The combined reforming, FT (kinetics and chain growth probability for products distribution), simulation (convergence) and a typical input-output data point of GTL system are presented in the Section S3 of Supplementary Information. To seek the optimal operating condition, we may optimize some decision variables under uncertainty (input for surrogate) to evaluate the corresponding process performance (output for surrogate) as shown in Table . Aspen simulations suffer from non-convergence issues when improper operating conditions are given, or the recycle stream is set too tight. Such problems also occur in our case.