Michael O. Daramola

Biohydrogen production as a potential energy fuel in South Africa

Biohydrogen production has captured increasing global attention due to it social, economic and environmental benefits. Over the past few years, energy demands have been growing significantly in South Africa due to rapid economic and population growth. The South African parastatal power supplier i.e. Electricity Supply Commission (ESKOM) has been unable to meet the country’s escalating energy needs. As a result, there have been widespread and persistent power cuts throughout the country. This prompts an urgent need for exploration and implementation of clean and sustainable energy fuels like biohydrogen production in order to address this crisis. Therefore, this paper discusses the current global energy challenges in relation to South Africa’s problems. It then examines the feasibility of using biohydrogen production as a potential energy fuel in South Africa. Finally, it reviews the hydrogen-infrastructure development plans in the country.

Xylene Vapor Mixture Separation in Nanocomposite MFI-Alumina Tubular Membranes: Influence of Operating Variables

In this study, we present the results of a preliminary investigation on the influence of operating variables (temperature, sweep gas flow rate, and total feed vapor pressure) on xylene vapor mixture separation using tubular nanocomposite MFI-alumina zeolite membrane prepared by the pore-plugging synthesis technique. Within the detection limit of our analytical system, neither m- nor o-xylene was detected in the permeate stream, the membranes displaying therefore “infinite” p-xylene selectivity. The mixtures p-xylene flux displayed a maximum value of ca. 3.5 µmol·m−2·s−1, corresponding to a mixture permeance of 11 nmol·m−2·s−1·Pa−1, at 473 K and for a feed composition 0.63 kPa p-xylene/0.27 kPa m-xylene/0.32 kPa o-xylene, being almost unchanged for sweep gas flow rates (N2) higher than 20 mL(STP)/min and increasing with the total xylene vapor pressure at 1 : 1 : 1–3 p/m/o-xylene composition. The experimental p-xylene fluxes can be well predicted by a Maxwell-Stefan model, as expected for a mass transfer process driven by competitive adsorption / surface diffusion. Unlike film-like MFI membranes, the membranes presented here preserved their selectivity to p-xylene for total xylene pressures as high as 150 kPa. This behavior is attributed to the intimate contact between the alumina confining pores and MFI nanoparticles, reducing long-term stresses and thus preventing distortion of the MFI framework during p-xylene adsorption. These results open up potential applications of nanocomposite MFI-alumina for selective p-xylene separations at high loadings, for instance in pervaporation, where the use of film-like MFI membranes is discouraged.

Microbial cell immobilization in biohydrogen production: a short overview

Abstract The high dependence on fossil fuels has escalated the challenges of greenhouse gas emissions and energy security. Biohydrogen is projected as a future alternative energy as a result of its non-polluting characteristics, high energy content (122 kJ/g), and economic feasibility. However, its industrial production has been hampered by several constraints such as low process yields and the formation of biohydrogen-competing reactions. This necessitates the search for other novel strategies to overcome this problem. Cell immobilization technology has been in existence for many decades and is widely used in various processes such as wastewater treatment, food technology, and pharmaceutical industry. In recent years, this technology has caught the attention of many researchers within the biohydrogen production field owing to its merits such as enhanced process yields, reduced microbial contamination, and improved homogeneity. In addition, the use of immobilization in biohydrogen production prevents washout of microbes, stabilizes the pH of the medium, and extends microbial activity during continuous processes. In this short review, an insight into the potential of cell immobilization is presented. A few immobilization techniques such as entrapment, adsorption, encapsulation, and synthetic polymers are discussed. In addition, the effects of process conditions on the performance of immobilized microbial cells during biohydrogen production are discussed. Finally, the review concludes with suggestions on improvement of cell immobilization technologies in biohydrogen production.

Evaluation of Physicochemical Properties of South African Cashew Apple Juice as a Biofuel Feedstock

Cashew apple juice (CAJ) is one of the feedstocks used for biofuel production and ethanol yield depends on the physical and chemical properties of the extracted juice. As far as can be ascertained, information on physical and chemical properties of South African cashew apple juice is limited in open literature. Therefore, this study provides information on the physical and chemical properties of the South African cashew apple juice. Physicochemical characteristics of the juice, such as specific gravity, pH, sugars, condensed tannins, Vitamin C, minerals, and total protein, were measured from a mixed variety of cashew apples. Analytical results showed the CAJ possesses specific gravity and pH of 1.050 and 4.52, respectively. The highest sugars were glucose (40.56 gL−1) and fructose (57.06 gL−1). Other chemical compositions of the juice were condensed tannin (55.34 mgL−1), Vitamin C (112 mg/100 mL), and total protein (1.78 gL−1). The minerals content was as follows: zinc (1.39 ppm), copper (2.18 ppm), magnesium (4.32 ppm), iron (1.32 ppm), sodium (5.44 ppm), and manganese (1.24 ppm). With these findings, South African CAJ is a suitable biomass feedstock for ethanol production.

