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Urea is the final product of protein metabolism in mammals and can be found in different biological fluids. Use of mammalian urine in agricultural production as organic fertilizer requires safe handling to avoid the formation of ammonia that will decrease the fertilizer value due to the loss of nitrogen. Safe handling is also required to minimize the decomposition of urea into con-densed products such as biuret and cyanuric acid, which will also have a negative impact on the potential sustainable production of crops and sanitation technologies. The study of thermodynamics and reaction kinetics of urea stabilization plays a key role in understanding the conditions under which undesirable compounds and impurities in urea‐based fertilizers and urea‐based selective catalytic reduction systems are formed. For this reason, we studied the reaction of urea in acid media to achieve urea stabilization by modeling the reaction of urea with sulfuric acid and phosphoric acid, and estimating the reaction enthalpy and adiabatic heat difference for control of the heat re-leased from the neutralization step using Ca(OH)2 or MgO for the safety of the process. Numerical and simulation analyses were performed by studying the effect of the surrounding temperature, the ratio of acid reagent to urea concentration, the rate of addition, and the reaction rate to estimate the required time to achieve an optimum value of urea conversion into ammonium dihydrogen phosphate or ammonium sulfate as potential technological opportunities for by‐product valorization. Full conversion of urea was achieved in about 10 h for reaction rates in the order of 1 × 10−5 s−1when the ratio of H2SO4 to CH4N2O was 1.5. When increasing the ratio to 10, the time required for full conversion was considerably reduced to 3 h. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Alcoholysis of triglycerides is a common method in the production of a renewable fuel - biodiesel, specifically methyl esters of fatty acids. In this work, kinetics of methanolysis was studied, with a focus on an undesired side reaction - hydrolysis. This side reaction, also called saponification, leads to deactivation of the used catalyst and affects the purity of the final product - biodiesel. For this reason, a model of methanolysis has been developed and verified considering both the main and side reactions. This mathematical model, assuming irreversibility of all reactions, is capable of describing measured experimental data under different initial reaction mixture composition and also different reaction temperature. The developed model was used for the prediction of optimal conditions of methanolysis under which saponification is reduced, and is important for the design of industrial manufacturing process, equipment and process control algorithms. ©ECMS Mauro Iacono, Francesco Palmieri, Marco Gribaudo, Massimo Ficco (Editors).

The aim of the present work is to perform the mathematical modelling and computer simulation of the lupine flour hydrolysis technology, which includes the calculations and also the partial comparison of different process variants. Lupine flour is deemed as a source of valuable protein with a substantial content of essential amino acids which has a significant impact on the prevention of various diseases in a human diet. The proposed mathematical model for the production process enables to accomplish the optimal operating conditions while the specific costs for the production of valuable hydrolyzate are minimal. The suggested process-economic mathematical model for the production hydrolysis unit comprises the three main processes for the implementation of the hydrolyzate production, i.e. the chemical reaction and its kinetics, the separation of solids from the reaction mixture by filtration and the thickening of the final product. The results have shown that in most of the simulation cases, the economic optimum occurs and thus the application of the model is valuable for the practical purposes of protein hydrolyzate production. © 2019, World Scientific and Engineering Academy and Society. All rights reserved.

In the present paper we studied the oxidation of ferrous sulfate salt with oxygen. ferric ammonium sulfate and ferrous sulfate were used to prepare standard solutions of Fe(III) and Fe(II) solutions. Oxidation experiments were carried out by mixing FeSO4·7 H2O in H2O. Air was supplied using a gas washing bottle in which air entered the bottle through the center tube, and exited into the bottom of the bottle. Samples were taken periodically and analyzed in the UV-Vis spectrophotometer. We consider that basic Fe(III) sulfate was one of the main compounds produced during the reaction and proposed a model to describe the process. We found solution to the differential equations that described the profile of FeSO4 and FwOHSO4 concentration in time and observed agreement between the experimental results and data predicted by the model. Moreover, we determined values of rate constants using the model and confirmed the determined values by means of experiments. This suggests that basic ferric sulfate was generated after aeration of ferrous sulfate solution. © 2018 The Authors, published by EDP Sciences.

