Black Citric Acid Polymer (PN) Capacity as Raw Material for Cationic Exchanger Realization

The molecular structure of black citric acid polymer (PN) and their hydracids acids functions allowed without doubt their capacities to be potential raw materials for realizing a cationic exchanger. So, the objective of this publication was to study this capacity after activation with sodium hydroxide (NaOH) solution. Two black citric acid polymers PN-2-crispy and PN-3-soft were synthesized whose PN equivalent contents and acidity were evaluated by NaOH-0.05N measuring-out and by Boehm titration. After NaOH-activation which efficacy depends on the PN-size after sieving, two activated-PN were obtained such as PN-2-Na and PN-3-Na whose Na + contents were determined by HCl-0,049N titration. Then, exchange cationic tests with CaCO3 solution were carried out on these activated-PN and the Ca 2+ contents of treated solution and Ca 2+ on used PN-2-Na, PN-3-Na was followed by EDTA-complexometric titration. Also, Na + and Ca 2+ on used activated-PN were measuring-out by HCl titration. Results showed clearly that PN once activated with NaOH could carried out cationic exchange and the PN-3-Na was largely active all the time than the PN-2-Na. A global mechanism evolution of these PN-cationic exchange was proposed and also its global kinetic study was done by following-up the [Ca 2+ ] concentration of treated solution. Results showed that these PN-cationic exchange was second order related with [Ca 2+ ] concentration of treated solution and the speed constant of PN-2-Na was inferior to the speed constant of PN-3-Na confirming its Ca 2+ retention capacity.


Introduction
Black citric acid polymer (PN) was synthesized and their water capacity adsorption were noticed. Then, they were characterized by Boehm titration and NaOH-0.05N titration and finally activated with NaOH to obtain activated black citric acid PN-Na which were characterized by HCl-0.049N to quantify Na's PN. To test the PN-Na's capacities to be a potential cationic exchange raw materials, cationic exchanger tests with a calcium carbonate solution were done and followed-up by complexometric-EDTA titration. Ca 2+ ions were retained and measuring-out on used PN-Na, also, evolutions of Ca 2+ concentration on salvage solution allowed to propose a global PN-cationic exchange evolution and its global kinetic.

Generalities
Black citric acid polymer (PN) (Figure 1) is the last polymer obtained by citric acid molecules polymerization catalyzed by acid sites like Brönsted acids H + from sulfuric acid or Lewis acids from iron. The first step of this polymerization was citric acid molecules dehydration to form the white monomers which combined together and dehydrated to form the yellow monomers. Then, yellow monomers reacted together with carbon dioxide emission to form red brick polymer, brown polymer and lastly black polymer [1][2][3].

Citric acid black polymer synthesis
Citric acid black polymer synthesis was done according to the procedure cited in the publication concerning its capacity as fuel oil additives [4][5]. But, exceptionally two black polymers were synthesized: for the first, the synthesis was stopped when visually large quantity of black polymer was formed, so we obtained a soft black polymer that we named PN-3 and for the second we didn't stopped the reaction if only we obtained a large quantity of crisp black polymer that we named PN-2.

Citric Acid Black Polymers -Products of Synthesis PN-2 and PN-3 Characterizations
To differentiate PN-2 and PN-3, Boehm titration and Na0H-0.05N measuring out were done to the synthesis.

Citric Acid Black Polymers Equivalent Content Determination of Synthesis Product by NaOH-0.05N Measuring Out
To determine the PN's citric acid black polymers equivalent content, we attacked each PN's oxygen bridge of hydracids-acids functions by NaOH-0,05N. Thus, we obtained Na-carboxylic salts and regenerations of PN's carboxylic acids ( Figure 2). For this, take respectively 0.0215[g] and 0.0132[g] of PN-2 and PN-3. Dilute each sample in 15[ml] of distillated water. Then, add two or three drops of helianthine indicator. The equivalent point; which indicated most approximately the transformation of all oxygen bridge; were reached when the solution's color just begin to change with orange-yellow color apparition. As a result, citric acid black polymers equivalent moles content of sample was NaOH's moles divided by 14. Results of citric acid black polymers equivalent content of synthesis titration were showed in the following table 1.

