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February 25, 2014

Volume 7 Issue 3

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Esters Gaining Popularity

In a world where overall lubricants volume demand is consistently flat, ester-based lubricants are carving an ever-larger slice of the pie and will grow at an average annual rate of 6 percent for the next several years, according to Chris Donaghy of Croda Inc. In a seminar at December’s ICIS Pan American Base Oils & Lubricants Conference, the New Castle, Delaware, U.S.-based executive reviewed the key markets, chemistries and opportunities for these high-value, man-made molecules.

Globally, today’s lubricants market still heavily favors mineral oil, and 91 percent of products are made of hydrocarbon base oils, he said. (That includes API Group III hydrocracked mineral oils, often marketed as synthetics). Rerefined base oils have grown to about 4.8 percent of the market, and simple vegetable oil based lubricants about 0.2 percent.

The category Croda labels “synthetics,” which excludes Group III products, accounts for 4 percent of worldwide lubricants demand. “Overall, demand is flat, but synthetics’ share of the pie is growing,” said Donaghy, who is Croda’s sales director of polymer additives and lubricants. “When you break down this 4 percent share that is synthetics, many would think polyalphaolefins have the majority, but they’re actually about 42 percent of the volume of synthetics sold worldwide. Esters are not far behind, with 32 percent of the market volume. Polyalkylene glycols we estimate at 13 percent of the synthetics market, and the rest is other types, like phosphate esters, silicones and more exotic specialties.”

Croda estimates global esters demand at around 100,000 metric tons per year. Refrigeration oils are the top end-use market, at 21 percent of the total, followed closely by aviation (20 percent). Aviation, however, is a relatively mature market, with esters already in place where needed, like jet turbine engine oils. Refrigeration, by contrast, has real potential to see demand surge over the next 10 years, Donaghy pointed out, as industrialized countries complete the shift to non-ozone-depleting refrigerants and as developing economies use more refrigeration.

By region, Europe and North America together take about 70 percent of esters’ global volume demand, but this geographic tilt is beginning to shift. Ester manufacturers have spent the past decade investing in production facilities in the regions where markets are expanding, Asia in particular and also Latin America. “Esters manufacturers themselves are becoming more global too, as seen in companies that formerly were regionally based,” Donaghy later observed to Lubes’n’Greases. “So we saw Croda, traditionally a European company, spead out to North America and to Asia, while Europe’s Oleon moved into Asia and Germany’s BASF began producing in Brazil.”

It’s important to remember that modern esters are not one single material, but an extremely diverse family of molecules, Donaghy pointed out. “Ester chemistry is so versatile that you can design it specifically for the application where you need it to go,” he said. “You can make an ester from biobased materials or from petrochemicals; it can be saturated or unsaturated; you can create the desired viscosity index or pour point or hydrolytic stability or biostability, exactly as needed.”

Esters are made by combining an alcohol and an acid, each selected from hundreds that are commercially available. The ingredients are reacted under specific temperatures and pressures to produce the desired properties. The resulting esters can be divided into four major types:

   1) Mono esters, the simplest, are made by combining a mono acid and mono alcohol. At 100 degrees C., these range in viscosity from less than 1.0 to 5.5 mm2/second. Major lubricant applications are metal processes such as cutting and rolling oils; biodiesel is another huge market.

   2) Diesters are built from a di-functional acid and monofunctional alcohol, and range from 2.5 to 18.0 mm2/s. “These are a little thicker, and they’re used primarily as a co-base oil in making products like driveline fluids and industrial gear oils,” Donaghy said.

   3) Polyol esters are the next step up the ladder, made from a mono acid and polyfunctional alcohol. “The most thermally stable types, these go into aviation oils and refrigeration oils,” Donaghy said. Viscosity ranges from 3.0 to 18.0 mm2/s.

   4) Complex esters tip the viscosity scale at 6.0 to 2,000 mm2/s, and are close to being polymers. They’re made by combining simpler esters, “and many are quite thick. These are used in smaller treat rates in metal processing and for things like thickening, to improve a lubricant’s viscosity index or lubricity effects.”

Because they are so diverse, lubricant formulators can use esters to boost specific properties, focusing exactly on the aspects that are most important for their application. If a fluid needs to have high polarity, greater lubricity, reduced volatility, deposit control, low-temperature fluidity, biodegradability or even electrical resistivity – there’s an ester for that. “At Croda, we sell a couple hundred commercial esters, including some which are combinations of both renewable and petrochemical materials,” Donaghy said. “But not all esters are alike. Precise back-end processes are needed to make and stabilize these molecules, especially to mitigate issues such as hydrolysis.”

Because cost is always a factor, and esters do cost far more than conventional base oils, Donaghy said these lubes are best used where enhanced performance solves a technical need, where they can trim operating costs, or where safety, health and environmental impacts must be addressed. So despite their higher initial cost, Croda expects healthy growth in two key areas for esters.

The first will be where technical demands are rising, such as automotive crankcase oils, chain oils and fire-resistant fluids, food-processing and compressor lubricants, hydraulic fluids, greases and gear oils. Croda also expects significant growth in demand for esters where environmental impact is a concern. Here, marketers of ester lubricants can demonstrate a wide range of benefits, including fuel savings, reduced emissions, biodegradability, renewable content, sustainable raw materials, and more.

Just being biodegradable or biobased, however, does not appear to rank high (yet) among the reasons why users opt for esters, Donaghy said. “Being biobased is the third or fourth value proposition we make at Croda, in talking to customers. We believe a biobased lubricant first has to perform.

“The important thing to remember,” he added, “is that if you can’t explain why they should use esters, your customers won’t adopt them, because they cost more.

“Selection is key,” he went on. “There’s a huge range of materials, and there are some 10,000 commercial esters on the market now. It’s important for blenders to know what’s out there, either on their own, or by working with an ester manufacturer that can dial in the lubricant performance that’s needed.”

Lube Report Asia will occasionally include articles originally published in sister publications of LNG Publishing Co. This article appeared in the February 2014 issue of Lubes’n’Greases – Volume 20, Issue 2 – under the headline, “Esters Seize the Day.”