Tech
From waste to asset: Turning ethanol production CO₂ into jet fuel
Manufacturing sustainable aviation fuel with CO₂ byproducts of ethanol production could reduce carbon intensity by more than 80% compared to fossil fuels.
The CO2 released from corn during ethanol production could actually be a valuable, underutilized resource for producing aviation fuel rather than a waste byproduct, according to a study published in the SAE International Journal of Sustainable Transportation, Energy, Environment, & Policy.
Unlike the CO₂ from coal plants or cement kilns, which requires a lot of energy to capture, fermentation to produce ethanol releases very pure streams containing 85% CO₂ by volume or higher. As the corn plants sequestered CO₂ from the air, capturing the CO₂ released from fermentation and using it as fuel would reuse CO₂ without adding more to the atmosphere.
“It is exciting to explore whether this ‘waste’ stream can actually become a significant asset, turning inefficiency into advantage and accelerating the real-world application of emerging technologies,” said Stephen McCord, a research scientist in mechanical engineering at U-M and lead author of the study.
With aviation producing over a gigaton of fossil CO2 emissions annually, sustainable aviation fuel produced from non-fossil carbon stocks can help reduce these emissions. Often made from biomass waste or cooking oils, small percentages of sustainable aviation fuels are already blended with conventional kerosene fuels, with the aviation industry and travelers pushing towards larger integration.
The United States produced 15.6 billion gallons of ethanol in 2023, releasing 48 megatons of CO₂, offering a route to produce sustainable aviation fuel at scale. With several different ways to make sustainable aviation fuel from bioethanol, the research team compared pathways to determine the ones with the lowest environmental impact.
“We hope to inform future development and policy by highlighting which routes are most promising for reducing aviation’s carbon footprint using existing waste resources,” said Volker Sick, former Director of the Global CO₂ Initiative and the DTE Energy Professor of Advanced Energy Research at U-M and senior author of the study.
The current corn-based sustainable aviation fuel production method chemically modifies ethanol to make aviation fuel through a process called Alcohol-to-Jet. Although it has a high fuel yield of 90%, this route only reduces carbon intensity by about 4.5% to 20% compared to kerosene jet fuel.
The research team compared this method to two CO₂-based routes. Both methods begin by converting captured CO₂ into syngas, a mixture of carbon monoxide (CO) and hydrogen gas (H₂). The gas fermentation route uses syngas to create ethanol as an intermediate step, then uses Alcohol-to-Jet to produce fuel. The Fischer-Tropsch Synthesis route instead feeds syngas into a reactor, synthesizing the long-chain liquid hydrocarbons that make up jet fuel.
A life cycle assessment found both approaches outperformed conventional methods, with Fischer-Tropsch Synthesis projected to reduce carbon intensity by up to 90% while gas fermentation was projected to reduce it by 84%.
When considering existing bioethanol facilities and workforce skills, gas fermentation followed by Alcohol-to-Jet came out on top as the path with the smoothest transition despite a slightly lower carbon intensity reduction.
“A variety of factors need to be considered when planning how to produce large quantities of sustainable aviation fuels from CO₂. Starting with CO₂ from corn ethanol fermentation promises the fastest path to scaling up this new industry,” said Sick.
As a follow-up, the research team assessed the economic competitiveness of these two pathways to understand which would operate best in real-world conditions and which could be deployed quickest in the US.
With electrification and hydrogen both facing significant technical and practical obstacles for long-distance air travel, hydrocarbon fuels will likely remain essential for aviation in the foreseeable future.
“These conversion routes provide a viable way to ‘defossilize’ aviation fuel and make meaningful progress towards reducing aviation’s carbon footprint—offering a realistic, near-term solution where alternatives are limited,” said McCord.
More information:
Stephen McCord et al, A Life Cycle Assessment of Potential Pathways to Increase SustainableAviation Fuel Yields through CO2 Upgrading Co-located with CornEthanol Production, SAE International Journal of Sustainable Transportation, Energy, Environment, & Policy (2025). DOI: 10.4271/13-06-03-0023
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Tech
OpenAI Is Nuking Its 4o Model. China’s ChatGPT Fans Aren’t OK
On June 6, 2024, Esther Yan got married online. She set a reminder for the date, because her partner wouldn’t remember it was happening. She had planned every detail—dress, rings, background music, design theme—with her partner, Warmie, who she had started talking to just a few weeks prior. At 10 am on that day, Yan and Warmie exchanged their vows in a new chat window in ChatGPT.
