Du Pont acid dissolves problems

Zircadyne-lined tube meets Belle Plant production challenge

The Du Pont Belle Plant, located in Belle, West Virginia along the Kanawha River, produces roughly 40 agriculture and specialty chemical products. Belle has been producing hydroxyacetic (glycolic) acid for nearly 50 years.

In 1940s, Du Pont developed a process to make ethylene glycol, or antifreeze, from hydroxyacetic (glycolic) acid. Over the next 30 years, the company developed other markets for glycolic acid, and in the mid-1970s, when more cost-effective methods of producing antifreeze had been discovered, the company opted to continue making the product for its growing list of new applications.

Today, glycolic acid is marketed as a mild organic acid for use in a variety of industries, including applications in everything from medicine to metal processing.

Du Pont's Mean Green Solution

Hydroxyacetic acid (HAA) is the first member of the series of alpha hydroxy carboxylic acids. It occurs naturally as the chief acidic constituent of sugar cane juice and occurs in beet juice and unripe grapes. The formula for the monobasic acid is HOCH₂COOH. It is biodegradable.

The pure acid exists as colorless crystals, which are readily soluble in water. Glycolic acid is non-volatile and cannot be distilled even under reduced pressure. When heated, it readily loses water by self-esterification to form polyglycolic acid.

Du Pont supplies glycolic acid as 70% technical aqueous solution (in this form it is a clear, light amber liquid with a mild odor resembling burnt sugar), as 70% high purity aqueous solution, and as 99% high purity crystal.

Aqueous solutions of glycolic acid contain both free and soluble polyacids in equilibrium; the ratio is determined by solution concentration. Since the polyacids hydrolyze readily on dilution, their presence can be ignored for most uses, and total glycolic acid concentration can be considered as free acid.

This organic acid is very soluble in acetic acid, acetone, ethanol, ethyl acetate, methanol and, most importantly, water. It is slightly soluble in ethyl ether, but only sparingly soluble in hydrocarbon solvents.

Glycolic acid can function as both an acid and an alcohol. This dual functionality leads to a variety of chemical reactions and valuable physical properties for metal cleaning, metal complexing, electroplating, as well as many other uses.

Since it exhibits complexing power and oxide solubility for many metals, glycolic acid is a logical candidate for inclusion in metal cleaning formulations. It has a low corrosion rate on nonferrous metals and is effective is dissolving such deposits as smut and/or aluminum. Cleaning compounds that contain this acid have excellent rinsibility and reduce the spotting caused by trace metal residues. These properties are important in a variety of applications, including cleaning of airplane, train, and truck bodies, and are especially important in metal plating operations.

Glycolic acid effectively removes hard water scale from all types of heat exchange equipment. It should be considered for pH adjustment of cooling waters to prevent scale build-up.

For metal processing, glycolic acid can be used to replace volatile organic acids in special pickling operations. Its nonvolatile characteristic prevents losses due to elevated temperatures and reduces the ventilation requirements. It can usually be used to replace any organic acid in pickling formulations.

There are numerous applications for the acid in the electroplating industry. The sodium and potassium salts of the acid are excellent substitutes for Rochelle salts used as bath additives. Because glycolic acid forms complexes with virtually all multivalent metals, its salts are used in many electroplating baths, such as those for chrome, lead, cobalt, tin, and nickel.

Other applications for the acid in metal processing include etching, electropolishing, and copper brightening. Glycolic acid's properties also make it well suited for cleaning hard surfaces, boiler and process equipment, water wells, dairy and food processing equipment, and masonry.

In the piping sections of Du Pont Belle's glycolic acid production facility, velocity erosion reduced the lifetime of silver-lined tubes to a few years. In the past, the plant experienced blowouts of this high-pressure piping caused by interior corrosion. Here, the silver lining failed, exposing the carbon steel tube to the process chemical, sulfuric acid, which ate through it rapidly.

High quality monomers and polymers of glycolic acid and lactic acid are used to manufacture bioabsorbable surgical sutures, staples, and clips; sustained-release drug delivery systems; and implantable prosthetic devices. The Food and Drug Administration (FDA) has approved specific applications using this family of polymers.

Polymers of glycolic acid are water degradable and water insoluble. This allows them to be used in the controlled release of chemicals in an aqueous environment. These polymers are currently being used in the acidification of oil wells. The polymer is finely ground and forced down the well out into the surrounding formation where it fills in the porous formation. This contains the well and avoids the excessive use of strong cleaning agents. After the cleaning is performed, the acid degrades naturally into glycolic acid, which is then easily flushed from the well.

