Research

Distillation is an energy-intensive and high-carbon-intensity process, widely used for separations in the chemical and process industries, and accounting for about 6% of U.S. energy consumption. An important application of distillation is in refining bioethanol for blending with gasoline and as a feedstock for renewable diesel, sustainable aviation fuel, polyethylene, and other products. Because the water + ethanol binary has an azeotrope at an ethanol mass fraction of 0.955, the state-of-the-art bioethanol refining process generally consists of two distillation steps to raise the ethanol (0.01-0.14) in the fermentation broth to a value between 0.9 and 0.955, followed by molecular sieve adsorption to “break” the azeotrope and raise the ethanol mass fraction to at least 0.99, the minimum value for blending with gasoline. The energy consumption is about 8-20 MJ/kg ethanol. The use of process heat (and the attendant second-law losses associated with heat transfer across large temperature differences) in the distillation steps is largely responsible for the high specific energy requirement, and the fact that this process heat is supplied by fossil-fuel combustion is responsible for the high carbon intensity. These factors contribute to the energetic and environmental costs of blending bioethanol with gasoline and its use in downstream products.

Here, we propose to purify bioethanol by a nonthermal, nonequilibrium separation using electrically-driven ultrasonic transducers to atomize, rather than vaporize, feed liquid, avoiding phase change and the large enthalpy change that requires so much process heat. Since the ultrasonic transducers are powered electrically, the proposed process has excellent potential to significantly reduce energy consumption and GHG emissions using renewable electricity. We have demonstrated the technical feasibility of the process in bench-scale semi-batch operation.

Ultrasonic separation can not only apply to ethanol-water separation but also to other organic-organic and organic-water separation, such as biobutanol purification, SAF refining, and other aqueous alcohol refining.

Utilization of bioenergy, biochemicals, and biomaterials can significantly reduce GHG emissions. Lipids are highly promising feedstocks that can synthesize these products. Unlike crude oil, the carbon chain lengths of fatty acids in fats/oils have a narrow range, and over 90% of fatty acids have carbon chain lengths of 16 and 18. The significant difference in the carbon chain length makes it challenging to transfer from a petroleum-based economy to a bioeconomy. Thermal cracking, catalytical cracking, and hydrocracking are generally used in the crude oil refining process, but they are not favored by sustainable bioeconomy for the high temperatures (400 to 900 oC), expensive catalysts and regeneration maintenance, and expensive renewable hydrogen. Additionally, the cracking products are randomly distributed. Sustainable energy-efficient technology with high selectivity for products is desired in reforming/refining oils/fats into various functional products. With fractions of unsaturated components ranging from 50 to 90%, the crude oil cracking/reforming can form aromatic chemicals unfavorable to use as diesel and aviation fuel because the combustion of aromatics can result in emission problems, such as PM. Here, ozone cracking is proposed to perform the cracking of oils/fats or the derivatives (such as free fatty acids and fatty acid esters) to cleave the carbon-carbon double bonds to short-chain and middle-chain fatty acids as the feedstocks to synthesize the biofuel, biochemicals, and biomaterials. The lipids could be obtained from crops, algae, and lignocellulosic sugar fermentation. The proposed technology has advantages in 1) the room temperature cracking process with the potential carbon neutrality using renewable electricity, 2) high yields of targeted products (>99%), and 3) the electrification process for decarbonization to mitigate climate change.

The resulting ozone-cracked intermediates can synthesize biokerosene, SAF, high-performance biolubricants, high-performance bio-dielectric coolants, biopolymers, and Metal-Organic-Frameworks (MOF) for chemical reaction, drug delivery, semiconductor, air conditioner, and carbon capture.

Fossil-based lubricants dominate the market (>95%) and own a high carbon footprint. Biolubricants based on fats/oils have been developed as alternatives to fossil-based lubricants to decarbonize the lubricant industry. However, current biolubricants bear several challenges, such as short oxidation stability, poor low-temperature performance, and low thermal stability. Herein, we innovated a technology to overcome these challenges to meet diverse lubricant demands. We will utilize efficient electrified ozone cracking to cleave the carbon-carbon double in the unsaturated lipids to form carboxylic/dicarboxylic acids. The synthesized products have demonstrated superior performance: 1) excellent low-temperature performance with the capability to be used in cold environments; 2) superior oxidation and thermal stability; 3) low toxicity and excellent biodegradability.

