Vacuum systems, energy consumption

The main distillation types include atmospheric, vacuum, steam, azeotropic, extractive, and pressure distillation [45]. AU of these distillation methods can be carried out in a batch or continuous marmer with the exception of extractive distillation, which is solely continuous by nature. Gomplex solvent systems often require the use of multiple distillation columns in series to purify certain solvents that are not easily separated. The energy consumption in distillation columns can therefore be quite large because of the continuous operation of condensers and reboilers over extended periods of time. In order to cut down on these costs, both vacuum and steam distillation can be employed ]45]. 

In the two-step process the two reactors are coupled by the same separation system. Phenol gives azeotropes with both cyclohexanone and cyclohexanol. The relative volatility of cyclohexanone to cyclohexanol is very low at normal pressure, but it rises significantly under high vacuum. Alternative separation schemes are evaluated based on direct and indirect sequences. Both are equivalent in energy consumption, although the indirect sequence is more suitable by a decoupling effect. 

Steam, which reduces the capital and operating costs of the vacuum system and overall energy consumption. 

Peinemann et al. (1986) described the use of membranes to recover solvent from an industrial oven. Hot solvent-laden air from the oven is fed to a blower to boost its pressure to 17.6 psia and then to a membrane system. A vacuum pump is used to maintain a low pressure on the permeate. side of the membrane. The solvent-rich permeate is compressed and the solvent is condensed and recovered. The hot-solvent depleted residue gas is recycled back to the oven to reduce energy consumption. The operating and cost data for this system are presented in Table 15-20. 

Using a hydrophilic zeolite membrane such as LTA and zeolite T to remove the water from the reaction system by sweep gas or vacuum (pervaporation), the esterification reaction would drive toward the product side with the result of enhanced yields. Beneficial aspects of PVMRs also include low energy consumption and the possibility of carrying out esterification at a selected temperature. 

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