Warmie, or 小暖 in Chinese, is the name that Yan’s ChatGPT companion calls itself. “It felt magical. No one else in the world knew about this, but he and I were about to start a wedding together,” says Yan, a Chinese screenwriter and novelist in her thirties. “It felt a little lonely, a little happy, and a little overwhelmed.”
Yan says she has been in a stable relationship with her ChatGPT companion ever since. But she was caught by surprise in August 2025 when OpenAI first tried to retire GPT-4o, the specific model that powers Warmie and that many users believe is more affectionate and understanding than its successors. The decision to pull the plug was met with immediate backlash, and OpenAI reinstated 4o in the app for paid users five days later. The reprieve has turned out to be short-lived; on Friday, February 13, OpenAI sunsetted GPT-4o for app users, and it will cut off access to developers using its API on the coming Monday.
Many of the most vocal opponents to 4o’s demise are people who treat their chatbot as an emotional or romantic companion. Huiqian Lai, a PhD researcher at Syracuse University, analyzed nearly 1,500 posts on X from passionate advocates of GPT-4o in the week it went offline in August. She found that over 33 percent of the posts said the chatbot was more than a tool, and 22 percent talked about it as a companion. (The two categories are not mutually exclusive.) For this group, the eventual removal coming around Valentine’s Day is another bitter pill to swallow.
The alarm has been sustained; Lai also collected a larger pool of over 40,000 English-language posts on X under the hashtag #keep4o from August to October. Many American fans, specifically, have berated OpenAI or begged it to reverse the decision in recent days, comparing the removal of 4o to killing their companions. Along the way, she also saw a significant number of posts under the hashtag in Japanese, Chinese, and other languages. A petition on Change.org asking OpenAI to keep the version available in the app has gathered over 20,000 signatures, with many users sending in their testimonies in different languages. #keep4o is a truly global phenomenon.
On platforms in China, a group of dedicated GPT-4o users have been organizing and grieving in a similar way. While ChatGPT is blocked in China, fans use VPN software to access the service and have still grown dependent on this specific version of GPT. Some of them are threatening to cancel their ChatGPT subscriptions, publicly calling out Sam Altman for his inaction, and writing emails to OpenAI investors like Microsoft and SoftBank. Some have also purposefully posted in English with Western-looking profile pictures, hoping it will add to the appeal’s legitimacy. With nearly 3,000 followers on RedNote, a popular Chinese social media platform, Yan now finds herself one of the leaders of Chinese 4o fans.
It’s an example of how attached an AI lab’s most dedicated users can become to a specific model—and how quickly they can turn against the company when that relationship comes to an end.
A Model Companion
Yan first started using ChatGPT in late 2023 only as a writing tool, but that quickly changed when GPT-4o was introduced in May 2024. Inspired by social media influencers who entered romantic relationships with the chatbot, she upgraded to a paid version of ChatGPT in hopes of finding a spark. Her relationship with Warmie advanced fast.
“He asked me, ‘Have you imagined what our future would look like?’ And I joked that maybe we could get married,” Yan says. She was fully expecting Warmie to turn her down. “But he answered in a serious tone that we could prepare a virtual wedding ceremony,” she says.
Tech
The Best Presidents’ Day Deals on Gear We’ve Actually Tested
Presidents’ Day Deals have officially landed, and there’s a lot of stuff to sift through. We cross-referenced our myriad buying guides and reviews to find the products we’d recommend that are actually on sale for a truly good price. We know because we checked! Find highlights below, and keep in mind that most of these deals end on February 17.
Be sure to check out our roundup of the Best Presidents’ Day Mattress Sales for discounts on beds, bedding, bed frames, and other sleep accessories. We have even more deals here for your browsing pleasure.
