Formaldehyde from incomplete combustion

Formaldehyde (HGHO), the simplest aldehyde, is obtained by oxidation of methanol. It is a gas at room temperature but is often used as a 40% aqueous solution called formalin. Although formaldehyde is an important starting material for polymers, it presents a number of health hazards because of its toxicity and carcinogenicity. Formaldehyde is also an air pollutant, being produced in trace amounts in the incomplete combustion of fossil fuels. One of the concerns about methanol as a fuel (Section 12.5) is the potential for increased levels of formaldehyde in urban areas because of the production of formaldehyde from incomplete combustion of methanol. 

Unlike carbon dioxide and water that are the inevitable by products of complete combustion of hydrocarbons, species such as carbon monoxide, ethene, toluene, and formaldehyde can be emitted because combustion has been interrupted before completion. Many factors lead to emissions from incomplete combustion. Emitted unburned hydrocarbons and carbon monoxide are regulated pollutants that must be eliminated. In automobiles with spark ignited engines, these emissions are almost entirely removed by the catalytic converter. 

Formaldehyde, HCHO, is a primary and necessary constituent of the first five synthetic adhesives in the listing. It is a simple organic chemical first identified during the latter half of the 1800s. Its irritating and toxic odor and preservative properties were known from the time of its early development. It is a ubiquitous chemical, formed naturally in small quantities by every process of incomplete combustion as well as in normal biologic processes. The human body has a natural formaldehyde level of about 3 lg/g, ie, 3 parts per million (ppm) in the blood at all times. 

SHELL SAND Phenol - Formaldehyde (Novalak) Resin Particulate matter - soot from the incomplete combustion of carbon based resins Carbon oxides Phenol, cresols and xylenols Ammonia Aldehydes Benzene PAH Odom problems more prevalent - treatment may be necessary although dispersion may suffice... 

Early versions of methanol-powered automobiles and heavy-duty engines tended to suffer from noticeably odorous formaldehyde emissions. The same odor is prevalent at Indianapolis 500 races. Formaldehyde is a product of the incomplete combustion of any carbon-based fuel, so poorly designed engine systems or lack of catalytic controls can give rise to readily detectable emissions, particularly when the engines are cold. The human nose can detect extremely low concentrations of formaldehyde, which is sensed as acrid and unpleasant. 

Formaldehyde and other aldehydes are receiving increasing attention both as toxic substances and as promoters in the photochemical formation of ozone in the atmosphere. They are released into residential buildings from plywood and particle board, insulation, combustion appliances, tobacco smoke, and various consumer products. Aldehydes are released into the atmosphere in the exhaust of motor vehicles and other equipment in which hydrocarbon fuels are incompletely burned. A sensitive method for analyzing aldehydes and ketones is based on the sorption of these compounds to an SPE sorbent and their subsequent reaction with 2,4-dinitrophenylhydrazine (DNPH) on the sorbent. They are then analyzed as their hydrazones by HPLC (Fig. 7.9). A gradient analysis by HPLC may separate as many as 17 components with detection by ultraviolet (UV) light. 

In the incomplete conversion mode, the mixture entering the absorption unit is a solution of about 42 wt% formaldehyde and containing methanol. The bulk of the methanol, formaldehyde, and water exits the first stage of the unit. The mixture is fed into the distillation column, from which a bottom product containing up to 55 wt% formaldehyde and less than 1 wt% methanol is obtained. The formic acid content in this bottom product is reduced by using an anion-exchange unit. The methanol in the overhead product is recycled and mixed with the fresh feed. The off-gas from the absorption unit is combusted to remove the residual methanol and other organic species. Part of it is then recycled into the reactor as inert diluent. 

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