Effect of temperature and pressure on the hydropyrolysis of cotton residue
Bhavya Balagurumurthy1, Rawel Singh1, Twinkle S Oza2 and Thallada Bhaskar1,*
1Bio-Fuels Division, CSIR-Indian Institute of Petroleum (IIP)

2BITS, Pilani

e-mail: tbhaskar@iip.res.in, thalladab@yahoo.com
Ph No: +91 135 2525820 Fax No: +91 135 2660202

Abstract
With growing concerns of fossil fuel resources availability and the volatility of crude oil price, it is becoming imperative day
by day to utilize the renewable sources of energy in a sustainable, environment friendly and energy efficient manner.
India is the world’s second largest producer of cotton after China. Cotton residue is one of the most abundant agriculturalresidues after rice and wheat residues but has the characteristics of forest residues. The hydropyrolysis of cotton
residues has been carried out at various pressures (1, 20 and 40 bar) and temperatures (300-450°C). The effect oftemperature and pressure have been studied to understand their yield patterns and it has been observed that 20barpressure and 400°C are the optimum conditions. The TG analysis shows that cotton residue has two significant
decomposition temperatures. The SEM, XRD patterns and FT-IR spectra clearly indicate the decomposition of themacromolecular structure of the cotton residue as the functionalities present in the feed are lost after hydropyrolysis.

Keywords: cotton stalks, cotton ginning waste, hydropyrolysis, bio-oil, bio-char

1. Introduction
As on date, an important current focus of research inchemistry, engineering, agriculture, and environmental
policy is the development of clean technologies thatutilize a sustainably produced feedstock like biomass tothe largest extent possible [1]. This research is especially
important in the hydrocarbon sector which is strongly
dependent on petroleum, a non-renewable fossil sourceof carbon. However as the world wide supply of
petroleum diminishes, it is becoming increasingly
expensive and, accordingly, less attractive as a carbon
source. Second generation bio-fuels are obtained from
non-edible sources such as agricultural and forest
residues etc. unlike the first generation bio-fuels which
are made from edible sources of biomass. Cotton is
produced in huge quantities all over the world and this isaccompanied by generation of tons of cotton waste eachyear. Cotton plant waste refers to the residue left unusedin the field after cotton is harvested. Cotton gin waste
typically includes products from the ginning process notincluding seed or lint [2]. Burning of cotton stalks should
be avoided as nutrients are lost and soil carbon levels
decline quickly but this is the most followed process as
on date all over the world [3]. Cotton residue, alignocellulosic biomass, is made up of cellulose,
hemicellulose, lignin and other inorganic matter.
Owing to the availability and its non-competence as foodor fodder, cotton residue can be a suitable feedstock forrenewable hydrocarbon production. It is observed thatthe cotton residue has the characteristics of forest
residue although it is an agricultural residue [4].
Researchers all around the world have subjected cotton
residue to various processes of conversion and several

products have been obtained yet there are no reports ofhydropyrolysis of cotton residue in the open literature.
There are several methods of conversion of biomass
which can be grouped as bio-chemical, chemical andthermo-chemical methods of conversion. The thermochemical methods of conversion do not require theenergy intensive pre-treatment step as in the biochemical methods and hence, it can utilize the feedstock
as such. Due to the disadvantages of fast pyrolysis biooil such as high TAN, high oxygen content and poor
miscibility with crude oil and their distilled fractions,process of hydropyrolysis has been used to produce
value added hydrocarbons [5]. In this process, hydrogenat high pressures is used and pyrolysis occurs at hightemperatures of 350-450°C.
In this paper, we have carried out the hydropyrolysis ofcotton residue and the optimal conditions for the same
have been evaluated. The products of hydropyrolysis
have been characterized and evidences for the openingof the macromolecular structure have been provided.

