Chemical engineering is the discipline in which knowledge of mathematics, physics, chemistry and biology, gained by study, experience and practice, is applied with judgement to develop economic and safe ways of converting raw materials into more useful products to benefit mankind. It is devoted to the chemical, physical or biological transformation of matter or energy into useful forms, economically and safely without compromising the natural environment.
Petroleum refining processes are those chemical engineering processes and other facilities used in petroleum refineries (also referred to as oil refineries) to transform...
Counter current exchangeLast Updated on 2014-06-19 15:47:30Counter current exchange is the mechanism by which some property of a fluid, such as heat or a chemical substance, is transferred from one fluid across a semi-permeable membrane or thermally conductive material to another fluid flowing in the opposite direction. The general requirements for counter current exchange are (1) that two fluids flow in close proximity to each other and (2) that the fluids flow in opposite directions. The purpose of counter current exchange is to maintain a concentration gradient between the two fluids in order to maximize movement from one fluid to the other. The opposite of counter current exchange occurs in concurrent exchange when two fluids flow in the same direction.
The principle of counter current exchange can be illustrated using fish gills. In the gills, oxygen diffuses from an area of high concentration, the water, into an area of lower... More »
Concentration expressions and notationsLast Updated on 2014-06-18 18:21:06In chemistry and other sciences, engineering and in fairly common usage, concentration is the measure of how much of a given substance there is in a given mixture of substances.
There are many different notations and quantitative expressions of concentration. The most commonly used expressions are discussed below:
The mole fraction is a measure of the concentration of a component substance in a mixture of substances. It is defined as the number of moles of a component substance in a mixture divided by the total number of moles of the mixture.
The mole percent (also referred to as the molar percent) is usually denoted by mole % and is equal to 100 times the mole fraction.
The mass fraction is also a measure of the concentration of a component substance in a mixture of substances. It is defined as the mass of a component substance in a mixture divided by the total... More »
Plastic products and estrogenic chemicalsLast Updated on 2014-06-14 12:26:55Chemicals that mimic or antagonize the actions of naturally occurring estrogens are defined as having estrogenic activity (EA), which is the most common form of endocrine disruptor activity.
This article, written by Chun Z. Yang, Stuart I. Yaniger, V. Craig Jordan, Daniel J. Klein, and George D. Bittner* appeared first in Environmental Health Perspectives—the peer-reviewed, open access journal of the National Institute of Environmental Health Sciences.
The article is a verbatim version of the original and is not available for edits or additions by Encyclopedia of Earth editors or authors. Companion articles on the same topic that are editable may exist within the Encyclopedia of Earth.
Most Plastic Products Release Estrogenic Chemicals:
A Potential Health Problem That Can Be Solved
Background: Chemicals having estrogenic activity (EA) reportedly cause many adverse health... More »
Biochar: Concept to Sequester CarbonLast Updated on 2014-06-11 15:45:52
Biochar is a charcoal produced under high temperatures using crop residues, animal manure, or any type of organic waste material. Depending on the feedstock, biochar may look similar to potting soil or to a charred substance. The combined production and use of biochar is considered a carbon-negative process, meaning that it removes carbon from the atmosphere.
Biochar has multiple potential environmental benefits, foremost the potential to sequester carbon in the soil for hundreds to thousands of years at an estimate. Studies suggest that crop yields can increase as a result of applying biochar as a soil amendment. Some contend that biochar has value as an immediate climate change mitigation strategy. Scientific experiments suggest that greenhouse gas emissions are reduced significantly with biochar application to crop fields.
Obstacles that may stall rapid adoption of biochar... More »
HydrodesulfurizationLast Updated on 2013-12-15 23:43:02Hydrodesulfurization (HDS) or Hydrotreating is a catalytic chemical process widely used to remove sulfur compounds from refined petroleum products such as gasoline or petrol, jet fuel, diesel fuel, and fuel oils. One purpose for removing the sulfur is to reduce the sulfur dioxide emissions resulting from using those fuels in automotive vehicles, aircraft, railroad locomotives, ships, or oil burning power plants, residential and industrial furnaces, and other forms of fuel combustion.
Another important reason for removing sulfur from the intermediate product naphtha streams within a petroleum refinery is that sulfur, even in extremely low concentrations, poisons the noble metal catalysts platinum and rhenium in the catalytic reforming units that are subsequently used to upgrade the of the naphtha streams.
Hydrogenation of the sulfur compounds results in the formation of undesirable,... More »
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