With increasing awareness of the global environment, sustainability is gaining the most focus in business practices. Manufacturers especially in the pharmaceutical and chemical sectors have positioned themselves at the center of the green industry with profound knowledge of consumer awareness and investment in better green process technologies.
Solvent recovery is essential in achieving the goal of sustainable processing and green chemistry since the pharmaceutical industry uses solvents quite frequently. It is a method of recovering valuable materials from waste or by-product extracted solutions during industrial process manufacturing.
The waste solvent treatment makes up one of the largest cost concerns in the chemical and pharmaceutical industries.
Utilizing these recovered chemicals dramatically decrease the requirement for additional solvents, while also reducing the amount of waste produced.
As a result, pollution and operational cost will significantly minimized.
What are Green Solvent Recovery Technologies
The extraction of valuable elements from waste solvents or by-product created during process manufacturing and recycling in the process production line is known as solvent recovery.
This process involves conventional technologies like precipitation, thermal distillation, membrane filtering, or adsorbing valuable solvents in the solution and reusing them. However, some less expensive solvents might be burned or disposed of in landfills for hazardous waste.
The green solvent recovery process is frequently employed instead of solvent replacement in order to generate less waste. It is appealing since it involves little modification to current procedures, similar to edge pollution prevention and process control.
Meanwhile, new processes, equipment, and technologies are making process engineering safer, highly efficient, and low energy consumption.
Process intensification will greatly improve the production capacity and decreases waste discharging without sacrificing the efficiencies or changing the existing process production units.
Let us explore more information about solvent recovery process technologies.
Continuous Distillation / Rectification Process
Distillation or rectification separates components in which a liquid sample is volatilized to create a vapor and then condensed back to liquid. Volatilization is normally conducted by heating the liquid, it can also be completed under reduced pressure or by combining the two phases. It uses variations in component concentration between the liquid and vapor phases.
Continuous distillation has been widely employed in the industry because it is quick, effective, and efficient. This process is even more commonly utilized in preparative chemistry and throughout the manufacturing industry to concentrate products and chemical intermediates. Although the investment cost of complete equipment is the lowest, this process consumes a mass of energy according to the law of conservation of energy.
A typical continuous rectification unit consists of a rectifying tower, a reboiler, a preheater, a condenser, matched with the automatic control system, etc. With recovery capacity specially designed to obtain up to 95% ethanol from a feed stream of about 30% to 50% water-ethanol solutions.
The distillation column provides vapor-liquid contact for interphase mass transfer. For solvent material reacting systems that do not form an azeotrope, the distillate will be the volatile component with high purity and the product at the bottom of the column will be the none volatile component with high purity as long as it is properly designed and operated.
When feed material is preheated to the center of the distilling tower, the liquid in the feed from the upper column descends along the tower, and the vapor from the lower column rise along the tower together. The rectification column section above the feed inlet further concentrates the volatile components in the rising steam.
The column section below the feed port, where volatile components are extracted from the descending liquid. The combination of the two stages enables a more complete separation of the components in the liquid solvent mixture to get the products of the required purity.
The reboiler at the bottom of the tower partially vaporizes the liquid, and the steam rises up the tower, leaving the remaining unvaporized liquid at the bottom.
The complete rectification system has high performance on alcohol aqueous solution for recovery of up to 95% alcohol solution. the stainless steel bellow-type packing rate is over 90% which will make sure the recovery efficiency is over 98%.
Thin-Film Evaporation
Precisely known as a Rotary and Wiped Film Evaporator is high-efficiency evaporation and distillation equipment, which uses variable speed rotation to distribute liquid into a uniform film, a thin layer (0.1 mm to 1.0 cm) of flowing substance under regulated circumstances using indirect heat transfer.
Thin film evaporators can successfully separate difficult and complex materials due to precise design principles. It is featured of a high heat transfer ratio and evaporation capacity. The viscosity of materials can be as high as 100000 (CP) and flexible adapting to a wide range of viscosity changes. The process can also carry out deodorization, desolvation reaction, preheating, cooling, and other process operations.
Conductive heat transmission causes the fast evaporation of volatile components. Depending on the application’s needs, the heating medium moves through the device either co-current or countercurrent with precise temperature and pressure control. Meanwhile, vapors are prepared for condensing or further processing after leaving the vapor discharge section.
At the outlet, non-volatile components are released. Continuous rotor blade agitation and mixing decrease thermal wall fouling where the product or residue is most concentrated. The right configuration and the ideal combination of wiped film evaporators and short path distillation units provide reliability as well as savings on both energy and cleaning in minor solvent purification and separation applications.
