Separation of glycerol from FAME using ceramic membranes

International standards (e.g., ASTM D6751 and EN14214) limit the presence of free glycerol in biodiesel. The traditional water wash method for removing glycerol from crude fatty acid methyl esters (FAME) obtained in the production of biodiesel results in waste waters that cannot be readily discharged. To circumvent the water wash purification method, a membrane separation system using ceramic membranes was designed, constructed and tested for the removal of glycerol from crude FAME from a biodiesel production process. Ceramic membranes in the ultrafiltration (0.05 μm) and microfiltration (0.2 μm) ranges were tested at three different operating temperatures: 0, 5 and 25 °C. All runs separated glycerol from the crude FAME. International standards for glycerol content in biodiesel were met after 3 h when utilizing the ultrafiltration membrane setup at 25 °C with a concentration factor greater than 1.6.     

Refining of biodiesel by ceramic membrane separation

A ceramic membrane separation process for biodiesel refining was developed to reduce the considerable usage of water needed in the conventional water washing process. Crude biodiesel produced by refined palm oil was micro-filtered by ceramic membranes of the pore size of 0.6, 0.2 and 0.1 μm to remove the residual soap and free glycerol, at the transmembrane pressure of 0.15 MPa and temperature of 60 °C. The flux through membrane maintained at 300 L m^− 2 h^− 1 when the volumetric concentrated ratio reached 4. The content of potassium, sodium, calcium and magnesium in the whole permeate was 1.40, 1.78, 0.81 and 0.20 mg/kg respectively, as determined by inductively coupled plasma-atomic emission spectroscopy. These values are lower than the EN 14538 specifications. The residual free glycerol in the permeate was estimated by water extraction, its value was 0.0108 wt.%. This ceramic membrane technology was a potential environmental process for the refining of biodiesel.     

Prospects of non-catalytic supercritical methyl acetate process in biodiesel production

Conventional biodiesel production methods utilize alcohol as acyl acceptor and produces glycerol as side product. Hence, with escalating production of biodiesel throughout the world, it leads to oversupply of glycerol and subsequently causes devaluation in the market. In this study, methyl acetate was employed as acyl acceptor in non-catalytic supercritical methyl acetate (SCMA) process to produce fatty acid methyl esters (FAME) and side product of triacetin, a valuable fuel additive instead of glycerol. Consequently, the properties of biodiesel produced (FAME and triacetin) are superior compared to conventional biodiesel method (FAME only). In this research, the effects of reaction temperature, reaction time and molar ratio of methyl acetate to oil on the yield of biodiesel were investigated. Apart from that, the influence of impurities commonly found in waste oils/fats such as free fatty acids and water were studied as well and compared with methanol-based reactions of supercritical and heterogeneous catalysis. Results show that biodiesel yields in SCMA process could achieve 99 wt.% when the operating conditions were fixed at 400 °C/220 bar for reaction temperature, methyl acetate/oil molar ratio of 30:1 and 60 min of reaction time. Furthermore, SCMA did not suffer from adverse effect with the presence of impurities, proving that SCMA has a high tolerance towards contamination which is crucial to allow the utilization of inexpensive waste oils/fats as biodiesel feedstock.     

Distribution of soap in a membrane reactor in the production of fame from waste cooking oil

A continuous‐flow membrane reactor was constructed for the production of fatty acid methyl ester (FAME) from waste vegetable oil with high free fatty acid (FFA) content. FAME was produced via base‐catalysed transesterification with methanol at two FFA levels: 4.8 and 10 mass%. The effect of the ceramic membrane pore size on the separation of soap and triglycerides from the FAME in the reactor was investigated. In all cases, the triglyceride was completely retained in the reactor, yielding free and total glycerine contents in the produced FAME significantly below the maximum limits of the ASTM D6751 standard. The soaps produced in the reaction mixture were not completely retained in the reactor and did not affect the FAME production process. © 2012 Canadian Society for Chemical Engineering     

