Increasing HCl Concentration Research Articles

Wormlike Acid-Doped Polyaniline: Controllable Electrical Properties and Theoretical Investigation

Polyaniline doped with hydrochloride acid was prepared via a chemical oxidative polymerization between APS oxidant and aniline monomer in hydrochloric acid solution with different concentrations. The diameter of each PANI wormlike nanorod is fairly uniform, and the diameter of PANI nanorod decreases with increase in concentration of HCl. For the degradation stage of the polymeric backbone, the rate of degradation increases with decrease in the HCl concentration, which means the samples synthesized in higher HCl concentration possess the more stable structures. The highest conductivity of 1.04 S/cm is achieved when HCl concentration is 1.0 mol/L, which generated uniformly branched knobbles with good dispersion and higher aspect ratio. The variation tendency of complex permittivity keeps coordinate with the conductivity. First-principles calculations verified that N(E) of PANIs in the protonated states are larger than that of the unprotonated PANI, which means that the conductivity is promoted by the intera...

Insights into the Chemical Mechanism for CO2(aq) and H+ in Aqueous Diamine Solutions - An Experimental Stopped-Flow Kinetic and 1H/13C NMR Study of Aqueous Solutions of N,N-Dimethylethylenediamine for Postcombustion CO2 Capture.

In an effort to advance the understanding of multiamine based CO2 capture process absorbents, we report here the determination of the kinetic and equilibrium constants for a simple linear diamine N,N-dimethylethylenediamine (DMEDA) via stopped-flow spectrophotometric kinetic measurements and 1H/13C NMR titrations at 25.0 °C. From the kinetic data, the formation of monocarbamic acid (DMEDACOOH) from the reaction of DMEDA with CO2(aq) is the dominant reaction at high pH > 9.0 (k7 = 6.99 × 103 M-1·s-1). Below this pH, the formation of protonated monocarbamic acid (DMEDACOOH2) via the pathway involving DMEDAH+ and CO2(aq) becomes active and contributes to the kinetics despite the 107-fold decrease in the rate constant between the two pathways. 1H and 13C NMR spectra as a function of decreasing pH (increasing HCl concentration) at 25.0 °C have been evaluated here to confirm the protonation events in DMEDA. Calculations of the respective DMEDA nitrogen partial charges have also been undertaken to support the NMR protonation study. A comparison of the DMEDA kinetic constants with the corresponding data for piperazine (PZ) reveals that despite the larger basicity of DMEDA, the enhanced and superior kinetic performance of PZ with CO2(aq) above its predicted Bronsted reactivity is not observed in DMEDA.

Extraction and separation of palladium(II), platinum(IV), gold(III) and rhodium(III) using piperidine-based extractants

Extraction of palladium(II) from hydrochloric acid media with novel piperidine-based extractants N-decylpiperidine (P-C10), N-dodecylpiperidine (P-C12), N-tetradecylpiperidine (P-C14) and N-hexadecylpiperidine (P-C16) has been investigated. Over 90% of palladium(II) from 0.1M HCl solution can be effectively extracted with P-C12, P-C14 and P-C16 in toluene and the extraction equilibrium is achieved after 10min. Increase in HCl concentration has a negative effect on the effectiveness of palladium(II) extraction. From among the examined stripping solutions the most effective are 0.5M aqueous solution of ammonia and 0.1M thiourea in 1M HCl. The percentage of palladium(II) stripped from loaded organic phase (P-C12) reached nearly 100%. Also the selectivity of palladium(II) extraction over rhodium(III), platinum(IV) and gold(III) with the synthesized N-dodecylpiperidine (P-C12) has been investigated. The selectivity of extraction of palladium(II) over rhodium(III) from 0.1 and 3M HCl with P-C12 was the best. Separation of palladium(II) from platinum(IV) or gold(III) is not so effective and it depends upon the acidity of aqueous solution. N-dodecylpiperidine also shows the extraction ability towards examined noble metal ions in the following order Au(III)>Pd(II)~Pt(IV)>>Rh(III) from 0.1M HCl and Au(III)>Pt(IV)>Pd(II)>>Rh(III) from 3M HCl. Palladium(II), platinum(IV) and gold(III) can be successfully separated through stripping from the loaded organic phase.

