Malodor

Of the general formula, R - S — H, where R represents an aliphatic or cyclic radical, the thiols —also known as mercaptans— are acidic in behavior owing to their S—H functional group they are corrosive and malodorous. Their concentration in crude oils is very low if not zero, but they are created from other sulfur compounds during refining operations and show up in the light cuts, as illustrated in Table 8.6. 

These compounds can be malodorous as in the case of quinoline, or they can have a plecisant odor as does indole. They decompose on heating to give organic bases or ammonia that reduce the acidity of refining catalysts in conversion units such as reformers or crackers, and initiate gum formation in distillates (kerosene, gas oil). 

Malic acid [97-d7-d] Malnutrition Malodor evaluation Malolacticfermentation Malonate [1797-75-7] Malonate esters Malonates... 

Fatty acids are susceptible to oxidative attack and cleavage of the fatty acid chain. As oxidation proceeds, the shorter-chain fatty acids break off and produce progressively higher levels of malodorous material. This condition is known as rancidity. Another source of rancidity in fatty foods is the enzymatic hydrolysis of the fatty acid from the glycerol. The effect of this reaction on nutritional aspects of foods is poorly understood andhttie research has been done in the area. 

Toxic or malodorous pollutants can be removed from industrial gas streams by reaction with hydrogen peroxide (174,175). Many Hquid-phase methods have been patented for the removal of NO gases (138,142,174,176—178), sulfur dioxide, reduced sulfur compounds, amines (154,171,172), and phenols (169). Other effluent treatments include the reduction of biological oxygen demand (BOD) and COD, color, odor (142,179,180), and chlorine concentration. 

Industry has standardized procedures for the quantitative sensory assessment of the perceived olfactory intensity of indoor malodors and their relationship to the deodorant efficacy of air freshener products. Synthetic malodors are used for these evaluation purposes. These malodors should be hedonicaHy associated to the "real" malodor, and must be readily available and of consistent odor quaUty. These malodors should be tested in various concentrations and be representative of intensities experienced under normal domestic conditions. 

Panehsts are trained to evaluate malodor intensity and the degree of modification. It is important that the paneflst be able to smell through any extraneous odor(s), such as the fragrance of the product, to evaluate the efficacy of products making elimination or neutralization claims, as opposed to the phenomenon of masking. 

Specific scales may be used to rate the perception of intensity of (/) the malodor, and (2) the malodor along with an odorous material designed to modify the malodor. Rating scales may consist of numerical assignments to words, eg, from 0 = no odor to 10 = very strong odor. These same type of scales maybe used to describe both the hedonic acceptabiUty of the net result, ie, from 0 = very unpleasant to 10 = extremely pleasant, and the degree of modification, ie, from 0 = does not modify to 10 = complete elimination or cover-up. 

Protocols allow for at least two vessels to test both the untreated control malodor and the treated malodor(s). The untreated control malodor is used as a reference point for the maximum malodor score. When panehsts evaluate each of the two or more vessels, they must wait a period of time (usually 30—60 s) for recovery from adaptation before smelling the next vessel. This step is always repeated between each evaluation. 

Liquid Fabric Softeners. The principal functions of fabric softeners are to minimize the problem of static electricity and to keep fabrics soft (see Antistatic agents). In these laundry additives, the fragrance must reinforce the sense of softness that is the desired result of their use. Most fabric softeners have a pH of about 3.5, which limits the materials that can be used in the fragrances. For example, acetals cannot be used because they break down and cause malodor problems in addition, there is the likelihood of discoloration from Schiff bases, oakmoss extracts, and some specialty chemicals. Testing of fragrance materials in product bases should take place under accelerated aging conditions (eg, 40°C in plastic bottles) to check for odor stabiUty and discoloration. 

Initial evaluations of chemicals produced for screening are performed by smelling them from paper blotters. However, more information is necessary given the time and expense required to commercialize a new chemical. No matter how pleasant or desirable a potential odorant appears to be, its performance must be studied and compared with available ingredients in experimental fragrances. A material may fail to Hve up to the promise of its initial odor evaluation for a number of reasons. It is not at all uncommon to have a chemical disappear in a formulation or skew the overall odor in an undesirable way. Some materials are found to be hard to work with in that their odors stick out and caimot be blended weU. Because perfumery is an individuaHstic art, it is important to have more than one perfumer work with a material of interest and to have it tried in several different fragrance types. Aroma chemicals must be stable in use if their desirable odor properties are to reach the consumer. Therefore, testing in functional product appHcations is an important part of the evaluation process. Other properties that can be important for new aroma chemicals are substantivity on skin and cloth, and the abiHty to mask certain malodors. 

