operation oaxaca: blue pill or red pill?
economics & effectiveness of desorption methods (016)
this is carlos.
we just finished a deal with a lab.
processing has begun.
entry to the lab will be this week, if God permits.
and now, we mentioned that the status quo of metal ion filtration cannot recycle all materials, chemical-intense, non-environmentally friendly, and not an abundant organic material (economical).
our way to the new way of water filtration is on adsorption.
the only roadblocks left for an adsorption-based material are:
- low selectivity
- production of waste products
- scaling it up into industry-standard
number two is resolved when we use mother nature;
the waste products are biodegradable (the mango peels).
now i’ll tackle the “low selectivity” problem.
this time, we completed the content relating to our desorption choices;
we chose these compounds because:
- they are already used in your house as cooking & cleaning appliances
- they’re also used to remove magnesium/calcium metal ion stains in your home.
and those are white vinegar and lemon juice.
specifically, acetic acid and citric acid.
and from the articles, they both do the task of desorbing ions from our mango peel.
but which one is more economical for use?
and which one is more effective at the job?
sit down and read.
CJ
red pill, plz.
i will not consider artificial forms of acetic acid and citric acid.
only vinegar and lemon juice.
ok.
vinegar is acetic acid & water → CH3COOH + H2O
lemon juice is citric acid & water → C6H8O7 + H2O
acetic acid looks like this:
and citric acid looks like this:
acetic acid has one carboxyl group (COOH).
citric acid has three carboxyl groups and one hydroxyl group (OH).
these functional groups can adsorb heavy metal ions due to the fact the COOH & OH groups are anionic.
why are they anionic?
electronegativity.
(p.s. — yes, there’s other factors like pH and hydrogen bonding, but not right now).
the carboxyl group (COOH), is attached with a double bond between carbon and an oxygen atom.
carbon’s electronegativity is 2.55
oxygen’s is 3.44
subtract the smaller number from the bigger one: “3.44 — 2.55”…
and we get 0.94.
this is a chart that determines what bond we have between the two elements.
since the carboxyl bond with “C=O” has a difference of 0.94, this bond is a polar covalent bond.
covalent bond → “equal distribution/sharing” of electrons between two or more elements.
but a polar covalent bond means that the electron density (or where the electron might be between two elements) is no longer equally shared. it will tend to be ‘located’ closer to the more electronegative element.
electron density → a ‘migration’ of negative charge (the electron) to a specific location of the molecule.
since oxygen is 3.44, and carbon is 2.55… the negative charge will be found more on oxygen than carbon.
and for the -OH group in the carboxyl group? (COOH)
oxygen is 3.44
hydrogen is 2.1
so if we subtract the big one from the small one, we get 3.44 — 2.1 = 1.34
also polar. but this difference is stronger, so the shifting of negative charge will be stronger, and want to stay closer to oxygen…
because oxygen has higher electronegativity.
i’d forgive you if you thought that citric acid will do better than acetic acid at desorbing ions because citric has more carboxyl groups than acetic.
because u’re half right.
having more carboxyl groups gives you more places for metal ions to adsorb onto.
that’s a plus.
but we also need to consider the kPa.
remember:
the pH measures the concentration of hydrogen ions in a solution.
pKa measures the strength of an acid in a solution.
the lower the pKa number is, the measured acid can be very strong and the higher the chance to “give away” its protons.
the pKa of citric acid is 3.13.
the pKa of acetic acid is 4.76.
this means citric acid is the stronger adsorber than acetic acid.
great!
and the pH also aligns with us!
an aqueous solution of 1 mM of citric acid is pH 3.
an aqueous solution of acetic acid (aka vinegar) has pH 3.39.
citric acid wins again.
chemistry-wise, citric acid dominates.
but what about economically?
pay up.
as i mentioned earlier, i don’t care about additives or artificial forms of citric acid, acetic acid, vinegar, or lemon juice.
i just want the real thing.
and this is what i DO know.
if we want to go the long way for citric acid:
buy the citric acid powder.
found it on amazon for $12.89 LOL to use 100 grams of it.
and an acetic acid bottle with 1mM for 1 liter for $25.99
as for vinegar and lemon juice…
i found these glass bottles of distilled white vinegar for $16.99 ($0.53 per fluid ounce)
and i found this 100% lemon juice for $8.99 ($0.28 per fluid ounce)
as for mexico and usa…
mexico had 3,101,000 tons of lemons produced at the end of 2022.
usa had 1,112,000 tons of lemons produced by the end of 2023.
in the past year, the approximate wholesale price range for vinegar in usa was $ 1.37-$ 2.74 /kg ($ 0.62 -$ 1.24 /lb.)
and last year, the approximate wholesale price range for lemons in usa was $0.98-$1.94 /kg ($0.44-$0.88 /lb.)
overall, the economics favor lemon.
lemon juice is $0.28 per fluid ounce.
vinegar is $0.53 per fluid ounce.
the economics are doable for either choice.
it will all come down to chemical properties.
i’ll select citric acid/lemon juice.
although i won’t discard acetic acid.
i’ll test them both, and see which one works.
for next time, we will tackle the big question:
how would we scale up the filter AND deliver the technology to thousands of people in usa & mexico?
© 2024–2100 by Carlos Manuel Jarquín Sánchez. All Rights Reserved.
