How hydrocarbons are extracted

State of science and technology

Rapeseed processing in Europe currently takes place in classic oil mills and consists of pressing and re-extraction of the press cake with hexane in order to increase the oil yield. Rapeseed oil is the value-determining product. The technologies that have been optimized over the past decades enable maximum yields. The rapeseed meal or the rapeseed press cake are marketed as a by-product as conventional animal feed. Bioactive and valuable ingredients contained in rapeseed, such as sinapine, phytic acid and tocopherol, are not used, as these cannot be obtained mildly with the classic method. On this basis, there is hardly any potential for increasing the added value in conventional oil mills. However, the technological development of rapeseed peeling in recent years has created the basis for minimizing the proportion of anti-nutritional compounds and fiber components in the rapeseed kernels so that the quality of the oil and rapeseed meal can be increased and, in the end, a higher quality rapeseed kernel concentrate is available on the market can be brought.

Cell disruption and direct extraction in the new process

In addition to pressing the seeds, conventional extraction takes place via solvent extraction with hexane. The presence of crude fiber and dietary fiber is essential for the use of pressing processes. These are necessary for the product transport and for maintaining the pressure in the press. However, if peeled seeds (i.e. with reduced fiber content) are processed, the use of pressing processes is not possible. In this case, the oil must be extracted exclusively by means of solvent extraction, the so-called direct extraction.

In the conventional process for extraction with hydrocarbons, such as hexane, undesired accompanying substances are also extracted, which increase the cost of oil refining. On the other hand, the hydrocarbons used up to now are not suitable for extracting specific valuable ingredients from the seed.

In contrast, alcohols can be used to eliminate anti-nutritional substances from rapeseed. In addition, it is possible to use alcohols to extract oil from the rapeseed with simultaneous elimination of anti-nutritional substances in one process step. Methanol, ethanol and isopropanol in particular have proven to be suitable alcohols. In contrast to ethanol and isopropanol, damage to health cannot be ruled out if the methanol is used on an industrial scale, so that it is unsuitable as a solvent in oilseed processing. In comparison, isopropanol shows better oil-dissolving power, which is still favorable even with a relatively high water content (10 ... 15%). Ethanol, however, has the decisive property for rapeseed processing of better dissolving power for the anti-nutritional substances and other valuable plant constituents.

The husking of rapeseed before the ethanolic extraction

By peeling rapeseed before further processing, the proportion of anti-nutritional substances and fiber components can be minimized, so that the quality of the products can be increased. Conventional pressing processes of the classic oil mills cannot be used on the peeled rapeseed with a correspondingly low proportion of residual husk, as the fiber content in the material to be processed is too low. According to the current state of the art, the process of peeling rapeseed consists of the steps of breaking open the seed and then separating the husks from the rapeseed kernels in air currents. Industrial plants for peeling rapeseed will have capacities of up to 1,000 t / d and higher. Thus, there is an obvious need for development for industrial implementation. The aim must be to use the results that have already been achieved on a small scale in order to develop a continuous process with the appropriate system technology, which will have an output of around one tonne per day in the pilot system and higher. This performance class allows product handling and is also scalable in order to obtain the necessary knowledge for the design of a practical system.

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