Patent ID: 8461383
Filing Date: 2013-06-11
Classification: C07C

Abstract:
1. A process for starting up a separating process for purifying removal of acrylic acid crystals from a suspension S of crystals thereof in mother liquor with an apparatus which comprises a hydraulic wash column which has a process space which is rotationally symmetric with respect to its longitudinal axis running from the top downward and is bounded by a cylindrical outer wall and two opposite ends on the axis of symmetry, in which one or more filter tubes extend through the process space from the upper end of the process space parallel to the longitudinal axis thereof, which run toward the lower end of the process space opposite the upper end, and have, in the half of the process space toward the lower end of the process space, at least one filter F which constitutes the only direct connection between the particular filter tube interior and the process space, and are conducted out of the wash column outside the process space, the quotient Q=L/D of the distance L between the upper and lower ends of the process space and the diameter D of the process space is 0.3 to 4, the lower end of the process space is followed in the downward direction by the crystal melt space of the wash column, a rotatable removal device being integrated between the two spaces and a crystal melt circuit which is conducted through the crystal melt space comprising, outside the crystal melt space, connected upstream of the upper end of the process space in the upward direction is a distributor space which is separated from the process space at least by one end B which has passages U which lead into the process space on the side of the end B facing the process space and into the distributor space on the side of the end B facing away from the process space, a delivery pump P a delivery pump P the pump P optionally, the pump P overall, a stream SM comprising mother liquor and optionally control liquor is conducted as waste liquor stream into the filter tube interior via the filters F of the filter tubes, and out of the wash column via the filter tubes, and this waste liquor stream SM conducted out of the wash column is used as the source QT for the control liquor, the conduction of mother liquor and optionally control liquor in the process space of the wash column maintains the development of a crystal bed of acrylic acid crystals which has a buildup front facing the upper end of the process space, at which crystals of the stream ST of the suspension S supplied are added continuously onto the crystal bed, the crystal bed is conveyed from the top downward past the filters F toward the rotating removal device by the force which results from the hydraulic flow pressure drop of the conduction of mother liquor and optionally control liquor in the process space, the rotating removal device removes acrylic acid crystals from the crystal bed which meets it, the stream of the acrylic acid crystals removed is conveyed through the rotating removal device and/or past the rotating removal device into the crystal melt space which follows downstream of the process space in conveying direction of the crystal bed, and melted in the crystal melt circuit conducted through the crystal melt space as a result of introduction of heat with the heat transferer W to give a crystal melt stream, and the flow through the outlet A is regulated such that, based on the flow rate of the aforementioned crystal melt stream, proceeding from the crystal melt space, a substream of crystal melt flows as wash melt stream through the rotating removal device and/or past the rotating removal device against the direction of movement of the crystal bed back into the process space, where it ascends within the crystal bed conveyed downward and in doing so washes the mother liquor off the crystals and forces it back, said mother liquor remaining in the crystal bed having been conveyed with the latter under the filters F, which forms, in the longitudinal section of the process space which extends from the filters F to the lower end of the process space, in the crystal bed, a wash front which divides the crystal bed, from the top downward, into a mother liquor zone and into a wash melt zone, and the remaining substream of the aforementioned crystal melt stream leaves the crystal melt circuit through the outlet A, wherein, in the course of startup of the separating process for first development of the crystal bed in the process space, the crystal melt circuit comprising the crystal melt space, and the process space of the previously unfilled wash column, are at first filled with an acrylic acid-comprising startup liquid AT such that the fill height of the startup liquid AT in the process space overtops at least the removal device, then the filling of the wash column is continued by using the pump P