ORIGINAL PAPER

A novel cleaning process for industrial production of xylosein pilot scale from corncob by using screw-steam-explosiveextruder

Hong-Jia Zhang • Xiao-Guang Fan • Xue-Liang Qiu • Qiu-Xiang Zhang •

Wen-Ya Wang • Shuang-Xi Li • Li-Hong Deng • Mattheos A. G. Koffas •

Dong-Sheng Wei • Qi-Peng Yuan

Received: 3 December 2013 / Accepted: 11 May 2014

� Springer-Verlag Berlin Heidelberg 2014

Abstract Steam explosion is the most promising tech-

nology to replace conventional acid hydrolysis of ligno-

cellulose for biomass pretreatment. In this paper, a new

screw-steam-explosive extruder was designed and explored

for xylose production and lignocellulose biorefinery at the

pilot scale. We investigated the effect of different chemi-

cals on xylose yield in the screw-steam-explosive extrusion

process, and the xylose production process was optimized

as followings: After pre-impregnation with sulfuric acid at

80 �C for 3 h, corncob was treated at 1.55 MPa with 9 mg

sulfuric acid/g dry corncob (DC) for 5.5 min, followed by

countercurrent extraction (3 recycles), decoloration (acti-

vated carbon dosage 0.07 g/g sugar, 75 �C for 40 min), and

ion exchange (2 batches). Using this process, 3.575 kg of

crystal xylose was produced from 22 kg corncob, almost

90 % of hemicellulose was released as monomeric sugar,

and only a small amount of by-products was released

(formic acid, acetic acid, fural, 5-hydroxymethylfurfural,

and phenolic compounds were 0.17, 1.14, 0.53, 0.19, and

1.75 g/100 g DC, respectively). All results indicated that

the screw-steam-explosive extrusion provides a more

effective way to convert hemicellulose into xylose and

could be an alternative method to traditional sulfuric acid

hydrolysis process for lignocellulose biorefinery.

Keywords Xylose � Pilot scale � Steam explosion �Cleaning process � Extrusion

Abbreviations

SSEE Screw-steam-explosive extrusion

DC Dry corncob

TSAH Traditional sulfuric acid hydrolysis

HMF Hydroxymethylfurfural

RSM Response surface methodology

ANOVA Analysis of variance

CI Crystallinity index

HPLC High-performance liquid chromatography

FC Folin–Ciocalteu

Hong-Jia Zhang and Xiao-Guang Fan have contributed equally to this

work.

Electronic supplementary material The online version of thisarticle (doi:10.1007/s00449-014-1219-0) contains supplementarymaterial, which is available to authorized users.

H.-J. Zhang � X.-G. Fan � W.-Y. Wang (&) � Q.-P. Yuan (&)

College of Life Science and Technology, Beijing University

of Chemical Technology, Beijing 100029, China

e-mail: wangwy@mail.buct.edu.cn

Q.-P. Yuan

e-mail: yuanqp@mail.buct.edu.cn

X.-L. Qiu

Research Center of Futaste Pharmaceutical Co. Ltd,

Yucheng 251200, China

Q.-X. Zhang � S.-X. Li

College of Mechanic and Electronic Engineering, Beijing

University of Chemical Technology, Beijing 100029, China

L.-H. Deng

College of Material Science and Technology, Beijing Forest

University, Beijing 100083, China

M. A. G. Koffas

Department of Chemical and Biological Engineering, Rensselaer

Polytechnic Institute, Troy, NY 12180, USA

D.-S. Wei

Department of Microbiology, College of Life Science, Nankai

University, Tianjin 300071, China

123

Bioprocess Biosyst Eng

DOI 10.1007/s00449-014-1219-0

Introduction

Xylose is a sugar purified from plants, which constitutes

the hemicellulose, one of the main components of ligno-

cellulose [1]. Xylose has wide food, medicinal, and

industrial applications [2]. For example, xylose is an ideal

alternative to regular table sugar as it is safe, healthier and

toxin-free, and is not associated with obesity or other

medical conditions commonly associated with sugar such

as diabetes. It has become popular in Europe, Japan, and

the USA since the 1960s, and it received FDA approval [3].

In addition to its uses in food applications, in the past

decades, xylose from lignocellulose has been used exten-

sively to produce a wide variety of fuels or chemical

compounds by chemical or biotechnological processes,

such as xylitol, green surfactant, ethanol, furfural, 2,3-

butanediol, hydroxymethylfurfural (HMF), and furan resins

[1, 4–6].

In industrial practice, xylose is produced by hydrolysis

of xylan-enriched lignocellulose with diluted acid such as

2 % (m/v) sulfuric acid, a process known as traditional

sulfuric acid hydrolysis (TSAH). The hydrolytic solution

can then be used as substrate for further biorefinement, or it

can be used in decoloration, desalination, concentration,

and crystallization processes to produce xylose with com-

mercial purity. The whole process is considered to be

environmentally unfriendly. China is one of the largest

xylose-producing countries in the world, and in 2012, more

than 45 million tons of waste water full of acids and salts

were produced, which is a big environmental challenge.

