Synthesis of glycerol-free fatty acid methyl ester using interesterification reaction based on solid acid carbon catalyst derived from low-cost biomass wastes

The current research was aimed to corroborate as well as compare the feasible applicability of waste banana peel and empty fruit bunch (EFB) in synthesising high-performing heterogeneous catalysts. The solid acid catalysts originated from biomass wastes were employed for the synthesis of glycerol-free fatty acid methyl ester (FAME) using catalytic interesterification process pathway. Acetic acid was produced as the by-product instead of glycerol. The heterogeneous acid catalysts were synthesised utilising sulphuric acid through direct sulfonation with thermal treatment. The concentration of the sulphuric acid was manipulated from 2 to 13 mol L^?1 to investigate its effects on the resulting FAME yield while maintaining the sulfonating ratio at 10 mL g^?1. The catalytic performances of the as-synthesised catalysts were studied under reaction conditions of 12 wt % catalyst loading, 50:1 methyl acetate to oleic acid molar ratio for a duration of 8 hours at 60°C. The catalyst produced by activated carbon derived from EFB and sulfonated with 13 mol L^?1 sulphuric acid exhibited the highest FAME yield at 44.3%. The parameter studies on reactant ratio (45:1-70:1), reaction temperature (90°C-130°C) and time (4-24 hours) of interesterification reaction discovered a general increasing trend in the FAME yield up to 52.3% with the optimum conditions of 50:1, 110°C and 8 hours, respectively. The catalyst was recyclable with 82% of the catalytic performance retained after five successive cycles with catalyst reactivation. This study confirmed that the renewable heterogeneous catalyst derived from biomass waste could catalyse the glycerol-free interesterification process via an environmentally benign and promising approach for green fuel production.     

Fatty acid methyl ester production from wet microalgal biomass by lipase-catalyzed direct transesterification

The aim of this work was to optimize the production of fatty acid methyl ester (FAME, biodiesel) from wet Nannchloropsis gaditana microalgal biomass by direct enzymatic transesterification. This was done in order to avoid the high cost associated with the prior steps of drying and oil extraction. Saponifiable lipids (SLs) from microalgal biomass were transformed to FAME using the lipase Novozyme 435 (N435) from Candida antarctica as the catalyst, and finally the FAME were extracted with hexane. t-Butanol was used as the reaction medium so as to decrease lipase deactivation and increase mass transfer velocity. A FAME conversion of 99.5% was achieved using wet microalgal biomass homogenized at 140 MPa to enhance cell disruption, a N435:oil mass ratio of 0.32, methanol added in 3 stages to achieve a total of 4.6 cm³ g⁻¹ of oil and 7.1 cm³ g⁻¹ oil of added t-butanol, with a reaction time of 56 h. The FAME conversion decreased to 57% after catalyzing three reactions with the same lipase batch. This work shows the influence of the polar lipids contained in the microalgal biomass both on the reaction velocity and on lipase activity.     

Microwave treatment of wet algal paste for enhanced solvent extraction of lipids for biodiesel production

The role of microwave treatment as a precursor to lipid extraction from Nannochloropsis oculata using solvent extraction was investigated. Two microwave power settings were used, corresponding to wall plug powers of 635 and 1021 W. To limit the maximum temperature rise of the wet algal samples, exposure times were capped to 15 s intervals and followed by 15 min of cooling. Samples were treated in total from 1 to 5 min of microwave treatment (i.e. 1 min was 4 × 15 s treatments). The lysed fraction increased with exposure time for both power levels and the extracted lipids closely followed the lysed fraction. The highest extracted lipid content, after 5 min, was 0.036 g/g dry algae weight (g/g) for 635 W (68.86% cell lysis), while with 1021 W the yield was 0.052 g/g (92.81%). The control sample, which did not receive any microwave treatment, was only 0.016 g/g dry algae weight. Significance was observed between treatment time, cell lysis and lipid yield, (p < 0.05). For the 5 min of treatment, the lipid produced per total number of Joules consumed was found for each microwave power setting; yielding values of 1.889 × 10⁻⁴ g/g/kJ (635 W) and 1.697 × 10⁻⁴ g/g/kJ (1021 W).     