Methanol recycling in the production of biodiesel in a membrane reactor

Membrane reactor technology was used to overcome challenges in biodiesel production. The membrane reactor produces a permeate stream which readily phase separates at room temperature into a fatty acid methyl ester (FAME)-rich non-polar phase and a methanol- and glycerol-rich polar phase. To decrease the overall methanol:oil molar ratio in the reaction system, the polar phase was recycled. Three recycle ratios were tested: 100%, 75% and 50%, at the same residence time and operating conditions. The permeate consistently separated to yield a FAME-rich non-polar phase containing a minimum of 85 wt.% FAME (the remainder being methanol) as well as a methanol/glycerol polar phase. At the highest recycle ratio, the FAME concentration ranged from 85.7 to 92.4 wt.% in the FAME-rich non-polar phase. In addition, the overall molar ratio of methanol:oil in the reaction system was significantly decreased to 10:1 while maintaining a FAME production rate of 0.04 kg/min. As a result, a high purity FAME product was produced.     

Reactive extraction and in situ esterification of Jatropha curcas L. seeds for the production of biodiesel

Jatropha curcas L. has recently been hailed as the promising feedstock for biodiesel production as it does not compete with food sources. Conventional production of biodiesel from J. curcas L. seeds involve two main processing steps; extraction of oil and subsequent esterification/transesterification to fatty acid methyl esters (FAME). In this study, the feasibility of in situ extraction, esterification and transesterification of J. curcas L. seeds to biodiesel was investigated. It was found that the size of the seed and reaction period effect the yield of FAME and amount of oil extracted significantly. Using seed with size less than 0.355 mm and n-hexane as co-solvent with the following reaction conditions; reaction temperature of 60 °C, reaction period of 24 h, methanol to seed ratio of 7.5 ml/g and 15 wt% of H₂SO₄, the oil extraction efficiency and FAME yield can reached 91.2% and 99.8%, respectively. This single step of reactive extraction process therefore can be a potential route for biodiesel production that reduces processing steps and cost.     

The effect of flux and residence time in the production of biodiesel from various feedstocks using a membrane reactor

Biodiesel produced from lipid sources is a clean-burning, biodegradable, nontoxic fuel that is free of aromatic hydrocarbons. Current biodiesel production processes are tedious and involve two to three reaction steps each followed by separation and purification. Process integration of reaction and separation in a single step within a membrane reactor (MR) offers several advantages over conventional reactors.This investigation is aimed at studying the effect of membrane flux and residence time on the performance of a membrane reactor in treating a variety of raw and used feedstocks. A membrane reactor having three selectable reactor volumes was designed to decouple the effect of residence time in the reactor from membrane flux on the performance of the reactor. Low free fatty acid (FFA) oils (FFA < 1%), i.e. canola, corn, sunflower and un-refined soy oils, and high FFA waste cooking oil (FFA = 5%) were base transesterified and the quality of the biodiesel produced was determined in terms of free glycerine, mono-glyceride, di-glyceride and tri-glyceride content. All oils were base transesterified without pretreatment.Based on the composition of the final product, the MR could be operated at the upper limit of the flux tested (70 L/m²/h) and a residence time of 60 min. The ASTM D6751 and EN 14214 standards for glycerin and glycerides were reached in the washed biodiesel product for all feedstocks and run conditions. The operating pressure in the reactor was exceeded at 70 L/m²/h in treating waste oils and pre-treated corn oil. For these oils, reasonable operating pressures in the reactor were reached at a membrane flux of 30–40 L/m²/h. The quality of the washed biodiesel always met ASTM and EN standards. The FAME produced from WCO at intermediate fluxes and high residence times met the ASTM and EN standards without water washing.     

