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Sunflower stalks as a possible fuel source
Short Communications
Sunflower
stalks as a possible
J. L. Bonilla,
A. Chica,
J. L. Ferrer,
fuel source
L. Jimenez
and A. Martin
Dpto. lngenieria Quimica, Facultad de Ciencias, Universidad (Received 7 June 7989; revised 25 September 7989)
de Cbrdoba,
14071-Chdoba,
Spain
Sunflower (Helianthus annus) is a deciduous plant whose yearly production has grown dramatically in Spain over the last few decades. From sunflower wastes, consisting chiefly of stalks, it is possible (by acid hydrolysis and subsequent fermentation of the hydrolysate) to obtain ethanol for use as fuel. The kinetics of the acid hydrolysis of sunflower stalks has been studied in the temperature range llO-140°C using hydrochloric acid at concentrations between 0.5 and 6.0 wt%. The experimental results obtained conform k k, to a sequence of two consecutive first-order reactions: cellulose residue 4 sugar decomposition products. The rate constants k, and k, are proportional to the acid concentration and exponentially related to the temperature. (Keywords: hydrolysis; fuel; kinetics)
Sunflower (Helianthus annus) is a deciduous plant whose yearly production has increased dramatically in Spain over the last few decades’, to about 1 x lo6 tonnes of sunflower seeds per year. This cultivation leaves a residue consisting chiefly of stalks, which are chopped up and spread or burnt on site. The availability of this raw material (over 2.3 x lo6 tonnes per year), the lack of exploitation, the possibility of collecting it mechanically and its high holocellulose content (71 wt%) are good arguments for studying new practical applications, such as acid hydrolysis and subsequent fermentation of the hydrolysate to ethanol, which can be used as a fuel. This paper reports and correlates the results obtained in the hydrolysis of sunflower stalks with hydrochloric acid. The interest in this process is warranted by a number of recently published papers’-‘.
All experiments were conducted on suspensions with a solid content of 4 wt%. Higher concentrations prevented thorough mixing because of the increased resultant viscosity. The hydrolysis reaction was monitored by titration of reducing sugars at different times following the procedures of Somogyi and Nelson”.
1
g sugar/g
RESULTS
AND DISCUSSION
Figures 1 and 2 show the average variations of the reducing sugar concentration as a function of time. These results were obtained in experiments carried out to study the influence of the acid concentration and experiments aimed at determining the influence of the
potential
sugar
( WAO)
t
0,:
0,: EXPERIMENTAL Materials The sunflower stalks (Texas variety) used in this study had a moisture content of 12 wt% and particles of size < 1 mm in diameter.
0,1
Apparatus and procedure The cylindrical reactor used had volume 150 ml, and was made of a special type of stainless steel with a PTFE interchangeable liner and a PTFE cap lining. A PTFE coated Ni/CrNi thermosensor was used for measurement and control of the internal temperature. The heating mantle had means for internal temperature measurement and control. Maximum possible temperature was 250°C and maximum possible pressure was 100 atm. Agitation was provided by a magnetic stirrer. 001&2361/90/060792~3 0 1990 Butterworth-Heinemann 792
FUEL,
1990,
Ltd.
Vol 69, June
C
20 t,minut es Figure 1
Influence of temperature on the acid hydrolysis of sunflower
stalks
Short Communications
[----
g sugar/g
acid hydrolysis can be assumed to take place via two homogeneous first-order reactions’ ’ : k k2 Cellulose residue 4 Sugars -
potent ial sugar (CAICA~)
(C) Decomposition (P)
(A) products
Therefore, the variation of the relative concentration of potential sugars with time can be expressed as
CAIC,,=CkAk2-k,)l xCw(-k,t) -exp(-k,t)l
2,o % 0 4,0% A
A 6,OYe 20
40
60
60
100
120
t mai=(In k,-ln
Influence of acid concentration
on the hydrolysis of sunflower stalks
temperature on hydrolysis. The standard deviations in the reducing sugar concentrations ranged between 5.3 x 1O-3 and 15.1 x 10m3 g sugar per g of potential sugar. The shapes of the curves suggest the involvement of consecutive reactions.