Carboxylic, Phenolic and Lactonic Equivalent
Content of Citric Acid Black Polymer Determination by Boehm Titration PN's surface oxygen functional groups quantification (In the majority carboxyl function) based on the Boehm's titration method [6] was carried out. Thus, respectively, 0.0306 [g] and 0.0305 [g] of PN-2 and PN-3 were shaken in 6.04[ml] of NaOH 0.05N [7][8][9] during one hour. We obtained a brown mixture solution. Then, the excess of NaOH was titrated (using helianthine indicator) by HCl 0,1N. The equivalent point was reached when in the mixed solution appears red vivid color. Results of Boehm titration were showed in the following table 2.

Citric Acid Black Polymer -Product of Synthesis Water Molecules Retention Capacity
PN's surface chemistry, characterized by Boehm titration and NaOH-0.05N as shown in the table 2, significantly influences the wettability, adsorptive, electrical, electrochemical, catalytic, acide-base, redox, hydrophilic-hydrophobic, and other properties [7]. It was shown that, in particular, oxygen which constitutes 42.77 (%w/w) of citric acid black polymer (PN), influenced its auto-inflammation and improve the auto-inflammation of PN-Fueloil mixes [4][5]. In this case, at ambient air also it was noticed that citric acid black polymer product of synthesis PN-2 and PN-3 adsorbed significantly water. It was followed-up by their weights evolutions.

Water Molecules Weight Evolution Within the Time
As shown in the following figure 3, at ambient air and in general, PN's water adsorption increase proportionately in time. This result is interesting because it confirmed the capacity of PNs synthesized to be easily activated, then to be a potential cationic resin exchanger raw materials.

Water Molecules Evolution Within the Citric Acid Black Polymer -Product of Synthesis Characteristics
To confirm each PN's water retention capacity and to show the acidity total contributions on this water retention, the following table 3 and figure 4 compared the PN-2 and PN-3 water molecules retention according to each acidity content measuring out by NaOH-0.05.  The presence of important quantity of equivalent PN in PN-3 per sample weight, 1.39 times more than the PN-2 (Table 1), explained the high quantities of acidity total on PN-3 and its high capacity to retain water molecules than PN-2 (Table 3). Now, it's interesting to view their capacity to be a raw material for polymer cationic exchanger after sieving and activation by NaOH. An ion-exchange resin or ion-exchange polymer is an insoluble matrix or support structure that acts as a medium for ion exchange [10]. Their molecular structure include acids or basics radicals apt to permutate with other ions in the same sign which are in solution with them. This permutation named "ion exchange" presume modification of the solution ionic composition to be treated without modification of the total charge present in solution before exchange [11][12]. According to these ionic exchanger generalities, black citric acid polymer-PN and other citric acid polymers (like brown citric acid polymers) which were water insoluble materials but may be carrying in small quantity by water molecules by hydrogen-bond link could be a potential raw material for the water softening which consist to the reduction/removal of calcium and magnesium ions, principal cause of hardness in water. That is the subject of this manuscript, studying the black citric acid polymer -PN synthesized capacity to be a potential raw material for water softening. Thus, it's necessary to sieve the PN-synthesized for facilitating the NaOH-activation after which PN-Na material was able to play the cationic-exchange polymer according to the following figure 5.

Sieving System of Citric Acid Black Polymers -Products of Synthesis -Results and Characteristics
The sifting is the action to separate and retain the coarse parts of flour, ashes or chemical powder product through a sieve [13]. Professor Terence Allen characterizes sieving as "The aperture of a sieve may be regarded as a series of gauges which reject or pass particles as they are presented to the aperture" [14]. Many properties can be influenced by the particle of materials size such as: Their strength Their taste Their dissolution properties Their surface activity Also, it was said in the literature that to limit the pressure losses of the water filtration or purification columns, the balls ion exchanger diameters must be ranging between 0.3[mm] and 1.2[mm] [2-3-15].
Seeing that, the black polymer product of synthesis PN-3 was soft, their sieving was practically impossible but we have agglomerated these materials to obtain PN-3ball whose diameters are ranging between T i : the lower sieve 0.8[mm] to 2[mm], T S : the superior sieve. However, the black polymer product of synthesis PN-2 was crisp and after a slight crushing mortier porseleinen we sieved using a vibrating sieve machine with simultaneously two sieves; T S : the superior sieve and T i : the lower sieve; whose meshes diameters was respectively 0.8 [mm] and 0.25[mm] [2][3]. We obtained the refusals indicating the part of PN retained by the lower sieves. The refusal sizes that we obtained during this sieving procedure was very important because it's one of the responsible of the well diffusion and well reactions of NaOH during the PN-activation step ( Figure 5).
Results and characteristics of PN-2 and PN-3 is shown in the following table 4.

