Aerosols....

From Chemical Engineering point of view it is basically a suspension of solid particles or liquid droplets in gas. Few examples can be smog, haze, smoke etc. The aerosol product consists of the following components: Propellant, Container,  Valve and Actuator and Product concentrate.

Propellant: The propellant is generally regarded as the heart of the aerosol package. It is responsible for development of pressure within the container, supplying the necessary force to expel the product when the valve is opened. The propellant also acts as a solvent and as a diluent and has much to do with determining the characteristics of the product as it leaves the container. Examples of propellants include Chloro fluro carbons (CFCs), Hydro fluoro alkanes (HFA)and Fluorinated hydrocarbons

Containers: Different materials are used for the manufacture of aerosol containers. The materials must be inert, non-toxic and must withstand pressure as high as 140 to 180 psig at 130ºF. Examples include aluminum containers, glass etc.

Valves: Valve must be multifunctional in that it is capable of being easily opened and easily closed and capable of delivering the contents in the desired form. Also in case of metered dose inhaler aerosol, the valve is expected to deliver a given amount of medication.

Applications of Dimethyl Ether

1.   Dimethyl ether (DME) has been increasingly used as a propellant in aerosol formulations to replace chlorofluorocarbons (CFCs), which are found to destroy the ozone layer of the atmosphere. DME is nontoxic and easily degrades in the troposphere. Several aerosol-based household products include colognes, hair sprays and dyes, personal care mousses, antiperspirants, and room air fresheners.

2.   DME has very promising uses as an ultra-clean transportation fuel as well as a fuel for power generation. DME has a high cetane value of about 55-60 and can be directly and effectively used for DME diesel engines. Burning DME in diesel engines results in a lower NOx with no SOx, thus also contributing to the societal air quality. The advantages of using DME are not only ultralow emissions of nitrogen oxides (NOx), but also, reduced engine noise or quiet combustion, practically soot-free or smokeless operation and high diesel thermal efficiency.

3.   DME is a useful intermediate for the preparation of many important chemicals, including methyl sulphate and dimethyl sulphate is an important commercial commodity as a solvent and also as an electrolyte in high energy density batteries. 

4.  Dimethyl ether is also an essential intermediate in the synthesis of hydrocarbons from coal or natural gas derived syngas (synthesis gas). Lower olefins like ethylene and propylene or higher molecular weight compounds such as gasoline range boiling hydrocarbons are produced from syngas using dimethyl ether as an intermediate. A variety of specialty industrial chemicals such as oxygenates, acetaldehyde, acetic acid, ethylene glycol etc. can be formed using dimethyl ether as a feedstock.

5.  Dimethyl ether is a low-temperature solvent and extraction agent, applicable to specialised laboratory procedures. Its usefulness is limited by its low boiling point (−23 °C), but the same property facilitates its removal from reaction mixtures. Dimethyl ether is the precursor to the useful alkylating agent, trimethyloxonium tetrafluoroborate.

Introduction to Dimethyl Ether

Dimethyl ether (DME) also known as methyl ether, methyl oxide and wood ether, is the organic compound with the formula CH3OCH3. The simplest ether, it is a colourless liquid or compressed gas that is a useful precursor to other organic compounds and an aerosol propellant. DME consists of two methyl groups bonded to a central oxygen atom, as expressed by its chemical formula CH3-O-CH3. It has been used in a variety of consumer applications viz., personal care (e.g., hairspray, shaving creams, foams and anti perspirants), household products, automotive, paints, food products, insect control, animal products and other related applications. It is commonly used in organic synthesis as a reaction solvent for systems requiring volatile polar solvents and is also promising as a clean-burning hydrocarbon fuel.

DME can be produced from natural gas—providing an alternative way of its utilization, in competition to such technologies as Fischer-Tropsch synthetic fuels—as well as from other carbon-containing feed stocks, including coal and biomass. DME has replaced CFC gases (freons) as an environmentally friendly and safe aerosol propellant, which is one of its major current applications. Potential future uses of DME include an alternative automotive fuel, a substitute for other fuels in power generation and in the household and a source of hydrogen for fuel cells. Worldwide DME production grew from 100,000-150,000 tons per annum in the 1990s to some 200,000 tons in the mid-2000s.

With the chemical structure somewhat similar to methanol, DME contains oxygen and no carbon-carbon bonds, thus seriously limiting the possibility of forming carbonaceous particulate emissions during combustion. However, unlike methanol, DME has a high enough cetane number to perform well as a compression-ignition fuel. Also unlike methanol, DME is a gas at ambient temperature and pressure, so it must be stored under pressure as a liquid similar to LPG (liquefied petroleum gas). When used as a diesel fuel, DME provides reduced PM (Particulate Matter) and NOx emissions.

The physical properties of DME (density, viscosity, etc.) are so different from the diesel fuel that the entire fuel system must be redesigned. It seems clear that DME, like perhaps some other alternative fuels, would be able to produce many larger emissions reductions than it is possible with diesel fuel. Therefore, from today’s perspective, the DME fuel is more likely to be used in certain niche applications, rather than provide a wide-scale alternative to liquid diesel fuels.