A facile route to synthesize mesoporous SBA-15 silica spheres from powder quartz

A facile route is demonstrated to synthesize mesoporous SBA-15 silica spheres from powder quartz as an inexpensive silica source. P123 dissolved in an HCl solution was used as a structure-directing agent followed by hydrothermal processing of the product at 100°C for 24h. No other additives were used in the preparation. The morphology and structural order of the samples were strongly influenced by the HCl concentration (MHCl=2–4.5) of the P123 solution. At MHCl<2.5 the SBA-15 silica morphology was rod-like with a length that decreased and a diameter which increased with increasing HCl concentration. As MHCl increased between 3 and 4, the morphology became increasingly sphere-like leading to well-formed SBA-15 silica spheres of size ranging from 1 to 4µm. At MHCl=4.5 a less ordered mesoporous structure was observed.

Development of HCl-treated titania nanotube photocatalysts for dye photodegradation and low-concentration elemental mercury removal

TiO2 nanotube (TNT) photocatalysts were synthesized through a facile one-step hydrothermal method using Degussa P-25 as precursor. The resulting TNTs were subsequently washed with deionized water and 0.1–1.0M HCl to possess a variety of physicochemical properties. Anatase was the major crystalline phase for the resulting TNTs. The Brunauer-Emmett-Teller surface area of TNTs was 307–392m2g−1. Hydroxyl groups and oxygen vacancies were shown to be generated on the surface of all TNTs. Photocatalytic activity of TNTs for Congo red and crystal violet dye decomposition was strongly determined by their pre-adsorption abilities, which are greatly affected by solution pH. Hg0 removal by the TNTs was enhanced with increased HCl concentration and the presence of O2 in the test environment; however, the presence of water vapor reduced the Hg0 capture due to competitive adsorption of H2O. The Cl functionality formed on the surface of TNTs due to HCl treatment appeared to act as one of the adsorption sites and enhance Hg0 removal, as well as helping in against the competition from water molecules. Nevertheless, the unwashed HCl residues also obstructed other active sites on TNT surface, such as oxygenated groups that also play important role in Hg0 oxidation and adsorption.

Influence of different molar concentrations of acid on morphological, physicochemical and pasting properties of Pakistani Basmati and Irri rice starches

Starches extracted from two dominant varieties of rice, Basmati and Irri were subjected to acid hydrolysis by preparing starch slurry of 35% (w/v) in HCl solutions of concentrations 0.1M, 0.3M and 0.8M. The scanning electron micrographs showed that granular morphology of starches significantly changed after acid hydrolysis. Acid thinning improved the solubility of starches whereas decline was observed in swelling power and water retention capacity. Paste clarity of both acid treated Basmati and Irri rice starches reduced gradually upon cold storage. Also reduction in values of pasting, peak viscosity, hot paste viscosity, cold paste viscosity and set back were observed in acid thinned Basmati and Irri rice starches. The DE values increased with the increase in HCl concentration for both Basmati and Irri starch. The hardness of 0.8M HCl treated Basmati starch gel was found significantly lower than all treated and untreated starches. The gelatinization enthalpy for Basmati starch significantly reduced after acid hydrolysis with 0.1M, 0.3M and 0.8M HCl solutions at p <0.05.

Effects of functionality and textural characteristics on the removal of Cd(II) by ammoniated and chlorinated nanoporous activated carbon

Virgin activated carbon (VAC) was chemically activated by hydrochloric acid and aqueous ammonia to obtain different surface functionalities and nanopore distributions. The N-tailored AC (NAC) acquired by alkali treatment significantly enhanced the cadmium sorption capacity, while the Cl-tailored AC obtained by acidic modification decreased the sorption capacity compared with that of VAC. With increasing ammonia concentration in the basic treatment, the NAC surface area was increased with declining pore volume and diameter, which increased the adsorption capacity for Cd(II) removal. However, increasing HCl concentration in the acidic modification decreased the surface area, with increasing pore volume and diameter, which decreased the cadmium adsorption capacity. The basic treatment created more alkaline-rich sites such as nitrogen-containing functional groups, on the carbon surface, thereby improving cadmium removal efficiency. However, the acidic treatment generated a stronger acidic chemical structure and much more the formation of the acyl- and alkyl chloride groups that greatly inhibited the Cd(II) sorption capacity.