The particle sizes used were small enough to rule out diffusion of the acid to the inside of the particles and diffusion of the sugars formed to the outside. This was checked with smaller particles, which resulted in similar sugar yields. Thus, the
Table 1 Values of the kinetic constants for the acid hydrolysis of sunflower stalks, and maximum yields of ethanol per unit time Acid (wt%)
Temperature (“C)
0.5
120 120 120 120 120 110 130 140
I .o 2.0 4.0 6.0 2.0 2.0 2.0
Table 2
Activation
k, (h-‘)
k, (h-j)
0.378 0.495 0.764
1.205
1.462
2.302 3.115 1.208 3.056 3.583
energies
for various
(g ethanol)/ (g potential
k, =(28X+41.3
Material
E, (kJ mol-‘)
E, (kJ mol-‘)
Ref.
Wood cellulose Fir wood Paper residue Poplar wood Sweetgum wood
191.7 179.5 188.7 147.1 105.0
145.9 137.6 137.3 87.9 _
12 11 13 14 15
(3)
C)109 T)
(4)
kz = (512.7+ 167.5 C)104 exp( - 12038/RT)
materials
(2)
Table 1 lists the k, and k, values found, as well as the maximum yields of ethanol from hydrolysis per unit time, assuming a yield of 46 wt% in the fermentation. A check was made to establish that the kinetic constants k, and k, are proportional to the acid concentration. The kinetic constants are also related to the temperature through the Arrhenius equation. By assuming the influence of the temperature on k, and k, to be independent of the acid concentration used, expressions relating both constants to these two variables were derived:
exp( -20033/R sugar x h)
0.061 0.080 0.126 0.246 0.332 0.067 0.297 0.44 1
1.385 1.747
1.976 0.414 1.775 2.608
k,)/@-k,)
[CA/CAo]mar = (k,/k 1)rk2’(k I- ‘2”
t, minutes Figure 2
(1)
The impossibility of linearizing Equation (1) prevented a simple check of whether the model proposed for calculation of the specific rate constants was obeyed. For each experiment, k, and k, were calculated using the T.S.P. (time series processor) program, which is a program of statistical calculus that allows least-squares estimation of nonlinear equations of any complexity. Version 4.0, made by T.S.P. International (Stanford, USA) was used with a Data General MV-15000 computer. Since the calculation algorithm requires initial k, and k, values to be provided, these were obtained from the expressions
(5)
The use of Equations (4) and (5) gives rise to reproducible variations of the sugar contents as a function of time: the errors were always less than 15%. The report activation energies for different materials are given in Table 2. The differences between the activation energies obtained in this work and those reported in the literature may arise from differences in the degrees of crystallinity of cellulose in various materials. Thus, the greater crystallinity of cellulose in wood and paper residues hinders its digestion, while its poor crystallinity in poplar and sweetgum wood and in sunflower stalks makes it more readily accessible to acids.
FUEL,
1990,
Vol 69, June
793
Short Communications ACKNOWLEDGEMENTS
4
The authors thank the ‘Junta de Andalucia’ for financial support in this research.
5 6
REFERENCES 1 2
3
I
‘Anuario de Estadistica Agrario’, Ministerio de Agricultura, Madrid, Spain, 1987 Brennan, A. H., Hoagland, W. and Schell, D. J. Biotechnol. Eioeng. Symp. 1986, 17(S), 53 Teng, K. F. and Mutharasan, R. Energy Biomass Wastes 1985, 9, 873
Wax deposition
8
9
of Bombay
10
Ullal, V. G., Mutharasan, R. and Grossmann, E. D. Biotechnoi. Bioeng. Symp. 1984, 14(6), 69 Singh, A., Das, K. and Sharma, D. K. .I. Chem. Technol. Biotechnol. 1984, 34, 51 Wright, J. D. and Power, A. J. EneryJT Biomass Was/es 1987. 10, 949 Kim, S. B. and Lee, Y. Y. Biotechnol. Bioeng. Symp. 1986, E(7), 81 Gonzalez, G., Lopez-Santin, J., Caminal, G. and Sola, C. Biotechnol. Biorng. 1986, 28(2), 288 Bienkowski, P. A., Ladisch, M. A., Yoloch, M. and Tsao, G. T. Biorerhnol. Bioeng. Symp. 1984, 14(6), 51 I
high crude
oil under
11 12 13
14
15
flowing
Marais, J. P., Wit, J. L. and Quiche, G. V. Anal. Biochem. 1966, 15, 373 Saeman, J. F. 2nd. Eng. Chem. 1945, 37(l), 43 Harris, E. E. and Kline, A. A. J. Phys. Colloid. Chem. 1949, 53, 344 R. D., Grethlein, H. G., Fagan, Converse, A. 0. and Porteons, A. Environ. Sci. Technol. 1971, 5(6), 545 Grethlein, H. G. and Converse, A. 0. ‘Int. Symp. on Ethanol from Biomass’, Winnipeg, USA, 1982 Goldstein, 1. S., Pereira, H., Pittman, J. L. et al. Biotechnol. Bioeng. Symp. 1983, 13, 17
