Advances in Ma terials Physics and Che mist ry, 2012, 2, 197-199
doi:10.4236/ampc.2012.24B051 Published Online December 2012 (htt p://www.SciRP.org/journal/ampc)
Industrialization Process of Pesticide Residue Grade n-Hexane
Can Quan1*, Xiongwei Yan2, Ting Huang1, Hongmei Li1，Junsu J in2
1National institute of metrology, 10013,Beijing, P.R.China
2Beiji ng university of chemical technology ,10029 ,Beijing, P.R.Chin a
Received 2012
ABSTRACT
This project is funded by the China government to develop the industrialization process of pesticide residue grade n-hexane, in which
the industrial n-Hexane is used as crude purified by decoloration, distillation and filtration process. The products are validated by
Nation al Research Cen ter for Envi ronmental Analysis and M easurement ( CNEAC), Nati onal Research Center for Geoanalysis, C hi-
nese Academy of Inspection and Quarantine (CAIQ), Chinese Academy of Agricultural Sciences (CAAS) and other government
originations for polychlorinated biphenyls, organochlorine pesticide or chiral pesticides analysis and further confirmed that it’s com-
petitive to all others imported n-Hexane currently occupied in China. This patented technique will meet pesticide residue grade
n-Hexane market in China and seek for cooperation globally.
Keywords: Pestici de Residue Analysis Grade; n-Hexane; Purification; Distillation
1. Introduction
High purity organic solvents such as pesticide residue grade
solvents play very crucial roles in scientific research field in-
cluding chromatographic anal ysis, spectrum analysis, pesticide
residue detect ion, mass spectrometry analysis, organic synthesi s ,
combinatorial chemistry, DNA and RNA synthesis etc. In re-
cent years, food safety problems have caused many concerns;
pesticide residue content is one of the most important factors
for food safety.
The objective of this study funded by Chinese government is
to develop a commercial industrial process which can produce
pestici de residue grad e n-Hexane directly from industrial grade
crude with capacity of 30 T annually.
2. Experimental
2.1. Chemicals and Raw Materials
Industrial grade n-Hexane crude was purchased from Beijing
local market. High perfo rmance silicon dioxide decoloring agent
with average particlon size of 100μm and specific surface area
of 500 m2/g was purchased from Qingdao Fine Chemical Cor-
poration (Shandong, China). All chemicals were used directly
without further purification. The pesticide residue standards
solutions were friendly contributed by the National Institute of
Metrology (Beijing, China). Pesticide residue n-hexane control
sample were kindly supported by Kingchemtune Co.Ltd.
2.2. The Impurities of Industrial n-Hexa ne
The industrial n-Hexane is mainly separ ated from 6# solvent
naphtha and raffinate oil which come from crude o il (Liang,T.X
and M.Zhu,2004), however crude oil contains some aromatic
and alkane compound, so industrial n-hexane may contain the
said impurities. In order to verify the impurities of industrial
n-Hexane whi ch help to discuss the more availably purification
process of pesticide residue grade n-Hexane, it is necessary to
ascertain these specific impurities, in this situation, GC/MS
analysis method is used to determine these impurities in qualit-
ative model.
2.3. Purification Pro ces
● Distillation
The feedstock after decoloration was pumped for distillation,
the 2-tower distillation apparatus were established with pat-
ented design. The industrial grade n-Hexane crude decolorated
was firstly pumped into the 1st distillation tower, in which those
light impurities were separated, and the remains at the bottom
were pumped again into the 2nd distillation tower, in which
tho se heavy impurities w er e switched at the bottom, the product
can be collected on the top of the 2nd tower, the product can be
online monitored by a online GC/ECD.
2.4. Analytical Method
● UV Value analysis
For the analysis for the product of this process, UV value
was measured via UNICO 2102-PCS ultraviolet spectropho-
tometer (USA) at the wavelengths from 195nm to 250nm, with
ultrapure water as blank in 1cm cuvette.
industrial n-hexanesilicon dioxide
Dicorloring
Tower Rinsing Tower
The
first
Distillation
Tower
The
second
Distillation
Tower
Distilled Waterpesticide residue
grade n-hexane
Heavy
components
Light
components
filter unit
Figure 1. Purification process of pesticide residue grade n-Hexane.

C. QUAN ET AL.
198
● Gas chromatography-electron capture detector (GC/ECD)
analysis
For the analysis for the product by this process, GC/ECD
analysis was carried out by Agilent 6890(USA) gas chroma-
tography equipped with Ni63 electron-captu re detecto r. Samples
were introduced into the GC-column via electronic pressure
control, with cold-column injector mode.
● Gas chromatography-mass spectr ometry (GC/MS) analysis
For the analysis for industrial grade n-hexane and the product
by this process, GCMS analysis was carried out by SHIMAD-
ZU GCMS-QP2010 Plus. Samples were introduced into the
GCMS via el ectronic pressure cont rol, with cold-column injec-
tor mode.
3. Results and Discussion
3.1. Impurities Determination of Industrial n-H exane
● Solvent peak
In GC/MS analysis, solvent peak should be found and cut.
Industrial n-hexane contain many impurities, however, whose
purity is still up to 96%, after it is injected to GC/MS, the
n-Hexane cannot be detected by MS, or the MS will be dam-
aged by n-Hexane solvent, meanwhile it is hard to analysis
those impurities peak because of ultra high main solvent peak.
