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Environmental Sciences
CaO is a key component of eggshells. Biodiesel is usually produced in a homogeneous manner using chemical catalysts.
- transesterification
- heterogeneous catalysis
- eggshells
1. Introduction
Increasing environmental pollution is caused by various factors, including the usage of vehicles. Legislation is being promoted to increase the use of renewable energy sources for fuel production. The use of electric cars is also being promoted, however, these are fairly new and expensive methods of transport. It is expedient to increase the amount of renewable energy in diesel fuel production, as 31.6% of all new cars registered in the European Union are powered by diesel engines in 2019 [1]. Also, most agricultural machinery is powered by diesel fuel [2], as are water vehicles such as, for example, boats [3], and therefore research on biodiesel production is relevant.
Biodiesel is usually produced in a homogeneous manner using chemical catalysts, for example, base catalysts NaOH, KOH, or acid catalysts H2SO4 [4]. Homogeneous catalysts can be used only once, so it is important to use heterogeneous catalysts that can be reused. CaO is known to be an efficient catalyst for biodiesel production [5], and research results show that CaO can be used as neat CaO, doped CaO, loaded CaO, and mixed with metal oxides [6].
CaO is a key component of eggshells. The amount of worldwide egg production increased more than 14% during the past decade and reached 76.7 million tons in 2018 [7]. Eggshell forms around 10% of a chicken‘s egg by weight [8]. Experts from the European Commission predict that the production and consumption of eggs will increase over the next few years. It is predicted that egg consumption per capita is likely to increase to 15.0 kg (14.2 kg in 2021) and production is expected to increase to 6.77 million tons (with an average annual growth rate of 0.7%) by 2030 [9]. As egg consumption increases, quantities of eggshells increase too.
The Circular Economy Action Plan is one of the key instruments of the new European Green Deal in the European Union. European Green Deal should lead to a climate-neutral, competitive, empowered consumer economy. The European Parliament wants Europeans to move towards a circular economy through the more efficient use of raw materials and by reducing amount of waste, which is of vital importance. The focus will be on waste prevention and the recycling of waste into high-quality secondary raw materials, for which a well-functioning secondary raw materials market will be important [10]. As it is not possible to reduce the amount of eggshells, it is important to try to use them. Currently most of the eggshells are treated as waste and are disposed in landfills with no or minimal pre-treatment [11]. Eggshell waste can be used as calcium supplement in animal feed [12], and as calcium absorption is better when it is natural in origin, eggshells are a good calcium source for use in pharmaceutical industries [13]. Calcium is important for living organisms, and for this reason eggshells can be used as a soil amendment [14] or even for human consumption [15].
2. Physical and Chemical Properties of Produced Biodiesel
In order to determine whether the produced biodiesel can be used in the transport sector, the physical and chemical properties were investigated and compliance with the requirements of the standard LST EN 14214 was assessed. These are presented in Table 1.
Table 1. The physical and chemical properties of rapeseed oil methyl esters.
| Parameter | Units | EN 14214 Requirements | Rapeseed Oil Methyl Esters |
|---|---|---|---|
| Ester content | % | min 96.5 | 97.79 ± 0.32 |
| Density at 15 °C | kg m−3 | min 860 max 900 |
885 ± 0.24 |
| Viscosity at 40 °C | mm2 s−1 | min 3.50 max 5.00 |
4.83 ± 0.02 |
| Acid value | mg KOHg−1 | max 0.5 | 0.39 ± 0.002 |
| Sulfur content | mg kg−1 | max 10 | 7.2 ± 0.05 |
| Moisture content | mg kg−1 | max 500 | 228 ± 0.34 |
| Iodine value | g J2100−1 g−1 | max 120 | 117 ± 0.18 |
| Linolenic acid methyl esters content | % | max 12.0 | 9.5 ± 0.07 |
| Monoglyceride content | % | max 0.8 | 0.47 ± 0.04 |
| Diglyceride content | % | max 0.2 | 0.09 ± 0.01 |
| Triglyceride content | % | max 0.2 | 0.04 ± 0 |
| Free glycerol content | % | max 0.2 | 0.02 ± 0 |
| Total glycerol content | % | max 0.25 | 0.22 ± 0.15 |
| Methanol content | % | max 0.2 | 0.08 ± 0.001 |
| Phosphorus content, ppm | 10 | 8 ± 0.05 | |
| Oxidation stability 110 °C | h | min 8 | 8.3 ± 0.1 |
| Cetane number | - | min 51 | 53.8 ± 0.15 |
| Cold filter plugging point | °C | −5 °C (in summer) −32 °C (in winter) |
−10 ± 0.05 |
The main indicator of biodiesel quality is the ester yield. It shows the degree to which the transesterification reaction took place and how many fatty acid methyl esters were formed from the oil. According to EN 14214, biodiesel must contain at least 96.5% fatty acid methyl esters. The amount of biodiesel ester produced was found to meet the required standards and was 97.79 ± 0.32 wt%.
