A Review of Supercritical Technologies for Lipid-Based Biofuels Production: The Glycerol-free Processes

Supercritical transesterification of lipid-based biomasses, a recent technique to produce biofuel without a catalyst, is discussed. This review focused on a glycerol-free process. The supercritical reactants include dimethyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate (ETA), and methyl tert-butyl ether. The by-products from the glycerol-free process can improve both the quantity and quality of the resultant biofuel. This review suggests that supercritical transesterification of lipid-based biomasses using ETA as a co-reactant can provide the most valuable advantages, as involves inexpensive and renewable resources, which are important for biofuel production and sustainability

Continuous Production of Biodiesel with Supercritical Methanol: a Simple Compressible Flow Model for Tubular Reactors

From an industrial point of view, the continuous process for biodiesel production with supercritical methanol (SCM) is more appropriate than the batch process. However, lab-scale studies on the continuous process have shown that the maximum conversion always remains slightly lower than that obtained in the batch process. This work proposes a simple compressible flow model to predict the conversion of methanol and oils into methyl esters (ME) along the length of a tubular reactor and further demonstrates the effect of the development of the compressibility factor of the reaction mixture upon the conversion efficiency to ME. The governing equation was derived from a general molar balance in the tubular reactor using transesterification kinetics of refined-bleached-deodorized (RBD) palm oil in SCM coupled with a suitable thermodynamic model with adjusted binary interaction parameters. Vapor-liquid equilibrium data for triolein + methanol, methyl oleate + methanol and glycerol + methanol mixtures were obtained from the literature and then refitted with the thermodynamic model consisting of the Peng-Robinson equation of state and MHV2 mixing rules to find the set of adequate interaction parameters. In order to check the validity of the proposed model, the predicted ME contents were compared with observed values in a lab-scale continuous reactor at various operating temperatures, pressures and methanol to oil molar ratios. The proposed model proved to be adequate for predicting the final conversion to ME for operating temperatures below 320°C, when the thermal degradation reactions of unsaturated fatty acids did not interfere. Our results also illustrate the importance of taking into account the development of the compressibility factor with time and reactor length, since this was shown to be the cause of the lower transesterification reaction rate in the tubular SCM process. The findings in this work could be employed as a knowledge base to further develop a better model for continuous production of biodiesel with SCM in a tubular reactor

Recovery of Moringa oleifera Oil from Seed Cake by Supercritical Carbon Dioxide Extraction

Commercial Moringa oleifera seed oil has been currently produced via mechanical extraction using a screw press machine. Approximately 30 %wt. of the residue oil remains in the seed cake. Thus, this study aims to examine the effects of pressure and solvent-to-feed (S/F) ratio on the supercritical CO2 extraction of seed cake obtained from mechanical extraction. The antioxidant activities of extracted oil were determined using the standard in vitro biological assays. The supercritical CO2 extraction duration of seed cake is shortened because the mechanical extraction reduces oil content before performing supercritical CO2 extraction. At 50 °C and 30.0 MPa, S/F ratios of 0.4 /min and 1.0 /min have corresponded to an extraction duration of 300 min and 180 min, respectively. Up to 90 %wt. of the oil content in the seed cake can be recovered at 30.0 MPa, 50 °C, and after 200 min of extraction duration. Regardless of the extraction pressure, the antioxidant activities of M. oleifera seed oil were maximized at 60 °C

Experimental study and modeling of phase equilibrium of the methanol–tripalmitin system: application to palm oil transesterification with supercritical methanol

The phase behavior of the methanol–palm oil system was first experimentally assessed in the temperature range of 363–393 K and pressure range of 1–4 MPa. Second, comparative modeling of the phase equilibrium of the methanol–tripalmitin system was performed using the Peng–Robinson equation of state (PR EoS) with second-order modified Huron–Vidal (MHV2) mixing rules, in combination with the universal functional activity coefficient model (UNIFAC) and the universal quasi-chemical (UNIQUAC) excess Gibbs free-energy model. The agreement between experimental and modeling results was found to be satisfactory when MHV2 mixing rules are used in combination with the UNIQUAC model. Finally, the thermodynamic model was applied to predict fluid phase equilibria of palm oil transesterification with supercritical methanol. From the isochoric method in the temperature range of 373–693 K and the pressure range of 1–16 MPa, the model was found to predict global mixture behavior

Supercritical Transesterification of Palm Oil and Hydrated Ethanol in a Fixed Bed Reactor with a CaO/Al2O3 Catalyst

