**2. Experimental**

in FAME crystallized and precipitated in the gel upon addition of hydrocarbons such as engine lubricant oil. Therefore, the use of FAME-dissolved polystyrene as diesel fuel requires

**Figure 1.** Energy recovery using biodiesel fuel (FAME) derived from waste cooking oil selective-dissolved waste poly‐

Biodiesel consists of fatty acid methyl esters (FAME) and can be produced from a great variety of feedstocks including vegetable oil (e.g., soybean, palm, rapeseed oil) and animal fats, as well as waste cooking oils (e.g., used frying oils). FAME has been used as alternative fuel of diesel fuel. Many research projects have been carried out and have been published in books and journals [1-3]. Most of all are concerning to fuel quality, combustion and exhaust emission

Effective use of waste plastics is important in establishing a recycling-oriented society. FAME can dissolve plastics and rubbers, which are used as fuel system parts of diesel engines, resulting in the need to replace these parts. If a method to utilize FAME as a solvent to dissolve plastics can be developed, waste plastics could be recovered and could be utilized as liquid

Several studies on solubility report that *n-*alkenes and di-*n-*alkyl are better solvents for the low and medium molecular weight samples of polystyrene than the corresponding *n*-alkanes [4]. Also, it is shown that certain food items have been shown to be incompatible with the expanded polystyrene (EPS) used for the manufacture of food containers. Citronella, limonene and terpinene, which are constituents of many flavor oils, are excellent solvents for polystyrene [5]. Studies of solubility for volume reduction and waste management of polystyrene recycling have been conducted earlier [6,7]. Solubility values of extrude poly-styrene(XPS) in several solvents such as benzene, toluene, xylene, tetrahydrofuran, chloroform, 1,3-butanediol, 2 butanol, linalool, geranoil, *d*-limonene, *p*-cymene, terpinene, phellandrene, terpineol, metha‐

characteristics, which regards the utilization with the diesel engines.

attention to tribology.

206 Biofuels - Status and Perspective

styrene (PS).

fuel.

### **2.1. Solubility parameter determination**

Solubility parameters can be used to easily identify solvents for polymers. Many successful studies have used methods based on the solubility parameter [12-14]. The term "solubility parameter" was first used by Hildebrand and Scott [15]. The theory relates the energy of mixing to the energy of vaporization of the pure component. This theory was developed for mixing of nonpolar substances. However, many solvents and polymers in common use are polar compounds. Hansen divided the polar portion into a dipole-dipole contribution and hydro‐ gen-bonding contribution, both of which could be determined through solubility experiments with polymers [16]. The Hansen solubility parameter (HSP) separates the solubility energy into three parts: dispersion (*δ*D), polarity(*δ*P), and hydrogen bonding(*δ*H). The HSP concept can be described as "like vectors dissolve like vectors." For the vector "likeness," the HSP distance (*Ra*), which is the distance between the solvent and center of the polymer solubility sphere, was used. *Ra* is calculated using Eq.1:

$$R\_a = \sqrt{4\left(d\_{D1} - d\_{D2}\right)^2 + \left(d\_{P1} - d\_{P2}\right)^2 + \left(d\_{H1} - d\_{H2}\right)^2} \tag{1}$$

where subscript 1 represents the solvent, and subscript 2 represents the polymer.

This equation was developed from plots of experimental data where the constant "4" was found convenient and correctly represented the solubility data as a sphere encompassing the good solvents. When the scale for dispersion (*δ*D) parameter is doubled, in compari‐ son with other two parameters essentially spherical, rather than spheroidal, regions of solubility are found [16].

To determine if the parameters for the solvent and polymer are within an acceptable range, a value called the interaction radius (*R0*) of the polymer is applied to the substance being dissolved. Good solvents are within *R0*, and poor ones are outside it. A simple composite affinity parameter, relative energy distance (*RED)*, has been defined as:

$$RED = R\_a / R\_0 \tag{2}$$

Good solvents will have *RED* less than 1.0. Poor solvents will have increasingly higher *RED* values.

In this study, the solubility of polymer in methyl ester, methanol, and fatty acid was determined by HSPiP (Hansen solubility parameters in practice) software [17]. Fatty acids are source materials of FAME production by esterification process. Oleic acid methyl ester (methyl oleate) is a main component of FAME derived from waste cooking oil, because a typical raw material for cooking oil is the rapeseed oil and soybean oil. Tables 1 and 2 show the HSP from the dataset in HSPiP for methyl oleate, methanol, and oleic acid as solvents, and polystyrene (PS), polypropylene (PP), and polyethylene (PE) as polymers. The HSP generally in use for liquids have all been calculated at 25o C. In this study, the dataset at 25o C was used.


