Academia Journal of Scientific Research 2(3): 038-049, October 2014 DOI: http://dx.doi.org/10.15413/ajsr.2014.0115 ISSN: 2315-7712 ©2014 Academia Publishing

Research Paper

Solubility of crude oil in pure and modified supercritical carbon dioxide using supercritical fluid extractor

Accepted 26th April, 2014

ABSTRACT Supercritical Fluid Extractor has been used to determine the solubility of crude oil in pure and modified supercritical carbon dioxide at different pressures ranging from 20 to 60 MPa with interval of 5MPa at constant temperature (60°C) for 20 min of the extraction process. The solubility has increased with increasing pressure. Results showed that addition of co-solvents had increased solubility in oil as compared to solubility without co-solvent. The co-solvents used were methanol, ethanol, acetone, propanol and brine. The selection of these co-solvents were due to their higher capability to form hydrogen bonding with solutes of oil and enhance the density of supercritical carbon dioxide complying higher solubility of solvent in solutes of crude oil. The solubility was larger at high density conditions (high pressures for this isothermal extraction). The effect of co-solvents solubility was following this order Ethanol> Methanol> Propanol> Acetone > Brine. Best operating conditions to achieve highest solubility on the basis of results were P=60 MPa at 60°C using ethanol as a co-solvent with concentration of 0.075 g of ethanol / g of crude oil. The crude oil weight used in every experiment was 40 g. To study the effect of concentration of co-solvent on solubility, concentration of each co-solvent used was 0.125 g of co-solvent / g of crude oil at operating conditions of 20 to 60 MPa at constant temperature (60°C) for 20 min of the extraction process. Results showed that solubility had increased using higher concentrations of co-solvents. Results showed that selecting of specific operating conditions could extract selective components (hydrocarbons) of interest by using supercritical carbon dioxide extraction which could not be feasible with other solvent extraction operation. Key words: Supercritical fluid extractor, solubility, co-solvent, hydrogen bonding, oil recovery, extraction process, density.

INTRODUCTION Extraction of desired compounds from the solid and liquid matrices is the most well-established and investigated application of scCO2. Maher Al-Jabari (2002) reported that scCO2 is highly efficient in the extraction process because of its superior combination of the liquid and gas like properties in the supercritical state. Park et al. (2007) investigated that the pressure-dependent solvating ability of supercritical fluid enables it an excellent solvent for separation processes. Low surface tension, high molecular

diffusivity and low viscosity of supercritical fluid makes it excellent mass transfer solvent allowing its better penetration into the sample matrix as compared to liquid solvents.

Sanli et al. (2012) investigated that mass transfer rates of scCO2 are significantly higher than that of liquid solvents which increases the ability of penetration of scCO2 to the depths of the highly porous structures as well. The solvent power of scCO2 is a function of its density which increases

Shahid Hussain Graduate in Oil and Gas Technology, Aalborg University Esbjerg • Niels Bohrs Vej 8 • DK-6700 Esbjerg • Denmark. Email: hussainshahid56@gmail.com

Academia Journal of Scientific Research; Hussain. 039 with pressure for isothermal process. They reported that scCO2 has very low surface tension and interfacial tension decreases dramatically within the vicinity of critical pressure of CO2 which continues to decrease with increasing pressure. They also implied that scCO2 having higher diffusion coefficients than that of liquids, low surface tension and viscosities closer to gases, CO2 provides complete wetting of the substrates and better penetration which is an important advantage to using scCO2 for extraction processes as compared to conventional solvents.

According to William et al. (1996), to extract desired compounds, there must be an appreciable solubility of compounds in scCO2. Two main factors are important for the solubility of compounds in scCO2: first factor is the solvent strength of scCO2 which is a function of density, and the other factor is the volatility of compounds which is a function of temperature. In addition to solubility, mass transfer also plays an important role for high efficiency of the extraction process. In the beginning of extraction process, the solubility of a substance is the limiting factor. Solubility can be increased by increasing the pressure which, in turn, increases the scCO2 density, and solvent strength.

The solvating power of Supercritical Fluid (SCF) is a strong function of its density. It is possible to control the density of fluid through operating pressure and temperature that lead to selective manipulation of solvating power of the fluid. On the basis of the solubilization power of Supercritical Fluid, optimum conditions can be designed where the fluid has ability to extract a desired specific solute by varying the solvating power of the fluid. Mukhopadhyay (2000) implied that SCF process conditions can be determined through studies of the solute solubility of individual components in a mixture that can result in separation of individual solutes or selective extraction. Raeissi and Peters (2005) reported that physical properties of a fluid change rapidly with small changes in pressure in the vicinity of fluid critical point which can change the solubility of solutes dramatically. The increase in pressure increases the density of CO2 that decreases the mean intermolecular distance between CO2 molecules resulting in higher interactions between the solute and solvent molecules.

Supercritical fluid extraction is capable of separating components depending upon a variety of physical properties. Anitescu and Tavlarides (1997) implied that the solubility of different polycyclic aromatic hydrocarbons varied largely on specific process conditions depending on physical properties such as molecular weight, melting and boiling points etc. as well as structural properties such as molecular shape, angularity of the compound.

