Economic model predictive control formulations that combine online optimizing control with offset-free methodologies such as modifier adaptation have been proposed recently. These new algorithms are able to achieve asymptotic optimal performance despite the presence of plant-model mismatch. However, there is a major requirement stemming from the modifier-adaptation part, namely, the necessity to know the static plant gradients at the sought (and therefore still unknown) steady-state operating point. Hence, for implementation purposes, the algorithms need to be enhanced with plant gradient estimation techniques. This work proposes to estimate modifiers directly, based on steady-state perturbations and using Broyden's approximation The proposed economic MPC algorithm has been tested in simulation on the Williams-Otto reactor and provides plant optimality upon convergence. Copyright (C) 2020 The Authors.