ExxonMobil & Georgia Tech CMS membrane brings advantages of reverse osmosis separations to hydrocarbon mixtures; potential significant cuts in chemical manufacturing energy use & emissions
Scientists from ExxonMobil and the Georgia Institute of Technology have developed new free-standing carbon molecular sieve (CMS) membrane technology that could significantly reduce the amount of energy and emissions associated with manufacturing plastics. Results of the research were published in Science. Using a molecular-level filter, the new process employs a form of reverse osmosis to separate para-xylene, a chemical building block for polyester and plastics, from complex hydrocarbon mixtures. The current commercial-scale process used around the world relies on energy and heat to separate those molecules.
Reverse-osmosis membranes are already widely used to desalinate seawater, consuming a fraction of the energy required by thermally driven processes. The new organic solvent reverse osmosis process is believed to be the first use of reverse osmosis with carbon membranes to separate liquid hydrocarbons.
If brought to industrial scale, this breakthrough could reduce industry’s global annual carbon dioxide emissions by up to 45 million tons—equivalent to the annual energy-related carbon dioxide emissions of about five million US homes. It could also reduce global energy costs used to make plastics by up to $2 billion a year.
The research successfully demonstrated that para-xylene can be separated from like chemical compounds known as aromatics by pressing them through a membrane. Commercially practiced separations involve energy-intensive crystallization or adsorption with distillation. Globally, the amount of energy used in conventional separation processes for aromatics is equal to about 20 average-sized power plants.
The ExxonMobil and Georgia Tech team first developed a new carbon-based membrane that can separate molecules as small as a nanometer. The membrane was then incorporated into a new organic solvent reverse osmosis process, during which aromatics were pressed through the membrane, separating out para-xylene.
In effect, we’d be using a filter with microscopic holes to do what an enormous amount of heat and energy currently do in a chemical process similar to that found in oil refining.—Mike Kerby, corporate strategic research manager at ExxonMobil
The carbon-based membrane developed by the ExxonMobil-Georgia Tech team is about 50 times more energy efficient than the current state-of-the-art membrane separation technology. Because the new membrane is made from a commercially available polymer, ExxonMobil believes it has potential for commercialization and integration into industrial chemical separation processes.
By applying pressure at room temperature, the membrane is able to concentrate para-xylene from a mixture at high rates and low energy consumption relative to state-of-the-art membranes. This mixture could then be fed into a conventional thermal process for finishing, which would dramatically reduce total energy input.—Ryan Lively, an assistant professor in Georgia Tech’s School of Chemical & Biomolecular Engineering and the lead researcher
The technology still faces challenges before it can be considered for commercialization and use at an industrial scale. The membranes used in the process will need to be tested under more challenging conditions, as industrial mixtures normally contain multiple organic compounds and may include materials that can foul membrane systems. The researchers must also learn to make the material consistently and demonstrate that it can withstand long-term industrial use.
The implications could be enormous in terms of the amount of energy that could be saved and the emissions reduced in chemical and product manufacturing. Our next steps are to further the fundamental understanding in the lab to help develop a plan for pilot plant-scale demonstration and, if successful, proceed to larger scale. We continue to work the fundamental science underlying this technology for broader applications in hydrocarbon separations.—Benjamin McCool, an advanced research associate at ExxonMobil and co-author
Chemical plants account for about 8% of global energy demand and about 15% of the projected growth in demand to 2040. As global populations and living standards continue to rise, demand for auto parts, housing materials, electronics and other products made from plastics and other petrochemicals will continue to grow.
Dong-Yeun Koh, Benjamin A. McCool, Harry W. Deckman, Ryan P. Lively (2016) “Reverse osmosis molecular differentiation of organic liquids using carbon molecular sieve membranes” Science 804-807 doi: 10.1126/science.aaf1343