The phrase "a device that separates" is correct and usable in written English.
It can be used when describing a tool or mechanism that divides or distinguishes between different elements or components.
Example: "The engineer designed a device that separates the different materials in the recycling process."
Alternatives: "an apparatus that divides" or "a mechanism that distinguishes".
As background, a thresher is a device that separates the seed from the stem of grains.
The mass spectrometer is a device that separates atoms or molecular fragments of different mass and measures those masses with remarkable accuracy.
So it seems rational to welcome a device that separates the dangerous part of smoking (the tar, carbon monoxide and smoke released by the process of combustion) from the nicotine.
In practice, since many signals at different wavelengths are traveling simultaneously down each fiber, the MEMS package requires a device that separates the arriving wavelengths and directs each to a different mirror so that it can be switched to its specific destination.
Studies of light emitted by flames led to its analysis in the spectroscope, a device that separates a mixture of light waves into the component waves, and to spectral analysis generally, including theories of atomic and molecular spectra, which in turn contributed to an understanding of the nature of flames.
Typical deployment of an ADSL line requires what's known as a "splitter," a device that separates a phone line's voice signal from the DSL data spectrum, requiring trained technicians to do house-to-house installations, a prohibitively expensive prospect.
One way that Liu sorts her stem cells into groups is using an inertial microfluidic separation device that separates cells of large diameter cells from those of small diameter.
By exploiting acoustic metamaterials and compressive sensing, we present here a single-sensor listening device that separates simultaneous overlapping sounds from different sources.
The software at issue makes a pollution-control catalyst heat up faster, improving performance of the device that separates smog-causing nitrogen oxide into nitrogen and oxygen gases.
It's not immediately clear how Apple will respond to the introspection engine; while it has worked to give consumers security features meant to thwart even sophisticated attackers, the company might not be fond of a device that can separate an iPhone from all networks.