During the TSAH process, in order to hydrolyze the

hemicellulose, the lignocellulose is usually kept in diluted

acid at liquid-to-solid ratios of 7:1–15:1 with steam-heating

to 120 �C for 2 h which accounts for 40 % of total energy

consumption; furthermore, at least 100 tons of water is

consumed, which accounts for 30 % of the total water

consumption for production of 1 ton of crystal xylose.

Therefore, the TSAH process is considered to be non-

competitive, because of environmental pollution, high cost,

and the release of undesirable side-products [7]. Conse-

quently, the reduction of wastewater release and

improvement in energy conservation are the two main

challenges in industrial xylose production.

Steam explosion was developed initially in 1925, and it

was used for the pretreatment of lignocellulose in the early

1980s on aspen wood [8]. In the steam explosion, most of

the hemicellulose is degraded and released [9–11]. When

the wheat straw was steam-exploded for 4.5 min with

moisture of 34.01 %, a pressure of 1.5 MPa without acid or

alkali, the sugar of steam-exploded hemicellulose mostly

existed in the soluble oligosaccharides form [12]. Pre-

treatment of 0.175 % (w/w) H2SO4-impregnated

Eucalyptus grandis chips at 210 �C for 2 min resulted in

almost 70 % of the hemicellulose in the water soluble

fraction (mostly as xylose) [11].

In comparison with the traditional acid-based hydrolysis

process, the steam explosion process could reduce the

wastewater release and energy consumption significantly

[11] without reduction of the xylose production. However,

because of the large scale and high-throughout needs

associated with industrial production, the steam explosion

process is not sufficient due to its noncontinuous nature, the

chemical recycling problems, and higher costs [13, 14].

Extrusion, as manufacturing process, has been used

extensively in food, rubber, and plastics industries and is a

novel and promising physical pretreatment method for

biomass conversion [15–17]. In extrusion, lignocellulose is

subjected to heating, mixing, and shearing, resulting in

physical and chemical modifications during the passage

through the extruder [18]. It is suitable for large-scale

production because of its high-throughput character, and it

can also be adapted to treat the material in combination

with many different processes, such as steam explosion,

high pressure, chemical addition, and reactive extrusion

[19]. In order to improve the enzymatic degrading and

sugar recovering abilities, it has been applied for the pre-

treatment of a number of feedstocks, such as switch grass,

prairie cord grass and corn stover by Karunanithy et al.

[20].

In the present paper, a new extruder was designed and

applied to hydrolyze lignocellulose into xylose, which

was named screw-steam-explosive extruder. In this

apparatus, the lignocellulose could be treated by the

combination of extrusion and steam explosion; addition-

ally, a retention system was designed to connect with the

extruder to extend the retaining time of treated biomass.

The aim of the research is to develop a clean and effi-

cient process for the production of xylose from biomass,

which can reduce wastewater and energy consumption

significantly.

Materials and methods

Raw materials

Corncob was collected from Futaste Co., Ltd and air-dried

in the sun. The dried corncob (DC) was mechanically

milled and screened to obtain particles with size of about

4 cm that was stored at room temperature (7 % initial

moisture content). Structural carbohydrates and lignin in

corncob were determined by using NREL method [21]. The

corncob raw material contained 42.23 ± 0.25 % cellulose,

39.01 ± 0.20 % hemicellulose, 14.42 ± 0.18 % lignin,

Bioprocess Biosyst Eng

123

with the remaining 4.34 ± 0.15 % containing acetyl

groups, extractives, ash, etc.

Screw-steam-explosive extruder

Figure 1 shows the schematic diagram of screw-stream-

explosion extruder which consists of the feed system

(weigh-metric screw feeder, single-screw extruder, and

regulating installation), retention system, and steam

explosion system (pneumatic valve, supersonic laval

nozzle). In the feed system, the single-screw extruder,

with a screw diameter of 80 mm and a length-to-diam-

eter ratio (L/D) of 14, has a motor of 11 KW. Raw

material is crushed and delivered into the retention sys-

tem under the control of regulating installation by the

single-screw extruder. The retention system is comprised

of 2 barrels (3,500 mm) and continuous screw

(U190 mm, screw pitch of 90 mm), which delivers raw

materials in plug flow to the steam-explosive system

within a limited time; high-pressure steam (0–2.5 MPa)

is pumped continuously into the system. Finally, a

pneumatic valve is burst open, and raw materials steam-

explode by the supersonic laval nozzle (25 mm). The

screw-streaming explosive extruder is furnished with

multiple temperature control zones that allow imple-

menting precise thermal manipulation.

Ion exchange

Two ion-exchange columns (75 cm 9 225 cm) were used

for each batch. The cation-exchange column was packed

with 001 9 7 cation-exchange resin (20–50 mesh) and was

connected with an anion column packed with D301 anion

resin (20–50 mesh). The 001 9 7 resin is a strongly acidic

cationic resin, and D301 resin is a macroporous strongly

basic anionic resin. The resins are of a gel type with the

matrix made of styrenedivinylbenzene copolymer and were

purchased from the Shanghai Resin Factory (Shanghai,

China).

Process description

The flow sheet shown in Fig. 2 represents the pilot process

of xylose production from corncob. The process includes

pretreatment, screw-steam-explosive extrusion, pressure

filtration, decoloration, ion exchange, concentration, and

crystallization.