Optimization of microwave pretreatment on wheat straw for ethanol production

An orthogonal design (L₉(3⁴)) was used to optimize the microwave pretreatment on wheat straw for ethanol production. The orthogonal analysis was done based on the results obtained from the nine pretreatments. The effect of four factors including the ratio of biomass to NaOH solution, pretreatment time, microwave power, and the concentration of NaOH solution with three different levels on the chemical composition, cellulose/hemicellulose recoveries and ethanol concentration was investigated. According to the orthogonal analysis, pretreatment with the ratio of biomass to liquid at 80 g kg⁻¹, the NaOH concentration of 10 kg m⁻³, the microwave power of 1000 W for 15 min was confirmed to be the optimal condition. The ethanol yield was 148.93 g kg⁻¹ wheat straw at this condition, much higher than that from the untreated material which was only 26.78 g kg⁻¹.     

Effects of additives on the hydrogen generation of Al–H2O reaction at low temperature

Water displacement method is used to study the influence of temperatures (60–80°C), additives (Na₂CO₃, NaCl, Na₂CO₃/NaCl) and concentrations on the reaction characteristics and kinetics of Al–H₂O. Results show that the reaction rate and the hydrogen yield are enhanced with the increase of the temperature or by adding Na₂CO₃. The reaction rate is decreased by adding NaCl, but which has less effect on the hydrogen yield. For the mixture additive, Na₂CO₃ plays a key role in improving the hydrogen yield and the reaction rate. The influence degree of different factors is analyzed by orthogonal method. The most obvious factor is additive, but additive concentration has a minimum influence. The solid products are collected and analyzed by X‐ray diffraction and transmission electron microscopy. Al, Al(OH)₃ and AlO(OH) are detected. The spherical particles are obviously found at the initial reaction stage. However, they change to flocs at the end of reaction. Kinetic analysis shows that the reaction mechanism of Al–H₂O is changed by adding Na₂CO₃ or mixture, but it is not affected by adding NaCl. Moreover, the apparent activation energy of Al–H₂O is 74.49 kJ mol^?1, while it is only 43.03 kJ mol^?1 for Al–H₂O with 5 wt% Na₂CO₃ addition. Copyright © 2017 John Wiley & Sons, Ltd.     

Evaluation and optimization of two stage sequential in situ transesterification process for fatty acid methyl ester quantification from microalgae

This study demonstrates a direct transesterification (DT) method for reliable quantification of microalgal lipid. Primary screening of various transesterification methods and the types of biomass (wet, oven dried and lyophilized) were performed with heterotrophically grown Chlorella sp. FC2 IITG which revealed two stage DT with lyophilized biomass using NaOH in first stage and H₂SO₄ in second stage as the best combination with fatty acid methyl ester (FAME) yield of 39.17% (w/w, dry cell weight). Further optimization of transesterification parameters for selected method using response surface methodology, predicted the optimum values for catalyst to biomass ratio 0.67 (w/w) and 2.07 (v/w), methanol to biomass ratio 49.51 (v/w) and 61.07 (v/w) and reaction time 19.33 (min) and 10 (min) for first and second stages respectively. The optimum conditions showed 462.6% and 445.4% increment in FAME yield when compared with Bligh and Dyer method for Chlorella sp. FC2 IITG and Chlorella sorokiniana FC6 IITG respectively with highest transesterification efficiency of 98.96%. Improved transesterification efficiency of two stage DT was attributed to efficient destabilization of cell wall as confirmed by scanning electron microscopic imaging. FAME produced via DT of Chlorella sp. FC2 IITG satisfied most of the biodiesel properties as per ASTM D6751 and hence, could be an alternative to petro-diesel.     

Hydrogen production from dry spirulina algae with downstream feeding in microwave plasma reactor assisted under atmospheric pressure

Advancement in the field of biomass and bioenergy has pulled in researchers to produce biofuels derived from naturally accessible feedstock by adopting diverse innovative approaches in biomass pretreatment. In this study, pyrolysis of micro algae with downstream processing of biomass from the resonator cavity under atmospheric pressure was conducted and hydrogen production produced under different microwave power was analyzed. With the increase in microwave power, the hydrogen gas yield accounted to be as twice as that at lower power, where the concentration of produced hydrogen accounts for about 30.80%, 33.20%, and 37.58% at microwave power levels of 800, 900 and 1000 W. It was also observed that no methane was produced in this study since most of the methane produced from microwave plasma conversion has reacted with CO₂ and produced CO and H₂, hence dropped in the concentration of CO₂ with decline in power intensity.     