Electrochemical mechanism of tin membrane electro‐deposition in chloride solutions

AbstractBACKGROUNDA new membrane electro‐deposition based process for tin recovery from stannous solid waste was introduced. Linear sweep voltammetry (LSV), cyclic voltammetry (CV) and chronoamperometry (CHR) was applied to investigate the electrodeposition of tin(II) from a stannous chloride acid electrolyte containing an amine non‐ionic surfactant by using a membrane cell.RESULTSElectrochemical mechanism analysis results showed that 0.3% vol. amine non‐ionic surfactant facilitated ions diffusion by increasing the diffusion coefficient from 8.32E‐12 m2 s−1 to 2.85E‐11 m2 s−1, and inhibited tin(II) ions reduction as well as tin nucleation and hydrogen evolution. The applied ionic membrane did not hinder tin electrodeposition, while tin(II) ions reduction and hydrogen evolution was weakened with increasing HCl concentration from 1.5 to 4.5 mol L−1 and Sn2+ concentration increased from 20 to 80 g L−1.CONCLUSIONSThe tin(II) reduction process is proved to be irreversible and diffusion‐controlled, while the nucleation and growth of tin was involved in the process of diffusion for the proton reduction occuring in parallel with tin electrodeposition, and the process follows the mechanism of three‐dimensional instantaneous nucleation and subsequent grain growth limited by diffusion. © 2016 Society of Chemical Industry

Redox Stability of Uranium in High Ionic Strength Media: An Electrochemical and Spectroscopic Study

Knowledge of redox behavior of uranium in concentrated solutions of the hexary oceanic salt system is essential for the transport modeling of radioactive nuclides in repositories for the long-term disposal of radioactive wastes in rock salt formations. Especially critical is the behavior of the couple U(IV)/U(VI) in the surrounding high ionic strength saline milieu, which regulates the release of mobile U(VI) species at given redox conditions defined by the presence of trace oxygen. The redox potential (Eredox) and the solubility in brines in particular implicate the activity of the different ligand- and hydroxo-complexes (ai): Eredox = f(mi, ai, βj), where βj is the complexation constant. Thus, the prediction of transport behavior of uranium at given chemical environments needs appropriate complexation and thermodynamic models assuming the ionic activities beyond the limited Debye-Hückel theory. This latter is supplied by the Pitzer formulation1, where deviations from the limit Debye-Hückel behavior are given by specific interaction parameters among the constituting ionic species, which have to be determined experimentally. For the determination of the redox potential, an approach consisting in unfolding the redox system in two electrochemical reactions is pursued: (i) U(VI) → U(V) and (ii) U(IV) → U(V), where the kinetics of each partial reaction is studied systematically at different concentrations of the ground electrolyte. Thus ir i (Eredox) = ia ii (Eredox). In this work, we focus on the aqueous chloride system. The kinetics of the electrochemical reduction and oxidation reactions was studied in a three-electrodes type cell using a Au working electrode, Pt wire counter electrode and a Ag/AgCl in3 M KCl reference electrode. Experiments were performed under an oxygen-free atmosphere in a glove-box. Cyclic voltammetry (CV) and normal pulse voltammetry (NPV) were applied to investigate the influence of chloride concentrations in the kinetics parameters, such as reaction rate, k, and the diffusion coefficient in solutions containing U(VI) or U(IV) in HCl solutions from 0.1 to 1.3 M. The solution speciation of uranium was investigated by UV/vis absorption spectroscopy. CV and NPV experiments show that the reduction of U(VI) occurs in two steps. The first wave appearing between -0.2 V and -0.3 V vs ref. can be ascribed to the reaction U(VI) àU(V), in line with previous reports2,3,4. The second cathodic wave occurs with a simultaneous gas generation. The cathodic process involved in the second wave can be described in terms of an acceleration of hydrogen evolution reaction by adsorbed intermediary species. According to thermodynamic calculations using the extended Debye-Hückel equation as a rough ionic activity approximation and NEA-data base5, the predominating species in the systems under study are UO2 2+ and UO2Cl+. The concentration of the chloride complex increases with increasing HCl concentration, as indicated by the spectral changes on UV-vis absorption data. Spectroscopic measurements with U(IV), on the other hand, do not indicate a strong complexation effect. According to the results of voltammetric experiments, chloride complexes seem to influence the second electron transfer step. A reaction mechanism will be discussed in terms of electrochemical, spectroscopic and modeling results. References K.S. Pitzer in Activity coefficients in electrolyte solutions, Ch.3, CRC Press, Boca Raton, Florida, 1991.R.E. Dueber, A.M. Bond, P.G. Dickens, J. Electrochem. Soc. 141 (1994) 311.K. El Kacemi, B. Tyburce, S. Belcadi, Electrochim. Acta 27 (1982) 729.S. Kihara, Z. Yoshida, H. Aoyagi, K. Maeda, O. Shirai, Y. Kitatsuji, Y. Yoshida, Pure Appl. Chem. 71 (1999) 1771.I. Grenthe, J. Fuger, R.J.M. Konings, R.J. Lemire, A.B. Muller, C. Nguyen-Trung, H. Wanner, in H. Wanner and I. Forest (Ed.), NEA-Data bank, Chemical Thermodynamics of Uranium, OECD Publications, Paris, 2004.

