Previous work has shown that very high yields of charcoal are obtained when pyrolysis of the biomass feedstock is conducted at elevated pressure in a closed vessel, wherein the pyrolytic vapors are held captive and in contact with the solid products of pyrolysis. In this paper, we show that, for some biomass species, the yield of carbon produced by this process effectively attains the theoretical value predicted to exist when thermochemical equilibrium is realized. Various agricultural wastes (e.g., kukui nut, macadamia nut, and pecan shells) and tropical species (e.g., eucalyptus, leucaena, and bamboo) offer higher yields of carbon than the hardwoods traditionally employed by industry in the U.S. and Europe. Moreover, the yields of carbon from oat and rice hulls and from sunflower seed hulls are nearly as high as the yields of carbon from hardwoods. There is a correlation between the yield of carbon and the acid-insoluble lignin content of the feed. Charcoal briquettes made from agricultural wastes and lump charcoal from tropical species are promising sources of renewable carbon for use in the smelting of metal ores.

Catalytic conversion of lactic acid to 2,3-pentanedione over sodium salts and base on low surface area silica support has been studied. Yield and selectivity toward 2,3-pentanedione are optimal at around 300 °C, 3−4 s residence time, and 0.5 MPa total pressure. Anions of initial salt catalysts used do not participate in lactic acid condensation to 2,3-pentanedione once steady-state conditions have been achieved; instead, sodium lactate has been identified by postreaction FTIR spectroscopy as the primary, stable species on the support during reaction. Sodium lactate is believed to be an intermediate in 2,3-pentanedione formation. Conversion of a sodium salt to sodium lactate is greatest when the salt used has a low melting point and a volatile conjugate acid; the extent of conversion depends weakly on reaction time and temperature within experimental conditions. At high temperature (∼350 °C), sodium lactate decomposes to sodium propanoate and sodium acetate, which may explain reduced 2,3-pentanedione yields at higher temperatures.

A novel, three-step process for the production of high-quality activated carbons from macadamia nut shell and coconut shell charcoals is described. In this process the charcoal is (i) heated to a high temperature (“carbonized”), (ii) oxidized in air following a stepwise heating program from low (ca. 450 K) to high (ca. 660 K) temperatures (“oxygenated”), and (iii) heated again in an inert environment to a high temperature (“activated”). By use of this procedure, activated carbons with surface areas greater than 1000 m2/g are manufactured with an overall yield of 15% (based on the dry shell feed). Removal of carbon mass by the development of mesopores and macropores is largely responsible for increases in the surface area of the carbons above 600 m2/g. Thus, the surface area per gram of activated carbon can be represented by an inverse function of the yield for burnoffs between 15 and 60%. These findings are supported by mass-transfer calculations and pore-size distribution measurements. A kinetic model for gasification of carbon by oxygen, which provides for an Eley−Rideal type reaction of a surface oxide with oxygen in air, fits the measured gasification rates reasonably well over the temperature range of 550−660 K.

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Studies of lactic acid catalytic conversion over alkali salts and bases on silica demonstrate that the yield of 2,3-pentanedione (23P) increases with decreasing Lewis acidity of the alkali metal, from 15% for lithium hydroxide at 320 °C to 49% for cesium hydroxide at 280 °C. The rate of 23P formation varies linearly with alkali metal loading up to saturation at 2 mmol of catalyst/g of support. Experiments with different silica supports showed that acetaldehyde formation increases with support acidity, reducing 23P yield. Postreaction FTIR studies indicate the presence of alkali lactate as the dominant species on the support surface at reaction conditions. These results, along with the kinetic model developed, support the proposed mechanism of 23P formation as a condensation between lactic acid and alkali lactate.

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A high-yield activated carbon is produced from macadamia nut shell charcoal by (i) carbonization of the charcoal at 1173 K, (ii) air oxidation of the carbonized charcoal in boiling water (AOBW) at 503−553 K, and (iii) activation (a second carbonization) of the oxygenated carbon. In step ii, air is bubbled through a sparger to maintain a relatively high concentration of dissolved oxygen in the water, and the boiling water serves to control the temperature of the carbon during its gasification by the dissolved oxygen. Carbon dioxide is observed to be the only gaseous product of the oxidation chemistry. The oxidation results and the properties of the activated carbons from AOBW are similar to those obtained by controlled atmospheric air oxidation. However, the rate of CO2 formation is observed to increase with time to a plateau for AOBW, whereas the gasification rate decreases with time for atmospheric air oxidation. Multiple cycles, involving AOBW followed by activation, efficiently increase the specific surface area of the carbon to values approaching 1000 m2/g. Increases in the specific surface area occur by the removal of carbon during the AOBW step(s) and the activation step(s). Our findings indicate that carbon removal by desorption of chemisorbed oxygen during the activation step creates a specific surface area more efficiently than a prolonged, low-temperature gasification of the carbon during the AOBW step. If we assume a simple kinetic model in which the gasification reaction is first order with respect to dissolved oxygen and zero order in carbon, the activation energy for AOBW is estimated to be 108 kJ/mol between 513 and 533 K, according to measured CO2 evolution rates and dissolved oxygen concentrations. This value is near the range of activation energies observed in gaseous air oxidation at low temperatures.

Ammonia is often used for pH adjustment during fermentation of glucose to lactic acid. Its presence as ammonium lactate in the catalytic upgrading of lactic acid to 2,3-pentanedione over CsOH/silica reduces diketone yields to nearly zero at high ammonia levels. Removal of ammonia from the feed restores 2,3-pentanedione yield, indicating that the catalyst itself is not poisoned by ammonia. Instead, 2,3-pentanedione continues to form in the presence of ammonia and is consumed in secondary reactions downstream of the catalyst bed. Both base-catalyzed self-condensation of 2,3-pentanedione to duroquinone (and oligomeric species) and direct reaction of ammonia with the diketone are observed.