In order to remove the impurities (such as dust, coloring

material, and wax) from the corncob and let the corncob

absorb the pretreated chemicals, the corncob was immersed

into pretreated solution. Different chemicals were used to

compare impregnating pretreatment efficiencies, including

pure water (H2O), sulfuric acid (H2SO4), hydrochloric acid

Fig. 1 Screw-steam-explosive

extrusion (SSEE) a screw-

steam-explosive extruder; a the

feed system; b retention system;

c steam-explosive system

b steam explosion process of

SSEE

Bioprocess Biosyst Eng

123

(HCl), oxalic acid (C2H2O4), acetic acid (CH3COOH),

sulfuric acid (H2SO3), carbon dioxide (H2CO3), sodium

hydroxide (NaOH), and ammonium hydroxide (NH4OH).

The corncob was immersed into different chemicals solu-

tion for 12 h at room temperature with the chemical to DC

ratio of 7.5 mg:1 g by dehydration. The same immersion

time and temperature were also applied in the response

surface methodology (RSM) experiment. In the pilot scale

experiment, 3 different impregnating pretreatment tem-

peratures (25, 50, 80 �C) and times (60, 180, 300 min)

were evaluated in order to decrease the time and energy

consumption.

In the screw-steam-explosive extrusion (SSEE) process,

the immersed corncob (1.5–19.5 mg sulfuric acid/g DC)

was fed to the screw extruder and then was subjected to

shearing and dehydration at about 40 % solid loading. The

extruded corncob was delivered through the retention

system prior to rapid decompression (explosion) by con-

tinuous screw, with the steam explosion pressure and

treatment time corresponding to 0.3–2.3 MPa and

1–21 min, respectively. Next, the SSEE corncob was

obtained by steam explosion treatment.

The method of simulated countercurrent wash was used

to extract xylose from SSEE corncob according to Chen

(Fig. S1) [12]. The whole filter pressing process was car-

ried out by several screw dehydrators, and the screw

dehydrators were connected by the shut-off valve. The

SSEE corncob was water extracted continuously, and for

each recycle, the mixture of the elution water and SSEE

corncob was kept at 60 �C for 30 min before the extraction.

Recycling was repeated 1–5 times to obtain the optimum

recycle time of diminish-return point. Decolorization

included two steps: The used activated carbon was first

applied to remove the pigment followed by the application

of the same dosage of new activated carbon; in each step,

the hydrolysate is stirred with activated carbon and frame-

filtered to remove activated carbon. For each desalting

operation, the decolorized solution passed through a

001 9 7 cation-exchange resin column and a D301 anion

resin column, successively. For crystallization, the xylose

solution was concentrated to nearly 750 g/L and heated up

to 80 �C; subsequently, the syrup was stirred at 2 r/min,

and it was cooled down to 50 �C at a rate of 2 �C per hour.

Next, crystal xylose was added to the syrup as seeds and

stirred for 3 h. Finally, the xylose solution was cooled

down to 4 �C at a rate of 1.5 �C per hour, and the crystal

xylose was separated by centrifugation.

Analytical methods

Xylose, glucose, and arabinose were measured at 80 �C by

high-performance liquid chromatography (HPLC) system

(Hitachi, Tokyo, Japan) equipped with a Sugar-pak1 col-

umn (Waters, Milford, MA, USA) and a refractive index

detector (Hitachi, Tokyo, Japan). The ultra-pure water was

used as the mobile phase at a flow rate of 0.5 mL/min.

Xylooligosaccharide was determined by a secondary acid

hydrolysis treatment (4 % H2SO4, 121 �C, 20 min) [22].

Acetic acid, formic acid, 5-HMF, and furfural in

hydrolysates were quantified using HPLC with a BioRad

Fig. 2 The flow sheet of

production of xylose from

corncob in a pilot scale by using

screw-steaming-explosive

extruder

Bioprocess Biosyst Eng

123

Aminex HPX-87H column (300 9 7.8 mm) (Hercules,

CA) with 5 mM of H2SO4 eluent (isocratic) at 35 �C and a

flow rate of 0.5 ml/min. Phenolic compounds were ana-

lyzed with the Folin–Ciocalteu (FC) method. The trans-

mittance was determined at 420 nm with the UV

spectrophotometer.

Results and discussion

The effect of pretreatment with different chemicals

on the hydrolyzation of corncob lignocellulose

In order to improve the efficiency of hemicellulose deg-

radation and xylose production, an experimental apparatus

that combined extrusion with steam explosion was

designed and named screw-steam-explosive extruder.

Different chemical pretreatments were applied in order to

explore the efficiency of hemicellulose degradation and

xylose production. When water-immersed corncob was

treated with SSEE under 1.5 MPa for 5 min, only few

monosaccharides were produced (xylose 1.36 g, glucose

0.289 g, arabinose 0.399 g per 100 g corncob) (Fig. 3).