Different authors (Chung and Shing, 1992; Iawai et al., 1995; Lee et al., 1988; Lucein and Foster, 1996; Lucien and Foster, 2000) studied multi-component systems and showed that solute-solute or solute-solvent interactions are important in the supercritical fluid extraction process,

leading to higher solubility of the components relative to their binary system, especially for solutes having good hydrogen-bonding potential.

Nonpolar compounds have high solubility in scCO2

because CO2 is relatively non-polar solvent. Nevertheless, CO2 can also dissolve non-polar compounds to some extent due to the large quadrupole moment of CO2. The lack of polarity and capacity of CO2 to form specific solvent–solute interactions with polar compounds and higher molecular weight compounds (non-volatile organic compounds) are the limitations to use pure scCO2 as a solvent. Solvating power and extraction of polar compounds into scCO2 can be increased with the addition of small amounts of polar co-solvent or modifier. Sauceau et al. (2004) suggested that the choice of co-solvent not only depends on its ability to increase the solvating power of scCO2 , but also its purity, chemical and physical characteristics, for example, for pharmaceutical industries, the co-solvent must not be toxic.

Co-solvents are highly polar compounds. The small addition of co-solvents can change solvating power of SCF-CO2 . In most cases, increase in solvating power of SCF is due to an increase in the density of the mixture. Nevertheless, a dramatic enhancement in the solubility with the addition of polar co-solvent is not explained by the changes of density but result of chemical interactions between the solute (Lu et al., 1990) and co-solvent because of acid-base forces (Dobbs and Johnston, 1987; Eugster, 1986; Herrero et al., 2006; Ting et al., 1993a). Commonly used polar co-solvents are acetonitrile, dichloromethane and alcohols (methanol, ethanol, isopropanol).

Different authors have investigated that the solvating power of scCO2 has increased significantly by using polar co-solvents. Li et al (2011) used three co-solvents, ethanol, acetone and ethylene glycol, for supercritical CO2 extraction of benzamide in a temperature range of 308 to 328 K for pressure range of 11 to 21 MPa using a dynamic flow method. They reported that solubility and extraction rates have enhanced with additions of three co-solvents, and ethanol has enhanced extraction yields 11 times higher than acetone and ethylene glycol. This enhancement in the extraction of solute (benzamide) was due to strong interaction between the solute (benzamide) and ethanol, especially hydrogen bonding. Li et al (2010) used acetone, acetic acid, heptanes and ethanol as co-solvents with scCO2

for Poly DI Vinyl Benzene (PDVB) microspheres yield . Their results showed that the addition of co-solvents have increased polydivinylbenzene microspheres yield in supercritical CO2 and acetone has increased yield higher than other co-solvents at same volume concentration. Acetone is a polar, aprotic solvent in a variety of organic reactions.

Lemert and Johnston (1990) studied the effect of methanol as a co-solvent on the selectivity of 2-naphthol in a 2-naphthol/phenanthrene mixture. In pure supercritical carbon dioxide, the solubility of both solutes was the same but 2-naphthol interacted more efficiently with methanol

Academia Journal of Scientific Research; Hussain. 040 than phenanthrene. Sauceau et al. (2004) used two co-solvents (ethanol and dimethylsulphoxide) to investigate their effects on solubility of eflucimibe in supercritical carbon dioxide. They reported that dimethylsulphoxide had increased the solvating power of scCO2 higher than ethanol at the same operating conditions. They showed that this enhancement in solvating power of scCO2 could be attributed to three effects: specific interactions between the solute and co-solvent, modifications in the phase equilibria, increased density of the fluid mixture.

To develop supercritical extraction of a desired product, its solubility in the selected medium is a key parameter. Unfortunately, this quantity is frequently unknown, and it can be determined by experiment. A supercritical fluid extractor was used to carry out accurate measurements of solute solubilities in pure and mixed supercritical solvents.

Theory, fundamentals, and equations of states for estimating the solubility of various compounds are available in the literature (Clifford and Westwood, 1993; Sameena et al., 1992; Bartle et al., 1992; Kane et al., 1993). In this paper, experimental determination of the solubility of crude oil components in supercritical carbon dioxide was focused.

As a preliminary work, the influence of pressure on the crude oil solubility has been measured in pure CO2. Afterwards, the solubility has been studied in CO2/co-solvent mixtures using the same procedure and apparatus. The solubility of crude oil in pure and modified supercritical CO2 in the broad range of pressure such as 20 to 60 MPa at 60°C was investigated. Co-solvents used were methanol, ethanol, propanol, acetone and brine. Different concentrations of co-solvents such as 7.5 and 12.5% for each co-solvent were also used to study the effect of concentration of co-solvent on the solubility of crude oil. THEORY Measurement methods of solubility in supercritical carbon dioxide Solubility is defined as weight fraction or mole fraction of solute in the supercritical fluid that is in equilibrium with the bulk solute. Various methods for measurement of solubility have been identified. These methods are generally divided into two major categories: (i) Static methods (ii) Dynamic methods

Static methods In static methods, the solute is in static contact for a long time with the supercritical fluid in order to achieve equilibrium. There are three variations depending on the type of high-pressure vessel and sampling.