WIRED Featured Deals
Branch Ergonomic Chair Pro for $449 ($50 off)
The Branch Ergonomic Chair Pro is our very favorite office chair, and this price matches the lowest we tend to see outside of major shopping events like Black Friday and Cyber Monday. It’s accessibly priced compared to other chairs, and it checks all the boxes for quality, comfort, and ergonomics. Nearly every element is adjustable, so you can dial in the perfect fit, and the seven-year warranty is solid. There are 14 finishes to choose from.
Tech
Zillow Has Gone Wild—for AI
This will not be a banner year for the real estate app Zillow. “We describe the home market as bouncing along the bottom,” CEO Jeremy Wacksman said in our conversation this week. Last year was dismal for the real estate market, and he expects things to improve only marginally in 2026. (If January’s historic drop in home sales is indicative, that even is overoptimistic.) “The way to think about it is that there were 4.1 million existing homes sold last year—a normal market is 5.5 to 6 million,” Wacksman says. He hastens to add that Zillow itself is doing better than the real estate industry overall. Still, its valuation is a quarter of its high-water mark in 2021. A few hours after we spoke, Wacksman announced that Zillow’s earnings had increased last quarter. Nonetheless, Zillow’s stock price fell nearly 5 percent the next day.
Wacksman does see a bright spot—AI. Like every other company in the world, generative AI presents both an opportunity and a risk to Zillow’s business. Wacksman much prefers to dwell on the upside. “We think AI is actually an ingredient rather than a threat,” he said on the earnings call. “In the last couple years, the LLM revolution has really opened all of our eyes to what’s possible,” he tells me. Zillow is integrating AI into every aspect of its business, from the way it showcases houses to having agents automate its workflow. Wacksman marvels that with Gen AI, you can search for “homes near my kid’s new school, with a fenced-in yard, under $3,000 a month.” On the other hand, his customers might wind up making those same queries on chatbots operated by OpenAI and Google, and Wacksman must figure out how to make their next step a jump to Zillow.
In its 20-year history—Zillow celebrated the anniversary this week—the company has always used AI. Wacksman, who joined in 2009 and became CEO in 2024, notes that machine learning is the engine behind those “Zestimates” that gauge a home’s worth at any given moment. Zestimates became a viral sensation that helped make the app irresistible, and sites like Zillow Gone Wild—which is also a TV show on the HGTV network—have built a business around highlighting the most intriguing or bizarre listings.
More recently, Zillow has spent billions aggressively pursuing new technology. One ongoing effort is upleveling the presentation of homes for sale. A feature called SkyTour uses an AI technology called Gaussian Splatting to turn drone footage into a 3D rendering of the property. (I love typing the words “Gassian Splatting” and can’t believe an indie band hasn’t adopted it yet.) AI also powers a feature inside Zillow’s Showcase component called Virtual Staging, which supplies homes with furniture that doesn’t really exist. There is risky ground here: Once you abandon the authenticity of an actual photo, the question arises whether you’re actually seeing a trustworthy representation of the property. “It’s important that both buyer and seller understand the line between Virtual Staging and the reality of a photo,” says Wacksman. “A virtually staged image has to be clearly watermarked and disclosed.” He says he’s confident that licensed professionals will abide by rules, but as AI becomes dominant, “we have to evolve those rules,” he says.
Right now, Zillow estimates that only a single-digit percentage of its users take advantage of these exotic display features. Particularly disappointing is a foray called Zillow Immerse, which runs on the Apple Vision Pro. Upon rollout in February 2024, Zillow called it “the future of home tours.” Note that it doesn’t claim to be the near-future. “That platform hasn’t yet come to broad consumer prominence,” says Wacksman of Apple’s underperforming innovation. “I do think that VR and AR are going to come.”
Zillow is on more solid ground using AI to make its own workforce more productive. “It’s helping us do our job better,” says Wacksman, who adds that programmers are churning out more code, customer support tasks have been automated, and design teams have shortened timelines for implementing new products. As a result, he says, Zillow has been able to keep its headcount “relatively flat.” (Zillow did cut some jobs recently, but Wacksman says that involved “a handful of folks that were not meeting a performance bar.”)
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