conditions
K. M. Agrawal, H. U. Khan, M. Surianarayanan and G. C. Joshi Indian Institute of Petroleum, Dehradun, India (Received 8 February 7989; revised 12 October 1989)
The wax deposition rate of Bombay high crude oil under flowing conditions in a horizontal pipe was studied at different flow rates and at different temperature differentials between the oil and the cold surface. The deposition was found to increase asymptotically with time and reach a final fluctuating value. The time to obtain equilibrium deposition varied with test conditions. A mathematical equation correlating the flow rate and temperature differential with the equilibrium deposition was also developed. (Keywords: waxes; crude oil; storage stability)
During flow of waxy crude oil through pipelines, some of the wax gets deposited. This deposition of wax severely affects the pipeline throughput. There is therefore considerable interest’-’ in the determination of wax deposition rate, and quantity and thickness of wax deposited during flow of crude oil. However, wax deposition data are very specific to the crude for which they were obtained. Such information allows schedules to be planned for periodic removal of deposits. Bombay high crude (Indian offshore) is highly waxy in nature (wax content ll-14%), and has a high pour point (+ 30°C). The effect of time, flow rate and temperature on the wax deposition of Bombay high crude oil under flowing conditions has been studied in this paper.
Deposition
Thermometer \
Jacketed oil bath
-7
-
00162361/90/060794-03 0 1990 Butterworth-Heinemann
794
FUEL,
1990,
Ltd.
Vol 69, June
Figure 1
Laboratory
set up for wax deposition
Thermometer /
Thermostat
EXPERIMENTAL Figure 1 shows the deposition assembly used in this investigation. The assembly consisted of a 25 cm long, 6 mm i.d.
tube
I
Sunflower
stalks as a possible
J. L. Bonilla,
A. Chica,
J. L. Ferrer,
fuel source
L. Jimenez
and A. Martin
Dpto. lngenieria Quimica, Facultad de Ciencias, Universidad (Received 7 June 7989; revised 25 September 7989)
de Cbrdoba,
14071-Chdoba,
Spain
Sunflower (Helianthus annus) is a deciduous plant whose yearly production has grown dramatically in Spain over the last few decades. From sunflower wastes, consisting chiefly of stalks, it is possible (by acid hydrolysis and subsequent fermentation of the hydrolysate) to obtain ethanol for use as fuel. The kinetics of the acid hydrolysis of sunflower stalks has been studied in the temperature range llO-140°C using hydrochloric acid at concentrations between 0.5 and 6.0 wt%. The experimental results obtained conform k k, to a sequence of two consecutive first-order reactions: cellulose residue 4 sugar decomposition products. The rate constants k, and k, are proportional to the acid concentration and exponentially related to the temperature. (Keywords: hydrolysis; fuel; kinetics)
Sunflower (Helianthus annus) is a deciduous plant whose yearly production has increased dramatically in Spain over the last few decades’, to about 1 x lo6 tonnes of sunflower seeds per year. This cultivation leaves a residue consisting chiefly of stalks, which are chopped up and spread or burnt on site. The availability of this raw material (over 2.3 x lo6 tonnes per year), the lack of exploitation, the possibility of collecting it mechanically and its high holocellulose content (71 wt%) are good arguments for studying new practical applications, such as acid hydrolysis and subsequent fermentation of the hydrolysate to ethanol, which can be used as a fuel. This paper reports and correlates the results obtained in the hydrolysis of sunflower stalks with hydrochloric acid. The interest in this process is warranted by a number of recently published papers’-‘.
All experiments were conducted on suspensions with a solid content of 4 wt%. Higher concentrations prevented thorough mixing because of the increased resultant viscosity. The hydrolysis reaction was monitored by titration of reducing sugars at different times following the procedures of Somogyi and Nelson”.