This paper presents a preliminary study of Raman spectroscopic measurement of chromium traces in leather and its processed forms such as shavings, hydrolyzate and ash. The emphasis is given on the valence of chromium, especially two most stable forms trivalent and hexavalent, as they have adverse effect on human health. Trivalent form is mainly beneficial. Compounds of hexavalent chromium are classified as carcinogens. The conventional methods for chromium assessments (e.g. FAAS) are often time-consuming and destructive. Some of methods give only the total chromium content value, which is not sufficient due to the nature of different valences. The official UV-VIS spectrophotometry is designed mainly for liquid samples. The innovative approach is the study of Raman spectroscopy possibilities. Raman spectroscopy is an efficient method for material identification reflecting the molecular structure. This method provides many benefits such as rapidity, non-invasiveness, no requirements for sample preparation, applicability to various materials. The results of the performed experiments show the hidden potential of Raman spectroscopy for the chromium detection with the benefit of direct determination of valence. The limitation can be by emerging luminescent. Silver colloidal treatment of luminescent samples indicated more intense Raman signal. An agreement was reached with trivalent and hexavalent chromium content in specially treated leather samples and the ash. © 2018 IEEE.

The issue of this article is one stage washing of reaction blend after enzyme hydrolysis under which we are able to recycle almost all contained chromium in solid leather waste. During hydrolysis we gain protein hydrolysate as a filtrate that is appropriate substance for use. On the basis of equation for streaming of liquids through layer of substance we determined optimal pressure differential for filtering and washing of reaction mix and we applied mathematical description valid for filtering and one stage washing and on the basis of this models we able to optimize washing process that is add to filtering and which aim is to reduce content of protein hydrolysate in filter cake.

This paper suggests a methodology for the adsorption of chromium from tannery wastewater as an ecological alternative to the contamination and toxic problems associated with this industry. The effect of mixtures of quarry stone and silica gel or activated carbon, particle size and pH were analyzed using a Box-Behnken design to evaluate and optimize the adsorption of chromium up to 88%.

In this paper, the mathematical modeling in the area of treatment the leather waste material is presented. Leather industry contributes significantly to the production of several types of waste and pollutes the environment for many decades. A reasonable solution for processing of certain part of tannery wastes, such as shavings, is a hydrolysis reaction. This reaction enables to separate collagen that can be effectively re-utilized in various forms. The attention in the paper is paid to the mathematical model of the main operating expenses for producing a collagen hydrolyzate from leather shavings. The first stage is mathematical description of the real nature of processes - the deterministic model. The modeling is performed for a batch reactor and pilot plant conditions. It is based on physical and chemical processes ongoing in the reactor and other parts of the production system, such as kinetics of the hydrolysis, mass balances, dry matter balances and protein balance in the equilibrium. The goal is to determine optimal time of hydrolysis reaction, optimal mass fraction of decomposed protein and hence the main operating expenses. The obtained results clearly demonstrate the sense of the mathematical modeling and the contribution to the economical evaluation of production process - to acquire collagen hydrolyzate from a waste material. © 2017 IEEE.

The content of the paper is the industrial application of enzyme hydrolysis of tanning solids waste with a view to minimizing the price of enzyme hydrolysate product, which has widely used. On the base of the energy balance of the enzymatic hydrolysis we estimated the critical minimal charge of a tanning drum. We performed of the critical minimal on the basis of a balance model for heat transport from reaction mixture into the environment through reactor wall. Employing a tanning drum for hydrolytic reaction allows to process tanning wastes in the place of their origin. It means thus considerably to enhancing economics of the whole process. © The Authors, published by EDP Sciences, 2017.

Nitrous oxide is a very inert gas used generally as oxidant as it offers some advantage compared with other oxidants such as O2 but a considerably higher temperature (> 526 °C) is often required. For particular cases such as the oxidation of sugar alcohols, especially for the oxidation of primary alcohols to aldehydes, N2O has the advantage over O2 of a higher reaction selectivity. In the present paper we present the modelling of oxidation reaction of sugar alcohols using an oxidizing agent in low concentrations, which is important to suppress subsequent oxidation reactions due to the very low residual concentrations of the oxidizing agent. For orientation experiments we chose nitrous oxide generated by thermal decomposition of ammonium nitrate. Kinetic modeling of the reaction was performed after determination of the differential equations that describe the system under study. © The Authors, published by EDP Sciences, 2017.

