Sugarcane is the raw material for producing sugar. The sugar is one of the most important commodities in the world market. Besides cane, sugar can be obtained from the sugar beet. The sugar is extracted from these two feedstocks in the form of sucrose crystals (Figure 3.1) with high purity. The annual worldwide production of sugar was 163.3 million ton (raw value) in 2007, according to the International Sugar Organization (ISO, 2008). The world sugar consumption, in turn, was 157.7 million ton (raw value) in the same year. Main producers of sugar are Brazil, India, the European Union (EU), and China (Table 3.3). Sugar is mostly produced

FIGURE 3.1 Chemical structure of sucrose.

from sugar beets in the case of the EU countries. Brazil is the main actor in the world sugar market (first producer, third consumer, and first exporter), thus, any change in the production in this country, due to either changes in climate or the balance of ethanol production related to sugar, provokes changes in the inter­national sugar price. This situation will continue in the future considering that Brazil is expanding the area dedicated to sugarcane plantations. It is expected that about 40 and 50 new sugar mills will be put into operation by 2010 (Decision News Media SAS, 2006).

Mature cane is collected manually or mechanically. Hand cutting is the most usual method. The cane is transported to the sugar mills where the sucrose is extracted and crystallized. The first step in the production of cane sugar in mills consists in the cane juice extraction (Figure 3.2). For this, the cane is sampled, washed, weighed, and prepared using rotating knives to shred the stalks into pieces. Then, the shredded cane is ground in heavy-duty roller mills, which extract the raw juice while hot water is sprayed onto the cane bed to dissolve the sugars. The sucrose extraction yield reaches 90 to 95% in modern sugar mills. The fiber fraction of the cane, called bagasse, is generated in this step. This material is pre­dried and utilized in the same sugar mill as an energy source burning it in special

boilers to produce steam that generates electricity through turbo generators. The raw juice is clarified by adding sulfur dioxide (SO2) to oxidize color substances, destroy microorganisms, and favor the agglutination of colloids. Then, lime is added to neutralize the juice, thus avoiding, in this way, the sucrose hydrolysis into glucose and fructose (sucrose inversion). The limed juice is heated to 105 to 110°C in the clarifiers, to which flocculants also are added. Solid separation is favored because the calcium sulfite formed is insoluble and precipitates removing the suspended particles and other impurities. This precipitate (known as mud) is mixed with flocculants, lime, and small amounts of the light fraction of bagasse, separated from the juice, and sent to vacuum rotary filters where the filter cake is recovered. The filter cake (press mud) is a fibrous material that can be used for animal feed or composted to produce manure. Part of the clarified juice can be used for ethanol production. In the evaporation step, the clarified juice is con­centrated by removing up to 75% of the water in multiple-effect evaporators. The removed water is used in other process steps either as steam or as condensate. The concentrated juice or syrup contains 58 to 62% solids (about 60° Brix).

The obtained syrup is treated with direct steam to reduce its viscosity. Then, the syrup is clarified by adding SO2, phosphoric acid, and lime. After this treat­ment, the syrup is sent to a flotation tank where it is clarified. This clarified syrup can be used for ethanol production. In the next step or pan stage, the sucrose con­tained in the syrup is crystallized by removing excess water with vacuum evapo­rators called pans. In order to increase the speed of this process, the pan stage operates in a manner that utilizes seed crystals and a combination of products
with varying levels of sugar content to produce a range of crystal sizes and, hence, qualities. The crystals are separated from the mother liquor in centrifuges. After three evaporation/centrifugation stages, crystals of raw sugar and the residual mother liquor (called C-molasses) are obtained. The molasses is one of the most employed feedstocks, not only for ethanol production, but also for producing a wide range of microbiological products. The sucrose crystals are dried in rotary drum driers where the commercial raw sugar is obtained. To produce refined sugar, the raw sugar is redissolved in clean water and treated with phosphoric acid and saccharate to remove the remaining impurities. The clarified solution is treated with activated carbon to remove colors and then filtered. Finally, this mass is evaporated and crystallized in vacuum pans. The refined crystals are washed with steam and hot water, air-dried, classified according to crystal size, and stored.