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Diesel from waste.

The route for diesel synthesis could also run parallel to fairly established mode of making ethanol from garbage. Most of the urban waste comprises a bulk of cellulose which is the woody part of trees. Cellulose is a complex sugar which cooked with acids is broken into a mixture of sugars. These sugars are then brewed into ethanol. This alcohol is already being added into transport fuels in Brazil, France, the USA and some other countries. It can also be used as substitute for petroleum to prepare thousands of chemicals.

Imagine truck loads of trash of used paper, tyres and other organic waste entering a sprawling complex of chambers and two separate sets of pipes leaving the site carrying diesel to the filling stations and ethanol feed stocks to other chemical industries. The scenario seems a fantasy about an elusive dream of recycling urban waste for the requirements of a self-sustaining society. But the chemists endeavouring to convert the urban waste have almost made it come true and pilot plants to evaluate its entire feasibility and implications are almost being built. At the heart of this recycling bonanza lies the efficiency to convert garbage into methane and a series of new catalysts that can transform the resulting methane into diesel, a mixture of hydrocarbons or ethanol.

The practice of converting garbage into methane is certainly not new. Even in the rural areas of a country like Pakistan, there has been much, albeit abortive planning to promote its production from garbage. It is a principal component of natural gas and also formed in marshes by the action of certain bacteria. Human affair with this gas, in fact, dates back to 1000 year B.C., and history also reveals some strange ideas associated with the mysterious fires lit by the gas gushing out of marshes and faults in the oil-rich ranges. In ancient Russia, the sporadic eruptions and disappearances of these fires were considered to be the manifestations of spirits and other supernatural forces. Their swift spreading, dancing flames and sudden dying out as the gaseous flow from below ceased, awed and baffled the believers and savants alike. Then, gradual taming of these gaseous spirits by the priests sprawned new religious myths and connotations.

The priests at Baku were clever enough to tame these wild spirits to enhance their power and prestige. Supplies of gas from the surrounding Caspian shores through secret pipes were carried to their shrines to sustain a continuously burning flame, the fascinating sights of these eternal flames made pilgrims to pour in from the remotest corners of Europe, Iran and India. The folk tales about these mystic fires probably also inspired Henry Haggard Rider to set the spectacle of magic contests beside the surging columns of fire. Ayesha, the roving enchantress, in his "Return of She" probably was also a privy to the secret of these wild fires. Alexander the Great, in 331, was also surprised to see a perennial flame in issuing from earth in the suburbs of Kirkuk in present Iraq.

Methane, in coal mines, has left yet another glory trail. It caused several disasters in mines and collieries as its amounts ranging from 5-14 per cent in air turn explosive and result in the devastating fire damps.

Knowledge about the nature of gas, its behaviours and handling, however, gradually became better. Enthusiast, started to fill it in human bladders and conduct several types of experiments to explore its properties. In the late nineteenth century pipelines began to be laid for its transmission to the homes and factories and now it accounts for one-fifth of the entire fuel energy generated in the world.

It is also a major source of organic chemicals including methanol, formaldehyde, chloroform, carbon tetrachloride nitromethane, carbon black, several dyes, drugs and fertilizers. The entire production of urea in Pakistan, for instance, is based upon methane contained in natural gas. Even its purification at the wells has become a rich source of sulphur chemicals and the gaseous products condensed into cylinders and marketed as liquefied petroleum gas. The route to convert methane into various chemicals generally runs through the following steps.

The gas is burnt to obtain carbon monoxide and hydrogen. Carbon monoxide, in turn, is changed into methanol under the influence of a catalyst. Methanol itself is an important fuel and precursor to hundreds of other chemicals.

The conversion of carbon monoxide to methanol, however, requires a higher temperature and hence a large energy input. So the boffins for some time had been searching to circumvent this path to eliminate the necessity of splitting the methane molecule. Efforts for direct conversion of methane into a petroleum like mixture of hydrocarbons were being pursued in several prestigious laboratories. A report in the highly specialised research journal, the Catalytic letters recently described how methane absorbed on a calcium, nickel and potassium mixed oxide catalyst was transformed into a mixture of hydrocarbons. The reaction, compared to methanol route, was interestingly completed at a far less temperature and pressure. Yet an even more promising innovation in the chemistry of methane has been its conversion into diesel fuel.

Diesel is produced from petroleum but the gas employed for its recent synthesis was generated from the city garbage - A small factory in Colorado USA has already prepared a high quality diesel better than the currently available premium grades. The new diesel from garbage, unlike the currently popular brand, is free from sulphur. The contents of sulphur in a fuel on its combustion give out some obnoxious pollutants like sulphur dioxide. Sulphur dioxide, like carbon dioxide is responsible for acid rain. It is also involved in raising the earth's temperature, through the greenhouse effect. The new diesel similarly is also free from aromatic compounds. These compounds on entering the living systems cannot be decomposed into safer fragments and create several types of cancer and the related ailments.

Another plus for process is that it removes vast amounts of methane gas which is another culprit for the greenhouse effect. So the technique not only cuts the cost but also improves the environment by reducing the pollutants. Further, the process can be plugged into the existing technology of manufacturing transport engines and fuels.

The technology of synthesizing diesel in itself is fairly straight forward. The organic waste is first changed into methane through the fermentation carried out by bacteria. Methane is then split into carbon monoxide which aided by steam and an iron catalyst grows into a mixture of larger molecules contained in diesel. The step involving the splitting of methane in due course, may be dropped by the discovery of a new diesel making catalyst.

The route for diesel synthesis could also run parallel to the fairly established mode of making ethanol from garbage. Most of the urban waste comprises a bulk of cellulose which is the woody part of trees. Cellulose is a complex sugar which cooked with acids is broken into a mixture of sugars. These sugars are then brewed into ethanol. This alcohol is already being added into transport fuels in Brazil, France, the USA and some other countries. It can also be used as substitute for petroleum to prepare thousands of chemicals. But ethanol made from corn or molasses is certainly not an attractive alternative for petroleum. Corn crops and sugarcane are required for food and entail vast inputs of water, energy, fertilizers and pesticides. Garbage, on the contrary is mostly free. And if it is established as a viable supplementary source of fuel and chemicals the firms engaged in its processing, may one day tend to promote a "grow more garbage campaign".
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Copyright 1992 Gale, Cengage Learning. All rights reserved.

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Author:Ullah, Habib
Publication:Economic Review
Date:Feb 1, 1992
Words:1267
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