Aciduric, pH-Elevating Bacillus which Cause Noneffervescent Spoilage of Underprocessed Tomatoes

In the preliminary phase of this study, a selective isolation medium was developed. Using the new medium, 24 strains of Bacillus Spp. that elevate tomato juice pH were isolated from garden soil or natural vegetative materials. Two jars of home-canned, water-bathed tomatoes contained sporeformers which produced noneffervescent spoilage. All strains were morphologically and physiologically different from 2 flat-sour strains of B. coagulans and B. licheniformis strains, but similar to a previous isolate from home-canned, spoiled green beans that elevated pH. The new medium may have future applications in isolation and enumeration of other acidurics including yeast-like microorganisms.     

新型钨基催化剂上环己烯环氧化反应

烯烃环氧化在现代化学中具有重要的学术和工业价值,但采用绿色氧化剂过氧化氢仍面临传质的挑战。采用过氧缩合法制备了一种新型钨基催化剂,用于过氧化氢与环己烯环氧化研究,环己烯的转化率为51.2%,环氧环己烷的选择性为69.2%。结果显示该催化剂催化活性高,环氧环己烷的选择性好,反应条件温和,工艺无溶剂且绿色环保。     

碳酸钠预处理对麦草酶水解糖化的影响

麦草是一种具有很大潜力的制取生物乙醇的可再生木质纤维素原料。文章探讨了碳酸钠预处理预浸时间、保温时间、碳酸钠用量对麦草化学成分及酶水解效率的影响。结果表明,延长碳酸钠预处理保温时间对木质素脱除无明显影响,但浆料得率和酶水解总糖转化率有所下降;合理的预浸时间为30 min,继续延长预浸时间对预处理浆料酶水解总糖转化率无促进作用;增加预处理Na2CO3用量有助于促进木质素的脱除,大部分碳水化合物保留在浆料中。在8% Na2CO3(Na2O计)用量下,麦草于80℃预浸30 min后升温至130℃,不保温所得到的浆料在纤维素酶用量为20 FPU/g(对纤维素)时,其总糖转化率为60%。     

A Risk-Based Performance Analysis of Plate-andFrame Heat Exchangers Subject to Fouling: Economics of Heat Exchanger Cleaning

Fouling is one of the major uncertainties associated with the operation and maintenance of plate-and-frame heat exchangers (PHEs) in the steel and process industries. The decision regarding periodic maintenance (i.e., cleaning) to meet the target performance level is generally based on both thermal and economic behavior of the process. In this paper, we present a cost model that includes the risk level and the scatter parameter of random fouling growth models. Two models (namely, power law and exponential fouling growth) are integrated in the model. The non-dimensional cost function of reduced time is examined by considering dimensionless cost parameters, representing additional cost due to a decrease in effectiveness, pumping power cost, anti-foulant cost, cleaning cost, additional pumping power cost of the standby unit during cleaning, and miscellaneous costs. These dimensionless cost elements are examined for a PHE operating in the steel industry. The results are presented in terms of the risk level and scatter parameter for the underlying fouling models. Furthermore, a simplified closed-form solution is also obtained to study the optimal cycle time, which represents the minimum cost of operation and maintenance of heat exchangers. It is found that the optimum dimensionless cost increased by about 21 and 14% for the power law and exponential fouling models, respectively, as the risk level decreased from 0.5 to 0.01