Synthesis of a Mass Integrated Biodiesel Process

A hierarchical decision procedure is proposed for the synthesis of processes that are mass integrated to an existing industrial environment. The procedure takes the information about already installed processes as input. Decisions required to complete the design of the new process are then made considering this environment. The procedure decides among alternative technologies for producing the new product and on the use of output streams from the environment as inputs to the new process and vice versa. It also decides whether this use should be done through new processing facilities to condition these streams. The hierarchical decision procedure described by Douglas was adapted to include these mass integration decisions and to resort to mass exchange network synthesis and source–sink allocation procedures at the appropriate level of the hierarchy. The procedure is illustrated by designing a new biodiesel process, integrated to the agro-industrial complex already existing in the city of Reconquista, Argentina. The alternative technologies considered for producing biodiesel are acid, basic, and enzymatic catalyzed transesterification processes. The considered raw materials are a pretreated stream from an edible oils refinery and residual fatty streams from other factories, with high free fatty acid content. The acid raw materials could be converted to biodiesel either directly through an acid process or after an esterification treatment through the same basic process that is utilized for good quality edible oils raw material. The produced biodiesel could be sold to oil companies or to the local agro-machinery business. The raw glycerin byproduct could be sold as glycerin after purification, fermented to ethanol in a cereals bioethanol factory, used as fuel in properly designed boilers, or used in the formulation of cattle food in local feed lots. This paper discusses (i) the trade-off between implementing mass exchangers or separation processes in the case of methanol added in excess and alkali added as a catalyst in the reaction step, (ii) the adaptation of the standard source sink allocation approach adding constraints of the diet problem, and (iii) the order of decisions in the hierarchy, which strongly affects the programming effort to solve this synthesis and design problem. Results analysis shows that both the economic and environmental performance of the biodiesel process is significantly improved when taking into account the local industrial environ