Methods Of Preparation


2.1 METHODS

There are three methods for manufacturing Amyl Alcohol.

2.2 Fusel OiL

Fusel oil is obtained as a by-product in carbohydrate fermentation to produce alcohol. The material varies widely in composition, depending upon the fermentation raw material, but contains chiefly is Amyl Alcohol and active Amyl Alcohol, Isobutyl Alcohol 20%, n-Propyl Alcohol 3-5% and small amounts of other alcohols, esters and aldehydes. The oil is treated chemically, and refined by distillation. All the “A” fore mentioned alcohols are recovered with the Amyl Alcohols especially Isoamyl Alcohol, predominating Refined Amyl Alcohol from Fusel Oil contains about 85% Isoamyl Alcohol and 15% Active Amyl Alcohol.

2.3 Oxo- Process

In Oxo Process, Olefins react with CO and Hydrogen at high Pressure 3.4 M Pa and temperature 150-180oC in the presence of a homogeneous catalyst generally Cobalt Carbonyl. The reaction proceeds via an aldehydes intermediate which is usually hydrogenated to primary alcohol with out intermediate recovery. In actual practice, a wide range of olefin cut is usually run to achieve the economics of scale. In some plants and aldehydes recovery unit is interspersed between catalyst recovery and hydrogenation.

Since raw materials comprise seventy to eighty percent of total alcohol cost, initial step is economically the most critical. Many trade-offs are possible between product yield and minimum investment. Aldehydes yield depends upon temperature, pressure, reaction time, and catalyst concentration. High pressure enables in-situ production of the active cobalt carbonyl species from materials like the cobalt saps, whereas mild conditions, while reducing reactor costs, require a separate high-pressure reactor for catalyst generation. The reaction media are quite corrosive, necessitating the use of stainless steel reactor linings.

Catalyst recovery is readily accomplished by reducing CO partial pressure, whereby the soluble complex is readily converted to insoluble cobalt metal or coabtous ion by thermal decomposition or aqueous acid hydrolysis.

The hydrogenation step must be quite severe, since un-reacted olefins or aldehydes have a very adverse effect on alcohol quality. Nickel, cobalt, or molybdenum sulfides, supported on an inert base such as alumina, are generally used as catalyst.

Final refining entails conventional distillation. By-products, mainly un-reacted butylenes, pentanes, and aldol condensation products in the C10 range, are readily recycled or blended to gasoline or fuel.

2.4 Chlorination Process

The commercial source of Amyl Alcohol is the Pentane chlorination process. A Pentane fraction from petroleum distillation is chlorinated in either liquid or vapor place and result in the formation of Amyl Chlorides, which are further reacted with any unconverted chlorination giving Amyl Dicholorpantane which is separated. Amyl Alcohol is hydrolyzed with aqueous Sodium Hydroxide to corresponding alcohols.

  1. C5H12 + Cl2                         =           C5H11Cl + Hcl
  2. C5H11Cl + Cl2                      =          C5H10Cl2 + Hcl
  3. C5H11Cl+NaOH                  =          C5H11OH + NaCl

 

2.5 Selected Process

On the basis of  above given information and comparing these three methods the selected method is Chlorination of Pentane which is economically best suited.

Fundamental Chemistry

The fundamental chemistry related to these processes is very simple. The chlorination is carried out in vapor phase because higher yields to primary chlorides are obtained. The vapor phase chlorination affects more control over formation of dichloros. The principle in this chlorination of pentane proceeds with formation of amyl chloride and HCl.

C5H12 + Cl2               =                   C5H11Cl + HCl

During the rectification of amyl chlorides of 2-methyl-2-chlorbutane, it decomposes to form 2-methyl-2-butene. Olefins can be recycled to the chlorination step and under the condition used, in vapor phase at high temperature and pressure, until chlorinate rather than add chlorine to double bond.

Hydrolysis of amyl chloride is carried out in the presence of sodium oleate using aqueous caustic.

C5H11Cl + NaOH         =        sodium oleate     =      C5H11Cl + NaCl

2.6 Process Description

Chlorination

Pentane from the storage tank having composition of 96% Pentane and 4% water is sent to the dehydration tank where, its dehydration of pentane is taken place at pressure of 1atm and temperature of 27. The HCl which is being recycled and used for dehydration contains 98.9% Hcl and 1.1% pentane enters the dehydration tank at pressure of 1atm and 350C. In dehydration tank 95% of the water of feed is removed and goes to the liquid stream leaving the dehydration tank containing 1% of pentane of feed and 22% of HCl coming from the recycle stream. Remaining 5% of water goes along with the excess amount of HCl vapors (having 77% composition of recycled stream)leaving the dehydration tank. Here 100% dehydration of pentane is done.