2. Materials and Methods
The feedstock cotton residue has been obtained from anagricultural farm in Andhra Pradesh, India. The thermogravimetric analysis, trace metal analysis, SEM, XRD
and FT-IR of cotton residue has been carried out. Inaddtition, the mositure content and calorific value havealso been found out.
The designed prototype hydropyrolysis reactor is heatedelectrically which is controlled by a temperature
programmed controller. The thermocouples are placed in
the skin and in the heart of the reactor inside thethermowell provided. The gas from the hydrogen cylinder

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013

is passed into the reactor and the needle valve controls
the pressure in the unit. The product stream from thereactor is sent into a condenser. The non condensable
gases are collected in a tedler bag for gas analysis andliquid is collected separately.
The hydropyrolysis of cotton residue has been carriedout at various temperatures of 300, 350, 400 and 450°C
and pressures of 1, 20 and 40 bar with a heating rate of
30°C/min. The oven dried feedstock is weighed (20 g)
and loaded into the reactor. The reactor is then placed in
the furnace and pressurized using hydrogen gas till thedesired value of pressure is reached and then the flow isstopped. The required final temperature and heating rate
are set and the final temperature is maintained for 1 h or
until the gases evolve whichever is earliest. The pressure
is maintained constant by intermittently removing theproducts from the system. The products are finallycollected separately and analyzed on a carbon paper
coated adhesive followed by gold coating.

3. Results and Discussion
The TG/DTG of cotton residue showed two significant
decompositon temperatures. Na, Mg, P and Ca are major
elements present in the feedstock naturally occurring intheir structure. The gross calorific value of the feed has
been found out as 16.08 MJ/kg.
It can be seen from table 1 that with increase intemperature from 300 - 400°C, there is an increase in theyield of bio-oil. At 450°C, the yield of bio-oil is seen to bedecreased due to secondary reactions. It can also beobserved that the yield of gases has increased which is
attributed to high temperatures and cracking of highmolecular weight hydrocarbons to low molecular weight
non-condensable hydrocarbons with 2°C cooling water.
With respect to pressure, it can be observed that theyield of bio-oil increases from 1 bar to 20 bar and drops
when pressure is increased to 40 bar. At higher
temperatures of 350 - 450°C, it can be observed that withincrease in pressure from 20 bar to 40 bar, the yield of
bio-char is increased. This is in line with the results ofopen literature that presence of vapours in the vicinity ofchar leads to increased production of char. This is acombined effect of increase in temperature and pressure.
The bio-char produced by hydropyrolysis of cotton
residue has been characterized using SEM, XRD and
FT-IR. It has been observed that the macromolecular
structure of the cotton residue has been decomposed.
The significant functionalities present in the cotton
residue do not exist after hydropyrolysis. The porous
nature of the cotton residue bio-char is clearly evident at
400°C and 20 bar beyond which the structure seems tohave collapsed.

Table 1. Hydropyrolysis of cotton residue yields
Pressure,
bar
300°C
1

Bio-oil,wt.%

Gas,wt.%Char,wt.%

Conversion,
%

6.8

38

55.2

44.8

20

8.2

35.7

56.1

43.9

40
350°C

5.8

38.2

5644

1
20

12.6
14.5

46.5
40.5

40.9
4559.1
55

40

1239

49

51

400°C
115.144.7

40.2

59.8

2040

18.7
13.2

38.7
42.3

42.6
44.5

57.4
55.5

450°C
1

14.9

47.8

37.3

62.7

20

18.3

43.7

3862

40

13.1

46

40.9

59.1

4. Conclusions
Cotton residue is an interesting feedstock for thermochemical methods of conversion to produce value addedhydrocarbons in a sustainable manner. Hydropyrolysis ofcotton residue has been carried out and it has been
observed that the optimum conditions in the used
experimental set up at 400°C and 20 bar pressure ofhydrogen. The data obtained by the analytical techniques
have provided supplementary information to arrive at thisresult. When hydropyrolysis is integrated withhydroconversion, fungible hydrocarbons can be obtained
directly from this process.

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[2] RR Sharma‐Shivappa, Y Chen Y. Conversion ofCotton Wastes To Bioenergy And Value‐AddedProducts. Transactions of the ASABE 51(6) (2008) 22392246 American Society of Agricultural and BiologicalEngineers.
[3] D King, I Rochester. Managing cotton
stubble/residues. Australian Cotton Production Manual(2011) 112-114.
[4] SN Pandey, AJ Shaikh. A study on ChemicalComposition of Cotton Plant Stalk of Different Species.
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[5] B Balagurumurthy, TS Oza, T Bhaskar, DK Adhikari.
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7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013