Photosynthesis may be source for fuels
1
Hydrogen bonds link adenine and uracil in DNA fragment, adenylyl-3', 5-uridine >7Γ ^ | Phosphorus Ο Oxygen φ Nitrogen Carbon — Hydrogen bond newer results come out in much greater detail. To explain the difference in tech- niques, the MIT scientists use an analogy. If the genetic material is like a book, a fiber x-ray diffraction study is the equivalent of photographing every page without advancing the film. The average structure of the page comes through, but the details of the words are lost. By contrast, single-crystal studies of nucleic acid fragments correspond to taking the picture of a single page. This is so because in the crystal the molecules line up in identical rows. The final "picture" of the page emerges after interpreting mathematically the pattern of x-rays coming through these rows. The data the MIT scientists present are especially sharp because of the fine discrimination of their methods. The limit of x-ray diffraction data in these studies is just 0.80 Α., small enough to resolve all the atoms, according to Dr. Rich's group. Although at first blush anticlimactic after two decades of discovery in molec- ular biology, the results the research group reported in Atlantic City had the authority of direct observation. The re- search group's summation rests on this point: "These structures are the only fragments of double helices yet seen at atomic resolution, and they remove any doubts about the correctness of the Watson-Crick hypothesis." TECHNOLOGY Converting scrap tires to useful products Hydrogénation may provide a route to converting discarded tires into salable products at a cost competitive with methods of handling used tires other than dumping. The basic process, cov- ered by U.S. Patent 3,704,108, involves hydrogénation at conventional petro- leum refining industry operating con- ditions, says Ronald H. Wolk of Hydro- carbon Research, Inc., Trenton, N.J. Products of hydrogénation of ground discarded tires are fuel gas, naphtha, gas oil, and carbon black. The yield of carbon and inorganic compounds is quantitative with respect to the original composition of the tires, Mr. Wolk told the Division of Industrial & Engineering Chemistry at the ACS national meeting in Dallas. Process operating conditions in a stirred autoclave reactor range from 660° to 850° F., and from 500 to 2000 p.s.i.g. No additional carbon-containing ma- terial such as coke is produced. The carbon black and oil produced in pilot- plant-scale tests of the process ap- pear to be satisfactory for re-use in commercial rubber compounds. Mr. Wolk and his associates, Michael C. Chervenak and Carmine A. Battista, estimate that a commercial-size plant to convert 1000 tons a day of ground rub- ber would cost $9.5 million. The main factors affecting the profitability of the plant are the cost of the ground rubber feed and the value of the carbon black sold. If the rubber costs $30 a ton, car- bon black can be sold for 6 cents a pound and liquid oils for $3.00 a barrel, and payout on the plant will be 3.9 years. If the rubber costs $20, carbon black is sold at 8 cents, and liquid oils at $3.00; payout will be reduced to 1.4 years. The calculations assume 6% interest on working capital and 15-year, straight-line depreciation. Hydrogénation was selected as a method of handling waste tires because hydrogen will not react with the carbon in the tires, and hence the carbon could be recovered nearly unchanged, Mr. Wolk points out. Pilot-plant runs have been made with catalysts such as cobalt or nickel molybdate on alumina and without catalysts. Catalyst type and use appear to have little effect on carbon quality. Noncatalytic operation results in relatively high concentrations of sulfur —0.5 to 0.7% by weight—in the gas oil fraction, some 40% of the products. With a catalyst, sulfur concentrations in the gas oil fraction generally are below 800 p.p.m., Mr. Wolk says. Photosynthesis may be source for fuels Photosynthesis has been proposed as a route to fuels that could cost about the same as fossil fuels within this decade. "Energy plantations" could be a way to overcome the two drawbacks in use of plentiful solar energy—its being dilute and intermittent. If 0.4% of the solar energy falling on fields or forests were converted to fuel value, energy cost might be in the range of $1.50 per million B.t.u., according to Dr. Clinton C. Kemp of InterTechnology Corp., Warrenton, Va. Speaking to the Division of Industrial & Engineering Chemistry at the ACS meeting, he said that if the amount of solar energy con- verted could be doubled through more intensive crop growing, the cost of energy might fall to about $1.10 per million B.t.u. The energy plantation method to har- ness solar energy would require about a tenth of the capital cost of photothermal methods and a thousandth that of photovoltaic methods, Dr. Kemp and Dr. George C. Szego estimate. A major reason for the reduced capital needs of a photosynthetic method of harnessing solar energy is that the process is its own energy accumulator or battery. Both photovoltaic and photothermal systems require storage for night operation and must be overdesigned relative to their instantaneous power vs. average power. The advantages of photosynthesis over other forms of energy, such as nuclear energy, are many, says Dr. Kemp, who advocates that research money be spent on photosynthesis development. Ther- mal pollution would be about 25% less than that with nuclear systems. Toxic fuel and waste product handling would be avoided. Locating the energy-pro- ducing unit could be done with more freedom. About 400 square miles of energy plantation would be required to support a 400-Mw. electric generating station, Dr. Kemp says. He assumes the station operates with a thermal efficiency of 34%, with a load factor of 55%—equal to the national average load factor—and at a conversion to fuel of 0.4% from 1200 B.t.u. per sq. ft. per day of solar energy. If the daily isolation rate of solar energy were higher and the conversion were higher through more intensive cul- tivation to increase plant yield, the area required to supply generating stations could decrease radically. For example, if the rate were 1400 B.t.u. per sq. ft. per day and the conversion 0.7%, the area required for the 400-Mw. station would be reduced to 190 square miles. 20 C&EN April 30, 1973
Transcript of Photosynthesis may be source for fuels
Hydrogen bonds link adenine and uracil in DNA fragment, adenylyl-3', 5-uridine
>7Γ
^ | Phosphorus Ο Oxygen φ Nitrogen
Carbon — Hydrogen bond
newer results come out in much greater detail. To explain the difference in techniques, the MIT scientists use an analogy. If the genetic material is like a book, a fiber x-ray diffraction study is the equivalent of photographing every page without advancing the film. The average structure of the page comes through, but the details of the words are lost.
