DESC:FIELD OF THE INVENTION
The present invention relates to process intensification techniques used in Liquid-Liquid extraction. Particularly, the present invention relates to Liquid-Liquid extraction method and system for extracting/recovering acetic acid from its aqueous solution (i.e., chemical waste/industrial effluent).

BACKGROUND OF THE INVENTION
Acetic acid is known as a valuable component and building block in the chemical industry. For example, acetic acid is used to make cellulose acetate that is used in photographic film; and polyvinyl acetate that is used in wood glue, synthetic fibers, and fabrics. In addition, diluted acetic acid is commonly used as a descaling agent in homes. Acetic acid is a food additive used in the food industry as an acidity regulator and a condiment. For example, in the production of rubber, acetic acid is employed as a coagulant. Acetic acid is also used to make dyes, fragrances, and rayon, among other things. The global demand for acetic acid is around 6.5 million tons per year (Mt/a), with about 1.5 million tons from recycling and the rest from petrochemical feedstock.

The recovery/extraction of acetic acid from its aqueous solution is important for both industry and environment. Several chemical processes including but not limited to dehydrogenation of alcohols, oxidation of aldehydes, conversion (e.g., fermentation, pyrolysis, liquefaction) of biomass, and similar other chemical conversion processes produce aqueous streams containing acetic acid as a side (waste) product. Even though acetic acid and water do not form an azeotrope (possessing constant boiling point), separating these two components by traditional distillation is extremely inefficient. This is because the water end of the system has a tangent pinch, indicating a high number of column stages or a high reflux ratio to obtain pure products.

Extractive distillation, reactive distillation, liquid-liquid extraction, reactive extraction, etc., are common ways to recover acetic acid from water. Among all these technique/methods, the liquid-liquid extraction (also known as solvent extraction) is a powerful and cost-effective approach. The key principle of liquid-liquid extraction resides in physical contacting of two liquid feed phases to achieve high interfacial area and efficient interfacial mass transfer between the phases. This technique is primarily used in the petroleum, nuclear, chemical, metallurgical, pharmaceutical, food processing, and bioprocessing industries. Separating small amounts of high-boiling contaminants, typically in aqueous solutions, is one of the key advantages of liquid-liquid extraction.

The extraction of carboxylic acids is studied in various kinds of liquid-liquid extractors. Liquid-liquid contactors are mostly made up of mixer-settlers and agitated or pulsed columns. Conventional contactors, such as agitated contactors (Quadros & Baptista, 2003), packed bed columns (Verma & Sharma, 1975), and others, have been utilized in chemical process industries to carry out liquid-liquid extraction for several decades. On the other hand, these units necessitate substantial solvent inventories and long residence times, even though flow fields are often uneven and mixing is poor. Mass transfer in a mixer settler unit is limited to one equilibrium stage. Mechanical agitators for mixer settler units are generally bulky, inefficient, and expensive. To overcome all these limitations/disadvantages of the existing/conventional liquid-liquid extraction technique/methodology, the present invention proposes a new Liquid- Liquid Extraction method and system (as a part of process intensification) for recovery of carboxylic acids, particularly acetic acid, from its aqueous phase/solution (i.e., chemical waste/ industrial effluents) by employing continuous counter-current packed column and/or micro channels, and selecting suitable solvents.

The prior arts related to the present invention are discussed hereunder.

Zina (2006) built an extraction column to separate the water-acetone-acetic acid system using chloroform as the solvent. The column was simulated using Aspen Hysys and compared to hand calculations, yielding a variation of around 1.3.

Dehkordi (2001) conducted experiments on liquid-liquid extraction of succinic acid from its aqueous solution using normal butanol (BSW), iodine from its aqueous solution using kerosene (KIW), and acetic acid from kerosene using distilled water (WAK).

Verma and Sharma (1975) studied the mass transfer characteristics of 3.5, 7.3, 10.6, and 15.6 cm i.d. packed liquid-liquid extraction columns with a variety of packings, including 3/8, 1/2 and one ceramic Raschig rings, 1/2 and one ceramic intalox saddles, 5/8 and one stainless steel Pall rings, and one polypropylene intalox saddles and pall rings.

Weeranoppanant et al. (2017) conducted experiments using a multistage counter-current liquid-liquid extraction (MCCE) system that incorporates segmented flow mixing and membrane-based phase separators to achieve equilibrium extraction.

Hosni et al. (2019) used a Non-Random Two Liquid model built as a thermodynamic approach in Aspen to simulate counter-current liquid-liquid extraction.

Mohadesi et al. (2021) explored liquid-liquid extraction of the three-component n-hexane + benzene + sulfolane system in a micro extractor. Experiments were conducted in a microtube with a diameter of 800m and a residence time of 15s utilizing a T-shaped micromixer. As operational variables, temperature and the ratio of solvent (sulfolane) to feed (95 percent n-hexane + 5% benzene) were studied. The temperature was investigated at (313.15, 323.15, and 333.15) K, and the solvent to feed ratio was investigated in five states, including (0.33, 0.50, 1.00, 2.00, and 3.00) mL/mL.

H. Liu et al. ( 2020) found good extraction selectivity of Cu2+ from water with new microchannel equipment by employing di-(2-Ethylhexyl) phosphoric acid (D2EHPA) as an extractant and kerosene as a solvent.

Sahu et al. (2016) measured mass transfer performance in a well-stirred batch vessel and stratified and slug flow in microchannels using experiments. The test system utilized was the extraction of propionic acid from toluene to water.

However, no study/report/literature is available till date regarding the implication/configuration of random/structured packing type packed columns, and/or micro channels for acetic acid extraction; possibly it may due to lack of knowledge/understanding of the fluid behaviour therein. Therefore, in view of the above limitations of the conventional/existing approaches, techniques, methods and system, there exists a need to develop an improved approach, method/process and system which would in turn address a variety of issues including, but not limited to, contributing to process intensification in liquid-liquid extraction used for acetic acid recovery from industrial effluents, minimizing solvent usage, reducing extraction time and energy, improving extraction quantity in more simple and cost-effective manner. Moreover, it is desired to develop a technically advanced method and system of extracting acetic acid from its aqueous solution (i.e., chemical waste/industrial effluent), which includes all the advantages of the conventional/existing techniques/methodologies and overcomes the deficiencies of such techniques/methodologies.

OBJECT OF THE INVENTION
It is an object of the present invention to provide a method of acetic acid extraction/recovery from its aqueous solution (chemical waste/industrial effluent) using counter current random/structured column contactors.

It is one more object of the present invention to provide a method of acetic acid extraction/recovery from its aqueous solution using microchannels.

It is another object of the present invention to study process intensification on liquid-liquid extraction method/system used for acetic acid recovery/extraction by way of investigating mass transfer characteristics KLa (mass transfer coefficient), percentage extraction, Number of Transfer Units (NTU), and Height of Transfer Units (HTU) in a continuous counter current extraction glass packed column with different solvent to feed flow rate ratios (S/F ratio), different feed compositions, and different packing types.

It is further object of the present invention to investigate KLa, percentage extractions for different channel dimensions with different residence times, and the flow behaviour inside the slugs in a micro channel with vector cross correlations and adaptive correlations obtained by using Micro-Particle Image Velocimetry (PIV).

SUMMARY OF THE INVENTION
In one aspect, the present invention provides a method of acetic acid extraction/recovery from industrial effluents (i.e., aqueous streams containing acetic acid produced by various chemical processes in the industries). The method comprises: providing, in a first reservoir, an aqueous feed containing 10-30 volume % of acetic acid obtained from the industrial effluents; providing, in a second reservoir, at least one organic solvent selected from a group consisting of Ethyl Acetate (EA), Toluene, Methyl Iso Butyl Ketone (MIBK), Di Iso Propyl Ether (DIPE), 1-Decanol, 1-Butanol, Chloroform, Di Chloro Methane (DCM), Di Ethyl Ether (DEE), and mixture thereof; introducing the solvent and the aqueous feed from the reservoirs into a Y-junction microchannel at a solvent-to-feed (S/F flow rate) ratio of 1, or into a packed column at a solvent-to-feed (S/F flow rate) ratio ranging from 1-4, using two pumps; collecting raffinate (heavy phase) and extract (acetic acid rich/ light phase) in two separate tanks.

