved final values are shown in Table 3.

Table 3

Values of measured values of adsorption and desorption - adsorbent activated carbon (80 g)

activated carbon charge weight 80 grams ADSORPTION volume of stock solution 1 liter ethanol concentration in the stock solution before adsorption 1.1% duration of adsorption 12 hours DESORPTION condensate volume 34 milliliters ethanol concentration in the condensate 13.7% duration of desorption 4 hours

Example 4

In Example 4, the procedure was the same as in Example 3, except that the initial concentration of ethanol in the stock solution was 2.0%. The resulting values are shown in Table 4.

Table 4

Values of measured values of adsorption and desorption - adsorbent activated carbon (80 g)

activated carbon charge weight 80 grams ADSORPTION volume of stock solution 1 liter ethanol concentration in the stock solution before adsorption 2.0% duration of adsorption 12 hours DESORPTION condensate volume 28 milliliters ethanol concentration in the condensate 31.5% duration of desorption 4 hours

Example 5

In Example 5, the procedure was the same as in Example 3, except that the initial concentration of ethanol in the stock solution was 5.2%. The resulting values are shown in Table 5.

Table 5

Values of measured values of adsorption and desorption - adsorbent activated carbon (80 g)

activated carbon charge weight 80 grams ADSORPTION volume of stock solution 1 liter ethanol concentration in the stock solution before adsorption 5.2% duration of adsorption 12 hours DESORPTION condensate volume 30 milliliters ethanol concentration in the condensate 35.6% duration of desorption 4 hours

Example 6

In Example 6, the procedure was the same as in Example 3, except that the initial concentration of ethanol in the stock solution was 10.6%. The resulting values are shown in Table 6.

Table 6

Values of measured values of adsorption and desorption - adsorbent activated carbon (80 g)

activated carbon charge weight 80 grams ADSORPTION volume of stock solution 1 liter ethanol concentration in the stock solution before adsorption 10.6% duration of adsorption 12 hours DESORPTION condensate volume 30 milliliters ethanol concentration in the condensate 43.7% duration of desorption 4 hours

Example 7

In Example 7, the procedure was the same as in Example 3, except that the initial concentration of ethanol in the stock solution was 14.9%. The achieved final values are shown in Table 7.

Table 7

Values of measured values of adsorption and desorption - adsorbent activated carbon (80 g)

activated carbon charge weight 80 grams ADSORPTION volume of stock solution 1 liter ethanol concentration in the stock solution before adsorption 14.9% duration of adsorption 12 hours DESORPTION condensate volume 33 milliliters ethanol concentration in the condensate 65.2% duration of desorption 4 hours

The conclusion from the experimental measurements is that the product of the adsorption-desorption device is a condensate which has approximately 4.5 times (in the case of a higher initial value of the concentration in the stock solution - Example 7) to 12 times (in the case of a low initial value of the concentration in the stock solution solution - Example 3) a higher concentration of ethanol than in the stock solution used at the beginning.

Although the examples focus only on the volatile organic compound ethanol, given that in practice the most common requirement is to concentrate this volatile organic compound, the apparatus and method of the present invention are equally applicable to concentrating other volatile organic compounds.

Industrial applicability

The principle of concentrating the volatile organic compound by adsorption and subsequent desorption by means of a closed-cycle adsorbent can be used, for example, in a fermentation process in the food industry or, for example, in a wastewater treatment process to capture specific organic compounds unsuitable for re-discharge.

List of reference marks

- blower

- throttle valve

3 - aerator

- storage tank

- first heat exchanger

- oil thermostat

- adsorbent

8 - second heat exchanger

- cooler

- condensate tank

- place for taking stock solution

- condensate collection point

Claims (9)

PATENT CLAIMS Device for concentrating volatile organic compounds by adsorption and desorption, characterized in that it consists of a blower (1) for supplying stripping gas to a storage tank (4) to form a stripped gas formed by stripping a stock solution of volatile organic compounds in a storage tank ( 4) by means of an aerator (3) located in the storage tank (4) of the solution of volatile organic compounds, behind the storage tank (4) the first heat exchanger (5) and the second heat exchanger (8) are connected in series, which are equipped with an oil thermostat (6). ) to reach the desired temperature of the stripped gas in the second heat exchanger (8), the second heat exchanger (8) being filled with an adsorbent (7) for adsorption or desorption of the stripped gas fed from the first heat exchanger (5) downstream of the expensive heat exchanger (8) a condenser (9) is connected to cool the stripped gas from the second heat exchanger (8) after desorption of volatile organic compounds, the condenser (9) being connected to the tank (10) to condensate from the condenser (9) and to the blower (1) by removing stripped gas from the condenser (9). Set according to claim 1, characterized in that the handles (1) to the storage tank (4) are actuated by a throttle valve (2). Device according to Claim 1, characterized in that the alcohols have one -OH group. The device of claim 1, which is ethanol. Device according to claim 1, polymeric sorbents or zeolites. The device of claim 1, CO ₂ , N ₂ . characterized in that the supply of stripping gas from the pulp is a volatile organic compound, that the volatile organic compound is that the adsorbents (7) are activated carbons, that the stripping gases are air, Process for concentrating volatile organic compounds by adsorption and desorption using an apparatus according to claim 1, characterized in that it takes place in a closed cycle and comprises the following steps: adsorption of volatile organic compounds, wherein stripping gas is fed from the blower (1) at ambient temperature to of the storage tank (4) via an aerator (3) with a stock solution with a low concentration of organic volatile substances, and the formed stripped gas of volatile organic compound is led from the storage tank (4) to the first heat exchanger (5) and subsequently the expensive heat exchanger (8) with a porous bed formed by the adsorbent (7) for adsorbing the volatile organic compound on the surface of the adsorbent (7), and subsequently the stripped gas freed of part of the volatile organic compound after its adsorption in the expensive heat exchanger (8) is led to the cooler (9) and after passing through the condenser (9) is returned via the blower (1) to the storage tank (4), after the end of the adsorption process, the stock solution is pumped out of the storage tank (4) and measuring the decrease in volume and concentration of the volatile organic compound in the stock solution; and subsequent desorption of volatile organic compounds, in which stripping gas is fed from the blower (1) to the storage tank (4) via an aerator (3), stripped gas is fed from the storage tank (4) to the first heat exchanger (5) and then the second heat exchanger (8) with heating controlled by an oil thermostat (6) to the temperature required for the process of desorption of the volatile organic compound from the adsorbent (7), the volatile organic compound being desorbed from the surface of the adsorbent (7) after desorption in the expensive heat exchanger (8) the stripped gas is led to a condenser (9), where it is cooled and, after cooling in the cooler (9), the liquid phase with desorbed molecules of organic volatile compound is separated by condensation into a condensate tank (10), the stripped gas is returned from the cooler (9) through the blower (1) to the storage tank (4), after the desorption is completed, the concentration of the organic volatile compound in the condensate is measured. Process according to Claim 7, characterized in that the temperature during the desorption is in the interval between the boiling point of the volatile organic compound and the temperature which does not cause degradation of the adsorbent (7). Method according to claim 7, characterized in that the cooling temperature in the cooler (9) is lower than the dew point temperature of the organic volatile compound.