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Published in Joseph C. Salamone, Polymeric Materials Encyclopedia, 2020
In the course of preparing PVAm from amide or carbamate precursors, byproducts are generated during the hydrolysis. Stoichiometric acid is typically a minimum requirement for acid hydrolysis and generates the acid salt of PVAm. In the case of PNVF or PNVA, formic acid or acetic acid is also generated in water, or an alkyl formate with PNVF in alcohol. Base hydrolysis generates formate salts with PNVF2 and is very slow with PVTBC. In many applications, the presence of these byproducts may be tolerable. In other applications, these byproducts may interfere with the performance of PVAm or may cause other problems. Byproducts can be removed, at least on a lab scale, by dialysis or ultrafiltration.40 Other options to remove unwanted byproducts include base hydrolysis in lower alcohols to precipitate sodium formate, and formate removal by polymer precipitation via crosslinking with polycarboxylic acids at neutral pH and redissolution on acidification.40,48 PVAm-HCl, after acid hydrolysis, can also be converted to the free base amine by column treatment with Amberlite IRA-400 anion exchange resin in the hydroxide form.49 A particularly elegant method for removing PNVF hydrolysis byproducts involves partially hydrolyzing PNVF using aqueous ammonia at elevated temperatures, followed by degassing of the ammonia and catalytic removal of the remaining formate by decomposition of the formate on supported metal catalysts.50
Surface Properties and Analysis
Published in Ko Higashitani, Hisao Makino, Shuji Matsusaka, Powder Technology Handbook, 2019
The material chemically adsorbs the atmospheric carbon dioxide and forms a carbonic acid salt. For instance, carbonate and a surface hydroxyl group are formed with the carbon dioxide and water vapor in air on MgO, CaO, and the surface of the MgO–ZnO complex oxide. Water vapor is easily chemically adsorbed in general, and the surface becomes covered by hydroxyl groups on the oxide surface. Figure 1.6.2 shows the chemisorptions of water vapor on the surface of MgO having a simple crystal structure as one example. The chemisorption of water vapor has the ability to adsorb only on the surface layer and adsorb into a layer in the solid. Not only the first surface layer but even the inside of the solid MgO can absorb.
Biorefineries
Published in M.R. Riazi, David Chiaramonti, Biofuels Production and Processing Technology, 2017
Isabella De Bari, Daniela Cuna, Nicola Di Fidio, M.R. Riazi, David Chiaramonti
Bioproduction of organic acids often results in dilute concentrations of the product because of product inhibition. Buffering or neutralization results in the formation of the acid salt rather than the acid, implying the need for subsequent neutralization and purification for the recovery of the free acid. Separative-bioreactors, which use the electrodialysis technology, can increase the process performances (Huang et al. 2007). These bioreactors simultaneously separate the organic acids from the biocatalyst as they are produced, thus avoiding product inhibition (Arora et al. 2007). In addition, they recover the product in its acid form and avoid neutralization.
Water transport channel of cement paste modified by hydrophobic agent: X-ray nanotomography based analysis
Published in Nondestructive Testing and Evaluation, 2023
Hao Zhang, Song Mu, Jingshun Cai, Jianzhong Liu, Jinxiang Hong
Previous studies [24,25] about the microstructure of cement pastes containing hydrophobic admixture have proved that the addition of carboxylic acid salt type hydrophobic agent generated the flaky carboxylic acid salt crystals in the matrix of hydration products. Meanwhile, there are some solid phases observable in the pore space in 2D images. The representative inner space of pores in the presence and absence of hydrophobic agents was selected. Figure 5 depicts the rendering images of a single 3D pore structure in cement pastes in the presence of a 1.2% hydrophobic agent. It can be observed in Figure 5(b) that the large pores are partially filled with the flaky crystal, resulting in the pore being divided into two parts. The representative example showcases the feature of pores in cement pastes in the presence of a hydrophobic agent, which would modify the water transportation channel. An additional problem needed to be addressed is whether the pore can be divided into two categories of the closed pore and the interconnected pore. The latter can determine water transportation. It can be inferred from the results of the water resistance experiments that the generation of flaky crystals mainly modifies the interconnected pores, as section 3.3 will show.
Removal of tartrazine, ponceau 4R and patent blue V hazardous food dyes from aqueous solutions with ZnAl-LDH/PVA nanocomposite
Published in Journal of Dispersion Science and Technology, 2023
Ofeliya O. Balayeva, Abdulsaid A. Azizov, Mustafa B. Muradov, Rasim M. Alosmanov
The buffer solutions were used to study the optimal pH of adsorption of dye compounds onto ZnAl-LDH/PVA nanocomposite using hydrochloric acid (HCl), acetic acid (CH3COOH), ammonium acetate (CH3COONH4) and ammonium hydroxide (NH4OH). Thus, as pH 1 and pH 2 solutions were used 10−1 M and 10−2 M hydrochloric acid solutions, respectively. Buffer solutions of pH 3- pH 7 were prepared using different ratios of 10−1 M CH3COOH and 10-1 M CH3COONH4. Buffer solutions of pH 8- pH 11 were prepared using different ratios of 10−1 M NH4OH and 10−1 M CH3COONH4. The pH of the solutions was measured on a Mattler Toledo pH meter. The volumes of acetic acid, ammonium acetate salt solution and ammonium hydroxide solution used in the preparation of the ammonium acetate buffer solution were calculated using acid-salt and base-salt concentration ratios (2) and (3).[16] where: pKa - acid number of acetic acid; ca - concentration of acetic acid; cs - concentration of ammonium acetate salt; pKb - basic number of ammonium hydroxide; cb is the concentration of ammonium hydroxide.
Synergistic impacts of climate change and human activities on spatiotemporal organic nitrogen burial variation in a plateau lake in southwest China
Published in Inland Waters, 2023
Tao Huang, Yang Luo, Quanliang Jiang, Zhigang Zhang, Hao Yang, Changchun Huang
Total nitrogen (TN) was determined after digestion using persulfate solution (K2S2O4 + NaOH) at 121 °C for 30 min. To determine the NH4-N and NO3-N contents, 2 mol L−1 KCl was added to the samples and shaken for 30 min. The filtrate was then extracted using a 0.45 μm membrane filter. NO3-N was directly determined using a UV-3600 spectrophotometer (Shimadzu Corp., Japan). The NH4-N content was analyzed using salicylic acid and hypochlorous acid salt spectrophotometry. The ON concentration was obtained by subtracting the inorganic N content, which includes NH4-N and NO3-N, from the TN content. Total organic carbon (TOC) was measured using a TOC analyzer (Shimadzu Corp., Japan).