Sustainable Separation Solutions Laboratory @ IISc

The Sustainable Separation Solutions Laboratory is a facility at the Centre for Sustainable Technologies (CST) at the Indian Institute of Science (IISc) in Bangalore, India led by Dr. Yagnaseni Roy

Basic concept of a separation technology: one or more incoming streams are split into two or more exiting streams by the separation process.

What are separation technologies?

The basic concept of a separation technology is shown in the schematic on the left. One or more streams (called feed streams) enter the separation process and are separated to two or more exiting streams. There are several separation technologies that are important for our everyday lives: the masks that we wear as a precaution against the corona virus are filters to separate any nearby viruses from the air we breathe in. Evaporation of pure water from a salty solution is a separation critical to the lives of people in arid regions with limited freshwater resources.

Separation technologies in industry

As explained above, separation technologies are critical in our daily lives. However, they comprise a major chunk of industrial activities, associated costs and energy requirements. Consider any product that you use from the time you wake up till the end of the day - plastics, paper, pharmaceuticals, soaps and detergents, textiles, and many more - separations typically account for 40-70% of the total cost of the complete manufacture process of the item and cumulatively, separations in various industries add up to 15% of the world’s energy requirements. Separation technologies are responsible for several important processes within the product manufacture scheme, such as extracting the final product from the synthesis medium; treating effluent streams before environmental discharge; recovering materials that can be reused for subsequent manufacture cycles; or isolating valuable intermediate products that can be used in a different industry or sold.

In our group, we focus on developing techno-economically optimized separation schemes for industry-relevant processes. Short descriptions of some of our ongoing projects are given below.

Ongoing projects

Solvent recovery using pervaporation

Pervaporation is a membrane technology in which certain species in the liquid feed effectively evaporate through the membrane due to the vacuum pressure applied on the permeate side (using a vacuum pump), and the membrane’s selectivity in favour of the permeating components. Consequently, the separation is determined by a combination of the vapor-liquid equilibrium characteristics at the operating conditions and the membrane’s selectivity behaviour. Due to the role of membrane selectivity in allowing selective evaporation, pervaporation is particularly useful for breaking azeotropes, which is traditionally done by extractive distillation, azeotropic distillation, pressure swing distillation, or solvent dehydration using molecular sieves. These conventional techniques suffer from several drawbacks such as complexity, contamination of the final products by a third solvent, and relatively high energy requirement.  Pervaporation is currently used at the industry-scale for applications such as ethanol dehydration during the synthesis of biofuels and various chemicals, breaking other azeotropes such as ethanol-ETBE (in the petrochemical industry) and isopropyl alcohol-water (in the food processing and pharmaceutical industries), as well as for the removal of volatile organic compounds from waste water. In our group, we are exploring pervaporation for various new industrial applications relevant to the pharmaceutical industry and biofuel synthesis. We model systems comprising stand-alone pervaporation, pervaporation-distillation hybrids, and traditional enhanced distillation (extractive distillation, azeotropic distillation, pressure swing distillation) for a given application and propose the techno-economically optimized system design for industrial applications. Our pervaporation modeling is aided by our experimental results, which provide values for modeling parameters.

Purification of extracted phytochemicals using membrane processes

Phytochemicals are plant-derived compounds, several of which have important properties such as anti-microbial or pesticidal properties, or protection against environmental agents such as ultraviolet (UV) radiation and extreme temperatures – to name a few. Hence, they are widely used in creating pharmaceutical, as well beauty products, and in the food industry. A few examples relevant to our daily lives are carotenoids extracted from carrots or tomatoes which are primary components in immunity-boosting medication, and  the flavonoid galangin is used in sunscreen lotions. Phytochemicals are also essential components in medication of critical disease, for example, the plant alkaloid Paclitaxel is used as an anti-cancer chemotherapy drug component. Typically, solvent extraction is used to extract phytochemicals from the raw plant material, after which a large fraction of the solvent is evaporated, and further isolation of valuable phytochemicals is conventionally done using chromatography, crystallization, or centrifugation. Membrane separations offer a method to reduce the energy requirement in evaporative techniques as well as reduce the cost and complexity of several of the conventional molecule-solation techniques named earlier. Furthermore, membrane separations can fractionate different classes of extracted molecules in several cases. In our work, we aim to achieve a techno-economic optimization of phytochemical extraction processes with the help of membrane separations used in conjunction with the other critical steps for phytochemical isolation. As shown in the diagram on the right, our current phytochemical extraction and isolation work focuses on curcumin obtained from turmeric.

Arsenic remediation scheme inclusive of adsorption

Adsorbent beads prepared in our lab

Adsorption is a fundamental surface phenomenon in which molecules or ions from a fluid (liquid or gas) adhere to the surface of a solid material. This process occurs due to attractive forces between the adsorbate molecules/ions and the adsorbent surface. Our group employs adsorption techniques to address the pressing issue of arsenic contamination in groundwater, a widespread global environmental challenge. As shown in the above picture, we synthesize our own adsorbent beads using novel recipes that ensure the use of non-toxic material, and biodegradability after use. Furthermore, our work focuses on sustainability by investigating the regeneration and reuse of the adsorbent. The safe disposal and management of arsenic-containing sludge and waste generated after treatment is still a grave concern in existing arsenic-remediation technologies, and our ongoing research aims to establish a suitable approach for the safe management of isolated arsenic by means of a patentable scheme, as shown in the schematic above (the details of the patent application are shown on the 'Group Achievments' page).