Other aspects, advantages, and salient features of the present invention will become apparent to those skilled in the art from the following detailed description, which delineate the present invention in different embodiments.

BRIEF DESCRIPTION OF DRAWINGS
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying figures.

Fig. 1 illustrates various method steps of acetic acid extraction/recovery from its aqueous solution, in accordance with an embodiment of the present invention.

Fig. 2 shows a packed column experimental set up used for acetic acid extraction/recovery, in accordance with an embodiment of the present invention.

Fig. 3: Fig. 3(a) shows a random packed column and Fig. 3(b) shows a structured packed column, in accordance with an embodiment of the present invention.

Fig. 4 shows a micro channel experimental set up used for acetic acid extraction/recovery, in accordance with an embodiment of the present invention.

Fig. 5 shows flow of liquid inside the microchannel (i.e., slug formation and internal fluid circulation), in accordance with an embodiment of the present invention.

Fig. 6 illustrates mutual solubility curves (Binodal curves) for Water + Acetic Acid + different Solvents, in accordance with an embodiment of the present invention.

Fig. 7 is a selectivity diagram plotted between Xbc/(Xbc+Xac) and Xba/(Xba+Xaa) that shows performance of various alternative solvents used, in accordance with an embodiment of the present invention.

Fig. 8 illustrates graphical representations of impact of diameter of microchannel, and residence time on mass transfer characteristics in microchannels, in accordance with an embodiment of the present invention.

Fig. 9 illustrates graphical representations of impact of dimensionless numbers on mass transfer characteristics in microchannels, in accordance with an embodiment of the present invention.

Fig. 10 illustrates the flow pattern of Micro Particle Image Velocimetry for water-acetic acid-ethyl acetate system at different time intervals, in accordance with an embodiment of the present invention.

Fig. 11 shows graphical comparison of experimental results between packed column and micro channels, in accordance with an embodiment of the present invention.

List of reference numerals
100 method of acetic acid extraction/recovery
S1: providing aqueous feed of acetic acid
S2: providing organic solvent
S3: introducing solvent/aqueous feed into Y-junction microchannel or packed column
S4: collecting raffinate and extract
200 Packed column experimental setup
1: aqueous feed reservoir
2: solvent reservoir
3: T-shaped burette
4: pumps
5: valves
6: U-shaped tube
7: raffinate tank
8: extract tank
9: packed column
9a: top outlet
9b: bottom outlet
9c: top inlet
9d: bottom inlet
9e: structured/random packing
9f: distributor
300 Microchannel experimental setup
10 microchannel
11 phase separator
12 camera
13 light source

DETAILED DESCRIPTION OF THE INVENTION
Various embodiments described herein are intended only for illustrative purposes and subject to many variations. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but are intended to cover the application or implementation without departing from the scope of the present invention. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

The use of terms “including,” “comprising,” or “having” and variations thereof herein are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Further, the terms “an” and “a” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. Furthermore, the terms “at least one” and “one or more” herein are used to indicate one minimum number of components/features to be essentially present in the invention.

In accordance with an embodiment of the present invention, as shown in Fig. 1-5, the method of acetic acid extraction/recovery from industrial effluents comprises a step (S1) of providing, in a first reservoir (1), an aqueous feed containing 10-30 volume % of acetic acid obtained from the industrial effluents. The industrial effluents include but not limited to aqueous solutions containing acetic acid produced during various chemical processing in the industries such as crude oil refining, metal extraction, and fuel processing.

The method comprises a step (S2) of providing (S2), in a second reservoir (2), at least one organic solvent selected from a group consisting of Ethyl Acetate (EA), Toluene, Methyl Iso Butyl Ketone (MIBK), Di Iso Propyl Ether (DIPE), 1-Decanol, 1-Butanol, Chloroform, Di Chloro Methane (DCM), Di Ethyl Ether (DEE), and mixture thereof.

The method comprises a step (S3) of introducing (S3) the solvent and the aqueous feed from the reservoirs (2, 1) into two branch inlets of a Y-junction microchannel (10) at a solvent-to-feed (S/F flow rate) ratio of 1 using two pumps (4). Preferably, the solvent and the aqueous feed are introduced into the Y-junction microchannel (10) at an equal flow rate ranging from 0.04 ml/min to 0.08 ml/min. The microchannel (10) configured herein has a diameter ranging from 0.7mm to 1.8mm with a constant volume through which the solvent/aqueous feed phases travel in a segmented (slug) flow pattern with increased internal recirculation.

The method comprises a step (S4) of collecting (S4) raffinate and extract (acetic acid rich) in two separate tanks using a phase separating funnel (11) connected to a common outlet of the Y-junction microchannel (10).

Further, a continuous counter current Packed Column (9) having structured or random packing (9e) may be used instead of the microchannel (10) in the step S3. Particularly, the packed column (9) comprises a bottom inlet (9d) to receive the solvent, a top inlet (9c) to receive the aqueous feed, a bottom outlet (9b) to release raffinate (heavy phase), a top outlet (9a) to release extract (acetic acid rich light phase), and a structured/fixed or random packing (9e) internally filled between the bottom inlet (9d) and the top outlet (9a) to cause phase separation therein.

In case of the packed column the solvent and the aqueous feed from the reservoirs (2, 1) are introduced into a packed column (9) at a solvent-to-feed (S/F flow rate) ratio ranging from 1-4 using two pumps (4). Preferably, the solvent is introduced at a flow rate of 4ml/min, where the aqueous feed is introduced at a flow rate ranging from 4ml/min to 16 ml/min. The raffinate is collected in a raffinate tank (7) connected to the bottom outlet (9b), where the extract is collected in an extract tank (8) connected to the top outlet (9a). Further, a pressure difference is maintained between the bottom outlet (9b) and the top outlet (9a) of the column (9). Preferably, the packed column has an internal diameter of 45mm, a column length of 500mm, and a packing length of 200mm with pore volume of 40 cm3.

In a preferred embodiment, the organic solvent used in the step (S2) is pure Ethyl Acetate.

In accordance with an embodiment of the present invention, as shown in Fig. 2-3, the continuous counter-current extraction system (200) for acetic acid recovery/extraction comprises an extraction column (9), aqueous solution feed reservoir (1) for carrying acetic acid effluent, a solvent feed reservoir (2), two dosing pumps (4), a raffinate tank (7), and an extract tank (8).

The column is made of a glass tube having 45mm internal diameter and 500 mm length. The column has a packing length of 200 mm and two disengaging spaces at the top and bottom, respectively, where the light and heavy phases are withdrawn. The dispersed phase (solvent) is fed into the column via a distributor (9f) with pores at the bottom. The advantage of this distributor (9f) is to distribute the solvent evenly to the packing.

The solvent reservoir (2) is connected to one end of an inverted T-shaped burette (3) with the help of silicone tubing, and the other end of this burette is connected to the solvent pump (4). The inverted 'T' shaped burette is calibrated, and its primary use is to measure the solvent flow rate. The solvent reservoir (2) has a valve adapted to stop the fluid flow therefrom into the burette (3) while measuring the flow rates. A similar setup is placed on other side. The (effluent) feed reservoir (2) is connected to a burette (3) and the other end of this burette to the feed pump (4), which is again connected to the column's top containing a top inlet (9c) using silicon tubing. The continuous phase (aqueous phase) is fed from the feed pump (4) through the top of the column, and it falls through gravity from the top inlet (9c).

There are two exits/outlets (9a, 9b) in the column (9); one is at the right top for extract collection, and the other is at the bottom. The bottom exit is connected to a U-shaped tube (6) that approximately equals the column's size and contains an opening at the bottom for the collection of raffinate in the raffinate tank (7). This can be regulated by using a (raffinate) valve provided at the bottom of this U tube. The primary purpose of this U-shaped tube is to maintain the pressure difference at the extract exit. The column may be filled with two different types of packings i.e., random packing and structured packing (as shown in Fig. 3).