Low carbon intensity seaweed Sargassum is a promising feedstock for biofuels and biochemicals without influence on food supply and cropland. This project provides a carbon-neutral ultrasonic drying to rapidly dry the fresh Sargassum after harvest to avoid quality deteriorations and save ship/space costs. The ultrasonic-dried Sargassum is pretreated to produce carbohydrates and uronic acid, which is fermented to produce lipids. The resulting lipids will be cleaved to the middle/short-chain carboxylic/dicarboxylic acids using fully electrified ozone cracking at room temperature and atmosphere. The ozone-cracked intermediates can be synthesized into esters or oligoesters as high-performance high-value biolubricants (e.g., engine oils and gear oils). The long-chain lipids can be used to synthesize SAF. Biolubricants and SAF can decarbonize fuel, lubricants, and related industries. Therefore, this technology provides a promising solution to inhibit the problem of Sargassum blooming while offering economic and social benefits for the local community.

High oleic oils are new varieties characterized by high oleic acid content (75 to 90%), and the annual production rate is expected to be over 12 million metric tons (MMT) in the United States over the next few years1. In addition to the food supply, industrial applications (e.g., biofuel) of high oleic oils have become attractive due to their unique fatty acid profile, which improves their qualities and reduces costs. Aligning with the net-zero emissions goals, we propose sustainable aviation fuel (SAF) and biokerosene production from ozone-cracked high oleic oils.

Carbon-carbon double bonds in the unsaturated components will be cleaved into carboxylic acids and dicarboxylic acids using fully electrified efficient ozone cracking at room temperature2. These ozone-cracked intermediates (dominant carbon chain length of 9) can be synthesized into esters with biobased alcohols (e.g., ethanol, butanol, or isobutanol) as high-performance biokerosene. Ethanol is the most available biobased alcohol in the United States, with annual production rates of over 16 billion gallons. However, using isobutanol can reduce the carbon footprint of biokerosene for its carbon sequestration in anaerobic fermentation while improving biokerosene properties and combustion performance. Alternatively, due to the suitable carbon chain lengths, these intermediates can be converted to hydrocarbons as SAF without downstream refining or fractionation to reduce up to 50% of energy consumption in SAF production.

Separation is an essential technology in the chemical and process industries (CPI) to obtain pure chemicals. Distillation is a typical separation process with over 40,000 distillation columns in over 200 chemical processes in the United States. Moreover, distillation accounts for about 5 % of total domestic energy consumption in the United States. Unfortunately, the thermal efficiency of distillation is low, with 10% being typical. Another challenge for conventional distillation is inefficient for azeotropic solution separation. Bioethanol is currently widely produced from fermentation as the additive to gasoline for carbon neutralization in the transportation section. However, the vital constraints for bioethanol to fully replace gasoline are the low heating value (about 60 % of gasoline)and high energy consumption in purification depending on the ethanol concentrations. In addition, with the electrification of passenger vehicles by 2035, ethanol should be used to develop new products, such as renewable diesel or sustainable aviation fuel (SAF). However, the yield of renewable diesel or SAF is about 60 % (wt) because of the dehydration step in the synthesis. Compared to ethanol, butanol is considered a more suitable additive to gasoline without significant energy loss because of its comparable energy density. In addition, the yields of renewable diesel or SAF from butanol are 80 % (wt). However, the commercialization of butanol production through fermentation is mainly inhibited by the low butanol concentration (≤ 2%) in fermented broth since butanol energy content is much less than the energy used for purification by distillation with current fermentation technology. Ultrasound-mediated separation technology can significantly cut purification energy consumption based on our previous studies on ultrasonic ethanol/water separation. However, in addition to butanol and water, the butanol fermentation broth contains acetone, ethanol, and other ingredients. These chemicals also affect the ultrasonic separation and need to determine the separation efficiency in ultrasonic separation. Ultrasonic separation has been applied to the aqueous-organic separation but not to organic mixture separation. The success of using ultrasonic separation to organic-organic separation can provide an energy-efficient solution to the current petroleum refinery industry. Ultrasonic separation has been applied to simple binary systems but not complicated multi-component systems. The success of this study can extend the ultrasonic separation scope to deal with the complicated multi-component separation process. Besides providing an energy-efficient separation technology for butanol fermentation commercialization, ultrasonic separation establishes a platform for aqueous-organic and organic-organic separation for future applications, such as petroleum refineries, biochemical refineries, etc. This proposed project aims to develop and validate a new, energy-efficient, and environmentally friendly technology --fully electrified ultrasonic separation-- for obtaining fuel-grade butanol from the fermentation broth. The aim is to provide a novel, scalable technology to broaden the development of technology with low carbon footprints as an alternative to distillation in the United States.