1
g sugar/g
RESULTS
AND DISCUSSION
Figures 1 and 2 show the average variations of the reducing sugar concentration as a function of time. These results were obtained in experiments carried out to study the influence of the acid concentration and experiments aimed at determining the influence of the
potential
sugar
( WAO)
t
0,:
0,: EXPERIMENTAL Materials The sunflower stalks (Texas variety) used in this study had a moisture content of 12 wt% and particles of size < 1 mm in diameter.
0,1
Apparatus and procedure The cylindrical reactor used had volume 150 ml, and was made of a special type of stainless steel with a PTFE interchangeable liner and a PTFE cap lining. A PTFE coated Ni/CrNi thermosensor was used for measurement and control of the internal temperature. The heating mantle had means for internal temperature measurement and control. Maximum possible temperature was 250°C and maximum possible pressure was 100 atm. Agitation was provided by a magnetic stirrer. 001&2361/90/060792~3 0 1990 Butterworth-Heinemann 792
FUEL,
1990,
Ltd.
Vol 69, June
C
20 t,minut es Figure 1
Influence of temperature on the acid hydrolysis of sunflower
stalks
Short Communications
[----
g sugar/g
acid hydrolysis can be assumed to take place via two homogeneous first-order reactions’ ’ : k k2 Cellulose residue 4 Sugars -
potent ial sugar (CAICA~)
(C) Decomposition (P)
(A) products
Therefore, the variation of the relative concentration of potential sugars with time can be expressed as
CAIC,,=CkAk2-k,)l xCw(-k,t) -exp(-k,t)l
2,o % 0 4,0% A
A 6,OYe 20
40
60
60
100
120
t mai=(In k,-ln
Influence of acid concentration
on the hydrolysis of sunflower stalks
temperature on hydrolysis. The standard deviations in the reducing sugar concentrations ranged between 5.3 x 1O-3 and 15.1 x 10m3 g sugar per g of potential sugar. The shapes of the curves suggest the involvement of consecutive reactions.
The particle sizes used were small enough to rule out diffusion of the acid to the inside of the particles and diffusion of the sugars formed to the outside. This was checked with smaller particles, which resulted in similar sugar yields. Thus, the
Table 1 Values of the kinetic constants for the acid hydrolysis of sunflower stalks, and maximum yields of ethanol per unit time Acid (wt%)
Temperature (“C)
0.5
120 120 120 120 120 110 130 140
I .o 2.0 4.0 6.0 2.0 2.0 2.0
Table 2
Activation
k, (h-‘)
k, (h-j)
0.378 0.495 0.764
1.205
1.462
2.302 3.115 1.208 3.056 3.583
energies
for various
(g ethanol)/ (g potential
k, =(28X+41.3
Material
E, (kJ mol-‘)
E, (kJ mol-‘)
Ref.
Wood cellulose Fir wood Paper residue Poplar wood Sweetgum wood
191.7 179.5 188.7 147.1 105.0
145.9 137.6 137.3 87.9 _
12 11 13 14 15
(3)
C)109 T)
(4)
kz = (512.7+ 167.5 C)104 exp( - 12038/RT)
materials
(2)
Table 1 lists the k, and k, values found, as well as the maximum yields of ethanol from hydrolysis per unit time, assuming a yield of 46 wt% in the fermentation. A check was made to establish that the kinetic constants k, and k, are proportional to the acid concentration. The kinetic constants are also related to the temperature through the Arrhenius equation. By assuming the influence of the temperature on k, and k, to be independent of the acid concentration used, expressions relating both constants to these two variables were derived:
exp( -20033/R sugar x h)
0.061 0.080 0.126 0.246 0.332 0.067 0.297 0.44 1
1.385 1.747
1.976 0.414 1.775 2.608
k,)/@-k,)
[CA/CAo]mar = (k,/k 1)rk2’(k I- ‘2”
t, minutes Figure 2
(1)
The impossibility of linearizing Equation (1) prevented a simple check of whether the model proposed for calculation of the specific rate constants was obeyed. For each experiment, k, and k, were calculated using the T.S.P. (time series processor) program, which is a program of statistical calculus that allows least-squares estimation of nonlinear equations of any complexity. Version 4.0, made by T.S.P. International (Stanford, USA) was used with a Data General MV-15000 computer. Since the calculation algorithm requires initial k, and k, values to be provided, these were obtained from the expressions
(5)
The use of Equations (4) and (5) gives rise to reproducible variations of the sugar contents as a function of time: the errors were always less than 15%. The report activation energies for different materials are given in Table 2. The differences between the activation energies obtained in this work and those reported in the literature may arise from differences in the degrees of crystallinity of cellulose in various materials. Thus, the greater crystallinity of cellulose in wood and paper residues hinders its digestion, while its poor crystallinity in poplar and sweetgum wood and in sunflower stalks makes it more readily accessible to acids.
