Sugar: Fuel for the future

Press, 28 February 1986, Page 12

Sugar: Fuel for the future

By

PETER DE GROOT

Rising oil stocks and falling prices make it unfashionable at present to talk of an energy crisis. But for many developing countries suffering from high inflation, the cost of oil has escalated dramatically, soaking up hard-earned foreign exchange. Consequently, the search for alternative energy supplies is on in earnest in many parts of the world.

One of the largest and best known programmes is in Brazil, which now has around two million vehicles powered entirely by alcohol made from the juice of sugar cane. The country’s remaining eight million or so vehicles are run on a 20 per cent alcohol/petrol blend. The alcohol (ethanol) is made by fermenting the cane juice using yeast, in a process that mimics that of the home brew beer or wine kit. The alcohol is then extracted, purified and has most of the water removed.

The production of biomass energy (the ugly term used to describe energy derived from plant and animal matter) has become big business in Brazil, which last year produced 10.7 billion litres of fuel alcohol. It is estimated that by the turn of the century the country will have between 11 and 14 million vehicles fuelled by agricultur-ally-produced alcohol. But for sugar cane, its new role as a source of energy is only just beginning. The most abundant source of “free” energy is the sun; and plants, by means of photosynthesis (made possible by the green pigment, chlorophyll, found in their leaves), are the best converters of solar radiation into energy-rich materials.

The tropical grasses, a group that Includes sugar cane, are

among the most efficient photosynthesizers. Modern sugar cane varieties are the result of the wilful selection of those plants producing the most sucrose, since even primitive man and woman apparently enjoyed a sweet chew. So important was this need to satisfy our sweet tooth that around 150 years ago “King Sugar,” then the most lucrative commodity on the world market, determined the lives of many thousands of labourers and made the fortunes of a few.

But these days with the increase in use of artificial sweeteners and the dumping by the West of large surpluses of home-produced sugar on to the world market, the price of sugar has dropped so low that it often does not cover the cost of manufacture. Many sugar-producing countries, therefore, are on the verge of bankruptcy. It was to rid itself of excess sugar that Brazil embarked on its programme of converting sugar into alcohol. It was not until the spectacular oil price increases of the early Seventies that the replacement of imported oil became a priority. Other countries have followed. Zimbabwe, for example, produces 40 million litres of alcohol from homeproduced sugar cane, which is blended in a 12 per cent mixture with petrol and saves some $l5 million each year on the fuel import bill. It may come as a surprise to learn that sugar production is not what sugar cane does best. Until now selection has concentrated on those varieties that store the largest amount of “free sugar”

(sugar not bound to or incorporated into the plant tissue) which can be extracted by simply crushing the stem. The extracted juice is the basis for sugar, and now alcohol, production; The fibrous waste that is left after the milling process is traditionally kept to a minimum. These practices have, however, prevented sugar cane from realising its full potential as an energy crop. The fibrous waste (known as bagasse) is composed of cellulose, hemicellose and lignin. They are the universal building blocks of the plant world and have been the source of food, shelter, clothing and building material from our earliest history. They are known collectively as lignocellulose, and making lignocellulose is what sugar cane does best. Bagasse has around 70 per cent of the heat value of wood and can be burnt to provide energy to power the sugar mill. Many sugar factories throughout the world now produce all their own energy from burning sugar cane bagasse. In some countries, for example Mauritius, Hawaii and South Africa, the sugar industry “exports” energy in the form of electricity to the national grid. Mauritius derives around 10 per cent of its electricity from sugar factories. Several research groups, notably in Puerto Rico and at the Louisiana State University, are working on ways of capitalising on this potential to obtain energy from the plant tissue itself — or biomass. The results have been staggering. The selective breeding of vigorously growing varie-

ties has produced new types of sugar cane which have several stems, produce a more luxurious leaf canopy and grow to more than 3.6 metres. These distinctive new varieties have been dubbed “energy cane.” Ordinary sugar cane will yield 60 to 100 tonnes of green biomass per hectare each year, but energy cane will give an of 315 tonnes per hectare per year — equal to the highest yield of any plant recorded. Furthermore, it is predicted that it will be possible to reach annual yields of up to 380 tonnes per hectare. Energy cane yields less sugar on a weight basis than traditional sugar cane (8 per cent, against sugar cane’s 14 per cent). But the phenomenal growth rate of the energy cane means that the amount of sugar that can be obtained from a hectare of energy cane js at least as much as that from sugar cane. The important point for the growers is that because of the three-fold increase in bagasse, energy cane produces in total around three times the energy of a sugar cane crop. In the short term energy cane bagasse will continue to be used as a boiler fuel. Its heating value increases as it is dried, and once the technology for compression into pellets or briquettes (for easier storage and transportation) is perfected, it will become a substitute fuel for wood and charcoal.

But bagasse can also be used in the manufacture of paper and card, and to make construction materials such as hardboard and chipboard.

The sugar will still be used for traditional purposes (as a sweetener and, for example, in Puerto Rico for making rum).

But for many countries that already possess the expertise and the machinery for growing and processing sugar cane, the possibility of "growing their own fuel” will become Increasingly attractive. Even if fuel is not of prime importance, there is always the option to export the fermentable syrups to countries with energy deficits. But ethanol could also become the basis of a chemical industry (an option under serious consideration in Brazil), bringing energy cane into activities never before associated with sugar. From ethanol it is possible to .generate ethylene, and from there it seems that the sky is the limit. The manufacture of ethylene is one of the most fundamental operations in the chemical industry as it is the starting point for many materials essential to modern life: plastics (polyethylene, polystyrene, PVC) and polyester fibres; anti-freeze and paints; industrial solvents and synthetic rubber; even cigarette filters. All can be made from ethylene via ethanol. Perhaps the most exciting (and important) prospect is that in the longer term, the bagasse will become a substitute for natural gas, coal and oil in the “petrochemical” industry. These fossil fuels are at present used to produce synthesis gas (a mixture of hydrogen and carbon monoxide), which is the first step in the manufacture of industrial ethanol, ethylene and other petrochemicals. Synthesis gas. manufactured from biomass will probably become increasingly important in the next century as supplies of natural gas begin to dwindle and energy cane looks like becoming one of the most productive sources of biomass. King Sugar may be dead, but citizen cane is alive and well and has a rosy future.