Hevea brasiliensis (rubber seed) oil: modeling and optimization of extraction process parameters using response surface methodology and artificial neural network techniques

ABSTRACT In the present study, results of parametric effects and optimization of extraction of rubber seed oil from under-utilized rubber seeds using response surface methodology (RSM) and artificial neural network (ANN) based on a statistically designed experimentation via the Box–Behnken design (BBD) are reported. A three-level, three-factor BBD was employed using rubber seed powder weight (X1), solvent volume (X2) and extraction time (X3) as process variables. A quadratic polynomial model was obtained to predict oil yield. The RSM model predicted an optimal oil yield of 42.98 wt.% at conditions of X1 (60 g), X2 (250 mL) and X3 (45 min) and validated experimentally as 42.64 wt.%. The ANN model predicted optimal oil yield of 43 wt.% at conditions of X1 (40 g), X2 (202 mL) and X3 (49.99 min) and validated as 42.96 wt.%. Both models are effective in describing the parametric effect of the considered operating variables on the extraction of oil from the rubber seeds. However, the ANN describes the effect more accurately than the RSM model, with a lower percentage relative error and absolute average deviation (AAD). The extracted oil possesses physicochemical properties that support biodiesel production and other industrial applications.

Influence of operating variables on the transesterification of waste cooking oil to biodiesel over sodium silicate catalyst: A statistical approach

Abstract This study examined the use of surface response methodology to investigate the influence of operating variables on the transesterification of waste cooking oil (WCO) to biodiesel over sodium silicate catalysts. The individual and interactive effects of three variables namely, reaction time, reaction temperature and amount of catalyst was evaluated using full 23 (+1) factorial design. The conversion of WCO to biodiesel was achieved through the transesterification reaction over the catalyst at a methanol-to-oil molar ratio of 6:1 in a batch reactor. Physicochemical properties of the sodium silicate catalyst were obtained using Fourier transform infrared spectroscopy (FT-IR) for surface chemistry, thermo-gravimetric analysis (TGA) for thermal stability, N2 physisorption test for Brunauer–Emmett–Teller analysis and scanning electron microscopy (SEM) for morphology. The reaction temperature, reaction time and weight of the catalyst (expressed as a percentage of the amount of WCO) were varied to understand their effect on the yield of biodiesel via response surface methodology (RSM) approach. The BET analysis showed a surface area of 0.386 m2/g for the catalyst. Results from the transesterification reaction reveal that change in catalyst weight percentage had no considerable effect on the biodiesel yield and that there was no mutual interaction between the reaction time and catalyst weight percentage. The results also conveyed that the reaction temperature and reaction time were limiting conditions and a slight variation herein altered the biodiesel yield. The transesterification of WCO produced 57.92% maximum FAME yield at the optimum methanol to oil molar ratio of 6:1, catalyst weight of 2.5%, reaction time of 240 min and a reaction temperature of 64 °C. The variance ratio, VR < Fvalue obtained from the cross-validation experiments indicate perfect agreement of the model output with experimental results and also testifies to the validity and suitability of the model to predict the biodiesel yields.

Effect of dispersion method and CNT loading on the quality and performance of nanocomposite soy protein/CNTs adhesive for wood application

