Citrus oil producer uses vacuum distillation

Italian company Capua 1880 uses dry screw vacuum technology from Busch Vacuum Pumps and Systems to produce high-quality essential oils from citrus fruits for use in food flavouring and perfumes.

Capua 1880 is the world’s largest producer of natural essences from bergamot, which is a cross between lemon and bitter orange. The company has two production plants located in Calabria, where over 96% of the world’s production of bergamot is grown. Oils are also extracted from lemons, oranges, blood oranges and mandarins.

Between October and May, the citrus fruits are harvested and processed at Capua 1880’s Reggio Calabria plant. The essential oils containing water are extracted mechanically from the fruit skins on 12 production lines. First, the remaining solids and then the water are separated from this emulsion in the downstream multistage centrifugal separators. The raw oils extracted in this way are refined throughout the year at the Campo Calabro plant and mixed for individual customers. 5% of the bergamot essences produced in this way is used in the beverage industry for flavouring.

The raw oils extracted in the first stage are refined on a total of five distillation lines and then temporarily stored in a controlled atmosphere. Distillation of the essential raw oils must be carried out as carefully as possible so that the scents are not influenced by other ingredients in terms of fragrance or colour.

Capua 1880 uses vacuum technology from Busch Vacuum Pumps and Systems for the distillation processes, which are carried out in thin-film evaporators or short-path distillers depending on the type of fruit. All the distillers use only COBRA screw vacuum pumps that are free of operating fluids. The frequency-controlled vacuum pumps guarantee the required vacuum level which, together with the temperature, ensures the desired product quality.

The company decided to switch to dry COBRA screw vacuum technology from Busch in the late 1990s. The liquid ring vacuum pumps previously used only achieved a vacuum of 40 to 60 millibar, and a higher temperature was therefore required for evaporation. This was 80–90°C for thin-film evaporators, depending on the type of fruit.

All thin-film evaporators are now equipped with COBRA screw vacuum pumps, which maintain a higher permanent vacuum. This means the distillation processes can be carried out at ambient temperature. Varying ambient temperatures or different oils can mean that fine adjustments of the operating vacuum and the pumping speed of the vacuum pump are required. This is possible by regulating the frequency-controlled motor of the vacuum pump.

Figure 1: Short-path distiller for obtaining essential oils from citrus fruits. Source: Capua 1880.

Short-path distillers (Figure 1) operate at even lower pressures. This is why vacuum boosters, also driven by frequency-controlled motors, are installed upstream of the COBRA screw vacuum pumps. In short-path distillation, the exact operating pressures also depend on the oils to be distilled. The operating temperatures are usually slightly higher than the ambient temperature but significantly lower than when liquid ring vacuum pumps were used.

COBRA screw vacuum pumps have been specially developed for applications in which low pressures and the compression of extracted gases and vapours without operating fluids are necessary, for example, to prevent contamination between the gas or vapour with an operating fluid.

Figure 2: COBRA screw vacuum pumps run without operating fluids. Source: Busch Dienste GmbH.

Two screw-shaped rotors rotate in opposite directions (Figure 2). The extracted vapours are trapped between the cylinder and screw chambers, compressed and transported to the gas outlet. During the compression process the screw rotors do not come in contact with each other or the cylinder. Precise manufacturing and minimal clearance between the moving parts enable this operating principle and guarantee a low ultimate pressure of <0.1 mbar.

The pumps operate using water cooling, which ensures an even temperature distribution throughout the pump body and thus thermal stability in the entire process. Due to the variable pitch in the screw coils, the process gas is pre-compressed. The advantage of this is that both gas temperatures and the power consumption of the vacuum pump are reduced significantly. Generally, dry screw vacuum pumps operate at higher temperatures than liquid ring vacuum pumps. This prevents condensation of the vapours in the vacuum pump, eliminating the possibility of contamination with an operating fluid.

Figure 3: The sight glass in the foreground shows the distilled end product; in the background, the oil extracted from the fruit skins of the blood orange. Source: Busch Dienste GmbH.

The switch from liquid ring to dry screw vacuum technology has provided a number of benefits for Capua 1880. Quality impairments caused by higher temperatures during the distillation process can be eliminated completely. Distillation at low pressures, precisely adjusted to the product, allows the process to run under optimum conditions and guarantees the best results for the fragrance. This also produces a completely clear, colourless oil (Figure 3). Getting rid of the liquid ring vacuum technology means that the operating fluid water, its costs and the additional expenditure for maintenance work were also eliminated.

Top image: Bergamot during processing. Source: Capua 1880.