Hydrogen production from autothermal CO2 gasification of cellulose in a fixed-bed reactor: Influence of thermal compensation from CaO carbonation

Biomass gasification is a promising technology to produce renewable syngas used for energy and chemical applications. However, biomass gasification has challenges of low process energy efficiency, low syngas production with low H₂/CO ratio and the sintering of biomass ash which limit the deployment of the technology. This work investigated the influence of in-situ generated heat from CaO–CO₂ on cellulose CO₂ gasification using a fixed bed reactor, thermogravimetric analysis-Fourier transform infrared spectroscopy (TGA-FTIR) and differential scanning calorimetry (DSC). Experimental results indicate an approximate 20 °C temperature difference in the fix-bed reactor between cellulose CO₂ gasification with the energy compensation of CaO carbonation (denoted auto-thermal biomass gasification) and conventional CO₂ gasification of cellulose after the power of external furnaces were turned off. Around 5 times H₂/CO molar ratio is obtained after switching off the power in the auto-thermal biomass gasification compared with conventional gasification. The gas yield enhances significantly from 0.29 g g^?1 cellulose to 0.56 g g^?1 cellulose when CaO/cellulose mass ratio increases from 0 to 5. Furthermore, the TGA-FTIR results demonstrate the feasibility of adopting energy compensation of CaO carbonation to reduce the gasification temperature. DSC analysis also proves that the released heat from the CaO–CO₂ reaction reduces the required energy for cellulose degradation.     

Cobalt oxide nanosheets anchored onto nitrogen‐doped carbon nanotubes as dual purpose electrodes for lithium‐ion batteries and oxygen evolution reaction

Transition metal oxides (TMOs) have been extensively explored as promising electrode materials for electrochemical energy storage and catalysis. However, TMOs intrinsically have low electronic conductivity and suffer severe volume change during electrochemical cycling. In this study, we develop an effective strategy to enhance conductivity and buffer volume changes of TMOs, in which networked nitrogen‐doped carbon nanotubes (N‐CNTs) are incorporated into Co₃O₄ nanosheets system. Based on the whole mass of Co₃O₄ and N‐CNT, the composites can maintain a stable discharge capacity of ~590 mAh g^?1 after 80 cycles at a current density of 0.5 A g^?1. Moreover, the composites also exhibit greatly enhanced catalysis ability towards oxygen evolution reaction (OER), ie, small Tafel slope of 84 mV dec^?1, low overpotential of 310 mV at a current density of 10 mA cm^?2, and almost no activity decay throughout 30‐hour continuous operation. This study lays a new route for smartly designing advanced electrode materials for energy storage and electrochemical catalysis.     

Study on deactivation and reaction mechanism of Co thiolate complexes in photocatalytic hydrogen production system

Hydrogen is an environment‐friendly source with high efficiency, which is also an important alternative to traditional energy sources. In this paper, noble‐metal‐free photocatalyst Co thiolate complexes Co(bpy)(pyS)₂ (M1) and Co(phen)(pyS)₂ (M2) were synthesized and used in photocatalytic decomposition of water to generate hydrogen. The deactivation and reaction mechanism of Co thiolate complexes in photocatalytic hydrogen generation system were studied. The results of photocatalytic hydrogen generation with regeneration of system by re‐addition of catalyst and fluorescein exhibited that the main reasons for the deactivation of system were probably the deactivation of catalyst and small part of decomposition of photosensitizer. The results of UV‐vis spectra of the system after irradiation revealed that the electron transfer mode between fluorescein, catalyst, and triethylamine was favorable for the stability and life of fluorescein. Furthermore, the electron transfer rates from fluorescein to M1 and M2 were 2.1 × 10¹²M^?1 S^?1 and 1.5 × 10¹²M^?1 S^?1. This investigation may lay the theories foundation for further research on hydrogen evolution of noble‐metal‐free catalysts and also may provide a novel approach for building a feasible and more environmental‐friendly photocatalytic hydrogen production system.     

