• Korean Chemical Engineering Research
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• v.54 no.3
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• pp.394-403
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• 2016

$H_2$ production by chemical looping is an efficient method to convert hydrocarbon fuel into hydrogen with the simultaneous capture of concentrated $CO_2$. This process involves the use of an iron based oxygen carrier that transfers pure oxygen from oxidizing gases to fuels by alternating reduction and oxidation (redox) reactions. The enhanced reactivities of copper oxide doped iron-based oxygen carrier were reported, however, the fundamental understandings on the interaction between $Fe_2O_3$ and CuO are still lacking. In this study, we studied the effect of dopant of CuO to $Fe_2O_3/ZrO_2$ particle on the morphological changes and the associated reactivity using various methods such as SEM/EDX, XRD, BET, TPR, XPS, and TGA. It was found that copper oxide acted as a chemical promoter that change chemical environment in the iron based oxygen carrier as well as a structural promoter which inhibit the agglomeration. The enhanced reduction reactivity was mainly ascribed to the increase in concentration of $Fe^{2+}$ on the surface, resulting in formation of charge imbalance and oxygen vacancies. The CuO doped $Fe_2O_3/ZrO_2$ particle also showed the improved reactivity in the steam oxidation compared to $Fe_2O_3/ZrO_2$ particle probably due to acting as a structural promoter inhibiting the agglomeration of iron species.

• Korean Journal of Agricultural Science
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• v.15 no.1
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• pp.95-113
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• 1988

In order to find out changes of chemical components related to browning of dried jujube, four varieties were subjected to the proximate analysis. Boeun, one of the major varieties in Korea, was sun-dried and stored for 12 months and analyzed periodically for one year. Browning, titrable acidity, pH, contents of ascorbic acid, organic acid, total amino acid, free amino acid, free sugar, hydroxymethylfurfural (HMF) and phenolic compounds were determined and compared with those of fresh jujube. The results obtained are summarized as follows; 1. In comparison with other similar fruits, jujube was high contents of ascorbic acid (62-79mg%) and carbohydrate (22-28%) excluding fiber. 2. Browning was increased in both steam-treated and nontreated plot together as storage period was prolonged. 3. Ascorbic acid content of fresh jujube was as high as 297.4mg% DB, but it was decreased to 20.2mg% DB, after 12 months storage. Therefore, loss of ascorbic acid was very great up to 93% of its original content. 4. Five kinds of organic acid, oxalic, succinic, fumaric, malic and citric acid were identified as major organic acids. It was interesting that only fumaric acid content was increased while others decreased during storage. 5. Seventeen kinds of amino acid were identified in the analysis of total amino acid content. Major amino acids were found to be proline, threonine, glutamic acid and lysine. During 12 months storage, 30% of original total amino acid was decreased and this was mostly accounted for free amino acids. 6. Threonine, proline, alanine and valine were identified as free amino acids which showed 85% decrease after 12 months storage. 7. Free sugars of jujube were composed of fructose, glucose and sucrose. They showed 24% decrease after 12 months storage, Especially sucrose was not detected after 4 months storage. 8. HMF of dried jujube was isolated and identified. Its content was increased up to great extent as storage period prolonged. 9. Caffeic, ferulic and P-coumaric acid were identified as jujube phenolic compounds which were significantly decreased during storage. In conclusion, non-enzymatic browning was thought to be more important than enzymatic reaction in the dried jujube. Amino-carbonyl reaction, ascorbic acid oxidation and reaction between phenolic compounds and sugar or nitrogen compounds were observed to be related to this browning.