‘The Way Forward’

FROM THE AUGUST ISSUE: Membrane dehydration technologies save energy, reduce carbon emissions and provide flexibility in ethanol purity. More plants are installing them and more technology developers are offering them.
By Tim Albrecht | July 17, 2018

Membrane dehydration tec-hnology is another cog in ethanol producers’ push toward higher efficiency in their plants. The technology brings a bevy of benefits to a facility, including steam and water savings, flexibility and less fusel oils in the distillation process.

As the ethanol industry continues to grow and mature, it’s important that it invest in reducing costs and improving sustainability, particularly in terms of energy and water use, says Gillian Harrison, CEO of Whitefox Technologies Ltd. “This ensures it remains competitive, survives when margins are stretched and can fend off attacks from critics on its sustainability credentials.

“Energy and water costs become an even bigger issue when considering cellulosic renewable fuels, when the front-end energy and water usage is higher than with corn ethanol,” she says. “In cellulosic production, the solvent content coming out of fermentation can be as low as 2 percent with, say, isobutanol, so efficient water removal is essential to commercial success.”

Whitefox’s membrane technology is installed in three ethanol plants, with five more in the works. Meanwhile, Mitsubishi Chemical Corp. is bringing its technology to the U.S. ethanol sector.

Same Goal, Different Technology
Each membrane option has its own specific process. Generally, membrane dehydration involves passing a fuel stream through a membrane to remove water from the ethanol, but each technology is a little different.

Common mole sieve processes in ethanol plants require a periodical regeneration. Zeolite beads used for dehydration collect water as ethanol passes through the process, leaving nearly pure ethanol, and collected water that needs to be purged. So, the process is reversed and ethanol is pushed back through the beads. The water and ethanol mix resulting from that step is reintroduced to the plant’s distillation column and the dehydration process begins again, Harrison says.

Whitefox’s integrated cartridge efficiency (ICE) membrane technology cuts that regeneration cycle out. The technology uses polymeric hollow fiber membranes. As the mix of ethanol and water passes through the membrane, water is absorbed by the layer on the membrane, essentially dissolving on the layer. A vacuum pulls the water through the layer. Ethanol is resistant to the membrane and exits the system dry, Harrison says. “The membrane technology itself is a continuous dehydration technology that separates the water from the ethanol. It does that a little bit like a filter, but it’s not by particle size, rather by chemical affinity.

“It’s a continuous separation process,” she adds. “So, unlike a molecular sieve, we don’t have a stop-start batch process, because there’s no regeneration. You don’t have to regenerate or repurify or clean the membrane. It’s just continuously separating the water from the ethanol.”

Mitsubishi Chemical Corp., a new entrant in the U.S. corn ethanol industry, offers its Zebrex membrane dehydration technology, also a continuous process. The Zebrex system is already used in more than 70  plants across the world, seven of which are ethanol plants in Europe and Japan. Mitsubishi is currently working in partnership with ICM Inc. to bring its technology to the U.S.

Mitsubishi will manufacture the membranes and work with ICM on engineering. ICM will manufacture the overall modules in the U.S. and then provide full engineering, procurement and construction services to plants, along with startup support and process guarantees, says Mayumi Kiyono-Shimobe, business development manager for Mitsubishi Chemical America Inc. “We see a key to success for Zebrex is having not just the membrane, but also the ability to properly integrate it into the ethanol plant and provide a turnkey construction and startup solution.”

The replacement of the modules created by ICM will be a simple process, Steve Hartig, vice president of technology development for ICM, said in June at the International Fuel Ethanol Workshop & Expo in Omaha. “One of the nice parts of modules is each element is a separate unit. So, if there are issues with maintenance or failure, a single element can be taken out and replaced at very low cost. You’re looking at an average of about five to six years of replacement cycle for the elements.”

Both Whitefox and Mitsubishi’s membrane systems can run in vapor phase, while Mitsubishi’s Zebrex system can run in liquid phase, as well. Each system can be implemented alongside existing pressure swing adsorption processes (PSA)—such as mole sieves—or as a replacement.

Operating in vapor phase enables Whitefox’s system to get better process conditions and performance in a large biofuels plant, Harrison says. “We’re less likely to deal with some of the impurities in the production process that you might see in a liquid-based process.”

Staying Flexible
Energy reduction, purity flexibility and debottlenecking distillation capacity and dehydration are the main benefits of membranes Hartig shared with his audience at the FEW.