Low temperature deposition of polycrystalline silicon thin films on a flexible polymer substrate by hot wire chemical vapor deposition

For the applications such as flexible displays and solar cells, the direct deposition of crystalline silicon films on a flexible polymer substrate has been a great issue. Here, we investigated the direct deposition of polycrystalline silicon films on a polyimide film at the substrate temperature of 200°C. The low temperature deposition of crystalline silicon on a flexible substrate has been successfully made based on two ideas. One is that the Si–Cl–H system has a retrograde solubility of silicon in the gas phase near the substrate temperature. The other is the new concept of non-classical crystallization, where films grow by the building block of nanoparticles formed in the gas phase during hot-wire chemical vapor deposition (HWCVD). The total amount of precipitation of silicon nanoparticles decreased with increasing HCl concentration. By adding HCl, the amount and the size of silicon nanoparticles were reduced remarkably, which is related with the low temperature deposition of silicon films of highly crystalline fraction with a very thin amorphous incubation layer. The dark conductivity of the intrinsic film prepared at the flow rate ratio of RHCl=[HCl]/[SiH4]=3.61 was 1.84×10–6Scm−1 at room temperature. The Hall mobility of the n-type silicon film prepared at RHCl=3.61 was 5.72cm2V−1s−1. These electrical properties of silicon films are high enough and could be used in flexible electric devices.

Inhibition Behaviour of 2-[(2-Methylquinolin-8-yl) Oxy] Acetohydrazide on the Corrosion of Mild Steel in Hydrochloric Acid Solution

A hydrazide derivative containing quinoline moiety namely 2-[(2-methylquinolin-8-yl)oxy]acetohydrazide (MQH) has been synthesized and its corrosion inhibition performance and adsorption behaviour on mild steel in 0.5 and 1 M HCl solution have been tested by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The inhibition efficiency of MQH increases with increase in its concentration and decreases with increase in HCl concentration. Further the, inhibition efficiency of MQH increases in 0.5 M HCl and decreases in 1 M HCl with increase in temperature. Polarisation curves indicate that MQH is a mixed inhibitor, affecting both cathodic and anodic corrosion currents. The adsorption of MQH at the mild steel/HCl solution interface obeys Langmuir adsorption isotherm model and inhibition process follows mixed adsorption with predominantly chemisorption in 0.5 M and physisorption in 1 M HCl. The activation and thermodynamic parameters for the corrosion inhibition process have been calculated to explore the mechanism of corrosion inhibition.

Corrosion of hot-rolled 430 stainless steel in HCl-based solution

The mixtures of hydrochloric acid and hydrogen peroxide were employed as the environmental friendly pickling solution for 430 hot-rolled stainless steel in this study. Increase of HCl concentration accelerates the corrosion rate of base metal, however aggravates the intergranular attack in sole hydrochloric acid solution. Addition of oxidant (H2O2) boosts the corrosion potential of stainless steel significantly resulting in the change of electrode action. At high oxidant content (0.6 mol l−1 H2O2), a corrosion product film accumulates onto the surface and the corrosion is then governed by the mass-transport at the film/stainless steel interface. The random dissolving of metal ions because of the film leads to brightening of stainless steel surface and the local corrosion is suppressed.

Extraction study of rare earth elements with N,N′-dibutyl–N,N′-di(1-methylheptyl)-diglycolamide from hydrochloric acid

A novel, unsymmetrical diglycolamide, N,N′-dibutyl–N,N′-di(1-methylheptyl)-diglycolamide (DBD1MHDGA), was synthesized. The extraction of rare earth elements (REEs) from a hydrochloric acid medium with DBD1MHDGA was investigated. The results of the extraction experiments indicated that the distribution ratios of RE(III) ions increase with an increase in HCl concentration, atomic number, and extractant concentration. The calculated thermodynamic data show that the extraction process is an exothermic reaction. The organic phase loaded rare earth ions were characterized by infrared spectroscopy. The composition of the extracted complex was determined.

