Design of Phthalic Anhydride Production Process Student Contest Problem Competition 2009 - EURECHA Acácio Mendes,
[email protected] Ana Rita Seita,
[email protected] Instituto Superior Técnico – Av. Rovisco Pais, 1049-001, Lisboa, Portugal
Abstract This paper illustrates a way of producing phthalic anhydride (PA) in a continuous plant, with an annual production of 80,000 tonnes of PA (99.8 % wt purity), through the oxidation of o-xylene. Maleic anhydride is also obtained as a by-product of the process with 99.5% wt purity. ®
The process was simulated using the process simulator software ASPEN Plus 2006.5 . A market demand forecast was made, as well as a capital and operating cost estimation. The payback time and profitability were calculated.
1. Introduction Phthalic Anhydride (PA) is an organic product which can be obtained from substances as oxylene or naphthalene, through oxidation in presence of a catalyst, usually a vanadium/titanium oxide. PA is an important chemical intermediate. Its major outlets are phthalate plasticizers, unsaturated polyesters and alkyd resins for surface coatings while its smaller volume applications include polyester polyols, pigments, dyes, sweeteners and flame retardants. The major outlet for phthalic anhydride (PA), accounting for just over half of production, is in the manufacture of phthalate plasticizers, the main product being dioctyl phthalate (DOP) which is used as a plasticizer in polyvinyl chloride (PVC). Hence, the consumption of PA is mainly dependent on the growth of flexible PVC, which is sensitive to general economic conditions as it is consumed in the construction and automobile industries. Others 10% Unsaturated Polyesters 18%
Plasticizers 57%
Alkyd Resins 15% Figure 1 – Main applications of PA in industry
[1]
.
2. Market Demand Forecast 2.1. PA market
[2]
Global demand for PA was forecasted by consultants to have been around 3,600,000 tonnes/year in 2006 with worldwide growth rates expected to be around 3.0-3.5%/year over the next five years. This growth is led by the Asia-Pacific region where demand is forecast to
increase at 4.0-4.5%/year. Demand growth in the US and Western Europe is much lower at 1.01.5%/year. For example, demand in the US is only expected to grow at a relatively modest rate of 1.5%/year to 2009. CMR predicted that PA production would reach 458,000 tonnes in 2009, whereas demand in Europe is growing at 2-3%/year, but this is mainly due to the rising consumption in central and east European markets, notably from the construction sector. Demand growth in northwest Europe is to remain low, but stable.
Crude oil
o-xylene
PA
Plasticizers
PVC
Applications
Figure 2 – Major product chain of phthalic anhydride in chemical industry.
2.2. Plasticizers
[3]
Plasticizers are organic esters added to polymers to facilitate processing and to increase the flexibility and toughness of the final product by internal modification of the polymer molecule. Flexible polyvinyl chloride (PVC) accounts for 80–90% of world plasticizer consumption. Flexible applications for PVC accounted for 35% of PVC consumption in 2005. From 2002 to 2005, world capacity for plasticizers grew at an average annual rate of 3.8%, a much higher rate than world consumption, which grew at an average annual rate of 2.0% during the same period. The following pie chart shows world consumption of plasticizers and the large percentage of consumption accounted for Other Asia, excluding Japan.
Figure 3 – World consumption of plasticizers in 2006.
The United States, Europe and Asia including Japan are the largest markets for plasticizers, accounting for nearly 89% of world demand in 2005. Demand for plasticizers in the United States and Western Europe is expected to grow moderately at an average annual rate of 1.0– 1.5% until 2010. Increasing imports of finished vinyl products, mainly from Asia (primarily China), softening demand in construction/remodelling activity (particularly in the United States), and declining exports are the main factors behind this slow growth. Recent consolidations and capacity reductions in the Western European plasticizers market have resulted in improved efficiencies and capacity utilization. Japanese consumption is forecast to experience 0.1%
average annual growth until 2010. Other Asian growth, excluding Japan, is expected to occur at 3.0% annually during the same period; China is the main growth factor in this region. Demand for most downstream plasticizer markets is greatly influenced by general economic conditions. As a result, demand for plasticizers largely follows the patterns of the leading world economies. The major end-use markets include construction/remodelling, automotive production and original equipment manufacture (OEM). Communication and building wire and cable, film and sheet (calendared and extruded), coated fabrics and dispersions (flooring and other) are the largest markets for plasticizers. 2.3. PVC market The consumption of PA is mainly dependent on the growth of flexible PVC, which is sensitive to general economic conditions as it is consumed in the construction and automobile industries. The United States, Western Europe and China are the major consumers of PVC, as shown in figure 4. The PVC is mainly used in building & construction sector (67%). The major applications are profiles (29%) and pipes & fittings (26%).