The sugar composition of hydrolysate for different

chemical pretreatments is also shown in Fig. 3; we found

that xylose is the highest mono-sugar. Among those pre-

treatments, the highest hydrolysis of hemicellulose

occurred with sulfuric acid pretreatment and the yield was

more than 25 g xylose/100 g DC, which is the industrial

standard for yield. Xylose yield of HCl pretreatment

reached 21.5 g/100 g DC; pretreatment with oxalic acid

also resulted in higher yield of xylose (10.4 g/100 g DC);

none of the other acid treatments resulted in yields of

more than 10 g/100 g DC. Further optimization of SSEE

operating conditions for HCl and oxalic acid pretreatment

resulted in yields as high as 25 g xylose/100 g DC

(unpublished data); however, the use of HCl vapor

resulted in severe instrument erosion, and the amount of

oxalic acid was sixfold higher than that of sulfuric acid

(data not shown), which is uneconomical for industrial

production. In the case of alkaline treatment, almost no

xylose, glucose, and arabinose were detected from the

hydrolysate of NaOH and NH4OH pretreatment. Hemi-

cellulose is more amorphous than cellulose and less lig-

nified, so it is thought to be hydrolyzed by acetic acid and

other acids released from lignocellulose during steam

explosion treatment [10]. The SSEE combination with

water pretreatment was not applicable for xylose produc-

tion, because this process suffered from low xylose yield

and higher energy consumption. Addition of acid [such as

H2SO4, SO2, CO2, oxalic acid, etc., typically 0.3–3 % (w/

w)] in steam explosion can decrease treatment time and

temperature, effectively improve hydrolysis, decrease the

production of inhibitory compounds, and lead to almost

complete degradation of hemicellulose [9]. This finding

indicated that acids improved the fragmentation of hemi-

cellulose in the corncob, which amplified the effect of the

steam explosion treatment [23]. As described above, the

sulfuric acid treatment was more advantageous compared

to the other chemicals, and it was chosen as the pre-

treatment method for further experiments.

Optimization of operating parameters of the screw-

steaming-explosive extruder for xylose production

in pilot scale

During the SSEE process, corncob hydrolysis should result

in higher xylose yield and lower yield of other sugars and

by-products in order to increase the efficiency of xylose

purification. Sulfuric acid concentration, SSEE pressure,

and treatment time are three key factors during SSEE

treatment of lignocellulose. In order to elucidate the effect

of these factors on xylose yield, sulfuric acid concentra-

tions were varied from 1.5–19.5 mg/g, steam explosion

pressure from 0.3–2.3 MPa, and the treatment time from

1–21 min.

Figure 4a shows the effect of different concentrations of

sulfuric acid on the yields of xylose, glucose, and arabi-

nose. Sugar recovery increased with increasing sulfuric

acid concentration. Xylose yield reached 25.6 g/100 g DC,

glucose yield reached 3.5 g/100 g DC, and arabinose yield

reached 4.0 g/100 g DC when the sulfuric acid concen-

tration was 7.5 mg/g DC, and more than 85 % of the xylan

Fig. 3 The effect of SSEE in combination with different chemical

pretreatment on the hydrolization of corncob. Yield of xylose,

glucose, and arabinose in the SSEE process was investigated with

different chemicals impregnating pretreatment at a chemicals to

corncob(m/m) ratio of 7.5 mg:1 g DC (chemical‘s concentration

0.5 %(m/v), liquid-to-solid ratios 1.5:1). The SSEE treatment was

carried out with a pressure of 1.5 MPa and treatment time of 5 min

Bioprocess Biosyst Eng

123

Fig. 4 Effects of screw-

steaming-explosive extrusion

treatment on the hydrolization

of corncob. Yield of xylose/

glucose/arabinose, pH, and

electric conductivity in the

SSEE process was investigated

with different sulfuric acid

concentration, SSEE pressure,

and treatment time. The

impregnating pretreatments of

corncob were carried at room

temperature for 12 h. Each

simple 1 kg SSEE corncob (dry

weight) was extracted with

1,000 ml water at 60 �C for 1 h.

a Effect of different sulfuric

acid concentrations on the

hydrolization of corncob (SSEE

pressure 1.3 MPa, treatment

time 8 min). b Effect of

different pressures on the

hydrolization of corncob

(sulfuric acid concentrations

7.5 mg/g DC and treatment time

of 8 min). c Effect of different

treatment time on the

hydrolization of corncob

(sulfuric acid concentration

7.5 mg/g DC, pressure

1.5 MPa)

Bioprocess Biosyst Eng

123

was released as monosaccharide. When the SSEE pressure

and treatment time were 1.5 MPa and 5 min, the xylose

yield reached a maximum of 26.0 and 26.4 g/100 g DC,

respectively (Fig. 4b, c). Due to the high xylan content,

xylose was the major product in the hemicellulosic

hydrolysate. Glucose and arabinose were found in low

concentrations, and the ratio of xylose to glucose/arabinose

in the hydrolysate satisfied the xylose crystallization.

Besides the xylose yield, the increased conductivity and

decreased pH were caused by the increase of sulfuric acid

concentration, SSEE pressure, and treatment time, which

indicated that the degradation of monosaccharides and

lignin increased gradually when conditions are becoming

severe [24].