Citric Acid Black Polymer -Product of Synthesis Activations by NaOH Procedure
Weigh the crisp and soft black citric acid polymer -product of synthesis respectively PN-2 and PN-3 to be activated. Then, calculate the moles quantity of PN equivalent with taking account of its content for PN-2 and PN-3 measuring out by NaOH-0.05 ( §2.3.1. Table 1). And then, prepare a NaOH solution such as the moles quantities of NaOH (99%) was 28 times more than the sample PN equivalent moles quantities and the distillated water volume was 1.5 times more than the NaOH-weight. Agitate the NaOH-solution until all NaOH are soluble in the distillated water. Now, take a syringe-10[ml] and put inside firstly a thin layer of absorbent cotton and then the PN black citric acid polymer to be activated. Press carefully the set with the syringe press button. Finally, pour the NaOH solution into the syringe, it was noticed that this flowed uniformly through the PN to be activated. When the NaOH solution reached the cotton, it's necessary to block its syringe orifice leaving by putting the syringe press button, then let the activation process during one hour.
NaOH activation characterizations are showed in the following table 5.

Citric Acid Black Polymers -Products of Synthesis Cationic Exchanger Na Content Determination by HCl-0.049N
After one hour activation, samples were taken on top and on low of the citric acid black polymers-product of synthesis cationic exchanger (PN-Na) to determine their Na content by HCl-0.049N measuring out.
Thus, respectively, samples PN-2-Na and PN-3-Na were taken and diluted in 15[ml] of distillated water. We obtained a brown mixture solution. Add helianthine indicator, the orange yellow color appeared in solution. Then, NaOH content was titrated by HCl 0,049N. The equivalent point was reached when in the mixed solution appears red color. Results of this titration were showed in the following table 6. It was confirmed that the PN citric acid black polymer product of synthesis activation lead up to the PN-Na a raw material able to play the cationicexchange polymer rule. Likewise, it was confirmed that the PN-size obtained after the sieving procedure influenced the activation procedure. The PN-2 had 3 times specific diameter lesser and 29 times specific surface more than the PN-3 (Table 4). Consequently, because of the better contact with PN-2, first, the activation of PN-2 was the best such as 70.09[%] of the initial Na moles was retained by PN-2 versus only 10.49[%] for the PN-3; secondly, the total Na moles retained in PN-2 was 6 times more than those of PN-3. Then, comparing the specific diameter, specific surface (  Table 6] and 6.67 [=19.6(2)/2.94(3)- Table 6], the activation reaction during one hour between NaOH and PN citric acid black polymer product of synthesis ( Figure 5 Noticed that nNa/sample weight PN-Na proportionality between on low and on top samples was normal for the PN-2 (=0.99 equals to one) but for the PN-3, this value was 1.93; that is to say most of Na + (=1.93 times) located on low. Seeing that the NaOH-solution density was more than one and the contact specific surface was little for the PN-3, on low a part of NaOH was probably in hydrogen bond link with the PN-Na activated (particularly for the PN-3-Na) and lead up to think that a part of NaOH might be in hydrogen bond link with the on low PN-3-Na activated confirming its low activation rate (only 10.49[%]). In the following figure 6 and figure 7 are shown the activated citric acid black polymers -products of synthesis PN-2-Na and PN-3-Na according to the HCl-0.049N measuring out ( §4.3. - Table 6).

