Mechanical Separation Processes Research Articles

Catalyzed reaction of carbon disulfide and o-phenylene diamine by tertiary amine

The reaction of carbon disulfide and o-phenylene diamine in a two-phase solution to synthesize 2-mercaptobenzimidazole (MBI) catalyzed by the inexpensive tertiary amine was carried out. The reaction, which is accelerated by adding a small amount of tertiary amine, occurs in the organic phase. The mechanism was identified by two steps. First, the reaction of carbon disulfide and tertiary amine takes place to produce an active intermediate (R 3NCS 2) within a short time of reaction. Then, this active intermediate further reacts with o-phenylene diamine to produce MBI. A kinetic model based on the proposed mechanism was built up. The advantage of using two-phase reaction is that the product precipitates from the reaction solution. Only mechanical separation processes, such as: filtration and centrifugation, are required to remove the product from the solution. A pseudo-first-order rate law is sufficiently to describe the reaction. Factors, which affect the conversion of o-phenylene diamine and the reaction rate, were investigated in detail.

High-pressure filtration—a chance for the downstream processing of biological dispersions

High-pressure filtration is a common practice in solid-liquid separation. A pressure up to 150 bar is used first for short-time drainage and then to press the filter cake with the help of an elastomer diaphragm. After the principal investigation of this concept and measurements to separate biological dispersions, its use in several processes is proposed. For suspensions of cells a filter cake with a high proportion of dry residue can be obtained within a very short time. The optimal regulation of this process on an industrial scale can be obtained by evaluation of laboratory experiments. For separation procedures with biomass and fermentation liquid the high pressure can be used to shorten the filtration time. Bacterial dispersions may be separated effectively with a cross-flow filtration apparatus which is to be developed for work at high pressure. The filtration experiments were performed on bakers' yeast (leaven) and Escherichia coli (E. coli) bacteria as model substances with a laboratory filter press apparatus. The filtration velocity and the specific filtration resistance are reported. Furthermore, the processing costs in relation to the proportion of dry residue were calculated as a function of pressure. The minimum cost corresponds to the economical operation range. Though this process is unjustifiably considered as relatively expensive, it is possible that, worked at its best, it will be able to compete with other mechanical separation processes.

Advanced Night Soil Treatment by Mechanical Solids Separation and Biological Processes

The authors studied a new method of night soil treatment where suspended solids in night soil were first removed by a rotary screen to reduce BOD loading to the following biological treatment. After treatment by a cationic polymer coagulant (1.3-1.4%/dry solids), night soil was passed through a rotary screen, and separated into thickened sludge and filtrate. The thickened sludge was best dewatered by a screw press giving sludge cake with 60% moisture content. The dewatered sludge cake was combustible without supplementary fuel. The filtrate was treated by the biological nitrification-denitrification process steadily giving treated water with T-N 60mg/l (98% removal), BOD 32mg/l (99% removal), COD 530mg/l (74% removal), color 3,400 units and SS 110mg/l. Extraordinary foam trouble at the nitrification tank was not met in this process and foam was suppressed mostly by spraying nitrified liquor with the aid of antifoam agent, as little as 0.03 kg/kl-night soil. For coagulation of the effluent from the biological treatment, poly (ferric sulfate) or ferric chloride was better than alum. The optimum pH for the ferric coagulants was 4–5 and the optimum dosage was 500mg/l as Fe. The treated water was CODMn 90mg/l, color 200 unit and PO4-P less than 0.5mg/l. It was possible to reSuce CODMn and color to less than 20mg/l and 20 units respectively by activated carbon adsorption.

Wirtschaftlichkeit als Kriterium für die Entwicklung, Auslegung und Auswahl von Apparaten und Maschinen für Prozeßstufen

AbstractEconomy as a criterion for development, design, and choice of equipment and machines for process steps. The object of this paper is to show how a supplier of individual machines can influence the total costs of a chemical processing plant. This influence is quantified using actual examples based on the development of a product range, the optimizing and matching together of mechanical and thermal separation processes, and the selection of the most suitable types of equipment. Studies show that the products and services of an equipment manufacturer can influence substantially more than just capital investment costs and interest charges with their consequent effects on the annual running costs of a plant. It is possible to reach more economical solutions for important stages in a manufacturing process if the plant designers and the equipment manufacturers work closely together. A too tightly specified enquiry can prevent a manufacturer from offering the technically and economically optimized solution. By involving equipment manufacturers and correctly using their know‐how one can tap a substantial potential for the reduction of plant running costs.