DescriptionAgriculture-based biorefineries utilizing e.g. corn and wheat as raw materials are already today a reality and membranes as high selectivity and low energy consumption separation technologies are established in these biorefinery concept.
The aim of this presentation is given a state-of-art overview on realized and potential applications of membrane process in agriculture biomass biorefineries using a wheat-based biorefinery for bioethanol as an application study. The presentation will refer to the key production areas in the wheat-based biorefinery: starch extraction, starch conversion to sweetener, fermentation, downstream processing and stillage handling plus wastewater treatment.
The first step in wheat-based biorefineries is extraction of the starch from the wheat. For this the wheat flour is mixed with water and then separated by a 3-phase decanter resulting in an A-starch fraction, a gluten and B-starch fraction, and a fraction consisting of solubles and pentosanes. In order to optimize the water consumption it is possible to apply ultrafiltration (UF) for concentrating the solubles and pentosanes and recovering water for recycling in the process. The overall water balance for the starch extraction can be improved by using this concept.
An important step in the subsequent conversion of starch to sweeteners is the removal of the mud fraction after liquification and saccarfication. A combination of UF with a decanter can be used as an alternative to rotary vacuum filters achieving higher purities and a mud fraction which is not contaminated with filter aid kieselguhr and can therefore be added directly in the bioethanol production. Hence, the closed process avoids potentially hazardous filter aids and results in a value-added by-product.
After the polishing, the sweetener can be concentrated by evaporator before further utilization. The evaporator condensate can be upgraded for recycling by nanofiltration (NF) / reverse osmosis (RO) by removing up 90% of the chemical oxygen demand (COD).
In the classic process, the sweeteners can then be used in the bioethanol fermentation which is often still batch-wise followed by distillation in the mash and rectification column and final bioethanol concentration with molecular sieves.
Alternatively, continuous fermentation combined microfiltration (MF)/UF, either submerged or as side-stream, can be applied to separate the bioethanol directly from the fermentation broth. In this way, the production can be moved from batch to continuous thus preventing product inhibitions. Furthermore, combining this step with hydrophobic pervaporation can increase the bioethanol concentration so that the mash column of the distillation step can be eliminated and allow the recycle of sugars removed together with the bioethanol from the fermenter. Additionally, the molecular sieves can be replaced hydrophilic pervaporation or vapor permeation to sequential process which requires regeneration to continuous process.
Further, the stillage from the mash column can be handle with the help of membrane technology. In case of distiller’s dried grain solubles (DDGS) production, MF/UF can be applied to concentrate the stillage decanter centrate before evaporation. Furthermore, the permeate from the decanter centrate concentration combined with the evaporator condensate from the thin stillage concentration by evaporation can be treated by RO to achieve a permeate with water quality suitable for recycling and a concentrated retentate stream for wastewater treatment. Alternative, the stillage can be treated anaerobic digestion to produce biogas. Before the digester the stillage can be pre-concentrated by MF/UF to reduce plant size and increase plant efficiency.
Finally, the concept of the membrane bioreactor can be also utilized in biorefinery wastewater treatment plant.
Overall, this presentation will show that membrane processes have a great potential in current and future agriculture-based biorefineries.
|Period||2017 Jun 26 → 2017 Jun 30|
|Event title||34th EMS Summer School: Membranes in Biorefineries|
|Degree of Recognition||International|
UKÄ subject classification
- Chemical Engineering
- Membrane applications