Energy saving and emission reduction is critical to the carbon peaking and carbon neutrality goals, and taking social responsibility is an important way for enterprises to achieve sustainable operations. In this work, we study the joint production decision problem of two products with independent demand through by-product synergy (BPS) technology. Through BPS technology, on the one hand, the disposal cost of the waste materials is reduced, leading to achieve the goal of emission reduction; on the other hand, the procurement cost of raw materials for by-product is also reduced, leading to achieve the goal of energy saving. In this work, we assume the purpose is to maximize the weighted firm’s profit and consumer surplus. The main findings of this work are as follows: (1) when the benefit from emission reduction of BPS is not significant, the optimal decision is to reduce the production of the by-product; when the benefit from energy- saving of BPS is not significant, the optimal decision is to increase the production of the original product. (2) The conversion rate of BPS technology is not as high as good. (3) Loss-for-surplus is decreasing in the level of social responsibility, which means that sacrificing a little firm’s profit can improve consumer surplus significantly. (4) The remanufacturing model differs significantly from BPS in that the optimal remanufacturing decision fully leverages emission reduction benefits, leading to a positive correlation among corporate profits, consumer surplus, weighted social welfare, and resource utilization rates. In addition, when the corporate social responsibility (CSR) level is low, firms cannot enhance consumer surplus by sacrificing profits in the remanufacturing period.