Performance of a domestic cooking wick stove using fatty acid methyl esters (FAME) from oil plants in Kenya

With depletion of solid biomass fuels and their rising costs in recent years, there has been a shift towards using kerosene and liquefied petroleum gas (LPG) for domestic cooking in Kenya. However, the use of kerosene is associated with health and safety problems. Therefore, it is necessary to develop a clean, safe and sustainable liquid bio-fuel. Plant oil derivatives fatty acid methyl esters (FAME) present such a promising solution. This paper presents the performance of a wick stove using FAME fuels derived from oil plants: Jatropha curcus L. (Physic nut), Croton megalocarpus Hutch, Calodendrum capense (L.f.) Thunb., Cocos nucifera L. (coconut), soyabeans and sunflower. The FAME performance tests were based on the standard water-boiling tests (WBT) and compared with kerosene. Unlike kerosene all FAME fuels burned with odorless and non-pungent smell generating an average firepower of 1095 W with specific fuel consumption of 44.6 g L^?1 (55% higher than kerosene). The flash points of the FAME fuels obtained were typically much higher (2.3–3.3 times) than kerosene implying that they are much safer to use than kerosene. From the results obtained, it was concluded that the FAME fuels have potential to provide safe and sustainable cooking liquid fuel in developing countries.     

Comparison of oil extraction methods,energy analysis and biodiesel production from flax seeds

In recent years, the commercial potential of oil extraction and biodiesel production derived from vegetable seed is being realized. The process energy input requirements are important factors in oil extraction and biodiesel production. This research work investigated oil extraction from flax seeds and compared extraction yield with the energy load. The effect of moisture content on the oil yield was compared between a mechanical oil expeller, organic solvent extraction, organic solvent and microwave assisted, organic solvent and ultrasonic assisted, and combined microwave and ultrasonic with organic solvent. The maximum oil yields % wt/wt from these techniques was 22.6%, 36.3%, 10.0%, 42.0% and 27.8%, respectively. The moisture content had a significant effect on oil yield with the mechanical oil expeller, organic solvent method and ultrasonic assisted extraction, whereas no or little effect was found on microwave‐assisted extraction. The microwave‐assisted extraction showed better results compared with the ultrasonic‐assisted and combined treatment methods. The relative energy consumption of these processes was experimentally investigated; energy ratios were calculated based on the amount of energy recovered to the amount of energy supplied to the flax seed for oil extraction. The net energy ratios showed that microwave‐assisted extraction had the highest (25.21%), followed by organic solvent method (14.04%), ultrasonic method (6.33%) and lowest was with combined ultrasonic and microwave assisted treatment (5.73%). These results showed that flax seed oil can be extracted using microwave‐assisted methods efficiently and in an energy feasible manner. In situ ultrasonic transesterification was applied to powdered samples with 4%, 8% and 12% moisture content (on % dry basis) within an ultrasonic bath having an intensity of 0.124 W/cm². The flax seed biodiesel produced showed a highest conversion yield of 93%, and the effect of different moisture content on the yield showed that 4% moisture content sample produced the greatest biodiesel yield. Copyright © 2013 John Wiley & Sons, Ltd.     

Polypyrrole supported Co–W–B nanoparticles as an efficient catalyst for improved hydrogen generation from hydrolysis of sodium borohydride

Effective and reusable catalysts with high performance are essentially necessary for NaBH₄ based on-demand hydrogen generators to the widespread use for energy conversion in fuel cell power systems. Herein, we report a facile synthesis of surfactant-directed polypyrrole-supported Co–W–B nanoparticles as a robust catalyst for efficient hydrolysis of NaBH₄ reaction. This non-noble metal catalyst provides much higher catalytic activity than a conventional cobalt boride catalyst. By incorporating tungsten to catalyst composition and tuning molar ratio of W/(Co + W), about a four-fold higher hydrogen generation rate was attained compared to bare Co–B. Among the all catalysts tested, Co–W–B/PPy with 7.5% W possessed the remarkable catalytic performance of 9.92 L min^?1 g^?1 and high stability over five cycles with the apparent activation energy of 49.18 kJ mol^?1.     