(i) Analytical method (ii) Synthetic method (iii) Gravimetric method Analytical method: In this method, a constant volume equilibrium vessel is used in which solute is equilibrated with a known quantity of supercritical fluid. The sample of fluid phase in small quantity is removed and analyzed for the concentration of the solute. In this extraction process, the Known amount (weight, gram) of crude oil was introduced and supercritical carbon dioxide was injected into the extractor vessel, and desired operating conditions were achieved using regulatory pump and heater. After achieving equilibrium, extracted oil was collected. Solubility of solute in mole fractions is calculated as:

2122 / nnny 1

Where: Y2= solubility of solute, n1= moles of supercritical carbon dioxide, n2= moles of collected samples (crude oil). For dilute solute concentrations, carbon dioxide moles are calculated as the product of sample volume (V) and pure carbon dioxide molar density (ῤ). Equation1 is valid for supercritical fluid without co-solvent. If co-solvent is used, then Equation1 is modified so that n1 represents the sum of CO2 and co-solvent moles. Synthetic method: In this method, a variable volume cell can be used to adjust operating conditions. Generally, the vessel is equipped with a sapphire window for visual observations. Conditions can be adjusted to gradually decrease the solubility of the mixture and cause precipitation. The beginning of precipitation can be recorded as a measure of solubility condition. Many solubility points can be calculated by varying pressure and temperature independently for a given solute/fluid loading. In this method, sample collection or its analysis is not required and solubility can be calculated by following equation:

2122 / nnny 2

Where: n2 = moles of solute, moles, n1= carbon dioxide taken in the variable-volume view cell, moles. This synthetic method is very convenient to determine binary-phase equilibria and phase boundaries in multi-component mixture and also measurements can be conducted in a relatively short time. Gravimetric method: In this method, the solute is kept in a small vial inside the pressure vessel containing supercritical fluid. A solute of known amount is put in a vial and the vessel is filled with a fluid, then, the fluid moves the vial, dissolves the solute, and brings it out. After the equilibrium is reached, the vessel is depressurized, and mass of residual solute in the vial is gravimetrically

Academia Journal of Scientific Research; Hussain. 041 measured. The solubility of the solute can be calculated as:

2122 / nnny 3

Where: ∆n2 =initial minus final moles of solute in the vial, ∆n1 =total moles of CO2 minus that in the vial. It is relatively a simple method, but it can be used effectively only for solids that accomplish solubility greater than 10-3 mole fraction, which do not melt under the experimental conditions. In the static methods, inaccuracies can exist due to leaks from number of valves and fittings, and hence, there must be careful to ensure a leakproof apparatus. Additionally, errors can also arise from multiple samplings, especially when data at different temperatures and pressures are collected from a single solute/carbon dioxide loading. Dynamic method In this method, the solute is filled in the vessel and supercritical carbon dioxide is fed continuously into the vessel. To achieve equilibrium in the vessel, supercritical carbon dioxide is fed with mild flow rate. The outlet stream is analyzed for solute concentration by chromatography, gravimetric, spectroscopic, dielectric, and other techniques. The sample is collected in the solvent or cold trap for the desired time, and then analyzed for solute amount. Solubility is calculated as a follows:

2122 / nnny = 2112 / ntQn

4 Where: n1=moles of carbon dioxide, n2=solute collected in

time t, Q1 =volumetric flow rate of carbon dioxide, 1 =

molar density of carbon dioxide.

MATERIALS AND METHODS The crude oil for the experiments was supplied by the Maersk oil company from the North Sea oilfield. This crude oil was dead, intense dark brown almost black in color.The pure carbon dioxide (99.9%) was supplied by Strandmollen A/S, Denmark. Methanol, acetone, ethanol and propanol of 99.9% of purity were purchased from the VWR Pro - lab. Brine was taken from the North sea.

Preparation of the sample

Before inaugurating the experiment, a dry towel and an empty beaker were weighed. The sample consists of towel of 5 g and crude oil (40 g). The towel was soaked in crude oil for at least 72 h to achieve proper saturation. The excess oil was stripped from the towel, and the towel saturated with crude oil was weighed. Then the sample was put into

