Table 1. Click image for larger view.
One of the most unusual products in the Advanced Aromatics portfolio is THN, sometimes known by its trade name Tetralin® (C10H12). THN is created through the partial catalytic hydrogenation of naphthalene, which produces one completely hydrogenated ring and leaves the other ring unchanged. Because the molecule is basically half aromatic and half aliphatic, it has some characteristics of each and has opened the door to numerous possibilities.

Aromatic and Aliphatic Capabilities

With this unique two-sided, both aromatic and aliphatic structure, THN has incredible potential in the coatings market. Though the product has been available for years, small quantities and high prices have precluded suppliers from benefiting from this special solvent. However, since Advanced Aromatics makes THN with a new, continuous process developed in-house using a much purer feedstock, the price should no longer prohibit THN from bringing a wide array of benefits to the coatings industry.

THN is a colorless liquid with a mildly pungent odor, and is miscible with most solvents, especially petroleum thinners. The solvent is also compatible with natural and synthetic vehicles, but is insoluble in water. (See properties noted in Table 1.)

THN has very powerful solvency characteristics (kB value > 150) and has been used in a wide variety of applications. It has been used as a solvent for oils, waxes, greases, naphthalene, metallic soaps, rubber, plastics, PVC, coumarone resins, ketone-formaldehyde resins, tung oil, mastic, asphalt, aminoplasts, colophony, most resonates, Al-bertols and linoxyn, to name a few. However, it does not dissolve cellulose esters, hard copals, shellac, bakelites, and it is not miscible with alcohol or with water.

Other Useful Applications

THN has found its way into several other industries. In the textile industry, it has been used in combination with textile soaps and oils in such processes as open scouring and kier boiling cotton, piece goods, wetting and cleaning prior to dyeing, removal of oil from rayon and yarn and the scouring of fabricated silk and wool.

In the printing ink field industry, THN has found considerable use. It is effective in de-inking paper (a process by which old telephone books are reclaimed) and is an ingredient in many special-purpose inks designed for printing on such materials as rubber, leather and plastics, as well as in quick-drying inks. THN has also been incorporated into shoe creams, floor waxes and motor fuels.

THN Adds Numerous Benefits for Coatings

With THN being used in products from shoe creams to motor fuels, the versatility of the product seems endless. With the aid of incredibly strong solvency characteristics, it has made a peripheral splash in the coatings industry with its use as a solvent and thinner in the paint and varnish industry and as a liquid drier in surface coatings.

Due to the product's unique characteristics, the potential applications in coatings are numerous. THN can perform as a retarder solvent for coatings since it serves primarily to slow down evaporation, permitting the coating to level. Since THN has a very low evaporation rate, it can be a great additive to organic surface coatings and inks. Environmentally, it is a great alternative to turpentine or high-flash naphtha as it evaporates considerably slower and does not have some of the inherent ecological issues as aromatic naphthas.

One current customer that uses THN in his paint claims he cannot get the finish he needs without THN in his formula. The improved finishing characteristics with THN are directly related to the evaporation rate of the solvent. Since THN slows down the evaporation rate, the coating has time to level and dry smoothly.

With paints that dry by chemical reactions between the paint and oxygen in the air, THN may be used to accomplish another role. THN is auto-oxidative and thus acts as an oxygen carrier in drying oils.

Yet another promising characteristic of THN is its processability. THN has the ability to dissolve solid or highly viscous binder components without causing a chemical reaction, thereby giving the binder a processable consistency. When THN evaporates, it leaves the binder components to form their hardened surface. Adjusting the amount of THN in the blend provides a means of accurately adjusting the viscosity for paint application. Appropriate solvent composition improves the wetting and dispersion of the pigments, degassing the wet film of occluded air and condensation products, and leveling and gloss are also increased.

Solvents are graded roughly into three groups: ‘low boilers' (B.P. below 100 °C), ‘medium boilers' (B.P. 100 to 150 °C) and ‘high boilers' (B.P. above 150 °C). THN is graded as a high boiler and is used to give flow and can be the sole solvent where the paint must be kept fluid for fairly long periods, e.g., where brushed paint must ‘marry in' when two areas overlap. In hot weather, when standard mineral spirits evaporate too quickly, a painter may have a hard time overcoming the drag of their viscous paints. By adding THN, a high boiler solvent, the painter can maintain the flow properties of his paint, and ease the job.

A Practical Chemistry Lesson

Paint chemist, Burrell, suggested that for every liquid, two parameters will govern its solvency. The first is the hydrogen bonding capacity of the liquid and the second is called the solubility parameter. Solubility parameter is a calculated value derived from the latent heat of evaporation (by use of thermodynamic equations). The numerical value of the solubility parameter is a measure of the attractive force between the liquid molecules. Solvents having solubility parameter values ranging from about 8.0 to 10.0 are usually considered good solvents to dissolve a wide selection of resins and polymers. Roughly speaking, the parameter of a mixture of liquids is the average parameter. For example, a polyester resin would not dissolve in n-butanol (11.4) or xylene (8.8). However, a 1:4 butanol/xylene mixture dissolved the resin. The mixture's parameter is roughly calculated thus:

Butanol contribution: 1 x 11.4 = 11.4

Xylene contribution: 4 x 8.8 = 35.2


Total = 46.6 divide by 5 (total parts)

= 9.3

However, this resin will most probably dissolve in THN, which has a solubility parameter of 9.5. Thus, using THN as a single solvent instead of a mixture of solvents can save both time and money in many applications.

To round out the barrage of unique characteristics, tetrahydronaphthalene imparts good flow properties to paints and produces high-gloss, smooth surfaces. It also assists in cutting down sedimentation with metallic paints and increases the efficiency of solvent-based paint removers.

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Advanced Aromatics, a privately owned petrochemical company with a 16-acre plant site in Baytown (near Houston), specializes in the making of naphthalene and a variety of unusual fused-ringed products.

The company makes three grades of naphthalene (78 °C, 79 °C and 80°C naphthalene), derivatives tetrahydronaphthalene and decahydronaphthalene, and a growing line of unique aromatic solvents called Advasol.