In accordance with an embodiment of the present invention, as shown in Fig. 4-5, the microchannel system (200) for acetic acid recovery/extraction comprises a feed reservoir (1), a solvent reservoir (2), two high-precision HPLC (High Performance Liquid Chromatography) pumps (4), Y-junction microchannel (10), and a phase separating funnel (11) for separating raffinate and extract. The liquids are drawn at desired flow rates using these pumps (4) from the reservoirs (1, 2). The feed reservoir (1) contains 20% acetic acid in the water, and the solvent reservoir (2) contains pure ethyl acetate. The inlets of the pumps are connected to the respective reservoirs (1, 2), and the outlets of the pumps are connected to the adjacent branches of the Y-junction microchannel (10). The outlet of this microchannel is connected to the phase separating funnel (11) in which both the raffinate and the extract are collected which are then analysed for acetic acid concentration.

WORKING EXAMPLE
Selection of appropriate solvent for acetic acid extraction from water
Wastewater discharge from chemical process industries has a severe threat to the environment. These outlet waters consist of traces of organic solvents. Liquid-Liquid extraction is a suitable method when traces of compounds have to be extracted. A strategy for selecting solvents for chemical recovery from dilute solution is disclosed in the present invention. Low solvent losses and high solute distribution coefficient are the significant objectives of solvent selection.

The various solvents that are used in the present invention are Ethyl Acetate (EA), Toluene, Methyl Iso Butyl Ketone (MIBK), Di Iso Propyl Ether (DIPE), 1-Decanol, 1-Butanol, Chloroform, Di Chloro Methane (DCM), Di Ethyl Ether (DEE) and a mixed solvent (EA + MIBK). The list of solvents used to extract acetic acid from industrial effluent and their properties are shown in table 1.
Table 1
Sl. No. Solvent Formula Molar
Mass (g/mol) Chemical structure Density g/cm3 Melting point (oc) Boiling point (oc)
1. Toluene C7H8 92.141 0.87 -95 111
2. Ethyl Acetate C4H8O2 88.106 0.902 -83.6 77.1
3. Chloroform CHCl3 119.37 1.489 -63.5 61.15
4. 1-Decanol C10H21OH 158.28 0.8297 6.4 232.9
5. Methyl Iso Butyl Ketone MIBK C6H12O 100.16 0.802 -84.7 117-118
6. DIPE
Di Iso Propyl Ether C6H14O 102.17 0.725 -60 68.5
7. 1-Pentanol (Amyl Alcohol) C5H12O 88.15 0.811 -78 137-138
8. 1-Butanol C4H10O 74.123 0.81 -89.8 117.7
9. Di Chloro Methane (DCM) CH2Cl2 84.93 1.33 -96.7 °C 39.6 °C
10 Di Ethyl Ether (C2H5)2O 74.12 0.7134 -116.3 °C °C

The tertiary system of water + acetic acid + solvents produce various results. At 293.15 K and 1 atm, binodal curves and tie-line liquid-liquid equilibria data from experiments are obtained using the method of titration. The distribution coefficients and selectivity for the zone of immiscibility are evaluated. Hand, Othmer, and Ishida correlations are used to test the reliability of experimental tie-line data.

Binodal Curves
The binodal curve indicates mutual solubility i.e., solvent's ability to extract acetic acid from an aqueous solution. The binodal curve is obtained by setting up a titration setup with acetic acid in the burette and the other two components in a conical flask. For determining the aqueous phase data, 10 ml of distilled water is poured into a conical flask and then 1 ml of required solvent is added to it, which becomes a heterogeneous phase, and titrate the mixture against the third component, acetic acid until the turbidity disappears and a homogeneous phase is formed. Then, the experiment is repeated by taking different volumes of solvent, i.e., 2ml, 4ml, 6ml, 8ml, 10ml, by keeping the volume of water constant, i.e., 10 ml for each run. For determining the organic phase data, 10 ml of required solvent is poured into a conical flask and then 1 ml of distilled water is added to it, which becomes a heterogeneous phase. Next, titrate the mixture against acetic acid's third component until the turbidity disappears and a homogeneous phase is formed. Finally, the experiment is repeated by taking different volumes of distilled water, i.e., 2ml, 4ml, 6ml, 8ml, 10ml, by keeping the solvent volume constant, i.e., 10 ml, for each run.

Referring to Fig. 6, the area under the curve illustrates that the proposed solvents have the potential to separate. The solvent toluene has a relatively high heterogeneity area, implying that it may be employed for higher feed concentrations. When the feed concentration is low, ethyl acetate can be employed; however, as the feed concentration rises the solvent ethyl acetate becomes ineffective.

Tie-Line Data Experimentation
For the tie-line data generation, 20 ml of water, a solvent of 30 mL, and 5 ml of the solute are taken in a conical flask and placed in a shaking incubator for an hour. After 1 hour, the contents are transferred into a separating funnel, and the contents are allowed to settle for an hour in it. Two immiscible clear liquids of organic and aqueous phases are separated. Titration of the aqueous phase liquid against a known concentration of NaOH using the Phenolphthalein indicator yields tie-line data for the first extract. The exact amount of water, i.e., 20 mL, is added to the organic phase obtained in the first extract and shaken for one hour and allowed to settle to get a second tie line. The same procedure is repeated for other tie-lines.

Table 2 represents the data from the experimental tie-lines in the phases of equilibrium, where Xna and Xnc denote the weight fractions of the nth compound in the raffinate phase and extract phase, respectively, ranging from (a-c).
Table 2
Xna: Aqueous Phase (Raffinate Phase) Xnc: Organic Phase (Extract Phase)
Xa (water) Xb (Acetic Acid) Xc (EA) Xa (water) Xb (Acetic Acid) Xc (EA)
0.9711 0.028855 0.007219 0.008452 0.0943 0.9057
0.938 0.062 0.015919 0.023687 0.1104 0.8896
0.904611 0.095389 0.091896 0.068242 0.1286 0.8714

Xa (water) Xb (Acetic Acid) Xc (1-Pentanol) Xa (water) Xb (Acetic Acid) Xc (1-Pentanol)
0.9676 0.032363 0.008123 0.015743 0.1118 0.8882
0.9462536 0.053746 0.013717 0.030876 0.1152 0.8848
0.9142662 0.0424538 0.04328 0.080681 0.056119 0.8632

Xa (water) Xb (Acetic Acid) Xc (1- Butanol) Xa (water) Xb (Acetic Acid) Xc (1- Butanol)
0.9595 0.04049 0.008614 0.017577 0.1322 0.8678
0.9300613 0.069939 0.015247 0.037132 0.091468 0.8714
0.8957582 0.084242 0.0199998 0.052411 0.069989 0.8776

Xa (water) Xb (Acetic Acid) Xc (MIBK) Xa (water) Xb (Acetic Acid) Xc (MIBK)
0.9781 0.021917 0.006196 0.009081 0.0886 0.9114
0.909693 0.081031 0.009276 0.01824 0.11116 0.8706
0.89433363 0.105664 0.114177 0.088909 0.1322 0.8678

Xa (water) Xb (Acetic Acid) Xc (DIPE) Xa (water) Xb (Acetic Acid) Xc (DIPE)
0.9334 0.01626 0.00034 0.009988 0.067212 0.9228
0.9659852 0.034015 0.009895 0.015296 0.126 0.874
0.8645219 0.135478 0.148497 0.137521 0.1397 0.8603

Xa (water) Xb (Acetic Acid) Xc (1- Decanol) Xa (water) Xb (Acetic Acid) Xc (1- Decanol)
0.9845 0.015537 0.006891 0.007137 0.093 0.907
0.9573914 0.042609 0.019192 0.02204 0.122 0.878
0.8940976 0.105902 0.169575 0.095699 0.1356 0.8644

Xa (water) Xb (Acetic Acid) Xc (DCM) Xa (water) Xb (Acetic Acid) Xc (DCM)
0.9865 0.009548 0.003952 0.039933 0.010267 0.9498
0.9368038 0.0551612 0.008035 0.052923 0.073377 0.8737
0.845887 0.154113 0.144231 0.176449 0.1412 0.8588

Xa (water) Xb (Acetic Acid) Xc (DEE) Xa (water) Xb (Acetic Acid) Xc (DEE)
0.9553 0.034736 0.009964 0.00998 0.07792 0.9121
0.9486549 0.051345 0.011021 0.012061 0.1163 0.8837
0.8821805 0.1117819 0.097328 0.076107 0.1357 0.8643