the extractor carefully so that crude oil from the sample should not leak from the bottom of the extractor. Additionally, mass of co-solvent (either 7.5% or 12.5%, depending upon experiment) was added into the extractor carefully. The extractor vessel containing the sample was inserted into the SFE to commence the experiment. Apparatus and experimental procedure The experiments of extraction process were performed in Supercritical Fluid Extractor (SFE). Figure 1 shows the flow sheet diagram for the supercritical fluid extractor. It is numbered from 1 to 13 to identify every part of the apparatus. After introducing the sample into the extractor vessel (7), all outlet valves (5, 10, 11) and inlet valve (13) were closed tightly. When the required temperature of 60°C in the oven (8) and pressure (4) were achieved, outlet valve of CO2 (2) and inlet valve (13) were opened so that CO2 could flow inside the extractor vessel (7). The system was left for 20 min to equilibrate. A pump (4) was used to maintain the required pressure. Carbon dioxide was continuously supplied to the system by this pump (4). Meanwhile, empty test tubes were weighed to collect the extracted liquid. After 20 min, outlet (10) and exit valve (11) were opened to collect the extracted oil in the test tube. The test tubes having extracted crude oil were weighed again to calculate extracted oil. The extraction of crude oil was ended when it was visually observed that no more extracted crude oil was collected in the test tubes.Afterwards, the inlet valve (13) was closed and outlet valves (10, 11) were opened till CO2 from the system vanished completely. The towel with un-extracted crude oil was taken out from the extractor vessel (7) and weighed for calculations. The extractor vessel was cleaned properly to make it ready for the next experiment. A constant flow rate of CO2 was maintained throughout the experiment. Each experiment was conducted three times to minimize experimental errors, and reproducibility of the data was good. This apparatus is equipped with High Pressure Alarm (HPA) and High Temperature Alarm (HTA) to ensure the safety. It has also latest control systems to control temperature, flow and pressure resulting in more precise experimental work.

Calculations for recovered oil The extracted oil was calculated as weight difference of empty tubes and tubes containing extracted oil as described below: W ex o = W ex tube -W e tube 5

Academia Journal of Scientific Research; Hussain. 042 Where: W e tube = the weight of the empty test tube, gram, W ex tube = the weight of the test tube with extracted oil after experiment, gram,W ex o = the weight of the extracted oil, gram. The oil recovery was calculated by using the following formula: Ro = W ex o / Ws *100 6 Where: Ro = Percentage oil recovery, %, W ex o = Weight of extracted oil, gram, Ws = Weight of crude oil (40 g). The experimental results were plotted as percentage recovery of extracted oil versus other parameters to explain the extraction process.

Calculations for density Firstly, density of oil was calculated by using the following standard formula:

ooo vm / 7

Where: o = density of crude oil, kg/m3, mo= mass of crude

oil, kg, vo = volume of crude oil, m3. Density of oil calculated was 833.33 kg/m3. Towel occupied 57 ml of extracted vessel which was calculated manually. Volume of CO2 in the extractor vessel was calculated as follows: Vco2 = (100-57-V0) ml 8 Where: Vco2 = Volume of CO2 in the extractor vessel, m3, V0 = the volume of oil in the extractor vessel, m3. The mass of CO2 is calculated as:

0222 * ccoco vm

9

Where: mco2 = mass of carbon dioxide, kg, o = density of

carbon dioxide, kg/m3, Vco2= volume of carbon dioxide, m3. Density data for CO2 in the pressure range of 20 to 60 MPa at 60°C was taken from Nist (National Institute of Standards and Technology) (http://webbook.nist.gov/cgi/fluid.cgi?ID=C124389&Action=Page)

Calculations of solubility Solubility of crude oil in pure supercritical carbon dioxide was calculated as follows:

yo= w2 / w1 +w2 10 Where: yo = solubility of crude oil, w2= extracted mass of

crude oil, kg, w1= mass of supercritical carbon dioxide, kg. When co-solvent is added to enhance polarity of pure carbon, then its amount shall also be added as shown in equation below Solubility of crude oil in modified supercritical carbon dioxide was calculated as follows: yo = w2 /(w1 +w2+ w3) 11 Where: yo = solubility of crude oil, w2= extracted mass of crude oil, kg, w1= mass of supercritical carbon dioxide, kg, w3 = mass of co-solvent, kg. For all experimental calculations, the same procedure, sample (crude oil) and apparatus was used. RESULTS AND DISCUSSION The composition of crude oil is highly complicated constituting highly volatile components such as methane, ethane to highly non-volatile hydrocarbons (heavy hydrocarbons). The aim was to achieve maximum possible solubility of crude oil at optimum operating conditions, and efficient co-solvent. In experiments, reservoir possible operating conditions (Pressure of 20 to 60 MPa at 60°C temperature) and environment (towel was saturated with oil like a reservoir rock) was developed. Solubility of crude oil in pure carbon dioxide Berna et al. (2000) measured the solubilities of essential oil components in supercritical carbon dioxide in pressure ranges of 69 to111 bars at fixed temperature, and showed that the solubility of oil components of supercritical carbon dioxide increases with increase in pressure.

As shown in Figure 2(a), the solubility of crude oil increases till 40 MPa, and then decreases.

This behavior shows that the best conditions for supercritical extractions will be at pressures > 40 MPa for this isothermal system in order to obtain the maximum amount of product.

Sovova et al. (2001)investigated fatty oil influence on the solubility of limonene in CO2 under pressures 8–12 MPa at 313.2 K, and reported that solubility increases linearly with increase in pressure.

Catchpole and Proells (2001) measured the solubilities of lipids into supercritical CO2 with a pressure range of 40–200 bar at 343 K, and reported that solubility increased logarithmically with increasing pressure at fixed temperature.

Sousa et al. (2002) measured the solubility of the essential oil in CO2 by the dynamic method in which the solvent is saturated by the solute as it flows through the bed of solids at a predetermined constant flow rate. They demonstrated that solubility increases with rise in pressure.