Oxy–steam gasification of biomass for hydrogen rich syngas production using downdraft reactor configuration

The paper focuses on the use of oxygen and steam as the gasification agents in the thermochemical conversion of biomass to produce hydrogen rich syngas, using a downdraft reactor configuration. Performance of the reactor is evaluated for different equivalence ratios (ER), steam to biomass ratios (SBR) and moisture content in the fuel. The results are compared and evaluated with chemical equilibrium analysis and reaction kinetics along with the results available in the literature. Parametric study suggests that, with increase in SBR, hydrogen fraction in the syngas increases but necessitates an increase in the ER to maintain reactor temperature toward stable operating conditions. SBR is varied from 0.75 to 2.7 and ER from 0.18 to 0.3. The peak hydrogen yield is found to be 104 g/kg of biomass at SBR of 2.7. Further, significant enhancement in H₂ yield and H₂ to CO ratio is observed at higher SBR (SBR = 1.5–2.7) compared with lower range SBR (SBR = 0.75–1.5). Experiments were conducted using wet wood chips to induce moisture into the reacting system and compare the performance with dry wood with steam. The results clearly indicate the both hydrogen generation and the gasification efficiency (η_g) are better in the latter case. With the increase in SBR, gasification efficiency (η_g) and lower heating value (LHV) tend to reduce. Gasification efficiency of 85.8% is reported with LHV of 8.9 MJ Nm^?3 at SBR of 0.75 compared with 69.5% efficiency at SBR of 2.5 and lower LHV of 7.4 at MJ Nm^?3 at SBR of 2.7. These are argued on the basis of the energy required for steam generation and the extent of steam consumption during the reaction, which translates subsequently in the LHV of syngas. From the analysis of the results, it is evident that reaction kinetics plays a crucial role in the conversion process. The study also presents the importance of reaction kinetics, which controls the overall performance related to efficiency, H₂ yield, H₂ to CO fraction and LHV of syngas, and their dependence on the process parameters SBR and ER. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance enhancement of dye‐sensitized solar cells via cosensitization of ruthenizer Z907 and organic sensitizer SQ2

Cosensitization is a highly effective technique to enhance the photovoltaic performance of a dye‐sensitized solar cell. The main objective of this work is to improve the performance of dye‐sensitized solar cell using cosensitization approach and investigation of the effect of the organic cosensitizer concentration on the power conversion efficiency of the fabricated solar cell devices. In this work, Z907, a ruthenium dye, has been cosensitized with SQ2, an organic sensitizer, and an overall efficiency of 7.83% has been achieved. The fabricated solar cells were evaluated using UV‐Vis spectroscopy, current‐voltage (I‐V) characteristics, and electrochemical impedance spectroscopy analysis. Our results clearly indicate that the concentration of organic cosensitizer strongly affects the photovoltaic performance of fabricated solar cells. Upon optimization, the cell fabricated with 0.3 mM Z907 + 0.2 mM SQ2 dye solution demonstrated J_sc (mA/cm²) = 21.38, V_oc (mV) = 698.37, FF (%) = 52.46, and power conversion efficiency of η (%)  = 7.83 under standard AM1.5G 1 sun illumination (100 mW/cm²). It was observed that the efficiency of cosensitized solar cells is significantly superior than that of individual sensitized solar cells (Z907 [η  = 5.08%] and SQ2 [η  = 1.39%]). This enhancement in efficiency could be attributed to the lower electron‐hole recombination rate, decrease in competitive absorption of I^?/I^?₃, and less dye aggregation because of the synergistic effect in cosensitized solar cells.     

Energy extraction from seaweed under low temperatures by using an alkaline fuel cell

Marine macroalgae are considered to be one of the most important biomass sources. They can grow rapidly under various conditions, leading to extensive algal blooms. In this work, a reusable solid-acid catalyst, silicotungstic acid, was used to treat the seaweed Enteromorpha prolifera. Under optimum conditions, 237.354 mg/g (23.735%) of total reducing sugar yield was obtained. The hydrolysate was used as the substrate for bioenergy production in an alkaline fuel cell, and the fuel cell achieved the maximum power density of 6.616 W/m² under the condition of 3 M KOH and 8.572 mg/mL reducing sugar in hydrolysate, which is higher than any other reported algae-fed fuel cells.     