Cleaner gasoline production by using glycerol as fuel extender

Glycerol, a major by-product of biodiesel production, was employed as a fuel extender in this study. The process was originally investigated by etherifying the entire fluidized catalytic cracking (FCC) gasoline with glycerol. The reactions were carried out in a pressurized liquid phase reactor in the presence of three different catalysts (i.e. Amberlyst 16, Amberlyst 15, and β-zeolite) at 70 °C and 2.6 MPa with a volume ratio of FCC gasoline to glycerol ratio of 84:16 for 10 h. The catalytic activity could be ordered as Amberlyst 16 > Amberlyst 15 >> β-zeolite. The properties of FCC and etherified FCC products were determined by the standard analysis of Research Octane Number (RON), blending Reid vapor pressure (bRvp), distillation temperature following the standard methods of ASTM D-2699, ASTM D-5191 and ASTM D-86, respectively. It was found that the olefin content decreased opposing with increasing of octane number due to ethers of glycerol formation and the etherified gasoline product has lower bRvp than that of original FCC gasoline. The process of FCC gasoline etherification with glycerol showed great environmental benefits; in addition, ethers produced renewably from glycerol could extend the gasoline volume.     

Importance of water content in formation of porous anodic niobium oxide films in hot phosphate-glycerol electrolyte

Niobium has been anodized at a constant current density to 10 V with a current decay in 0.8 mol dm⁻³ K₂HPO₄-glycerol electrolyte containing 0.08-0.65 mass% water at 433 K to develop porous anodic oxide films. The film growth rate is markedly increased when the water content is reduced to 0.08 mass%; a 28 μm-thick porous film is developed in this electrolyte by anodizing for 3.6 ks, while the thickness is 4.6 and 2.6 μm in the electrolytes containing 0.16 and 0.65 mass% water respectively. For all the electrolytes, the film thickness changes approximately linearly with the charge passed during anodizing, indicating that chemical dissolution of the developing oxide is negligible. SIMS depth profiling analysis was carried for anodic films formed in electrolyte containing ∼0.4 mass% water with and without enrichment of H₂¹⁸O. Findings disclose that water in the electrolyte is a predominant source of oxygen in the anodic oxide films. The anodic films formed in the electrolyte containing 0.65 mass% water are practically free from phosphorus species. Reduction in water content increased the incorporation of phosphorus species.     

Biodiesel production from tobacco (Nicotiana tabacum L.) seed oil with a high content of free fatty acids

The production of fatty acid methyl esters (FAME) from crude tobacco seed oil (TSO) having high free fatty acids (FFA) was investigated. Due to its high FFA, the TSO was processed in two steps: the acid-catalyzed esterification (ACE) followed by the base-catalyzed methanolysis (BCM). The first step reduced the FFA level to less than 2% in 25 min for the molar ratio of 18:1. The second step converted the product of the first step into FAME and glycerol. The maximum yield of FAME was about 91% in about 30 min. The tobacco biodiesel obtained had the fuel properties within the limits prescribed by the latest American (ASTM D 6751-02) and European (DIN EN 14214) standards, except a somewhat higher acid value than that prescribed by the latter standard (<0.5). Thus, tobacco seeds (TS), as agricultural wastes, might be a valuable renewable raw material for the biodiesel production.     

Phase transition at subcritical and supercritical conditions of triglycerides methanolysis

The analysis of phase equilibrium between methanol and glycerides during methyl esters of fatty acids (FAME or biodiesel) synthesis at high pressure and temperature is very important for describing the kinetic and process design. It was studied at pressure between 1.1 and 28.0 MPa and temperature from 150 to 270 °C. The transition of phases and composition of identified phases was calculated using RK-Aspen EOS and obtained values were also compared to experimentally determined data at subcritical condition (1.1-4.5 MPa and 150-210 °C).Results of experimental investigation, as well as performed simulation of some specified composition of reaction mixture, showed that system of triglycerides and methanol, at the beginning of reaction (at all analysed conditions except for supercritical state of mixture) is in equilibrium between two liquid phases. During the methanolysis of triglycerides, the phase's distribution was changed accordingly and it highly depends on actual composition of reaction mixture, temperature and pressure. Calculated and measured values indicated that distribution of methanol between the oil phase, the methyl esters, and the glycerol rich phase exists and depends of working condition. As a consequence of fact, that the methanolysis of triglycerides (oil) is mainly realized in the oil-rich phase, at the end of reaction, after all triglycerides are converted into FAME and glycerol, the oil phase disappears. Furthermore, according to the results of phase composition calculation, it was shown that from the beginning to the end of reaction one phase only exists, for methanolysis performed at 270 °C and 20.0 MPa.     

