Preparation Of Superwetting Cellulose-based Separation Membranes And Their Application In The Treatment Of Kitchen Oily Sewage

Kitchen sewage is difficult to treat centrally because of its high oil content,complicated component and scattered sources.National policies and local implementation methods require on-site dewatering and harmless treatment of kitchen sewage.The process involving oil-water separation has become one of the most popular issues that urgently needed to be solved.Traditional oil-water separation technology has many disadvantages for dispersed household treatment and cannot meet the real needs.In essence,oil-water separation belongs to interface problem.Superhydrophilic materials show two opposite wetting behaviors to water phase and oil phase in oil-water mixture,which can efficiently separate oil-water mixture by gravity as driving force,making up for the deficiency of traditional separation technology in treating a small amount of household oily wastewater.Cellulose is widely found in plants.It is the most abundant natural biomass material with good biodegradability and chemical stability in the world.Cellulose macromolecule contains hydrophilic hydroxyl group,which is an ideal material for constructing hydrophilic separation membrane.However,it has some disadvantages such as complicated preparation process,smaller pores and poor mechanical properties in the current studies on the construction of superhydrophilic separation films based on cellulose.Therefore,this study directly uses textile-formed fabric as the separation membrane substrate and uses a simple micro-dissolution preparation process to modify the surface of the fabric to make its surface super-wettable,thus achieving efficient oil-water separation of kitchen sewage.In this paper,cellulose,which constitutes cotton fabric,was used as a hydrophilic material,then micro-and nano-scale copper hydroxide was in situ prepared to construct fabric surface microstructures to obtain super-wettable surfaces on the surfaces of cotton and polyester fabrics,respectively.These fabrics are used to achieve gravity-driven separation of insoluble oil-water mixed solutions and stable oil-water emulsions.The main work is as follows:（1）Based on the micro-dissolution effect of sodium hydroxide-urea system on the surface cellulose of cotton fabric,the surface micro-dissolution technology was combined with in-situ growth method to generate micro-nano copper hydroxide on the surface of cotton fiber.The micro-nano rough structure was constructed on the surface of the fabric,so that the cotton fabric had superhydrophilic property.The cotton fibers were swollen in the process of surface micro-dissolution.The effect of the processing time of sodium hydroxide-urea system on the structure and morphology of cotton fabric was analyzed.Meanwhile a large number of hydroxide ions were stored inside the fibers,and after impregnation with cupric sulfate solution,the microsolubilized cellulose macromolecules were solidified and copper hydroxide particles were in situ grown on the fibers’surface.The effect of cupric sulfate solution concentration on the apparent morphology of Cu（OH）₂@cotton fabrics was investigated.The wettability of Cu（OH）₂@cotton fabrics prepared by sodium hydroxide-urea system was studied.The results show that the treatment of cotton fibers with microsolubilization of sodium hydroxide/urea system for2 h is suitable for copper ion loading;when the concentration of copper sulfate in the cellulose solidification bath is 10 w%,it is conducive to the formation of uniform copper hydroxide protruding rough structures and the preparation of superwettable separation membrane materials.The preparation technique is mature,but it requires a longer micro-dissolution treatment of cotton fabric at low temperature,the required amount of copper sulfate is large,the reaction takes place simultaneously on the fiber and in the solution,the controllability of the two-phase reaction is relatively poor,and the copper sulfate particles are easy to form a platelet state on the fiber surface,which affects the construction of micro-and nanostructures and is not conducive to the generation of superwettable cellulose-based membrane materials.（2）To deal with the problems that the sodium hydroxide/urea system for the preparation of Cu（OH）₂@cotton fabric requires a long time at low temperature to form the microdissolution phenomenon and the large concentration of copper sulfate required in the solidification bath,the copper ethylenediamine complex was used as the micro-dissolving agent for cotton fabrics.After surface micro-dissolving cotton fabrics,the copper ethylenediamine complex and copper sulfate were hydrolyzed to solidify cellulose macromolecules,and copper hydroxide particles were deposited on the surface of cotton fibers.The copper ions inside and outside the fiber are involved in the growth of copper hydroxide particles on the surface of cotton fabric,which improves the reaction environment for the in-situ synthesis of micro-nano copper hydroxide on the cotton fibers,and is conducive to the formation of micro-rough surface structures.The effect of copper ethylenediamine complex concentration on the structure of cotton fabrics was analyzed by controlling the reaction conditions.In cupric sulfate solution,copper hydroxide micro-nano particles were grown in-situ on the fiber surface.The effect of concentration of cupric sulfate solution on the apparent morphology of copper hydroxide on the fabrics was investigated.The wettability of Cu（OH）₂@cotton fabrics prepared by copper ethylenediamine complex was studied.The results show that the concentration of copper ethylenediamine complex at 0.25 mol L^-1 is suitable for copper ion loading;when the concentration of copper sulfate in the cellulose solidification bath is 1 w%,it is favorable for the formation of uniform copper hydroxide protruding rough structures and the preparation of superwettable cotton fabrics.The use of copper ethylenediamine solution as a microsolubilizer treatment of cotton fabrics is carried out at room temperature,and the dose of copper sulfate required to generate copper hydroxide particles on the fabric surface is only 1/10 of that required to microsolubilize cotton fabrics in the sodium hydroxide/urea system,which is much more efficient.However,the reaction is still carried out simultaneously on the fiber and in the solution,and a large number of two-phase reactions also bring about the problems of poor controllability and easy slabbing of copper hydroxide particles on the fabric surface.