Based on the above results, response surface meth-

odology (RSM) was applied to optimize the operating

parameters further. The RSM was designed based on 23

full-factorial central composite design and conducted

using Design Expert 8.0.1. The statistical optimal values

of variables were obtained when moving along the major

and minor axis of the contour, and the response at the

center point yielded maximum xylose (Fig. S2). When

time was fixed at 5.64 min, predicted maximum

response was calculated at 28.03 g/100 g DC of xylose

recovery with SSEE pressure 1.57 MPa and 8.8 mg

sulfuric acid/g DC. The analysis of variance (ANOVA)

for the response surface quadratic model is shown in

Table S2. The determination coefficient (R2) implies that

the sample variation of 97.92 % for xylose production

was attributed to the independent variables (P \ 0.0001),

and only about 2.08 % of the total variation cannot be

explained by the model. Referring to the industrial

practice, the final optimum parameters were sulfuric acid

concentration 9 mg/g DC, treatment time of 5.5 min, and

treatment pressure of 1.55 MPa. When the corncob was

treated in pilot scale under the optimum condition

(Table 1), almost 90 % of hemicellulose was released as

monomeric sugar. The xylose yield was 27.6 g/100 g

DC, while the yield of other sugars (glucose, arabinose,

xylooligosaccharide) was lower than 5 g/100 g DC

(Table 1). The percentage of xylose was more than

70 % of total carbohydrate in the hydrolysate because of

the relatively low acid used for the treatment of SSEE.

Acid hydrolysis of biomass coincides with a side reac-

tion that dehydrates sugars and releases by-products.

Therefore, side reactions involving dehydration of the

sugars affect the kinetics of hydrolytic release of sugars

[25], resulting in the decrease of xylose production. The

yields of formic acid, acetic acid, fural, 5-HMF, and

phenolic compounds were 0.17, 1.14, 0.53, 0.19, and

1.75 g/100 g DC, respectively. This composition of

hydrolysate can satisfy the crystallization and can also

be used for downstream biological process directly. Ta

ble

1C

om

po

siti

on

anal

ysi

so

fh

yd

roly

sate

un

der

op

tim

um

SS

EE

con

dit

ion

sa.

(g/1

00

gD

C)

Co

mp

osi

tio

nG

luco

seX

ylo

seA

rab

ino

seX

ylo

oli

go

sacc

har

ide

Ace

tic

acid

Fo

rmic

acid

Fu

rfu

ral

5-H

MF

bP

hen

oli

c

Yie

ld(g

/10

0g

DC

)3

.91

±0

.47

27

.53

±0

.93

3.7

6±

0.2

72

.42

±0

.79

1.1

4±

0.2

80

.16

±0

.04

0.5

3±

0.0

80

.19

±0

.03

1.7

5±

0.2

2

asu

lfu

ric

acid

con

cen

trat

ion

9m

g/g

DC

,S

SE

Ep

ress

ure

1.5

5M

Pa,

and

trea

tmen

tti

me

5.5

min

b5

-Hy

dro

xy

met

hy

lfu

rfu

ral

Bioprocess Biosyst Eng

123

Crystallization of xylose in pilot scale

On the basis of the optimum operating parameters for

SSEE process, impregnating pretreatment of sulfuric acid

was optimized at temperature of 80 �C and treatment time

of 180 min (Table S1). All the following pilot scale

experiments for crystallization were carried out under the

optimum SSEE process and optimum sulfuric acid

pretreatment.

By filter pressing, hydrolysate in SSEE corncob was

collected, to which the countercurrent extraction was

applied (Fig. S1). The optimum recycle times of counter-

current extraction were investigated. Water recycling

resulted in substantial reduction of the amount of fresh

water required and increased the concentration of sugars.

The amount of xylose in the first recycle accounted for

61.4 % of total xylose, and nearly 81 % of the sugars

obtained in the extract was xylose (Table 2). When second

recycle and third recycle were carried out, an additional

25.1 and 8.8 % of total xylose was recovered from SSEE

corncob. The three recycles recovered almost 95 % of total

xylose, while additional recycles (fourth and fifth recycles)

only recovered an additional 2.9 and 4.7 % of total xylose,

respectively (Table 2). The xylose recovered through

countercurrent extraction after SSEE to increase the con-

centration. Pretreated material and water were conversely

delivered continuously in this process, so that the concen-

tration of the extract in the residue could be controlled [12].

Considering the treatment capacity, energy consumption,

and the recovery efficiency of xylose, three countercurrent

extraction recycles were deemed to be optimal for the pilot-

plant production of xylose.

Activated carbon was applied to clean the hydrolysate by

removing protein, colloid, phenol compounds, and some

coloring material, while activated carbon also absorbed

small amounts of sugar [26]. Though increasing activated

carbon dosage could improve the removal of by-products,

the loss of sugar also increased (Fig. 5a). When the acti-

vated carbon dosage varied from 0.03 to 0.15 g/g sugar,

transmittance changed from 44 to 98.6 % and sugar loss

from 5.2 to 19.7 %. In industrial practice, the transmittance

value of 75 % was a standard for xylose crystallization;

thereafter activated carbon dosage of 0.07 g/g sugar

(transmittance 76 %, sugar loss 7.88 %) was chosen as the

optimum dosage for the following experiments (Fig. 5a).

The loss of xylose and transmittance were increased grad-

ually from 40 to 75 �C and then became stable from 75 to

90 �C (Fig. 5b) because the desorption rate suppressed the

adsorption rate, leading to reduction of the absorbing

capacity [27]. The xylose loss reached a stable level after

50 min, while transmittance became stable after 40 min

(Fig. 5c). The time difference between them indicated that

xylose needs a longer time to reach the adsorption–

desorption equilibrium [26]. Based on above results, the

optimum conditions were determined as activated carbon

dosage 0.07 g/g sugar, temperature 75 �C, and time 40 min.

