Decomposition behavior of five selected amino acids in high-temperature and high-pressure water was studied using a continuous-flow tubular reactor. The reaction was carried out in the temperature range of 200−340 °C at a pressure of 20 MPa. Alanine and its derivatives leucine, phenylalanine, serine, and aspartic acid were used as model amino acids. The effect of temperature on reaction products, pathway, and rate was determined as a function of reaction time. Alanine decomposed into lactic acid and pyruvic acid, then finally mineralized to carbon dioxide with an activation energy of 154 [kJ/mol] at 20 MPa. The degradation rate decreased in the following order:  aspartic acid, serine, phenylalanine, leucine, and alanine. The general reaction network of amino acids under hydrothermal conditions takes two main paths:  deamination to produce ammonia and organic acids, and decarboxylation to produce carbonic acid and amines. Deamination was the predominant reaction in the decomposition of aspartic acid, an acidic amino acid. Production of glycine and alanine from serine, an oxy amino acid, was also observed.

Poly(L-lactide) [i.e., poly(L-lactic acid) (PLLA)] was hydrolyzed in the melt in high-temperature and high-pressure water at the temperature range of 180-350 degrees C for a period of 30 min, and formation, racemization, and decomposition of lactic acids and molecular weight change of PLLA were investigated. The highest maximum yield of l-lactic acid, ca. 90%, was attained at 250 degrees C in the hydrolysis periods of 10-20 min. Too-high hydrolysis temperatures such as 350 degrees C induce the dramatic racemization and decomposition of formed lactic acids, resulting in decreased maximum yield of L-lactic acid. The hydrolysis of PLLA proceeds homogeneously and randomly via a bulk erosion mechanism. The molecular weight of PLLA decreased exponentially without formation of low-molecular-weight specific peaks originating from crystalline residues. The activation energy for the hydrolysis (deltaE(h)) of PLLA in the melt (180-250 degrees C) was 12.2 kcal x mol(-1), which is lower than 20.0 kcal x mol(-1) for PLLA and 19.9 kcal x mol(-1) for poly(dl-lactide) [i.e., poly(DL-lactic acid)] as a solid in the temperature range below the glass-transition temperature (21-45 degrees C). This study reveals that hydrolysis of PLLA in the melt is an effective and simple method to obtain l-lactic acid and to prepare PLLA having different molecular weights without containing the specific low-molecular-weight chains, because of the removal of the effect caused by crystalline residues.

Amorphous-made poly(l-lactide) [i.e., poly(l-lactic acid) (PLLA)], poly(l-lactide-co-d-lactide)-[P(LLA-DLA)](77/23), and P(LLA-DLA)(50/50) films and PLLA films with different crystallinity (X c ) values were prepared, and the effects of molecular weight, d-lactide unit content (tacticity and optical purity), and crystallinity of poly(lactide) [i.e., poly(lactic acid) (PLA)] on the water vapor permeability was investigated. The changes in number-average molecular weight (M n ) of PLLA films in the range of 9 ϫ 10 4 -5 ϫ 10 5 g mol Ϫ1 and d-lactide unit content of PLA films in the range of 0 -50% have insignificant effects on their water vapor transmission rate (WVTR). In contrast, the WVTR of PLLA films decreased monotonically with increasing X c from 0 to 20%, while leveled off for X c exceeding 30%. This is probably due to the higher resistance of "restricted" amorphous regions to water vapor permeation compared with that of the "free" amorphous regions. The free and restricted amorphous regions are major amorphous components of PLLA films for X c ranges of 0 -20% and exceeding 30%, respectively, resulting in the aforementioned dependence of WVTR on X c .

lbyohashi 441 -8580, Japan nvironmental pollution resulting from daily human and industrial solid waste discharges, including those from the seafood processing E industry, is becoming a serious social problem nowadays. In Japan, for example, about half of 9.8 million tons of fish processed in the industry per year is being put into waste. In this regard, technologies that would treat these waste or even better recover some useful organic materials before disposal are of significant importance. Martin (1 999) suggested a low-energy process of converting fish wastes by composting with peat. Dapkevicius et al. (1998) studied ensilage processes of upgrading protein residues in fish wastes by acid (using formaldehyde) and biological silages (using molasses or dehydrated whey). Other than the aforementioned processes, more efficient methods are strongly desired since large amount of fish wastes are being discharged from industries every day. One possible method for the treatment of fish wastes is the use of sub-or supercritical water.Sub-and supercritical water has attracted many scientists because of its fascinating properties as a reaction medium (Shaw et al., 1991;Savage et al., 1995). Supercritical water is completely different from water at ordinary pressure and temperature. For example, at room temperature and atmospheric pressure, water has a dielectric constant of 80 and ion product (K, ) of 1 O-14. The dielectric constant expresses the affinity of water, as a reaction medium, to reaction materials. These values can be controlled by changing temperature and pressure, and could greatly affect the reactivity of various compounds in water. In addition, ion product of water can also be adjusted by changing temperature and pressure to control the ability of hydrolysis. High ion product is good for hydrolysis. Under saturated vapour pressure, water has a maximum ion product at around 250°C. The use of sub-and supercritical water has been widely applied to various reactions such as reduction, pyrolytic, decomposition and dehydration (Savage et al., 1995). Examples are oxidation of phenols (Martino and Savage, 1999), pyridine (Aki and Abraham, 1999a, b) and methanol (Anitescu et al., 1999), and hydrolysis of esters (Krammer and Vogel, 1999) and thiodiglycol (Lachance et al., 1999), among others. The technique was also applied to chemical recycling processes such as hydrolysis of polyethylene terephthalate (PET) into ethylene glycol and terepthak acid (Arai and Adschiri, 1999). The most significant applications A resource recovery technique using sub-and supercritical water hydrolysis was applied to convert waste fish entrails into amino acids. The effect of reaction parameters such as temperature and time necessary for the control of reaction towards optimum yield of amino acids was investigated. Results showed a maximum yield of total amino acids (1 37 mg/g dry fish) from waste fish entrails a t T = 523 K (P = 4 MPa) and reaction time of 60 min in a batch reactor. Under supercritical conditions (e.g., T = 653 K, P = 4...

The possibility of amino acids and glucosamine production from the treatment of shrimp shells in high-temperature and high-pressure water was investigated. Under the tested conditions, the highest amount of amino acids (70 mg/g of dry shrimp shell) from hydrolysis of proteins was obtained at a reaction temperature of 523 K in 60 min. This amount was about 2.5 times the total amino acids obtained at 363 K, the temperature at which shrimp extracts for use in noodles soup are being prepared. The amount of simple amino acids such as glycine and alanine increased with increasing temperature up to 523 K and decreased thereafter. This behavior has also been observed from other seafood processing wastes such as fish entrails and scallop wastes. Glucosamine was not detected presumably because of its deamination to produce glucose or cellulose. To further investigate the reason for the nonformation of glucosamine from shrimp shells, experiments on chitin as the starting reaction material were carried out.

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