What caused the unexpected curve in my cellulose to sugar conversion process?

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Discussion Overview

The discussion revolves around the unexpected results observed in a cellulose to sugar conversion process using strong acid hydrolysis. Participants explore the relationship between acid concentration and sugar yield, examining the implications of varying conditions and methodologies in the experimental setup.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant describes their process of hydrolyzing cellulose with strong acid, expecting a yield curve that levels off, but instead observes a curve resembling that of a homogenous catalyst, suggesting potential reactions between the acid and sugars.
  • Another participant notes that the Benedict's test is pH dependent, implying that the pH of the solution could affect the results.
  • A participant mentions neutralizing the solution with sodium hydroxide prior to the Benedict's test, which may influence the outcome.
  • Questions are raised about the consistency of the experimental protocol, including the weights and volumes of reagents used across different runs.
  • One participant indicates that the initial mass of cellulose varied but was accounted for in calculations, along with the volume changes due to neutralization.
  • Another participant inquires about the range of acid concentrations tested, which spanned from 0.1 mol to 2 mol, noting that only the 2 mol concentration resulted in a dip in yield.
  • A participant reflects on the complexities of sugar chemistry, discussing how different acid concentrations affect hydrolysis and the challenges in understanding concentration dependence in industrial processes.
  • Suggestions are made to explore literature on paper pulp and related industries for insights into the observed phenomena.

Areas of Agreement / Disagreement

Participants express various hypotheses regarding the unexpected yield curve and the factors influencing it, but there is no consensus on the underlying cause or resolution of the issue. Multiple competing views and uncertainties remain present throughout the discussion.

Contextual Notes

Limitations include potential variations in experimental conditions, the influence of pH on chemical reactions, and the lack of detailed protocols that may affect reproducibility and interpretation of results.

Hootenanny
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My coursework was to basically develop a process to turn cellulose into sugar. I decided to use a strong acid to hydrolyse the acetal linkages in cellulose to form D-glucose. I wanted to find the optimum conditions for the process starting with concentration. So I plotted a graph of concentration (x-axis) against percentage yield(y-axis). As I was varying concentration I expected a curve that would level off at some point. However, I found that the curve resembled that of a homogenous catalyst, with an increasing yield to a maxium point then a decrease. I can only think that the strong acid was reacting in someway with the sugars. I used Benedict's solution to test for the sugars. Any ideas would be helpful.
 
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Far as using Benedict's, the reaction is pH dependent. Give you any ideas?
 
I neutralised the solution using sodium hydroxide before I carried out the benedict's reaction
 
What have you got for a "run" protocol? _ wt. cellulose in _ vol. water plus acid made up to what? And on, and on. The question being, "Were you running the same volumes, weights of reagents and Benedict's every time?
 
The initial mass of cellulose differed, but is accounted for in calculation as is the difference in volume due to neutalisation.
 
What range of acid concentrations did you cover?
 
from 0.1 mol to 2 mol, it was only on the 2 mol conc that it dipped, but five 'runs' were in agreement within acceptable limits.
 
I'm beginning to remember some of the things I never liked about sugar chemistry. Acid plus cellulose at "low" concentrations results in ~95% hydrolysis; at "medium" concentrations (say in acid pulp mills), it's great for hydrolyzing ligno-cellulose linkage without breaking down excessive amounts of cellulose; at high concentrations, acid solutions are very good solvents for cellulose. The only paper chemist I ever talked with (actually, ex-paper chemist) couldn't get near the actual processes in the plant --- three or four generations of hereditary jobs, actual family legacies for eldest sons, plus deep south suspicion of a "Damyankee," plus a "union shop" fighting any and all threats to progress, automation, and other "newfangled" ideas kinda left the particulars of the process (T, m, t) hazy. Same game in the explosives industry (acid solvent), rayon --- you get the picture? I've never run into a decent explanation for this really rather weird concentration dependence. Never had occasion to look for one, and never took courses from faculty who were veterans of years work on sugars or cellulose --- there weren't any clear through my post-doc.

Do a little browsing on paper pulp, rayon, nitrocellulose mfr., and you might trip over something a little more specific.

2 M, or 2 m, has to be crowding the paper process range.
 
Thanks for your help.