Figure 4 – World consumption of PVC in 2006
[3]
.
Figure 5 shows that world PVC demand is slightly higher than the Gross Domestic Products (GDP). However, PVC growth on mature markets such as USA, Canada and Western Europe is lower than the respective GDP from those regions.
Figure 5 – World PVC Demand vs. GDP since 1996 to 200 8
[4]
.
Developed regions as North America, Western Europe and Japan have a strategic position on global economy. They own more than three quarters of total GDP. However, regions under development are quickly growing. For instance, the fast and continuous growing of China, India and the rest of Asia (except Japan) has given their contribution for an important positioning on global economy. These statements are illustrated at table 1. Table 1 – World’s GDP data and forecast [4].
An interesting point is the fact that European Union was a PVC importer until 1999. However, since 2000, EU started to produce more PVC destined to exportation. 800
0 600 0 0 1 x ) 400 h / n o t ( 200 s t r o 0 p x 1994 e / s -200 t r o p m-400 I C V P -600
1996
1998
2000
2002
2004
2006
-800
Years
Figure 6 – PVC imports/exports of EU since 1995 to 2005
[4]
.
. n o i t a d i x o e n e l y x o a i v s s e c o r p n o i t c u d o r p A P f o t e e h s w o l f d e l i a t e D
– 6 e r u g i F
n o i t c u d o r P f o s s e c o r P e h T . 3
t e e h s w o l F . 1 . 3
. r o t a l u m i S s s e c o r P s u l P n e p s A n o n o i t a l u m i s e h t m o r f d e n i a t b o t e e h s w o l F
– 7 e r u g i F
3.2. Description The raw o-xylene is pre-heated and mixed with a compressed air stream. Then, it enters on an isothermal reactor were the crude product is obtained. Here, steam is generated which is used as an utility in the plant. In the reactor, four reactions are assumed to occur. (1) (2) (3) (4)
Reaction (1) is the main reaction and it is assumed a 70% selectivity. Reaction (2) refers to the formation of the by-product MA and a 10% selectivity is considered. Reactions (3) and (4) represent the complete and incomplete combustions of o-xylene with 15% and 5% selectivity, respectively. In the reactor, a molten salt is used to remove the heat generated. The salt is then fed to a steam generator, where 18 bar steam (medium pressure steam) is generated at 300 ºC. The stream leaving the reactor is condensed and the liquid fraction is separated from the offgases. However, this stream has some MA which is the by-product. In order to obtain the MA, the stream is condensed again and the condensables are mixed with the previous liquid phase. The resulting stream is heated and once again the vapor phase is separated from the liquid one, which is fed to the first distillation column, where the major fraction of water is mainly removed. The bottom stream, which is now composed exclusively by PA and MA, is cooled and fed to the second distillation column where the MA by-product stream is obtained on top while the PA final product on the bottom, both purified. 3.3. Mass and Energy Balance Table 2 – Inlet/outlet streams of the process and respective compositi ons, pressure and temperature, obtained from Aspen simulation. 1 2 21 22 23 25 Mole Flow kmol/hr H2O 0,00 0,00 0,00 0,00 3,73 321,00 O2 2755,41 0,00 0,00 0,00 0,00 2314,71 N2 10365,59 0,00 0,00 0,00 0,00 10365,59 O-XYLENE 0,00 92,78 0,00 0,00 0,00 0,00 M-XYLENE 0,00 0,94 0,00 0,00 0,00 0,94 P-XYLENE 0,00 0,05 0,00 0,00 0,00 0,05 TOLUENE 0,00 0,33 0,00 0,00 0,00 0,33 ETILBENZENE 0,00 0,09 0,00 0,00 0,00 0,09 BENZENE 0,00 0,06 0,00 0,00 0,00 0,06 MA 0,00 0,00 0,16 3,55 0,03 5,54 PA 0,00 0,00 63,94 0,00 0,00 1,01 BENZOIC ACID 0,00 0,00 0,00 0,00 0,00 0,00 PHTHALIC ACID 0,00 0,00 0,00 0,00 0,00 0,00 CO2 0,00 0,00 0,00 0,00 0,00 148,45 CO 0,00 0,00 0,00 0,00 0,00 37,11 Total Flow kmol/hr 13121,00 94,25 64,10 3,55 3,76 13194,88 Total Flow ton/hr 378,55 10,00 9,48 0,35 0,07 378,64 Temperature K 298,15 298,15 527,02 449,91 371,65 328,15 Pressure atm 0,99 0,99 0,50 0,50 1,00 0,99 Vapor Frac 1 0 0 0 0 1 Liquid Frac 0 1 1 1 1 0
4. Equipment Design The reactor is considered as multi-tubular and was designed considering a shell and tubes heat exchanger. The other heat exchangers are shell and tubes exchangers, as well. Both columns are sieve trays. T-201 has a total condenser and as two different diameters (0,2 m above the feed stream and 0,5 m below the feed stream) whereas T-202 has a partial condenser in order to remove incondensables. Pumps were designed considering the volumetric flow and the discharge pressure.