In order to determine the retention time of solvent peak, the
less injection volume and higher split ratio is chosen that is
0.1μL and 100:1 respect ively, th e r es ult is showed in Figure 2.
3.2. Parameters of Purification Process
● Two towers distillation
After the processes of the front two steps, the feedstock was
transferred to two distillation units, the use of the first tower
was to remove the low point constituents, then the remaining
liquid was transferred to the second tower, the use of which was
to remove the high point constituents, lastly the product was got
from the second tower top.
Distillation is a highly efficient separation method whose
advantages are simple process, high effect and flexible opera-
tion etc. The controlled indexes of this process included heating
temperature, reflux ratio and heavy constituents discharge rate
etc. After a lo t of experiment s the optimized process parameters
are got: the heating temperature of two towers distillation is
88℃ with reflux ratio of 15:1 and 4:1 for both respectively, the
discharge rate of heavy components is 20mL/min, the yield is
approximately 70%. If heating temperature was too high and
too low, they would cause flood and effect mass transfer,
meanwhile if reflux ratio was too high, it would cost too much
energy, else if the reflux ratio was too low, products were hard
to meet the r equir ement, so it is necessary to find the best reflux
ratio which is the essential elements of distillation operation.
3.3. Quality Assessment of the Product
● UV value measure ment
Take n-Hexane crude and three bottl es of differen t b atch es of
products as the test sample with ultrapure water as blank, from
Table 1, it can be seen that cr ude n-hexan e cannot pass th e UV
value indexes, while UV value of all the products mee t the UV
value indexes at all the t es ted wavelengths.
The results show that the numbers of crude impurities are too
many and the height is too high, three products show thr ee time
points which are most easy to appear exceeding peak resp ect-
tively.
The results showed that the purity of crude is less than 97%
and the purity of these products reach 98% which meet the
requirement of pesticide residue standard that is higher than
97%.
3.4. The Comparation of the Quality of our Product
and Other Products Both at Domestic and
Aboard
From the test results, we can make the conclusion that the
products got by this process meet the requirement of pesticide
residue indexes. In order to analyze the market situation, we
bought 5 kinds of brands of pesticide residue grade n-hexane
both at domestic and abroad, all the products were tested in the
said test method, the results were showed in Table 1.
Figure 2. The main solvent peak.
Table 1. Qualit y comparison of pesticides residue n-Hexa n e .
title Foreign
product 1 Foreign product 2 Foreign prod uct 3 Foreign prod uct 4 Domestic product 1 The product
195nm absorb ance 0.702 0.713 0.662 0.732 0.908 0.943
210nm absorb ance 0.176 0.201 0.182 0.234 0.246 0.231
220nm absorb ance 0.061 0.079 0.072 0.058 0.098 0.071
230nm absorbance 0.029 0.042 0.038 0.028 0.049 0.028
240nm absorb ance 0.015 0.026 0.023 0.015 0.025 0.012
250nm absorb ance 0.010 0.018 0.016 0.011 0.016 0.005
Maximum peak height
(GC-ECD) (ng·ml-1) 2.83 0.26 0.18 6 .3 1 1.38 0.590
purity（%）(GC-FID) 97.31 99.61 98.53 98.59 97.33 98.48

C. QUAN ET AL.
199
The results show that the overall quality of the product got
by this process ranks middle, which is better than domestic
product and part of foreign products and have not big gap with
other be t te r f ore i g n products.
In addition, the products were tested by National Research
Center for Environmental Analysis and Measurement (CNEAC),
National Research Center for Geoanalysis, Chinese Academy
of Inspection and Quarantine (CAIQ), Chinese Academy of
Agricultural Sciences (CAAS) and other government origina-
tions for polychlorinated biphenyls, organochlorine pesticide or
chiral pesticides analysis and further confirmed that it’s com-
petitive to all others imported brand occupied China.
4. Conclusion
For the solvents of pesticide residue analysis, they not only
require high purity, but more importantly, which do not pro-
duce interference peak in pesticide chromatographic detection
when solution are concentrated dozens to hundreds times, so
the traditional purification methods are not suitable for the
preparation of this kind of solvents. This study build a new
proces s,which can remove the trace impurities that influence
the pesticide residue analysis and overcome some technology
bottleneck problems such as complex process, too much impu-
rities peak and heavy environment pollution, thus achieve the
process of transforming industrial n-Hexane to p es ticide r es idue
grade n-hexane directly.
Put industrial n-hexane as crud e, after thi s pr ocess contai nin g
decolour-two towers distillation-filter, pesticide residue grade
n-Hexane which can be ap p ly to pesti cid e resid u e anal ysis were
prepared.
This prod uct can meet the clients in the n eed of pesticide re-
sidue analysis, which would reduce the independent of do-
mestic laboratory to imported pesticide residue grade solvents
and could support the product of good quality and cheap price.
5. Acknowledgements
Can QUAN ackno wledges the Ministry of science and tech-
nology of People’s Republic of China for Key Projects in the
Nation al Science & Techno logy Pillar Pr ogram du ring the Ele-
venth Five-Year Plan Period (2009BAK61B02); the Minis- try
of science and technology of People’s Republic of China
(2011FY130100); the General Administration of Quality Su-
pervision, Inspection and Quarantine of the People’s Republic
of China (ASPAQ1101-1); the National Institute of Metrology
(21-JB1127) for financing.
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