Compression behaviour of bulk rapeseed: Effects of heat treatment, force, and speed

ABSTRACT

This study described the compression behaviour of bulk rapeseed using the universal compression testing machine and vessel diameter of 60 mm with a plunger. The pressing factors, namely the heat treatment temperature, speed, and force, were varied between 45 and 105°C, 5 and 25mm min⁻¹ then 40 and 120 kN, respectively. The bulk rapeseed samples were measured at pressing heights between 20 and 100 mm. The parameters determined were maximum deformation (mm), deformation energy (J), oil yield (%), oil point strain (–), oil point force (kN), and oil point energy (J). Clearly, maximum deformation, deformation energy, and oil yield increased with the increase in force and heat treatment temperature, while that of speed showed a downward trend. A plot of the amounts of force and deformation displayed a smooth and serration curve characteristic. The area under the smooth curve behaviour described the compression process where the maximum rapeseed oil was obtained, while the serration pattern represented the ejection of the rapeseed cake through the holes of the pressing vessel as a result of the higher force and speed. The lower and upper oil points of rapeseed were detected at pressing heights 80 mm and 100 mm with corresponding strain values of 0.38 and 0.49 (–). This study provided vital information on rapeseed in axial pressing which can be applied in the industrial technology for optimizing the mechanical screw press oil production.

KEYWORDS:

• Rapeseed
• Linear pressing
• Deformation curves effect
• Energy requirement
• Oil leakage

Introduction

Rapeseed (Brassica napus L.) is a member of the Brassicaceae family grown annually in the temperate regions. In some cultivars, it is known as Canola or Mustard. The bright yellow flowering crop is grown mainly for its seed containing an oil content between 35 and 45% with high-protein animal feed between 17 and 25%. The yields of rapeseed oil range from 940 to 1880 litres per hectare.^[1,2] The EU, Canada, the United States, Australia, China, and India are the leading producers. However, Germany, Poland, the United Kingdom, France, Belgium, and Sweden are the main consumers.^[3] Rapeseed oil is one of the main sources of biodiesel due to its low sulphur content and low carbon dioxide emission.^[4–6] In Europe, rapeseed oil for biofuel accounts for 77% followed by sunflower and soybean oils being 3% and 18%, respectively.^[7–9]

In-depth knowledge of the compression behaviour of bulk oilseeds such as rapeseed in linear pressing where a universal testing machine and vessel chamber with a plunger are used is essential for optimizing the oil extraction technology involving a mechanical screw press.^[10,11] The mechanical screw press is commonly used in the developing countries due to several advantages including low cost of operation, chemical-free protein-rich cake, and quick adaptation for processing of different oilseeds.^[12] However, its efficiency is lower compared to the solvent extraction method which is mostly used in the developed countries.^[13,14] Pretreatment of the oilseed such as cleaning, conditioning, decorticating, cracking, flaking, cooking, extruding, and drying to optimal moisture content have been reported to improve the oil recovery efficiency.^[15] Thermal treatment has been also proven to be an effective process to increase the oil yield since the process decreases the viscosity of oil which in turn increases the flowability of oil resulting to high oil yield.^[15]

The study on the physical and mechanical properties of the bulk oilseeds has been also directed towards the optimization step. The physical properties include the dimensions, length, diameter, geometric mean diameter, surface area, sphericity, volume, 1000-seedweight, bulk and true densities, porosity, terminal velocity, the angle of repose, and coefficient of static friction.^[16,17] The mechanical properties, on the other hand, include the maximum deformation, deformation energy, oil point strain, oil point force, and force and deformation curve behaviour in terms of smooth and serration characteristics.^[18–21]

In the literature, information on the compression behaviour of bulk rapeseed, i.e., the mechanical properties at different processing factors, is limited. Therefore, the objective of the study was to investigate the effects of heat treatment temperature, force, and speed on the bulk rapeseed under compressing loading.

Materials and methods

Sample

Bulk rapeseed was purchased from the Ceska Skalice, Czech Republic. The moisture content (MC d. b.) (Eq. 1) of the sample was determined using the standard method.^[22]

The procedure was that the initial mass of the sample before and after oven drying was weighed using an electronic balance (Kern 440–35, Kern & Sohn GmbH, Balingen, Germany). The test was repeated thrice and results averaged. The moisture content of 5.92 (% d. b.) was evaluated as ^[23]

(1)

where and represent the mass of rapeseed sample before and after heat treatment (g)

Compression test

The loading test was done with the universal compression device (ZDM 50, Czech Republic).^[24] Variations of the heat treatment temperature, force, and speed between 45 and 105°C, 40 and 120 kN then 5 and 25 mm min⁻¹ were examined for bulk rapeseed pressing heights 60 and 100 mm using the vessel diameter of 60 mm (Fig. 1). The equipment (MEMMERT GmbH + Co. KG, Germany) was used for the heat treatment. The parameters determined were maximum deformation (mm), energy (J), oil yield (%), oil point strain (–), oil point force (kN), and oil point energy (J). The test was repeated thrice and statistically analysed employing the STATISTICA 13 software.^[25]

Figure 1. Schematic of pressing vessel diameter D of 60 mm with plunger.

