A Review of the Research: Biodiesel and Petrodiesel Fuels
Crude oils have been primary sources of energy and fuels, such as petrodiesel. However, significant public concerns about their sustainability, price fluctuations, and adverse environmental impact have emerged since the 1970s (Ahmadun et al., 2009;
Atlas, 1981; Babich and Moulijn, 2003; Haritash and Kaushik, 2009; Kilian, 2009; Leahy and Colwell, 1990; Perron, 1989). Thus, biooils (Bridgwater and Peacocke, 2000; Czernik and Bridgwater, 2004; di Blasi, 2008; Gallezot, 2012; Mohan et al., 2006; Mortensen et al., 2011) and biooil-based biodiesel fuels (Agarwal, 2007; Chisti, 2007; Hill et al., 2006; Lapuerta et al., 2008; Ma and Hanna, 1999; Mata et al., 2010; Meher et al., 2006; Zhang et al., 2003a-b) have emerged as alternatives to crude oils and crude oil-based petrodiesel fuels in recent decades. Nowadays, although petrodiesel fuels are used extensively, biodiesel fuels are being used increasingly in the transportation and power sectors (Konur, 2021a-ag).
However, for the efficient progression of the research in this field, it is necessary to develop efficient incentive structures for the primary stakeholders and to inform these stakeholders about the research (Konur, 2000, 2002a-c, 2006a-b, 2007a-b; North, 1991a—b).
Although there have been over 5,500 reviews, book chapters, and books in this field, there has been no review of the 50-most-cited articles (cf. Konur, 2012, 2015). Thus, this chapter reviews these articles on both biodiesel and petrodiesel fuels. Then, it discusses the findings of the review.
Materials and Methodology
The search for the literature was carried out in the ‘Web of Science’ (WOS) database in February 2020. It contains the ‘Science Citation Index-Expanded' (SCLE), the Social Sciences Citation Index’ (SSCI), the ‘Book Citation Index-Science’ (BCI-S), the ‘Conference Proceedings Citation Index-Science’ (CPCI-S), the ‘Emerging Sources Citation Index’ (ESCI), the ‘Book Citation Index-Social Sciences and Humanities’ (BCI-SSH), the ‘Conference Proceedings Citation Index-Social Sciences and Humanities’ (CPCI-SSH). and the ‘Arts and Humanities Citation Index’ (A&HCI).
The keywords for the search of the literature were collated from the screening of the abstract pages for the first 1,000 highly cited papers in the related 11 research fields. These keyword sets are provided in the appendices of the related chapters (Konur, 2021e-ag).
The 50-most-cited articles were selected for this review and the key findings are discussed briefly.
Biodiesel Fuels in General
Van Zwieten et al. (2010) study the effects of biochar from the slow pyrolysis of paper-mill waste on agronomic performance and soil fertility in a paper with 722 citations. They modify two agricultural soils with two biochars and assess them in a glasshouse study. Both biochars had a high surface area and zones of a calcium mineral agglomeration, although they differed slightly in their liming values and carbon content. They find that both biochars significantly increased N uptake in wheat grown in a fertilizer-modified ferrosol. The concomitant increase in biomass production therefore suggested improved fertilizer-use efficiency. Likewise, biochar modification significantly increased biomass in soybean and radish in the ferrosol with fertilizer. There were no significant effects of biochar in the absence of fertilizer for wheat and soybean, while radish biomass increased significantly.
Vispute et al. (2010) study the production of chemicals from the integrated catalytic processing of pyrolysis oils in a paper with 672 citations. They combine hydroprocessing with zeolite catalysis. The hydroprocessing increased the intrinsic hydrogen content of the pyrolysis oil, producing polyols and alcohols. They find that the zeolite catalyst then converted these hydrogenated products into light olefins and aromatic hydrocarbons in a yield as much as three times higher than that produced with the pure pyrolysis oil. The yield of aromatic hydrocarbons and light olefins from the biomass conversion over zeolite was proportional to the intrinsic amount of hydrogen added to the biomass feedstock during hydroprocessing.
Evans and Milne (1987) carry out the molecular characterization of the pyrolysis of biomass in a paper with 633 citations. They apply the technique of ‘molecular-beam, mass spectrométrie' (MBMS) sampling to the elucidation of the molecular pathways in the fast pyrolysis of wood and its principal isolated constituents for the optimization of high-value fuel products by thermal and catalytic means. They find that the cellulose, lignin, and hemicellulose components of wood pyrolyze largely to monomer and monomer-related fragments and given characteristic mass spectral signatures. Whole wood behaves as the sum of its constituents, with few if any vapor species derived from interaction of the main polymer constituents. An important interaction, however, is the influence of mineral matter in the wood on the carbohydrate pyrolysis pathways.
