Variable and self-regulating permeate recycling in organophilic nanofiltration

A method of continuously separating a component from a liquid mixture using a membrane unit which comprises at least one membrane stage and is fed with the mixture as feed, wherein a membrane stage comprises at least a conveying device, at least two series-connected membrane modules, and a feed vessel upstream of the conveying device,

• wherein the method comprises the following steps in which:
• the mixture is guided from the feed vessel by means of the conveying device as feed to a first membrane module of the at least two membrane modules, which depletes the component to be separated off, based on the mixture guided to the first membrane module, in a resulting permeate stream from the first membrane module and enriches it in a resulting retentate stream from the first membrane module,
• the retentate from the first membrane module is guided to a second membrane module, which depletes the component to be separated off, based on the retentate from the first membrane module, in a resulting permeate stream from the second membrane module and enriches it in a resulting retentate stream from the second membrane module,
• wherein
• the at least two membrane modules are joined to one another on the permeate side by such means that the permeate stream from the first membrane module and the permeate stream from the second membrane module are each guided to a common pipeline, which gives rise to an overall permeate stream in the common pipeline, and
• wherein the at least two membrane modules are connected to the common pipeline on the permeate side in opposite directions such that a portion of the overall permeate stream, a recycled permeate, is recycled at least partly to the feed vessel and/or beyond the feed vessel but upstream of the conveying device, while the remainder of the overall permeate stream, a removed permeate, is at least partly guided out of the membrane stage, with the recycled permeate having a higher concentration of the component to be separated off than the removed permeate.