Babak Mokhtarani

Microalgae have been identified as a sustainable and versatile source of natural pigments. Their ability to convert carbon dioxide and sunlight into high-value bioproducts make them both an environmentally beneficial and commercially attractive resource. However, the commercialisation of microalgal pigment production remains constrained by several challenges, including high production costs, low pigment yields under standard conditions, and inefficient downstream processing. This review provides all aspects of pigment production from microalgae and not covered in previous reviews. The review encompasses pigment classification, cultivation strategies, factors affecting extraction, as well as extraction and purification processes. Environmental and operational parameters, such as light, temperature, nutrient availability, salinity, and pH, significantly affect pigment biosynthesis and must be optimised for each strain. The choice of cultivation mode (autotrophic, heterotrophic, mixotrophic) and system (open ponds, photobioreactors, hybrid) also plays a crucial role in determining biomass productivity and pigment quality. Downstream processing, including harvesting, cell disruption, extraction, and purification, remains a bottleneck due to high energy costs and pigment instability. Advanced extraction techniques, such as supercritical fluid extraction and microwave-assisted extraction, offer promise for more sustainable and efficient recovery. To advance the field, future research should focus on strain improvement via metabolic engineering, development of energy-efficient processing methods, and implementation of integrated biorefineries. Additionally, pigment stabilisation and public awareness of the benefits of natural pigments will support wider market adoption. With these advancements, microalgae can become a competitive and eco-friendly source of natural pigments.

The separation of synthesised ammonia from unreacted nitrogen and hydrogen is a crucial step in producing high-purity ammonia and enabling the efficient recycling of unreacted gases in the ammonia synthesis process. The separation of ammonia from nitrogen and hydrogen was studied using zeolite 13X. Experiments were performed using a custom-designed experimental apparatus developed specifically for this study. Adsorption isotherm data for ammonia, hydrogen, and nitrogen were obtained over a temperature range of 293–313 K and pressures up to 5 bar. The results show that the adsorption capacity of zeolite 13X for ammonia is significantly higher than for nitrogen and hydrogen. This indicates a substantially stronger affinity toward ammonia molecules, enabling highly selective adsorption. The experimental isotherm data were successfully fitted using the Sips model, which accurately described the adsorption behaviour of the gases and showed good agreement with the measured data. The adsorption performance of zeolite 13X was further evaluated through a series of dynamic breakthrough experiments under varying pressures and gas compositions. The results confirmed the high selectivity of zeolite 13X for ammonia, with negligible adsorption of nitrogen and hydrogen. Ammonia breakthrough time was found to increase with system pressure, reflecting enhanced adsorption capacity. These findings highlight zeolite 13X as an effective and reusable adsorbent for selective ammonia separation in multi-component gas streams, with promising potential for industrial applications.

This study explores biohydrogen production through dark fermentation, an alternative supporting sustainable hydrogen generation. Dark fermentation uses organic waste under anaerobic conditions to produce hydrogen in the absence of light. Key process parameters affecting hydrogen yield, including substrate type, microorganism selection, and fermentation conditions, were examined. Various substrates, such as organic wastes and carbohydrates, were tested, and the role of anaerobic and facultative anaerobic microorganisms in optimizing the process was analyzed. The research also focused on factors such as pH, temperature, and hydraulic retention time to enhance yields and scalability. Additionally, the study modelled the process using ASPEN Plus software 14. This simulation identifies the bottle necks of this process. Due to the lack of available data, modelling and simulation of the described processes in ASPEN Plus required certain approximations. The simulation provides insight into the key challenges that need to be addressed for hydrogen production. Future research should indeed explore current limitations, such as substrate efficiency, process scalability, and cost-effectiveness, as well as potential advancements like the genetic engineering of microbial strains and improved bioreactor designs.

Performance analysis of the adsorptive separation of ethylene downstream of an oxidative coupling of methane (OCM) process, being an alternative process for converting methane content of natural gas or other methane-rich sources to ethylene, was studied in this research for a production capacity of 1 Mt/yr. This was motivated by observing promising adsorption characteristics and efficiency in the selective adsorption of ethylene using 13X zeolite-based sorbent. The energy and economic performance of alternative scenarios for retrofitting the adsorption unit into an integrated OCM process were analyzed. Simulations of the integrated OCM process scenarios include OCM unit, CO₂-hydrogenation, ethane dehydrogenation and methane reforming sections. The use of efficient ethylene adsorption separation enabled the improvement of the economic and energy efficiency of the integrated OCM process under specific operating conditions. For instance, the invested amount of energy and the associated energy cost per ton of ethylene in the cryogenic ethylene-purification section of the integrated process using adsorption unit are, respectively, 75% and 89% lower than the reference integrated OCM process. Under the conditions considered in this analysis, the return on investment for the final proposed integrated OCM process structure using adsorption separation was found to be less than 9 years, and the potential for further improvement was also discussed.

In this study, the adsorption of thiophene compounds (TCs), including thiophene (T), benzothiophene (BT), and dibenzothiophene (DBT), from model fuels was investigated using modified activated carbon (AC). The model fuel, prepared as a single‐solute model at a concentration of 2000 ppm based on a mixture concentration of 3000 ppm, served as the basis for the adsorption experiments. Additionally, an examination of thiophene adsorption from commercial fuels, specifically kerosene, was conducted. Experimental data were used to calculate correlated parameters of adsorption isotherms, kinetic models, and the Fisher factor. The pseudo‐second‐order model demonstrated the best fit to the experimental data. Notably, the adsorbent consisting of 10% Cu⁺ supported on acid‐washed activated carbon (A1CN10) exhibited the highest adsorption capacity for TCs, achieving removal percentages of 78%, 96%, and 100% for T, BT, and DBT, respectively. Various methods were employed to investigate the physicochemical properties of the adsorbents, including N₂ adsorption–desorption surface analysis (BET), scanning electron microscopy (SEM), X‐ray diffraction (XRD), and energy dispersive spectroscopy (EDS). Furthermore, the regeneration of the adsorbent was studied using two techniques: agitation and ultrasound.