FUEL,
1990,
Vol 69, June
793
Short Communications ACKNOWLEDGEMENTS
4
The authors thank the ‘Junta de Andalucia’ for financial support in this research.
5 6
REFERENCES 1 2
3
I
‘Anuario de Estadistica Agrario’, Ministerio de Agricultura, Madrid, Spain, 1987 Brennan, A. H., Hoagland, W. and Schell, D. J. Biotechnol. Eioeng. Symp. 1986, 17(S), 53 Teng, K. F. and Mutharasan, R. Energy Biomass Wastes 1985, 9, 873
Wax deposition
8
9
of Bombay
10
Ullal, V. G., Mutharasan, R. and Grossmann, E. D. Biotechnoi. Bioeng. Symp. 1984, 14(6), 69 Singh, A., Das, K. and Sharma, D. K. .I. Chem. Technol. Biotechnol. 1984, 34, 51 Wright, J. D. and Power, A. J. EneryJT Biomass Was/es 1987. 10, 949 Kim, S. B. and Lee, Y. Y. Biotechnol. Bioeng. Symp. 1986, E(7), 81 Gonzalez, G., Lopez-Santin, J., Caminal, G. and Sola, C. Biotechnol. Biorng. 1986, 28(2), 288 Bienkowski, P. A., Ladisch, M. A., Yoloch, M. and Tsao, G. T. Biorerhnol. Bioeng. Symp. 1984, 14(6), 51 I
high crude
oil under
11 12 13
14
15
flowing
Marais, J. P., Wit, J. L. and Quiche, G. V. Anal. Biochem. 1966, 15, 373 Saeman, J. F. 2nd. Eng. Chem. 1945, 37(l), 43 Harris, E. E. and Kline, A. A. J. Phys. Colloid. Chem. 1949, 53, 344 R. D., Grethlein, H. G., Fagan, Converse, A. 0. and Porteons, A. Environ. Sci. Technol. 1971, 5(6), 545 Grethlein, H. G. and Converse, A. 0. ‘Int. Symp. on Ethanol from Biomass’, Winnipeg, USA, 1982 Goldstein, 1. S., Pereira, H., Pittman, J. L. et al. Biotechnol. Bioeng. Symp. 1983, 13, 17
conditions
K. M. Agrawal, H. U. Khan, M. Surianarayanan and G. C. Joshi Indian Institute of Petroleum, Dehradun, India (Received 8 February 7989; revised 12 October 1989)
The wax deposition rate of Bombay high crude oil under flowing conditions in a horizontal pipe was studied at different flow rates and at different temperature differentials between the oil and the cold surface. The deposition was found to increase asymptotically with time and reach a final fluctuating value. The time to obtain equilibrium deposition varied with test conditions. A mathematical equation correlating the flow rate and temperature differential with the equilibrium deposition was also developed. (Keywords: waxes; crude oil; storage stability)
During flow of waxy crude oil through pipelines, some of the wax gets deposited. This deposition of wax severely affects the pipeline throughput. There is therefore considerable interest’-’ in the determination of wax deposition rate, and quantity and thickness of wax deposited during flow of crude oil. However, wax deposition data are very specific to the crude for which they were obtained. Such information allows schedules to be planned for periodic removal of deposits. Bombay high crude (Indian offshore) is highly waxy in nature (wax content ll-14%), and has a high pour point (+ 30°C). The effect of time, flow rate and temperature on the wax deposition of Bombay high crude oil under flowing conditions has been studied in this paper.
Deposition
Thermometer \
Jacketed oil bath
-7
-
00162361/90/060794-03 0 1990 Butterworth-Heinemann
794
FUEL,
1990,
Ltd.
Vol 69, June
Figure 1
Laboratory
set up for wax deposition
Thermometer /
Thermostat
EXPERIMENTAL Figure 1 shows the deposition assembly used in this investigation. The assembly consisted of a 25 cm long, 6 mm i.d.
tube
I