Abstract
Previous research into the synthesis of urea-formaldehyde fertilizers was mostly based on orthogonal experimental designs or single factor tests; this led to low precision for synthesis and relatively large ranges of parameters for these processes. To obtain mathematical response models for the synthesis of urea-formaldehyde fertilizers with different nitrogen release properties, a central composite design (CCD) of response surface methodology was used in our research to examine the effects of different reaction times, temperatures, and molar ratios on nitrogen insoluble in either hot or cold water. Our results showed that nitrogen insoluble in cold or hot water from urea-formaldehyde fertilizers were mainly affected by urea: formaldehyde molar ratios. Also, quadratic polynomial mathematical models were established for urea-formaldehyde. According to the models, the optimal process parameters which maximize cold-water-insoluble nitrogen and minimize hot-water-insoluble nitrogen for the synthesis of urea formaldehyde were as follows urea: formaldehyde molar ratio was 1.33, reaction temperature was 43.5 °C, and reaction time was 1.64 h. Under these conditions, the content of cold-water-insoluble nitrogen was 22.14%, and hot-water-insoluble nitrogen was 9.87%. The model could be an effective tool for predicting properties of urea-formaldehyde slow release fertilizers if the experimental conditions were held within the design limits.
Highlights
The single factor test can only be optimized for one variable at a time, the orthogonal design can only obtain the relative optimal solutions of different variables and limited light combinations, the two-order polynomial model between the parameters and the response value of the whole variable with all combinations cannot be www.nature.com/scientificreports/
Many studies showed that suitable conditions for synthesizing urea-formaldehyde fertilizers involved a urea formaldehyde molar ratio of 1.2–1.5, reaction temperatures of 30–50 °C, and reaction times of 1–2 h, but the interactions between reaction factors were not clear[5,12]
The effects of reaction time, temperature, and urea-formaldehyde molar ratios on the design array for variable Y1 for nitrogen insoluble in cold water were evaluated through regression analyses (Table 1)
Summary
The single factor test can only be optimized for one variable at a time, the orthogonal design can only obtain the relative optimal solutions of different variables and limited light combinations, the two-order polynomial model between the parameters and the response value of the whole variable with all combinations cannot be www.nature.com/scientificreports/. There was an urgent need to solve the problem of varying the synthesis of urea-formaldehyde fertilizers so they would have dissolution rates that were tailored to the varying needs of different crops Another problem involves how to reduce the proportion of quick-acting components while increasing the proportion of slow-acting components[13]. It has been used to analyze optimal conditions in systems with multi-factor interaction analyses including among different factors It was widely used in different scientific fields to solve problems with a multivariate experimental design and methods of statistical analyses and was effective in helping to solve these problems[15,16]. To the best of our knowledge, no previous study has used response surface methodology to determine optimal methods for synthesis of urea-formaldehyde fertilizers. The results provide a theoretical basis for rapidly extracting nitrogen, which has been insoluble in either hot or cold water, from the urea-formaldehyde products
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