Waste products minimizing production

The manufacture of sugar was early understood to be an energy-intensive process. Cuba was essentially deforested to obtain the wood that fueled the evaporation of water from the cane juice. When the forests were gone, the bagasse burner was developed to use the dry cane pulp, called bagasse, for fuel. Bagasse was no longer a waste product its minimal value is the cost of its replacement as fuel. 

You should use the material balance information to identify the major sources of waste and pollution, to look for deviations from the norm in waste production, to identify areas of unexplained losses, and to pinpoint operations that contribute to flows that exceed national-, local-, or site-discharge regulations. Also, a good thing to remember is that, from a practical standpoint, process ciency is synonymous with waste minimization. 

Maximize atom economy. Synthetic methods should maximize the incorporation of all materials used in a process into the final product so that waste is minimized. 

Green chemistry (Chapter 11 Focus On) The design and implementation of chemical products and processes that reduce waste and minimize or eliminate the generation of hazardous substances. 

Catalysts accelerate reactions and thus enable industrially important reactions to be carried out efficiently under practically attainable conditions. Very often, catalytic routes can be designed such that raw materials are used efficiently and waste production is minimized. Consequently, the chemical industry is largely based upon catalysis Roughly 85-90 % of all products are made in catalytic processes, and the percentage is increasing steadily. 

However, some waste will be inevitable. While some waste represents minimal risk to the environment when emitted (such as the release to the marine environment of depleted brine in chlor-alkafi production), a fully sustainable process will (other things being equal) require aU harmful emissions to be treated to ensure zero impact on the environment. This... 

The TS-1 catalysed hydroxylation of phenol to a 1 1 mixture of catechol and hydroquinone (Fig. 2.16) was commercialized by Enichem (Romano et ai, 1990). This process offers definite advantages, such as higher selectivities at higher phenol conversions, compared to other catalytic systems. It also illustrates another interesting development the use of solid, recyclable catalysts for liquid phase (oxidation) processes to minimize waste production even further. 

The major emissions from the combustion of fuel are C02, SO, NO and particulates14. The products of combustion are best minimized by making the process efficient in its use of energy through efficient heat recovery and avoiding unnecessary thermal oxidation of waste through minimization of process waste. Flue gas emissions can be minimized at source by ... 

Also, by the very nature of chemical transformations, there are almost always unused chemicals remaining. These chemical leftovers include contaminants in the raw materials, incompletely converted raw materials, unavoidable coproducts, unselective reaction by-products, spent catalysts, and solvents. There have long been efforts to minimize the production of such waste products, and to recover and reuse those that cannot be eliminated. For those that cannot be reused, some different use has been sought, and as a last resort, efforts have been made to safely dispose of whatever remains. The same efforts apply to any leftovers from the production of the energy from the fuels produced or consumed by the processing industries. Of particular immediate and increasing concern are the potential detrimental effects of carbon dioxide emissions to the atmosphere from fossil fuel combustion, as discussed further in Chapters 9 and 10. 

Howden An early flue-gas desulfurization process using a lime or chalk slurry in wooden grid-packed towers. The calcium sulfate/sulfite waste product was intended for use in cement manufacture, but this was never commercialized. The key to the process was the use of a large excess of calcium sulfate in suspension in the scrubbing circuit, which minimized the deposition of scale on the equipment. The process was developed by Imperial Chemical Industries and James Howden Company in the 1930s and operated for several years at power stations at Fulham, London, and Tir John, South Wales, being finally abandoned during World War II. British Patents 420,539 433,039. 

Many more preparations of fine chemicals from renewables have been worked out, and even more are being developed. The following sections present several examples that catch the eye. Examples that are now an integral part of modern chemistry, with a future in which the use of chemicals that are harmful to the environment will be avoided and where novel processes will minimize the amounts of waste products. 

Thermal desorption treatment is generally considered to be an alternative to incineration. Thermal desorption operates at much lower temperatures than incineration and keeps the heating systems independent of the wastes, which minimizes off-gas production. The technology can be used as a waste minimization process, isolating and concentrating waste constituents, or as a product recovery process. Thermal desorption can also be used to separate contaminants in mixed waste streams by removing volatile constituents. 

Caution. Thallium is a toxic heavy metal, and care should be taken to minimize skin and respiratory exposure to TlPFg, and with respect to disposing of thallium waste products. 

Preservation of a habitable planet demands that we minimize waste production and responsibly dispose of waste that is generated (Box 2-1). Recycling of chemicals is practiced in industry for economic as well as ethical reasons it should be an important component of pollution control in your lab. 

Although photovoltaic conversion is nonpolluting, environmental, health, and safety aspects must be considered, especially with regard to harmful emission and waste products resulting from the production of the solar cell modules. It has been shown that, with proper encapsulation and a proactive recycling program, it should be possible to minimize environmental concerns. 

A.K. Hilaly, S.K. Sikdar, Pollution balance a new methodology for minimizing waste production in manufacturing process, J. Air Waste Manage. Assoc. 44 (1994) 1303-1308. 

Ionic liquids (ILs) tend to have good thermal stability, they exhibit liquid ranges of up to 300° C, and because they have negligible vapor pressure, they do not evaporate—all of which explains their use as replacements for volatile organic compounds. This also makes them very easy to contain and transfer, and allows their use under high vacuum conditions. Another quite important aspect is that ILs can be recycled (often with associated catalysts dissolved in them) this considerably minimizes waste production in accordance with green chemistry, and it lessens expenditure in view of the high cost of many ILs compared with that of conventional solvents. 

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