УДК 573.6.086.83.001.5;573.6.086.83
DESIGN AND ECONOMIC ANALYSIS OF THE TECHNOLOGICAL SCHEME FOR 1,3-PROPANEDIOL PRODUCTION FROM RAW GLYCEROL © 2013 г. J. A. Posada", C. A. Cardona" , J. C. Higuita", J. A. Tamayo*, Yu. A. Pisarenkoc
aDepartamento de Ingeniería Química, Universidad Nacional de Colombia, Manizales, Colombia
ccardonaal@unal.edu.co bDepartamento de Ingeniería Industrial, Universidad Nacional de Colombia, Manizales, Colombia cMoscow State University of Fine Chemical Technology pisarenko_yu@mail.ru Received 22.05.2012
A technological scheme for producing 1,3-propanediol from raw glycerol was designed, simulated, and economically assessed. The production process was composed of three main stages, namely: glycerol purification, glycerol fermentation, and 1,3-propanediol recovery and purification. First, a typical stream of raw glycerol was purified up to 98 wt %, and then the fermentation took place in a two continuous stages process by means of a Klebsiella pneumoniae strain. For the fermentation stage, a rigorous analysis was carried out using a kinetic model considering both substrate and products inhibition. Thus, multiplicity of steady states and hysteresis loops were studied for the first fermentation stage. Also, in order to optimize both the outlet concentration of 1,3-propanediol and its productivity, three different objective functions were analyzed. As result, each objective function led to an optimal condition, such as: the highest global yield to 1,3-propanediol (0.599 mol/mol), the highest outlet concentration of 1,3-propanediol (0.512 mol/L), and the highest global productivity (1.157 x 10-2), respectively. Then, the downstream process for 1,3-propanediol recovery and purification was designed based on a reactive-extraction process and a reactive-distillation process. This downstream process was applied to each scenario analyzed on the fermentation stage. Finally, the three scenarios were economically assessed and the lowest production cost was obtained for the third scenario. Simulation process and fermentation analysis were performed using Aspen Plus and MatLab respectively, while the economic assessment was carried out using the Aspen Icarus Process Evaluator.
DOI: 10.7868/S0040357113030093
INTRODUCTION
Glycerol is a byproduct of triglycerides transesteri-fication with alcohol in the biodiesel production and it is obtained in a weight ratio of 1 : 10 (glycerol/biodie-sel) [1]. Because of the high functionality of glycerol, it is a particularly attractive raw material for chemical and biochemical synthesis [2, 3]. Also, due to the increment in the use of biodiesel, a growth in the glyc-erol production could cause an oversupply and consequently an inevitable invasion of glycerol in the market [4, 5]. For this reason glycerol could become a cheaper feedstock for chemical synthesis obtained from biosustainable sources [6]. In this sense, the biodiesel production plants should work on glycerol transformation to products with an added value and a high demand [7, 8].
Glycerol bioconversion to metabolites has been widely studied in the last decade and many works have been focused on 1,3-propanediol production since it exhibits a wide range of potential uses [9]. 1,3-Pro-panediol can be used as an intermediate for the synthesis of heterocycles and as a monomer for polyesters synthesis (e.g., polypropyleneterephthalate (PPT) and
polyethyleneterephthalate (PET) [10]), where 1,3-propanediol improves their chemical and mechanical properties in comparison with other conventional monomers [11]. Also, biodegradability of plastics containing 1,3-propanediol is higher than those totally synthetic polymers [12, 13]. 1,3-Propanediol can also be used as lubricant, solvent, and functional fluid (e.g., antifreeze, unfreezing, and transfer of heat) [14]. 1,3-Propanediol has other important uses as an additive in foods, cosmetics, liquid detergents, wetter of tobacco, paintings, flavoring and fragrances, and as a precursor in the chemical and pharmaceutical industries [15, 16].Commercially, the oversupply of crude glycerol has caused a price fall from US $ 1/lb in 1996 to US $0.07/lb in 2010 [17]. Additionally, 1,3-propane-diol is produced at large scale and it has a growing market with an annual production up to one million pounds in the United States and an annual market growth of 4%, with a sale price around US $0.71/lb [18].
Fermentative production of 1,3-propanediol (13PD) under anaerobiosis takes place in two parallel ways. In the first one, a fraction of glycerol is oxidized by glycerol-dehydrogenase (Glyc-DH) to dihydroxy-acetone (DHA), and then phosphorrylated by DHA
kinase to enter glycolysis. The remaining glycerol is then dehydrated to 3-hydroxypropionaldehyde (3HPA) by glyceroldehydratase, where reduction continues by propanedioldehydrogenase (PPD-DH) and by a dependent NAD oxidorreductase to 1,3-propanediol [19, 20]. 1,3-Propanediol production can be performed biologically by several bacterial strains such as Klebsiella pneumoniae (KPNEUMON), Citrobacter freundii, Enterobacter agglomerans, Clostridium butyricum, and Clostridium acetobutylicum [21, 22]. K. pneumoniae and C. butyricum are the most commercially promising bacterial strains because of their high yield, productivity, and resistance to both substrate and product inhibition. Among these two bacteria, K. pneumoniae DSM-2026 has been presented as one of the most appropriate bacterial strain for glycerol fermentation to 1,3-propanediol [23].