In this article the effect of dispersion method and carbon nanotubes (CNTs) loading on the quality and performance of a nanocomposite adhesive is reported. The nanocomposite soy protein isolate adhesive was successfully developed by incorporating CNTs into the soy protein isolate (SPI) for enhanced bond strength and water resistance. Dispersion methods, namely mechanical (shear) mixing and mechanical/sonication were employed to aid good dispersion and interfacial interaction between soy protein matrix and the carbon nanofillers during the preparation of the adhesive. The concentration of the CNT was varied from 0.1–0.7 wt% in the nanocomposite adhesive. The morphology and the surface chemistry of the adhesives were checked with SEM and FTIR, respectively. The shear strength of the developed adhesives was investigated according to European standard (EN-204) for interior wood application on a tensile testing machine. The morphological structure of the nanocomposite adhesive obtained from SEM images showed homogeneous dispersion of CNTs in SPI using the two dispersion methods; shear mixing and sonication/shear mixing. Fourier transform infrared spectra showed chemical functionalities and successful interaction between CNTs and SPI adhesive. Thermogravimetric profile of the adhesive samples showed that the newly developed nanocomposite adhesive was thermally stable at a temperature up to about 600 °C at a higher percentage loading of 0.5 wt% CNTs. The result showed that sonication method of dispersion of CNTs into the SPI adhesive had a higher shear strength compared to the mechanical method of dispersion both at dry and wet state.

Coupled 1D-2D hydrodynamic inundation model for sewer overflow: Influence of modeling parameters

Abstract This paper presents outcome of our investigation on the influence of modeling parameters on 1D-2D hydrodynamic inundation model for sewer overflow, developed through coupling of an existing 1D sewer network model (SWMM) and 2D inundation model (BREZO). The 1D-2D hydrodynamic model was developed for the purpose of examining flood incidence due to surcharged water on overland surface. The investigation was carried out by performing sensitivity analysis on the developed model. For the sensitivity analysis, modeling parameters, such as mesh resolution Digital Elevation Model (DEM) resolution and roughness were considered. The outcome of the study shows the model is sensitive to changes in these parameters. The performance of the model is significantly influenced, by the Mannings friction value, the DEM resolution and the area of the triangular mesh. Also, changes in the aforementioned modeling parameters influence the Flood characteristics, such as the inundation extent, the flow depth and the velocity across the model domain.

Parametric Optimization of Citric Acid Production from Apple Pomace and Corn Steep Liquor by a Wild Type Strain of Aspergillus niger: A Response Surface Methodology Approach

In this work, parametric optimization of citric acid production (yield) from six process variables: apple pomace (AP) concentration, volume of corn steep liquor (CSL), pH, temperature, methanol concentration, and methanol addition time is reported. Fifty-four experiments were performed according to the Box-Behnken design method. A polynomial regression model was developed from the experimental data and effects of the variables were explained using response surface methodology approach. A coefficient of determination (R2) of 0.92 indicated the significance of the model. The optimum conditions for citric acid yield obtained from the model were 33.81 g/L of AP, 42.5 g/L of CSL, 2.05% (v/v) of methanol concentration, methanol addition time of 33 h, pH 4.54, and temperature of 32.88 °C with a corresponding yield of 62.00 g/L. Conducting an experiment using the optimum conditions gave citric acid yield of 68.26 g/L, a 10% increase over the model results.

Morphological modification of Chromolaena odorata cellulosic biomass using alkaline peroxide oxidation pretreatment methodology and its enzymatic conversion to biobased products

Abstract In this study, the structural modification of Siam weed (Chromolaena odorata) was performed using NaOH–H2O2- and Ca(OH)2–H2O2-based oxidative pretreatment for the enzymatic conversion of the biomass to a biocommodity, reducing sugar (RS). Pretreatment of raw sample was evaluated at temperatures of 60°C, 70°C, 80°C, 90°C for different time intervals of 3, 6, 9, 12 h in alkaline medium (NaOH or Ca(OH)2). The effects of pretreatment time and temperature were considered in obtaining the optimum conditions. The optimum conditions for NaOH–H2O2 was obtained at 70°C and 3 h with a maximum cellulose content of 44.29%(w/w), lignin content reduced to 21.09% from the initial raw value of 24.2%. Pretreatment with Ca(OH)2–H2O2 resulted in the optimum conditions obtained to be 70°C for 3 h with a cellulose content of 47.18%. Enzymatic hydrolysis on the pretreated biomass at the optimum conditions showed NaOH–H2O2-treated sample yielded 424.35 mg equivalent glucose/g biomass of RS while Ca(OH)2–H2O2-treated sample yielded 335.81 mg equivalent glucose/g biomass of RS. The untreated raw sample yielded 68.75 mg equivalent glucose/g biomass of RS. Consequently, NaOH–H2O2 pretreatment displayed a higher efficiency than Ca(OH)2–H2O2 pretreatment. Stereomicroscopic and scanning electron microscopic imaging of the treated and untreated samples revealed morphological disruptions brought about by the treatments.