Academia Journal of Scientific Research; Hussain. 043 The solubility–pressure curve of crude oil in supercritical CO2 is shown in Figure 2 (b).

Four parameters are extremely helpful to understand the solute behavior in supercriticalfluid, and thus, in executing successful analytical supercritical fluid extractions (King, 1989; Andersen et al., 1990): (i) The miscibility or threshold pressure (Seied and Seiedeh, 2007) which corresponds to the pressure at which the solute partitions occur effectively in the supercritical fluid. (ii) The pressure at which the solute achieves its maximum solubility. (iii) The fractionation pressure range, which is the pressure region between the miscibility and solubility maximum pressures (in this interval it is possible to extract selectivity one solute by choosing the correct pressure). (iv) A good knowledge of the physical properties of the solute, particularly, its melting point (in fact most solutes dissolve better when they are in their liquid state, i.e. above their melting point). The fluid pressure is the major parameter that affects the efficiency of the extraction process. The effect of pressure on the solubility of the solute follows the expected trends, that is, the solubility is increasing with increase in pressure for isothermal process. The rise in the pressure at a given temperature results in an increase in the fluid density as shown in Figure 2(b) which means an enhanced solubility of the solutes. As the density of CO2 increases with pressure, the mean intermolecular distance between CO2 molecules decreases which increases the interaction between the solute and solvent molecules. Solubility of crude oil in modified supercritical carbon dioxide Generally, the nature of the modifier depends on the nature of the solute to be extracted. The extraction of diuron, for example, is considerably enhanced with methanol instead of acetonitrile as a modifier (Gurdial et al., 1991). A reasonable choice of selecting a solvent as a modifier is its ability to be a good solvent in its liquid state for the target analyte. It is obvious that the addition of large amounts of a modifier will change the critical parameters of the mixture (Crowther and Henion, 1985). As a result, binary mixtures of carbon dioxide and an organic solvent are often used in a subcritical state where the diffusion coefficients are smaller than in a supercritical state. Modifiers may be introduced as mixed fluids in the pumping system with a second pump and mixing chamber (Taguchi et al., 1991) or by simply injecting the modifier as a liquid into sample before extraction (Wheeler and McNally, 1989) (the latter method is less successful because it leads to concentration gradients within the matrix).

Kohler et al. (1997) investigated the effects of modifier concentration and its nature on the solubility of

supercritical carbon dioxide extraction using methanol, ethanol and toluene as modifiers and reported that these modifiers gave similar results, but, the use of toluene presents a major drawback due to its high boiling point and concomitant longer evaporation times. Choi et al. (1999) investigate the effect of methanol and water as a modifier in supercritical carbon dioxide extraction on the extraction yields. They found that the addition of methanol drastically increased the extraction yield of solute in supercritical carbon dioxide as compared to water. Water did not show any significant influence on the extraction process. The poorer result of water relative to methanol can be because water could not sufficiently improve the polarity of CO2 as much as methanol did. The co-solvent has the ability to dilute the extract, diminish its viscosity, thereby enhancing the flow of the extract through the extractor. Cocero and Garcia (2001) studied supercritical fluid extraction of sunflower oil with carbon dioxide in a pilot plant at 30.0 MPa and 40°C with addition of different amount of methanol, ethanol, butanol and hexanol as co-solvents.Comparing the co-solvent extraction using neat CO2, they foundthat the use of 10% (w/w) of a co-solvent increases oil solubility 10-fold.

They investigated that solute recovery values using methanol values are higher than when using hexanol and ethanol. They also showed that mass transfer rises with co-solvent concentration depending on the nature of co-solvent. This variation may be caused by the change of physical properties in the supercritical mixture. Pourmortazavi et al. (2003) investigated the supercritical fluid extraction, and the effect of different modifiers as methanol, ethanol and hexane at a constant pressure (100 ATM) and temperature (35°C) on the extraction efficiency was also evaluated. They demonstrated that changing modifier type and identity could significantly affect not only extraction rate, but also the selectivity of the extraction process.

Different co-solvents such as methanol, ethanol, propanol, acetone, and brine were used to investigate the effect of co-solvent addition on the solubility of crude oil as well as to know which co-solvent can effectively increase the recovery of oil Figure 3 is showing the solubility of crude oil by using the modified supercritical carbon dioxide extraction of crude oil (40 g) under different operating conditions.

These results showed that the solubility of crude oil by supercritical CO2 significantly depend upon the pressure. At the higher pressure, solubility of crude oil is higher rendering the high extraction rate and extracted yields of crude oil. From these results, it was strongly observed that under high density conditions (low temperature and high pressure), the solubility of crude oil was high, while under low density conditions (low pressure and high temperature) the solubility of crude oil was lower. Thus, for isothermal system, increase is pressure increases the solvent (CO2) density, crude oil miscibility and solubility.

Academia Journal of Scientific Research; Hussain. 044

46

8

3

2

5

119

7

1

10

1213

Figure 1. The supercritical fluid extractor: (1) - CO2 Storage Tank, (2) - CO2 Outlet Valve, (3) – Cooler, (4) – PumpPreheatVent Valve, (6) - Pre-Heat Coil, (7) - Extractor Vessel, (8) – Oven, (9) - Sample (Towel saturated with oil), (10) - Outlet Valve, (11) - Exit Valve, (12) - Sample collector, (13) – Inlet Valve.