Xa (water) Xb (Acetic Acid) Xc (Toluene) Xa (water) Xb (Acetic Acid) Xc (Toluene)
0.9794 0.00575 0.01485 0.01994 0.04876 0.9313
0.9571936 0.0097164 0.03309 0.06216 0.07454 0.8633
0.8429973 0.157003 0.157481 0.222754 0.1426 0.8574

Xa (water) Xb (Acetic Acid) Xc (Chloroform) Xa (water) Xb (Acetic Acid) Xc (Chloroform)
0.9594 0.00606 0.03454 0.02768 0.01932 0.953
0.9265321 0.0173479 0.05612 0.09165 0.01485 0.8935
0.8286527 0.171347 0.211887 0.304326 0.1426 0.8574

Xa (water) Xb (Acetic Acid) Xc (EA+MIBK) Xa (water) Xb (Acetic Acid) Xc (EA+MIBK)
0.9702 0.029821 0.007973 0.010843 0.095 0.905
0.940108 0.059892 0.016385 0.027405 0.1117 0.8883
0.905041 0.094959 0.097129 0.072785 0.1282 0.8706

Distribution Coefficient and Selectivity
An effective solvent for the extraction is selected based on its selectivity value, which tells that acetic acid can be separated from water using that solvent. The distribution coefficient value (D water) of water is then calculated as the ratio of concentration of water in the organic phase to the concentration water in the aqueous phase. The acetic acid distribution coefficient value (D acetic acid) is calculated as the ratio of concentration of acetic acid in the organic phase to the concentration acetic acid in the aqueous phase, as shown in Table 3.
Table 3
Water + Acetic Acid + Ethyl Acetate (EA)
D water D acetic acid Selectivity (D acetic acid / D water)
0.0087 3.26806446 375.4871507
0.0253 1.780645161 70.51315748
0.0754 1.348163834 17.87116196
Water + Acetic Acid + 1- Pentanol
D water D acetic acid Selectivity (D acetic acid / D water)
0.0163 3.454562309 212.325128
0.0326 2.143415324 65.68902923
0.0882 1.321884025 14.97941131
Water + Acetic Acid + 1- Butanol
D water D acetic acid Selectivity (D acetic acid / D water)
0.0183 3.265003705 178.2312712
0.0399 1.307825391 32.75766948
0.0585 0.83080886 14.19938275
Water + Acetic Acid + MIBK
D water D acetic acid Selectivity (D acetic acid / D water)
0.0093 4.042524068 435.4138081
0.0201 1.371820661 68.41752482
0.0994 1.251135675 12.5851456
Water + Acetic Acid + DIPE
D water D acetic acid Selectivity (D acetic acid / D water)
0.0102 4.133579336 406.9845734
0.0158 3.704248126 233.9336341
Water + Acetic Acid + 1- Decanol
D water D acetic acid Selectivity (D acetic acid / D water)
0.0072 5.985711527 825.6876837
0.0230 2.863244854 124.3759528
Water + Acetic Acid + DCM
D water D acetic acid Selectivity (D acetic acid / D water)
0.0405 1.075303729 26.56417319
0.0565 1.330228494 23.54672086
0.2086 0.916210832 4.39226537
Water + Acetic Acid + DEE
D water D acetic acid Selectivity (D acetic acid / D water)
0.0104 2.243205896 214.722905
0.0127 2.265069627 178.1584778
0.0863 1.213971135 14.07152644
Water + Acetic Acid + Toluene
D water D acetic acid Selectivity (D acetic acid / D water)
0.0204 8.48 416.5151454
0.0649 7.6715656 118.1334217
0.2642 0.908262899 3.437258913
Water + Acetic Acid + Chloroform
D water D acetic acid Selectivity (D acetic acid / D water)
0.0289 3.188118812 110.501488
0.0989 0.85601139 8.653813761
0.3673 0.832229336 2.266086651
Water + Acetic Acid + (EA+ MIBK)
D water D acetic acid Selectivity (D acetic acid / D water)
0.0112 3.185674525 285.0448606
0.0292 1.865023709 63.97824154
0.0804 1.35005634 16.78719984

Hand, Othmer, Ishida Correlations
Hand, Othmer-Tobias, and Ishida correlations are employed in this investigation to determine the compatibility of the tie line data. The weight fractions of acetic acid, solvent, and water in ‘raffinate phase’ and ‘extract phase’ are denoted as Xba and Xbc, respectively. The weight fractions of water in ‘raffinate phase’ and ‘extract phas’s are denoted by Xca and Xcc, respectively.
The Hand Correlation :
(Xbc/Xcc) = p * (Xba/Xaa)q
The Othmer-Tobias correlation :
((1-Xcc)/Xcc)= p' * ((1-Xaa)/Xaa)
Ishida Correlation
(Xca*Xbc)/(Xba*Xcc) = p" *((Xac*Xca)/(Xaa*Xcc))
The above-mentioned correlation constants are mentioned below in table 4.
Table 4
System Hand Correlation Othmer Correlation Ishida Correlation
p q R2 p' q' R2 p" q" R2
Water (a) + Acetic Acid (b) + EA (c)
0.0016 28.802 0.9637 0.0002 46.003 0.9983 0.0198 32.504 0.9983
Water (a) + Acetic Acid (b) + AA (c)
0.0004 35.416 0.9577 0.0099 70.709 0.9218 0.00673 26.211 0.996
Water (a) + Acetic Acid (b) + Butanol (c)
0.053 41.037 0.996 0.0169 6.8319 0.9026 0.0202 12.404 0.915
Water (a) + Acetic Acid (b) + MIBK (c)
0.024 9.2186 0.96 0.0074 23.215 0.9325 0.0202 23.053 0.9627
Water (a) + Acetic Acid (b) + DIPE (c)
0.0006 31.552 0.8588 0.0002 47.288 0.9627 0.00247 43.588 0.9999
Water (a) + Acetic Acid (b) + Decanol (c)
0.0004 35.809 0.965 0.02 56.753 0.9496 0.0148 21.95 0.9997
Water (a) + Acetic Acid (b) + DCM (c)
0.0005 35.423 0.9993 0.0003 44.091 0.9958 0.00273 60.596 1
Water (a) + Acetic Acid (b) + DEE (c) 0.0012 29.807 0.9937 0.0005 38.525 0.9787 0.0729 55.816 0.9997
Water (a) + Acetic Acid (b) + Toluene (c) 0.033 49.004 0.959 0.0067 64.144 0.9709 0.00234 65.052 1
Water (a) + Acetic Acid (b) + Chloroform (c) 0.054 7.8614 0.9896 0.0011 38.11 0.9242 0.00268 52.057 1
Water (a) + Acetic Acid (b) + (EA+MIBK) (c) 0.0014 29.27 0.9988 0.0014 29.27 0.9988 0.00673 29.68 0.9983

The selectivity diagram for the systems is plotted between Xbc/(Xbc+Xac) and Xba/(Xba+Xaa) and shown in Fig. 7. The graph shows that the performance of acetic acid extraction is highest with EA (Dark Blue Line) and the least with Chloroform (Brown Line)

Conclusions
The reported system's selectivity values are more than 1, implying that acetic acid can be extracted from any of the 11 solvents mentioned above.
As the result of experimental data, the hierarchy of selecting the solvent based on the two-phase region (binodal curve) and selectivity is given in an order of ‘Ethyl Acetate > Mixed (EA+MIBK)> Amyl Alcohol > Butanol> Di Ethyl Ether > MIBK> Decanol> DIPE> DCM> Toluene > Chloroform’. This information is very useful for the selection of solvent in separation of acetic acid from aqueous phase.
The experimental studies with 11 solvents at 293.15 K and 1 atm show that Ethyl Acetate is the most suitable solvent to extract acetic acid from water, the least being chloroform, which is determined based on the selectivity value of the solvents. Ethyl acetate has a selectivity value of 17.87, whereas chloroform has a selectivity value of 2.26. The distribution coefficients obtained for all the solvents prove that the 11 solvents chosen in the present invention can extract acetic acid from the feed.
Compatibility of the tie line data determined using Hand, Othmer, and Ishida correlations proves that the data has reliability. All the systems have the coefficient of determination (R2) nearly equal to unity.
After conducting simulations by using the above experimental data in Aspen software, it is concluded that ethyl acetate and MIBK are two best solvents. Therefore, for low acetic acid concentration in the water, ethyl acetate would be the best choice, and for higher concentrations of acetic acid, MIBK would be the best solvent.

