Autocatalytic reaction and S-shaped curve

[gfd43tg]

Hello, I was working on a textbook problem that was referencing a paper regarding the mechanism for the production of Terephthalic acid (TPA). It piqued my interest so I found the original paper and did some reading. At least in 1987 when this paper was published, the intermediate reactions were not well known (I haven't followed up to see if any progress has been made on this specific reaction mechanism). The initial goal of the problem was to plot the concentration of the species vs. time in a batch reactor for this reaction

$A \xrightarrow {k_{1}} R \xrightarrow {k_{2}} S$ (catalyst)
$R + S \xrightarrow {k_{3}} 2S$ (autocatalytic)

where A = K-benzoate, R = lumped intermediates (K-phthalatis, K-isophthalates.
and K-benzenecarboxylates). and S = K-terephthalate.

The authors conjectured that there must be an autocatalytic side reaction to explain their resulting concentration-time curve.

During the series of experimental runs, we found that
in all cases the rate of formation of terephthalate product
follows an S-shaped curve, indicating the probable existence
of a parallel autocatalytic reaction involving the
conversion of intermediates (catalyzed by the product
potassium terephthalate).

(Revankar, Doraiswamy)

I plotted the concentrations over time and here are my Matlab results

I assume the "S-shape" is reference to species S, which has low concentration change at first, then rapidly increasing, then levels off. However, I was wondering why having an autocatalytic reaction would produce this curve which would lead the authors to make this conjecture.
[/PLAIN]
pubs.acs.org/doi/pdf/10.1021/ie00068a034

One off-topic sidenote: In this paper, I noticed they actually have their figure 1 and figure 2 reversed. I noticed some grammatical errors as well. I just started reading scientific papers, and I can find small errors in most of them. Are these not proof-read extensively before submitting to journals?? It seems like for only a 5 page paper, there should be virtually no blunders.

 

[Bystander]

(snip)
I assume the "S-shape" is reference to species S, which has low concentration change at first, then rapidly increasing, then levels off. However, I was wondering why having an autocatalytic reaction would produce this curve which would lead the authors to make this conjecture.

[PLAIN]http://pubs.acs.org/doi/pdf/10.1021/ie00068a034[/PLAIN]

Or, concentration of "S" with respect to time, yes. "Why?" Remember, this is a batch reactor. Reaction rates are proportional to some function of concentrations that are time dependent; autocatalysis means that a particular species catalyzes its own (or some of its own) reactions with itself or other species, and as it is consumed, not only do reactant, but also catalyst species fall. Rate of formation of final product is dependent upon starting species conc., some unknown intermediate species concentrations (initially zero), and initially slow, speeds up, and slows at the end since reactant concentrations drop.

(One off-topic sidenote: In this paper, I noticed they actually have their figure 1 and figure 2 reversed. I noticed some grammatical errors as well. I just started reading scientific papers, and I can find small errors in most of them. Are these not proof-read extensively before submitting to journals?? It seems like for only a 5 page paper, there should be virtually no blunders.

"Extensively?" Too extensively --- editors ask for changes, reviewers ask for changes, some labs/bureaus/centers have internal review boards that ask for changes --- at the end of the process, people are so sick of the sight of a paper that conflicts in "stets and deles" is just about forgotten --- omitted words, spelling errors, disagreements between subject and predicate, rearrangements from passive to active voice, and which version everyone's agreed upon --- it's a little like getting legislation through the house and senate.

 

[Ygggdrasil]

One off-topic sidenote: In this paper, I noticed they actually have their figure 1 and figure 2 reversed. I noticed some grammatical errors as well. I just started reading scientific papers, and I can find small errors in most of them. Are these not proof-read extensively before submitting to journals?? It seems like for only a 5 page paper, there should be virtually no blunders.

Completely offtopic sidenote: Here's an example of a paper a few papers that were clearly not proofread before submission:
https://twitter.com/e_gleich/status/531999058370777089
http://www.biomedcentral.com/1752-0509/5/S3/S4/comments

 

[DrDu]

About grammatical errors in papers: You also have to take in mind that many, if not most, papers are written by non-native speakers.

 

[gfd43tg]

You're right, based on the spoken English I have heard from many professors, I should be pleased that the writing in scientific papers is as good as it is. There is some major disconnect between many people's spoken and written abilities.

 

[Borek]

Completely offtopic sidenote: Here's an example of a paper a few papers that were clearly not proofread before submission:
https://twitter.com/e_gleich/status/531999058370777089
http://www.biomedcentral.com/1752-0509/5/S3/S4/comments

Actually this is a perfect example of a lack of a proofreading :P

 

[Bystander]

Maybe the proofreading needs to be split off for a separate thread --- if anyone has further comments on the reaction rate problem they'll be buried so far in the "proof" discussion no one will ever see them.