This paper deals with the problem of chromium recovery from chrome-tanned waste and thus with reducing the environmental impact of the leather industry. Chrome-tanned waste was transformed by alkaline enzymatic hydrolysis promoted by magnesium oxide into practically chromium-free, commercially applicable collagen hydrolysate and filtration cake containing a high portion of chromium. The crude and magnesium-deprived chromium cakes were subjected to a process of thermal decomposition at 650°C under oxygen-free conditions to reduce the amount of this waste and to study the effect of magnesium removal on the resulting products. Oxygen-free conditions were applied in order to prevent the oxidation of trivalent chromium into the hazardous hexavalent form. Thermal decomposition products from both crude and magnesium-deprived chrome cakes were characterized by high chromium content over 50%, which occurred as eskolaite (Cr2O3) and magnesiochromite (MgCr2O4) crystal phases, respectively. Thermal decomposition decreased the amount of chrome cake dry feed by 90%. Based on the performed experiments, a scheme for the total control of chromium in the leather industry was designed. © 2016, © The Author(s) 2016.

Fleshings, the main non-tanned solid waste of the tanning industry, are produced during the fleshing operation, which is the mechanical removal of subcutaneous fat and connective tissues. Relatively high content of fat and low (often even negative) price make fleshings a potential feedstock for biodiesel production. However, said benefit is reduced by the fact that the fleshings must be refined, i.e. it is necessary to remove residual sodium chloride, water, subcutaneous tissue (protein), and in many cases free fatty acids. The operating costs of the refining technology must not exceed the price of a traditional material that is vegetable oil. Another complication is associated with the relatively small production of tannery fats, which considerably extends the return on investment. To overcome these disadvantages it is necessary to optimize the refining operations and acquire secondary products of high utility value. The first task is related to using theoretical tools of process engineering that enable management of each refining process at low operating costs, the second task includes production of protein hydrolysates obtained from the hydrolytic treatment of subcutaneous tissue and processing of free fatty acids into commercially interesting products.

The reaction pathway for the conversion of glycerol into different products, namely glyceraldehyde, glyceric acid, glycolic acid, mesoxalic acid and tartronic acid was studied by means of electrochemistry. Multiple Pulse Amperometry technique was used to control the potential during the electrooxidation reaction. The estimation of the transfer function was realized on the basis of dynamic models for the oxidation reaction. The equations obtained in the s-domain were expressed in the time domain using Inverse Laplace transformation to describe the variation of glycerol and products concentration.

The mathematical modelling of diffusion of a bleaching agent into a porous material is studied in the present paper. Law of mass conservation was applied to analize the mass transfer of a reactant from the bulk into the external surface of a solid geometrically described as a flat plate. After diffusion of the reactant, surface reaction following kinetics of first order was considered to take place. The solution of the differential equation that described the process leaded to an equation that represents the concentration profile in function of distance, porosity and Thiele modulus. The case of interfacial mass resistance is also discused. In this case, finite difference method was used for the solution of the differential equation taking into account the respective boundary conditions. The profile of concentration can be obtained after numerical especification of Thiele modulus and Biot number.

In this paper there is described filtering process for separating reaction mixture after enzymatic hydrolysis to process the chromium tanning waste. Filtration of this mixture is very complicated because it is case of mixture filtration with compressible cake. Successful process strongly depends on mathematical describing of filtration, calculating optimal values of pressure difference, specific resistant of filtration cake and temperature maintenance which is connected with viscosity change. The mathematic model of filtr ation with compressible cake we verified in laboratory conditions on special filtration device developed on our department.