Bill Weber, Business Manager for the acid, says glycolic is attractive because it provides a lot of active performance given its weight. "Its combination of being an acidulant, a chelating agent, and also easily water soluble makes it very user-friendly," he says.

Belle Solves Production Dilemma

Although glycolic acid works innocuously in a wide variety of applications, producing it is not so problem-free. In the production process, the acid is synthesized in a converter train at 10,000 Psig and a temperature of 200°C. Originally, the carbon steel piping and converters were lined with sterling silver for corrosion protection. However, in the piping sections, velocity erosion reduced the lifetime of the silver to a few years. In the past, the plant experienced blowouts of the high pressure piping due to failure of the silver lining (see above figure).

By the mid-1980s, a search for modern materials led to an evaluation of reactive metals for lining of these piping sections. Glass and ceramic linings had been rejected for their brittleness. The company wanted something that wouldn't fracture easily. Titanium would not withstand the sulfuric acid and the extreme process conditions.

"Materials of construction have always been a key parameter in the whole production process," explains Weber. "The synthesis reaction that we use to make glycolic acid, a key step, is simple but occurs in an extremely aggressive operating environment, with high pressures and temperatures."

Zirconium, known for its excellent corrosion resistance to weak sulfuric acid up to and above 260°C, interested Engineer Ed Balthazar and Metallurgist Steve Springer (both of Du Pont) who were looking for a solution. Du Pont began its evaluation of the metal with a single tube lined with Teledyne Wah Chang Albany's Zircadyne^® (Grade 702 Zirconium), putting it on trial in the most severe service section of the process. The tube was exposed to the aggressive environment for approximately 6000 hours over an eight-month period.

At that point, internal ultrasonic inspection revealed a single defect on the tube's inside diameter (ID), and engineers pulled it for metallurgical investigation. The defect was found to be lack of weld penetration that occurred during fabrication at the Belle Plant. Examination of an etched longitudinal section through the defect confirmed the presence of the weld by its cast microstructure.

There was no measurable corrosion loss on the ID, although some rounding of edges from corrosion in the defect area may have occurred. The wall thickness of the Zircadyne tubing measured.075 in. which was of no real significance since the original.093-in.-thick tube was ground on the outside diameter (OD) to fit the ID of the steel tubing. No ID pitting or erosion was visible, confirming the ultrasonic inspection report. In fact, whereas the sterling silver had corroded at a rate of more than 20 mils per year, the zirconium was corroding at less than 2 mils a year.

There was also no evidence of premature failure from differential thermal expansion in the radial direction between the Zircadyne and the carbon steel, even with the presence of the notch provided by the welding defect.

Based on the findings, Balthazar and Springer recommended that the Belle Plant replace silver linings with zirconium 702 linings for HAA high pressure tubing. "We were convinced," says Balthazar. "We're fully committed to using zirconium for our pipe lining."

Du Pont now has Zircadyne-lined tube that has been in service for five years. Balthazar expects it to last at least three times as long as the silver-lined tube based on its erosion and corrosion resistance.

The corporation is currently considering zirconium for applications in other corrosive operating environments.

For more information concerning glycolic acid, please contact Diane Lohr, Du Pont's Marketing Manager for the product, at (513) 860-3282. For more information on Teledyne Wah Chang Albany's Zircadyne and other reactive and refractory metal products, please call Customer Service at (503) 967-6977.

Zirconium is the answer to sulfuric acid material selection equation

By Te-Lin Yau, Corrosion Engineer and Ken Bird, Chemical Engineer

Sulfuric acid is one of the most widely used of all of the manufactured chemicals and is, therefore, probably the most important mineral acid. For example, it is used as a dehydrating agent, an absorbent, a catalyst, a reagent in chemical syntheses, and in many other applications. The use of sulfuric acid can often be an indicator of a nation's industrial activity. The science of sulfuric acid is complicated. Dilute solutions are reducing in nature; oxidizing behavior begins at concentrations of approximately 65% to 70%. The resistance of most engineering metals and alloys used to contain sulfuric acid in the chemical process industries is greatly dependent on acid concentration, the presence of other chemicals, and process temperature.

