Researchers at the Korea Advanced Institute of Science and Technology (KAIST) and the Georgia Institute of Technology have demonstrated a membrane that separates crude oil at room temperature, without the high-temperature distillation traditionally used by refineries. The inexpensive, uncoated membrane uses a surprising buildup of heavy hydrocarbons inside its pores to create narrow separation channels. In process simulations, integrating the membrane with conventional refining equipment reduced energy use by 31.6%, carbon dioxide emissions by 37.6%, cooling-water consumption by 20.7% and operating costs by 36%.
Why crude oil refining consumes so much energy
The international research effort was led by Professor Dong-Yeun Koh of KAIST in collaboration with Professor Ryan Lively’s research group at the Georgia Institute of Technology. KAIST, whose chairman is Lee Kwang-Hyung, announced that the team had successfully demonstrated the room-temperature crude-oil separation technology. The findings were reported in Nature, one of the world’s leading scientific journals.
Crude oil is used for much more than gasoline and other transportation fuels. Refineries also produce raw materials for plastics, packaging, clothing and many other everyday products. Because refining costs influence the price of these materials, improving the efficiency of the process could have broad economic and environmental benefits.
For more than a century, refineries have relied largely on distillation to separate crude oil into useful fractions. The process heats the oil to temperatures above 350 °C, turns some of it into vapor, and then cools the vapor to collect different components.
Globally, crude-oil distillation consumes approximately 1,100 terawatt hours (TWh) of energy each year. That is equivalent to the combined annual output of about 130 continuously operating nuclear power plants, each with a capacity of approximately 1 gigawatt.
The energy demand makes distillation a major contributor to fuel consumption and greenhouse-gas emissions in the refining industry. Increasing economic pressure across the global petrochemical market is also driving interest in more efficient separation technologies.
A membrane that uses fouling to improve separation
Membranes are a potential alternative because they can separate substances without the extreme temperatures required by distillation. Earlier membrane designs, however, generally depended on very thin, specialized surface coatings.
Those coatings can provide precise molecular separation, but they are expensive to manufacture and can develop defects when produced at large scale. These limitations have made widespread industrial adoption more difficult.
Instead of adding a complex coating, the KAIST and Georgia Tech researchers used a bare membrane made from porous polyacrylonitrile, or PAN. This inexpensive, chemically stable polymer is already commonly used as a support material in industrial filtration systems.
The membrane behaved unexpectedly when crude oil passed through it. Heavier hydrocarbon molecules accumulated along the inner walls of the pores. Over time, this buildup narrowed the openings, creating channels with diameters of less than 2 nanometers.
In effect, the crude oil helped form the microscopic pathways needed to separate its own components. The channels allowed lighter fractions, including naphtha, gasoline and kerosene, to pass through quickly while making it more difficult for heavier materials to cross the membrane.
The finding reverses the usual understanding of fouling, the accumulation of material inside membrane pores. Fouling is normally considered a serious problem because it reduces filtration performance and can require cleaning or replacement. In this case, however, the buildup improved the membrane’s ability to separate molecules.
The uncoated PAN membrane achieved crude-oil permeability approximately 23 times higher than that previously reported for leading crude-oil separation membranes. It also operated stably for 28 consecutive days.
“One of the key challenges facing membrane systems for crude oil separation has been the low productivity of membrane units,” said Professor Ryan Lively of the Georgia Institute of Technology. “PAN membranes, with their amazing separation mechanisms, dramatically improve the productivity of membrane units, so industry should seriously consider implementing this technology.”
Potential reductions in energy use and emissions
The membrane does not necessarily require refineries to replace their existing equipment. It could be installed as a modular filtration system that processes crude oil before it enters conventional distillation units.
Pre-separating the oil would reduce the workload in the subsequent heating and separation stages while allowing facilities to continue using much of their current infrastructure.
Computer simulations indicated that adding the membrane to the purification process could reduce energy consumption by 31.6% and carbon dioxide emissions by 37.6%. The calculations also predicted a 20.7% reduction in cooling-water use and a 36% reduction in operating costs.
If adopted widely, the technology could have substantial environmental benefits. The researchers estimate that applying it across South Korea’s refining and petrochemical industries could prevent approximately 10 million tons of greenhouse-gas emissions each year. That is roughly equivalent to the annual emissions of 4 million vehicles with internal-combustion engines.
These figures are estimates from process simulations, not savings already demonstrated across operating refineries. The results nevertheless suggest that membrane filtration could offer a practical way to improve the efficiency of existing facilities.
Possible uses beyond crude oil
Although crude-oil separation was the primary focus of the research, the same approach could eventually be applied in other industries.
Potential uses include treating pyrolysis oil produced by breaking down waste plastics for recycling, recovering solvents used in battery manufacturing, purifying pharmaceutical compounds and improving biofuel production.
The approach may be particularly useful for complex liquid mixtures that can create the small filtration channels needed to separate their components. It could provide a less expensive and more versatile alternative to conventional membranes that depend on precisely manufactured surface coatings.
“This study reveals a new scientific principle that membranes interact with complex mixtures and spontaneously form their own separation channels,” said Professor Dong-Yeun Koh of KAIST. “By working with real crude oil sourced from the HD Modern Oil Bank, we were able to validate the technology under conditions relevant to industrial operations.”
Using actual crude oil was important because it allowed the researchers to test the membrane with the complex mixture of hydrocarbons found in industrial feedstocks, rather than with a simplified laboratory mixture.
Next steps toward industrial deployment
The researchers plan to improve large-scale membrane production and establish its reliability during long-term operation before pursuing wider deployment.
“By advancing large-area membrane modularization and long-term operational reliability, we hope to expand the adoption of membrane-based processes across the refining and petrochemical industries,” said KAIST Professor Jae W. Lee, a co-corresponding author of the study.
“Our goal is to precisely control this spontaneous pore shrinkage phenomenon and develop it into a membrane platform that can be applied throughout purification processes,” said the study’s co-lead authors, Dr. Jihoon Choi and Dr. Hyeokjun Seo of KAIST. “We also aim to extend this technology to plastic recycling, biofuel purification, and other sustainable chemical processes that support carbon neutrality.”
The research was supported by the Fundamental Research Program for Outstanding Young Researchers and the Engineering Research Center (ERC) Program of the Ministry of Science, Information and Communications of the Republic of Korea.
Source: www.sciencedaily.com