(2a) Figure 2(a). Solubility of obtained of oil in pure Supercritical CO2, (b) Effect of pressure at density of CO2 at 60°C.

These results were in good agreement with previously reported results (Park et al., 2007; Sanli et al., 2012; Modey et al., 1996; Mukhopadhyay, 2000; Raeissi and Peters, 2005).

It was also investigated from Figure 3 that solubility at early stages was constant, but as the extraction proceeded, it decreased gradually. It could be due to the solubility difference between low molecular and high molecular

Academia Journal of Scientific Research; Hussain. 045

(2b)

Figure 2(b). is showing that the crude oil is slightly soluble in CO2 till 40 MPa (threshold pressure), while as the pressure increases from 40 MPa (threshold pressure), the solubility increases significantly, especially around 60 MPa, up to its maximum value. The fractionation pressure ranges from 40 to 60 Mpa.

Figure 3. Solubility of crude oil using different co-solvents.

weight components.

The co-solvent addition has increased the density of pure solvent (CO2) and enlarged the interactions between solutes and modify CO2 resulting appearance of new specific interactions. Similar results were obtained by other authors(Anitescu and Tavlarides, 1997; Chung and Shing,

1992; Iawai, et al., 1995). It is revealed that solubility is approximately the same at

pressure range of 55 and 60 MPa using all co-solvents as compared to a pressure range of 20 to 50 MPa. It is due to rapid increase in density of supercritical CO2 at 55 and 60 MPa as shown in Figure 2(b) resulting in high miscibility

Academia Journal of Scientific Research; Hussain. 046

Table 1. Effect factor of each co-solvent using 7.5% concentration.

Pressure (MPa) Ethanol Methanol Propanol Acetone Brine

20 1,773072 1,573019 1,418109 1,245396 1,1152414

25 1,718533 1,533563 1,376573 1,25021 1,153067

30 1,63363 1,449876 1,306299 1,181424 1,11099

35 1,439047 1,24327 1,135189 1,069409 1,019208

40 1,438412 1,243847 1,114811 1,052198 1,027593

45 1,454165 1,261518 1,165401 1,118029 1,057432

50 1,344431 1,230025 1,143766 1,118678 1,047868

55 1,180788 1,143669 1,110733 1,082241 1,035106

60 1,169668 1,140901 1,091221 1,069554 1,041584

Table 2. Effect factor of each co-solvent using 12.5% concentration.

Pressure (MPa) Ethanol Methanol Propanol Acetone Brine

20 2,063936 1,817501 1,711705 1,540325 1,398947

25 2,035694 1,788613 1,646731 1,529932 1,367253

30 1,902403 1,649691 1,550623 1,43835 1,280864

35 1,639932 1,428831 1,346364 1,26542 1,146208

40 1,585713 1,381007 1,30317 1,232347 1,135384

45 1,614371 1,437692 1,347285 1,286347 1,177615

50 1,477042 1,333447 1,297007 1,225933 1,132586

55 1,345195 1,233497 1,195847 1,150197 1,085083

60 1,305499 1,230161 1,179234 1,125836 1,097747

and solubility of solutes in solvent. Effect of co-solvent concentration on solubility of crude oil In this study, different co-solvents with concentration of 7.5% were analyzed with their variable effect on the solubility of oil due to their participation of interaction between solutes of oil and Supercritical carbon dioxide. The concentration of each co-solvent has increased to 12.5% instead of 7.5% to study the effect of concentration of co-solvents.

The solubility of crude oil has increased with increasing the concentration of co-solvents as shown in the Figure 4(a), (b), (c), (d), and (e). In fact, increase of co-solvent concentration has increased the CO2 density that has in turn enhanced its solubility. Consequently, the increase in the concentration of each co-solvent has enlarged the interaction capability between the solutes of crude oil and CO2 due to formation of new possible interaction. Similar results were demonstrated by other authors (Anitescu and Tavlarides, 1997; Chung and Shing, 1992; Iawai, et al., 1995).

This effect of co-solvent is due to specific interactions between their functional groups and those of crude oil

components. The increase in solubility with co-solvent addition is mainly from the formation of specific interactions between the solutes of crude oil and co-solvent molecules, so largest effect of co-solvent is observed from ethanol due to its strongest interactions with solutes as compared to other used co-solvents (strongest hydrogen bonding).

The effect factor of cosolvent is defined as the ratio of solubility with co-solvent and without co-solvent (Ting et al., 1993b). e = yo

co-solvent / yopure 12

Tables 1 and 2 are representing an effect factor of each co-solvent using 7.5 and 12.5% concentration of each co-solvent, respectively. Conclusions The solubility of the crude oil by using super critical carbon dioxide with and without co-solvents were investigated. The solubility of crude oil can be successfully determined experimentally using a supercritical fluid extractor. Maximum solubility is achieved at 60 MPa at 60°C with and without co-solvent.

