# Terminology You Should Know

What the Heck Do All These Words Mean?

In a typical day in a separations plant, you will probably hear a few things you may or may not have run across before. If you have, fine, skip along on your merry way to the next really important topic. But if you haven't, be sure you learn them, 'cause you're going to be hearing them for a long, long time.

Absorption is the mass transfer of one substance from a gas stream to a liquid stream.

Carriers can be any compound or molecule or atom at all, so long as it is immiscible in the second liquid phase, and the extracted component is soluble in it. Major carrier loss can occur by irreversible side reaction or by solvent condensation on one side of the membrane.

Delta refers to that little triangular thingy before a variable. Delta usually means the difference between where you were when you started and where you are now.

Differential is related to change over a period of time. See also Delta.

Diffusion technically refers to molecular transfer, or the random equilization of a variable in a system. Diffusion can occur in two different ways, depending on theory and conditions, but essentially the effect is the same. Diffusion is the actual transport of individual atoms through a crystalline solid.

Diffusivity or Diffusion Coefficient is an experimental concept. It is one of several variables that relates the concentration difference across a membrane to the flux through the membrane. The most common place you will use this is in the Fick's Law Equations, but you will find it in others. It can be looked up in tables, or calculated using the other known variables, but is rarely derived in the undergraduate texts. Essentially what it is is a measure of the rate of mass transfer across the membrane, but is not related to the thicknes s of the membrane at all.

Flux is the rate at which a material passes through a particular area. In this case, it is the rate at which a particular material flows through the membrane.

Gradient is a term meaning a difference, usually a severe difference, in a measured variable. If you have a pot that you begin heating on one side only, then one side is going to be hot and one side is going to be warm, but not hot. That change in temperature, as you move your hand from the hot side to warm side, is a gradient.

Liquid-Liquid Extraction is the removal of a certain component from a liquid phase into a second liquid phase in contact with the first, by means of a carrier compound, which the component is also soluble in. Permeation is the broadest concept of all. It is used to refer to any kind of transfer across a gradient, be it a concentration, temperature, pressure, or electrical gradient. Permeation refers to the movement of atoms, molecules, or ions through a permeable substance.

Permeability can be defined just by looking at the root words. Permeability is the ability of a material to permit a substance to pass through it. From an actual quantitative level, it is the amount of a substance which passes through the material under given conditions.

Several (sev ar ul) adj. As in many, multiple, more than one, quite a few, boy what a lot of 'em, etc.

Solute is the substance that is dissolved by a solvent.

Solvent is the part of the solution that is present in the largest amount, most often the part that, if pure, is normally liquid.