Preconcentration of mercury on polyaniline expands the horizon for energy dispersive X‐ray fluorescence determination

Hg(II) was sorbed on polyaniline from aqueous solutions, followed by determination using energy dispersive X‐ray fluorescence spectrometry. Distribution coefficient of Hg(II) on polyaniline was about 4 × 103 in water, whereas distribution coefficient was 1.2 × 104 at 0.1 M HCl and decreased drastically with increase in HCl concentration. Rapid kinetics of sorption was evinced by the 80% uptake within the initial 1 min and quantitative sorption within 5 min of equilibration. The sorption was found to follow Langmuir isotherm model, and the Langmuir capacity was calculated as 19.7 mg g−1. The ability of polyaniline to form stable and homogeneous pellets facilitated the energy dispersive X‐ray fluorescence determination without recourse to elution. Detection limit of Hg was found to be 22 ng, considering 100 mg pellet of polyaniline. The apparent detection limit was 6 pg, as the preconcentration factor of Hg(II) on polyaniline was 4 × 103. The developed method is at par with the established method for mercury determination, namely, cold vapor atomic absorption spectrometry. Accuracy of the method was established by the analysis of the International Atomic Energy Agency reference materials, namely, hair and lichen, for Hg(II). Copyright © 2016 John Wiley &amp; Sons, Ltd.

Effect of acid modification of kaolin and metakaolin on Brønsted acidity and catalytic properties in the synthesis of octahydro-2H-chromen-4-ol from vanillin and isopulegol

Natural kaolin and the metakaolin obtained by calcination of kaolin at 650°C were chemically activated using 0.25–3.0 mol/dm3 HCl solutions. Structural and textural properties of samples were characterized by X-ray diffraction, elemental analysis and N2-adsorption/desorption analyses. The amount of Brønsted acid sites (BAS) was determined by infrared spectroscopy using pyridine as probe molecule. The amount of BAS for kaolin rose with increasing HCl concentration up to 1.0M, and decreased for higher concentrations, that is related with the leaching of Al from the solid. Effect of HCl concentration on amount of BAS was negligible for metakaolin. The catalytic performance of these materials was investigated in the Prins cyclization of (−)-isopulegol with vanillin to form octahydro-2H-chromen-4-ol, carried out in toluene at 50°C. The reaction rate and the selectivity toward octahydro-2H-chromen-4-ol depended on the Bronsted acidity, structural and textural properties of the catalysts. The reaction rate in the presence of kaolin modified by HCl correlated with the amount of BAS. HCl-kaolin samples were more active compared with HCl-metakaolin, while selectivity reaction toward octahydro-2H-chromen-4-ol was larger in the presence of HCl-metakaolin.

An enhancement method for the elemental mercury removal from coal-fired flue gas based on novel discharge activation reactor

Gas-phase oxidation of elemental mercury (Hg0) from flue gas by simulated electrostatic precipitators (ESP) electric field was explored in this paper. In order to enhance the removal efficiency of Hg0 by ESP electric filed, a novel discharge activation reactor was designed and employed. The influence of HCl concentration, temperature, fly ash, and flue gas components on the Hg0 removal were also considered, respectively. The Hg0 removal efficiency increased with the increase of HCl concentration, temperature and discharge voltage. It has also been found that O2, H2O and fly ash showed a light promotion on the removal of Hg0 while NO and SO2 had a slight inhibition effect on Hg0 oxidation. Furthermore, the novel discharge activation reactor could improve the generation of reactive chemical species, such as Cl· or Cl2, which facilitated the mercury removal. At the reaction temperature of 413K, about 60% Hg0 could be removed from simulated flue gas under 25.0kV in presence of 10.0ppmv HCl. When the novel discharge activation reactor was used, the Hg0 removal efficiency increased to about 80% at the same experimental conditions. It appeared to be a promising technique to enhance the removal of Hg0 by ESP.

Leaching of Copper from Metal Powders Mechanically Separated from Waste Printed Circuit Boards in Chloride Media Using Hydrogen Peroxide as Oxidant

The dissolution of copper from waste printed circuit boards in chloride media using hydrogen peroxide as oxidant was carried out. The effects of stirring speed, temperature, solid/liquid ratio and concentrations of HCl and H2O2 on the leaching of copper were investigated. The copper extraction increased significantly with the increase of HCl concentration. H+ and Cl− ions both improved the leaching of copper from waste printed circuit boards and had the synergetic effect on copper dissolution. The H2O2 was the main reagent which made possible the leaching of metallic copper from waste printed circuit boards in acidic chloride solutions. The copper extraction also increased with the increase of stirring speed, temperature and solid/liquid ratio. Finally, a reaction mechanism was proposed as well.

