New Reaction Engineering Concepts for Selective Oxidation Reactions

In order to enhance product yields in selective oxidation reactions, numerous reaction engineering concepts are being studied worldwide. Periodic operation has been investigated for decades, yet its application is limited to a few examples, such as the butane oxidation after DuPont or reverse-flow reactors for VOC removal. The use of microchannel reactors is a younger field, but it has already yielded promising results for process optimization. Catalytic wall reactors have proved to be a helpful tool for kinetic studies. On the laboratory scale, membrane reactors have displayed favorable behavior in selective oxidation. The Na vapor-catalyzed dehydrogenation of methanol to formaldehyde is a final example of an unusual new concept for selective oxidation.     

Catalytic conversion of low-density polyethylene using a continuous screw kiln reactor

Both thermal and catalytic cracking of low-density polyethylene (LDPE) have been investigated using a screw kiln reactor. Thermal degradation gives rise to a broad product distribution, whereas catalytic cracking over Al-MCM-41 leads mainly to hydrocarbons within the gasoline range (C₅–C₁₂) with selectivities up to 80%. The increase of the screw speed between 3 and 15 rpm in the catalytic experiments allows the plastic feed rate to be varied in the range 20–41 g h⁻¹. The changes observed in the TOF values when varying the screw speed point out a decrease of the activity per site with increasing residence times, which may be due to the catalyst deactivation or to a contribution of the degradative extrusion at higher screw speeds. Likewise, a certain increase in the selectivity towards the gasoline fraction is observed at short residence times. On the other hand, PIONA analyses indicate that, regardless of the screw speed, the main components of the gasoline are olefins (50%) and isoparaffins (20%), whereas the aromatic content is always below 6%, with a proportion of benzene lower than 0.1%.     

Polymer waste recycling over “used” catalysts

Catalytic degradation of high-density polyethylene (HDPE) was carried out under nitrogen using a laboratory fluidised bed reactor operating at 360 °C with catalyst to polymer feed ratio of 2:1 and at 450 °C with catalyst to polymer feed ratio of 6:1 under atmospheric pressure. The catalysts used in this study were ZSM-5, US-Y, ASA, fresh FCC (fluid catalytic cracking) commercial catalyst (Cat-A) and equilibrium FCC catalysts with different levels of metal poisoning were studied. The initial results for polymer degradation at 360 °C (catalyst to polymer ratio of 2:1) in a fluidised bed reactor in terms of the yield of volatile hydrocarbon products were: model catalysts>commercial FCC catalyst>E-Cats. However, when the process conditions more closely resembled to FCC conditions, the fresh commercial FCC catalyst was more favourable in terms of the yield of volatile hydrocarbon products. The degradation of HDPE over E-Cats although reduced was similar to ASA in product selectivity and yield, and the level of metal contamination did not affect the product stream generated. A simple economic evaluation of polymer recycling process is reported showing that a catalytic system based on E-Cats appears comparable in costs to a commercial thermal cracking plant.     

在役加氢反应器材料损伤分析

基于随加氢反应器运行 5a的试验试块 ,研究了加氢反应器运行 5a后筒体材料 2 .2 5Cr 1Mo钢的损伤。进行了化学成分分析、拉伸和冲击试验、脱氢和脱脆试验以及断口形貌分析。结果表明 :反应器运行 5a后筒体母材及其焊缝金属的拉伸性能未发生明显变化 ,而冲击韧性明显降低 ,且焊缝金属损伤程度较母材严重。经分析 ,材料的损伤主要是加氢反应器长期使用过程中高温回火所致     

循环流化床锅炉启动运行过"三关"

从循环流化床锅炉在启动运行中遇到的点火难、易结焦、磨损严重问题出发，阐述了产生这类问题的机理，并提出了解决措施。     

三聚氰胺反应器气体停留时间的探讨

分别从三聚氰胺反应机理和化学动力学的角度出发，讨论了三聚氰胺流化床反应器中气体流动状态和停时间和简化计算方法，指出影响三聚氰胺反应转化率和选择性的诸多因素，并就硅铝催化剂在三聚氰胺工业生产使用中应注意的问题提出了行之有效的建议。     

大颗粒尿素造粒工艺简介

介绍了大颗粒尿素造粒工艺，着重介绍了荷兰NSM公司的流化床造粒技术和法国K－T公司的流化床转鼓造粒（FDG）技术。     

浅谈流化床干燥器布风板的设计

介绍流化床干燥器所用各种形式布风板的结构。并对其使用情况作了分析。特别对高温布风板的形式进行了探讨。     

超声波气升式反应器内声压的测定

测定了在空气—水和空气—羧甲基纤维素水溶液体系中 (羧甲基纤维素含量 :2g/L)超声波气升式反应器声压随轴向位置、表观气速、黏度和超声电功率的变化。测定结果表明 ,小气速下声压在气升式反应器内的轴向分布与离开超声探头的距离有关 ,距离越远 ,声压越小 ;与气速的大小有关 ,气速越大 ,声压越小 ;与液体的黏度有关 ,黏度越大 ,声压越小 ;超声电功率越大 ,声压越大。     

硫铁矿沸腾炉掺烧含硫化氢酸性气体的研究

对合成氨装置排出的酸性气体掺入硫铁矿在沸腾炉内燃烧进行了试验研究，酸性气体φ（H2S）约31．8％，φ（CO2）约68％，掺烧试验结果表明，在正常的操作条件下，硫化氢燃烧生成二氧化硫的反应相当迅速和完全，通过调节投矿量沸腾炉可以适应硫化氢气体浓度和流量的变化，生产出符合硫酸生产的原料气，因此在硫铁矿中掺烧含硫化氢的酸性气体是可行的，建议在工业生产中，由沸腾炉的扩大层加入酸性气体，这样可防止泄漏，避免出气孔堵塞，并且可通过调节二次风量控制硫化氢气体的燃烧。