Effect of pelleting on the recalcitrance and bioconversion of dilute-acid pretreated corn stover under low- and high-solids conditions

Figures & data

Figure 1.  Monomeric and total xylose yields for corn stover formats following low-solids, dilute-acid pretreatment.

Mean ± 1 standard deviation; n = 4 for 6.35-mm and 2-mm formats; n = 3 for pellet meal due to a problem with high-performance liquid chromatography injection volume in one replicate.

Figure 2.  Glucan hydrolyzed during dilute-acid pretreatment for three corn stover formats.

Mean ± 1 standard deviation; n = 4 for 6.35-mm and 2-mm formats; n = 3 for pellet meal due to problem with high-performance liquid chromatography injection volume in one replicate.

Figure 3.  Percentage of theoretical maximum ethanol yield for three corn stover formats on days 3, 5 and 7 of simultaneous saccharification and fermentation.

Mean ± 1 standard deviation; n = 4.

TEY: Theoretical maximum ethanol yield.

Figure 4.  Xylose yield (monomeric and oligomeric) from high-solids pretreatment of pelleted and 6.35-mm ground stover using the ZipperClave® reactor. Mean ± 1 standard deviation; n = 3.

Figure 5.  Xylose yield from combined high-solids pretreatment and enzymatic hydrolysis of the pelleted and 6.35-mm ground stover.

Mean ± 1 standard deviation; n = 3.

Figure 6.  Furfural release from high-solids pretreated pelleted and 6.35-mm ground material.

Mean ± 1 standard deviation; n = 3.

Figure 7.  Glucose yield from combined high-solids pretreatment and enzymatic saccharification of pelleted and 6.35-mm source stover.

Mean ± 1 standard deviation; n = 3.

Figure 8.  Feedstock reactivity for high-solids pretreated 6.35-mm grind and pelleted stover (mean ± 1 standard deviation).

Reactivity is defined as the fraction of the glucose and xylose released from pretreatment and enzymatic hydrolysis, divided by the initial mass of glucose and xylose in the native feedstock.

Figure 9.  Scanning electron microscopy images.

(A) Native corn stover at 700× magnification and (B) native corn stover at 100× magnification; (C) pelleted corn stover at 700× magnification and (D) pelleted corn stover at 440× magnification.

Figure 10.  Brunauer–Emmett–Teller surface area, total pore volume and average pore size (mean ± standard error; n = 3) for source material (6.35 mm), pellets, pellets ground to 2 mm, acid-treated source material and acid-treated pellets.

There is a significant difference between treatments (p ≤ 0.05) if the letters above the bars are different (Bonferroni post-hoc adjustments).

BET: Brunauer–Emmett–Teller.

Table 1.  Pretreatment conditions for high-solids pretreatment experiments using the ZipperClave®.

Severity (log Ro)	Temperature (°C)	Reaction time (min)
1.51	125	6
2.07	150	4
2.47	150	10
2.81	175	4
3.29	175	12

Table 2.  Particle size distribution parameters (mean ± 1 standard deviation; n = 3) of corn stover formats†.

Treatment	D84	D50	D16
Source	2.27 ± 0.020	0.77 ± 0.01	0.30 ± 0.004
2 mm	1.22 ± 0.020	0.52 ± 0.01	0.18 ± 0.002
Pellet meal	1.35 ± 0.003	0.75 ± 0.01	0.24 ± 0.010

^†All dimensions are in mm. The source material (6.35 mm) was generated from a two-stage grinding process with the feedstock process demonstration unit. The 2-mm format was generated from the source material using a laboratory-scale knife mill. Pellet meal represents size-reduced pellets generated with a 2-mm screen on a laboratory-scale knife mill.

Table 3.  Degrees of freedom, F-values and p-values from a one-way analysis of variance for Brunauer–Emmett–Teller surface area, total pore volume and average pore size.

Effect	Degrees of freedom	F-value	p-value
Brunauer–Emmett–Teller surface area	4,10	99.477	5.21E-08
Total pore volume	4,10	280.120	3.23E-10
Average pore size	4,10	93.937	6.87E-08