Branched‐Chain Fatty Acid Methyl Esters as Cold Flow Improvers for Biodiesel

Biodiesel is an alternative diesel fuel derived mainly from the transesterification of plant oils with methanol or ethanol. This fuel is generally made from commodity oils such as canola, palm or soybean and has a number of properties that make it compatible in compression‐ignition engines. Despite its many advantages, biodiesel has poor cold flow properties that may impact its deployment during cooler months in moderate temperature climates. This work is a study on the use of skeletally branched‐chain‐fatty acid methyl esters (BC‐FAME) as additives and diluents to decrease the cloud point (CP) and pour point (PP) of biodiesel. Two BC‐FAME, methyl iso‐oleate and methyl iso‐stearate isomers (Me iso‐C_18:1 and Me iso‐C_18:0), were tested in mixtures with fatty acid methyl esters (FAME) of canola, palm and soybean oil (CaME, PME and SME). Results showed that mixing linear FAME with up to 2 mass% BC‐FAME did not greatly affect CP, PP or kinematic viscosity (ν) relative to the unmixed biodiesel fuels. In contrast, higher concentrations of BC‐FAME, namely between 17 and 39 mass%, significantly improved CP and PP without raising ν in excess of limits in the biodiesel fuel standard specification ASTM D 6751. Furthermore, it is shown that biodiesel/Me iso‐C_18:0 mixtures matched or exceeded the performance of biodiesel/Me iso‐C_18:1 mixtures in terms of decreasing CP and PP under certain conditions. This was taken as evidence that additives or diluents with chemical structures based on long‐chain saturated chains may be more effective at reducing the cold flow properties of mixtures with biodiesel than structures based on long‐chain unsaturated chains.     

Calcium oxide as a solid base catalyst for transesterification of soybean oil and its application to biodiesel production

In order to study solid base catalyst for biodiesel production with environmental benignity, transesterification of edible soybean oil with refluxing methanol was carried out in the presence of calcium oxide (CaO), -hydroxide (Ca(OH)₂), or -carbonate (CaCO₃). At 1 h of reaction time, yield of FAME was 93% for CaO, 12% for Ca(OH)₂, and 0% for CaCO₃. Under the same reacting condition, sodium hydroxide with the homogeneous catalysis brought about the complete conversion into FAME. Also, CaO was used for the further tests transesterifying waste cooking oil (WCO) with acid value of 5.1 mg-KOH/g. The yield of FAME was above 99% at 2 h of reaction time, but a portion of catalyst changed into calcium soap by reacting with free fatty acids included in WCO at initial stage of the transesterification. Owing to the neutralizing reaction of the catalyst, concentration of calcium in FAME increased from 187 ppm to 3065 ppm. By processing WCO at reflux of methanol in the presence of cation-exchange resin, only the free fatty acids could be converted into FAME. The transesterification of the processed WCO with acid value of 0.3 mg-KOH/g resulted in the production of FAME including calcium of 565 ppm.     

Variables affecting the in situ transesterification of microalgae lipids

This paper describes the effect of important reaction variables on the production of biodiesel from non-edible microalgae lipids, using the acid-catalysed in situ transesterification process. The specific gravity of the biodiesel product was used to monitor the conversion progress. The results indicate that increasing the reacting alcohol volume and the temperature lead to improved fatty acid methyl ester (FAME) conversions. With the exception of in situ transesterification carried out at room temperature (23 °C), the equilibrium FAME conversions appear to approach asymptotic limits for reaction times greater than 8 h for all temperatures investigated. Stirring the reaction vessel had a significant positive influence on the rate of biodiesel formation. Increasing the moisture content of the microalgae biomass had a strong negative influence on the equilibrium FAME yield, and in situ transesterification was inhibited when the biomass water content was greater than 115% w/w (based on oil weight).     