Energetic optimization of microalgal cultivation in photobioreactors for biodiesel production

Traditionally, algal cultivation in sparged photobioreactors has been optimized to maximize biomass productivity. In this study, an energy-based methodology is presented to maximize the net energy gain of the cultivation process by minimizing the energy input for sparging and by maximizing the energy output. Options for minimizing energy input through optimal gas-to-culture volume ratio and CO₂-air ratio and options for maximizing lipid production through optimal levels of nutrition and CO₂ are presented and validated with results from 900-mL bubble column reactors. In contrast to the traditional practice, the proposed energy-based optimization resulted in positive net energy gains. In single stage approach under optimal conditions (CO₂ enrichment of 0.5%, gas-to-culture volume ratio of 0.18 min⁻¹, and nitrate level of 1 mM), tests with Nannochloropsis salina resulted in positive net energy gain of 20 W/m³. In a test under nitrate starvation, the net energy gain in a reactor sparged with CO₂ enrichment of 0.5% was double that in the reactor sparged with ambient air (8 vs. 19 W/m³).     

Transient analysis and performance studies of two tubular photobioreactors for outdoor culture of spirulina

A mathematical model to make a transient thermal analysis and to estimate the incident solar energy for two designs of tubular photobioreactor installed outdoors is presented here. In the first photobioreactor design the tubes were arranged in one plane, whereas in the second the tubes were arranged in two planes. The model was validated by comparing the experimental data and predicted values of culture temperature. Both the input solar energy and culture temperature in a tubular photobioreactor may be predicted with a reasonable degree of accuracy by employing the model. The performance of the two photobioreactors for mass culture of Spirulina was also studied in relation to their design and culture temperature. The average biomass yield obtained in one-plane and two-plane photobioreactors were (dry weight) 23.7 g m^?2 day^?1 and 27.8 g m^?2 day^?1 respectively. Such biomass yields corresponded to a volumetric productivity of (dry weight) 0.466 g litre^?1 day^?1 in the one-plane reactor and 1.5 g litre^?1 day^?1 in the two-plane reactor. We further observed that biomass yield could be increased by about 21% when the culture temperature was maintained at the optimal value of 35°C compared to another culture in which temperature changed according to the ambient temperature from 20 to 39°C during the day.     

Utilization of summer legumes as bioenergy feedstocks

Sunn hemp (Crotolaria juncea), is a fast growing, high biomass yielding tropical legume that may be a possible southeastern bioenergy crop. When comparing this legume to a commonly grown summer legume – cowpeas (Vigna unguiculata), sunn hemp was superior in biomass yield (kg ha^?1) and subsequent energy yield (GJ ha^?1). In one year of the study after 12 weeks of growth, sunn hemp had 10.7 Mg ha^?1 of biomass with an energy content of 19.0 Mg ha^?1. This resulted in an energy yield of 204 GJ ha^?1. The energy content was 6% greater than that of cowpeas. Eventhough sunn hemp had a greater amount of ash, plant mineral concentrations were lower in some cases of minerals (K, Ca, Mg, S) known to reduce thermochemical conversion process efficiency. Pyrolytic degradation of both legumes revealed that sunn hemp began to degrade at higher temperatures as well as release greater amounts of volatile matter at a faster rate.     

Microwave pyrolysis of polystyrene and polypropylene mixtures using different activated carbon from biomass

In this study, microwave pyrolysis was experimented with mixed types of plastic waste. Two different plastic wastes polystyrene waste (PSW) and polypropylene waste (PPW) were used as feedstock. Carbon and activated carbon were synthesized from different biomass; rice husk (RH), corn husk (CH) and coconut sheath (CS) respectively which are used as microwave susceptors. The effect of impregnation on product yields was studied. Microwave pyrolysis at 900 W and with a polymer to an absorbent ratio of 10:1, produced the highest oil yield of 84.30 wt% when coconut sheath activated carbon (CSAC) was used as an absorbent. The reaction time was 10 min for the complete decomposition of polymer mixtures. Oil properties were determined and a high calorific value of 46.87 MJ kg⁻¹ was obtained. These properties were compared to conventional fuel properties and the product oil has a density of 0.76 g ml⁻¹ and viscosity of 2.4 cSt which is an equivalent fraction obtained to that of gasoline. Product oil has a styrene recovery of 67.58% from microwave pyrolysis. The results demonstrate that, microwave pyrolysis has a great potential for energy recovery from mixed plastic waste and the use of agricultural residues as absorbents enhanced the production efficiency of the process.