Experimental procedure of acetic acid recovery/extraction in Packed Column
In an exemplary embodiment, the first set of experiments is conducted with randomly packed 483 Raschig rings is made up of glass with dimensions 6.5 mm, 4.5 mm, and 8 mm outer diameter, internal diameter, and height, respectively [as shown in Fig. 3(a)]. The other packing set is Sulzer Penta- PakTM PS- 500M1 structured packing [as shown in Fig. 3(b)] having height 200 mm under the same conditions.

The Raschig rings used to pack the column are first properly washed with water to eliminate all dirt, then washed with ethyl acetate saturated with water, followed by distilled water. The column is packed by putting one by one piece of packing into a column filled with distilled water. To eliminate larger voids, the packing is moved gently whenever necessary. The water is emptied from the column once the necessary packing height is obtained.

The pore volume of the packed column is determined by the difference in the volume of water filled in the column before packing and after packing, and it is determined to be 70 cm3 for the packing with Raschig rings and 40 cm3 for the Sulzer packing. The solvent ethyl acetate used is always pure. The aqueous feed contains concentrations of acetic acid, namely 10, 15, 20, 25, and 30 volume % of acetic acid in water. Experiments are performed by varying dispersed phase (ethyl acetate phase) flow rates by keeping the continuous phase (aqueous phase) flow rate constant. The packed volume is 192.5 cm3. The column is initially filled with an aqueous feed phase saturated with ethyl acetate solvent (organic phase). Then the feed flow (aqueous) is adjusted to the desired rate, i.e., 4ml/min, which passes through the dip let provided at the column's top.

The dispersed phase is introduced from the bottom and experiments are performed by varying the ethyl acetate (organic phase) flow rate from 4 to 16 ml/min; in other words, the solvent/feed flow rate ratio is changed from 1 to 4. The flow rates can be checked and adjusted at regular intervals by using the inverted T-shaped burette. To measure either the solvent or feed flow rates, initially, before the start of the experiment, it is ensured that the valves of the solvent or feed tanks are completely opened and some level of liquid flows into these inverted T-shaped burettes. While the solvent and feed pumps are turned on, the liquid from the burette will flow through the pump. At the same time, some amount of liquid gets displaced into the burettes from the respective tanks maintaining a constant level of liquid in the burette. So to determine the flow rates, the solvent and feed tank valves are completely closed, which ensures that no liquid flows through these tanks, and then it can be possible to observe the decrement of liquid in these burettes with time. Hence, measuring the change in the liquid level in the burette for a particular time makes it possible to measure the feed and solvent flow rates. If the flow rate needs to be adjusted, then the tuning of the pumps can be changed, and once again, the above-said process has to be repeated until the predetermined flow rate is obtained. After some time, the extract overflows from the top of the column's extract valve into the extract tank, while the water-rich phase is collected in the raffinate tank by the raffinate valve located at the lower end of the column simultaneously.

At the lower end of the column, U- tube needs to be kept open at a flow rate less than that of the feed. This process ensures the continuous flow of feed and solvent. Continuous collection of extract and raffinate in the extract and raffinate tanks provided, respectively. After a certain period during this process, one can observe the separation zone above the packing, as shown in Fig. 3. The level of separation zone is maintained constant at 30 mm above the packing, and the solvent zone level is kept at 90 mm above the separation zone's level by adjusting the flow rate at the raffinate valve. Similarly, the same experimental procedure is repeated with the same column but with structured packing called Sulzer packing with the same packing height of 200mm.

Sample Analysis
5ml of each sample of extract and raffinate are collected at different time intervals in a pipette and analysed for the acetic acid concentration. Simple acid-base titration with sodium hydroxide (NaOH) as the titrant is used for the analysis. Before starting the experiment, a solution of NaOH is prepared and standardized with the known concentration of oxalic acid, and the normality of NaOH is calculated. In all these experiments phenolphthalein indicator is used to determine the endpoint. Before the titration, two drops of phenolphthalein are added to the 5ml collected samples. This known normality of NaOH solution is taken in a titration burette. The sample solutions of raffinate are titrated using this NaOH solution. At the endpoint, these colorless solutions turned pale pink, and the corresponding burette readings are noted to calculate concentrations of acetic acid in the respective samples.

The samples are collected at different intervals and analysed until a steady state is reached. Using material balance, the quantity of acetic acid extracted by the extract phase is estimated. After the steady-state is reached, the whole system is shut down, and the column is drained off, washed thoroughly with distilled water, and dried for the next experiment.

The mass transfer characteristics in Packed Column may be calculated by following procedure:
Consider a system of water + acetic acid (Feed) + ethyl acetate (solvent)
Let
Vf = Feed flow rate in ml/min
Vs = Ethyl acetate (solvent) flow rate in ml/min
X = Acetic acid concentration in the aqueous phase in g/ml
Y = Acetic acid concentration in the organic phase in g/ml
Subscripts: 1: Top of column
2: Bottom of column
Mass Balance:
Acetic acid extracted from the aqueous phase (Feed)
= Vf (X1 – X2)
Acetic acid extracted by the organic phase (Solvent)
= Vs (Y1 – Y2)
Here, since ethyl acetate in the solvent tank is pure and hence Y2 = 0
= Vs (Y1 – 0)

Therefore theoretically, Rate of solute (acetic acid) transfer is,
= Vf (X1 – X2) = Vs(Y1 – 0)
Mass transfer coefficient (KLa):
= Rate of acid Transfer / Volume of Packing X Mean driving force
Where Log mean driving force: (?X1-?X2) / ln (?X1/?X2)
?X1 = Driving force at the top of the column = (X1-X1*)
?X2 = Driving force at the bottom of the column = (X2-X2*) = X2

Where X1* and X2* are the concentrations in the aqueous phase, which would be in equilibrium with concentrations Y1 and Y2 (= 0.0) in the organic phase, respectively. The equilibrium values can be found using the distribution coefficient for the chemicals used (Assuming that Y = KdX relation holds at equilibrium for a constant Kd).

In dilute solutions at equilibrium, the solute concentration in the two phases is called the distribution coefficient or distribution constant 'Kd.'
Kd =Y/X = concentration of solute in the organic phase/ concentration of solute in the aqueous phase
Where the Y and X are the concentrations of the solute in the extract and the raffinate phases respectively at equilibrium.

The volume of packing = pr2l
Where r = radius of the column
l = length of the packing or height of the packing
The packed height (Z) is related to the following formula:
Z = N x H
Where
N = number of transfer units (NTU) - dimensionless
H = height of transfer units (HTU) - dimension of length

The number of transfer units (NTU) required is a measure of the difficulty of separation. A single transfer unit gives the change of composition of one of the phases equal to the average driving force producing the change. Hence, many transfer units will be required for the very high purity of the product.

The height of a transfer unit (HTU) measures the separation effectiveness of the particular packing for a specific separation process. As such, it incorporates the mass transfer coefficient. The more efficient the mass transfer (i.e., more significant mass transfer coefficient), the smaller the value of HTU.

NTU = (X2 – X1)/ (X*-X)LM
(X*-X)LM = [(X2* - X2) – (X1* - X1)]/ ln [ (X2* - X2)/( X1* - X1)]
HTU = Z / NTU

The simulations are carried out (in Aspen Plus software) using an aqueous feed comprising acetic acid concentrations of 10, 15, 20, 25 and 30 volume percent in water, with 16 mL/min solvent and 4 ml/min feed [S/F ratio =4]. The Extract model is selected to simulate continuous counter-current packed column extraction of acetic acid-water–ethyl acetate. The thermodynamic model used is UNIFAC, and almost 99 percent extraction is obtained with the number of stages =3.

Table 5 shows a comparison of impact of Solvent/Feed ratio on Mass Transfer Characteristics in random and structured packings for water+ acetic acid+ ethyl acetate (20% acetic acid, h=20 cm, vp =192.5 cm3, eR=0.363, eS = 0.197, Y2=0).

