The excessive utilization of petroleum resources leads to global warming, crude oil price fluctuations, and the fast depletion of petroleum reserves. Biodiesel has gained importance over the last few years as a clean, sustainable, and renewable energy source. This review provides knowledge of biodiesel production via transesterification/esterification using different catalysts, their prospects, and their challenges. The intensive research on homogeneous chemical catalysts points to the challenges in using high free fatty acids containing oils, such as waste cooking oils and animal fats. The problems faced are soap formation and the difficulty in product separation. On the other hand, heterogeneous catalysts are more preferable in biodiesel synthesis due to their ease of separation and reusability. However, in-depth studies show the limited activity and selectivity issues. Using biomass waste-based catalysts can reduce the biodiesel production cost as the materials are readily available and cheap. The use of an enzymatic approach has gained precedence in recent times. Additionally, immobilization of these enzymes has also improved the statistics because of their excellent functional properties like easy separation and reusability. However, free/liquid lipases are also growing faster due to better mass transfer with reactants. Biocatalysts are exceptional in good selectivity and mild operational conditions, but attractive features are veiled with the operational costs. Nanocatalysts play a vital role in heterogeneous catalysis and lipase immobilization due to their excellent selectivity, reactivity, faster reaction rates owing to their higher surface area, and easy recovery from the products and reuse for several cycles.
Yagiz et al. [116] investigated biodiesel production using the immobilized lipase (Lypozyme TL IM) by physical adsorption on hydrotalcite and four different zeolites (13-x, 5A, FM-8, and AW-30) from the waste cooking oil. The amount of protein adsorbed was higher in the hydrotalcite 13 mg/g matrix than the zeolites 9 mg/g. After the seventh cycle, the enzyme retained 36% of its initial activity at 45 C and 15% at 55 C. Almeida et al. [114] immobilized a Burkholderia cepacia lipase on guava seed biochar, a new, effective alternative support material. The maximum yield of 48% biodiesel was achieved at the optimum conditions of 40 C, 7:1 ethanol to coconut oil molar ratio, and 96 h using the immobilized catalyst.
Manufacture Of Soaps Using Enzyme Pdf Download
Enzyme molecules adsorbed on the non-porous nanomaterials hinder the internal diffusion compared to the porous immobilized nanomaterials. In recent times, magnetic nanoparticles based on Fe3O4 have been extensively studied due to their easy and rapid recovery with a magnetic field. Magnetic nanoparticles also have high stability and low toxicity. Magnetic Fe3O4 nanoparticles have to be coated with chemically active substances to provide functional groups to immobilize enzymes [133]. Badoei-Dalfard et al. [134] synthesized magnetic Fe3O4 functionalized with 3-aminopropyltriethoxysilane to acquire amino activated functional group. CLEAs of lipase were mixed with 3-aminopropyltriethoxysilane-functionalized magnetic graphene oxide and formed a maGO-CLEA-lipase nanocomposite and used for biodiesel production using Ricinus communis oil. The maximum yield of 78% was obtained at the optimum reaction conditions of 3:1 methanol to oil molar ratio, 0.2 wt% enzyme loading at room temperature, 160 rpm, and 24 h. The enzyme could retain the activity up to 5 cycles but continuously started decreasing. Several conventional and nanomaterial supports used for lipase immobilization in biodiesel production with optimum biodiesel conditions are summarized in Table 4.
Lipases are sensitive to the high concentration of methanol or ethanol depending on the source of lipase. Candida antarctica lipase showed the maximum activity at 4:1 methanol to waste frying oil [109], and Candida rugosa lipase showed the maximum activity at 3:1 methanol to Jatropha curcas oil [143]. So the stepwise alcohol addition is recommended to preserve the catalytic activity. Firdaus et al. [144] studied biodiesel production using Thermomyces lanuginosus (Eversa Transform) liquid lipase. As the enzyme is sensitive to a high alcohol concentration, the methanol was added in three steps to obtain a maximum biodiesel yield above 90%.
Continuous research is going on to improve the process economics using enzyme catalysts to implement on an industrial scale. EnzymoCore developed solid organic resin-supported modified-immobilized enzymes to produce biodiesel with high FFA containing oils on a commercial scale. Some immobilized lipases are currently commercially available, such as Novozyme 435, Lipozyme RM IM, Lipozyme TL IM, and Lipae P-SC. In the near future, enzyme catalysts can replace homogeneous catalysts on an industrial scale.
Antibacterial soaps are no more effective than plain soap and water for killing disease-causing germs outside of health care settings. There is no evidence that antibacterial soaps are more effective than plain soap for preventing infection under most circumstances in the home or in public places. Therefore, plain soap is recommended in public, non-health care settings and in the home (unless otherwise instructed by your doctor).
The chemical composition of crude glycerol mainly varies with the type of catalyst used to produce biodiesel, the transesterification efficiency, recovery efficiency of the biodiesel, other impurities in the feedstock, and whether the methanol and catalysts were recovered. All of these considerations contribute to the composition of the crude glycerol fraction. For instance, Hansen et al. [4] studied the chemical compositions of 11 crude glycerol collected from 7 Australian biodiesel producers and indicated that the glycerol content ranged between 38% and 96%, with some samples including more than 14% methanol and 29% ash. Such variations would be expected with small conversion facilities. In most cases, biodiesel production involves the use of methanol and a homogeneous alkaline catalyst, such as sodium methoxide and potassium hydroxide. Accordingly, methanol, soap, catalysts, salts, non-glycerol organic matter, and water impurities usually are contained in the crude glycerol. For example, crude glycerol from sunflower oil biodiesel production had the following composition (w/w): 30% glycerol, 50% methanol, 13% soap, 2% moisture, approximately 2-3% salts (primarily sodium and potassium), and 2-3% other impurities [5]. Moreover, while the same feedstocks were employed, the crude glycerol from alkali- and lipase-catalyzed transesterifications contained different purities of glycerol [6]. The salt content in crude glycerol, from biodiesel production via homogeneous alkaline catalysts, ranged from 5% to 7% [7] which makes the conventional purification techniques more costly. Heterogeneous processes using enzymes and solid metal-oxide catalysts have been promoted as good alternatives to homogeneous alkaline catalysts in terms of improving the quality of crude glycerol. However, even in heterogeneous transesterification processes, impurities existing in the natural raw feedstocks tend to accumulate in the glycerol phase. Therefore, purification of crude glycerol is required, in most cases, to remove impurities in order to meet the requirements of existing and emerging uses.
Poly(hydroxyalkanoates) (PHA) represent a complex class of naturally occurring bacterial polyesters and have been recognized as good substitutes for non-biodegradable petrochemically produced polymers. Ashby et al. [52] reported that crude glycerol could be used to produce PHA polymer. PHB is the most-studied example of biodegradable polyesters belonging to the group of PHA. The study of the feasibility of using crude glycerol for PHB production, with Paracoccus denitrificans and Cupriavidus necator JMP 134, showed that the resulting polymers were very similar to those obtained from glucose. But the PHB production decreased significantly when NaCl-contaminated crude glycerol was used. The authors suggested that the harmful effect of the NaCl-contaminant could be reduced by mixing crude glycerol from different manufacturers [53]. Further, a process based on the Cupriavidus necator DSM 545 fermentation of crude glycerol was designed for the large-scale production of PHB. However, sodium still hindered the cell growth [54]. Zobellella denitrificans MW1 could utilize crude glycerol for growth and PHB production to high concentration, especially in the presence of NaCl. Therefore, it was recommended as an attractive option for large-scale production of PHB with crude glycerol [55].
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