China: 3D Printing Customized Meshes for Separating Oil and Water

(a) Typical schematic illustration of the fused deposition modeling (FDM) 3D printing process. (b) Design of 3D printing orthogonal mesh with parameter of diameter, layers, and spacing. (c,d) Optical and SEM photographs of Fe/PLA composites mesh with through hole.

Researchers from China are trying to refine mesh fabrication for exercises such as separating oil from water, with their recent findings published in ‘3D Printing of an Oil/Water Mixture Separator with In Situ Demulsification and Separation.’ The authors state that there are many different types of ‘promising candidates’ to act as progressive oil/water separators. A truly suitable technique for creating such devices—along with matching post-processing methods—has been elusive though, although currently there are techniques for making:

• Oil skimmers
• Centrifuges
• Coalescers
• Flotation technologies

The scientists attempted to reach further though to find better tools, mainly for cleanup events in workshops, and areas where textiles, leather, and petrochemicals are produced. A 3D printed mesh could be extremely helpful in cleaning up oil spills too, some of which can be massive, spiraling out of control.Their goal was to break down oil/water combinations that have become very stable, thus making it difficult to separate them and clean up an area which may be of great size.

Previous researchers have done the work for them regarding materials, with hydrogels showing the most potential.

“The printed mesh was suspended in acrylic acid (AA) and acrylamide (AM) solution to induce PAA/AM hydrogel coating, bounding, and growing on mesh via the surface polymerization of Fe(II)-mediated redox reaction,” stated the researchers. “After being immersed in inorganic salt solution, the inorganic salt was incorporated into hydrogel coating to strengthen demulsification of oil-in-water emulsions. Due to superhydrophilic and underwater superoleophobic properties of hydrogel coating, the underwater oil contact angle of superhydrophilic and underwater superoleophobic mesh (S-USM) was over 150 °C with a low adhesion force.”

Illustration for the fabrication of S-USM. The hydrogel coating process involves polymerization of AA and AM, in which N,N′-methylenebisacrylamide (BIS) serves as a crosslinker and ammonium persulfate (APS) acts as a catalyst.

The researchers discovered that the salt-containing S-USM was effective as a separator. The team then used four different types of mixtures to further test the separation abilities:

• Dodecane-in-water
• Diesel-in-water
• Vegetable oil-in-water
• Crude oil-in-water

They used an FDM 3D printer with PLA filament to fabricate the meshes, afterward using customized equipment made in the lab—featuring one of the 3D printed meshes set in between two glass tubes. The amount of successful separation was measured by the weight ratio of the collected water and original water.

“The droplet size of oil/water mixtures before and after separation was detected by optical microscope and dynamic light scattering. In addition, further characterization for separation processes were observed in an optical microscope,” stated the researchers. “The recycle test of separation was carried out using several repeated experiments. Furthermore, the mesh was also designed into a particular spherical skimmer that succeeded in collecting floating oil.”

The researchers made two different kinds of skimmers—a spoon skinner with a spherical mesh and a straight hilt for ergonomics benefiting the user, along with a barrel skimmer also including spherical mesh and a curved hilt. Both skimmers were successful in design and use, removing oil from the water.

Floating oil removal by 3D-printed spherical oil skimmers. (a) The design of a spoon skimmer and (b) a barrel skimmer. Collecting floating oil of (c) dodecane dyed in blue on water by using spoon skimmer and (d) diesel dyed in green with barrel skimmer.

“Combining hydrogel-coated treatment with the new manufacturing technology of 3D printing, a series of specific, useful separation devices can be fabricated, bringing great convenience to personal life,” said the researchers.

The recycling separation test was very successful, sustained at 90 percent. The team stated that this showed high repeatability, with the salt-containing S-USM able to rapidly demulsificate oil and water mixes.

Optical microscopy images of oil-in-water emulsion demulsification and separation. (a–c) Showing oil demulsification and condensation process of AlCl3. (d,e) A scheme of synchronous demulsification and separation process. (f–h) Optical microscopy of separation process with water permeating through S-USM, leaving oil droplets above the mesh. (k) Optical imagines of milky emulsion on S-USM after separation.

The team was also able to enjoy one of the greater ‘highlights’ as they were able to use demulsification and separation in situ. The demulsification process occurs on the salt-containing S-USM surface, while water permeates through the mesh at the same time—leaving the oil above.

“… a key innovation was utilizing the flexible design and fabrication of 3D printing with subsequent hydrogel-coating treatment, concluded the researchers. “The spherical skimmers with hydrogel coatings were facilely created and capable of removing the floating oil. Various oil/water separators can be realized to meet future requirements and bring great convenience to personal life. In view of its simplicity, this work may pave the way for a new method using 3D printing technology, with more practical applications in the fields of separation, hydrogels, electronics, smart robots, and many others.”

You may be surprised to find that mesh is so important to researchers, but it can play a vital role not only in lab experiments, but also design, engineering, and manufacturing requirements from art installations to robotic structures and wound healing meshes.

What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

(a) The optical microscope photos of hydrogel coating growth on single Fe/PLA stick with reaction time. (b) The observation of hydrogel thickness increasing from approximately 50 to 400 μm until the pore is almost blocked, showing feasibility in controlling pore size.