Table 5

Table 6 shows comparison of results in packed column with random and structured packings for water+ acetic acid+ ethyl acetate (20% acetic acid, h=20 cm, vp =192.5cm3, eR = 0.363, eS = 0.197, Vf = 4ml/min, Vs=16 ml/min, Y2=0).
Table 6
Type of contactor Vf
ml/min Vs
ml/min
S/F ratio RA
g/min KLa×104 (sec-1) % E NTU HTU (cm) tE min
Packed column with
Random packing 4 4 1
0.432
3.56
51.42
1.1
19.4
390
4 16 4 0.72 7.45 85.71 2.15 9.30 320
Packed column with
Structured packing
4
4 1
0.470
3.9
56
1.125
17.7
315
4 16 4 0.744 8.14 88.57 2.35 8.50 230

Conclusion:
It is evident that for a constant feed concentration, S/F ratio, and volume of packing, the values of KLa, percentage extraction, NTU are higher for a structured Sulzer packing than a random Raschig ring packing. The HTU values are lesser for structured packing when compared with random packing. The time required for extraction decreases significantly for structured packing, which causes a reduction in solvent consumption.
For the fixed column diameter and the packing height, the porosity available for structured packing is 0.197, whereas random packing is 0.363. Thus, KLa, percentage extraction, and NTU values increase as HTU and time for extraction decrease due to decreased porosity of structured packing. This could be owing to an increase in available area for mass transfer and a hold-up in the dispersed phase.
Therefore, it is likely that the random packing surface renewal rate is less than that for the structured packing under otherwise uniform conditions. Hence structured packing is preferable than random packing.
Higher KLa and higher percentage acetic acid extraction from the feed utilizing a continuous counter-current packed column are obtained at an S/F ratio of 4 with a concentration equal to 20% of acetic acid in the feed.

The individual effect of the variables on mass transfer characteristics are compared among three systems (for feed concentration of 20 % acetic acid in structured Sulzer packing) which are mentioned in Table 7.
Table 7
Solvent Vf Vs S/F RA KLa×104 %E NTU HTU
Ethyl acetate 4 4 1 0.46670 2.85 55.56 0.821809 24.33655
4 8 2 0.67759 5.75 80.665 1.660814 12.04229
4 16 4 0.74304 7.52 88.457 2.172342 9.206655
MIBK 4 4 1 0.39398 2.27 46.902 0.656867 30.44755
4 8 2 0.52003 3.41 61.908 0.985877 20.28652
4 16 4 0.70910 6.56 84.417 1.894975 10.55423
Mixed solvent
4 4 1 0.40852 2.36 48.634 0.680742 29.3797
4 8 2 0.57336 4.04 68.254 1.166193 17.14982
4 16 4 0.71637 6.71 85.282 1.937209 10.32413

Conclusion:
Considering the solvent flow rate for each system, the % extraction of acetic acid increases by increasing the solvent flow rate, i.e., from 4ml/min to 16ml/min. This is due to the fact that while the dispersed phase flow rate increases, the mean drop diameter does not vary considerably. The greater the number of droplets, the better the mass transfer; this is owing to the increased internal circulation of more drops. The effective interfacial area is proportional to the dispersed phase (Solvent) flow rate at any specified value of continuous phase flow rate.
The above solvents and feed containing 20% acetic acid show that ethyl acetate has better extraction results than MIBK and their combination. This is because the distribution coefficient of ethyl acetate is higher than that of MIBK and their combination.

Experimental results obtained in the packed column are validated with the Aspen Plus Simulation results as shown in Table 8.
Table 8
Sl. No. Acetic acid concentration in feed (vol %) Feed
(ml/min) Solvent
(ml/min) S/F
ratio % Extraction corresponding to number of stages =2 % Extraction corresponding to number of stages =3
1 10 4 16 4 94.2 98.2
2 15 4 16 4 94.7 97.6
3 20 4 16 4 94.8 99.0
4 25 4 16 4 96.9 98.8
5 30 4 16 4 97.6 99.2

Conclusion:
A good agreement is observed between the experimental results obtained in the packed columns and the predicted results obtained from the ASPEN PLUS software simulation.
The Aspen Plus simulation results show that almost 97-99 % extraction can be achieved with the number of stages = 3, and nearly 94-97 % extraction can be performed with the number of stages =2.
The experimental results show that almost 85-90 % extraction can be obtained with NTU values greater than 2 and less than 2.5.
Around 8-10% deviation is observed from experimental results and results predicted from Aspen software, which is an acceptable deviation compared to the actual experimental work and theoretical prediction with software simulation.
In liquid-liquid continuous counter-current extraction system, the optimum number of stages=3 can be used to achieve about 95 % acetic acid extraction from water using ethyl acetate as a solvent with a S/F ratio =4.

Experimental procedure of acetic acid recovery/extraction in Microchannels
Surface tension, energy dissipation, and other properties of fluids at the microscale differ from those of macro fluids. Gravity has a negligible effect. A low flow rates Reynolds number, which characterizes the flow, is extremely low. So, the flow will remain laminar. Surface effects dominate this flow. Inertial forces are negligible when compared to friction, viscous effects, and electrostatic forces. Diffusion alone causes two fluids to mingle.

Once the setup as shown in Fig. 4 ready, both the solvent and feed pumps are turned on, and a specific flow rate is set through the pumps. After some time, the formation of uniform slugs is observed in the microchannel, as shown in Fig. 5. A coloured solution of ethyl acetate is fed to identify the organic slug. After some time, both the phases are collected in the phase separating funnel, and both the phases are withdrawn and are analysed for acetic acid concentration. Flow rates of 0.04 ml/min, 0.06 ml/min, and 0.08 ml/min are used in a series of experiments with S/F (solvent to feed flow rate) ratios of 1 in various channel diameters.

Further, in the experimental set up, a camera (12) and a light source (13) are used to monitor the extraction performance through particle image velocimetry (PIV) and Aspen (software) simulation models.

Sample Analysis
The analysis of the concentration of acetic acid in raffinate is done by titrating the raffinate phase with 0.5 NaOH using a phenolphthalein indicator. The amount of acetic acid that remains in the raffinate phase is determined using the NaOH readings on the burette at the endpoints. Finally, using material balance, the quantity of acetic acid extracted by the extract phase is estimated.

The mass transfer characteristics in microchannels may be calculated by following procedure:
Let
Qaq = Feed flow rate in ml/min
Qor = Ethyl acetate (solvent) flow rate in ml/min
Caq,i = Acetic acid concentration in the inlet aqueous phase in g/ml (feed)
Caq,o = Acetic acid concentration in the outlet aqueous phase in g/ml (raffinate)
Cor,i = Acetic acid concentration in the inlet organic phase in g/ml (solvent)
Cor,o = Acetic acid concentration in the outlet organic phase in g/ml (extract)

Mass Balance:
Acetic acid is extracted from the aqueous phase (raffinate).
= Qaq (Caq,i – Caq,o)
Acetic acid extracted by the organic phase (extract)
= Qor( Cor,o – Cor,i)
Here, since ethyl acetate in the solvent tank is pure, hence Cor,i = 0
= Qor (Cor,o – 0)
Therefore theoretically, Rate of solute (acetic acid) transfer is,
= Qaq (Caq,i – Caq,o) = Qor (Cor,o – 0)

The volumetric mass transfer coefficient KLa is calculated as follows to characterize the performance of the micro channel.

Mass transfer coefficient (KLa): Qaq (Caq,i – Caq,o) / Vm?Cm
Where Vm = volume of the micro channel = pr2l
r = radius of the micro channel
l = length of the micro channel
?Cm = logarithmic mean concentration driving force
and ?Cm = (?Caq,i- ?Caq,o) / ln (?Caq,i/ ?Caq,o)
?Caq,i = Caq,i– Caq,i* and ?Caq,o = Caq,o - Caq,o*
Where Cor = m Caq*
Caq,i* is the equilibrium concentration of the solute in the inlet aqueous phase, corresponding to the actual inlet concentration of the solutes in the organic phase, and Caq,o* is the equilibrium concentration of the solutes in the outlet aqueous phase, corresponding to the actual outlet concentration of the solutes in the organic phase.
Percentage extraction (E) = (1 – Caq,o / Caq,i )×100

The Reynolds number (NRe), Capillary number (NCa), and Weber number (NWe), all of which have no dimensions in one-phase flow, are frequently used to measure multiphase-fluid dynamics. Various forces acting inside the micro channels can be described by dimensionless numbers as shown below.