Table 3 – Parameters of both distillation columns obtained from Aspen simulation.
Trays Height (m) Diameter (m) Tray spacing (m) Refluxo Ratio Feed Stage Pressure (bar)
T-201 18 9 0,5 (bottom) 0,2 (top) 0,5 0,2 10 1
T-202 65 19,5 1 0,3 6 50 0,5
Table 4 – Parameters of all heat exchangers in the plant.
Utility T (ºC) P (bar) tonnes/h 2 A (m ) Q (MJ/h) 2 U (W/m .k)
E-201 Heat o-xylene
E-202 Heat bfw
E-203 Steam generator
E-205
E-206
E-207
E-208
E-209
E-210
Cond.
Heat
Cond.
Reboiler
Cond.
Reboiler
mps 185,8 7,2 0,9 15 2380,21 500
bfw 30 18 27 41 23700,60 700
bfw 240 18 27 63 81784,40 10497
cw 25,5 1 182 123 11043,75 700
lps 185,8 7,2 0,21 4,1 576,44 500
cw 25,5 1 3,3 2 198,99 500
mps 300 18 0,7 44 2137,45 500
cw 25,5 1 19,78 5 1199,01 500
mps 300 18 0,28 18 860,36 500
R-201 Heat Recov. Molten Salt 360 3 1529 18 81784,40 10497
mps – medium pressure steam; bfw – Boiler feedwater; cw – cooling water; lps – low pressure steam
5. Capital and Operating Costs 5.1. Equipment Cost [5,6,7]
The equipment cost was estimated based on correlations found at the internet . All equipment costs were updated to December 2008, using Chemical Engineering Economic indicators [5]. The original price estimation data of equipment is dated to 2002 [6], with exception [7] for the reboilers which original prices estimation report to the year of 2007. It is considered that 1 $ USD = 0,633 €. Table 5 – Estimated Costs of purchased equipments.
Heat Exchangers Pumps Compressor
€ 37889 40130
7437078
Distillation Columns
56678
Vessels
26675
Reactor
3811
Total
7602260
5.2. Fixed-Capital Investment
The Fixed-Capital Investment (FCI) was calculated base on that 40% of the costs refer to the equipment cost. All other assumptions are listed below. Table 6 – Percentage of FCI for all considered categories
€ Purchased equipment 7602260 1710509 Purchased-equipment installation Instrumentation and controls 950283 Piping 760226 Electrical system 760226 Buildings 950283 Yards improvements 380113 Service facilities 1330396 Land 380113 Direct Costs 14824408 Engineering and supervision 1710509 Construction 950283 Legal Expenses 190057 Contractor's fee 380113 Contingency 950283 Indirect Costs 4181243 Total FCI (€) 19005651
[8]
.
% 40% 9% 5% 4% 4% 5% 2% 7% 2% 78% 9% 5% 1% 2% 5% 22% 100%
The operating costs, namely steam, water and electricity, were also estimated based on 2002 [5] values . In order to actualize these values, it was assumed an annual inflation tax of 3%, from 2002 to 2008.
5.3. Operating Costs and Product Prices Table 7 – Estimated operational cost and raw material cost
[2,5]
.
€/h
€/year
205,28
4,4
35472,31
Electricity (kWh/h)
15267,50
1367,3
10992807
DI Water (tonne/h)
27,00
35,5
285125
O-xylene (tonne/h)
378,55 Total
9800 11207,1
78792000 90105404
Operational costs
CW (tonne/h)
The raw material and products prices
[2]
were considered from April last year.