Particle Size, Morphology and Color Characteristics of C.I. Pigment Red 57:1 : 2. Effect of Salt Milling Process

The effect of salt milling process on the crystal size, morphology, and color characteristics of C.I. Pigment Red 57:1 was studied. The primitive morphology and color properties of the pigment after synthesis were studied in the former series work. The size and morphology of primary particles and the second aggregation features should be considered because they are very important to determine pigment quality. We compared the primary morphology of pigment particles before drying with the secondary aggregated morphology of pigment particles after drying and salt milling process. Morphological properties were investigated by particle size analysis, X-ray diffraction, and scanning electron microscopy and color measurement was carried out. Significant reduction in particle size as well as enhanced crystallite size after salt milling process was observed. This result might give a difference in color of the pigment, turning into brighter and more blue-toned red color. It was revealed that synthesis condition affect the morphology and color of the pigment even after milling. Increase in HCl concentration in the synthesis process enhanced crystal size and quality forming bluer-red pigments but an increase in concentration resulted in more amorphous crystals forming darker-red pigments after salt milling.

Application of Phosphonium Ionic Liquids as Ion Carriers in Polymer Inclusion Membranes (PIMs) for Separation of Cadmium(II) and Copper(II) from Aqueous Solutions.

Facilitated transport through polymer inclusion membranes (PIMs) is a promising method for simultaneous separation and removal of valuable and toxic metal ions from aqueous solutions. Recently, ionic liquids (ILs) have been used as extracting agents for metal ions due to their unique physicochemical properties. This paper presents research on the facilitated transport of cadmium(II) and copper(II) ions from aqueous chloride solutions through PIMs with phosphonium ILs as new selective ion carriers. Cellulose triacetate membranes containing o-nitrophenyl octyl ether (ONPOE) as a plasticizer and Cyphos IL 101 [trihexyl(tetradecyl)phosphonium chloride] or Cyphos IL 104 [trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate] as the ion carriers have been prepared and applied for investigations. Cd(II) ions were transported preferably from hydrochloric acid solutions containing Cu(II) ions through the PIMs. Higher selectivity coefficient of Cd(II) over Cu(II) (SCd/Cu) from 0.1 mol·dm−3 hydrochloric acid was obtained for PIM with Cyphos IL 104 as the ion carrier. The influence of HCl and NaCl concentrations in the source phase on metal ion transport across PIM doped with Cyphos 104 was studied. It was found that the initial fluxes of Cd(II) and Cu(II) increase with increasing chloride ions concentration in the source phase. The selectivity coefficient for Cd(II) over Cu(II) decreases with increasing HCl concentration in the source phase. The results suggest that the separation system presented in this paper can be useful for the removal of Cd(II) from acidic chloride solutions in the presence of Cu(II).

Novel biological and chemical methods of chitin extraction from crustacean waste using saline water

BACKGROUND Several techniques have been proposed to recover chitin from shrimp waste using large amounts of freshwater and chemicals. The standard chemical recovery of chitin was first compared by replacing fresh water with seawater. In addition, a biotechnological process with Bacillus subtilis (B1) and Bacillus licheniformis (B2) using seawater during all steps of chitin extraction was studied. RESULTS The demineralization rate (DM) was statistically significant when using seawater (P=0.000020) and chemical recovery in comparison with deproteinization (DP). Increasing HCl concentration (from 1 to 1.28 mol L−1) and reaction time (from 60 to 90 min) resulted in DM similar to fresh water (P>0.05). Highest DP rates were obtained with crude protease (B1; DP ≈74%) and (B2: DP ≈84%), when fermentation was carried out for 24 h at an enzyme/substrate ratio of 2. Maximum DP was reached (≈79% for B1 and ≈ 82% for B2) after 15 days, while DM ranged between 55 and 60%. CONCLUSION Combined enzymatic DP (with B2) followed by a chemical DM process was used to produce chitin (DP≈84%, DM≈94%) which, on transformation to chitosan, showed a degree of deacetylation equivalent to ≈ 71%. This combined approach using seawater could transform crustacean waste into chitin products of commercial value. © 2015 Society of Chemical Industry