Multistage Pilot Plant for the extraction of hemicellulose with subcritical water

Hemicellulose is a natural polymer, made up of several sugars. It can be used to replace oil in many applications, like:

  • production of biofuels;
  • production of films for packaging;
  • production of gels for drug delivery;
  • production of xylitol, compound of great interest in the medical field;
  • production of furfural, which is used in the production of plastics and also in the pharmaceutical industry.
Figure 1: Multistage Pilot Plant for the extraction of hemicellulose
Figure 1: Multistage Pilot Plant for the extraction of hemicellulose

Industrial systems for extracting hemicellulose use acids or bases; with the need to purify the product and eliminate toxic waste. However, hemicellulose can be extracted with water at a temperature above 100 ° C. This has numerous economic and environmental advantages, as well as that no toxic waste is produced. The main problem is that the wet biomass swells and compacts in the system, with high difficulties in removing it at the end of the process. Existing plants using this process are usually stopped once the extraction is completed, opened to remove the biomass and replenished with fresh biomass. This involves very long downtime. For this reason it was decided to study a system that makes the extraction operation possible in a continuous way, without having to stop the plant during the loading and unloading phases. The system also allows to collect entirely the exhausted solid, critical operation in the process.

A pilot plant has been designed consisting of 5 reactors, each of which works in series with the others or can be excluded from the system. Each reactor consists of:

  • An open cylinder, constructed with a metal mesh that can be opened longitudinally.
  • Two stainless steel cylinders with the same diameter, one of which has a lower part with holes. The metal mesh is inserted between the two cylinders, forming a cartridge, which is filled with biomass.
  • An outer stainless steel cylinder closed at the upper end and with a ball valve at the lower end. The cartridge is inserted from the bottom into this system until it is fully inserted. At that time the valve closes. When the extraction is finished, the valve opens and the cartridge falls into a stopping system.

A flow of hot water enters and leaves each unit, moving to the next, extracting the hemicellulose from the biomass contained in the cartridges. Once the entire product has been extracted from a unit, it can be isolated from the system (via a valve system), and the cartridge can be removed without stopping the extraction process. At the same time, a cartridge with fresh biomass is inserted in another unit, and the hot water flow is directed towards the new cartridge to continue extracting. Until 97 % of energy is recovered in the system through a heat exchanging system.

Figure 2: Hemicellulose obtained after extraction and spry drying.
Figure 2: Hemicellulose obtained after extraction and spry drying.

Gianluca Gallina, FPI (MINECO) BES-2013-063556

Project Reference: CTQ2015-64892-R (MINECO/FEDER)

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