Table 8 – Cost of products and exported steam
[2,5]
.
tonnes/h
€/h
€/year
PA
9,5
11855
95318120
MA
0,3
0,3
2800
24,9 Total
446,8 12303
3592481 98913400
Incomes
Steam mps
6. Economic Evaluation 6.1. Pay-Back Time
It was considered that the life time project was 10 years. Accumulated cash-flows were calculated for the ten years of the project, considering that the whole investment is made on the year “zero”. The year “one” is the first year that registers incomes. The annual cash-flow is calculated based on equation (5): (5) where j is the referring year. The expenses are calculated by summing all operating cost and considering an increment of 1% of this value for operating labor costs. Table 9 –
Investment, annual incomes and annual expenses.
Investment (€)
19005646
Incomes (€/year)
98913400
Expenses (€/year)
91058614
The cash-flows were also actualized considering an interest rate ( i ) of 7%, according to the equation: (6)
Table 10 –
Annual accumulated cash-flows and respective actualized values.
Year
CFaccumulated CFact. accumul.
0
-19005646
-19005646
1
-11150859
-10421364
2
-3296073
-2878918
3
4558714
3721269
4
12413501
9470200,4
5
20268288
14451009
6
28123074
18739592
7
35977861
22405204
8
43832648
25511000
9
51687435
28114540
10
59542221
30268246
Finally, the pay-back time is the year where accumulated actualized cash-flow sum is equal to zero: (7)
Calculations reveal that the sum of equation (7) equals zero for a PB between 5 and 6. 6.2. Profitability
There are many parameters which describes the profitability of a project. In this case, this index is supported by the internal rate of return (IRR) which can be calculated by the following equation: (8)
The IRR obtained for this project was 26.5 %. 7. Discussion and conclusion
As it is referred on marked demand forecast, PA is an intermediary in PVC production. Hence, PA market depends largely on PVC market. Also, both markets are dependent of petroleum demand. However, despite fragile situation of global economy, a growth in PA/PVC consumption is expectable, especially in regions under development (such as China, Asia, etc). For the economical evaluation, it was considered a life-time project of ten years, which is considered reasonable for this kind of industry, despite the fact that other life-times could be made. The investment is recovered after a period of five to six years, near to half of the project’s life-time, which is acceptable. Also, the profitability obtained is interesting, with an IRR above 20%. There are many processes to produce phthalic anhydride from oxidation of o-xylene. One [9] possibility is described by Healy et al. . Is this process, the outlet stream from reactor is cooled using a set of switch condensers. On one hand, this equipment works in a discontinuous way, while on the other hand, this type of equipment is very expensive and for these reasons, this process wasn’t adopted.
Because simulating a set of switch condensers is extremely difficult, a simple heat-exchanger was used for the required conditions of the outlet reactor’s stream, referred on several patents for this process. This decision had necessarily some implications in a few topics of this project, including economical evaluation, which is definitely underestimated. In this project, indirect energy integration was opted by producing medium pressure steam in the reactor. This steam was used to heat all the necessary streams in the process. Also, exceeding is sold to optimize the plant’s profit. The treatment for off-gases (stream 25) and waste water (stream 23) from the process is not described in this paper. Once again, this fact has some impact on economical evaluation. Also, in stream 14 more than half of the by-product MA is lost. The entire MA obtained on reactor, however, is much lower than PA. Hence, the incomes due to the selling of MA are negligible comparing to PA, which table 8 illustrates. For this reason, the project would be more expensive and less profitable if a full recovery of MA was made. Despite all the assumptions made in this process, a successfully simulation was made in order to achieve the main requirements of this problem, including purity of PA and annual production. 8. References th
[1] Ullmann’s Encyclopedia of Industrial Chemistry, 5 Edition, VCH; [2] www.icis.com (consulted in March 2009); [3] www.sriconsulting.com (consulted in April 2009); [4] CMAI - Chemical Market Associates, Inc.; [5] http://web.ist.utl.pt/ist11061/de/ (consulted in April 2009); [6] http://www.mhhe.com/engcs/chemical/peters/data/ce.html (consulted in March 2009); [7] http://matche.com/EquipCost/ (consulted in April 2009); [8] Peters, Max S., et al, Plant Design and Economics for Chemical Engineers, 5 McGraw-Hill;
th
Edition,
[9] Process for disposal of phthalic anhydride decomposer vapors, United States Patent no. 5,214,157, May 25, 1993; [10] Liquid phthalic anhydride recovery process, United States Patent no. 5,508,443, April 16, 1996; [11] Kirk-Othmer, Encyclopedia of Chemical Technology, 5th Edition, John Wiley & Sons, Inc.;