Human health and considerate approach to the environment are very topical nowadays. Both are inseparably related to the waste of leather industry management and their efficient processing. The research dealing with the automation of process control of complex hydrolytic processing of tannery waste materials has been solved in a long term scale on our faculty. In this paper a contribution to this issue concerning spectroscopic measurement of two prevalent forms of chromium is presented. Trivalent chromium is largely beneficial, whereas compounds of hexavalent chromium are classified as carcinogens. Salts of trivalent chromium participate within the process of the most widely used method for tanning the hides. Risk of chromium-containing materials consists in the possibility of spontaneous oxidation of compounds of trivalent to hexavalent chromium compounds. In terms of thermodynamics, this conversion is possible due to the values of the free enthalpy for the oxidation reactions. The direct contact of hexavalent chromium with the human body can cause serious health problems. For the analysis two spectroscopic methods were used. UV-VIS spectrophotometry as the most common method for detection chromium compounds in liquids and their quantitative evaluation and an innovative method Raman spectroscopy. Raman spectroscopy was used for the study of valence of chromium compounds contained in leather samples, shavings and dry matter of collagen hydrolysate as an efficient tool for material identification. Raman spectroscopy brings advantages over traditional laboratory techniques in terms of effective, rapid, non-contact and reagent-free way of measurements. The possibility to distinguish trivalent and hexavalent chromium was proved. For the samples performing luminescence Surface Enhanced Raman Spectroscopy was applied. The results show that Raman spectroscopy is a potential technique for hazardous hexavalent chromium detection with the benefit of direct determination ofvale

Annually, a great amount of waste fats and oils not suitable for human consumption or which cannot be further treated are produced around the world. A potential way of utilizing this low-cost feedstock is its conversion into biodiesel. The majority of biodiesel production processes today are based on the utilization of inorganic alkali catalysts. However, it has been proved that an organic base - tetramethylammonium hydroxide - can be used as a very efficient transesterification catalyst. Furthermore, it can be employed for the esterification of free fatty acids - reducing even high free fatty acid contents to the required level in just one step. The work presented herein, is focused on biodiesel production from waste frying oils and animal fats using tetramethylammonium hydroxide at the pilot-plant level. The results showed that the process performance in the pilot unit - using methanol and TMAH as a catalyst, is comparable to the laboratory procedure, even when the biodiesel is produced from waste vegetable oils or animal fats with high free fatty acid content. The reaction conditions were set at: 1.5% w/w of TMAH, reaction temperature 65. °C, the feedstock to methanol molar ratio to 1:6, and the reaction time to 120. min. The conversion of triglycerides to FAME was approximately 98%. The cloud point of the biodiesel obtained from waste animal fat was also determined. © 2015 Elsevier Ltd.

Transesterification of triglycerides (oils and fats) catalyzed by bases is a common method for production of fatty acid methyl esters (FAME) - a renewable fuel (biodiesel) and basic oleochemical. Hydrolysis of esters - saponification - represents the main side reaction. Saponification leads to catalyst deactivation and impedes products purification. In this work, kinetics of the competing triglyceride hydrolysis and methanolysis (i.e. transesterification) is investigated. Furthermore, an alternative organic catalyst - tetramethylammonium hydroxide (TMAH) - is compared with potassium hydroxide and sodium methoxide. TMAH is less active but the methanolysis is more selective towards FAME formation and hydrolysis proceeds at a slower rate in comparison to the inorganic catalysts. FAME are less susceptible to hydrolysis than glycerides. A simple mathematical model assuming irreversibility of all reactions is capable to describe the measured data well (40-60°C, TMAH concentration 0.5-1.5wTMAH/woil, molar ratio methanol:oil=6). © 2015 Elsevier B.V..

This paper is focused on the mathematical model for alkaline hydrolysis of leather shavings. Leather industry produces annualy a large amount of wastes. For the environment-friendly solution the processing of certain part of wastes arising from the leather industry is reasonable to utilize hydrolysis processes. Collagen protein contained in e.g. leather shavings can be further effectively processed. The description of the hydrolysis process is based on the linearized state model. The mathematical-physical model is built on the mass balance of the input substances and the resulting hydrolysate protein, moreover on an enthalpy balance for the reaction mixture and saturated steam serving in reactor as the heat transfer medium. The simulations of the protein hydrolysis process model are performed in Matlab Simulink and are closely discussed in the paper. © 2016, North Atlantic University Union. All rights reserved.