Worldwide oil spills and industrial oily wastewater introduce various toxic compounds to clean oil systems and thus threaten the global ecology. Compared to burning the oil, separating oily wastewater effectively should be a preferable solution to address such a global environmental issue. A highly efficient separation technique is not only advantageous for significantly decreasing environmental pollution, but also energy saving in addition to resource recycling approach. Conventionally, gravity separation, flotation techniques, filtration, oil skimmers, and centrifugation methods are utilized to separate oil/water mixtures successfully, but these technologies’ effectiveness still needs to be upgraded (e.
g. long operation time, separated liquids containing residual oil/water) besides reducing operation costs. Moreover, the traditional technologies confront enormous challenges towards oil/water emulsion separation.In recent years, advanced interface materials with superwetting property have emerged as a new research direction. Superwetting or superantiwetting surfaces are particularly attractive in oil/water separation.
Special wettability oriented water/oil separation materials are generally known as superhydrophobic/superoleophilic “oil-removing” or superhydrophilic/superoleophobic “water-removing” materials. Because of the good reusability and high separating efficiency, the wettability regulated separation display great benefits over conventional separation approaches, which has a promising perspective in oil clean up area including water/oil emulsion. Principally, application of polymeric membranes for oily wastewater treatment affords plentiful advantages such as work ability, relatively low operation cost, stable quality of permeate and lesser space condition as well.
The objective of this thesis, is to fabricate a complex membranes for oil-water separation by using two techniques: (1) Chemical bath deposition (CBD) of methylcellulose/poly(acrylic acid) complex membrane on the surface of stainless steel mesh. (2) Layer by layer method for hydroxyethyl cellulose/poly(acrylic acid) complex membrane on the surface of poly ethylene terephthalate (PET) non-woven fabric.In the first part, membranes for oil-water separation are fabricated by forming a reusable and stable layer with methylcellulose (MC) and poly(acrylic acid) (PAA) on stainless-steel mesh (SSM) via chemical bath deposition method. It is anticipated that the interaction between the carboxyl group (-COOH) in PAA and the hydroxyl group (-OH) in MC through hydrogen bonding will result in the formation of PAA/MC complex membranes. The MC/PAA membrane is then modified by trichloromethanesilane (TCMS) to obtain the hydrophobicity and oleophilicity.
This design can adequately repel water and allow oil to penetrate through the membrane freely, thus achieving oil selectivity with a high flux of more than 1055 L m-2 h-1 for sunflower oil, and excellent separation efficiency of 99.9%. This easy and simple methodology with low cost for fabricating oil-water separators has great potential to be widely used in the fields of oil and petroleum industries.In the second part, a versatile and simple pathway to separate oil from water-in-oil emulsion is reported using a low-cost and green material to achieve a highly efficient membrane. Hierarchical structure of Hydroxyethyl cellulose “HEC” and poly(acrylic acid) PAA complex membranes on the surface of PET nonwoven fabric was prepared via layer by layer “LbL” assembled method. The as-prepared HEC/PAA modified through thermal treatment and modified chemically.
The structure and the behaviors of HEC/PAA-PET before and after surfaces crosslinked were deeply characterized. The modified HEC/PAA-PET applied to be an oil filter from numerous water-in-oil emulsions concentrations. The as-prepared membranes showed an excellent separation efficiency of more than 99.9% for various water-in-oil emulsions.
Therefore, we have successfully fabricated a polymer complex membranes on SSM and PET non-woven fabric surfaces with MC, HEC and PAA via chemical bath deposition and layer by layer procedures, respectively. They were then then modified to obtain a high hydrophobicity behavior. The modified MC/PAA-SSM membrane effectively separated oil from various oil/organic solvents mixture with water.
On the other hand, the modified HEC/PAA-PET efficiently separated oil from a series of water-in-oil emulsions.