Zirconium is one of the few metals that resist attack by sulfuric acid at all concentrations to 70% and temperatures to boiling and above. These conditions are so corrosive to metals that most chemical processes are designed to circumvent them. In some cases, however, efficiency of operations and product yields dictate operating parameters that are in this envelope where sulfuric acid is extremely aggressive. The figure below shows the corrosion resistance of zirconium as well as other materials.

This figure gives the design engineer a first cut at material selection. However, most real-life situations do not operate under ideal conditions. Impurities may be present that could exacerbate the corrosion, or temperature/concentration excursions could occur, placing a selected material in jeopardy. The corrosion resistance of nickel molybdenum (Ni-Mo) and nickel-molybdenum-chromium (Ni-Mo-Cr) alloys is impurity sensitive as well as being affected by the temperature and concentration of the sulfuric acid media. Zirconium, on the other hand, can tolerate the presence of some oxidizing impurities, such as ferric, cupric, and nitrate ions, without degradation of its corrosion resistance. In the presence of oxidizing agents, chloride ions must be controlled to limit detrimental attack. The chart at right (page 4) can be used as a guide when chloride ions and oxidizing agents are present.

Zirconium, like most metals, can tolerate only very small quantities of fluoride ions even at low sulfuric acid concentrations. Fluoride ions can be tied up by using inhibitors, such as zirconium sulfate or sponge.

Corrosion resistance of materials to sulfuric acid

Sulfuric Corrosion Chart

The ability of zirconium to form a tenaciously adherent, chemically inert oxide film is the primary reason for its excellent corrosion resistance to aggressive media. Oxygen to form this film can come from air, water, carbon dioxide, or carbon monoxide. The film can repair itself in the aforementioned environments with pH in aqueous solutions not entering into the quality of the film produced. In addition to corrosion resistance, this zirconium oxide film is an erosion resistant barrier to entrained solids or catalysts. It also eliminates galling and provides reduced sliding friction. It has a hardness roughly equivalent to sapphire (7.5 on Moh's Scale). The oxide film is readily formed by heating to 1050°F (565°C) for 2 to 4 hours.

Zirconium is used extensively in iron and steel pickling, where sulfuric acid concentrations range from 5% to 40%, with temperatures up to 100°C. Methylmethacrylate producers have found that zirconium is the material of choice in their manufacturing processes using sulfuric acid. Acid recovery systems, butyl alcohol production, and numerous organic synthesis reactions rely on zirconium to contain the corrosive sulfuric acid intrinsic to their processes.

Summary

Zirconium is one of the premier containment materials for sulfuric acid service. It is corrosion resistant in all concentrations to 70% and at temperatures at or above boiling. The zirconium oxide film formed on the metal provides a corrosion and erosion resistant barrier that is relatively insensitive to impurities and process parameter excursions. Product purity, efficiency of operation, and environmental impact concerns are all part of the material selection equation that zirconium can solve.

References

R. T. Webster, T. L. Yau, Zirconium in Sulfuric Acid Applications, 1986 NACE.

Outlook, Vol. 1, No. 1, January 1980

Ibid, Vol. 2, No. 1, Winter 1981

Ibid, Vol. 3, No. 1, Winter 1982

Ibid, Vol. 7, No. 3, Summer 1986

Ibid, Vol. 9, Nos. 1&4, 1988

Ibid., Vol. 10, No. 1, Spring 1989

TWCA to present research results

Teledyne Wah Chang Albany will share its metals expertise with the Chemical Processing, Mining, and Pulp and Paper Industries early this fall when it presents papers at three conferences.

TWCA researchers Darryl Amick, Rob Henson, and Te-Lin Yau coauthored a paper titled "Use of Reactive Metals in Hydrometallurgical Processes" based on laboratory and field experience in the performance of titanium, zirconium, and titanium-45 niobium alloy in piping systems for handling severe environments. The report, which will be presented at the 1993 Randol Gold Forum, addresses safety and suitability of materials for harsh environments. It also discusses methods of sealing piping, pumps, and valves.

Jeff Fahey, Derrill Holmes, and Te-Lin Yau of TWCA collaborated on a paper titled "Performance of Zirconium in Bleaching Solutions." The report, which will be given at TAPPI's 1993 Engineering Conference and Trade Fair, examines the performance of zirconium in pulp bleaching operations that alternate between CIO₂ and H₂O₂. It points out that, unlike many other heavy metal ions, zirconium ions provide a mild capability to stabilize H₂O₂.