Academia Journal of Scientific Research; Hussain. 047

(4a)

(4b)

(4c)

Academia Journal of Scientific Research; Hussain. 048

(4d)

(4e)

Figure 4(a), (b), (c), (d), and (e). Showing comparison of solubility using 7.5 and 12.5% concentration of ethanol, methanol, propanol, acetone and brine respectively with solubility using pure supercritical CO2 in pressure ranges of 20 to 60 MPa at 60°C.

The operating conditions are selected as pressure range from 20 to 60 MPa with interval of 5 MPa at 60°C (constant temperature) for an interval of 20 min of extraction process after considering literature and similar works done by other authors. All co-solvents have effectively participated, but ethanol has increased the extraction yields higher than any other co-solvent. The effect of co-solvent on solubility is following this order: Ethanol> Methanol> Propanol> Acetone >>Brine The solubility has increased significantly with an increase in concentration of each co-solvent (from 7.5 to 12.5%) because a larger amount of a co-solvent has increased its

capability to form a complex molecule clustering between the molecules of solvent and solutes (intermolecular interactions) resulting in larger local density than the density in bulk.

It is also concluded that at high density conditions (high pressure) solubility has increased than at low density conditions (low pressure) and vice versa.

ACKNOWLEDGEMENT

I would strongly appreciate my supervisor, Dr. Svetlana Rudyk, for her constant guidance and support to write this paper because without her efforts this work could not be possible.

Academia Journal of Scientific Research; Hussain. 049 REFERENCES Andersen MR, King JW, Hawthorne SB (1990). in: M.L. Lee, K.E. Markides (Eds.), Chromatography Conferences, Provo, UT. pp.313. Angel B, Amparo C, Juan BM (2000). Solubilities of Essential Oil

Components of Orange in Supercritical Carbon Dioxide. J. Chem. Eng. Data. 45(5):724–727.

Anitescu G, Tavlarides LL (1997). Solubilities of solids in supercritical fluids — I. New quasistatic experimental method of polycyclic aromatic hydrocarbons (PAHs) + pure fluids. J. Supercrit. Fluids. 10:175–189.

Brunner G (2005). Supercritical fluids: technology and application to food processing. J. Food Eng. 67:21–33.

Choi YH, Chin YW, Kim J, Jeon SH, Yoo HP (1999). Strategies for supercritical fluid extraction of hyoscyamine and scopolamine salts using basified modifiers. J. Chromatogr. A, 863:47.

Chung ST, Shing KS (1992). Multiphase behaviour of binary and ternarysystems of heavy aromatic hydrocarbons with supercritical carbon dioxide, Fluid Phase Equilib. 81:321–341.

Chunsheng Li, Jingcui L, Xiaoli Z, Xiang ZK (2010). Preparation of polydivinylbenzene microspheres in supercritical carbon dioxide using acetone as cosolvent. 288 (16-17):1571-1580.

Clifford AA, Westwood SA (1993). Supercritical Fluid Extraction and its Use in Chromatographic Sample Preparation, Chapman & Hall, London, p:1.

Cocero MJ, Garcia J (2001). Mathematical model of supercritical extraction applied to oil seed extraction by CO2 + saturated alcohol - I. Desorption model, J. Supercrit. Fluids, 20:229.

Crowther JB, Henion JD (1985). Supercritical fluid chromatography of polar drugs using small-particle packed columns with mass spectrometric detection, Anal. Chem. 57:2711.

Dobbs JM, Johnston KP (1987). Selectivities in pure and mixed supercritical fluid solvents, Ind. Eng. Chem. Res. 26:1476–1482.

Eugster HP (1986). Minerals in hot water. Am. Miner. 71:655–673. Gurdial GS, Foster NR, Yun JSL, Lee ML, Markides KE (1991). (Eds.),

Chromatography Conferences, Provo, UT. pp.66. Helena S, Roumiana PS, Anatolii AG (2001). Essential oils from seeds:

solubility of limonene in supercritical CO2 and how it is affected by fatty oil. J. Supercrit. Fluids. 20:113.

Herrero M, Cifuentes A, Ibańez E (2006). Sub and supercritical fluid extraction of functional ingredients from different natural sources: plants, food-by-products, algae and microalgae: a review. Food Chem. 98:136–148.

http://webbook.nist.gov/cgi/fluid.cgi?ID=C124389&Action=Page (13-10-12).

Iawai Y, Mori Y, Hosotani N, Higashi H, Furuya T, AraiYYomam-oto K, Mito Y (1995). Solubilities of 2,6- and 2,7-dimethylnaphthalenes in supercritical carbon dioxide. J. Chem. Eng. Data. 38:509.

Keith DB, Anthony AC, Gavin FS (1992). Estimation of solubilities in supercritical carbon dioxide: A correlation for the peng-robinson interaction parameters. J. Supercrit. Fluids. 5(3):220–225.

King JC (1989). Low-level wind profiles at an Antarctic coastal station. J. Chromatogr. Sci. 27:355.

Kohler M, Haerdi W, Christen P, Veuthey JL (1997). Extraction of artemisinin and artemisinic acid from Artemisia annua L. using supercritical carbon dioxide. J Chromatogr A. 17;785(1-2):353-60.

