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US researchers have made Molecular Sieve fibers that open up new possibilities for large scale chemical separations that use much less energy than conventional distillation methods. Sankar Nair and his Georgia Institute of Technology team have shown their metal–organic framework (MOF)-lined fibers can perform similarly to distillation in separating propylene and propane. That’s the same post-cracking raw mixture that the majority of the 77 million tons of propylene produced in 2011 was distilled from. ‘The degree of separation by the membrane is comparable, but uses vastly less energy,’ Nair says.
Though scientists recognize MOF membranes’ separation potential, they’ve mostly been fabricated on large tubes, whose surface area-to-volume ratio is too low for producing cheap separation modules. Micron-scale fibers would be better, but inside them conditions for successful membrane formation change significantly, Nair explains. ‘The amount of reactant present in the fiber is miniscule, and molecular transport and reaction processes are quite different,’ he says.
The Georgia Tech team’s new approach uses two solutions – one containing zinc ions and another containing methyl imidazole. With one solution inside 250µm diameter hollow poly(amide-imide) porous fibers and another outside them, they start forming a zeolitic imidazolite framework (ZIF) where the two meet. They initially explored conditions where the solution inside the fiber didn’t move, but got patchy coatings. When they realized this setup wasn’t supplying enough reactant, they pumped the inner solution through the fiber, getting better coatings but struggling to control thickness and quality. Finally, they devised an intermittent approach, allowing the membrane to grow under static conditions, then periodically replenishing the reactant supply.
This lets Nair’s team direct film growth inside the fiber or on its inner or outer surfaces through different reagent and solvent permutations. Using tiny pores in MOF films inside the bore of the fibers as selective Carbon Molecular Sieves they then separated hydrogen or propylene from propane. ‘We have a demonstrated path to “scale down” MOF membranes to hollow fibers, in a manner that we can now look to “scale up” by an in-parallel replication of the process to many fibers bundled together into a module,’ Nair explains.
What are Pneumatic Solenoid Valves?
Pneumatic solenoid valves are electromechanical devices that control the flow of air or process gas. They are mostly used for controlling pneumatic actuators such as cylinders, turbines (pneumatic motors), diaphragms, and tubes. Pneumatic Valve and actuators form auxiliary air circuits. These devices are used to control plant equipment.
Other pneumatic solenoid valves are used as an integral part of some pieces of equipment or processes. Examples are compressed air systems, vacuum systems, ventilation systems, and air-operated equipment.
Pneumatic solenoid valves are commonly seen in many industrial and manufacturing plants. One of their main benefits is being remote controlled by sending low-power electric signals over large distances. These electric signals are easily handled by the plant‘s control system. A control panel or unit distributes signals that manipulate the valve at unattended locations in the process area. Pneumatic solenoid valves are employed in a wide range of industries such as oil and gas, power generation, chemical, and plastics.
The heart of a Shuttle Valve is the solenoid. A solenoid is an electromagnetic actuator that converts electrical energy into mechanical action. It consists of a coiled wire tightly wrapped around an iron core, and a ferromagnetic plug or plunger. As an electrical current passes through the coil, a magnetic field is generated. The magnetic field lines can be imagined as a series of circles with the direction of their current axis. In the case of a current flowing through a looped coil, the circles combine forming the magnetic field.
The magnetic field around the coil causes the ferromagnetic plunger to become attracted. The electromagnetic force generated can be increased using two ways. The first is by adding more loops or windings in the coil. This increases the number of magnetic field lines or flux emanating from the coil.
The second method is by increasing the amount of current flowing through the coil. This increases the supply voltage into the solenoid. Solenoid Valves operate with either DC or AC voltages.
The other main part of a pneumatic solenoid valve is the valve. The valve is the part in contact with air or gas. It is made up of components designed to withstand the pressure of the system. It also resists corrosion and erosion brought by contaminants entrained into the pneumatic system.
Parts of a Pneumatic Solenoid Valve
The previous chapter generally describes the two main parts of a pneumatic solenoid valve, the solenoid, and the valve. To further understand its operation, it is useful to note its detailed components. Below are the parts of a 2 Way Solenoid Valve common to almost every design.
The core, also referred to as the armature or plunger, is the moving part of a solenoid. This is a soft magnetic metal (soft, meaning a ferromagnetic metal that can easily be magnetized and demagnetized at low magnetic fields). When the coil is energized generating a magnetic field, the core is attracted which opens or closes the valve.