On the other hand, recovering and purification of 1,3-propanediol from the fermentation broth is a complex task because of both its high hydrophilic character and its high boiling point. The purpose of this article is to design and analyze the complete technological scheme for the production of 1,3-pro-panediol using raw glycerol as feedstock.
METHODS
In order to perform the design and economic analysis of the 1,3-propanediol production process from raw glycerol, the complete technological scheme was first stated using a sequential strategy based on knowledge. This strategy allowed not only designing but also comparing process alternatives, considering mainly techno-economic criteria and leading to a technological configuration with high performance [7, 8, 24—26]. After obtaining a high performance technological scheme for 1,3-propanediol production, the process simulation took place. Aspen Plus (Aspen Technology, Inc., USA) was the main tool used for defining, structuring, specifying, and simulating the complete technological scheme. Then as result of the simulation process, mass and energy balances were obtained which gave the requirements for raw materials, consumables, service fluids, and energy requirements. Finally, these results were used to estimate the capital and operational costs of 1,3-propanediol production from raw glycerol using the software Aspen Icarus Process Evaluator (Aspen Technologies, Inc., USA).
For the production process of 1,3-propanediol from raw glycerol three main stages can be distinguished, named: glycerol purification, glycerol fermentation, and 1,3-propanediol recovery and purification.
Glycerol purification. A typical composition of a raw glycerol stream obtained in the biodiesel production process is: methanol 32.59 wt %, glycerol 60.05 wt %,
NaOCH3 2.62 wt
fats 1.94 wt
and ash
2.8 wt % [7, 8, 17]. The purification process of raw glycerol up to different commercial qualities (crude
glycerol at 88 wt % and pure glycerol at 98 wt %) was previously designed and analyzed by Posada et al. [7, 8, 17]. Initially the raw glycerol was subjected to an evaporation process where 90% of methanol at 99 wt % was recovered and recycled to the transesterification process (biodiesel production process). The resulting product was neutralized with an acid solution and formed salts and ashes were discarded by centrifuga-tion. The clarified mixture was then washed with water and in a later evaporation process more than 90% of the water content and the remaining methanol were withdrawn. Finally, the required quality of glycerol (98 wt %) was achieved throughout a distillation process [17]. This quality of glycerol was the one required for the fermentation process.
Glycerol fermentation. The material balances for continuous glycerol fermentation in one single stage were solved using two independent variables namely the glycerol concentration in the feed stream and the dilution rate. Since, acetic acid and ethanol were also produced during glycerol fermentation to 1,3-pro-panediol by K. pneumoniae, the material balances in a dynamic state needed to be solved for biomass, substrate, and all the obtained products as shown in equations (1) to (5):
dX,
Out
dt
Out
dCGU
dt
-- D{ (x/n - X,0ut )-X°ut, (1)
D - cGUt )- qG,xOut, (2)
dC
Out
dC
dt
Out HAc
~~ = Di (CPD,i CPD,i ) + qPD,iXi , (3)
dC
dt
Out EtOH,
- - Di ( Chac,( CHAc,i ) + qHAc,iXi ,
(4)
i - Di (CEtOH,i CEtOH,i) + qEtOH,iXi , (5)
dt
where X, CG, CPD, CHAc, and CEtOH are the concentrations for biomass (g/L), glycerol (mol/L), 1,3-pro-panediol (mol/L), acetic acid (mol/L), and ethanol (mol/L), respectively, D is the dilution rate (i.e., ratio between volumetric flow rate and reactor volume) (h-1), ^ is the specific rate of cellular growth (h-1), qG is the specific rate of glycerol consumption, and qPD, qHAc, and qEtOH are the generation rates of each product (h-1). Subscript i indicates the fermentation stage for a multistage system. In the ith fermentation stage, In and Out superscripts indicate the in and the out conditions, respectively.
The kinetic model of glycerol fermentation by K. pneumoniae has been previously explained [28-30].
Specific rates of cell growth, substrate consumption, and products formation are given in equations (6) to (11):
C,
Hi Ц m
G,i
' CG,i + KS
1 --
C,
C
G£
*
G J
V \f
1 - CPD,i
qGi
= mr, +
C*
PD J
Hi
1 --
C
HAc,i
\f \ 1 - CEtOH,i
C
+ Aq"c
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