Biodiesel production from palm oil and hydrated ethanol in a fixed bed reactor using CaO/Al2O3 as the catalyst was investigated and optimized using response surface methodology. The investigated parameters were temperature, pressure, ethanol/palm oil molar ratio, residence time and total mass flow rate. The approach was divided into two parts, a preliminary study using broad scale changes over a reasonable range of the above operating parameters and then, using this data to select a narrower range, a finer scale study to optimize the selected narrower operating parameters from the preliminary study. The resultant biodiesel obtained under the optimal conditions (285 °C, 20 MPa, 30:1 ethanol/oil molar ratio, 2 g/min flow rate and 4.85 min residence time) was measured for 11 fuel properties following the International Biodiesel Standard (EN14214), and was found to comply with this International Standard. Moreover, ZnO/Al2O3 and La2O3/Al2O3 catalysts were tested for their activity and stability. Although the La2O3/Al2O3 catalyst had a slightly higher initial activity than that of CaO/Al2O3, it is some 800-fold more expensive. Therefore, the CaO/Al2O3 catalyst has a greater industrial potential than La2O3/Al2O3, when comparing together the technical and economic benefits

Comparison of Essential Oils Compositions of Lemon Basil Ocimum citriodourum Vis. Straw Obtained by Hexane Extraction, Supercritical Carbon Dioxide Extraction and Hydrodistillation

การสกัดน้ำมันหอมระเหยจากต้นแมงลักที่สีเมล็ดออกแล้ว (ฟางแมงลัก) ด้วยเฮกเซน คาร์บอนไดออกไซด์ภาวะเหนือวิกฤต (SCCO2) และการต้มกลั่น วิเคราะห์ตัวอย่างที่สกัดได้ด้วยเครื่อง GC-MS เพื่อหาองค์ประกอบน้ำมันหอมระเหยการสกัดด้วยเฮกเซนในเครื่องสกัดแบบซอกส์เลตมีค่าร้อยละผลได้การสกัดสูงสุดเท่ากับ 4.04 ร้อยละผลได้ของการสกัดด้วย SCCO2 (350 บาร์ และ 70 องศาเซลเซียส) และการต้มกลั่น เท่ากับ 1.50 และ 0.29 ตามลำดับ องค์ประกอบหลักที่ได้จากการสกัดด้วยเฮกเซนประกอบไปด้วย คารีโอฟิลลีนออกไซด์ นีรอล เจอแรนเนียล เช่นเดียวกับการสกัดด้วยคาร์บอนไดออกไซด์ภาวะเหนือวิกฤต การต้มกลั่นสารสกัดประกอบไปด้วย คารีโอฟิลลีนออกไซด์ ทรานส์แอลฟาเบอร์กาโมทีน ลินาลูออลเป็นองค์ประกอบหลักExtraction of essential oil from lemon basil (Ocimum citriodourum) straw using hexane, supercritical carbon dioxide (SCCO2) and hydrodistillation was investigated in this study. The extracted samples were subjected to GC-MS to analyze the composition. The extraction yield of hexane in Soxhlet extractor was highest as 4.04%. The extraction yields of supercritical carbon dioxide (350 bar and 70oC) and hydrodistillation were 1.5% and 0.29%, respectively. The main components in essential oil from hexane extraction were caryophyllene oxide, neral, and geranial which were similar to sample from supercritical carbon dioxide extraction. The major components in essential oil from hydrodistillation were caryophyllene oxide, trans-alpha-bergamotene and linalool

Density of Ethyl Acetate-Palm Oil Mixture in Supercritical Condition

The non-catalytic interesterification of palm oil in supercritical ethyl acetate in continuous system to produce biofuel is complex to understand thermodynamic properties during extreme condition, particularly density of two reactants. In this study, an indirect procedure for density measurement of palm oil and ethyl acetate mixture in a batch system at high temperature and pressure was experimentally investigated using isochoric method. Its apparatus comprise a constant volume reactor which was individually loaded with a mixture of ethyl acetate and palm oil in different molar ratios (10:1 to 30:1) and global densities (0.26 to 0.53 g/cm3). During temperature increment, the changing of pressure was recorded in real-time to obtain the pressure-temperature relationship. After measuring the change of pressure at various global densities, the pressure-temperature related specific global density diagram was successfully constructed. At high global densities and high molar ratios of ethyl acetate to palm oil, the transition point took place closing to the estimated critical point of the mixture. The results will be further employed as database for accurately residence time calculation in continuous reactor, especially for biofuel production from palm oil in supercritical ethyl acetate