The purity of the biodiesel is defined by the content of free glycerol, mono-, di- and triglycerides and the total glycerol content of biodiesel. These parameters depend on the production method and the method of cleaning and purification of the final product. The content of free glycerol in biodiesel shall not exceed 0.02% (wt/wt). If it is higher, it indicates that glycerol was not separated efficiently enough during purification and washing. The content of mono-, di- and triglycerides and the content of total glycerol in biodiesel is also very important. It must be less than 0.8%, 0.2%, 0.2% and 0.25% (wt/wt), respectively. Low concentrations of mono-, di- and triglycerides are obtained only if optimal process conditions are met or biodiesel is distilled. If the values in the final product are above the limit values, the use of such biofuels may result in sedimentation at the bottom of the fuel tank, interaction with other compounds and damage to the engine injection system or corrosion of metal alloys. The content of free glycerol, mono-, di- and triglycerides and total glycerol in the produced biodiesel meets the requirements of the standard.
Excess methanol is used in the production of biodiesel to transesterify oils or fats. The unreacted methanol is evaporated and washed with water, at the end of the process. In the case of quality biodiesel, the methanol content shall not exceed 0.2% (wt/wt). Higher amounts of methanol can pose a risk during transport and storage of fuels due to its relatively low flash-point and ignition temperatures. The methanol content of the produced biodiesel is only 0.08–0.001%.
The iodine value indicates the degree of saturation of the fatty acids and is expressed in grams of iodine, which reacts with 100 g of biodiesel (g J2100−1 g−1). The maximum iodine value allowed is 120 g J2100−1 g−1. In addition to this indicator, the degree of unsaturation of the fatty acids in biodiesel is limited by the content of linolenic acid methyl ester, which must not exceed 12%, and the content of polyunsaturated (≥4 double bonds) methyl esters, which must not exceed 1%. Biodiesel, which is characterized by a high content of mono- and polyunsaturated fatty acids, has been found to tend to polymerize and form deposits on the nozzles and piston rings. In addition, unsaturated esters with engine lubricants form high molecular weight compounds that degrade lubricating properties. The iodine value also correlates with other properties of biodiesel, such as viscosity and cetane number, both of which decrease with an increasing degree of unsaturation. As rapeseed oil is used in the production of biodiesel, which does not contain high amounts of mono- and polyunsaturated fatty acids, the resulting fuel meets the requirements of the standard.
The acid value indicates the content of mineral and free fatty acids in the biodiesel and is expressed in milligrams of potassium or sodium hydroxide required to neutralize the acids contained in 1 g of fatty acid methyl esters. The maximum limit for the acid value given in the European standard is 0.5 mg KOHg−1. The number of acids depends on the feedstock used for the production of biodiesel and the production process, which was used, as free fatty acids are also formed during transesterification and storage. Using biodiesel with high acid content can cause corrosion and sedimentation in the engine. The acid value of the obtained fuel is 0.39 ± 0.002 mg KOHg−1.
Biodiesel has a higher density than mineral diesel. According to the requirements of the standard, it must be in the range of 860–900 kg m−3 under a temperature of 15 °C, while the density of mineral diesel is 820–845 kg m−3. This difference in density affects the calorific value of the fuel and the amount of fuel, which enters the combustion chamber. The density depends on the nature of the biodiesel (the fatty acid composition of the raw material) and its purity. The density of produced biofuels is 885 ± 0.24 kg m−3.
Sulfur-rich fuels have a negative impact not only on the environment, but also on the human body, and therefore the amount of sulfur in biodiesel, as in the mineral diesel, is limited and must not exceed 10 mg kg−1. Sulfur-rich fuels not only increase sulfur oxide emissions, but also cause shorter engine life, reduced catalytic converter efficiency and service life, and reduced lubricity and damage to the injection pump. Conventional biodiesel—rapeseed oil fatty acid methyl esters are essentially free of sulfur compounds, and very low levels of sulfur may be due to glucosinolates or other compounds in rapeseed oil. The sulfur content of the produced biodiesel is 7.2 ± 0.05 mg kg−1.
High quality biodiesel should not contain more than 500 mg kg−1 of moisture. Water is formed in the biofuels during the production process and is removed by drying the product. Due to the hygroscopic nature of fatty acid methyl esters, they can also absorb water during storage. The amount of water is limited as it causes microbiological processes, the formation of sludge and sediment can clog fuel lines and filters. In addition, in the presence of water, hydrolysis processes of biodiesel take place and free fatty acids are formed, which can also clog the filters, and the corrosion of chromium and zinc parts occurs.
In addition to the mentioned physical and chemical parameters above, it is very important that the fuel is stable and retains the required properties during extended storage and transportation. This is especially important for biodiesel, as contact with atmospheric oxygen results in oxidation processes that form free fatty acids, peroxides, aldehydes, and polymers that degrade the fuel and make the fuel unusable. The EN 14214 standard includes an indicator of oxidation stability, with a limit of at least 8 h at 110 °C. Oxidation stability of 8.3 h was obtained for our fuel.
It is very important that both mineral fuels and biofuels are usable during cold periods. They must not crystallize or freeze at low temperatures. There are different requirements for the limit cold filter plugging point (CFPP) value depending on the climatic conditions. In (Arctic climate class 2), fuels with an CFPP not higher than minus 32 °C must be used during the winter CFPP—not higher than minus 15 °C (temperate zone class E), CFPP not higher than minus 5 °C (temperate zone C). CFPP of our obtained biodiesel is minus 10 ± 0.05 °C.
This entry is adapted from the peer-reviewed paper 10.3390/catal12030246
References
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- Available online: https://www.hartmann-packaging.com/world/think-news/2-2021-european-egg-market/ (accessed on 15 November 2021).
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