low pressure, the reboiler may have to be heated as high as 370°C (700°F) for such high-boiling distillates.
Molecular distillation is a non-equilibrium process and the atmospheric equivalent boiling range of a fuel or a fraction of a fuel that cannot be measured directly. The atmospheric equivalent boiling point (AEBP) concept was developed to compensate for this and can be estimated from one of the following equations:
The mid-AEBP is the temperature for the 50% mass point on the distillation curve of the fraction, and Mn is the molecular weight. Either the specific gravity (sp. gr.) or atomic hydrogen/carbon (H/C) ratio, which can be readily measured in the fractions, can also be used. Using the mid-AEBP concept, even fractions of the non-distillable residue can be included in the boiling range curves and relationships such as the variation of sulfur and nitrogen contents can be derived as a function of the AEBP.
Typically, as the mid-AEBP increases, the sulfur and nitrogen concentrations of the fraction generally also increase. Also, the highest concentrations of both sulfur and nitrogen appear in the non-distillable fractions. This behavior follows the heteroatom behavior observed for refinery distillation cuts. Thus, the higher the boiling range of the fraction, the higher the heteroatom concentration. This also establishes that the heteroatom concentration continues to increase as the volatility of the compounds decreases, which was not known previously for the 540°C+ (1000°F+) residuum.
Atomic Energy
Atomic energy (or, more correctly, nuclear energy) is a term that represents the energy with an atom and includes (i) nuclear binding energy, (ii) nuclear potential energy, (iii) nuclear reaction, which is a process in which nuclei or nuclear particles interact, resulting in products different from the initial ones, (iv) radioactive decay which is a descriptor for the various processes by which unstable atomic nuclei (nuclides) emit subatomic particles, and (iv) the energy of inter-atomic or chemical bonds, which holds atoms together in compounds.
Atomic energy is the source of nuclear power which uses sustained nuclear fission to generate heat and electricity. It is also the source of the explosive force of an atomic bomb. The energy originates from the splitting of uranium atoms (nuclear fission) which generates heat to produce steam, which is used by a turbine generator to generate electricity. Because nuclear power plants do not burn fuel, they do not produce greenhouse gas emissions but, caution is advised, and although the risk of accidents in nuclear power plants is low, the consequences of an accident can be drastic and highly detrimental to the surrounding flora and fauna (including human life).
See also: Nuclear Energy, Nuclear Fission, Nuclear Fusion.
Attapulgus Clay
Attapulgus clay (attapulgite or palygorskite) is a magnesium aluminum phyllosilicate [(Mg.Al)2Si4O10.4H2O) which occurs in a type of clay soil common to the Southeastern United States. It is one of the types of fuller’s earth.
The name attapulgite is derived from the U.S. town of Attapulgus, Georgia, in the extreme southwest corner of the state, where the mineral is abundant. It is surface-mined in the area, dry-ground and air-separated into precise particle sizes, and transported in covered hopper cars via the railroad, and is also shipped in 50-lb bags and bulk bags by truck. The name palygorskite is given after the place in the Ural Mountains where it was discovered.
Attapulgite clays are swellable clays like bentonite, although more acicular (or needle like). Attapulgite, unlike bentonite, will swell in salt water and is used in special salt water drilling mud for off shore oil drilling. Like many clays, they can be considered as charged particles with zones of positive and negative charges. Standard attapulgite clays are agglomerated bundles of clay particles between 20 and 100 µm long and below 1 µm in diameter. Most grades contain up to 25% non-attapulgite material in the form of mineral carbonates and other inclusions. The advantage of attapulgites is that their performance is not temperature sensitive and they have lower water demand. They must have free ions in an aqueous system to work.
See also: Clay Minerals, Clay Treating Process.
Attrition Catalyst
Typically, a relatively inexpensive catalyst that is designed to remove impurities and unwanted by-products from gas streams which, at the same time, is sacrificed. For example, alumina (Al2O3) guard beds serve as protectors by the act of attrition and may be referred to as an attrition reactor containing an attrition catalyst may be placed ahead of the molecular sieves to remove the sulfur compounds. Downflow reactors are commonly used for adsorption processes, with an upward flow regeneration of the adsorbent and cooling using gas flow in the same direction as adsorption flow.
See also: Guard Bed, Guard Bed Reactor.
Azeotrope
Two main types of azeotropes exist, i.e., the homogeneous azeotrope, where a single liquid phase is in the equilibrium with a vapor phase; and the heterogeneous azeotropes, where the overall liquid composition which form two liquid phases, is identical to the vapor composition. Most methods of distilling azeotropes and low relative volatility mixtures rely on the addition of specially chosen chemicals to facilitate the separation.
The five methods for separating azeotropic mixtures are: (i) extractive distillation and homogeneous azeotropic distillation where the liquid separating agent is completely miscible, (ii) heterogeneous, (iii) azeotropic distillation, or more commonly, azeotropic distillation where the liquid separating agent (the entrained) forms one or more azeotropes with the other components in the mixture and causes two liquid phases to exist over a wide range of compositions – this immiscibility is the key to making the distillation sequence work, (iv) distillation using ionic salts in which the salts dissociate in the liquid mixture and alters the relative volatilities sufficiently that the separation become possible, (iv) pressure-swing distillation in which a series of column operating at different pressures are used to separate binary azeotropes which change appreciably in composition over a moderate pressure range or where a separating agent which forms a pressure-sensitive azeotrope is added to separate a pressure-insensitive azeotrope, and (v) reactive distillation where the separating agent reacts preferentially and reversibly with one of the azeotropic constitutes; the reaction product is then distilled from the non-reacting components, and the reaction is reversed to recover the initial component, (v) simple distillation in which a multi-component liquid mixture is slowly boiled in a heated zone and the vapors are continuously removed as they form and, at any instant in time, the vapor is in equilibrium with the liquid remaining on the still; because the vapor is always richer in the more volatile components than the liquid, the liquid composition changes continuously with time, becoming more and more concentrated in the least volatile species.
A simple distillation residue curve is a means by which the changes in the composition of the liquid residue curves on the pot changes over time. Residue curve map is a collection of the liquid residue curves originating from different initial compositions. Residue curve maps contain the same information as phase diagrams, but represent this information in a way that is more useful for understanding how to synthesize a distillation sequence to separate a mixture.
All of the residue curves originate at the light (lowest boiling) pure component in a region, move toward the intermediate boiling component, and end at the heavy (highest boiling) pure component in the same region.
