TECHNOLOGY
GC Moves Toward Fine Chemical Making Conoco licenses F&M Scientific Corp. to make and market a preparative gas chromatograph with 4-in. diameter columns "We feel entirely confident that we should be able to eliminate at least 50% of our current laboratory distillation operation within the next two years." This is one result of large-scale preparative gas-chromatographic columns, as seen by Continental Oil's Dr. W. C. Hamilton. The columns are 4-in. and larger diameter columns which have been used successfully at Conoco's research and development laboratory at Ponca City, Okla., to perform separations which previously had required complex distillations. The Conoco work points up what some feel could be the next big growth area for gas chromatography: use of large preparative units to make fine chemicals for research work and for preparing analytical standards. Conoco, in fact, is now experimenting with 6-in. columns and volumes of a few hundred milliliters. A. B. Car el and Dr. Gerald Perkins, co-inventors of Conoco's large-scale chromatographic apparatus, believe that scaleups of 25 to 100 times using liters of solution at a single injection are possible and that resolutions would be as good as those currently obtainable. Preliminary work at Conoco indicates that use of cheap carrier gases and cheap packing materials can be developed. To this end, Conoco has licensed F&M Scientific Corp., of Avondale, Pa., to manufacture and market a unit based on the pending patent applications and technology it has developed. F&M has just introduced a unit called the PrepMaster. Large Quantities. The large-column chromatograph will give the organic chemist large enough quantities of pure materials to be of practical value in carrying out reactions, Conoco says. Because of the cost and difficulty of purifying his reagents, the organic chemist is sometimes prevented from carrying out his reactions with truly pure materials. Although the use of the large preparative chro46
C&EN
FEB.
15,
1965
LARGE COLUMNS. A 4-in.-diameter column is inserted into place on a large-scale preparative gas chromatograph by A. B. Carel of Conoco's research and development laboratory at Ponca City, Okla.
matograph will not allow the purification of all organic compounds, Conoco adds, it should permit rapid purification of many compounds at a reasonable cost. Production of fine chemicals for research is also a market for large preparative units. Conoco believes that any chemical which sells for more than a few dollars per pound and is adaptable to gas chromatographic purification could be economically separated by this technique. Analytical standards, too, are a potential market. Although currently available preparative gas chromatographs have been used for preparing analvtical standards, these standards
have been expensive and limited in number because most units cannot handle big volumes. Conoco says that its unit can give resolutions as good as any currently obtainable, and it gives a larger volume of sample. Where applicable, Conoco has found that the large gas chromatographic columns give a purer product than that obtained from distillation. One supplier of standard samples points up the potentials. He says that a preparative unit equivalent in resolution to a 20-ft., 1 / 4 -in.-column analytical unit would enable him to tear out most of his distillation equipment if he could obtain more than 200 ml. of pure material.
More than 50 such separations have already been accomplished by the preparative gas chromatograph at Conoco. One of these, for example, was the separation of 250 cc. of undecane, dodecane, and tridecane in a little over 30 min. with resultant product purity of about 99.9%. To do the same job by distillation would take three eight-hour days and a sacrifice of either purity or yield, Conoco says. In addition to this separation, the large-column chromatograph at Conoco has been used to: • Separate the individual isomers of linear alkylbenzene to study biodegradation of the sulfonates made from them. • Separate cis- from trans-l,4-dichlorobutene-2 (purity of the separated material is 9 9 . 9 % ) . • Remove about 200 p.p.m. of propane and other impurities from research-grade neopentane. • Separate a-tetr alone from 1methyl-4-tetralone. Separated. F&M, using a prototype of the 775, separated 3980 ml. of rectified turpentine. Of the 3480 ml. collected during the separation (a collection efficiency of 87.5%) 1733 ml. was 99.9% pure a-pinene; 701 ml. was 9 8 + % pure /?-pinene; and 1046 ml. was other materials. Samples of 65 ml. were injected at 30-min. intervals, and the total instrument running time was 30.6 hr. F&M also separated C 8 , C 9 , and C 1 0 methyl esters of a fatty acid. Over seven hours, 970 ml. was injected in 10 separate injections. Collected was 906 ml. (93.4% efficiency) of 99.8% pure C 8 , 99.2% pure C 9 , and 99.7% pure C 1 0 . F&M has designed the 775 with versatility in mind. The unit offers both analytical and preparative characteristics from a wide variety of interchangeable column sizes. Column fitting adaptors on the 775 allow using V 4 -, V r , V 2 -, V 4 -, 2V 2 -, and 4-in.-o.d. columns in the same oven. Interchangeable sample reservoirs, a high-capacity sample injector and vaporization unit (up to 125 ml.), and a high-temperature manifold for handling high-boiling components add to adaptability of the unit. The 775 has also been automated to give repetitive sample injection. Dials on the instrument allow the chemist to adjust sample injection quantity, vaporization temperature, and other parameters. F&M will market the 775 as a high-
low unit. For example, a research chemist could use the 1 / 4 -in. columns to resolve the composition of the material under study, then, using this knowledge, operate the 4-in. columns to get milliliter quantities of the desired product for reaction studies. F&M's PrepMaster can accommodate four 20-in.-long segments of the 4-in.-diameter columns. Each segment contains a porous metal disk called a "flow homogenizer." The flow homogenizers and other design elements correct one of the problems of nonuniform gas flow, which could lead to resolution loss in large-scale columns, F&M says. According to the company, these disks ensure a homogeneous flow in the large-diameter columns. Efficiencies of about 200 theoretical plates per foot for a 1-ml. sample are obtainable, the company adds. Most other manufacturers of preparative chromatographs have been skeptical of the use of large columns. Some of them have experimented with large columns (greater than 3 / 4 in.) and found a great gain in H E T P (height equivalent to a theoretical plate) as diameter increases. Other problems involve temperature maintenance, vaporization of large quantities of sample, use of large quantities of carrier gases, and collection of purified material. The approach of most gas chromatograph manufacturers has been to increase sample injection capacity and to build dual-purpose analytical units which become preparative systems when equipped with automatic repetitive sample injections. Beckman, for example, introduced the GC-4 last year. The GC-4 is basically an analytical unit which uses 5 / 8 -in. columns. It can, however, be automated. By using three columns in parallel, it gives a scale-up of 35 times for preparative work. Somewhat the same approach has been taken by other gas chromatograph manufacturers. Wilkens Co., maker of the Autoprep, offers automatic sample injection and up to 1 / 2 in.-diameter columns. This year, the size of sample injection has been increased to 20 cc. Fisher Scientific is directing its efforts toward the development of a versatile dual-purpose analytical and preparative unit. Nester & Faust (which uses an annular column), and Loenco, Inc., are also offering dual-purpose chromatographs.
perhaps this MILESAMINE H
0
-CH2-N-CH2-|A|
N, N-DIBENZYLAMINE
II
I
one of our many aralkyl amines U
jy
Description — Colorless to pale yellow liquid. Assay 9 6 % minimum. Specific gravity 1.020 at 27°C. Ref r a c t i v e index 1.5720-1.5735 at 25°C. Melting range of Hydrochloride 259 to 265°C.
can make your problems disappear
Other uses — As an intermediate in the synthesis of quaternary ammonium compounds and various other types of organic compounds. It has antirust properties.
MILES
CHEMICAL COMPANY DIVISION OF MILES LABORATORIES, INC. • ELKHART, INDIANA General Sales Offices: Elkhart, Ind., COngress 4-8716; Clifton, N.J., 772-4800; New York, N.Y., MUrray Hill 2-7970.
FEB.
15, 1965
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