Transesterification of sunflower oil in a countercurrent trickle-bed reactor packed with a CaO catalyst

Transesterification of sunflower oil with methanol to form biodiesel was performed in a countercurrent trickle-bed reactor, using calcium oxide particles 1-2 mm in diameter as a packed, solid base catalyst. Although biodiesel production generally requires a reaction temperature below the boiling point of methanol to maintain a heterogeneous, liquid-liquid reaction, in the present study the reaction temperature was varied from 80 to 140 °C to confirm the progress of transesterification in a gas-liquid-solid phase reaction system. Oil droplets released from a thin tube flowed downward, while vaporized methanol flowed upward in the bed. The effects of the reaction temperature, methanol and oil flow rates, and the bed height on the FAME yield were investigated. The oil residence time in the reactor, which was controlled by changing both the oil flow rate and the bed height, had a significant effect on the FAME yield. In addition, the FAME yield increased with reaction temperature and was maximal at 373 K due to the change in residence time associated with reduced oil viscosity at higher temperatures. The FAME yield was 98% at a reaction temperature of 373 K when the methanol and oil flow rates were 3.8 and 4.1 mL/h, respectively.     

Non-catalytic biodiesel process with adsorption-based refining

Different feedstocks of varying acidity ranks and water contents were subjected to a series of discontinuous steps that simulated a biodiesel production process. The three steps comprised: (i) the non-catalytic transesterification with supercritical methanol at 280 °C; (ii) the distillation of the unreacted methanol, water and volatile products; and (iii) the adsorption of the impurities with adequate adsorbents. Refined soy oil, chicken oil and waste cooking oil were subjected to the same simple procedure. The process produced biodiesel complying with the water, acid, glycerides and methyl esters content specifications of the EN 14214 standard.Biodiesel production by the reaction of oils in supercritical methanol at 280 °C and methanol-to-oil molar ratios of 15 and 20 produced amounts of glycerol as small as 0.02%. This simplified the subsequent refining of the biodiesel and is considered an advantage over the classic alkali-catalyzed process (that produces 10% of glycerol by-product) because washing steps can be spared.The contents of methyl esters, water and free fatty acids showed a volcano pattern when plotted as a function of the reaction time. In the case of the free fatty acids this was attributed to the initial reaction of water and triglycerides to form acids and glycerol that increased the acidity of the product mixture. At longer reaction times these acids were likely transformed into methyl esters or were decarboxylated to hydrocarbons and CO₂. Water formation was attributed to glycerol decomposition and esterification of free fatty acids.The design of a simple process for biodiesel production using a single reaction step with negligible glycerol production and an adsorption-based refining step was thus studied. A possible scheme integrating reaction, methanol recycling, biodiesel purification and heat recovery was discussed. Advantages and disadvantages of process units were analyzed on terms of operating cost and simplicity.     

Continuous production of fatty acid methyl esters from corn oil in a supercritical carbon dioxide bioreactor

Continuous production of fatty acid methyl esters (FAMEs) from corn oil was studied in a supercritical carbon dioxide (SC-CO₂) bioreactor using immobilized lipase (Novozym 435) as catalyst. Response surface methodology (RSM) based on central composite rotatable design (CCRD) was employed to investigate and optimize the reaction conditions: pressure (11-35 MPa), temperature (35-63 °C), substrate mole ratio (methanol:corn oil 1-9) and CO₂ flow rate (0.4-3.6 L/min, measured at ambient conditions). Increasing the substrate mole ratio increased the FAME content, whereas increasing pressure decreased the FAME content. Higher conversions were obtained at higher and lower temperatures and CO₂ flow rates compared to moderate temperatures and CO₂ flow rates. The optimal reaction conditions generated from the predictive model for the maximum FAME content were 19.4 MPa, 62.9 °C, 7.03 substrate mole ratio and 0.72 L/min CO₂ flow rate. The optimum predicted FAME content was 98.9% compared to an actual value of 93.3 ± 1.1% (w/w). The SC-CO₂ bioreactor packed with immobilized lipase shows great potential for biodiesel production.     