Reynolds number (Inertial forces)/(Viscous forces) NRe= (?.u.d_H)/µ
Weber number (Inertial forces)/(Liquid-liquid surface tension ) NWe =(u^2.d_H.?)/s
Capillary number (Viscous forces)/(Liquid-liquid surface tension) NCa=(µ.u)/s

Reynolds number = Inertial forces /Viscous forces, for the liquid mixture of two immiscible phases can be calculated as
NRe = DHUM ?M /µM
Where:
Where A is the cross-sectional area and P is the wetted perimeter of the cross-section.
For a circular tube, this checks as:

Uaq = Qaq / A and Uor = Q or / A
UM = Uaq + Uor

Weber number is given by NWe = UM2 DH ?M / sM
And Capillary number is given by NCa = µM UM / sM

Density of the feed ,
?aq = ?water × mass fraction of water + ?acetic acid × mass fraction of acetic acid

The viscosity of the feed is calculated using the Refutas equation. The calculation is carried out in three steps. The first step is to calculate the Viscosity Blending Number (VBN) (also called the Viscosity Blending Index) of each liquid blend or liquid mixture component.

Where v is the kinematic viscosity in centistokes (cSt), the kinematic viscosity of each component of the blend must be obtained at the same temperature.

The next step is to calculate the VBN of the blend, where xX is the mass fraction of each component of the mixture.

Once the viscosity blending number of a blend has been calculated, the final step is to determine the kinematic viscosity of the blend by solving the equation for v:

Where VBNBlend is the viscosity blending number of the blend.

Properties of water, ethyl acetate, and acetic Acid at 25oc and 1 atm are given in table 9.
Table 9
Compound Density (gm/cm3) Viscosity (centistokes) Viscosity
(milli Pascal seconds)
Water 0.997 0.892 0.890
Acetic acid 1.049 1.063 1.116
Ethyl acetate 0.900 0.475 0.428

Hence from above equations and table, the viscosity of feed mixture containing 20 % acetic acid by volume in water is determined with a mass fraction of acetic Acid = 0.21 and mass fraction of water = 0.79. The calculated value of viscosity of the feed using the properties from Table is µaq= 0.932 MilliPa.s.

sM = interfacial tension between the aqueous and organic phase
the interfacial tension between water and ethyl acetate at 250c was given as = 6.8m N/m and hence sM = 6.8 m N/m

Residence time in seconds is given by tR = volume of the channel ×60 / (Vor + Vaq)

Slug flow is characterised by elongated bubbles travelling in the axial direction and occurs at very modest flow rates. The organic and aqueous segment ratios are equal due to equal volumetric flow rates. The experiments are conducted using 20% acetic acid in the feed and the data collected are presented in Table 10. The individual effect of the variables (i.e., diameter of microchannel, residence time) on mass transfer characteristics (under conditions of 20% acetic acid, Vm=0.1708 cm3, Cor,i= 0) is also illustrated in graphical format as shown in Fig. 8.
Table 10
Diameter (mm) Qaq
ml/min Qor ml/min S/F ratio Caq,i
g/ml Caq,o g/ml Cor,o g/ml tR
(s) KLa
(sec-1 ) % E

1.8
0.08 0.08 1 0.21 0.09
0.12 64.05 8.98×10-3 57.142
0.06 0.06 1 0.21
0.075 0.135 85.4 7.74×10-3 64.28
0.04 0.04 1 0.21
0.066 0.144 128.1 5.6×10-3 68.57

0.9
0.08 0.08 1 0.21
0.084 0.126 64.05 9.49×10-3 60
0.06 0.06 1 0.21
0.057 0.153 85.4 9.21×10-3 72.85
0.04 0.04 1 0.21
0.045 0.165 128.1 6.97×10-3 78.57

0.73
0.08 0.08 1 0.21
0.07 0.14 64.05 1.08×10-2 66.66
0.06 0.06 1 0.21
0.045 0.165 85.4 1.04×10-2 78.57
0.04 0.04 1 0.21
0.036 0.174 128.1 7.75×10-3 82.85

Conclusion:
It appears that for a given residence time, KLa increases as the diameter of the micro channels decreases. This is because the surface-to-volume ratio rises, reducing the mean distance between the specified fluid volume and the reactor walls or the domain of the second fluid. As a result, the mass transfer performance of the channel or a second fluid is improved.
For fixed residence time, with the decrease in the diameter of the micro channels of constant volume, there was an increase in the percentage extraction. Such behaviour is attributed to an increase in surface-to-volume ratio due to a decrease in diameter. However, all the flows are in the laminar regime only, and the elements flow as laminar. Hence, as the distance for molecular diffusion decreases, the interaction between molecules increases, which improves the percentage extraction. Slug flow extraction depends on molecular diffusion for mass transfer, which is accelerated by internal circulation.
To achieve higher KLa and percentage extraction values, channels with smaller diameters can be preferred. Still, the too-small diameter is not advisable, and therefore an optimum value should be chosen.
The micro channel residence times ranges from 64.05 seconds to 128.1 seconds. Using lower flow rates to increase the residence time is one technique to achieve equilibrium. Reduced flow rates, on the other hand, may result in a lower % extraction due to the slugs' reduced internal circulation. Despite this, the percent extraction for all three channels increased dramatically due to resident time dominance at lower total flow rates.
As residence time increases (total flow rate decreases) volumetric mass transfer coefficient decreases for all three channels. This indicates that as the resident time decreases, the total flow rate increases, the slug movement velocity increases, and the slug movement velocity increases, and the slugs' internal circulation flow increases, promoting surface renewal and increasing mass transfer between organic and aqueous slugs. As a result, the highest KLa value must be considered.
As residence time increases (total flow rate decreases), % extraction increases for all three channels. This demonstrates that the drop in percent extraction at more flow rates is attributable to the microchannels' short time of residence, which does not achieve equilibrium. Complete equilibrium is achieved when the extraction time is extended by using lower flow rates. Furthermore, mass transfer occurs faster when the slugs are of similar size, whereas small organic slugs extract large sample slugs, which requires longer extraction times. This indicates that the relative size of the slugs are important in obtaining a complete mass transfer. Here the residence time dominating factor than internal recirculations generated inside the slugs. Hence higher percentage extraction can be achieved with an increase in residence times.

When two phases are injected as flows side by side in the same channel, The first phase wets the edges first and encapsulates the second fluid as discrete drops. Establishing a clear interface might also help to stabilize the flow. When scaled down, the gravitational force becomes less relevant. The Reynolds number (NRe), Capillary number (NCa), and Weber number (NWe), all of which have no dimensions in one-phase flow, are frequently used to measure multiphase-fluid dynamics. Wetting characteristics, flow velocities, fluid viscosity, and geometrical features all play a role in segmenting or stratifying multiphase channel flow patterns. A segmented flow creates stable interfaces with discrete quantities of fluid, whereas a stratified flow creates stable interfaces with fluids that are continuously fed into the system. Dimensionless number analysis is performed on the experimental data and the results are summarized in Table 11 and Fig. 9 (which show effect of Dimensionless numbers on Mass Transfer Characteristics in microchannels at 20% acetic acid, Vm=0.1708 cm3, Cor,i= 0).
Table 11
D
(mm) Qaq
ml/min Qor ml/min S/F ratio NRe NWe NCa NRe/NCa NRe/NWe KLa
(sec-1) % E

1.8
0.08
0.08 1 3.05 2.76× 10-4 9.04× 10-5 33816.37 11065.19 8.98×10-3 57.14
0.06
0.06 1 2.29 1.55× 10-4 6.78× 10-5 33820.05 14753.59 7.74×10-3 64.28
0.04
0.04 1 1.52 6.91× 10-5 4.52×10-5 34955.7 22130.38 5.6×10-3 68.57

0.9
0.08 0.08 1 6.11
2.21× 10-3 3.61× 10-4 16936.28 2766.298 9.49×10-3 60.0
0.06
0.06 1 4.58 1.24× 10-3 2.71× 10-4 16918.81 3688.397 9.21×10-3 72.85
0.04
0.04 1 3.05 5.53× 10-4 1.81× 10-4 16889.5 5532.596 6.97×10-3 78.57