Cationic Exchange Test Principle
The cationic exchange test consist of passing a calcium carbonate (CaCO 3 ) solution directly through the syringe which contained the activated PN-Na. Salvage the solutions which passed through the PN-Na in beakers continually with paying attention to record the treated-samples solution volume and the interval time (the duration) related to each treated-samples solution volume. Thus, the flow test rate, the time on stream, the weight hour space velocity (whsv) was deduced. Then, each treated-samples solution Ca 2+ contents was measured out.
The characteristics of the calcium carbonate solution to be treated is shown in the following table 7. Noticed that for the PN-3-Na tests, the treated-samples solution color was enough brown than the PN-2-Na because of a lot of NaOH molecules located underside the PN-3-Na which can sharp the hydrogen bond links between black and brown citric acid polymers. These last were responsible of the brown solution color and the NaOH molecules can reacted not only with their non-activated sites (-COOH) but also with the CaCO 3 to produce another -COONa sites and may be Na 2 CO 3 and Ca(OH) 2 .

Ca 2+ Measuring out of Treated Solution and Used Citric Acid Black Polymers -Products of Synthesis Cationic Exchanger
Once salvaged, each treated-samples solution was titrated with EDTA. Also, the used PN-Na was titrated with EDTA.

Exchange Test Results in Terms of Retained Ca 2+ Evolution (Na effect-Ca(OH) 2 )
Treated-samples characteristics and operational conditions are show in the following table 8. Exchange tests results for PN-2-Na and PN-3-Na were shown in the following table 9 according to the treated-samples characteristics and operational conditions. Na sites importance were confirmed during the exchange test results in table 9 such as more they were more is the Ca 2+ retained rate. But, their nature play an important role. Logically, more is the contact time and the Na sites of PN-Na more must be the Ca 2+ retained quantities (moles) versus time. However, the following figures (Figure 8 -Figure 9 - Figure 10 -Figure 11) showed that the PN-3-Na which has less Na sites than PN-2-Na (Table 6 -Table 9) was all the time more active than the PN-3-Na, even if we plotted the Ca 2+ retained per Na per contact time evolution versus time (Figure 10 -Figure 11).    These results explained that NaOH sites which are more numerous in PN-3-Na than PN-2-Na (Table 6 - §4.3) and sharped the hydrogen bond links between black and brown citric acid polymers. These last were responsible of the brown solution color and the NaOH molecules can moves through the polymers and reacted not only with their non-activated sites (-COOH) but also with the CaCO 3 to produce another -COONa sites and may be Na 2 CO 3 and Ca(OH) 2 . Seeing that the Ca(OH) 2 water solubility (8.24E-1[g.l -1 ]) was more important than its CaCO 3 , they move easily and became more retained by exchange mechanism with PN-Na sites. But the Na 2 CO 3 were directly transported out with water because of their high solubility (2.33E+2[g.l -1 ]). These sites [which are the total quantities of (-COOH) sites equals to fourteen twice the PN-equivalent moles] activities were confirmed on the figure 11; noticed that the sites increase the initial activity of PN-2-Na and PN-3-Na compared with initial activities considering only Na sites. As it happens, Na + and Ca 2+ measuring out by HCl-0.033N and HCl-0.0027N for respectively used PN-2-Na and PN-3-Na were carrying-out. So, weight the used sample PN-Na to be titrated in a beaker, add 15[ml] of distillated water and three drops of Bromophenol Blue BPB indicator, the solution turn to dark red-brown. Begin the titration with HCl and equivalent point is reached when a light red color appeared in solution. The results were shown in the following table 10. Ca 2+ quantities differences between EDTA-titration and HCl titration were due to the presence of other organic molecules with functions which can reacted with HCl during the HCl-titration. For the crisp PN-2-Na, the functions can be alcohol and or ester with alkene from the citric acid yellow monomers [1-2-3-4-5], and for the soft PN-3-Na, the function majority is alkene from the citric acid yellow monomers. That why the difference PN/∆ between PN-2-Na and PN-3-Na. However, it's important to say that these functions are negligible in front of PN-Na sites (Table 10).
So, seeing that the Ca 2+ quantified by EDTA-titration was exact, rectifications of the Na + quantities in used PN-2-Na and PN-3-Na deduced by HCl-titration were done and shown in the following table 11. These results on table 10 and table 11 confirmed that during exchange test NaOH molecules can moves through the polymers and reacted not only with their non-activated sites (-COOH) but also with the CaCO 3 to produce another -COONa sites and Na 2 CO 3 ; seeing that Na 2 CO 3 high soluble (2.33E+2[g.l -1 ]) in water, they were directly transported on low out with treated water, that is to say their concentration in the treated solution increases with time. All results conducted to suggest the following exchange PN-Na evolution on figure  12.
[+/-] referred to the less (-) or more (+) quantities of the chemicals according to the citric acid black polymer synthesized PN like PN-2 and PN-3.
Plotting the initial retained Ca 2+ per PN-equivalent moles quantities (Table 5) and per initial Ca 2+ concentration versus contact time we obtained the table 12 and figure 13 which confirmed that PN-equivalent quantities and contact time influenced the initial Ca 2+ retained moles quantities and showed the initial activities of Na sites belonged to PN-2-Na (19.6 per PN) and PN-3-Na (only 2.94 per PN).