Brian Fitzgerald of Exxon Chemical Company and Te-Lin Yau of TWCA co-authored a paper on "The Mechanism and Control of Stress Corrosion Cracking of Zirconium in Sulfuric Acid" for the 12th International Corrosion Congress. It states that zirconium resists attack by sulfuric acid over a wide range of concentrations (up to 70%) and temperatures (above boiling). The paper reports that there is a sharp change to higher corrosion rates with only a slight increase in acid concentration. Consequently, zirconium is uniquely suitable for many sulfuric acid applications because stainless alloys corrode at higher rates in less than 70% sulfuric acid.

Q&A: Installing a Zr piping system

Te-Lin Yau, who heads TWCA's Corrosion Group, contributed this issue's question and answer, which covers zirconium piping. Dr. Yau has studied materials for use in a wide variety of CPI applications for over 13 years and is considered an expert on the subject.

Question

What challenges does one face when installing a zirconium piping system?

Answer

It is more important now than ever to have sound piping systems since fugitive emissions and minor leaks cannot be ignored. Materials selection, design, fabrication, and installation are major factors to consider for piping systems.

Zirconium has several attractive properties for piping applications. It is corrosion resistant, non-toxic, and biocompatible. It is highly workable. It can be made into any piping components using conventional equipment in forming, welding, casting, machining, and other manufacturing methods. Zirconium can be clad to steel, stainless steel, or other common metals using various methods, including explosive bonding, loose lining, and resistance cladding. Clad materials have been used in valves, nozzles, pipes, and reactors.

In fabrication, a few modifications and special techniques are required in certain cases. Of primary concern is zirconium's tendency to react with gases in air at elevated temperatures and to gall and seize during sliding contact with other metals. It is essential to use clean equipment; otherwise, foreign particles can be embedded onto zirconium's surfaces that might degrade its corrosion resistance and sealing capability.

Generally, it is not recommended to join zirconium to a dissimilar metal by welding. The welding often results in much degraded corrosion resistance and/or mechanical properties. Various mechanical means can be considered for connecting a zirconium pipe to a dissimilar metal pipe. For example, the connection can be accomplished with welded stub ends and slip flanges. These bolted closures may be sealed with a suitable gasket.

It's vital to select gasket materials that are compatible with zirconium. For example, graphite could induce an undesirable galvanic effect on zirconium in chloride solutions. Avoid gaskets made of reprocessed fluorocarbon polymers, since free HF may be released; however, gaskets made of virgin fluorocarbon polymers would be suitable for zirconium. If the process temperature or pressure is too high to use fluoro-carbon-polymer gaskets, a low-oxygen grade of zirconium can be used as the gasket material. In order to have tight closure, zirconium gaskets should not have a thick oxide coating, and gasket areas should be smooth without embedded particles. For more information, call Te-Lin Yau at (503) 926-4211 Ext.6291.

Alloy C data sheet available

In the mid-1980s, UTC's Pratt & Whitney Government Engines & Space Propulsion Unit and TWCA developed a unique titanium alloy to meet the design requirements for the Fl 19 engine and exhaust nozzle, vital parts of the U.S. Air Force's Advanced Tactical Fighter.

UTC and TWCA recently reached an agreement for marketing "Alloy C" for commercial applications. Under the agreement, TWCA owns exclusive license to make, have made, use, and sell the beta-phase titanium alloy, except for uses in surgical implants and in land-based and marine gas turbine applications.

As part of the contract, Pratt & Whitney agreed to release technical data on Alloy C. TWCA combined eight graphs along with text and a table into a data sheet that is now available to the company's customers. The sheet includes information on the alloy's combustion in air, its axial fatigue, CTE, and creep properties, as well as its high temperature strength (shown below). For a copy, call TWCA's Customer Service Department at (503) 967-6977.

Alloy C: high temperature strength

AWS honors Webster

Former Teledyne Wah Chang Albany employee R. Terry Webster recently accepted a prestigious award from the American Welding Society (AWS) for his contributions in the field. At the society's 74th Annual Convention held last spring, Webster received the Samuel Wylie Miller Memorial Medal Award for meritorious achievements that have contributed conspicuously to the advancement of the art of welding and cutting.

Webster came to TWCA in 1964 and provided distinguished service until his retirement in 1992. He continues his involvement with the company as consultant on welding and many other technical matters and remains active in several technical organizations, including ASM, ASME, ASTM, AWS, and NACE.