An apparatus for producing a multimodal polyolefin, comprising: a first reactor configured to produce a first polyolefin; a second reactor configured to produce a second polyolefin and a third polyolefin, where the second reactor comprises: a riser configured to produce the second polyolefin; an upper conduit having an end fluidly connected to a top portion of the riser; a separator fluidly connected to an opposite end of the upper conduit; a downcomer configured to produce the third polyolefin, wherein a top portion of the downcomer is fluidly connected to the separator, optionally via a liquid barrier in the top portion of the downcomer; and a lower conduit having an end fluidly connected to a bottom portion of the downcomer and an opposite end fluidly connected to a bottom portion of the riser, wherein: the second reactor is configured to receive the first polyolefin from the first reactor, or, the first reactor is configured to receive the second polyolefin and the third polyolefin from the second reactor; and wherein: the second reactor has an internal surface which is polished to a root mean square of less than about 150 microinches. a first reactor configured to produce a first polyolefin; a second reactor configured to produce a second polyolefin and a third polyolefin, where the second reactor comprises: a riser configured to produce the second polyolefin; an upper conduit having an end fluidly connected to a top portion of the riser; a separator fluidly connected to an opposite end of the upper conduit; a downcomer configured to produce the third polyolefin, wherein a top portion of the downcomer is fluidly connected to the separator, optionally via a liquid barrier in the top portion of the downcomer; and a lower conduit having an end fluidly connected to a bottom portion of the downcomer and an opposite end fluidly connected to a bottom portion of the riser, wherein: the second reactor is configured to receive the first polyolefin from the first reactor, or, the first reactor is configured to receive the second polyolefin and the third polyolefin from the second reactor; and wherein: the second reactor has an internal surface which is polished to a root mean square of less than about 150 microinches. a riser configured to produce the second polyolefin; an upper conduit having an end fluidly connected to a top portion of the riser; a separator fluidly connected to an opposite end of the upper conduit; a downcomer configured to produce the third polyolefin, wherein a top portion of the downcomer is fluidly connected to the separator, optionally via a liquid barrier in the top portion of the downcomer; and a lower conduit having an end fluidly connected to a bottom portion of the downcomer and an opposite end fluidly connected to a bottom portion of the riser, wherein: the second reactor is configured to receive the first polyolefin from the first reactor, or, the first reactor is configured to receive the second polyolefin and the third polyolefin from the second reactor; and wherein: the second reactor has an internal surface which is polished to a root mean square of less than about 150 microinches. the second reactor is configured to receive the first polyolefin from the first reactor, or, the first reactor is configured to receive the second polyolefin and the third polyolefin from the second reactor; and wherein: the second reactor has an internal surface which is polished to a root mean square of less than about 150 microinches. <EOS>