8 replies to this topic

[mak is back]

I am working on Acrylonitrile production......via PCUK technology......which uses fixed bed reactor.

In Propylene ammoxidation process, ammonia, propylene, air and steam are allowed to enter in reactor.

I have some queries regarding the process.....as follows...

 

1) what is the function of steam in feed? and is it taking part in to reaction or not? Is it to be taken in account for material balance calucation?

2)Here, it is specified for fixed bed reactor,, so i want to know that, is it multitube reactor?

3) i have done material balance over reactor, but i m not satisfied with that....so i want  help to carry out the material balance......as per my material balance ...Material in is not equal to material out......Data are as follows.....

please help me out for doing material balance over reactor.....

Production rate : 11356.21 kg/hr

Feed stock: Propylene (90% pure, 10% paraffins which do not take part in reaction)

                   Ammonia: 100% pure

 molar % of reactor inlet :

Propylene : 7%

Ammonia : 8%

steam :  20%

Air :  65%

 

Reactor outlet stream:

Based upon a pure propylene feed, the carbon distribution by weight in the product from the reactor is

Acrylonitrile 58%

Acetonitrile 2%

Carbon dioxide 16%

Hydrogen cyanide 6%

Acrolein 2%

Unreacted propylene 15%

Other byproducts 1%

 

4) can we take acetic acid as by product?

5) what is carbon distribution ?

[mak is back]

As per process discription.

acrolein cynohydrin is sent back to the reactor (which is seperated from cynohydrin seperator), so quantity of acrolein cynohydrin also to be taken in account for material balance calculation...

so can we consider as recycle?

[mak is back]

Process Flow;:

Propylene, ammonia, steam, and air are fed to a vapor-phase catalytic reactor (item A). The feed stream composition (molar percent) is propylene 7; ammonia 8; steam 20; air 65. A fixed-bed reactor is employed using a molybdenum-based catalyst at a temperature of 4508C, a pressure of 3 bar absolute, and a residence time of 4 seconds. Based upon a pure propylene feed, the carbon distribution by weight in the product from the reactor is

Acrylonitrile 58%

Acetonitrile 2%

Carbon dioxide 16%

Hydrogen cyanide 6%

Acrolein 2%

Unreacted propylene 15%

Other byproducts 1%

The reactor exit gas is air-cooled to 2008C and then passes to a quench scrubber ( through which an aqueous solution containing ammonium sulfate 30 wt percent and

sulfuric acid 1 wt percent is circulated. The exit gas temperature is thereby reduced to 908C.

From the quench scrubber ( the gas passes to an absorption column © in which the acrylonitrile is absorbed in water to produce a 3 wt percent solution. The carbon dioxide, unreacted propylene, oxygen, nitrogen, and unreacted hydrocarbons are not absorbed and are vented to atmosphere from the top of column ©. The solution from the absorber © passes to a stripping column (D) where acrylonitrile and lower boiling impurities are separated from water. Most of the aqueous bottom product from the stripping column (D), which is essentially free of organics, is returned to the absorber ©, the excess being bled off. The overhead product is condensed, and the aqueous lower layer returned to the stripping column (D) as reflux. The upper layer which contains, in addition to acrylonitrile, hydrogen cyanide, acrolein, acetonitrile, and small quantities of other impurities, passes to a second reactor (E) where, at a suitable pH, all the acrolein is converted to its cyanohydrin. (Cyanohydrins are sometimes known as cyanhydrins.) The product from the reactor (E) is fed to a cyanohydrin separation column (F), operating at reduced temperature and pressure, in which acrolein yanohydrin is separated as the bottom product and returned to the ammoxidation reactor (A) where it is quantitatively converted to acrylonitrile and hydrogen cyanide.

The top product from column (F) is fed to a stripping column (G) from which hydrogen cyanide is removed overhead. The bottom product from column (G) passes to the hydroextractive distillation column (H). The water feed rate to column (H) is five times that of the bottom product flowfrom column (G). It may be assumed that the acetonitrile and other byproducts are discharged as bottom product from column (H) and discarded. The overhead product from column (H), consisting of the acrylonitrile water azeotrope, is condensed and passed to a separator. The lower aqueous layer is returned to column (H). The upper layer from the separator is rectified in a column (I) to give 99.95 wt percent pure acrylonitrile.

[mak is back]

What is role of steam in this process?
Is it taking part in to reaction..?
How to start material balance for reactor?
I am confused because both inlet and outlet streams composition is given,and on which basis I have to start...?
Can any one help me out from that?

[Art Montemayor]

Some experienced suggestions that can help you:

• Furnish all your data and process information - including all process reactions balanced equations - in electronic spreadsheet format with the data all tabulated and accessible for use in formulas and calculations.
• Draw at least a process flow diagram for your process and show a related table for the required process flow mass and heat balance.  Show all the pertinent and important streams that you have to identify or calculate.  Furnish all the equations or simulation printouts in spreadsheet tables.
• DO NOT RELY ON TELLING A POETIC, WRITTEN STORY to engineers.   Real engineers work with hard, real, accurate basic data.  That data is best and accurately described in an engineering format:  Tables, graphs, drawings, sketches, etc.   If you are not an English native speaker, your written and verbal descriptions often confuse and give an erroneous description.  Engineering graphs, tables, and drawings are an international language that we all understand - regardless of what country we are from or in.
• SMART engineers always furnish their detailed calculations and drawings for other engineers or peers to check and review before issuing their product or their responses to a problem.  This is always done in all world engineering houses or organizations and the faster you get used to this requirement, the better engineer you will be.

[mak is back]

dear sir Art Montemayor

•  

I already draw a flow diagram based on process discription, and on that basis, I asked about the above queries.

And here I am not telling any poetic, written story.

 

And is your reply is my problem solution?

 

I have all reaction.

And if my queries are confusing to you then why you replied it. 

 

I asked about the steps and basis on which the calculation to be started. I am not clear about the role of steam in the reaction.

so i need help to get it clear on this process.....

if anybody can clear my doubts in the above topic....

 

thanks

[Art Montemayor]

It is good that you have at least generated a process flow diagram.  But what good does it do in your sole possession, without sharing it with the expert persons that can answer your queries?  Are they supposed to guess what you have drawn?

 

What you respond with are excuses for not furnishing our members with the vital data that describes your problem and the extent of what work you have done.  This could be understandable if you are dealing with secretive, arcane process information.  But what you describe is an ordinary academic problem.

 

You are a student, I presume, so you are subject to ignoring how the world of engineering works.  However, it is best you learn the basic procedures now, before venturing out in the hard, competitive world.  Other engineers who are willing to help you (for free!) can only do so when you furnish them with ALL the facts, data, and explanations of your dilemma.

 

You are asking for free help - but only under YOUR terms, not the Forum's.  That is not logical.

 

I will leave it to our members to decide whether they work to contribute help to someone who is not willing to help them.

[navdeeptrident]

sir I have the same problem Will you please help me Iam designing a project and Iam a btech final year student Will you please help me

[navdeeptrident]

I may give you the reactions and other data Will you please help me