Outdoor Large scale Microalgae consortium culture for biofuel production in South Africa: Overcoming adverse environmental effects on microalgal growth

In nature, microalgal blooms occur regularly and in contrast with laboratory cultivation procedures, these blooms are not axenic and this seems to add to the longevity and intensity of the bloom. For this reason a consortium of microalgae and bacteria is used at InnoVenton for large scale biomass cultivation. The biomass produced, has successfully been used to produce biocrude. Laboratory cultivation procedures also require a large energy input in terms of artificial lighting, heating and aeration making it a costly endeavour. However, this stringent control of the culture to avoid contamination and ensure optimal growth conditions is essential when cultivating the microalgae for medical and pharmaceutical applications. When culturing for a chemical application such as biofuel production, this is not the case, therefore allowing for the economical outdoor consortium cultivation approach employed at InnoVenton. In this study we investigated whether morning heating of the media will overcome low consortium growth rates experienced in winter and whether the use of glucose, ethanol and acetate will overcome biomass loss exhibited at night. The results showed that heating increased the growth rate relative to those measured in summer and that heating all day in winter did not induce better growth rates in comparison to only heating for an hour at sunrise. We show that all three carbon sources are efficient at overcoming biomass loss at night with glucose being the most effective. In conclusion, employing these two techniques, the same growth rate theoretically can be achieved year round with large scale outdoor cultivation. Keywords: consortium, microalgae, biocrud

Development of a small production platform for citronellal processing

The aim of the project was to develop a small production platform for citronellal processing. The objective of the study was to develop a single continuous flow reactor system for the synthesis of novel derivatives of citronellal and isopulegol. The first step was to develop a continuous flow reactor system for the isopulegol synthesis. The stainless steel tubular fixed-bed reactor equipped with a reaction column (I.D: 9.53 mm and length: 120 mm) was used for the study. The reactor column was packed with H-ZMS-5 zeolite extrusion catalyst. The solvent-free cyclisation reaction of citronellal was investigated and at optimum conditions, 100% of citronellal conversion and almost 100% selectivity towards isopulegol was achieved. A good catalytic performance was observed from the H-ZSM-5 catalyst and proved to be stable for a prolonged reaction time. The second reaction step was to develop a continuous flow reactor system for the synthesis of isopulegyl-ether derivatives. A UniQsis FlowSyn reactor system equipped with a stainless steel reactor column was used for the study. The reactor column was packed with amberlyst-15 dry catalyst. Wherein, n-propanol was employed as a model etherifying agent and as a reaction solvent. At optimum reaction condition, only 30% selectivity of isopulegyl propoxy-ether was achieved. The reaction was found to depend highly on temperature and residence time. The increase of these parameters was found to increase the side reactions and reduced the selectivity of the desired product. Other heterogeneous catalysts such as H-beta zeolite, aluminium pillared clay, Aluminium oxide and H-ZSM-5 were also evaluated in the reaction. Among these catalysts, a catalytic activity was observed with H-beta zeolite (19%) and aluminium pillared clay (5%). Based on these results, none of the evaluated catalysts provided the desired selectivity (greater than 70%) towards the isopulegyl propoxy-ether, therefore the process was not investigated further. In light of this, the isopulegol etherification synthetic route was terminated. Consequently, another analogue of citronellal was used as an alternative intermediate in place of isopulegol, namely para-menthane-3,8-diol (PMD). The initial studies for the synthesis of the novel PMD di-esters from isopulegol were performed in the batch-scale reactor. In a solvent-free reaction, acetic anhydride was initially used as a model acetylating agent. The reaction was performed using polymer-bound scandium triflate (PS-Sc(OTf)3) catalyst. The effect of reaction parameters such as temperature, molar ratio, and reaction time were studied towards the PMD conversion and di-esters selectivity. At optimum reaction conditions, PMD conversion of 70% and di-acetate selectivity of 67% were observed. The reaction was found to follow the zeroth-order kinetics with respect to PMD conversion and obeyed the Arrhenius equation. Other types of di-ester derivatives were synthesized from PMD by varying the carbon chain length of the acetylating agent. The prepared compounds were separated from the product mixtures by vacuum distillation, purified on a column chromatography and characterised by FT-IR, GC-MS, and 1H-NMR, 13C-NMR. The developed methodology was optimised in flow by using an ArrheniumOne microwave-assisted continuous-flow fixed-bed reactor system. A detailed experimental design was used to carry-out the reactions. The reaction parameters such as temperature and flow-rate were studied towards the PMD conversion and di-ester selectivity. From the experimental design analysis, the di-ester selectivity was found to depend highly on the residence time (flow-rate) and significantly on temperature. The PMD conversion and di-ester selectivity were found to increase with decrease in the flow-rate. The conversion and selectivity achieved in the continuous flow process were significantly higher than the achieved in the batch-scale process with respect to the residence time

Reclamation of ultra-fine coal with scenedesmus microalgae and comprehensive combustion property of the Coalgae® composite

Combustion of South African discard ultra-fine coal (i.e. coal dust), charcoal, microalgae biomass, and composites of the three under air were studied. The study involves to find out the effect of Scenedesmus microalgae biomass on the comprehensive combustion characteristics of the ultra-fines. Coal dust is considered as waste material, but it could be modified and combusted for energy. The composites were designed with Design Expert, and unlike blending with the dry microalgae biomass, fresh slurry was blended with the ultra-fine coal and charcoal. Non-isothermal combustion was carried out at heating rate of 15 C/min from 40 – 900 ºC and at flow rate of 20 ml/min, O2/CO2 air. Combustion properties of composites were deduced from TG-DTGA and analysed using multiple regression. On combustion, the interaction of coal-charcoal-microalgae was antagonistic (b = - 1069.49), while coal-microalgae (b = 39.17), and coal-charcoal (b = 80.37), was synergistic (p = 0.0061). The coal-microalgae (Coalgae®) indicated first order reaction mechanism unlike, coal, and the charcoal. Comprehensive combustion characteristics index of Coalgae®, (S-value = 4.52E8) was superior relative to ultra-fine (S-value = 3.16E8), which indicated high quality fuel. This approach to combusting ultra-fine coal with microalgae biomass is partly renewable, and it would advance the production of heat and electricity. Key words: coal-dust, combustion, s-value, Coalgae®, renewable

Selective Direct Synthesis of Trialkoxysilanes in a Packed Bed Flow Tubular Reactor

Trialkoxysilanes were synthesized in a packed bed flow tubular reactor by the reaction of silicon and alcohol in the presence of a variety of copper catalysts. The effect of key parameters, which affect the silicon conversion rates and selectivity for the desired trialkoxysilanes, were investigated and optimized using ethanol as the model reagent. The study was extended to the other alcohols namely methanol, <i>n</i>-propanol, and <i>n</i>-butanol. Copper catalysts which were tested in the alkoxylation reaction included CuCl, Cu­(OH)₂, CuO, and CuSO₄; with CuCl showing the most activity while the uncatalysed reaction resulted in negligible reaction rates. High temperature catalyst preheating (>500 °C) resulted in a lower rate of reaction than when lower temperatures were used (<350 °C). The optimum reaction temperature range and alcohol flow rate were 230–240 °C and 0.1 mL/min, respectively. The reaction was deduced to be best described by the first-order kinetic model. The effect of alcohol (C1–C4) on the reaction revealed that conversion and selectivity generally decrease with an increase in carbon chain length. Ethanol showed the highest selectivity (97%) and conversion (64%) as compared to other alcohols studied, showing that it was the most efficient and stable alkoxylation alcohol for this reaction