Modeling Direct Ethylene Hydration over Zirconium Tungsten Catalyst : Fundamental of Ethanol Production Using the Biggest Global Ethylene Feeding Pipeline in Iran

Ethanol is produced through two methods of fermenting and hydration of ethylene. In this article, regarding low rates of ethanol production in Iran (1.510 liters per year) and extreme requirement of global industry to ethanol as a fuel additive, the capacity of ethanol production in Iran has been discussed. Adding ethanol to fuels would make them environmental friendly and as a result, huge amounts of ethanol would be required. It is declared that Iran, having the biggest ethylene pipeline in the world, has the potential of massive ethanol production and could play a pivotal role for global ethanol manufacturing in the near future. In addition, producing ethanol and exporting it is investigated via the simulation of an ethanol factory. Direct hydration of ethylene is the recommended method in this study. Simulation of this process was done using HYSYS software and the optimization results are illustrated based on Aspen Plus software.

Ethanol as one of the most well-known oxygen-containing organic materials has a wide variety of applications.Ethanol in medical applications such as sterilization of medical instruments, dressings, directly in the formulation of some drugs and non-medical costs, as additives to fuel motor vehicles, production of vinegar, a variety of solvents, paints and other fields of application are numerous (Renewable Fuels Association, 2012).
Official statistics illustrate that global produced ethanol was around 1.02 10 11 liters in year 2010 (Ethanol Industry News, 2011).Most ethanol (approximately 93 percent) in the world is produced through fermentation and only about 7 percent is made synthetically (Nelson, 1951;Maki et al, 1998).The principal suppliers of synthetic ethanol are multi-national companies' plants like Sasol companies in Europe and South Africa, Equistar Company in the United States and SADAF Company in Saudi Arabia (Ethanol Industry News, 2011).The initial stages and materials vary based on production methods of ethanol.Moreover, the biggest synthetic ethanol manufacturing plants are in Germany and Scotland with a production rate of 1.710 8 liters per year (Gilmartin, 2005;Bristow, 2011).
It has been declared that ethanol production through fermentation is much too volatile to allow for a secure and constant supply of ethanol in the region (Chemical Industry News & Intelligence, 1998).On the other hand, it is said that synthetic production of ethanol seems to be less economical in the U.S. which is due to high costs of ethylene, the initial materials of the Regarding the existence of many incomplete and unoptimized technologies for the production of reaction, and the great features of their farming products that allow them use fermenting methods for agricultural wastes (Chemical Industry News & Intelligence, 1998, 2005).Figure 1 shows the main global exports of ethanol in 2005 (FO Licht, 2006

Process Simulation of the Synthetic Plant with 87% Purity
Direct hydration of ethylene has been invented about 50 years ago in chemical industry over catalysts consisting of diatomaceous earth or silica gel, impregnated with loadings of orthophosphoric acid (Millidge, 1969).In brief, ethanol synthesis process includes three steps: reacting, recycling, and purifying (Sommer & Bücker, 1983;Devon, 1972).We simulated the process using NRTL FLUID PACKAGE model with HYSYS 3.2 software looking for the efficiency of reaction progress in the reactor.Figure 2 shows the results of this simulation.The flow then enters reactor feed heater.This heat exchanger heats the contents using the steam to prepare the input flow for the reactor reaction conditions that is a temperature of 229°C (Sommer & Bücker, 1983;Millidge 1969;Logsdon, 1994).
The reaction that takes place in reactor R-201 is in equilibrium and incomplete.As a result, majority of initial materials remain inactive in the output of the reactor.The reaction has been experimented over various catalysts.In this article, a mixture of Zirconium and Tungsten is the offered catalyst and it later discusses facilities and investments that should be noted for construction and running of the plant (Reynolds & Pittwell, 1956;Thomson & Reynolds, 1952).The considerable reaction (1) occurs in the reactor and r 1 defines forward reaction and r 2 implies backward reaction rate.Partial pressures are calculated in atmospheric situation.Catalyst void fraction is 0.5 and bulk density is 1.8gr/ml.Because of using Tungsten-Zirconium catalyst, ethanol will not dehydrate.But the acetylene that is sent to the reactor with ethylene is able to make a reaction with water and produces acetaldehyde too.