Lee YY, Kim H, Lee H, Hong WH (1995). One fluid mixing rules for cubic equations of state: II. Solubility of solid mixtures in supercritical fluids. Korean J. Chem. Eng. 5:116–122.

Lemert RM, Johnston KP (1990). Solubilities and selectivities in supercritical fluid mixtures near critical end points. Fluid Phase Equilib. 59:31–55.

Li J, Jin J, Zhang Z, Wang Y (2011). Measurement and correlation of solubility of benzamide in supercritical carbon dioxide with and without cosolvent. Fluid Phase Equilibr. 307(1):11-15.

Lu BCY , Zhang D, Sheng W (1990). Solubility enhancement in supercritical solvents. Pure Appl. Chem. 62:2277–2285.

Lucein FP, Foster NR (1996). Influence of matrix composition on the solubility of hydroxybenzoic acid isomers in supercritical carbondioxide. Ind. Eng. Chem. Res. 35:4686–4699.

Lucien FP, Foster NR (2000). Solubilities of solid mixtures in supercritical

carbon dioxide: a review. J. Supercrit. Fluids 17:111–134. Maher A (2002). Kinetic models of supercritical fluid extraction. J. Separ.

Sci. 25(8):477-489. Mark K, John RD, Steve MH, William RT, Roy L (1993). Tranter and

Christopher J. Dowle , Quantitative structure–extraction relationships: a model for supercritical fluid extraction. Analyst. 118:1261-1264.

McHugh MA, Krukonis VJ (1994). Supercritical Fluid Extraction Principles and Practice, 2nd ed., Butterworth–Heinemann, London.

Mukhopadhyay M (2000). Natural Extracts Using Supercritical Carbon Dioxide, CRC press, London.

Owen JC, Katrin P (2001). Solubility of Squalene, Oleic Acid, Soya Oil, and Deep Sea Shark Liver Oil in Subcritical R134a from 303 to 353 K. Ind. Eng. Chem. Res. 40(3):965–972.

Park HS, Lee HJ, Shin MH, Lee KW, Lee H, Kim YS, Kim KO, Kim KH (2007). Effects of cosolvents on the decaffeination of green tea by Supercritical CO2. Food Chem. 105(3):1011-1017.

Pourmortazavi SM, Sefidkon F, Hosseini SG (2003). Supercritical Carbon Dioxide Extraction of Essential Oils from Perovskia atriplicifolia Benth. J. Agric. Food Chem. 51:5414.

Raeissi S, Peters CJ (2005). Application of double retrograde vaporization as an optimizing factor in supercritical fluid separations, J. Supercrit. Fluids. 33:115–120.

Sameena A, Keith DB, Anthony AC, Robert M, Mark WR, Gavin FS (1992). Prediction of the conditions for supercritical fluid extraction of atrazine from soil. Analyst. 117:1697-1700

Sanli D, Bozbag S, Erkey C (2012). Synthesis of nanostructured materials using supercritical CO 2: Part I. Physical transformations. J. Mater. Sci. 47(7):2995-3025.

Sauceau M, Letourneau JJ, Freiss B, Richon D, Fages J (2004). Solubility of eflucimibe in supercritical carbon dioxide with or without a co-solvent, J. Supercrit. Fluids. 31:133–140.

Seied MP, Seiedeh SH (2007). Supercritical fluid extraction in plant essential and volatile oil analysis. J. Chromatogr. A 1163:(1–2)7:2–24.

Sousa EMBD, Chiavone-Filho O, Moreno MT, Silva MOM, Marques MAA (2002). Meireles, experimental results for the extraction of essential oil from Lippia sidoides cham. Using pressurized carbondioxide. Braz. J. Chem. Eng. 19:229.

Taguchi M, Hobo T, Maeda T (1991). Evaluation and application of a supercritical fluid extraction system using capillary supercritical fluid chromatography. J. High Resolut. Chromatogr. 14:140.

Ting SS, Macnaughton SJ, Tomasko DL, Foster NR (1993a). Ind. Eng. Chem. Res. 32:1471–1481.

Ting SST, Macnaughton SJ, Tomasko DL, Foster NR (1993b). Solubility of naproxen in supercritical carbon dioxide with and without cosolvents, Ind. Eng. Chem. Res. 32:1471–1481.

Wang L, Weller CL (2006). Recent Advances in Extraction of Nutraceuticals from Plants. Trends Food Sci. Technol. 17:300–312.

Wheeler JR, McNally ME (1989). Supercritical fluid extraction and chromatography of representative agricultural products with capillary and microbore columns. J. Chromatogr. Sci. 27:534.

William KM, Dulcie AM, Mark WR (1996). Analytical Supercritical Fluid Extraction of Natural Products. Phytochem. Anal. 7(1):1–15.

Zosel K (1981). Process for Decaffeination of Coffee. US Pat. 4247570.

Cite this article as: Hussain S (2014). Solubility of crude oil in pure and modified supercritical carbon dioxide using supercritical fluid extractor. Acad. J. Sci. Res. 2(3):038-049. Submit your manuscript at http://www.academiapublishing.org/journals/ajsr