（3）To address the problem of poorly uniformity of the two-phase reaction in the preparation of Cu（OH）₂@cotton fabric by microsolvation of copper ethylenediamine complexes,cotton fabric was treated by surface micro-dissolution of copper ammonia complex.When the surface of cotton fibers was partially dissolved,a large number of copper ammonia complex existed between cellulose macromolecules,and the copper ammonia complex was separated by cellulose macromolecules.Through heating,ammonia volatilizes rapidly,copper ammonia complex and cellulose copper ammonia complex becomes unstable,reverse reaction occurs,copper hydroxide precipitation is generated.At the same time,cellulose macromolecules lose coordination bonds and resolidify,which helps to adhere to copper hydroxide particles.Due to the isolation of cellulose macromolecules,agglomeration of copper hydroxide is not easy to be formed,which is conducive to the controllable rough structure of the surface of cotton fabric.The results suggest that no agglomeration of copper hydroxide particles on the cotton fabric surface occurrs after the treatment of different concentrations of copper-ammonia complex solutions,and the best morphology of copper hydroxide particles on the cotton fiber surface is achieved at a copper-ammonia complex concentration of 0.04 mol L^-1,forming a uniform copper hydroxide protrusion rough structure,which is favorable for the preparation of superwettable cotton fabrics.The preparation of Cu（OH）₂@cotton fabric using copper-ammonia complex can be carried out at room temperature with shorter reaction time,and the reaction is a confined reaction within the fiber due to the rapid volatilization of ammonia,which is much more controllable and does not form platelets on the fiber surface,which is beneficial to the preparation of superwettable cellulose-based film materials.（4）The copper ammonia complex can dissolve cellulose,and the cellulose-copper ammonia complex solution not only contains hydrophilic cellulose,but also contains copper ions,which can provide the material basis for constructing superwettability surface.Therefore,cellulose-copper ammonia complex solution is used in this chapter to coat polyester fabric.By heating,copper hydroxide micro-nano particles are formed and cellulose solidifies on the surface of the polyester fiber.The polyester fabrics were modified by the solution of cellulose-copper ammonia complex,which not only provided abundant hydrophilic groups（hydroxyl）on the surface of cellulose,but also modified the microstructure of the surface by the copper hydroxide particles.The superwettability of polyester surface could be achieved in single step.The effect of concentration of cellulose-cupramine solution on the structures and surface wettability of cotton fabrics was analyzed.It is found that the cellulose-copper ammonia complex can produce hydrophilic groups on the surface of polyester fabric by simple dipping and drying,and it has little effect on the thermal properties of polyester fiber;when the concentration of cellulose-copper ammonia complex is 10 g L^-1,it is favorable to form a uniformly distributed protruding rough structure on the surface of polyester fabric,which is conducive to the construction of super-wettable surface.（5）The self-made gravity driven oil-water separation device was used to separate different types of oil-water mixtures by using superhydrophilic materials prepared in Chapter four and Chapter five.The oil-water separation ability of the membrane was characterized by calculating the separation efficiency and water flux,and the influence of the number of cycles on the continuous separation performance was analyzed.By observing the optical microscopic images of emulsified oil before and after separation,the separation ability of oil-water emissions by membrane material was studied.The composition of kitchen sewage is complicated,which not only contains oil,but also may contain a lot of salts,acids or alkali and other substances,which will contaminate or corrode the membrane materials during the separation process,and has certain requirements for the environmental stability of the membrane materials.To solve this problem,the effect of salt,acid and alkali environment on separation performances was simulated and studied.The results demonstrate that the Cu（OH）₂@cotton fabric modified by copper-ammonia complex solution and the polyester fabric modified by cellulose-copper-ammonia complex solution can successfully separate light oil-water mixtures and oil-in-water type emulsions with separation rates above 99.0%,and are stable to salt,acid and alkali environments.This simple and low-cost preparation of superwettable membrane material can efficiently achieve oil-water separation under gravity drive and is expected to be used for practical oil-water separation of household food waste oily sewage.（6）The inter-fiber and inter-yarn gaps in the fabric structure are regarded as capillary pore channels,and a mathematical model is established based on the capillary effect mechanics theory to analyze the physical quantities related to the process of oil-water mixture separation by superhydrophilic membranes,and to discuss the mechanism of superhydrophobicity and oil-water separation by superhydrophilic membranes underwater.It is shown that the superhydrophilic solid surface is theoretically and necessarily superoleophobic underwater.The fluid penetration flux T is positively related to the square root of the ratio of surface tensionγand viscosityηof the fluid;the larger the capillary radius R,the larger the flux T;with the extension of the separation time t,the flux T will have a decrease.However,if the capillary radius R is too large,the penetration height h_o of oil will tend to zero,and then the separation membrane cannot retain the oil droplets.The capillary mechanics analysis explains that the superhydrophilic membrane has the theoretical basis for gravity-driven realization of oil-water separation.