Confronting Chemistry

Sometimes chemistry won't cooperate with the needs of industry. If a company produces chlorine, for example, to meet strong demand, it also has to move coproduct caustic soda.

The linear -olefins (LAO) industry faces an even more complex problem of coproduct economics. The wide-ranging molecules coming out of LAO plants are used in applications as unrelated as polyethylene comonomers, detergent alcohols, oil-field chemicals, and lubricant additives-and demand for some of these products grows faster than for others.

LAO producers want to focus on the more desirable products and are stepping up efforts to get around the coproduct problem with technologies that allow them to narrow in on only certain LAOs.

Mark L. Morgan, senior consultant with Nexant ChemSystems, explains that traditional LAO plants oligomerize ethylene to make butene, hexene, and octene, all primarily used as comonomers in linear low-density polyethylene (LLDPE) production; decene, used mostly for poly -olefin lubricants; C₁₂-C₁₈ olefins, used to make detergent alcohols; and higher fractions used in many different specialty applications.

For example, Morgan says a Chevron Phillips plant using the conventional full-range technology makes about 45% butene, hexene, and octene; about 12% decene; and 28% products in the detergent alcohol range, plus a balance of heavier olefins production. If you build an -olefin plant that is a full-range plant, you do have this ongoing challenge that you have to move all the products you make, not just pick out the ones you want, he says.

Pat Quinlan, vice president of monomers of Sasol olefins and surfactants, said in a speech at a Chemical Market Associates conference, held in Houston in March, that this shotgun output can be unprofitable. All the products, he said, have a similar cost base. But some products, like the ones used in detergents, are not as profitable as others, like the comonomers.

Not surprisingly, the more profitable products are also the faster growing ones. Morgan projects that global demand for butene, hexene, and octene will grow at, respectively, 6.2%, 7.9%, and 5.4% annually from 2003 through 2010. Over the same period, decene will grow at 3.2%, and the C₁₂-C₁₄ and the C₁₆-C₁₈ fractions are forecast to grow by 4.8% and 3.4%, respectively.

New conventional LAO capacity built to meet demand for the faster growing products will tend to oversupply slower growing markets, Morgan says. The disparity in growth rates means that in order to supply the needs for hexene and octene, if you build an -olefins plant using the conventional approach, then you are pushing markets of C₁₂ and C₁₄ into substantial oversupply, he says.

Quinlan projects that the global oversupply in C₁₀-C₁₄ LAOs will grow from 45,000 metric tons per year in 2001 to 234,000 metric tons by 2010. The challenge for the LAO industry, therefore, has been and will continue to be developing ways to meet the growing demand for comonomer-range olefins without producing a significant surplus of heavier LAOs, he said.

Companies have been responding with technologies to produce certain LAOs without higher olefin coproducts. Leaders in this field include Sasol, with its olefin extraction units in South Africa and an on-purpose octene process under development, and Chevron Phillips with its 1-hexene technology.

Sasol selectively extracts LAOs at its Secunda, South Africa, complex. This plant, based on a Fischer-Tropsch gas-to-liquids process, produces a liquid-fuels stream that is also rich in LAOs. Since the mid-1990s, when it opened its first hexene unit, the company has built capacity for heptene and octene as well as C₁₁ and C₁₂ fractions that it converts to detergent alcohols.

According to Quinlan, hexene capacity in Secunda is now 175,000 metric tons per year, representing about 24% of the global total; octene capacity is 96,000 metric tons, 16% of the world share. Thanks to Sasol's production of the comonomer-range olefins, he estimates that the surplus of heavier olefins is only 30,000 metric tons per year instead of 135,000 metric tons.

Sasol is also developing a process to produce octene via the tetramerization of ethylene. According to a paper the company published in the Journal of the American Chemical Society last October (2004, 126, 14712), the technology uses an aluminoxane-activated chromium-based catalyst with diphosphinoamine ligands to produce octene at a selectivity of up to 70% for the first time, plus some hexene.

Sasol says the process becomes commercially viable when the yield of octene and hexene approaches 90%. The firm says it may be commercialized as soon as 2009.

Chevron Phillips started up a 47,000-metric-ton-per-year hexene unit at its Q-Chem ethylene/polyethylene joint venture with Qatar Petroleum in Qatar early in 2003. It uses chromium catalysts to yield 90–95% hexene from ethylene. Chevron Phillips says another 1-hexene unit is slated for an ethylene complex it is planning in Saudi Arabia with Saudi Industrial Investment Group (C&EN, Sept. 12, page 19).

In the late 1990s, Chevron Phillips had planned to build a unit in Texas. Nexant ChemSystems' Morgan says the company may have opted for the Middle Eastern location because the process needed low-priced feedstocks to cover the high capital cost of the plant. The company, however, says the efficiency of the process renders it an attractive technology for a variety of production environments.

These firms are not alone. ABB Lummus is working on a technology to get hexene from butene metathesis. Saudi Basic Industries Corp. is commercializing an ethylene-oligomerization technology with Linde that emphasizes the comonomer-range -olefins.

Dow Chemical is said to be working on a process to make octene from butadiene. The company has enormous requirements for octene as an LLDPE comonomer. In fact, when Sasol built its first octene extraction unit in Secunda, Dow agreed to take all of the output.

Shell Chemicals, one of the companies that uses ethylene oligomerization, has a different strategy for dealing with the coproducts problem, says Dan Carlson, business manager for higher olefins at Shell. The Shell higher olefins process converts butene and C₂₂ and up via isomerization and disproportionation steps into C₈-C₁₈ range internal olefins that it uses largely for its own detergent alcohols business.

Shell Chemicals' large integrated alcohol and ethoxylate business provides a stable outlet for higher molecular weight olefins, which generally gives us more flexibility than other full-range ?-olefin producers to balance production, Carlson says. We use both internal and -olefins to make our linear alcohols and can shift the relative proportions of each based on our overall carbon balances.

The company has also been aggressively developing higher olefin markets by introducing new products into markets such as personal care and oil-drilling fluids.

Rick Mingione, projects optimization manager for Innovene, another broad-based LAO supplier, says his firm has not opted for this strategy and actually closed an alcohols plant in Pasadena, Texas, three years ago. This year, the company is closing an LAO plant on the same site. He says LAO-based detergents have a difficult time competing with detergents based on paraffins and vegetable oil. While LAOs can offer certain advantages, demand is cyclical and competing paraffins are generally available at lower cost, he says.

Innovene has, however, updated its LAO process. Its plant in Joffre, Alberta, which started up in 2001, can recycle butene to produce more octene, a capability that its Pasadena unit did not have.

According to Quinlan, the on-purpose technologies will help ameliorate some of the business's problems. As we move further into the 21st century, these targeted, as opposed to broad-range processes, will play an even more prominent role in the LAO market, he says. By 2015, Morgan says, up to 500,000 metric tons per year of hexene will come from on-purpose projects.

Shell's Carlson agrees that the on-purpose LAO technologies will help everybody. The commercialization of single-cut technologies is clearly helping to create a more healthy balance in the LAO industry, and we think that is good for customers and producers in the long run, he says.