0.73
0.08
0.08 1 7.53 4.14 × 10-3 5.49× 10-4 13728.59 1819.951 1.08×10-2 66.66
0.06
0.06 1 5.65 2.33× 10-3 4.12× 10-4 13720.87 2426.061 1.04×10-2 78.57
0.04
0.04 1 3.76 1.04 × 10-3 2.75× 10-4 13705.4 3639.901 7.75×10-3 82.85
Conclusion:
The laminar profile can be seen in these micro channels, regardless of the fact that the Reynolds values attained is less than 10.
There is an increase in the value of KLa and a drop in the percentage extraction of acetic acid when Reynolds number, Weber number, and Capillary number increase for a certain channel.
When compared to channels with larger diameters, a decrease in diameter results in greater Reynolds number, Capillary number, and Weber number, leading to higher KLa and percentage extraction.
For NRe variations of 1 to 8, NWe ranges from 0.001 to 0.005 for any given diameter. This reveals that interfacial tension has a greater impact on flow in microchannels than inertial forces.
For the same NRe change of 1 to 8, NCa ranges from 0.0001 to 0.0006, suggesting that interfacial forces have a greater impact on flow than viscous forces.

Further, referring to Fig. 10, Micro-Particle Image Velocitymetry (Micro PIV) experiment is used to determine the hydrodynamic behavior inside the micro channel. The extraction process is carried out in a 0.73mm micro channel with organic and aqueous phase flow rates of 0.04 ml/min each to determine the hydrodynamic behavior in the organic (ethyl acetate) slugs created in the microchannel. To match the refractive index of glass and ensure image clarity, the laser is allowed to fall on the microchannel, which is then placed in a beaker containing glycerol solution. The solvent and feed pumps are then turned on and run at 0.04 ml/min. After a while, uniform slugs appeares on the computer screen, which can be viewed clearly. The camera takes several photos during the flow to determine the flow sense of the liquid inside the channel, with a time interval of 0.25 seconds between each image. Vector cross-correlation and adaptive correlation are used to analyse the data. Fig. 10a, Fig. 10b and Fig. 10c show the flow pattern of Micro PIV for water-acetic acid-ethyl acetate system at different time intervals ranging from 5.5s to 6.0s, 6.25s to 7.0s, and 8.2500s to 8.750s, respectively.

Conclusion: It is observed that the vector directions inside the channel are random (non-linear). The slugs are found to have a lot of internal (organic) fluid recirculation, so a new surface is produced to transfer aqueous phase acetic acid into the organic slug. Because of the continuous regeneration of new surface and high diffusion, better mass transfer, and hence a liquid-liquid extraction operation in microchannels is achieved with high mass transfer coefficients and high percentage extraction. Hence, a high surface-to-volume ratio and high mixing efficiency can be obtained in microchannels, enhancing the mass transfer coefficients compared with macro columns.

Different feed concentrations and S/F ratios are used to extract acetic acid from water in a packed column with structured and random packing. The same extraction is done in micro channels with S/F =1 for different channels with constant volume, varying diameters, lengths, and acetic acid concentration of 20 % in the feed. The results obtained from the macro (packed columns) and micro channels are compared and shown in Fig. 11 and Table 12.
Table 12

Type of contactor Acetic acid
Percentage in the feed
S/F ratio Maximum value of KLa (sec-1) obtained Maximum value of Percentage extraction
Packed column with Random packing 20% 1 3.56×10-4 51.42
20% 4 7.45×10-4 85.71
Packed column with
Structured packing 20% 1 3.9×10-4 56
20% 4 8.14×10-4 88.57
Micro channels 20% 1 1.08×10-2 82.85

Conclusion:
For the S/F ratio=1, the KLa values obtained in micro channels are almost 30 times greater than macro packed columns. At the solvent to feed flow rate (S/F) ratio equal to 1, micro channels achieve a very high percentage extraction compared to packed columns. In packed columns, on the other hand, to achieve the same level of percentage extraction, practically S/F =4 must be used, which necessitates the use of more solvent and increases the cost of operation. Hence, to obtain maximum percentage extraction of acetic acid with less solvent consumption, i.e., ethyl acetate, one should prefer performing liquid-liquid extraction in micro channels than macro columns.
Higher KLa and higher mass transfer are achieved in micro channels because of the higher surface/volume ratio than packed columns.
,CLAIMS:We claim:
1. A method of acetic acid extraction/recovery from industrial effluents, the method comprising steps of:
providing (S1), in a first reservoir (1), an aqueous feed containing 10-30 volume % of acetic acid obtained from the industrial effluents;
providing (S2), in a second reservoir (2), at least one organic solvent selected from a group consisting of Ethyl Acetate (EA), Toluene, Methyl Iso Butyl Ketone (MIBK), Di Iso Propyl Ether (DIPE), 1-Decanol, 1-Butanol, Chloroform, Di Chloro Methane (DCM), Di Ethyl Ether (DEE), and mixture thereof;
introducing (S3) the solvent and the aqueous feed from the reservoirs (2, 1) into two branch inlets of a Y-junction microchannel (10) at a solvent-to-feed (S/F flow rate) ratio of 1 using two pumps (4), wherein the microchannel has a diameter ranging from 0.7mm to 1.8mm with a constant volume through which the solvent/aqueous feed phases travel in a segmented (slug) flow pattern with increased internal recirculation; and
collecting (S4) raffinate and extract (acetic acid rich) in two separate tanks using a phase separating funnel (11) connected to a common outlet of the Y-junction microchannel (10).

2. The method as claimed in claim 1, wherein the organic solvent used in the step (S2) is pure Ethyl Acetate.

3. The method as claimed in claim 1, wherein in the step (S3) the solvent and the aqueous feed are introduced into the Y-junction microchannel (10) at an equal flow rate ranging from 0.04 ml/min to 0.08 ml/min.

4. A method of acetic acid extraction/recovery from industrial effluents, the method comprising steps of:
providing (S1), in a first reservoir (1), an aqueous feed containing 10-30 volume % of acetic acid obtained from the industrial effluents;
providing (S2), in a second reservoir (2), at least one organic solvent selected from a group consisting of Ethyl Acetate (EA), Toluene, Methyl Iso Butyl Ketone (MIBK), Di Iso Propyl Ether (DIPE), 1-Decanol, 1-Butanol, Chloroform, Di Chloro Methane (DCM), Di Ethyl Ether (DEE), and mixture thereof;
introducing (S3) the solvent and the aqueous feed from the reservoirs (2, 1) into a packed column (9) at a solvent-to-feed (S/F flow rate) ratio ranging from 1-4 using two pumps (4), wherein the packed column (9) comprises a bottom inlet (9d) to receive the solvent, a top inlet (9c) to receive the aqueous feed, a bottom outlet (9b) to release raffinate (heavy phase), a top outlet (9a) to release extract (acetic acid rich light phase), and a structured/fixed packing (9e) internally filled between the bottom inlet (9d) and the top outlet (9a) to cause phase separation; and
collecting (S4) the raffinate in a raffinate tank (7) connected to the bottom outlet (9b), and the extract in an extract tank (8) connected to the top outlet (9a).

5. The method as claimed in claim 4, wherein in the step (S3) the solvent is evenly distributed into the packing (9e) by using a distributor (9f) provided thereunder.

6. The method as claimed in claim 4, wherein in the step (S4) a pressure difference is maintained between the bottom outlet (9b) and the top outlet (9a) of the column (9).

7. The method as claimed in claim 4, wherein the organic solvent used in the step (S2) is pure Ethyl Acetate.

8. The method as claimed in claim 4, wherein in the step (S3) the solvent is introduced at a flow rate of 4ml/min, and the aqueous feed is introduced at a flow rate ranging from 4ml/min to 16 ml/min.

9. The method as claimed in claim 4, wherein the packed column used in the step (S3) has an internal diameter of 45mm, a column length of 500mm, and a packing length of 200mm with pore volume of 40 cm3.

10. The method as claimed in claim 4, wherein the packed column used in the step (S3) comprises a random packing in place of the structured/fixed packing (9e).