Researchers in South Korea and the United States have reported a membrane that separates crude oil at room temperature, and the mechanism that makes it work is the one the filtration industry spends its money trying to prevent.
The work was led by KAIST, the Korea Advanced Institute of Science and Technology, in collaboration with Georgia Tech, and published in Nature under the title "Crude oil fractionation by means of mesoporous polyacrylonitrile membranes". KAIST issued the accompanying release.
The problem it addresses is a large one. Conventional refining separates crude by distillation, heating the oil above 350 degrees Celsius. Distillation worldwide consumes roughly 1,100 terawatt hours a year, about the output of 130 one-gigawatt nuclear plants.
The membrane itself is unglamorous: a bare, uncoated porous polyacrylonitrile film, a low-cost polymer already used as a support layer in industrial filtration. It has no precision-engineered separating coat.
What happens in use is that heavier hydrocarbons accumulate on the inner walls of the pores, narrowing the openings until they become channels less than 2 nanometres across. Lighter fractions, including naphtha, gasoline and kerosene, pass through quickly; heavier molecules move through with much more difficulty.
The separating structure, in other words, is assembled by the crude oil rather than by the manufacturer. Dong-Yeun Koh of KAIST said the work "reveals a new scientific principle in which a membrane interacts with a complex mixture".
The throughput numbers are the headline result. Permeation was about 23 times higher than previous leading crude oil separation membranes, and the team reported 28 consecutive days of steady performance using real crude supplied by HD Hyundai Oilbank. "One of the key challenges facing membrane systems for crude oil separation was the low productivities," said Ryan Lively of Georgia Tech.
Process simulations, rather than operating plants, produced the efficiency figures: energy use down 31.6 per cent, carbon dioxide emissions down 37.6 per cent, cooling water down 20.7 per cent and operating costs down 36 per cent. Applied across Korea, the team projects about 10 million tonnes of greenhouse gas emissions prevented a year, roughly the output of four million combustion-engine vehicles. The unit would be installed upstream of conventional distillation rather than replacing it.
Fouling is the accumulation of material inside a membrane's pores. In every other filtration process on earth it is the problem: the thing that cuts flow, raises pressure and eventually forces the membrane to be cleaned or thrown away. Here it is the product.
The membrane does not resist fouling, and is not designed to. It fouls, and in fouling it acquires the sub-two-nanometre channels that make the separation possible. A clean membrane of this type would not work at all.
This inverts the industry's principal maintenance question. Ordinarily the question is how long a membrane can be run before it must be cleaned. Here the answer is that cleaning it would restore it to the condition in which it does not function.
Our analysts note that the reported figure of 28 consecutive days of steady performance can be stated two ways, both accurate. The membrane ran for 28 days without degrading. The membrane also degraded continuously for 28 days, which is the thing it was doing.
The team's stated next step is to control the pore-constriction phenomenon precisely and to extend the platform to plastic recycling, biofuels and pharmaceutical purification. Precise control of the phenomenon means, on the published account, deciding exactly how blocked a membrane should become and then keeping it there.
The Department of Unnecessary Research accepts the finding without reservation and asks only that the vocabulary be settled before the technology scales. A membrane that works by clogging has not solved fouling. It has promoted it.