Oil point determination

For the detection of the lower and upper oil points,^[25] the bulk rapeseed sample was measured at pressing height of 100 mm and then subjected to deformation values of 10.95 mm, 19.87 mm, 29.54 mm, 38.08 mm, and 48.74 mm at a speed of 10 mm min⁻¹.

The deformation values were determined from the bulk rapeseed pressing heights 20, 40, 60, 80, and 100 mm at a speed of 10 mm min⁻¹ and force 100 kN (Table 1).

Table 1. Determined amounts with varying pressing height, force, speed, and heat treatment temperature.

Factors	Factor level	Deformation (mm)	Energy (J)	Oil yield (%)
Pressing height ^a, b (mm)	20	10.95 ± 0.06	231.08 ± 1.91	17.80 ± 0.46
	40	19.87 ± 0.03	324.96 ± 1.26	12.99 ± 0.24
	60	29.54 ± 0.07	464.93 ± 0.88	13.21 ± 0.27
	80	38.08 ± 0.04	567.57 ± 0.62	12.64 ± 0.01
	100	48.74 ± 0.09	757.72 ± 2.40	12.88 ± 0.01
Force ^a, c (kN)	40	45.10 ± 0.03	538.99 ± 1.19	8.10  ± 0.21
	60	48.21 ± 0.05	678.35 ± 1.97	10.81 ± 0.13
	80	47.59 ± 0.03	727.90 ± 2.56	12. 23 ± 0.10
	100	47.07 ± 0.10	756.64 ± 2.11	13.16 ± 0.39
	120	50.43 ± 0.09	1045.59 ± 2.33	15.14 ± 0.02
Speed ^b, d (mm min^−1)	5	29.70 ± 0.18	482.79 ± 1.42	16.03 ± 0.17
	10	29.64 ± 0.52	469.65 ± 3.69	13.40 ± 0.46
	15	28.15 ± 0.24	458.30 ± 12.48	12.47 ± 0.13
	20	28.13 ± 0.12	453.36 ± 10.62	11.58 ± 0.36
	25	27.86 ± 0.13	452.63 ± 9.43	11.18 ± 0.10
Temperature ^a, b, d (°C)	45	30.05 ± 0.09	503.40 ± 5.57	15.55 ± 0.92
	60	29.71 ± 0.28	513.54 ± 19.50	15.98 ± 0.43
	75	30.65 ± 0.78	555.24 ± 10.54	19.37 ± 1.26
	90	30.56 ± 0.33	550.17 ± 8.19	19.74 ± 1.22
	105	31.44 ± 1.63	580.45 ± 7.52	22.50 ± 0.54

^aAt a constant speed of 10 mm min⁻¹; ^bConstant force of 100 kN; ^cBulk rapeseed pressing height of 60 mm; ^dBulk rapeseed pressing height of 100 mm.

Oil yield

The oil yield of bulk rapeseed was determined by ^[24]

(2)

where is the percentage oil yield (%), is the mass of bulk rapeseed oil (g), and is the mass of initial height (g).

Deformation energy

The deformation energy of rapeseed was determined by^[24]

(3)

where E is the deformation energy (J), F is the compressive force (N), and x is the deformation (mm) which was converted to meters during the calculation.

Results and discussion

Deformation, deformation energy and oil yield

Table 1 shows the results of the compression test of bulk rapeseed at varying pressing heights (mm), forces (kN), speeds (mm min⁻¹), and heat treatment temperatures (°C), respectively. Clearly, for bulk rapeseed pressing heights (mm) at a constant speed of 10 mm min⁻¹ and force 100 kN, maximum deformation, deformation energy, and oil yield ranged from 10.95 ± 0.06 to 48.74 ± 0.09 (mm), 231.08 ± 1.91 to 757.72 ± 2.40 (J), and 17.80 ± 0.46 to 12.88 ± 0.01 (%). For varying forces, maximum deformation, energy, and oil yield ranged from 45.10 ± 0.03 to 50.43 ± 0.09 (mm), 538.99 ± 1.19 to 1045.59 ± 2.33 (J), and 8.10 ± 0.21 to 15.14 ± 0.02 (%). In addition, for the different speeds, maximum deformation, energy, and oil yield ranged from 29.70 ± 0.18 to 27.86 ± 0.13 (mm), 482.79 ± 1.42 to 452.63 ± 9.43 (J), and 16.03 ± 0.17 to 11.18 ± 0.10 (%). Furthermore, for heat treatment temperatures, the above-mentioned measured parameters ranged from 30.05 ± 0.09 to 31.44 ± 1.63 (mm), 503.40 ± 5.57 to 580.45 ± 7.52 (J), and 15.55 ± 0.92 to 22.50 ± 0.54 (%). Generally, oil yield and deformation energy increased with increased temperatures and forces but decreased with increased speeds. The results were statistically significant (p < 0.05) or (F_rat > F_crit) as shown in Table 2. Similar results were reported on Jatropha bulk seeds.^[10,24] Figures 2–4 show the relationships between oil yield (%) and speed, force, and temperature.