Demirbas (2000) studies the mechanisms of liquefaction and the pyrolysis reactions of biomass in a paper with 617 citations. In the liquefaction process, the micellar-like broken-down fragments produced by hydrolysis are degraded into smaller compounds by dehydration, dehydrogenation, deoxygenation, and decarboxylation. These compounds once produced, rearrange through condensation, cyclization, and polymerization, leading to new compounds. He finds that thermal depolymerization and decomposition of biomass, cellulose, hemicelluloses, and products were formed, as well as a solid residue of charcoal. Cleavage of the aromatic C-0 bond in lignin led to the formation of one oxygen atom product, and cleavage of the methyl C-0 bond, to form two oxygen atom products, is the first reaction to occur in the thermolysis of 4-alkyl-guaiacol at 600-650 K.
Sharma et al. (2004) characterize biochars from the pyrolysis of lignin and its reactivity towards the formation of polycyclic aromatic hydrocarbons (PAHs) in a paper with 551 citations. They find that the biochar yield in pyrolysis decreased rapidly with an increase in temperature up to 400°C, after which there was a gradual decrease in the yield to ca. 40% at 750°C. In oxidative atmosphere, the char yield decreased to ca. 15% at 550°C. The pyrolysis led to the formation of melt, liquid phase, vesicles, precipitates of inorganic salts, and surface etching when these structures decomposed rapidly at high temperatures. There was a gradual decrease in the amounts of OH and CH, with increasing temperature. Both the H: C and O:C ratios of the biochar decreased with increase in temperature. The surface area.
presence of inorganics, and aromaticity of char are important factors in PAH formation. These biochars have low reactivity, compared to chars from other biomass constituents probably due to the highly cross-linked and refractory nature of the lignin char.
Orfao et al. (1999) study the behavior of biomass components, cellulose, the xylan-representative of hemicelluloses, and lignin - thermogravimetrically with linear temperature programming, in N and air - in a paper with 546 citations. They find that the thermal decomposition of xylan and lignin could not be modeled with acceptable errors by means of simple reactions. They determine thermograms for pine and eucalyptus woods and pine bark, in an inert (N) or oxidizing (air) atmosphere. They model the pyrolysis of these lignocellulosic materials with good approximation by three first-order independent reactions. One of these reactions is associated with the primary pyrolysis of cellulose, its parameters being previously determined and fixed in the model. The model parameters are the activation energies and preexponential factors for the pyrolysis of the remaining two pseudo-components and two additional parameters related to the biomass composition.
Mohan et al. (2007) study biochar by-products from fast wood/bark pyrolysis as adsorbents for the removal of the toxic metals from water during biooil production in a paper with 500 citations. They obtain the biochars for oak bark, pine bark, oak wood, and pine wood at fast pyrolysis of 400 and 450°C in an auger-fed reactor. They find that maximum adsorption occurred over a pH range of 3-4 for arsenic and 4-5 for lead and cadmium. The optimum equilibrium time was 24 h with an adsorbent dose of 10 g/L and a concentration similar to 100 mg/L for lead and cadmium. Oak bark outperformed the other biochars and nearly mimicked Calgon F-400 adsorption for lead and cadmium. In an aqueous lead solution with initial concentration of 4.8 x IO-4 M, both oak bark and Calgon F-400 (10 g/L) removed nearly 100% of the heavy metal. Oak bark (10 g/L) also removed about 70% of arsenic and 50% of cadmium from aqueous solutions. Overall, the data are well fitted with both the models, with a slight advantage for the Langmuir model.
Biodiesel Fuels in General
Hill et al. (2006) compare environmental, economic, and energetic costs and benefits of biodiesel and bioethanol biofuels in a paper with 1,597 citations. They find that corn-based bioethanol yields 25% more energy than that invested in its production, whereas soybean-based biodiesel yields 93% more. Compared with bioethanol, biodiesel releases just 1.0, 8.3, and 13% of the agricultural N. P, and pesticide pollutants, respectively, per net energy gain. Relative to the fossil fuels they displace, greenhouse gas emissions are reduced by 12% by the production and combustion of bioethanol and by 41% by biodiesel. Biodiesel also releases less air pollutants per net energy gain than bioethanol. These advantages of biodiesel over bioethanol come from lower agricultural inputs and more efficient conversion of feedstocks to fuel. However, it is clear that neither biofuel can replace much petroleum without impacting food supplies. Even dedicating all US corn and soybean production to biofuels would meet only 12% of gasoline demand and 6% of diesel demand. Until recent increases in petroleum prices, high production costs made biofuels unprofitable without subsidies. Biodiesel provides sufficient environmental advantages to merit subsidy. Transportation biofuels such as synfuel hydrocarbons or cellulosic bioethanol, if produced from low-input biomass grown on agriculturally marginal land or from waste biomass, could provide much greater supplies and environmental benefits than food-based biofuels.
Dasari et al. (2005) study the low-pressure hydrogenolysis of glycerol to propylene glycol in a paper with 642 citations. They use nickel, palladium, platinum, copper, and copper-chromite catalysts. They find that at temperatures above 200°C and a hydrogen pressure of 200 psi, the selectivity to propylene glycol decreased due to excessive hydrogenolysis of the propylene glycol. At 200 psi and 200°C the pressures and temperatures were significantly lower than those reported in the literature while maintaining high selectivities and good conversions. The yield of propylene glycol increased with decreasing water content. They validate a new reaction pathway for converting glycerol to propylene glycol via an intermediate by isolating the acetol intermediate.