Ion exchange could decrease conductivity by removing

ion from SSEE hydrolysate. The conductivity of SSEE

hydrolysate can decrease from 5,624 to 6.8 lS/cm by two

batches of ion exchange, while it takes three batches for the

conductivity of TSAH to decrease from 23,652 to 8.1 lS/

cm (Table 3). The conductivity of SSEE and TSAH pro-

cess is attributed to the amount of sulfate in the hydroly-

sate. In the SSEE process, 9 mg sulfuric acid/g DC was

used for xylan hydrolyzation, and in the TSAH process,

300 mg sulfuric acid/g DC was applied, which caused the

significant difference in initial conductivity between SSEE

and TSAH.

Technical data are shown in Table 4 for each step of

xylose production in pilot scale from corncob by using

screw-steaming-explosive extruder. The content of total

monosaccharides was 7,327 g in the hydrolysate (glucose

661 g, xylose 5,844 g, arabinose 842 g) from 22,000 g DC,

indicating that nearly 33.4 % of monosaccharides were

extracted by the SSEE. After applying 513 g of activated

carbon (0.07 g activated carbon/g sugar) for hydrolyzate

decoloration (75 �C and 40 min), monosaccharides

decreased from 33.4 to 28.7 % and the transmission

increased from 7.6 to 75.8 %. Two batches of ion exchange

were adopted for desalination of 4,886 g of monosaccha-

ride, and finally, 3,525 g xylose was obtained from

22,000 g corncob.

Table 2 The effect of countercurrent extraction recycle times on xylose production

Recycle

batch

Glucose

(g)

Xylose

(g)

Arabinose

(g)

Reducing sugar

(g)

Recovery rate

(%)

1 20.2 ± 1.2 217.9 ± 5.3 30.8 ± 1.4 268.9 ± 6.1

2 33.6 ± 0.8 297.8 ± 6.6 47.5 ± 1.7 378.9 ± 6.2 40.91 ± 3.1

3 36.5 ± 1.5 329.8 ± 5.8 51.2 ± 1.1 417.5 ± 5.5 10.27 ± 1.9

4 37.8 ± 0.9 340.2 ± 4.3 52.2 ± 1.4 430.2 ± 5.2 3.04 ± 1.3

5 39.1 ± 1.2 346.1 ± 4.2 52.9 ± 1.1 438.1 ± 4.8 1.84 ± 1.4

For each sample, 5 kg of SSEE corncob (1.32 kg dried weight) was selected for analysis; the SSEE corncob was treated with sulfuric acid at a

concentration of 9 mg/g DC, SSEE pressure of 1.55 MPa, and treatment time of 5.5 min; 2,000 ml fresh water was used for each cycle

Bioprocess Biosyst Eng

123

Fig. 5 Effect of activated

charcoal treatment on the

decoloration of hydrolysate

from SSEE treatment. Results of

transmittance and sugar loss rate

of SSEE hydrolysate were

investigated under the same

impregnation treatment (80 �C,

180 min) and SSEE conditions

(9 mg sulfuric acid/g

DC,1.55 MPa, 5.5 min) a The

effect of activated carbon

dosage on decoloration

(temperature 75 �C, time

40 min). b The effect of

temperature on decoloration

(activated carbon dosage

0.07 g/g sugar, time 40 min).

c The effect of treatment time

on decoloration (activated

carbon dosage 0.07 g/g sugar,

temperature 75 �C)

Bioprocess Biosyst Eng

123

Effect of SSEE treatment on the corncob structure

The structural changes of corncob with different treatments

were monitored by scanning electron microscopy (SEM)

(Fig. 6). The untreated corncob exhibited rigid and highly

ordered fibrils (Fig. 6a), and the fibers that had undergone

SSEE and water impregnation treatment appeared to be

distorted and have cracked stratification (Fig. 6b).

Impregnating corncob with SSEE and sulfuric acid

(Fig. 6c) increased the more external surface area and the

porosity of microfibrils compared to those of TSAH

corncob (Fig. 6d); the microfibrils were also separated

from the original structure and fully exposed. SSEE-treated

biomass felt much softer than the untreated one, and the

structure became fleecy, increasing its availability for

enzymatic attack.

Table 5 shows the crystallinity index of corncob that

underwent different treatments. The untreated corncob

showed a lower crystallinity (CI = 32.4 %) compared with

water pretreatment (CI = 46.25 %) and sulfuric acid pre-

treatment (CI = 49.6 %). After explosion, 5 kg sulfuric

acid and water-pretreated SSEE samples were used for the

subsequent extraction of xylose. The dried weight of 5 kg

SSEE corncob is 1.32 kg. After extraction, nearly 0.77 kg

dry residue was obtained from sulfuric acid SSEE and

0.93 kg from water SSEE, which means 41.3 % of sulfuric

acid treated and 29.5 % of water-treated biomass degraded

and dissolved in the solution. The phenomenon is mainly

due to the removal of a certain amount of lignin and

hemicellulose (amorphous substances), but not due to

changes in the crystalline structure of the biomass. As

expected, the crystallinity index of the corncob pretreated

with sulfuric acid SSEE (49.6 %) was higher than that of

water-pretreated corncob (46.25 %), which indicated that

more amorphous components were released during the

sulfuric acid SSEE. The results coincided with higher

xylose yield from sulfuric acid SSEE.

