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O meio ambiente é uma grande preocupação mundial existindo cada vez mais imposições legais no sentido de o proteger. Torna-se assim necessário que as indústrias adoptem e desenvolvam processos alternativos mais limpos.
A indústria de curtumes transforma a pele animal em couro, material resistente à putrefacção e com estabilidade térmica suficiente para ser manufacturado nas indústrias do calçado, estofos, vestuário e marroquinaria. A transformação referida é efectuada através duma série de processos entre os quais o caleiro, processo que visa depilar a pele e promover o relaxamento da estrutura fibrilar, tem um papel importante.
O processo de caleiro produz um efluente bastante poluente. Tendo em conta esse facto, este trabalho teve como objectivo desenvolver processos de depilação de pele caprina sem destruição do pêlo, com vista à redução da quantidade de sulfureto e sulfidrato de sódio utilizada e da carga poluente do efluente. Além disso, o processo permite a recuperação do pêlo e este pode ser reaproveitado como fertilizante orgânico, hidrolisado de queratina, compostagem, etc.
Todo o trabalho foi realizado tomando por base um processo de caleiro padrão utilizado industrialmente, alterando-o de forma a obter um processo de caleiro óptimo de depilação sem destruição do pêlo com e sem utilização de enzimas.
Numa primeira fase, desenvolveu-se um processo de depilação sem destruição do pêlo normalmente utilizado para a pele de bovino que foi adaptado com resultados positivos, designado de processo sem enzimas. Numa segunda fase, desenvolveu-se um processo enzimático em que se utilizou uma protease (Erhavit DMC), uma lipase (Defat 50) e uma amilase (Mayzme SD-L); este processo deu bons resultados tal como o anterior.
A redução da quantidade de sulfureto de sódio foi de 33% e 53% para o processo sem enzimas e processo com enzimas, respectivamente, em relação ao processo padrão. O efeito dos processos na carga poluente, à escala piloto, comprova uma redução de 37% nos SST, 37% nos SDT, 60% na CQO, 9% no S2- e 73% no Azoto para o processo sem enzimas e uma redução de 93% nos SST, 63% nos SDT, 69% na CQO, 69% no S2- e 83% no Azoto para o processo com enzimas, quando comparados com o processo padrão.
. Uma análise de custos, com incidência apenas nos agentes químicos utilizados, permitiu concluir a existência de uma redução de custos anuais de 30% para o processo com enzimas e de 13% para o processo sem enzimas, quando comparados com o processo padrão. Como conclusão, os processos desenvolvidos apresentam um grande potencial para serem explorados industrialmente.
The environment is a global concern. There are more and more legal charges as an effort to protect the environment. So, it becomes necessary that companies develop and adapt alternative and cleaner processes. The leather industry turns animal skin in leather that is a resistant material to the putrefaction and with enough thermal stability to be manufactured in footwear, upholstery, clothing and other leather goods manufacturing. This transformation takes place through a series of processes including liming, important process which aims to unhair the skin and promote relaxation of its structure. The liming process produces a very pollutant effluent. Given that, this thesis aimed to study the environmental effect of unhairing the goat skin without destroying the hair, in order to reduce the amount of sodium sulphide and sodium hydrogen sulphide used in liming and the pollution load of wastewater. Furthermore, the process allows the hair recovery which can be reused as an organic fertilizer, hydrolyzed keratin, composting, etc. All the work was done based on a standard liming process used on industry. It was modified to get a liming optimum process of unhairing without hair damage, with or without use of enzymes. Initially a depilation process without enzymes based was developed without destroying the hair, which is normally used with positive results in the cow skin. Secondly, it was developed an enzymatic process in which was used a protease (Erhavit DMC), a lipase (Defat 50) and an amylase (Mayzme SD-L); this processes gives as good results as the previous one. The reduction of sodium sulphide quantity was 33% and 53% in the without enzymes process and enzymatic process respectively comparing to the standard process. The trials done at pilot scale proves a reduction in the pollutant load, comparing to standard process, of 37% in SST, 37% in SDT, 60% in CQO, 9% in S2- and 73% in Nitrogen for the without enzymes process, and of 93% in SST, 63% in SDT, 69% in CQO, 69% in S2- and 83% in Nitrogen for the enzymatic process.. A cost analysis, focusing only on the chemicals used, showed that the enzymatic process leads to a cost reduction of 30% compared to the standard process. The without enzymes process showed a reduction of 13% compared to the standard process. As a conclusion, the processes developed have a great potential to be exploited in industry.
The environment is a global concern. There are more and more legal charges as an effort to protect the environment. So, it becomes necessary that companies develop and adapt alternative and cleaner processes. The leather industry turns animal skin in leather that is a resistant material to the putrefaction and with enough thermal stability to be manufactured in footwear, upholstery, clothing and other leather goods manufacturing. This transformation takes place through a series of processes including liming, important process which aims to unhair the skin and promote relaxation of its structure. The liming process produces a very pollutant effluent. Given that, this thesis aimed to study the environmental effect of unhairing the goat skin without destroying the hair, in order to reduce the amount of sodium sulphide and sodium hydrogen sulphide used in liming and the pollution load of wastewater. Furthermore, the process allows the hair recovery which can be reused as an organic fertilizer, hydrolyzed keratin, composting, etc. All the work was done based on a standard liming process used on industry. It was modified to get a liming optimum process of unhairing without hair damage, with or without use of enzymes. Initially a depilation process without enzymes based was developed without destroying the hair, which is normally used with positive results in the cow skin. Secondly, it was developed an enzymatic process in which was used a protease (Erhavit DMC), a lipase (Defat 50) and an amylase (Mayzme SD-L); this processes gives as good results as the previous one. The reduction of sodium sulphide quantity was 33% and 53% in the without enzymes process and enzymatic process respectively comparing to the standard process. The trials done at pilot scale proves a reduction in the pollutant load, comparing to standard process, of 37% in SST, 37% in SDT, 60% in CQO, 9% in S2- and 73% in Nitrogen for the without enzymes process, and of 93% in SST, 63% in SDT, 69% in CQO, 69% in S2- and 83% in Nitrogen for the enzymatic process.. A cost analysis, focusing only on the chemicals used, showed that the enzymatic process leads to a cost reduction of 30% compared to the standard process. The without enzymes process showed a reduction of 13% compared to the standard process. As a conclusion, the processes developed have a great potential to be exploited in industry.
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Instituto Politécnico do Porto. Instituto Superior de Engenharia do Porto.