Exchange test Results in Terms of Treated Water Ca 2+ and Na + Concentration Evolution Versus Time
This paragraph try to study this PN-Na exchange kinetic according to the previous results and exchange PN-Na evolution ( Figure 12) with putting conditions operatory to make it easy.
First, in general the exchange reaction speed was according These concentrations evolutions were shown in the following table 13.  These results confirmed also the PN rule as organic structure where ions exchange carried out because first, the PN-3-Na whose PN quantities was 1.39 times more than those PN-2-Na realized all the time important Ca 2+ retention. Then, secondly noticed that even if low was the PN-3-Na's Na + after activation, it was all the time more active and take to think that activation-exchange-deactivation phenomenon ( Figure 12) existed and easier on PN-3-Na.

Conclusion
Black citric acid polymer synthesis duration influence the PN's nature especially its equivalent PN content measuring out by NaOH-0.05N. Thus, two black citric acid polymer was synthesized, the PN-2-crispy with equivalent PN content equals to 3.9037E-4 [moles.g -1 ] and the PN-3-soft whose synthesis duration was lower and its equivalent PN content was 5.4113E-4 [moles.g -1 ] which correspond respectively to 61.31 (wt.%) and 84.98 (wt.%). Also, Boehm titration was done and confirmed the acidity differences between these two samples. However, it was noticed that for the Black citric acid polymer PN whose structure was composed in the majority of acid functions, the NaOH-0.05N acidity measuring-out is more suitable. Noticed also that PN adsorbed efficiently water on their surfaces and allowed us to study its potentiality as cationic exchanger after NaOH activation. PN particles sizes influenced the activation because the PN-2 crispy whose specific diameter size was 0.503[mm] retained more Na + [(nNa+/nPN-2) = 20] than the PN-3 soft whose specific diameter size was 1.437[mm] with [(nNa+/nPN-2) = 3]. These Na contents were measuring out by 0.049N-HCl. Cationic exchange tests with CaCO 3 solution were done with PN-2-Na and PN-3-Na activated PN to show their potentiality to be raw materials for polymer cationic exchanger. So, Ca 2+ contents of treated solutions was followed-up by EDTA-complexometric titration. Also, Ca 2+ and Na + of used PN-2-Na and PN-3-Na contents were measuring-out by HCl. Results permitted to suggest a global evolution during the activated PN cationic exchange where PN equivalent and Na + contents were very important. However, it was noticed that the PN-3-Na was all the time more active than the PN-2-Na and the global evolution of retained Ca 2+ with contact time allowed a parabolic curve. So, the PN's nature and its Na contents at activated status were important for their cationic exchange tests efficacy. The one problem was during the tests NaOH molecules slice the hydrogen-bond link between black citric acid polymer, brown citric acid polymer and other unsaturated functions and allowed to the brown coloration of the treated solution. So, it's a necessity to search solutions to make its color clear using adequate filter. However, it didn't challenge the PN capacity to be a potential raw material for realizing a polymer cationic exchanger not miscible in water after technologic amelioration. Indeed, actually industrialists suggested ions resins formed with a macro-molecular structure which was made up of a substance that allows the resin to be insoluble in water, but also serves as support for functional groups characteristic of resin properties [18][19]. Finally, a global kinetic of those PN-2-Na and PN-3-Na tests cationic exchange was done by following the Ca 2+ concentration evolution in solution and showed that the Ca 2+ speed formation was very important on the PN-2-Na solution than the PN-3-Na solution and confirmed its (PN-3-Na) high capacity to retain Ca 2+ .