Residence time, in reactors

Molecular weight distribution function for the case where the length of the growth stage is short compared to the residence time in reactor. (Reprinted with permission from Chemical Reactor Theory, by K. G. Denbigh and J. C. R. Turner. Copyright 1971 by Cambridge University Press.)... 

Boltzmann constant Dimensionless time Residence time in reactor Thiele modulus... 

Industry has applied radiotracers in a very large variety of ways. More than half of the SOO largest manufacturing concerns in the United States use radioisotopes in the production of metals, chemicals, plastics, pharmaceuticals, paper, rubber, clay and glass products, food, tobacco, textiles, and many other products. Radioisotopes are used to study mixing efficiency, effect of chamber geometry, residence time in reactors, flow rates and patterns in columns and towers for fractionation, absorption, racemization, etc. Some of die many uses are listed in Table 9.6 and a few are described below to reflect the scope and value of the industrial applications of radioisotopes. Quite often the radionuclide used is not isotopic with the system studied. 

Low conversion => low residence time in reactor => lower chance of 2nd and 3rd reactions occurring. Large excess of CgHg => CI2 much more likely to encounter CgHg than substituted CgHg higher selectivity. 

Figure 3.9. The influence of reaction mixture movement on distribution of reagents residence times in reactor of cylindrical type. Apparatus III (Table 2.2) w [cmVsec] 130 (1) 91 (2) 62 (3) 36 (4).

Figure 4. Chaotic oscillation in the potential of a Pt redox electrode in the chlorite-thiosulfate reaction in a flow reactor. Note the aperiodic alternation between large and small amplitude peaks. Input concentrations, [ClOfJo = 5 x 10 M, [S203 ]o = 3 X 10 M, pH = 4, residence time in reactor = a) 6.8 min, b) 10.5 min, c) 23.6 min. Reproduced from Orbdn et al. (14). Copyright 1982 American Chemical Society.

These conditions lead to interesting extraction yields, but residence times in reactors have to be kept short in order to not degrade the biomass components substantially. In the following, lignin from lignocellulosic biomass was separated by subcritical water (<220 °C, <5 MPa) and was characterized by various analytical methods. Its efficient utilization as a matrix for thermoplastic materials could be proved. It is important in material manufacturing to have a simple method for quality control of the raw materials. One of them can be Near Infrared Spectroscopy (NIRS), for example [53-55]. 

Was the degree of conversion sufficient If not, some of the reactants may be getting lost since they may not be getting converted to required products (due to loss of activity of catalyst, less residence time in reactors, poor heat transfer in process units, poor mixing of reactants, and side reactions taking place due to... 

The partially converted latex from the first reactor would be comprised of particles with broad size and age distributions. If no new particles are formed in the second reactor, which would be the normal situation, the particles leaving reactor 1 would be overcoated with copolymer rich in monomer 2 in reactor 2. The latex effluenct from the second reactor would have a narrower size distribution, but particles of the same size could have quite different structures. A particle with a small residence time in reactor 1 would have a small core and a large shell. On the other hand, a particle that was large when it was removed from reactor 1 may only accumulate a thin shell if its residence time in reactor 2 is small. 

Particle residence times in reactor Minutes or hours Seconds Once through system... 

Given the specifics of the fast pyrolysis process in terms of feedstock requirements and process conditions, ie, fast heating and short residence time in reactor, it can be expected to yield biochar with a different set of properties compared to other conversion processes, such as slow pyrolysis or gasification. The short residence time can lead to incomplete charring of the biomass particle, as observed by Bruun et al. (2011,2012). This in turn leads to lower environmental stability of biochar, and therefore lower carbon sequestration potential. This is the case even when the biomass conversion during pyrolysis is apparently complete, as reported in Brewer et al. (2009). These authors observed lower stability of fast pyrolysis biochar, assessed based on fixed carbon content and aromaticity, compared to slow pyrolysis and gasification biochar produced from the same feedstock. 

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