Pervaporation Membrane Dehydration
Pervaporation is an innovation of membrane separation, especially suitable for the separation and purification of azeotropes and near-boiling point solvent mixtures. Compared with other traditional separation technologies like distillation or adsorption, pervaporation has outstanding advantages of high efficiency, low consumption, high recovery, convenient operation, safety, and environmental protection features.
Suppose the solvent mixture flows upstream of the membrane. In that case, the permeable components are selectively dissolved and adsorbed by a hydrophilic membrane, diffuse with the membrane, and flow through the membrane under the impact drive of the differential steam pressure along both sides of the membrane. It will be vaporized and collected in the membrane downstream, achieving the purpose of separation and recovery of organic solvent component.
According to our economic cost calculation on the case projects, a tetrahydrofuran water waste solvent with a treatment capacity of 5000 tons per year. It realized a 98% recovery of tetrahydrofuran when using a pervaporation membrane dehydration unit for separation and dehydration.
From a feed concentration of 8% aqueous tetrahydrofuran solution, the result from the outlet product side consists of only as low as 0.1% water, 99.8% tetrahydrofuran, and other fraction of 0.1%, permeate side with 99% water for discharging.
The operation cost of steam, electricity, cooling water, and membrane materials on a complete pervaporation membrane dehydration unit is about 26% of the cost of conventional distillation or adsorption process.
With pervaporation membrane dehydration technology, the process realized extremely operation savings of US$332353 per year, recovery appreciation of US$1300000, and labor-saving of US$29415, making the total benefit of US$1661768 per year for a complete tetrahydrofuran recovery project.
Furthermore, the complete equipment assembly is only covering an area of 4m*4.5m*3.5m in length*width*height based on the optimized process design and process intensification structure.
Liquid-Liquid Extraction
Liquid-liquid extraction, while largely utilized as a separation technique, it is an effective enrichment alternative when above process technologies are not applicable. An immiscible or partially immiscible solute is transferred from one solvent to another during a separation process known as liquid-liquid extraction. Water or an aqueous combination is frequently one of the solvents, while an organic nonpolar liquid is the other.
Liquid-liquid extraction involves mixing (contacting), followed by phase separation by density difference, similar to all extraction techniques. The technique entails having an immiscible combination, represented by A+C and B, where the parts can be transported, mixed, and separated. By combining it with another non-homogenous solvent where the solute can be dissolved, it extracts a solute from a two-part solution. From there, the liquid mixes are separated, and the soluble solutes are then distributed as needed.
What is Most Important About Solvent Recovery?
Solvents have significant effects on our health and the environment, which must be the most important consideration criteria for proper solvent recovery process technologies.
Health Effects of Solvents
Your health may be impacted by various solvents in various ways. A high concentration of typical solvents in the air might result in unconsciousness and even death. Even short-term solvent exposure can bring eye, lung, and skin irritation as well as headaches, nausea, dizziness, or lightheadedness, etc.
Some of these consequences could also make you more likely to get into an accident. Repeated exposure to specific solvents can potentially have long-term impacts on your health such as dermatitis, liver, renal, and neurological conditions.
Environmental Effects of Solvents
Using solvents increases ozone pollution. Ground-level ozone is created when certain solvents react with sunlight in the atmosphere. A significant part of smog is ground-level ozone, which is bad for the health of people, animals, and plants.
Because chlorinated solvents take a long time to degrade in soil and water, they endanger ecosystems and groundwater aquifers. Some solvents can linger in the atmosphere for a very long time. In actuality, one of the most typical organic pollutants in groundwater is trichloroethylene. Furthermore, all chlorinated solvents must be eliminated from commercial process applications.
Certain solvents can diffuse across the environment and evaporate quickly. Others linger for a long time in subterranean soils and water, dispersing contaminated plumes close to the sites of spills or inappropriate disposal.
In Conclusion:
There you have it! Solvent recovery is very beneficial to pharmaceutical and chemical industries in terms of cost and reducing the risk of environmental & health effects caused by waste solvents.
As solvent recovery process technology advances, the demand for innovative, high-performance, and environmentally friendly cleaning solvents is growing.
As the march of process technology continues, we will keep innovating green solvent recovery processes to keep up with the challenges and provide more cost-effective recovery solutions for manufacturers in the pharmaceutical and chemical industries.
Let us know your thoughts and inquiries in the comment section below.
References:
https://www.sciencedirect.com/topics/earth-and-planetary-sciences/solvent-recovery
https://www.maratek.com/blog/what-is-solvent-recovery-and-how-does-it-work