Whitefox and Mitsubishi say their membrane systems are all about customization, able to be shaped to each specific facility. Mitsubishi’s Zebrex system is a “Swiss army knife-type technology” depending on what the plant needs and how it’s used, Hartig said. “It can be modified to each specific plant. It doesn’t do just one thing, it depends on the needs of the plant.”

Both membrane systems are easy to install. “If producing European ethanol or industrial alcohol, the Zebrex system can be put in a drop-in skid to create a separate stream,” Hartig said. “If you had a 100 MMgy plant and wanted to make 10 million gallons of European-grade ethanol, you could put in a small skid and just do that as a separate stream, or turn it on and off. It gives a lot of flexibility if a plant wants the diversification potential but not necessarily spend the money to have 100 percent of the capacity going up to the higher purity.”

With Whitefox’s technology, vapor  can be pushed through the membrane at 50 to 70 percent water to ethanol, Harrison says. “We can start that dehydration step much earlier in the process and it’s just a single step dehydration to whatever purity you want.

“With our membrane, we’re able to create whatever you want in and whatever you want out in a single step. It’s a function of vacuum, pressure and the flow, which is regulated by the operator.”

The combination of Whitefox’s membrane system with its design and process engineering provides a handful of energy benefits. The ICE solution provides the ability to increase capacity by up to 20 percent by taking out the recycle stream, while reducing energy use by 1,000 to 2,000 Btu per gallon, which provides steam savings. Linked to steam are carbon-emission reductions of about one to two carbon intensity points, Harrison says. “There’s also the overall improvement of operations where producers have seen their plants become more stable with no stop-start in the production process.”

Whitefox’s technology is also resistant to fusel oils, which can cause upsets in the distillation section of production. Occasionally, fusel oils can end up back in the system because of the typical recycle loops and can cause contamination of fermentation, Harrison says. “Our membranes are fusel oil-resistant, so we’re able to feed the fusel streams through the membranes, as well, to help take the fusel oils out of the recycling of the system.”

The Zebrex system allows for an increase of production capacity by about 20 percent compared with current PSA processes, energy savings of 10 to 20 percent and improved plant operating stability, Kiyono-Shimobe says, adding that a complete replacement of a plant’s current PSA with Zebrex can achieve energy savings of up to 30 percent.

The Vision
Harrison says membrane technology is “the way forward” and will become more popular as ethanol production continues to grow. Biorefineries will need all sorts of separations involving membranes, she says. “We want to stand alongside the existing ethanol producers to be a part of that future development.”

Mitsubishi sees a “significant opportunity” to help U.S. producers take advantage of plant debottlenecking solutions and energy savings with the Zebrex system, Kiyono-Shimobe says. “It is clear there is a trend in the U.S. ethanol market for energy reduction driven both by cost and by low-carbon fuel standards.”

Mitsubishi’s Zebrex system is slated to be installed at Aemetis Inc.’s facility in Keyes, California, by 2019. The 60 MMgy facility would be the first corn ethanol plant in the U.S. to use the system, with a goal of lowering carbon score, says Eric McAfee, chairman and CEO of Aemetis. “Our goals are reducing our natural gas use and thereby the amount of carbon used in our ethanol production by about 25 percent, eliminating regen from the PSA and thereby increasing production capacity at the plant. The overall goal, though, is the increased value of our ethanol product by decreasing the carbon intensity of each gallon.”

While Mitsubishi is looking to get its foot in the door of the ethanol industry, Whitefox’s ICE technology is currently operating in three plants across the U.S.: Pine Lake Corn Processors in Iowa, Fox River Valley Ethanol in Wisconsin and Pacific Ethanol in California. “We have four additional plants that are currently in engineering and installation,” Harrison says. “By the end of this year, we’ll definitely have seven with a possible eighth, which we’re in the final stages of discussions on.”

Whitefox is hoping to bring membranes to more parts of the ethanol production process, as well as other industries, Harrison says. “We draw a lot of inspiration from nature and nature uses membranes for all of its separations. You don’t see little Bunsen burners, distillation columns and separation of molecules by boiling point in nature. So, ultimately that’s our great ambition. Membrane technology installed in many different industrial processes—such as jet fuel, isobutanol—involve separation and that water removal step is often the most energy intensive of the whole process. Our vision is to develop membranes to help improve that separation process in products that we all use.”

Author: Tim Albrecht
Associate Editor, Ethanol Producer Magazine