(11)
Due to chemical kinetics of the reaction and requiring conversion rate, investigation of K is essential.K is the constant equilibrium and is computed as the following, assuming it as an ideal gas (Ewell, 1940;Wenner, 1949).
The constants relate to fugacity of materials by means of K ∏ fı in real equilibrium mixture.This components' fugacity shows real equilibrium of the mixture and they are functions of temperature, pressure and compositions Since gas-phase thermo chemical quantities are more readily found, it is preferable to formulate the chemical equilibrium condition for the vapor phase, as shown (Ravagnani et al., 2010;Schladt et al., 1998): Assuming the mixture as ideal, it is concluded that: . . .

(15)
Thus: 229 0.01568.Considering the average inlet and outlet reaction temperatures and high pressure conditions in the reactor the fugacity value is approximately ξ e =0.2598.
Regarding the volatility of ethylene, the output flow from the reactor enters the cooling exchanger reactor to gain the proper conditions of being separated from ethylene from product, the output flow enters the low pressure separator from the lower part of reactor feed heater.Flows 9 & 11, which are the upper outputs of the separators, are sent to ethanol absorber tower (T-201).To equalize the pressure of the flows 9 and 12, the reciprocating flash gas compressor (C-201) is used.
After mixing, flow No. 14 enters the ethanol absorber column.Owing to the fact that flow 14 contains some ethanol, the water enters the tower T-201 from the upper part through flow No. 15 and absorbs ethanol; the output flow is then sent to purifying column T-202 from the lower portion of the tower.
Flow No. 23 and 21 enter the purifying ethanol purification; the first through the 54 th plate and the latter, which is the product of T-201 adsorption column, through the 99 th plate.Flow 24 and the lower output of ethanol purification column that encompasses a little ethanol and lots of water will then enter waste water cooler to get cooled through cooling water.

Optimizing Process to 99.7 Percent Purity
The design of effective processes for environmental friendly fuels by means of additive ethanol implies implementation of the best procedure and definition of a suitable process.Configurations that make the production possible until the final product meets given characteristics must be specified.The task of defining a proper configuration of the process requires the assessment of many process simulators for finding the modifying process with improved and organized performance indicators.
Using ASPEN PLUS in a synthesis process can significantly enhance process condition predictions and products.This simulator allows optimization for attaining a raw ethanol with 99.7% purity produced in the earlier explained section.Much has been done about azeotrope fracturing in water-ethanol solutions so far; the prominent parts of studies however have been focused on purifying through extraction (Gerbaud et al., 2006;Langston et al., 2005).Until recently, benzene was the most important material for purifying studies due to its features of destroying azeotrope.However, the produced ethanol via this method was perilous enough to create quite irreplaceable damages.

Conclusion
According to the modeled process, ethanol is produced with 99.7% purity.Noting the fact that global environmentalist and scientists believe that ethanol is needed in massive amounts in the near future, the areas in which there is the potentiality of ethanol production should be examined.Increased costs of agricultural products and their shortage in Iran and therefore the inability of producing ethanol through fermenting method proves the idea that direct hydration is the best accessible method for mass production of ethanol that is economical referring to the available sources in the country.Besides, regarding the optimization and purity improvement of the produced ethanol in this study, an increased value of the product would be reached due to its high purity.
Noting the necessity of synthetic ethanol production and the economic justification of the issue, stable conditions would be held for internal production of ethanol in the country and later for massive exports.

Figure 2 .
Figure 2. The simulated factory of synthetic ethanol production in HYSYS According to Figure 2, flow lines 1 and 3, with a temperature of 25°C, are the flow inlets of the factory.After mixing with the reverse flow of the process (26), they reach the temperature of 85 °C and the result is flow No. 4.The flow then enters reactor feed heater.This heat exchanger heats the contents using the steam to prepare the input flow for the reactor reaction conditions that is a temperature of 229°C(Sommer & Bücker, 1983; Millidge  1969;Logsdon, 1994). ).

Table 1 .
Features of vapour and aqueous phase of production by the plant

Table 2 .
Component of ethanol produced by the first section of plant