Evaluation of SSEE process as a substitute of the TSAH

process for industrial xylose production

The SSEE process combined the steam explosion with

extrusion: In comparison with steam explosion, it substi-

tutes the batch process with the continuous process to make

the steam explosion effective and high throughput; in

comparison with extrusion, it can convert hemicellulose

into monoxylose effectively by steam explosion. In gen-

eral, SSEE process could reduce the amount of acid and

time in hydrolyzation and decrease wastewater release,

something that results in the reduction of cost and a more

competitive overall process. In SSEE process, it took 5 min

to hydrolyze the hemicellulose with 9 mg sulfuric acid/

100 g DC (0.32 %, liquid-to-solid ratios 1.5:1), while in

TSAH process, 105–300 mg sulfuric acid/100 g DC

(1.5–2 %, liquid-to-solid ratios 7–15:1) was steamed to

120 �C and kept for 120 min. Therefore, the SSEE process

decreased the amount of sulfuric acid and hydrolyzing time

by more than 90 and 95 %, respectively. Due to the lower

dosage of acid, the neutralization process in TSAH was not

required in the SSEE process. In addition, with the

reduction of acid amount in the desalination process, no

more than 50 tons of wastewater (5,600 lS/cm, brix 8) was

released per ton of xylose in SSEE process as opposed to

200 t of wastewater (23,000 lS/cm, brix 8) that was

released in the TSAH process. Consequently, the SSEE

process showed a great advantage over the TSAH process.

Table 3 Effect of ion-exchange on conductivity of hydrolysate

(ls/cm)

Extracting

solution

(Brix 8)

First ion

exchange

(Brix 7.5)

Second ion

exchange

(Brix 23)

Third ion

exchange

(Brix 18)

SSEE 5,624 ± 55 1,315 ± 45 6.8 ± 2.8 2.3 ± 0.15

TSAH 23,652 ± 154 8,742 ± 72 6,115 ± 58 8.1 ± 1.8

Brix is measured using a brix spindle (Kemu, Shanghai, China)

Table 4 Technical data in each step of xylose production in pilot scale from corncob by using screw-steaming-explosive extrudera

Purification steps Glucose

(g)

Xylose

(g)

Arabinose

(g)

Reducing

sugar

pH Brix Transmittance Volume

(L)

Conductivity

(ls/cm)

Filter pressing extraction 661 5,844 842 7,327 2.2 7.6 7.6 105 5,610

Decoloration 474 5,148 648 6,315 2.0 6.8 75.8 96 5,724

First ion exchange 407 4,682 493 5,582 4.7 5.2 84.8 112 306.6

First concentrate 389 4,559 48.3 5,431 4.0 25 69.3 24.5 1,394.4

Second ion exchange 322 4,205 359 4,886 6.9 17.8 96.5 27.8 6.64

Second concentrate 294 4,116 337 4,747 6.5 74 95.4 6.8 59.47

Fractional crystallization 58 3,392 75 3,525

a 22 kg of dry corncob was used for this experiment

Bioprocess Biosyst Eng

123

Conclusions

A screw-steaming-explosive extruder was designed and

applied to produce crystal xylose at pilot scale from

corncob. The SSEE process combined the steam explo-

sion with extrusion, providing a more efficient and high-

throughout method to produce xylose from hemicellulose

compared to the THSA method. The xylose in the

hydrolysate after SSEE treatment can also be biocon-

verted into xylose derivatives (xylitol, 2,3-butanediol,

etc.) directly due to the lower bio-inhibitors. After the

removal of hemicellulose, the residues in the lignocellu-

lose can be hydrolyzed with enzymes efficiently for fur-

ther biorefinery. In the future, the SSEE process could be

potentially applied to industrial xylose production and

pretreatment of lignocellulose for biorefinery.

Acknowledgments We are indebted to the National High-

tech Research and Development Program (2012AA022303,

2014AA021906, 2014AA021903) and the National Natural Science

Foundation (31170076) for their generous financial supports.

Fig. 6 Effect of different treatments on the microstructure of

corncob. a Control corncob; b corncob of water impregnating

pretreatment and screw-steaming-explosive extrusion; c corncob of

sulfuric acid impregnating pretreatment and screw-steaming-explo-

sive extrusion; d corncob of traditional sulfuric acid hydrolysis

Table 5 Effect of different treatments on the crystallinity indexa,b

Treatment 1 2 3

Crystalline index (%) 32.4 ± 1.2 46.25 ± 0.9 49.60 ± 0.7

1 Control corncob; 2 corncob pretreated by water impregnation and

screw-steaming-explosive extrusion; 3 Corncob pretreated with sul-

furic acid impregnation and screw-steaming-explosive extrudiona The crystallinity index was based on X-ray diffraction and con-

ducted using jade 5.0b Powder X-ray diffraction measurements were performed on the 2hrange of 5-65 with a step size of 0.026 and an exposure time of 300