Anhydrous pentane is passed through the makeup tank where the lost amount of pentane in dehydration process is added to fulfill the stiochiometric conditions of the reaction. Anhydrous pentane along with the recycled pentane is pumped to a steam heated vaporizer. The steam vaporizer is a steel and coil unit with steam in the shell. Here steam causes the pentane to be vaporized at the pressure of 75 psi and temperature of 850C. The vaporized pentane is entered to a mixer which is a modified venture mixing chamber. The mixer is made of cast steel. During this time, liquid chlorine from its storage tank is pumped to the steam heated vaporizer which yields vapors at 140 psi. The pressure is reduced by means of a pressure reducing valve and vapors pass through a flow meter at 80 psi and temperature of 500C. At a ratio of 15:1 pentane and chlorine are mixed in the mixer which is moving at very high velocity (above 60mph to minimize the danger of ignition). After sufficient mixing the mixture is led to the natural gas burned furnace where the reaction takes place in the horizontal tubes of the furnace at the pressure of 5.5 atm and temperature range of 120-2600C. Here first the chlorine 96% reacts with pentane and form amyl chloride which inturns react with the 4% unreacted chlorine and result in the formation of di-chloropentane as a by-product. HCl is produced in both of these reactions. The reacted gaseous mixture is passed through the cooler where cooling of this gaseous mixture from 260to 1650C. Then this cold mixture is sent to a partial condenser where condensation of unreacted amyl chloride, and di-chloropentane occurs while pentane and HCl remained uncondensed at 700C and 5.2 atm.

Fractionation

This semi-condensed mixture is fed to a flash column operating at atmospheric pressure. Flashing of HCl and Pentane occurs here and 98% of HCl and 70% of Pentane is flashed off here while remaining portion of them is sent along with the condensed amyl chloride and di-chloropentane from bottom of flash column to the fractionating column at 500C.

In second column the reboiler which is a steam heated one, causes the remaining  all HCl and  93% of Pentane to go to the top of the column from where they are with out being condensed is sent back to the middle of the first column at 360C. The column is operating at atmospheric pressure. The bottom of second column at 770Cis pumped to the third column which is a plate column where reboiler causes to go the all pentane and 99.7% of amyl chloride to top at 78 0Cwhile the di-chloropentane and 0.3% of amyl chloride (assumed to be traces) is taken from the bottom at 1350C and pumped to the storage tank.

Vaporous pentane and amyl chloride are passed through the condenser at atmospheric pressure and here amyl chloride is condensed and this semi condensed mixture is sent at 70 0C is sent to fourth column. Here again whole pentane is sent to the top at 37 0C which is after being condensed in the condenser is sent to the first column from where it is sent to the top. The condenser is used to avoid any excessive temperature disturbance which can occur in the first column. From the bottom of the fourth column at 95 0C the amyl chloride is sent to the make up tank.

Hydrolysis

From the make up tank the amyl chloride is pumped through a lobe pump at 14.1 atm and then sent to the digester where in the presence of sodium oleate as a catalyst, it reacts with 50% aq. caustic solution. The caustic is entered in the digester at high temperature to keep the temperature at required level which is 1200C. Here hydrolysis (reaction) takes place and amyl chloride conversion is 70% and yields amyl alcohol and sodium chloride as well.

The reaction mixture, containing all amyl alcohol, water, sodium chloride, caustic, unreacted amyl chloride is sent to the condenser which is erected after the digester.

Here condensation occurs at 120 0C and 13.5 atm. The condensed material is sent to the decanter and hence decantation is carried out here on the basis of density and water, caustic, sodium chloride being less dense is collected at one side of the baffle installed in the decanter while amyl alcohol, amyl chloride is collected at the other side.

Distillation

From the decanter the mixture of amyl alcohol and amyl chloride is sent to the final distillation column through a pressure reducing valve to reduce the pressure from 13.1 atm to 1.2atm. The mixture is fed to the distillation column operating at 1 atm at 120 0C. It is a sieve tray column having 17 plates giving 99.9% amyl alcohol at the bottom at 147 0C which is sent to the storage tank after being cooled through heat exchanger.

Advertisements

2 thoughts on “Methods Of Preparation

  1. Muhammad Dody

    This post is really usefull. Would you pls put references for this post? And pls post the flow diagram for this chlorination process

    Reply

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s