Table 2. Correlation analyzes of determined amounts in relation to the factors.

Determined amounts	Factors	R	Frat	Fcrit	P-value
Deformation (mm)	Height (mm)	0.99	11811	2.27	<0.05
	Force (kN)	0.78	20.22	2.27	<0.05
	Speed (mm min^−1)	–0.88	45.06	2.27	<0.05
	Temperature (°C)	0.57	6.27	2.27	<0.05
Energy (J)	Height (mm)	0.99	866.24	2.27	<0.05
	Force (kN)	0.93	83.98	2.27	<0.05
	Speed (mm min^−1)	–0.81	23.87	2.27	<0.05
	Temperature (°C)	0.93	81.08	2.27	<0.05
Oil yield (%)	Height (mm)	−0.73	14.97	2.27	<0.05
	Forces (kN)	0.98	332.87	2.27	<0.05
	Speed (mm min^−1)	–0.94	89.88	2.27	<0.05
	Temperature (°C)	0.93	81.08	2.27	<0.05

Significant (p < 0.05 or F_rat > F_crit).

Figure 2. Relationship between oil yield and speed of bulk rapeseed at a speed of 10 mm min⁻¹.

Figure 3. Relationship between oil yield and compressive force of bulk rapeseed at a speed of 10 mm min⁻¹.

Figure 4. Relationship between oil yield and temperature of bulk rapeseed at a speed of 10 mm min^−1.

Smooth and serration curve characteristics

The dependency between the amounts of force and deformation of bulk rapeseed at varying speeds is shown in Fig. 5. The area under the curve is denoted as the deformation energy.^[26]

Figure 5. Compressive force and deformation curves of bulk rapeseed at varying speeds.

Figure 6 shows a smooth and serration characteristic on the force and deformation curve. The smooth curve occurred in the force range of 100‒112 kN at a speed from 5 to 20 mm min⁻¹. On the other hand, the serration effect appeared at a force greater than 112 kN. However, the seration effect was also shown at a force of 100 kN and speed of 25 mm min⁻¹. Clearly, the smooth curve behaviour explains the oil output during compression, while the serration effect is characterized by the ejection of the rapeseed cake through the holes of the pressing vessel which was attributed to the higher compressive force and speed. Therefore, the optimal force and speed in terms of a smooth curve without the serration effect were found at 112 kN and 20 mm min⁻¹, respectively.

Figure 6. Compressive force and deformation characteristics of bulk rapeseed at a speed of 10 mm min⁻¹.

Lower and upper oil points

The oil point is described as the stage at which compression of the bulk material is squeezed for oil to be seen on the surface.^[27] The knowledge of the oil point among other variables including the heat treatment temperature, force, and speed are vital for improving the performance of oil extraction process.^[28,29] The lower and upper oil points were detected at strain values of 0.38 (–) and 0.49 (–) with their corresponding force and energy of 24.12 ± 0.76 kN and 333.81 ± 0.26 J then 112.15 ± 0.85 kN, and 918.51 ± 0.52 J, respectively (Table 3).

Table 3. Oil point amounts of bulk rapeseed at speed 10 mm min⁻¹.

Deformationlevel (mm)	Oil point strain (–)	Oil point force (kN)	Oil point energy (J)
10.95	0.11^e	4.11 ± 0.87	20.64 ± 0.67
19.87	0.20^e	7.87 ± 0.76	69.75 ± 0.28
29.54	0.30^e	14.34 ± 0.58	165.65 ± 0.86
38.08	0.38^f	24.12 ± 0.76	333.81 ± 0.26
48.74	0.49^g	112.15 ± 0.85	918.51 ± 0.52

^eNo oil point; ^fLower oil point; ^gUpper oil point.

Conclusion

In this study, the compression behaviour of bulk rapeseed was examined at different heat treatment temperatures, forces, and speeds. The results showed that oil yield and deformation energy increased with increased temperatures and forces but decreased with increased speeds. The relationship between the force and deformation demonstrated both the smooth and serration curve behaviours.

The area under the smooth curve behaviour described the oil output, while that of the serration effect was related to the rapeseed cake ejection from the holes of the pressing vessel. The maximum force of 200 kN and speed of 25 mm min⁻¹ contributed to the serration behaviour. The lower and upper oil points were noticed at strain values of 0.4 and 0.5 with corresponding deformation energy of 334 ± 0.3 and 919 ± 0.5, respectively.

Funding

The research was financially supported by the Internal Grant of Faculty of Engineering, CULS Prague [grant number IGA 2016: 31130/1312/3106].

Additional information

Funding

The research was financially supported by the Internal Grant of Faculty of Engineering, CULS Prague [grant number IGA 2016: 31130/1312/3106].