Production of biodiesel from waste fryer grease using mixed methanol/ethanol system

Transesterification of waste fryer grease (WFG) containing 5–6 wt.% free fatty acid (FFA) was carried out with methanol, ethanol, and mixtures of methanol/ethanol maintaining the oil to alcohol molar ratio of 1:6, and initially with KOH as a catalyst. Mixtures of methanol and ethanol were used for transesterification in order to use the better solvent property of ethanol and rapid equilibrium using methanol. Formation of soap by reaction of FFA present in WFG with KOH instigated difficulty in the separation of glycerol from biodiesel ester. To untangle this problem, two-stage (acid and alkali catalyzed) method was used for biodiesel synthesis. More than 90% ester was obtained when two-stage method was used compared to ∼ 50% ester in single stage alkaline catalyst. In the case of mixed alcohol, a relatively smaller amount of ethyl esters was formed along with methyl esters. Acid value, viscosity, and cetane number of all the esters prepared from WFG were within the range of the ASTM standard. Esters obtained from WFG showed good performance as a lubricity additive.     

Transesterification of vegetable oil to biodiesel fuel using acid catalysts in the presence of dimethyl ether

The immiscibility of methanol and vegetable oil leads to a mass-transfer resistance in the transesterification of vegetable oil. To overcome this problem, dimethyl ether (DME) was used as an environmentally friendly cosolvent to produce a homogeneous solution. Methylesterifications of corn oil in both the presence and the absence of DME were performed using p-toluenesulfonic acid (PTSA), benzenesulfonic acid and sulfuric acid. PTSA showed highest catalytic activity. The yield of FAME reached 97.1% when 4 wt% of PTSA based on the oil weight was used at 80 °C with a reaction time of 2 h in the presence of DME. The obtained biodiesel was composed of methyl palmitate (9.1 wt%), methyl oleate (33.9 wt%), methyl linoleate (53.5 wt%), methyl linolenate (3.0 wt%) and methyl arachidate (0.5 wt%), and it was similar to the biodiesel compositions from corn oil as reported. The effects of concentrations of FFA and water on FAME yields were also investigated. All results suggested that the reaction rate was greatly improved by the addition of DME to the reaction system.     

Determination of Free Glycerol in Biodiesel via Solid-Phase Extraction and Spectrophotometric Analysis

To date, the standardized method for glycerol quantification in biodiesel production utilizes gas chromatography (GC); however, availability to manufacturers and instrumentation cost limits GC as an analytical method for general quality enforcement among producers. The method developed here is a bench top technique for quantitative determination of glycerol in biodiesel, with practical application in pharmaceutical and environmental quality control. The method extracts the glycerol contaminant from biodiesel using a normal phase solid phase extraction column (SPE). The protocol proceeds by rinsing with hexane to remove residual methyl esters, then collecting the glycerol with water. The aqueous extract is analyzed spectrophotometrically by an anthrone coloring reagent. Use of 2-g SPE columns and the solvent system developed has achieved 85% glycerol recovery. The assay applied has a detection range of 0.004–0.400% free glycerol, comparable to the established American Society of Testing and Materials (ASTM) D 6584-07 GC technique. Results were confirmed by GC and high-pressure liquid chromatography (HPLC). The bench top technique reduces the costs of operation relative to current methods, completes analysis in proficient time, requires minimal labor, and has analytical limits comparable to existing standard methods of biofuel analysis.