Stereo micrographs of dilute acid pretreated (2 wt% H
, 160°C, 5 min) corn stover from three different reactors. (a) Control, (b) ZC, (c) SG, and (d) HS. Samples from all three reactors show a color change to an orange brown color and an observable reduction in particle size. Many long, intact fibers remained in the ZC samples (b, arrow). Particles from both the SG and HS reactors clump together (c, arrow). The SG caused extensive particle size reduction, but also left a number of larger particles intact (c’, arrow). The HS reactor caused extensive particle size reduction to generate uniformly small particles (d’, arrow). The shapes of the histograms confirm the observable patterns of reduced particle size of samples from the pretreatment reactors, dramatically reducing the largest (far right) size bins (a”,b”,c”,d”). Also, the reduction in number of long fibers is evident by fewer high aspect ratio counts (c”’,d”’). Bars = 1 mm. HS, horizontal screw; SG, steam gun; ZC, ZipperClave®.