By contrast, single-crystal studies of nucleic acid fragments correspond to taking the picture of a single page. This is so because in the crystal the molecules line up in identical rows. The final "picture" of the page emerges after interpreting mathematically the pattern of x-rays coming through these rows.
The data the MIT scientists present are especially sharp because of the fine discrimination of their methods. The limit of x-ray diffraction data in these studies is just 0.80 Α., small enough to resolve all the atoms, according to Dr. Rich's group.
Although at first blush anticlimactic after two decades of discovery in molecular biology, the results the research group reported in Atlantic City had the authority of direct observation. The research group's summation rests on this point: "These structures are the only fragments of double helices yet seen at atomic resolution, and they remove any doubts about the correctness of the Watson-Crick hypothesis."
TECHNOLOGY
Converting scrap tires to useful products Hydrogénation may provide a route to converting discarded tires into salable products at a cost competitive with methods of handling used tires other than dumping. The basic process, covered by U.S. Patent 3,704,108, involves hydrogénation at conventional petroleum refining industry operating conditions, says Ronald H. Wolk of Hydrocarbon Research, Inc., Trenton, N.J.
Products of hydrogénation of ground discarded tires are fuel gas, naphtha, gas oil, and carbon black. The yield of carbon and inorganic compounds is quantitative with respect to the original composition of the tires, Mr. Wolk told the Division of Industrial & Engineering Chemistry at the ACS national meeting in Dallas. Process operating conditions in a stirred autoclave reactor range from 660° to 850° F., and from 500 to 2000 p.s.i.g.
No additional carbon-containing material such as coke is produced. The carbon black and oil produced in pilot-plant-scale tests of the process appear to be satisfactory for re-use in commercial rubber compounds.
Mr. Wolk and his associates, Michael
C. Chervenak and Carmine A. Battista, estimate that a commercial-size plant to convert 1000 tons a day of ground rubber would cost $9.5 million. The main factors affecting the profitability of the plant are the cost of the ground rubber feed and the value of the carbon black sold. If the rubber costs $30 a ton, carbon black can be sold for 6 cents a pound and liquid oils for $3.00 a barrel, and payout on the plant will be 3.9 years. If the rubber costs $20, carbon black is sold at 8 cents, and liquid oils at $3.00; payout will be reduced to 1.4 years. The calculations assume 6% interest on working capital and 15-year, straight-line depreciation.
Hydrogénation was selected as a method of handling waste tires because hydrogen will not react with the carbon in the tires, and hence the carbon could be recovered nearly unchanged, Mr. Wolk points out.
Pilot-plant runs have been made with catalysts such as cobalt or nickel molybdate on alumina and without catalysts. Catalyst type and use appear to have little effect on carbon quality.
Noncatalytic operation results in
relatively high concentrations of sulfur —0.5 to 0.7% by weight—in the gas oil fraction, some 40% of the products. With a catalyst, sulfur concentrations in the gas oil fraction generally are below 800 p.p.m., Mr. Wolk says.
Photosynthesis may be source for fuels Photosynthesis has been proposed as a route to fuels that could cost about the same as fossil fuels within this decade. "Energy plantations" could be a way to overcome the two drawbacks in use of plentiful solar energy—its being dilute and intermittent.
If 0.4% of the solar energy falling on fields or forests were converted to fuel value, energy cost might be in the range of $1.50 per million B.t.u., according to Dr. Clinton C. Kemp of InterTechnology Corp., Warrenton, Va. Speaking to the Division of Industrial & Engineering Chemistry at the ACS meeting, he said that if the amount of solar energy converted could be doubled through more intensive crop growing, the cost of energy might fall to about $1.10 per million B.t.u.
The energy plantation method to harness solar energy would require about a tenth of the capital cost of photothermal methods and a thousandth that of photovoltaic methods, Dr. Kemp and Dr. George C. Szego estimate. A major reason for the reduced capital needs of a photosynthetic method of harnessing solar energy is that the process is its own energy accumulator or battery. Both photovoltaic and photothermal systems require storage for night operation and must be overdesigned relative to their instantaneous power vs. average power. The advantages of photosynthesis over other forms of energy, such as nuclear energy, are many, says Dr. Kemp, who advocates that research money be spent on photosynthesis development. Thermal pollution would be about 25% less than that with nuclear systems. Toxic fuel and waste product handling would be avoided. Locating the energy-producing unit could be done with more freedom.
About 400 square miles of energy plantation would be required to support a 400-Mw. electric generating station, Dr. Kemp says. He assumes the station operates with a thermal efficiency of 34%, with a load factor of 55%—equal to the national average load factor—and at a conversion to fuel of 0.4% from 1200 B.t.u. per sq. ft. per day of solar energy.
If the daily isolation rate of solar energy were higher and the conversion were higher through more intensive cultivation to increase plant yield, the area required to supply generating stations could decrease radically. For example, if the rate were 1400 B.t.u. per sq. ft. per day and the conversion 0.7%, the area required for the 400-Mw. station would be reduced to 190 square miles.
20 C&EN April 30, 1973