**Table 1.** Dispersion δD, polarity δP, and hydrogen bonding δH of methyl oleate, methanol, and oleic acid as solvents.


\* data from the dataset in HSPiP [17]

parameter" was first used by Hildebrand and Scott [15]. The theory relates the energy of mixing to the energy of vaporization of the pure component. This theory was developed for mixing of nonpolar substances. However, many solvents and polymers in common use are polar compounds. Hansen divided the polar portion into a dipole-dipole contribution and hydro‐ gen-bonding contribution, both of which could be determined through solubility experiments with polymers [16]. The Hansen solubility parameter (HSP) separates the solubility energy into three parts: dispersion (*δ*D), polarity(*δ*P), and hydrogen bonding(*δ*H). The HSP concept can be described as "like vectors dissolve like vectors." For the vector "likeness," the HSP distance (*Ra*), which is the distance between the solvent and center of the polymer solubility sphere,

( ) ( ) ( ) 22 2

This equation was developed from plots of experimental data where the constant "4" was found convenient and correctly represented the solubility data as a sphere encompassing the good solvents. When the scale for dispersion (*δ*D) parameter is doubled, in compari‐ son with other two parameters essentially spherical, rather than spheroidal, regions of

To determine if the parameters for the solvent and polymer are within an acceptable range, a value called the interaction radius (*R0*) of the polymer is applied to the substance being dissolved. Good solvents are within *R0*, and poor ones are outside it. A simple composite

Good solvents will have *RED* less than 1.0. Poor solvents will have increasingly higher *RED*

In this study, the solubility of polymer in methyl ester, methanol, and fatty acid was determined by HSPiP (Hansen solubility parameters in practice) software [17]. Fatty acids are source materials of FAME production by esterification process. Oleic acid methyl ester (methyl oleate) is a main component of FAME derived from waste cooking oil, because a typical raw material for cooking oil is the rapeseed oil and soybean oil. Tables 1 and 2 show the HSP from the dataset in HSPiP for methyl oleate, methanol, and oleic acid as solvents, and polystyrene (PS), polypropylene (PP), and polyethylene (PE) as polymers. The

where subscript 1 represents the solvent, and subscript 2 represents the polymer.

affinity parameter, relative energy distance (*RED)*, has been defined as:

HSP generally in use for liquids have all been calculated at 25o

1 2 12 1 2 4 *R= d d +d d +d d a DD PP HH* --- (1)

*RED = R R <sup>a</sup>* <sup>0</sup> (2)

C. In this study, the dataset

was used. *Ra* is calculated using Eq.1:

208 Biofuels - Status and Perspective

solubility are found [16].

values.

at 25o

C was used.

**Table 2.** Dispersion δD, polarity δP, and hydrogen bonding δH and interaction radius of polystyrene(PS), polypropylene(PP), and polyethylene(PE) as polymer.

### **2.2. Measurement of the solubility and fuel properties**

Expanded polystyrene (EPS) and food trays (PSP), cut to pieces, were stirred slowly into FAME and dissolved at room temperature. FAME was prepared by the batch-type production equipment using an alkaline catalyst method [3]. Commercial soybean cooking oil was used as the raw material to produce biodiesel, soybean oil methylester (SME).

To determine the dissolved molecular weight of the polystyrene, polystyrene standards with an average molecular weight (MW) of 4000 and 50,000 were also dissolved in FAME. The polystyrene molecular weight distribution in FAME was measured by gel permeation chromatography (GPC).

To clarify the fuel characteristics as diesel fuel, kinematic viscosity was measured according to JIS K2283, the ignition quality as diesel fuel was analyzed by fuel ignition analyzer (FIA) through constant-volume combustion (Fueltech, FIA-100 ver3). Diesel combustion property was evaluated by an ignition delay. Figure 2 shows the configuration of the FIA. In the experiments, conducted under constant pressure of 2.0MPa and initial temperatures of 450o C, the fuel was injected and the ignition delay was measured. Ignition delay was defined as the time difference between the fuel injection start time and the time at which combustion pressure was 0.02MPa greater than the initial pressure in the chamber, as shown in Figure 3.

The cetane number (*CN*) is used often for estimating ignition quality. In this study, the CN value of FAME-dissolved polystyrene was estimated by calibration of the *CN* obtained from a mixture hexadecane (*CN*=100) and heptamethylnonane (CN=15). For practical purposes, the FIA cetane number(*CNFIA*) was determined by Eq.3.

$$CN\_{FL} = 1413 \cdot t \stackrel{!}{\\\text{0.69}} \tag{3}$$

where *τ* denotes the ignition delay [ms].

Furthermore, the relationship between *CN* of FAME using FIA and *CN* value using the CFR standard institutional organization engine test, *CNCFR*, is described by the following relation [18]:

$$\text{CN}\_{\text{CFR}} = \text{CN}\_{\text{FH}} + \text{22} \tag{4}$$

One of the important characteristics of diesel fuel is the carbon residue (CR). The CR is a characteristic value related to the amount of carbon deposits stored inside the engine, carbon deposits for petroleum-based fuels in general are measured using a sample condensed to 10% in volume. For FAME, the high-temperature heating process under condensation results in thermal decomposition of FAME components. In addition, the chemical structure of the fatty acid methyl ester component is changed. For this reason, the CR value for FAME was measured using a sample without condensation in this study.

The heating value of fuel is related to fuel economy and engine power. In this study, the higher heating value of fuel was measured using an automatic bomb calorimeter (Shimadzu, CA-4PJ).

**Figure 2.** Configuration of fuel ignition quality analyzer (FIA).

**Figure 3.** Definition of ignition delay by FIA.