In addition to generating malodorous sulfur dioxide [7446-09-5], the acetone formed can undergo further condensation in the acidic medium to generate mesityl oxide [141-79-7], (CH2)2C=CHCOCH2, and higher products. 

Physical Properties. Thiophosgene [463-71-8] (thiocarbonyl chloride), CSCI2, is a malodorous, red-yeUow Hquid (bp 73.5°C, ( 20 1.5442). It is only slightly soluble with decomposition in water, but it is soluble in ether and various organic solvents. 

Reduction and Hydrodesulfurization. Reduction of thiophene to 2,3- and 2,5-dihydrothiophene and ultimately tetrahydrothiophene can be achieved by treatment with sodium metal—alcohol or ammonia. Hydrogen with Pd, Co, Mo, and Rh catalysts also reduces thiophene to tetrahydrothiophene [110-01-0] a malodorous material used as a gas odorant. 

The addition of therapeutic or cosmetic agents to dentifrices has paralleled advances in knowledge about factors affecting the human dentition. Agents added to dentifrices can act directly on the host tooth stmcture or on specific oral accumulations, for example, the principal action of fluoride is on the tooth enamel. The primary action of an abrasive, however, is on an accumulated stained pellicle. Oral accumulations of interest to preventive dentistry are dental pellicles, dental plaque, dental calculus (tartar), microbial populations responsible for oral malodor, and oral debris (food residues, leukocytes, etc). Plaque is most important because of its potential to do harm. 

Flares are mostly used for the disposal of hydrocarbons. Waste gases composed of natural gas, propane, ethylene, propylene, butadiene, and butane probably constitute over 95 percent of the material flared. Flares have been used successfully to control malodorous gases such as mercaptans and amines, but care must be taken when flaring these gases. Unless the flare is very efficient and gives good combustion, obnoxious fumes can escape unburned and cause a nuisance. 

Gaviion Because of the presence of malodorous by-products, it is recommended that the extraction and distillation be conducted in a well-ventilated hood. 

Colourless malodorous liquids that are spontaneously flammable in air and react violently with water... 

Elevated Flares See Flares for a general definition. The elevated flare, by the use of steam injection and effective tip design, operates as a smokeless combustion device. Flaring generally is of low luminosity up to about 20 % of maximum flaring load. Steam injection tends to introduce a source of noise to the operation, and a compromise between smoke elimination and noise is usually necessary. When adequately elevated (by means of a stack) this type of flare displays the best dispersion characteristics for malodorous and toxic combustion products. Visual and noise pollution often creates nuisance problems. Capital and operating costs tend to be high, and an appreciable plant area can be rendered unavailable for plant operations and equipment because of excessive radiant heat. 

PR valves discharging vapors which do not fall into the above categories but which would be significant contributors to atmospheric pollution. Such releases should not normally be used to size the closed system but should be tied in up to the limit of its capacity. The order of preference for tying in is (1) malodorous vapors, (2) unsaturated hydrocarbons, (3) saturated hydrocarbons. If local requirements do not permit such atmospheric discharges, it will be... 

General choice for total flare load, or as overcapacity flare In coniunction with multi)et flare. Generally the only acceptable flare where producu of combustion or partial combustion are toxic or malodorous. 

Suitable oitly for clean bunting gases, i.e. where products of combustion are not toxic or malodorous. 

Pollution Limitations - (i.e., smoke formation, malodorous or toxic combustion products, noise) which may be based on statutory and/or public relations requirements. 

In general, mercaptans are more malodorous than sulfides and hydrogen sulfide. The presence of significant amounts of sulfur can induce catalyst poisoning during the refining of crude oil. 

Industrial process contamination results in Cross-contamination Malodors and discoloration Sticky films and varnishes Stable foams Chemical incompatability Impingement corrosion Fluctuating pH/acid corrosion... 

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