Technology
Lignin conversion process shows promise Hydrocarbon Research Inc. process uses fluidized-bed hydrocracking and thermal hydrodealkylation to convert lignin to phenol, derivatives Hydrocarbon Research Inc. is developing a two-step process to convert lignin to phenol and its derivatives. In the company's Lignol process, lignin is first deploymerized by hydrocracking in a fluidized bed, and the resulting monoaromatic compounds are dealkylated to phenols and benzene. According to HRI's Hugh J. Parkhurst Jr., the feedstock of primary interest is the processed lignin derived from kraft pulping. About 25% of lignocellulosic biomass is lignin formed by polymerization of three major components: trans -coniferyl, trans-sinapyl, and trans-p- coumaryl alcohols. Natural lignin is greatly changed in the kraft process, which involves high-temperature digestion in caustic solutions. The resulting kraft lignin typically has a molecular weight of about 3500. The major changes in the lignin during kraft cooking are condensations involving formaldehyde and/or /3-carbonyl derivatives, which yield methylene-linked aromatic rings and, consequently, increase the molecular weight. There is also cleavage of the phenolic ethers in the strong alkaline reaction medium.
longer residence times than are used with conventional toluene hydrodealkylation. Parkhurst says that about 30% conversion is achieved in each pass. On the basis of the results obtained thus far, HRI estimates that kraft lignin can be processed to yield about 20% (by weight) phenol, 14% benzene, 13% fuel oil, and 29% fuel gas. If the hydrogen used in the process is generated from in-plant streams, the net fuel oil yield is reduced to about 11%. The preliminary process economic estimate is that a capital investment of about $45 million (1980 dollars) would be required for a plant processing 485 tons per day of kraft lignin. If the lignin is available at $107 per ton, the return on investment would be an estimated 25%. Actual revenue would depend on the prevailing prices for products issuing from the plant. Parkhurst notes, however, that the present price difference between phenol and benzene prompts HRI to seek ways to increase the phenol yield over that of benzene. Present catalyst selectivity for phenol is about 56%. If this could be increased to 80%, and if the dealkylation yields to phenol also could be increased to 80%, the net phenol yields from the process could exceed 38%. Parkhurst believes that these improvements and others are quite possible. The economics of the Lignol process become even more attractive if the alkyl phenols could find specialty markets. Parkhurst also notes that there is great interest in attaching a
Sufficiently depolymerized, the lignin winds up in solution in the black liquor of the kraft process. Acidification precipitates the dissolved phenolics from the liquor. Further purification is possible by alternatively dissolving and reprecipitating. This is the source of the lignin used in HRI's development of the Lignol process. Parkhurst says that catalytic hydrocracking is the preferred method of lignin depolymerization. The temperatures are high enough so that in the initial stages there is bond rupture to form free radicals. The free radicals then immediately stabilize with the hydrogen in the reaction slurry. Yields of phenols may suffer from repolymerization to heavy oils, and hydrogenation of the aromatic rings must be avoided for this reason. HRI's technology for the process depends greatly on the fluidized bed reactor. The feed is a slurry of pulverized kraft lignin and lignin-derived oil with hydrogen, which is fed at the bottom of the bed. Reaction is rapid and the lighter monoaromatics quickly exit the reactor before they can react further. The product slate from the fluidized bed is considered by HRI to be distinctly superior to that obtained from a fixed-bed process developed in Japan in the 1960's. The hydrodealkylation following depolymerization is accomplished best in a separate reactor and in the absence of catalysts. The thermal hydrodealkylation is highly selective because of the lower temperature and
Hydrocracking, dealkylation basis of Lignol process Recycle oil
1 — Kraft I ignin feed Î485 tons oer day)
Lignin hydrocracker
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Sulfur recovery plant
Sulfur product (4 J tons per day)
1
r Hydrogen Pkint
Product separation train
\—Mono arorraitics ^ • ^ ^
Product separation train
> Phenol (98 tons per day) Benzene (70 tons per day) > Fuel oil (53 tons per day)
Recycle phenol
Nov. 3, 1980C&EN
35
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Lignol unit in tandem to an ethanolfrom-cellulose plant. If this can be done, the prospect is that for every gallon of ethanol from newsprint, there also would be 1 lb of phenol and 0.7 lb of benzene. Asked whether there might be any interest by paper companies in using the Lignol process to convert kraft lignin, several pulping engineers agree that as long as there is a surplus of lignin available, the process might be attractive. Most lignin now finds use as a fuel in the paper mills and is highly valued for this purpose, but the value as a chemical feedstock may be higher in most places. D
Aluminum-air fuel cell tested at Livermore The recent successful tests at Law rence Livermore National Laboratory of an aluminum-air power cell for automobiles (C&EN, Oct. 20, page 32) could lead to a prototype vehicle in 1989 if the research schedule set by the Department of Energy moves along as anticipated. The schedule calls for building a refuelable cell next year, a multicell test module in 1982, and a 60-cell prototype auto battery in 1985. The tests, described recently at an Electrochemical Society meeting in Miami, were carried out on a single auto-sized test cell containing a rec tangular aluminum alloy plate 16 inches by 10 inches by V^inch thick. In operation, air and water are pumped through the cell and combine with the aluminum, producing elec tricity and a recyclable reaction product hydrargillite [Al(OH)3]. A crystallizer forms and collects the reaction product so it doesn't clog up the cell. The aluminum is used up gradually and uniformly in the oper ation. To refuel, a new aluminum plate is added. According to LLNL research chemist John F. Cooper, who along with electrical engineer Ervin Behrin manages DOE metal-air battery research efforts centered at the lab oratory, 60 of the cells connected to gether into a 970-lb battery ulti mately could power a full-perfor mance, five-passenger vehicle. It could travel 300 miles nonstop at 55 mph, 10 times the range of a car powered by the same weight of to day's lead-acid batteries. A vehicle would carry about 6 gal of water—enough to go about 250 to 300 miles without stopping. Then tap water would be added and the reac tion product removed for recycling. Aluminum alloy plates would be added—a 15- to 30-minute job—only