Bioprocess Biosyst Eng

123

References

1. Saha BC (2003) Hemicellulose bioconversion. J Ind Microbiol

Biotechnol 30:279–291

2. Rafiqul ISM, Sakinah AMM (2012) Design of process parameters

for the production of xylose from wood sawdust. Chem Eng Res

Des 90:1307–1312

3. Xu P, Lou M (2012) Xylose : Production, Consumption, and

Health Benefits. Nova Science Pub Inc, New York

4. Mussatto SI, Roberto IC (2004) Alternatives for detoxification of

diluted-acid lignocellulosic hydrolyzates for use in fermentative

processes: a review. Bioresour Technol 93:1–10

5. Wang L, Yang M, Fan XG, Zhu XT, Xu T, Yuan QP (2011) An

environmentally friendly and efficient method for xylitol bio-

conversion with high-temperature steaming corncob hydrolysate

by adapted Candida tropicalis. Process Biochem 46:1619–1626

6. Cheng KK, Liu Q, Zhang JA, Li JP, Xu JM, Wang GH (2010)

Improved 2,3-butanediol production from corncob acid hydroly-

sate by fed-batch. Process Biochem 45:613–616

7. Shah R, Clausen E, Gaddy J (1984) Production of chemical

feedstocks from biomass. Chem Eng Prog 80:76–80

8. Carvalheiro F, Duarte L, Girio F (2008) Hemicellulose biorefin-

eries: a review on biomass pretreatments. J Sci Ind Res India

67:849–864

9. Caraa C, Ruiza E (2008) Production of fuel ethanol from steam-

explosion pretreated olive tree pruning. Fuel 87:692–700

10. Sun XF, Xu F, Sun RC, Geng ZC, Fowler P, Baird MS (2005)

Characteristics of degraded hemicellulosic polymers obtained

from steam exploded wheat straw. Carbohydr Polym 60:15–26

11. Emmel A, Mathias A, Wypych F, Ramos L (2003) Fractionation

of Eucalyptus grandis chips by dilute acid-catalysed steam

explosion. Bioresour Technol 86:105–115

12. Chen HZ, Liu LY (2007) Unpolluted fractionation of wheat straw

by steam explosion and ethanol extraction. Bioresour Technol

98:666–676

13. Galbe M, Sassner P, Wingren A, Zacchi G (2007) Process

engineering economics of bioethanol production. Adv Biochem

Eng Bio 108:303–327

14. Agbor V, Cicek N, Sparling R, Berlin A, DB L (2011) Biomass

pretreatment: fundamentals toward application. Biotechnol Adv

29:675–685

15. Green M, Kimchie S, AI M, Rugg B, Shelef G (1988) Utilization

of municipal solid wastes (MSW) for alcohol production. Biol

Waste. 4:285–295

16. Noon R, Hochstetler T (1982) Production of alcohol fuels via

acid hydrolysis extrusion technology. Fuel Alcohol 4:14–23

17. Kadam K, Chin C, Brown L (2009) Continuous biomass frac-

tionation process for producing ethanol and low-molecular-

weight lignin. Environ Prog Sustain Energy 28:89–99

18. Chen WH, Xu YY, Hwang WS, Wang JB (2011) Pretreatment of

rice straw using an extrusion/extraction process at bench-scale for

producing cellulosic ethanol. Bioresour Technol 102:

10451–10458

19. Alvira P, Tomas-Pejo E, Ballesteros M, Negro MJ (2010) Pre-

treatment technologies for an efficient bioethanol production

process based on enzymatic hydrolysis: a review. Bioresour

Technol 101:4851–4861

20. Ng TH(2013)Twin screw extrusion pre-treatment of wheat straw

for biofuel and lignin biorefinery applications. PhD thesis. Brunel

University, School of Engineering

21. Laboratory NRE (2012) Determination of Structural Carbohy-

drates and Lignin in Biomass. BiblioGov

22. Gullon P, Gonzalez-Munoz MJ, van Gool MP, Schols HA (2010)

Production, refining, structural characterization and fermentabil-

ity of rice husk Xylooligosaccharides. J Agric Food Chem

58:3632–3641

23. De Bari I, Nanna F, Braccio G (2007) SO2-catalyzed steam

fractionation of aspen chips for bioethanol production: optimi-

zation of the catalyst impregnation. Ind Eng Chem Res

46:7711–7720

24. Ruiz E, Cara C, Manzanares P, Ballesteros M, Castro E (2008)

Evaluation of steam explosion pre-treatment for enzymatic

hydrolysis of sunflower stalks. Enzyme Microb Technol

42:160–166

25. Teng C, Yan Q, Jiang Z, Fan G, Shi B (2010) Production of

xylooligosaccharides from the steam explosion liquor of corncobs

coupled with enzymatic hydrolysis using a thermostable xylan-

ase. Bioresour Technol 101:7679–7682

26. Mussatto S, Roberto I (2004) Optimal experimental condition for

hemicellulosic hydrolyzate treatment with activated charcoal for

xylitol production. Biotechnol Prog 20:134–139

27. Parajo JC, Domınguez H, Domınguez JM (1996) Charcoal

adsorption of wood hydrolysates for improving their ferment-

ability: influence of the operational conditions. Bioresour Tech-

nol 57:179–185

Bioprocess Biosyst Eng

123